Search

Fatigue is one of the most important properties to be considered in ceramic dental implants due to cyclic mechanical stresses arising from the chewing process. In this work, the fatigue behaviour of hydrothermally degraded ZrO2-based ceramics stabilized with 3mol% Y2O3 (3Y-TZP) was studied in 4-point bending tests. Samples of 3Y-TZP were compacted (100MPa), sintered at 1475 °C for 2 h, polished and hydrothermally degraded in an autoclave as described in the ISO-13356 standard. The samples were characterized by their relative density, crystalline phase composition, microstructure and surface roughness. The highly dense (>99.6%TD) sintered 3Y-TZP ceramics has only tetragonal t-ZrO2 phase, even after hydrothermal ageing. Furthermore, the ceramic materials presented a Vickers hardness of 12.7±0.2GPa, a fracture toughness of 7.1±0.3MPa•m1/2 and a 4-point bending strength of 940.1±67MPa. Based on the bending test results 5 different stress levels for the fatigue tests were selected and conducted by cyclic 4-point bending obtaining the S-N curve. Weibull statistics was used for the statistical analysis. The fatigue tests indicate that the limit of fatigue resistance of this 3Y-TZP ceramics is around 550MPa, i.e. higher than the limits established in the ISO-13356 standard for the use of Y-TZP ceramics for the manufacture of implants. The fatigue behaviour of the investigated 3Y-TZP ceramics was related to the toughening mechanisms acting in Y-TZP ceramics, such as transformation toughening related to t→m phase transformation and microcracking.

This study evaluates the effect of aging in artificial saliva and thermal shocks on the microhardness of the bulk-fill composite compared to the nanohybrid composite. Two commercial composites, Filtek Z550 (3M ESPE) (Z550) and Filtek Bulk-Fill (3M ESPE) (B-F), were tested. The samples were exposed to artificial saliva (AS) for one month (control group). Then, 50% of the samples from each composite were subjected to thermal cycling (temperature range: 5–55 °C, cycle time: 30 s, number of cycles: 10,000) and another 50% were put back into the laboratory incubator for another 25 months of aging in artificial saliva. The samples’ microhardness was measured using the Knoop method after each stage of conditioning (after 1 month, after 10,000 thermocycles, after another 25 months of aging). The two composites in the control group differed considerably in hardness (HK = 89 for Z550, HK = 61 for B-F). After thermocycling, the microhardness decrease was for Z550 approximately 22–24% and for B-F approximately 12–15%. Hardness after 26 months of aging decreased for Z550 (approximately 3–5%) and B-F (15–17%). B-F had a significantly lower initial hardness than Z550, but it showed an approximately 10% lower relative reduction in hardness.

The project is aimed at investigating the effect of laser surface modification of dental-grade zirconia (3Y-TZP) to guide cellular behaviour. A nanosecond laser was employed to fabricate groove patterns on the surface of 3Y-TZP, yielding three different topographies according to the groove periodicity (30, 50 and 100µm). The resulting topography, microstructure, hardness and hydrothermal degradation resistance of the modified zirconia was assessed by means of advanced characterization techniques. A cellular study was conducted to evaluate the behaviour of human mesenchymal stem cells on the patterned samples in terms of adhesion and cell morphology. The results showed grooves of approximately 1.7µm heigh with pronounced pile-up due to the melting and re-solidification of the material. The phase analysis revealed that no phase transformation is induced during the laser modification; however, a non-homogeneous monoclinic phase distribution was observed on the patterned surfaces after hydrothermal degradation. Finally, all the patterned surfaces allowed cell attachment, increased cell area and favoured cell elongation and alignment in the direction of the laser patterns.

The changes in mechanical properties, hydrothermal degradation and cell adhesion were studied in 3Y-TZP under two different superficial modification patterns (uni- and multidirectional) with a surface roughness ranging from 16 to 603 nm. In this sense, mechanical properties (i.e. hardness, indentation fracture toughness and scratch) and accelerated tests in water steam were measured to evaluate the influence of the surface treatments on the superficially modified layer. Moreover, a detailed characterization through micro-Raman spectroscopy and X-Ray diffraction was performed. Finally, SaOS-2 osteoblasts were used for the evaluation of the cell adhesion behaviour on the surfaces. Overall, ground/polished specimens increased the mechanical properties and ageing resistance of mirror-like polished specimens, although resistance to degradation was maximum at intermediate conditions (Sa ˜ 40-180 nm). The studied surfaces allowed cell attachment, but promoted contact guidance (i.e. cell alignment) only on unidirectionally ground surfaces above Sa = 150 nm.

Itrio oksidu stabilizuotas cirkonio oksidas (Y-TZP) pasižymi geromis mechaninėmis ir biologinėmis savybėmis, dėl kurių Y-TZP yra patrauklus medicinos prietaisų gamybai. Nepaisant to, medžiagai būdinga degradacija drėgnoje aplinkoje (kaip ir žmogaus organizme), kurios metu Y-TZP tampa nestabilus, suprastėja medžiagos mechaninės savybės. Hidroterminės degradacijos metu, dėl vandens sukeltų įtempių, metastabili tetragoninė fazė persikristalizuoja į monoklininę, nuo implanto paviršiaus gali atsiskirti dalelės, kurios sukelia infekcijų riziką. Šios degradacijos mechanizmas ir kontrolė iki šios dienos nėra gerai žinoma ir Y-TZP pritaikymas medicinos prietaisų gamybai ribojamas dėl per didelių rizikų. Implantų paviršiai, tam, kad sudarytų kuo geresnes sąlygas kaulinio bei minkštųjų audinių integracijai, turi pasižymėti tam tikru paviršiaus šiurkštumu, todėl turi būti mechaniškai apdirbami. Mechaninis Y-TZP apdirbimas taip pat sąlygoja tetragninės fazės persikristalizavimą į monoklininę, todėl tokie paviršiai yra ypač jautrūs hiroterminės degradacijos poveikiui. Šiame darbe buvo tirta paviršiaus apdirbimo skirtingais metodais įtaka Y-TZP keramikos hidroterminei degradacijai. Atlikus tyrimus nustatyta, kad norint minimizuoti Y-TZP jautrumą hidroterminei degradacijai, paviršių apdirbimas turėtų būti atliekamas gaminius termiškai apdorojus dalinai, kadangi mechaninio apdirbimo metu susiformavusi monoklininė fazė, atliekant galutinį terminį apdorojimą aukštoje temperatūroje, persikristalizuoja atgal į tetragoninę., Yttria stabilized zirconia (Y-TZP) has good mechanical and biological properties, which makes Y-TZP an attractive material for medical device manufacturing. Nevertheless, material is prone to degradation in a humid environment (as well as in human body), during which Y-TZP becomes unstable, mechanical properties of the material reduce. During hydrothermal degradation, due to water-induced stresses, the metastable tetragonal phase transforms to the monoclinic, particles can be released from the implant surface and cause infection. The mechanism and control of hydrothermal degradation until these days are not well known and the production of Y-TZP medical devices is limited. The surfaces of implants must be roughened or smoothened in order to achieve the best possible integration of bones and soft tissues, and must therefore be machined. Like hydrothermal degradation, mechanical processing of Y-TZP causes transformation of the tetragonal phase to monoclinic (this process is known as transformation toughening), making such surfaces particularly sensitive to the effects of degradation in humid environment. In this work, the sensitivity of Y-TZP machined using different methods (sandblasting, polishing) to hydrothermal degradation was investigated. It was found that in order to minimize Y-TZP sensitivity to hydrothermal degradation, surface machining has to be performed on partially sintered surfaces, so monoclinic phases formed during machining, transform to tetragonal during sintering.

The market share of zirconia (ZrO2) dental implants is steadily increasing. This material comprises a polymorphous character with three temperature-dependent crystalline structures, namely monoclinic (m), tetragonal (t) and cubic (c) phases. Special attention is given to the tetragonal phase when maintained in a metastable state at room temperature. Metastable tetragonal grains allow for the beneficial phenomenon of Phase Transformation Toughening (PTT), resulting in a high fracture resistance, but may lead to an undesired surface transformation to the monoclinic phase in a humid environment (low-temperature degradation, LTD, often referred to as ‘ageing’). Today, the clinical safety of zirconia dental implants by means of long-term stability is being addressed by two international ISO standards. These standards impose different experimental setups concerning the dynamic fatigue resistance of the final product (ISO 14801) or the ageing behavior of a standardized sample (ISO 13356) separately. However, when evaluating zirconia dental implants pre-clinically, oral environmental conditions should be simulated to the extent possible by combining a hydrothermal treatment and dynamic fatigue. For failure analysis, phase transformation might be quantified by non-destructive techniques, such as X-Ray Diffraction (XRD) or Raman spectroscopy, whereas Scanning Electron Microscopy (SEM) of cross-sections or Focused Ion Beam (FIB) sections might be used for visualization of the monoclinic layer growth in depth. Finally, a minimum load should be defined for static loading to fracture. The purpose of this communication is to contribute to the current discussion on how to optimize the aforementioned standards in order to guarantee clinical safety for the patients.

The hydrolysis of lignocellulose is the first step in saccharide based bio-refining. The recovery of homogeneous acid catalysts imposes great challenges to the feasibility of conventional hydrolysis processes. Herein, we report a strategy to overcome these limitations by using stable sulfonated carbons as solid acid catalysts in a two-step process, composed of mechanocatalytic pretreatment and secondary hydrolysis in a semi-batch reactor. Without mechanocatalytic pre-treatment the hydrolysis of the insoluble substrate largely occurs through homogeneously catalyzed reactions. Ball-milling induced amorphization promotes a substantially higher substrate reactivity, because homogeneous hydrolysis occurs preferentially from less ordered structural domains in cellulose. In contrast, concerted ball-milling (CBM) of cellulose with the sulfonated carbon promotes a heterogeneously catalyzed hydrolysis to soluble oligosaccharides. By performing an in-depth physicochemical characterization of cellulose subjected to CBM treatment with different carbons, we reveal the crucial role of strong BrOnsted acid sites in facilitating mechanocatalytic depolymerization. Recyclability experiments confirmed that despite being subject to profound structural changes during repeated pre-treatment/semi-batch hydrolysis cycles, the sulfonated carbon retained its catalytic activity. The combination of mechanocatalytic pretreatment with strong solid acids and hydrolysis in the semi-batch reactor was successfully extrapolated for the first time to the hydrolysis of real lignocellulose to achieve quantitative yields in C-5 and high yields in C-6 derived products.

