Search

In the work developed, an overview and analysis of different types of shapes of ball mill lifters are made. An analysis has been made of the factors and parameters that are important to monitor in its operation to obtain the least wear of the grinding medium and to obtain the least consumption of electricity. Based on the analysis, 3 types of lifters and sizes were selected for further experiments. All components of the mill - drum, lifter liner, and grinding bodies will be designed using a CAD program, then printed using a 3D printer and installed on the laboratory ball mill. The material used for the grinding media will be made of bioplastic PLA (polylactide or polylactic acid). By using different shapes of lifters and different charge of ball mill it will be proven whether it affects the speed, trajectory and wear of the lifters in a ball mill. [ABSTRACT FROM AUTHOR]

Stricter environmental protection measures are being enacted with the aim of reducing carbon emissions as public awareness of climate change rises. Renewable resources are created as a result. In this work, Polylactic acid (PLA) is used as a matrix for the fabrication of hybrid composites for sustainability, and jute and sisal fibres are used as reinforcement materials. This paper has been presented for the replacement of harmful synthetics and plastics. The strength of hybrid compound material is enhanced. The composite containing continuous banana and sisal fibers is fabricated by hybridization, loading sequence, and alignment of unidirectional continuous fibers by PLA as it is biodegradable plastic used for binding. The composite is made by using the technique sandwich (PLA-raw fibers-PLA). Fabrication is technically done by using manual hydraulic compression molding method. The maximum tensile and flexural strength of 80Mpa and 93.4 MPa was obtained [ABSTRACT FROM AUTHOR]

In an effort to move towards a more sustainable future, bioplastics are being promoted as sustainable alternatives to plastics. Nevertheless, the market transition to bioplastics requires the materials to be incorporated into already existing manufacturing processes with the capability of creating a variety of three-dimensional customized shapes. Thermoforming is a widely used process in the plastics industry to manufacture a wide range of products of different sizes. However, thermoforming of several types of bioplastics has received relatively scant research to date. Therefore, this study examines the feasibility of thermoforming three bioplastics, Polylactic Acid (PLA), Cellulose Acetate Propionate (CAP), and Bio-Polyethylene Terephthalate (Bio PET). Materials were tested using an industrial Form-Fill-Seal (FFS) thermoforming line equipped with a custom-designed sheet-forming chamber. Additionally, the results were compared to a commonly used thermoforming plastic, multilayer polyethylene/polyethylene terephthalate. The aim is to provide insight into the possibilities of this transition from a perspective of energy efficiency, processing speed, and possible shape-making, with an assessment of the optimal forming window for materials and a detailed analysis of the formed products. A further investigation is conducted into factors that may hamper the thermoforming performance of the materials being investigated. Results indicate that the thermoforming performance and processability of the studied materials differ clearly; PLA and BioPET yet face limitations in