PURPOSE The aims of this study were to investigate mechanical properties and hydrothermal degradation behaviour of the cubic-containing translucent yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP). MATERIALS AND METHODS Four groups of Y-TZP (T, ST, XT, and P), containing different amount of cubic crystal, were examined. Specimens were aged by autoclaving at 122℃ under 2 bar pressure for 8 h. Phase transformation was analyzed using X-ray diffraction (XRD) to measure phase transformation (t→m). Kruskal-Wallis test was used to determine the difference. Surface hardness, biaxial flexural strength, and fracture toughness in values among the experimental groups and verified with Wilcoxon matched pairs test for hardness values and Mann Whitney U for flexural strength and fracture toughness. RESULTS XRD analysis showed no monoclinic phase in XT and P after aging. Only Group T showed statistically significant decreases in hardness after aging. Hydrothermal aging showed a significant decrease in flexural strength and fracture toughness in group T and ST, while group XT and P showed no effect of aging on fractural strength and fracture toughness with P

OBJECTIVES: To evaluate two-body wear of three zirconia ceramics stabilized with 3, 4 and 5mol% yttria and to compare their wear behavior with that of a lithium-disilicate glass-ceramic. METHODS: Sixteen rectangular-shaped specimens made from three grades of zirconia ceramics and a lithium-disilicate glass-ceramic were polished and dynamically loaded in a chewing simulator (2kg vertical load, 2.1Hz) under water at 90°C for 1.2×106 cycles (about 7 days) in the ball-on-plate mode against steatite antagonists. Surface roughness was measured before and after wear testing. Wear tracks were scanned with a non-contact 3D profilometer and super-impositions were used to determine wear loss of the antagonists. Wear surfaces were imaged by SEM. XRD and micro-Raman spectroscopy were used to characterize phase transformation and stress status in the worn and unworn areas of the zirconia ceramics. RESULTS: Independent of fracture toughness, strength and aging-susceptibility, the three zirconia ceramics showed a similar and limited amount of wear (∼10μm in depth) and were more wear-resistant than the lithium-disilicate glass-ceramic (∼880μm in depth). Abrasive wear without obvious cracks was observed for all investigated zirconias, whereas the glass-ceramic with a lower fatigue threshold and high susceptibility to surface dissolution exhibited significant abrasion, fatigue and corrosion wear. All three zirconia ceramics yielded a lower antagonist wear than the glass-ceramic and no significant differences were found between the zirconia ceramics. SIGNIFICANCE: In the context of this study, high-translucent zirconia ceramics stabilized with a higher yttria content, recently introduced in the dental field, were as wear-resistant and antagonist-friendly as conventional high-strength zirconia and suitable for monolithic restorations. ispartof: DENTAL MATERIALS vol:35 issue:12 pages:1776-1790 ispartof: location:England status: published

Namen in cilj diplomskega dela je bil raziskati hidrotermično degaradacijo odpadne embalaže iz polipropilena (PP) s pomočjo superkritične vode ter določiti nastale produkte. Izvedena je bila primerjava pisanega in brezbarvnega PP. Proučevali smo vpliv procesnih parametrov, kot so tlak, temperatura, razmerje voda/PP na potek in kinetiko reakcij razgradnje odpadne embalaže iz PP v superkritični vodi. PP je trd termoplastičen polimer z gostoto med 0,9 in 0,92 g/cm3. V mnogih pogledih je podoben polietilenu, vendar z večjo mehansko in natezno trdnostjo ter toplotno stabilnostjo. Odporen je proti polarnim topilom, kislinam, raztopinam soli in olju ter neodporen proti kloriranim ogljikovodikom. Zaradi dobrih mehanskih in fizikalnih lastnosti je eden izmed najbolj zastopanih polimerov v svetu. Uporablja se v različne namene, kot so folije, plastenke za mineralno vodo, povratne plastenke, v ploščah, ceveh, avtomobilski industriji ter v beli tehniki. Zaradi velike zastopanosti tega polimera in vpliva ter kopičenja v okolju smo izvedli hidrotermično degradacijo pisanega PP in brezbarvnega PP. Hidrotermično degradacijo smo izvajali v visokotemperaturnem in visokotlačnem šaržnem reaktorju pri temperaturah 425 °C in 450 °C ter reakcijskih časih od 15 do 240 min. Nastale produkte smo filtrirali ter analizirali s pomočjo plinske kromatografije/masne spektrometrije GC/MS ter določili vsebnost celotnega organskega ogljika (TOC). Ugotovili smo, da je največji izkoristek plina nastal pri 240 min degradaciji – tako barvnega kot brezbarvnega PP v superkritični vodi – najmanj pa ga je nastalo pri 15-minutni degradaciji. Najbolj zastopane komponente so metan, etan, propan, izobutan ter ogljikov dioksid. Dokazali smo, da je največji donos alkanov prisoten le pri višji temperaturi. Majhne razlike v vsebnosti alkanov, ki so prisotni pri isti temperaturi, lahko pripišemo aditivom ter različnim primesem, ki jih vsebuje pisani PP. Izkoristki nastale oljne faze s podaljševanjem reakcijskega časa upadajo, saj se dolgi ogljikovodiki cepijo na krajše. The purpose of the following work was to investigate the hydrothermal degradation of polypropylene waste packaging (PP) using supercritical water, and determine the resulting products. A comparison of a colored and colorless PP has been done. The impact of process parameters, such as pressure, temperature and water/PP proportion on the course of reaction and the kinetics of the decomposition of waste packaging from PP in supercritical water has been studied. Polypropylene (PP) is a solid thermoplastic polymer with density between 0.9 and 0.92 g/cm3. It is quite similar to polyethylene, but with greater mechanical and tensile strength and thermal stability. It is resistant to polar solvents, acids, saline and oil solutions and it is not resistant to chlorinated hydrocarbons. Because of its good mechanical and physical properties, it is one of the most represented polymers in the world. It is used for various purposes, such as foils, mineral water bottles, return bottles, plates, pipes, automotive and white goods. Due to the high abundance of this polymer and his influence and accumulation in the environment, hydrothermal degradation of the coloured PP and colorless PP has been investigated. Hydrothermal degradation was carried out in a high temperature and high pressure batch reactor at temperatures of 425 °C and 450 °C and reaction time of 15–240 min. The resulting products were filtered and analyzed by gas chromatography/GC and MS/mass spectrometry and we determined the total organic carbon content (TOC) has been determined. We found that the maximum gas yield was obtained at 240 min degradation of both the coloured and the colorless PP in supercritical water, and the minimum yield was obtained at 15 minute degradation. The most represented components are methane, ethane, propane, isobutane and carbon dioxide. The results of analyses showed that the maximum yield of alkanes is obtained only at a higher temperature. The small differences in the amount of obtained alkanes at the same temperature can be attributed to additives which are present in a coloured PP. The yield of the resulting oil phase decreases with the prolongation of the reaction time, beacuse the long hydrocarbons are splited into shorter molecules.

OBJECTIVES: For the use of partially stabilized zirconia (PSZ) as high-translucent zirconia, the importance of cubic phase (c-ZrO2) is commonly emphasized without much attention for the remaining tetragonal phase (t-ZrO2). The aim is to understand whether the crystal structure and microstructure of t-ZrO2 have paramount influences on the properties of PSZ. METHODS: Two grades of 5mol% yttria-stabilized PSZ ceramics were prepared by different processing routes. A 5mol % yttria co-precipitated zirconia (T5Y) was compared with a 3 and 8mol% yttria-stabilized powder mixture grade with a bimodal grain size distribution (B5Y). The phase composition and lattice parameters were studied with x-ray diffraction (XRD) and Rietveld analysis. Mechanical properties were compared in terms of hardness, toughness and biaxial bending strength with Weibull analysis. Their translucency and aging stability were also characterized, and the microstructure before and after aging were followed by scanning electron microscopy (SEM). RESULTS: T5Y and B5Y having similar phase composition (about 40% t- and 60% c-ZrO2) showed the same basic properties (density, hardness and toughness), but the lattice parameters of t-ZrO2 and the concomitant microstructure were completely different. The t-ZrO2 phase in T5Y had a higher yttria content and a lower tetragonality (c/a) of 1.0126±0.0002, whereas the t-ZrO2 phase in B5Y was comparable to that in conventional 3Y-TZPs with a tetragonality of 1.0153±0.0002. Consequently, B5Y showed a lower strength with lower Weibull modulus, being less translucent and more aging susceptible as compared to T5Y. The translucency and aging susceptibility of B5Y were even comparable to those of conventional 3Y-TZP. SIGNIFICANCE: Not only the phase composition with high cubic phase content but also the lattice parameters and the yttria content in the remaining t-ZrO2 played a determinant role for PSZs to be used as 'high-translucent' zirconia. ispartof: DENTAL MATERIALS vol:36 issue:4 pages:491-500 ispartof: location:England status: published

Polietilen tereftalat (PET) sodi med najbolj razširjene termoplastične smole. Ima dobre mehanske, toplotne in kemijske lastnosti. Uporabljamo ga predvsem za izdelavo embalaže za pitno vodo in živila. PET je nerazgradljiva plastika, zato se ga vedno več nabira v naravi. Zaradi negativnih posledic kopičenja PET v naravi, dajemo dandanes vse večji pomen ločevanju in recikliranju odpadne PET embalaže. PET lahko recikliramo na več načinov. Eden izmed najučinkovitejših načinov je kemijsko recikliranje s hidrotermično degradacijo. Namen diplomskega dela je bil preučiti recikliranje odpadne PET embalaže s pod in nadkritično vodo. Pod- in nadkritična voda je odličen reakcijski medij za degradacijo odpadne PET embalaže. Odpadna PET embalaža namreč po degradaciji v pod in nadkritičnih vodi razpade na monomere. Glaven monomer, ki nastane je tereftalna kislina (TPA). TPA predstavlja glavno korist recikliranja, iz nje namreč lahko ponovno izdelamo PET. Eksperimentalni del hidrotermične degradacije odpadne PET embalaže smo izvajali v visokotlačnem in visokotemperaturnem šaržnem reaktorju v pod in nadkritični vodi. Reakcije smo izvajali pri štirih različnih temperaturah 250, 300, 350 in 400 °C in reakcijskem času 1, 10 in 30 minut. Nastale produkte hidrotermične degradacije smo analizirali s HPLC, FT-IR in GC-MS metodami. Analize produktov hidrotermične degradacije odpadne PET embalaže so pokazale, da dobimo najvišji izkoristek glavnega produkta TPA pri podkritičnih pogojih, in sicer pri temperaturi 300 °C in času 30 minut. Izkoristek TPA pri degradaciji odpadne barvne PET embalaže je znašal 85%. Za primerjavo izkoristkov smo izvedli še hidrotermično degradacijo brezbarvne odpadne PET embalaže pri enakih pogojih. Dobljen izkoristek je znašal 90%. Z višanjem temperature v nadkritično območje se je izkoristek TPA zniževal, zaradi nastajanja sekundarnih produktov. Polyethylene terephthalate (PET) is one of the most widely used types of plastic resins. It has good mechanical, thermal and chemical properties. We use it primarily for the production of packaging for drinking water and food. PET is non-degradable plastic, which is why it has accumulated so much in the nature. Because of the negative consequences of the accumulation of PET in the nature, it is highly important to recycle PET packaging waste. PET can be recycled in several ways. One of the most effective solution is chemical recycling with hydrothermal degradation. The purpose of the diploma thesis was to examine the recycling of PET packaging waste with sub- and supercritical water. Sub- and supercritical water is an excellent reaction medium for the degradation of PET packaging waste, that can be decomposed into monomers. The main monomer that is produced is terephthalic acid (TPA). TPA is considered to be the main benefit of recycling because it is the compound that can be used fort the synthesis of PET again. The experimental part of the hydrothermal degradation of PET packaging waste was carried out in the high-pressure and high-temperature batch reactor in the sub- and supercritical water. Reactions were carried out at four different temperatures of 250, 300, 350 and 400 °C, and the reaction time was 1, 10 and 30 minutes. The resulting hydrothermal degradation products were analyzed by HPLC, FT-IR and GC-MS methods. The analysis of products of hydrothermal degradation of PET packaging waste showed that the highest yield of the main TPA product was obtained under subcritical conditions at a temperature of 300 °C and 30 minutes of reaction time. The yield of TPA obtained by degradation of coloured PET packaging waste was 85%. For comparison, hydrothermal degradation was carried out under the same conditions using colourless PET packaging waste. The obtained yield of TPA was 90%. By increasing the temperature to the supercritical area, the TPA yield decreased due to the formation of secondary products.

Submitted by Nayara Fernanda Barchetta Villalta (nayara.barchetta@unesp.br) on 2019-08-09T15:24:14Z No. of bitstreams: 1 TESE DOUTORADO NAYARA BARCHETTA (PARA IMPRESSÃO)-mesclado.pdf: 4168923 bytes, checksum: ba7c932170b2e4fc13f680fa2027cfca (MD5) Approved for entry into archive by Silvana Alvarez null (silvana@ict.unesp.br) on 2019-08-15T14:57:52Z (GMT) No. of bitstreams: 2 barchetta_nf_me_sjc_int.pdf: 4168923 bytes, checksum: ba7c932170b2e4fc13f680fa2027cfca (MD5) barchetta_nf_dr_sjc_par.pdf: 1000315 bytes, checksum: dfad59348ca795cab7b661b43aab3aee (MD5) Made available in DSpace on 2019-08-15T14:57:52Z (GMT). No. of bitstreams: 2 barchetta_nf_me_sjc_int.pdf: 4168923 bytes, checksum: ba7c932170b2e4fc13f680fa2027cfca (MD5) barchetta_nf_dr_sjc_par.pdf: 1000315 bytes, checksum: dfad59348ca795cab7b661b43aab3aee (MD5) Previous issue date: 2019-05-28 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Neste estudo avaliou-se por caracterização mecânica e microestrutural, a degradação em meio bucal e in vitro da cerâmica Y-TZP sinterizada por energia de micro-ondas em comparação ao método convencional. Foram confeccionados noventa e seis discos por CAD-CAM (ISO 6872), sinterizados de modo convencional (C) 1530°C/120 minutos e por energia de micro-ondas (M) 1450°C/15 minutos. E submetidos à degradação hidrotérmica em reator pressurizado (E) (1,5h/150°C/3 bar) e à degradação in situ (B) (240 horas em meio bucal), formando-se 8 grupos (n = 12): M, C, ME, CE, MB, CB, MEB e CEB. Foram realizadas análises de contração volumétrica, difração de raios-X (DRX), rugosidade superficial (Ra e Rz), ângulo de contato, microscopia eletrônica de varredura (MEV), quantificação do biofilme por UFC/mL e análise de resistência mecânica por flexão biaxial. Os resultados obtidos foram analisados estatisticamente por t-Student, Anova dois e três fatores, e teste de Tukey (5%). Por DRX observou-se transformação de fase tetragonal para monoclínica (t-m) nos grupos envelhecidos, exceto para o grupo MB. Não foram observadas diferenças significantes na contração volumétrica (p=0,274), na rugosidade Ra (p=0,137) e Rz (p=0,187), assim como nos valores de ângulo de contato entre os métodos de sinterização (p=0,669). Por MEV observou-se a presença de formação de biofilme inicial e na contagem de Unidades Formadoras de Colônias (UFC/mL) foi maior quando os espécimes foram previamente envelhecidos in vitro (p=0,001). No ensaio de resistência à flexão biaxial foi observado o efeito interação (p=0,005) para as três variáveis, sinterização, envelhecimento in vitro e envelhecimento in situ, com aumento da resistência para os grupos sinterizados pelo método convencional após os envelhecimentos, devido ao aumento de tensão de transformação superficial. E houve equivalência estatística entre todos os grupos micro-ondas comparados aos grupos controle. Concluiu-se que o método de envelhecimento in situ por 240 horas foi capaz de transformar a fase t-m da superfície da cerâmica, sendo que a sinterização por energia de micro-ondas influenciou positivamente a resistência à degradação hidrotérmica à baixa temperatura (LTD), além da redução no tempo de sinterização em mais de 80%. In this study ir was evaluated the effect of in situ low temperature degradation of yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics sintered by microwave energy in comparison to the conventional method. Ninety-six discs milled by CAD/CAM (ISO 6872) were divided in: conventionally sintered (C) at 1530 ° C / 120 minutes and microwave energy (M) 1450°C / 15 minutes. Specimens were submitted to hydrothermal degradation in a pressurized reactor (E) (1.5h / 150°C / 3 bar) and in situ degradation (B) (240 hours in the buccal medium), forming eight groups (n=12): M, C, ME, CE, MB, CB, MEB and CEB. Specimens were evaluated through analysis of volumetric contraction, X-ray diffraction (XRD), surface roughness (Ra and Rz), contact angle, scanning electron microscopy (SEM), biofilm quantification by CFU / mL and biaxial flexural strength. Results were statistically analyzed through t-Student, two, three-way Anova and Tukey tests (5%). By XRD, tetragonal to monoclinic phase transformation (t-m) was observed in the aged groups, except for the MB group. No significant differences were observed in the volumetric contraction (p = 0.274), Ra roughness (p = 0.137) and Rz (p = 0.187), as well as contact angle values between sintering methods (p = 0.669). SEM images showed that the initial biofilm formation was observed after 8 hours in situ, an increase of CFU / mL occurred when the specimens were previously aged in vitro (p = 0.001). Regarding biaxial flexural strength, the interaction effect (p = 0.005) for the three variables, sintering method, hydrothermal aging and in situ aging was observed, with increased resistance for the sintered groups by the conventional method after aging, and statistical equivalence for the microwave groups, aged or not, compared to the control groups. The in situ aging method for 240 hours was induced the t-m phase transformation the surface of the ceramic, and sintering by microwave energy had a positive effect on the resistance to low temperature hydrothermal degradation (LTD), besides reduction in sintering time by more than 80%. 2017/07636-9

© 2018 Elsevier Ltd The influence of 0.01–2 mol% Fe 2 O 3 powder addition on the microstructure, mechanical and optical properties, and hydrothermal stability of highly-translucent 3Y-TZP ceramics is assessed and compared with commercially available co-precipitated 0.18 mol% Fe 2 O 3 doped ZrO 2 powder-based ceramics. Only those ceramics with up to 0.1 mol% Fe 2 O 3 resulted in a proper shade for dental zirconia ceramics, with a typical composition of 87 vol% t-ZrO 2 and 13 vol% c-ZrO 2 . The amount of cubic phase increased at higher Fe 2 O 3 content. The hardness (∼13 GPa) and fracture toughness (∼3.6 MPa m 1/2 ) of the 0.01 mol% - 0.1 mol% Fe 2 O 3 doped 3Y-TZP was comparable, whereas the hardness decreased above 0.5 mol% Fe 2 O 3 and the fracture toughness decreased above 2 mol% Fe 2 O 3 . The hydrothermal ageing resistance slightly increased for Fe 2 O 3 concentrations up to 1 mol%, whereas the translucency slightly decreased with increasing Fe 2 O 3 content. ispartof: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY vol:39 issue:2-3 pages:499-507 status: published

The effect of hydrothermal conditions on enzymatic hydrolysis lignin (EHL) degradation in water-isopropyl alcohol co-solvent and optimal conditions were investigated. The yields and reactivity toward formaldehyde of degraded enzymatic hydrolysis lignin (DEL) were determined. The optimal conditions of temperature, time, and ratio of solids to liquids were 250 °C, 60 min, and 1:10 (w/v), respectively. The EHL and DEL were characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), thermal gravity (TG), and differential scanning calorimetry (DSC) analyses. The results revealed that the molecular weight and polydispersity of DEL were lower than that of EHL. Although the fundamental structure of lignin before and after hydrothermal degradation was retained, the ether (β-O-4, α-O-4, etc.) content decreased, while that of hydroxyl (phenolic and aliphatic) increased. The DTGmax and Tg values shifted from 334 and 117 °C to 304 and 105 °C, respectively.

Made available in DSpace on 2020-12-12T02:24:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) Objectives: The aim of this study was to evaluate the effect of hydrothermal aging on the mechanical properties and translucency of dental zirconia with different levels of translucency. Methods: Three different types of dental yttria-stabilized zirconia were used: 3Y-TZP (ZrO2 - 3 mol.% Y2O3) of medium opacity (designated Z3OP), 3Y-TZP of medium translucency (Z3MT), and 5Y-PSZ (ZrO2 - 5 mol.% Y2O3) of high translucency (Z5HT). A total of 120 specimens were sintered (n = 40 specimens/group). The control group (sintered→polished→heat-treated) and the aged group (sintered→polished→heat-treated→hydrothermally degraded at 134 °C, 2 bar, 5h) were characterized by relative density, quantitative phase analysis by X-ray diffraction using the Rietveld method, microstructural analysis by scanning electron microscopy, surface roughness and translucency. All groups were submitted to a biaxial flexural strength test. Data analysis using Kruskal-Wallis, Nemenyi (p-value = 0.05), and Weibull statistics were used. Results: All sintered specimens presented full densification. After aging, an increase of the m-ZrO2 phase content was observed for the Z3OP group. On the other hand, Z3MT and Z5HT did not show any m-ZrO2 phase, indicating resistance to the hydrothermal degradation. Smaller grains were observed in the Z3MT group in relation to Z3OP group and the Z5HT group presented a bimodal grain distribution, where the largest grains were associated to cubic ZrO2. Z3OP exhibited a slight increase in roughness as a function of degradation, while the roughness remained statistically stable in the other groups. Translucency was little influenced by degradation, but considerably affected by increasing thickness. The Z5HT samples were the group with the highest translucency among the control groups. Z3OP exhibited the highest flexural strength, while being the most susceptible to hydrothermal degradation. The lowest values were presented by Z5HT in all groups, due to the high concentration of c-ZrO2 grains. Conclusion: Hydrothermal aging is less critical to the flexural strength of zirconia-based materials than the materials’ composition and microstructure. Z5HT zirconia showed the highest translucency, however the measured difference is not visually perceptible. Z5HT was considered the most resistant to hydrothermal degradation. Fluminense Federal University Faculty of Dentistry Institute of Health of Nova Friburgo, Dr. Silvio Henrique Braune St, 22 - Downtown Pontical Catholic University of Rio de Janeiro Department of Chemical and Materials Engineering PUC-Rio, Marques de São Vicente St 225, Gávea University of Toronto Faculty of Dentistry, 124 Edward St #539 State University of Rio de Janeiro Faculty of Technology, Presidente Dutra Highway, Km 298 São Paulo State University Faculty of Engineering of Guaratinguetá UNESP/FEG, Ariberto Pereira da Cunha Ave, 333 - Portal Das Colinas São Paulo State University Faculty of Engineering of Guaratinguetá UNESP/FEG, Ariberto Pereira da Cunha Ave, 333 - Portal Das Colinas CNPq: 308684/2013-3/311119/2017-4 FAPERJ: E-26-201.476/2014

Made available in DSpace on 2019-09-11T20:58:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2018 Abstract This study aimed to investigate slow crack growth (SCG) behavior of a zirconia ceramic after grinding and simulated aging with low-temperature degradation (LTD). Complementary analysis of hardness, surface topography, crystalline phase transformation, and roughness were also measured. Disc-shaped specimens (15 mm Ø × 1.2 mm thick, n = 42) of a full-contour Y-TZP ceramic (Zirlux FC, Amherst) were manufactured according to ISO:6872-2008, and then divided into: Ctrl – as-sintered condition; Ctrl LTD – as-sintered after aging in autoclave (134°C, 2 bar, 20 h); G – ground with coarse diamond bur (grit size 181 μm); G LTD – ground and aged. The SCG parameters were measured by a dynamic biaxial flexural test, which determines the tensile stress versus stress rate under four different rates: 100, 10, 1 and 0.1 MPa/s. LTD led to m-phase content increase, as well as grinding (m-phase content: Ctrl – 0%; G – 12.3%; G LTD – 59.9%; Ctrl LTD – 81%). Surface topography and roughness analyses showed that grinding created an irregular surface (increased roughness) and aging did not promote any relevant surface change. There was no statistical difference on surface hardness among different conditions. The control group presented the lowest strength values in all tested rates. Regarding SCG, ground conditions were less susceptible to SCG, delaying its occurrence. Aging (LTD) caused an increase in SCG susceptibility for the as-sintered condition (i.e. G < G LTD < Ctrl < Ctrl LTD). [Pereira, Gabriel Kalil Rocha] Faculdade Meriodional, Brazil Amaral, Marina] Universidade de Taubaté, Brazil Weitzel, Isabela Sandim Souza Leite] Universidade de Taubaté, Brazil Silvestri, Tais; Guilardi, Luis Felipe; Valandro, Luiz Felipe] Universidade Federal de Santa Maria, Brazil

[EN] Self-reinforced polymer composites (SRCs) are proposed as a suitable alternative for composite development, based in the combination of a polymeric matrix and a polymeric fibre made of the same polymer. SRCs based in polylactide (PLA) could be fully biodegradable and their valorisation routes could presumably be assimilated to those for neat PEA. In this sense, the aim of this study was to develop new self-reinforced PLA-based composites and ascertain their biodegradability. For this purpose, PLA-based SRCs were obtained through a thermo-compression procedure and their biodegradability corroborated under standard conditions (ISO 20200). Moreover, a deep study of the effect of the different factors involved in the biodegradation of the composites such as the temperature, the water and the compost medium was considered relevant to delimitate the long-term properties and valorisation routes for these materials. The macroscopic and microscopic appearance as well as the thermo-oxidative stability, the thermal properties and the molar mass were evaluated. Although degradation was perceived due to the effect of temperature, the synergistic combination of water and temperature and compost was found to play a key role in the biodegradation of these materials. Overall, these SRCs can be considered as promising candidates, since their end-of-life management options can be guaranteed under standardised composting conditions. (C) 2018 Elsevier Ltd. All rights reserved., The authors would like to thank the support of the European Regional Development Fund and the Spanish Ministry of Economy and Competitiveness, through the Research Projects ENE2014-53734-C2-1-R and UPOV13-3E-1947. The Spanish Ministry of Education, Culture and Sports is also thanked for the FPU grant for O. Gil-Castell (FPU13/01916). Generalitat Valenciana is recognised for the APOSTD14/041 program for J.D. Badia.

cited By 3; International audience; Objectives: The dental market moves towards high-translucency monolithic zirconia dental crowns, which are usually placed either with – or without – a thin glaze layer. The microstructural features and the mechanical performances of these materials are still controversial, as well as their susceptibility to aging. This paper aims at studying these aspects in the current generation of zirconia dental crowns showing different degrees of translucency. Methods: Four different commercial zirconia materials were investigated, including one standard ‘full-strength’ 3Y-TZP and three grades with improved translucency. The microstructural features (phase composition and assemblage, grain size) were carefully studied, as well as mechanical properties (biaxial bending strength and indentation toughness), translucency and aging behavior (in autoclave at 134 °C). Aging was conducted on crowns with and without glaze to better represent clinical uses. Results: Important differences are found in terms of microstructures among the materials in terms of cubic phase content and yttria in the tetragonal phase, leading to different optical, mechanical and aging resistance properties. We show that higher cubic phase content leads to better translucency and stability in water steam, but at the expense of strength and toughness. A compromise is always inevitable between translucency and aging resistance on one side and mechanical properties on the other side. Significance: - Even so called ‘high translucent’ zirconia ceramics tested in this work should be considered as medium translucency materials.- Aging occurs in standard state-of-the-art dental zirconia and glazing does not fully avoid this issue. However, aging did not compromise strength even after prolonged duration.- Aging is null in the ‘highly translucent’ zirconia grades but at the expense of strength, which is then comparable to glass-ceramics. © 2018 The Academy of Dental Materials

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES This study is composed by three studies with respective goals: 1st study- to evaluate the effect of post-processing surface treatments (polishing, heat treatment/annealing and glazing), associated or not with autoclave aging (LTD– Low Temperature Degradation) on the surface micro-morphology, phase transformation (t-m) and mechanical behavior (flexural strength and structural reliability) of a Y-TZP ceramic; 2nd study- to evaluate the effect of postprocessing surface treatments and associations (polishing, heat treatment, glazing, polishing + heat treatment and polishing + glazing) on the surface micro-morphology, phase transformation (t-m) and fatigue behavior of Y-TZP ceramic; 3rd study- to evaluate the effect of different pre-sintering fabrication processing techniques (CAD/CAM milling x in-lab fabrication processing techniques) on the outcomes aforementioned. For three studies, discs of Y-TZP ceramic were manufactured according to ISO: 6872-2008. To the first study, the specimens were divided into 10 groups according to the aging (with or without) and surface treatment (Ctrl; “as-sintered”; Ctrl + Aut: ‘as-sintered” + aging; Gr: ground with diamond bur; Gr + Aut: ground with diamond bur + aging; Gr + HT: ground with diamond bur + heat treatment; Gr + HT + Aut: ground with diamond bur + heat treatment+ aging; Gr + Pol: ground with diamond bur + polishing; Gr + Pol + Aut: ground with diamond bur + polishing + aging; Gr + Gl: ground with diamond bur + glazing; Gr + Gl + Aut: ground with diamond bur + glazing + aging. To the second study, the specimens were divided into 7 groups: Ctrl: “as-sintered”; Gr: ground; Gr + HT: ground and heat treatment; Gr + Pol: ground and polishing; Gr + Pol + HT: ground, polishing and heat treatment; Gr + Gl: ground and glazing; Gr + Pol + Gl: ground, polishing and glazing. To the third study, the specimens were divided into 5 groups: Polished: polishing group (conventional process); Machined: CAD/CAM milling; Fine, Xfine and SiC: fabrication using a cutting machine followed by grinding with diamond bur fine, xfine and 220-grit silicon carbide, respectively. All of the grinding procedures of the third study were performed before sintering. Regarding the first study, it observed that polishing generated higher characteristic strength than the other surface treatments and reduced the surface roughness. These findings corroborate to ones from the second study: the polishing promoted higher fatigue strength. According to the third study, the grinding with fine diamond burs (46μm) before sintering showed to be the best protocol to mimic the surface and the mechanical behavior of Y-TZP ceramic milled by CAD/CAM. A presente dissertação está composta por três estudos com respectivos objetivos: estudo 1- avaliar o efeito de tratamentos de superfície (polimento, tratamento térmico e glaze), associados ou não ao envelhecimento em autoclave (LTD), na micromorfologia de superfície, na transformação de fase (t-m), na resistência à flexão biaxial e na confiabilidade estrutural (Análise de Weibull) de uma cerâmica Y-TZP desgastada por ponta diamantada; estudo 2- avaliar o efeito de diferentes tratamentos de superfície e de suas associações (polimento, tratamento térmico, glaze, polimento + tratamento térmico, polimento + glaze) na micromorfologia de superfície, na transformação de fase (t-m) e no comportamento em fadiga de uma cerâmica Y-TZP desgastada por ponta diamantada; estudo 3- avaliar o efeito de diferentes métodos de confecção de amostras pré-sinterizadas (usinagem em CAD/CAM x técnicas de confecção em laboratório) nos desfechos acima mencionados. Para os três estudos, discos de cerâmica Y-TZP foram confeccionados conforme ISO 6872/2008. No estudo 1, os espécimes foram alocados em 10 grupos de acordo com o fator ‘tratamento de superfície’(Ctrl: sem tratamento; Ctrl + Aut: sem tratamento e envelhecido; Gr: desgastado; Gr + Aut: desgastado e envelhecido; Gr + HT: desgastado e tratado termicamente; Gr + HT + Aut: desgastado, tratado termicamente e envelhecido; Gr + Pol: desgastado e polido; Gr + Pol + Aut: desgastado, polido e envelhecido; Gr + Gl: desgastado e glazeado; Gr + Gl + Aut: desgastado, glazeado e envelhecido e o fator‘envelhecimento’ (com ou sem). No estudo 2, os espécimes foram alocados em 7 grupos de acordo com o tratamento de superfície: Ctrl: sem tratamento; Gr: desgastado; Gr + HT: desgastado e tratado termicamente; Gr + Pol: desgastado e polido; Gr + Pol + HT: desgastado, polido e tratado termicamente; Gr + Gl: desgastado e glazeado; Gr + Pol + Gl: desgastado, polido e glazeado. Para o estudo 3, os espécimes cerâmicos foram divididos em 5 grupos: Polished: grupo polido (confecção convencional); Machined: usinados pelo sistema CAD/CAM; grupos Fine, XFine e SiC: discos obtidos em máquina de corte e desgastados com ponta diamantada fine, com ponta diamantada xfine, e com lixa de carbeto de silício, respectivamente. Todos os desgastes do estudo 3 foram realizados antes da sinterização. Em relação ao estudo 1, observou-se que o polimento gerou maior resistência característica quando comparado aos demais tratamentos de superfície, além de ter reduzido a rugosidade. Esses dados corroboram com os resultados do estudo 2: polimento gerou maior resistência a fadiga. De acordo com o estudo 3, o desgaste com ponta diamantada de granulação fina (46μm) previamente a sinterização, apresentou o maior potencial em mimetizar tanto as características superficiais, quanto o comportamento mecânico gerado pela usinagem CAD/CAM.

Namen te magistrske naloge je bil raziskati vpliv reakcijskih parametrov (temperature in časa) ter vrste plinov za vzpostavitev tlaka v sistemu na nastanek različnih produktov modelnega in realnega vzorca, ki sta vsebovala glikozidno vezane antioksidante. Najprej smo identificirali produkte hidrotermične razgradnje glikozidnega standarda – kvercetin-3-O-rutinozida (rutina) in ugotovili, kdaj ti produkti nastanejo ter pri kakšnih pogojih je bil izkoristek hidrolize maksimalen. Nadalje smo pri optimalno določenih pogojih eksperiment ponovili še na realnem vzorcu – ekstraktu čebulne lupine, ki smo ga pripravili iz posušenih čebulnih lupin s konvencionalno ekstrakcijo. Vsi eksperimenti so bili izvedeni v visoko temperaturnem, visokotlačnem avtoklavu ob prisotnosti ogljikovega dioksida oziroma dušika pri različnih temperaturah. Po obdelavi s subkritično vodo smo s pomočjo tekočinske kromatografije visoke ločljivosti določili produkte hidrotermične degradacije in koncentracijske profile. Izvedli smo kinetično študijo hidrotermične degradacije rutina v vzorcih oziroma njihovih komponet ter določili reakcijski mehanizem. Po izvedeni reakciji smo hidroliziran produkt (kvercetin) koncentrirali s pomočjo precipitacije. Končni produkt je vseboval 25,6 % kvercetina (modelni vzorec) oziroma 10,7 % kvercetina (ekstrakt čebulne lupine). The aim of this master thesis was to study the influence of reaction parameters (temperature and time) and type of gas used for the establishment of pressure in the system, on formation of different products in model and real samples, that contained glycoside bonded antioxidants. At first we identified the products of hydrothermal degradation of the glycoside standard – quercetin-3-O-rutinoside (rutin) and determined, when these products are formed and at which conditions the highest yield is obtained. In the next step, the experiments were repeated at previously determined optimal conditions on a real sample containing quercetin glycosides, namely – extract of onion peel. The extract was prepared from dry onion peel using conventional extraction. All experiments were performed in a high-temperature high-pressure autoclave using carbon dioxide or nitrogen atmosphere at different temperatures. After treatment with subcritical water the products and their concentration profiles were determined using high performence liquid chromatography. The kinetics of hydrothermal degradation of rutin to quercetin were evaluated and the reaction mechanism was proposed. After treatment with subcritical water have hydrolyzed product concentrated with precipitation. Final product contained 25,6 % of quercetin (model sample) or 10,7 % quercetin (extract of onion peel).

Namen tega diplomskega dela je bil izvesti hidrolizo ekstrakta čebulnih olupkov s pomočjo reaktivne subkritične vode. Čebulni ekstrakt je kompleksen matriks različnih spojin, predvsem kvercetina ter tudi različnih ogljikovih hidratov in proantocianidinov. Kvercetin v naravi običajno ni prisoten v svoji prosti obliki, ampak je najpogosteje vezan s sladkorji v t. i. glikozide. Koncentracija raztopine oziroma razmerje material : voda je procesni parameter, ki je pri mnogih študijah razgradnje s subkritično vodo pogosto ignoriran. Zato je bil cilj diplomskega dela preučiti vpliv koncentracije vodne raztopine ekstrakta čebule na nastanek prostega aglikona. Temperaturo in tlak smo pri tem vzdrževali konstantna (200 °C, 200 bar). Preučili smo tudi vpliv koncentracije vodne raztopine ekstrakta na nastanek drugih, predvsem razgradnih produktov kvercetina. V prvem delu smo izvedli ekstrakcijo čebulnih olupkov s konvencionalnim ekstrakcijskim postopkom. Ekstrakt smo v drugem delu uporabili za hidrotermične poskuse razgradnje v laboratorijskem visokotlačnem visokotemperaturnem avtoklavu (Andreas Hofer Hochdrucktechnik) pri subkritičnih pogojih vode in v prisotnosti plina CO2 za vzdrževanje tlaka v reaktorju. Dobljene vzorce smo analizirali z metodo HPLC (tekočinska kromatografija visoke ločljivosti) na sistemu Agilent 1100. Na podlagi rezultatov smo ugotovili, da je kinetika razgradnje kvercetina neodvisna od koncentracije. The purpose of this graduate thesis was to carry out the hydrolysis of an extract of onion peels using reactive subcritical water. Onion extract is a complex matrix of various compounds, in particular quercetin, and also a variety of carbohydrates and proanthocyanidins. Quercetin is usually not present in nature in its free form but is most commonly bonded to sugars in glicosides. Concentration of water solution or water to material ratio is a process parameter which in many studies of degradation with subcritical water often remains ignored. Therefore, the aim of the thesis was to examine the impact of the concentration of water solution of onion peel extract on the formation of free aglycone. The temperature and pressure were kept constant (200°C, 200 bar). We also studied the impact of concentration of water solution on the formation of main quercetin metabolites. In the first part, we performed extraction of onion peels with conventional extraction process. In the second part of the hydrothermal experiments of degradation the extract was treated in a laboratory high-pressure high-temperature autoclave (Andreas Hofer Hochdrucktechnik) in subcritical water with presence of CO2, used for maintaining constant pressure in the reactor. The resulting samples were analyzed by HPLC (high performance liquid chromatography) on an Agilent 1100 system. Based on the results, we found that the kinetics of quercetin degradation is not dependent on concentration.

International audience; Accelerated ageing was performed in distilled water at different temperatures (25, 30, 40 and 50°C) on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which is a biodegradable biopolymer, in order to estimate its lifetime in aqueous environment. In a first part, degradation mechanisms were followed by gravimetry, tensile tests and steric exclusion chromatography. Both immersion and relative humidity have been examined. In a second part, the strain at break was used as an indicator for lifetime prediction with an Arrhenius extrapolation. The study revealed the presence of only one irreversible degradation mechanism, i.e. hydrolytic degradation, which is temperature dependant. So, within the approach assumptions, the lifetime in distilled water of PHBV following Arrhenius behaviour can be predicted.

Kurkuma je začimba, zlato rumene barve, ki se pridobiva iz korenine rastline Curcuma longa L. Po tradicionalni vzhodni medicini so zdravilni učinki kurkume čiščenje krvi in prebavil, pomaga pri težavah z jetri in žolčnikom in pri hepatitisu. Ščiti jetra pred raznimi strupi in kemikalijami, je učinkovita pri zdravljenju virusnega hepatitisa in izboljšuje izločanje zaščitnih snovi v želodcu, ki ščitijo želodčno steno. Deluje protivnetno, kot antioksidant ter kemopreventivno. Kurkuma vsebuje fenolne spojine imenovane kurkuminoide, kateri dajejo rumeno oranžno barvo kurkumi in prav to naj bi bilo njena glavna zdravilna učinkovina. Kurkuma se v veliki meri uporablja tudi v živilstvu, kot barvilo ali začimba. Namen diplomskega dela je bil preučiti vpliv temperature na razgradnjo kurkuminoidov v subkritični vodi. Pri izvajanju eksperimentalnega dela diplomske naloge nas je zanimala maksimalna temperatura pri kateri so kurkuminoidi še stabilni. Preučili smo hitrost razgradnje posameznih kurkuminoidov v tem mediju. Prav tako smo preučili tudi reakcijski mehanizem razgradnje, torej razgradne produkte kurkuminoidov ter le te skušali kvantificirati. Eksperimente smo izvajali v laboratorijskem visoko-tlačnem visoko-temperaturnem avtoklavu (Andreas Hofer Hochdrucktechnik) pri subkritičnih pogojih vode. Spremljali smo vpliv temperature pri različnih reakcijskih časih. Ugotovili smo da se z višanjem temperature pri reakciji stabilnost kurkuminoidov manjša. Rezultati kažejo da so kurkuminoidi stabilni pri višjih temperaturah, pri temperaturi 180 °C pa močno razpadejo. Spremeni se njihova barva in s tem predvidevamo da razpadejo tudi zdravilne učinkovine ter nastaja vse več produktov razgradnje. Vzorce iz reaktorja smo analizirali s HPLC metodo in skušali kvalitativno kot tudi kvantitativno določiti produkte hidrotermične degradacije. V diplomskem delu je prikazan mehanizem degradacije kurkuminoidov in njihovih produktov. Naprej razpadejo na hidroksicinamične kisline, nato na vanilin, 4-hidroksibenzaldehid in še različne druge produkte, katerih nismo posebej obravnavali. Topnost kurkuminoidov v vodi je zelo slaba, zato prihaja tudi do manjših odstopanj in nihanj pri prikazu kinetičnega modela in časovne odvisnosti koncentracije komponent. Pri temperaturi 100 °C ni bilo mogoče prikazati kinetike razgradnje zaradi zelo slabe topnosti v vodi. Pri analizah smo uporabili kinetični model 1.reda in ugotovili, da je degradacija kurkuminoidov pri višjih temperaturah hitrejša kot pri nižjih. Turmeric is a spice of golden yellow colour, which is extracted from a root plant Curcuma longa L. In traditional eastern medicine turmeric is known for healing effects in blood cleaning and digestive system, it helps with liver and gall bladder problems and with hepatitis. It protects liver against various poisons and chemicals, it is efficient in healing of the viral hepatitis and it improves secretion of protective substances that protect stomach wall. It has anti-inflammatory effect as antioxidant and has chemo preventive effect. Turmeric consists of phenolic compound so called curcuminoids which give yellow orange pigment in turmeric and exactly this is supposed to be the main healing effect. Turmeric is broadly used in food technology as pigment or as a spice. The aim of diploma thesis is to study the influence of temperature on curcuminoids decomposition in subcritical water. The objective is to determine the maximum temperature, where curcuminoids are still stable. Furtheremore, the decomposition speed of the individual curcuminoids in this media has also been studied. The reaction mechanism of decomposition has been studied as well and the main decomposition products were quantified. Experiments were carried out in laboratory high-pressure high-temperature autoclave (Andreas Hofer Hochdrucktechnik) at subcritical water conditions. The influence of temperature at different reaction times was observed. It was observed that with temperature rise the stability of curcuminoids is decreasing. Curcuminoids are stable at higher temperatures, however at 180 °C they disintegrate firmly. Its colour is changed and we predict that consequently the healing effects disappears, more decomposition products are formed and the healing effects disappears samples were submitted to HPLC analysis and the products of hydrothermal degradation were analysed qualitatively and quantitatively. Degradation mechanism of curcuminoids and its products is presented in the thesis. First they degrade into hydroxy cinnamic acid, then into vanillin, 4-hydroxybenzaldehyde and then into other products, which were not treated separately. Solubility of curcuminoids in the water is very low therefore it comes to slight deviations of kinetic model and concentration dependence of compounds on time. It was not possible to show kinetic of decomposition at the temperature of 100 °C due to very low solubility in the water. Kinetic model of the 1st order was used in the analysis and we found out that degradation of curcuminoids is faster at higher temperatures than at lower.

This study aimed to determine the effects of grinding and low temperature aging on the surface micromorphology (roughness measurement, Scanning Electron Microscopy and Atomic Force Microscopy), phase transformation (t→m), biaxial flexural strength and structural reliability (Weibull analysis) of an yttrium-stabilized tetragonal zirconia polycrystalline ceramic. One hundred and eighty ceramic discs (15.0 × 1.2 ± 0.2 mm, VITA In-Ceram YZ) were prepared and randomly assigned into six groups according to 2 factors (n = 30): grinding (Ctrl without treatment, as-sintered; Xfine grinding with extra fine diamond bur - 30 μm; Coarse grinding by coarse diamond bur - 151 μm), and aging (without or with aging: CtrlLTD; XfineLTD; CoarseLTD). Grinding was performed in an oscillatory motion with a contra-angle handpiece under constant water-cooling. Low temperature degradation (LTD) was simulated in an autoclave at 134 °C, under 2 bar pressure, for 20 h. The roughness (Ra and Rz parameters) significantly increased after grinding in accordance with bur grit-size (Coarse > Xfine > Ctrl), and aging promoted distinct effects (Ctrl = CtrlLTD; Xfine > XfineLTD; Coarse = CoarseLTD). Grinding increased the m-phase, and aging led to an increase in the m-phase in all groups. However, different susceptibilities to LTD were observed. Weibull analysis showed a significant increase in the characteristic strength after grinding (Coarse = Xfine > Ctrl), while aging did not lead to any deleterious impact. Neither grinding nor aging resulted in any deleterious impact (no statistical decrease in the Weibull moduli) on material reliability. Thus, neither grinding nor aging led to a deleterious effect on the mechanical properties of the evaluated Y-TZP ceramic although a high m-phase content and roughness were observed. Este estudo avaliou o efeito do desgaste com brocas diamantadas de diferentes granulações (Grossa G e Extrafina FF), associado ou não ao envelhecimento em autoclave (LTD) na micromorfologia superficial, na transformação de fase (tetragonal para monoclínica, t→m), e nas propriedades mecânicas de uma zircônia policristalina parcialmente estabilizada por óxido de ítrio. Foram confeccionados 180 discos (15,0 Ø x 1,2 mm de espessura) conforme a ISO 6872-2008, que foram divididos em 6 grupos (n=30) de acordo com dois fatores em estudo: desgaste da superfície (controle C - sem desgaste; desgaste com broca G ou FF); e envelhecimento em autoclave (CLTD, GLTD FFLTD); Os desgastes foram executados por um operador treinado sob refrigeração constante; e a LTD em autoclave a 134ºC, sob 2 bar de pressão, por 20 horas. Os resultados indicam que o envelhecimento em autoclave associado ou não ao desgaste não foram prejudiciais às propriedades mecânicas da zircônia. Entretanto cabe ressaltar que estes estímulos promoveram grande aumento de fase monoclínica, o que pode ser um indício de degradação do material. A análise de Weibull (Módulo de Weibull) demonstrou que os tratamentos avaliados (desgaste, envelhecimento em autoclave) não promoveram efeitos deletérios, não resultando em maior variabilidade da resistência mecânica. Logo, não há indícios de que os diferentes tratamentos realizados impactem negativamente na resistência à flexão biaxial da Y-TZP. Adicionalmente, nota-se que as superfícies desgastadas com brocas diamantadas têm uma menor susceptibilidade à LTD (menor aumento de fase m).

In this doctoral dissertation, the application of subcritical water as a green medium for the extraction and processing of natural materials is presented. The work is divided into three main parts. In the first part, subcritical water is proposed as a solvent for the simultaneous extraction of oil- and water-soluble phase from oily seeds. The extraction parameters, such as temperature, time and material to solvent ratio that yield the highest amounts of both phases are examined. The quality of both obtained phases is examined. The characteristics of oils obtained using subcritical water is compared to that obtained using a conventional method. The second part of this work proposes subcritical water as an efficient solvent for the isolation of bioactive phenolic compounds from wood waste, that is produced by the forestry industry. Different wood fractions are firstly extracted in batch-mode and the fraction with the highest amounts of bioactive compounds is determined. Next, semi-continuous operation is applied, where the effects of different extraction parameters are studied on the extraction yield and quality of the extract. The effect of temperature and ethanol addition to the subcritical water on the content of single phenolic compounds identified in the extracts is observed. Lastly, the cost of manufacturing of such a product is estimated by evaluating the economics of different pilot- and industrial-scale processes operating at optimal conditions determined on the laboratory scale. The last part proposes the use of subcritical water as an efficient hydrolytic medium for glycoside bonded antioxidants, specifically those found in waste agro-industrial sources. Effect of temperature, treatment time, concentration and the atmosphere used for establishing the pressure in the reactor are first studied on a model glycoside compound - rutin and the optimal combination of reaction parameters are established for the batch-mode reactor. The degradation products of the model compound are identified and the concentration/time profiles of their degradation are observed. Furthermore, the reaction kinetics explaining the degradation of the rutin standard are evaluated. In the next step, the method is implemented on a real glycosides-containing extract. The extract is hydrolyzed at conditions obtained from the first step and the free aglycone is obtained at the highest yields possible. Lastly, the process is upgraded to continuous operation and the final hydrolyzed high-purity product is recovered. Glavni namen te doktorske disertacije je bilo raziskati uporabnost subkritične vode kot zelenega medija za izolacijo in procesiranje naravnih materialov. Delo sestoji iz treh delov. Prvi del se osredotoča na uporabnost subkritične vode kot topila za sočasno ekstrakcijo v olju in vodi topne faze iz oljnih semen. V ta namen smo študirali ekstrakcijske parametre, torej vpliv temperature, časa in razmerja material/topilo na izkoristek obeh faz. Kvaliteto obeh faz smo preverili. Kvaliteto olj pridobljenih s subkritično vodo smo primerjali z oljem pridobljenim s konvencionalno metodo. Drugi del te disertacije predlaga subkritično vodo kot efektivno topilo za izolacijo bioaktivnih fenolnih spojin iz odpadnega lesa. V prvem koraku smo ekstrahirali različne frakcije odpadnega lesa, ki nastanejo pri spravljenju lesa v gozdovih z uporabo šaržnega sistema, z namenom najti najprimernejšo frakcijo za izolacijo. V drugem koraku smo uporabili semi-kontinuirni ekstrakcijski postopek, kjer smo študirali vpliv ekstrakcijskih parametrov na ekstrakcijski izkoristek in kvaliteto ekstrakta. Določili smo vpliv temperature in dodatka etanola na hidrotemično degradacijo fenolnih spojin med samo ekstrakcijo. Na koncu smo ocenili še ekonomičnost pilotnih in industrijskih procesov z različnimi kapacitetami ekstraktorja, z namenom, približno ovrednotiti cene proizvodnje takšnega produkta. Zadnji del te doktorske disertacije predlaga subkritično vodo kot efektiven reakcijski medij za hidrolizo glikozidno vezanih antioksidantov najdenih v odpadkih živilskopridelovalne industrije. Preučili smo vpliv temperature, časa, koncentracije in atmosfere uporabljene za vzpostavitev tlaka v šaržnem reaktorju na potek hidrolize ter določili optimalno kombinacijo le-teh za modelni glikozid - rutin. Določili smo produkte hidroterminčnega razpada rutina ter degradacijske profile le-te v odvisnosti od časa. Poleg tega, smo razvili tudi kinetični model, ki matematično opisuje razgradnjo rutina v kvercetin. V naslednjem koraku smo metodo implementirali na realnem ekstraktu, ki vsebuje podobne glikozide kakor modelna komponenta in skušali dobiti proste aglikone v največjem možnem izkoristku. Na koncu smo izvedli hidrolizo tudi s kontinuirnim postopkom in skušali dobiti končni hidrolizirani produkt visoke čistosti.

Made available in DSpace on 2019-09-12T16:53:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2016 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) NUFFIC (Netherlands Organization for International Cooperation in Higher Education, The Netherlands) agency (Grants CAPES/NUFFIC) [056/14] The following study aimed to evaluate the effect of grinding and low-temperature aging on the fatigue limit of Y-TZP ceramics for frameworks and monolithic restorations. Disc specimens from each ceramic material, Lava Frame (3M ESPE) and Zirlux FC (Ivoclar Vivadent) were manufactured according to ISO:6872-2008 and assigned in accordance with two factors: (1) "surface treatment"-without treatment (as-sintered, Ctrl), grinding with coarse diamond bur (181 mu m; Grinding); and (2) "low-temperature aging (LTD)" - presence and absence. Grinding was performed using a contra-angle handpiece under constant water-cooling. LTD was simulated in an autoclave at 134 degrees C under 2-bar pressure for 20 h. Mean flexural fatigue limits (20,000 cycles) were determined under sinusoidal loading using stair case approach. For Lava ceramic, it was observed a statistical increase after grinding procedure and different behavior after LTD stimuli (Ctrl

Namen magistrskega dela je izvesti ekstrakcijo sončničnih semen z uporabo subkritične vode, ki velja za alternativno in okolju prijazno metodo za sočasno pridobitev olja in vodotopne faze. Prikazana je študija, kako različni parametri ̶ temperatura, tlak, čas in izbrana atmosfera za vzpostavitev tlaka v ekstraktorju vplivajo na izkoristek ekstrakcije obeh faz in vsebnost različnih produktov. Osredotočili smo se na kvalifikacijo in kvantifikacijo produktov hidrotermične degradacije, ki zajemajo olje in vodotopne ekstrakte pri teh pogojih. V oljih smo določili količino totalnih prostih maščobnih kislin s plinsko kromatografijo ter antioksidativnost le-teh s Photochem® metodo ter rezultate primerjali z oljem pridobljenim s konvencionalno Soxhlet metodo, pri čemer se je uporabil n-heksan kot topilo. Vodotopni fazi smo spektrofotometrično določili totalne amino kisline in amine, vsebnost totalnih fenolov in antioksidativno aktivnost. Izvedli smo tudi HPLC analizo za vsebnost klorogenske in kavne kisline ter 5-hidroksimetil furfurala. Rezultati kažejo, da temperatura in čas vplivata na količino in sestavo ekstrakta. Največjo količino olja smo dobili pri temperaturi 190 °C pri ekstrakcijskem času 30 min in uporabljeni atmosferi CO2 za vzpostavitev tlaka v sistemu, ki je znašal 100 bar. Za isti izkoristek smo s konvencionalno metodo potrebovali 2 h, vendar je ekstrakcijski izkoristek na koncu bil bistveno višji. Ugotovili smo, da se vsebnost totalnih maščobnih kislin v olju s povečanjem temperature povečuje, predvsem je to razvidno pri najvišji temperaturi, namreč 240 °C. Prav tako, s povišanjem temperature raste tudi antioksidativna aktivnost olj, ki so dosegla izredno visoke vrednosti v primerjavi z oljem pridobljenim s Soxhletovo metodo. Največja količina vodotopnega ekstrakta je bila pridobljena pri temperaturi 190 °C in ekstrakcijskem času 30 min. Rezultati kažejo visoko količino produktov hidrotermične degradacije. S povečanjem temperature smo zaznali nižje vrednosti antioksidativne aktivnosti vodotopnega ekstrakta. The purpose of the master's thesis was to perform the extraction of sunflower seeds with subcritical water, applicable as an alternative and environmentally friendly method for simultaneous extraction of oil and water-soluble phase. In the study presented, influence of different process parameters - temperature, pressure, time and chosen atmosphere for maintaining the pressure in the extractor on the extraction yield of both phases and presence of different components have been observed. We focused on quantification and qualification of different products of hydrothermal degradation of oil and water-soluble extracts at these conditions. In the oil, the amount of total free fatty acids was determined with gas chromatography. The antioxidant capacity of oil was determined with the Photochem® method. All obtained oils were compared with oil extracted with the conventional Soxhlet extraction method where n-hexane was used as solvent. For determination of total amino acids and amines, antioxidant capacity and content of phenols in water soluble phase spectrophotometric methods were used. The HPLC analysis of some phenolic compounds (5-hydroxymethylfurufral, chlorogenic acid and caffeic acid) was performed. The results indicate that the quantity of the extract was affected by temperature and extraction time. The highest amount of oil was obtained at a temperature of 190 °C, extraction time of 30 min using a CO2 atmosphere at 100 bar. We needed 2 h to get the same yield with the conventional extraction. The amount of total free fatty acids increases with increasing temperature and is highest at the highest temperature, namely 240 °C. With increasing temperature also the antioxidant capacity of oil rises, and reaches extremely high values in comparison with the oil extracted with convencional Soxhlet method. The highest quantity of water soluble extract was obtained at temperature 190 °C and extraction time of 30 minutes. The results show high degree of hydrothermal degradation, since many products have formed. With increasing temperature lower antioxidant capacity of water soluble extract could be observed.

Namen magistrske naloge je bil izvesti semikontinuirni proces ekstrakcije lesne biomase s subkritično vodo (SubCW). Poleg same ekstrakcije je pri našem procesu prisotna tudi hidrotermična degradacija lesne biomase v prisotnosti subkritične vode, pri čemer nastajajo različni produkti. Ekstrahirali smo svežo macesnovo skorjo, saj študije kažejo, da macesnov les vsebuje v vodi topne substance, fenolne spojine, ki imajo visoko dodano vrednost in antioksidativne lastnosti. Preučevali smo kako različni procesni parametri – temperatura, pretok, dodatek modifikatorja (etanol) vplivajo na vrsto in količino produktov ekstrakcije in preučevali pojav hidrotermične degradacije macesnove biomase. Ekstraktom smo določili vsebnost totalnih fenolnih spojin in antioksidativno aktivnost (DPPH metoda). Spremljali smo spreminjanje kumulativne mase fenolov in kumulativne mase suhega ekstrakta s časom. Izvedli smo HPLC analizo za nekatere fenolne spojine in izračunali izkoristke ekstrakcij. Rezultati kažejo, da temperatura vpliva na količino ekstrakta. Vsebnost totalnih fenolnih spojin je bila najvišja v ekstraktih pridobljenih z vodo, ki smo ji dodali 5 vol. % etanola pri temperaturi 300 °C. Z višanjem pretoka se viša količina ekstrakta, kar pa ne moremo trditi tudi za vsebnost totalnih fenolnih spojin. Ekstrakti imajo izjemno visoko antioksidativno aktivnost. HPLC analiza kaže, da ekstrakti vsebujejo največ 5-hidroksimetilfurfurala in 2,3-dihidroksi benzojske kisline, v primeru ekstraktov pridobljenih z vodnim medijem z dodanim 10 vol. % etanola, je poleg teh dveh komponent prisotne tudi dosti 3,5-dihidroksi benzojske kisline. Modelirali smo snovni prenos totalnih fenolnih spojin iz trdne v tekočo fazo in z difuzijskimi koeficienti pokazali, da je snovni prenos totalnih fenolnih spojin v prvi stopnji mnogo hitrejši od snovnega prenosa v drugi stopnji ekstrakcijskega procesa. The purpose of the master thesis was to establish a semi-continuous wood biomass extraction process utilized with subcritical water (SubCW) as a solvent. The extraction was accompanied by hydrothermal degradation of wood biomass leading to various products. Fresh larch bark was used for extraction since the recent studies have shown a presence of water soluble substances (phenols) with high added value and antioxidant properties. The influences of different process parameters such as temperature, flow rate and modifier addition (ethanol) on the type and quantity of extraction products and hydrothermal degradation of larch biomass were studied. The extracts were analyzed for total phenolic content and their antioxidant activity was determined. The change in cumulative weight of phenols and cumulative weight of dry extract with time was observed. The HPLC analysis of some phenolic compounds was performed and yields of extractions were calculated. The results indicate that the quantity of the extract was affected by temperature. The highest amount of total phenolic content in extracts was obtained by adding 5 volume percent of ethanol to water for extraction at 300 °C. The quantity of the extract increased with raising the flow rate of the solvent. The same cannot be said for the total phenolic content. Results indicate extremely high antioxidant activity of the extracts 5-hydroxymethylfurfural (5-HMF) and 2,3-dihydroxy benzoic acid (2,3-DHBK) were found to be the most abundant compounds according to the HPLC analysis. Beside these two components, relatively high content of 3,5-dihydroxy benzoic acid (3,5-DHBK) was also found in the extracts that were obtained with aqueous media implemented with addition of 10 volume percent of ethanol. Diffusion coefficients, which were obtained by modelling of total phenolic content mass transfer from solid to liquid phase showed, that mass transfer was much faster in the initial than latter stage of the extraction process.

In this study, the hydrothermal degradation of fats, carbohydrates and proteins in sunflower seeds after treatment with subcritical water was observed. Sunflower seeds were subjected to subcritical water in a wide temperature range (130–240 °C) for periods from 5 to 120 minutes. The oil- and water-soluble phases were analysed for products of hydrothermal degradation. Oil stability was investigated by analysing the content of free fatty acids using gas chromatography. The water-soluble phase was analysed for the presence of any formed amino acids, and the amount of carbohydrates remaining after treatment was determined. Total amino acids and carbohydrates were determined using the ninhydrin and phenol/sulphuric acid spectrophotometric methods, respectively. The results show that oils are the most stable macronutrient present in sunflower seeds. Only small amounts of free fatty acids had formed during processing but the amount drastically started to increase at 240 °C. Proteins seem to be less stable than oils, whereas carbohydrates have proven to be very susceptible to hydrothermal degradation.

Cilj diplomskega dela je bil raziskati vpliv reakcijskih parametrov (temperature, časa in koncentracije) na hidrolitsko sposobnost subkritične vode na osnovnem primeru diglikozida kvercetina – rutina. S pomočjo načrtovanja eksperimentov ter metodologije odzivnih površin smo skušali poiskati optimalne reakcijske parametre pri katerih dobimo najvišji izkoristek hidrolize rutina v kvercetin. Vsi eksperimenti so bili izvedeni v visoko-temperaturnem, visoko-tlačnem avtoklavu v inertni (dušikovi) atmosferi pri pogojih, ki smo jih v naprej določili z uporabo računalniškega programa Design-Expert 7.0. S pomočjo tekočinske kromatografije visoke ločljivosti smo določili koncentracijo kvercetina ter drugih produktov hidrotermične degradacije po obdelavi s subkritično vodo. Z uporabo metodologije odzivnih površin smo dobljene rezultate optimizirali in določili optimalne parametre, ki prispevajo k najvišjemu izkoristku kvercetina. The aim of this graduate thesis was to study the influence of reaction parameters (temperature, time and concentration) on the hydrolytic ability of subcritical water on the basic example of diglicoside quercetin – rutin. Highest yield of quercetin was based on experimental design and response surface methodology optimal reaction parameters at wich the highest yield of quercetin is obtained were determined. All experiments were performed in a high-temperature high-pressure autoclave using an inert (nitrogen) atmosphere at condition, which were predefined using Design-Expert 7.0 software. Yield of quercetin and other products of hydrothermal degradation in samples after treatment with subcritical water were determined using high-performance liquid chromatography. Obtained results were optimized using response surface methodology and the optimal parameters, which contributed to the highest yield of quercetin were determined.

The aim of this study is to establish a baseline for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) lifetime prediction in a marine environment, by means of mechanical and physico-chemical characterization of specimens immersed in continuously renewed and filtered natural seawater in the laboratory at different temperatures (4, 25 and 40°C). Samples were also aged at sea in Lorient harbour in order to compare laboratory and natural degradation mechanisms and kinetics. Due to its morphology, hydrolysis of PHBV in natural seawater is quite slow, and samples were observed to undergo preferentially an enzymatic surface degradation. Increasing the aging temperature in the laboratory promotes the water uptake and causes hydrolysis. As two degradation mechanisms occur in parallel, the choice of test conditions is critical, and the lifetime of PHBV in a marine environment is difficult to predict accurately.

[EN] The performance of biocomposites of poly(hydroxybutyrate-co-valerate) (PHBV) and sisal fibre subjected to hydrothermal tests at different temperatures above the glass transition of PHBV (TH ¿ 26, 36 and 46 C) was evaluated in this study. The influences of both the fibre content and presence of coupling agent were focused. The water absorption capability and water diffusion rate were considered for a statistical factorial analysis. Afterwards, the physico-chemical properties of water-saturated biocomposites were assessed by Fourier-Transform Infrared Analysis, Size Exclusion Chromatography, Differential Scanning Calorimetry and Scanning Electron Microscopy. It was found that the water diffusion rate increased with both temperature and percentage of fibre, whereas the amount of absorbed water was only influenced by fibre content. The use of coupling agent was only relevant at the initial stages of the hydrothermal test, giving an increase in the diffusion rate. Although the chemical structure and thermal properties of water-saturated biocomposites remained practically intact, the physical performance was considerably affected, due to the swelling of fibres, which internally blew-up the PHBV matrix, provoking cracks and fibre detachment., The authors would like to acknowledge the Spanish Ministry of Economy and Competitiveness, through the Research Project ENE2011-28735-C02-01. Generalitat Valenciana is thanked for the APOSTD/2013/054, APOSTD/2013/036 and ACOMP/2013/143 programs. The Vice-rectorate for Research of Universitat Politècnica de València is also thanked for additional support through the PAID-06-SP20120581 project. This paper is warmly dedicated to Vega Badia-Ombuena, in commemoration of her birth.

An accelerated hydrothermal degrading test was designed in order to analyse the synergic effect of water and temperature on PLA/sisal biocomposites with and without coupling agent. As well, the physicochemical properties of biocomposites were monitored along the hydrothermal test by means of Scanning Electron Microscopy, Size Exclusion Chromatography and Differential Scanning Calorimetry. The addition of fibre induced higher water absorption capability and promoted physical degradation, as observed in the surface topography. During the processing of biocomposites and throughout the hydrothermal ageing, a reduction of molecular weight due to chain scission was found. As a consequence, a faster formation of crystalline domains in the PIA matrix occurred the higher the amount of fibre was, which acted as a nucleating agent. Higher crystallinity was considered as a barrier against the advance of penetrant and a reduction in the diffusion coefficient was shown. The addition of coupling agent presented a different influence depending on the composition, showing an inflection point around 20% of sisal fibre. (C) 2014 Elsevier Ltd. All rights reserved., The authors would like to acknowledge the Spanish Ministry of Economy and Competitiveness, through the Research Project ENE2011-28735-C02-01. Generalitat Valenciana is thanked for the APOSTD/2013/054 and ACOMP/2013/143 programs. Universitat Politecnica de Valencia is thanked for the concession of a pre-doctoral grant to Oscar Gil Castell. O.G.C. wants to warmly dedicate this paper to Marita and Vicente for their endless and priceless support, and to Maria, his beloved pillar.

Zirconia has found wide application in dentistry because of its high mechanical strength and superior esthetic properties. However, zirconia degradation caused by phase transformation occurring in a hydrothermal environment is of concern. In the present study, phase transformation and microstructure of tetragonal zirconia polycrystal partially stabilized with yttrium oxide (Y-TZP) and alumina-toughened zirconia (ATZ) sintered at different temperatures were estimated. On grazing angle X-ray diffraction analysis, ATZ showed less phase transformation to the monoclinic phase during hydrothermal treatment and this transformation appeared to occur within a few micrometers below the surface. At a higher sintering temperature the monoclinic phase content of ATZ was found to be lesser than that of Y-TZP, indicating that the alumina in ATZ was effective in suppressing hydrothermal degradation. Examination by transmission electron microscopy and studying of electron backscatter diffraction patterns indicated that grain growth in ATZ was slightly suppressed compared with that in Y-TZP at higher sintering temperatures. The present study demonstrated the effect of adding alumina to zirconia for suppressing hydrothermal degradation and studied the effect of this addition on grain growth in zirconia.

International audience; Most of the organic nitrogen (Norg) on Earth is disseminated in crustal sediments and rocks in the form of fossil nitrogen-containing organic matter. The chemical speciation of fossil Norg within the overall molecular structure of organic matter changes with time and heating during burial. Progressive thermal evolution of organic matter involves phases of enhanced elimination of Norg and ultimately produces graphite containing only traces of nitrogen. Long-term chemical and thermal instability makes the chemical speciation of Norg a valuable tracer to constrain the history of sub-surface metamorphism and to shed light on the subsurface biogeochemical nitrogen cycle and its participating organic and inorganic nitrogen pools. This study documents the evolutionary path of Norg speciation, transformation and elimination before and during metamorphism and advocates the use of X-Ray Photoelectron Spectroscopy (XPS) to monitor changes in Norg speciation as a diagnostic tool for organic metamorphism. Our multidisciplinary evidence from XPS, stable isotopes, traditional quantitative coal analyses, and other analytical approaches shows that at the metamorphic onset Norg is dominantly present as pyrrolic and pyridinic nitrogen. The relative abundance of nitrogen substituting for carbon in condensed, partially aromatic systems (where N is covalently bonded to three C atoms) increases exponentially with increasing metamorphic grade, at the expense of pyridinic and pyrrolic nitrogen. At the same time, much Norg is eliminated without significant nitrogen isotope fractionation. The apparent absence of Rayleigh-type nitrogen isotopic fractionation suggests that direct thermal loss of nitrogen from an organic matrix does not serve as a major pathway for Norg elimination. Instead, we propose that hot H, O-containing fluids or some of their components gradually penetrate into the carbonaceous matrix and eliminate Norg along a progressing reaction front, without causing nitrogen isotope fractionation in the residual Norg in the unreacted core of the carbonaceous matrix. Before the reaction front can reach the core, an increasing part of core Norg chemically stabilizes in the form of nitrogen atoms substituting for carbon in condensed, partially aromatic systems forming graphite-like structural domains with delocalized pi-electron systems (nitrogen atoms substituting for "graphitic" carbon in natural metamorphic organic matter). Thus, this nitrogen species with a conservative isotopic composition is the dominant form of residual nitrogen at higher metamorphic grade.

The surface stability of yttria-doped tetragonal polycrystalline zirconia is critical for load-bearing biomedical applications. In this work, the small-scale mechanical behavior of this material is probed by employing the in situ micro-cantilever bending technique to near-surface regions. Micro-cantilevers are milled by the focused ion beam technique in the as-sintered condition as well as after hydrothermal degradation by water vapor and tested in order to investigate the effect of degradation on the local flexural response. Results demonstrate that the technique is reliable for assessing the mechanical properties of thin superficial layers and their dependence on orientation. In the non-degraded material, the flexural strength is surprisingly higher than in standard-size specimens and transformation-induced plasticity takes place during testing, inducing defects that become critical at the failure stress. The strength and stiffness of cantilevers obtained from the degraded surface are indeed much lower, and the magnitude of the effect clearly depends on their orientation with respect to the surface. These results are discussed in terms of the presence and spatial distribution of microcracks nucleated during hydrothermal degradation.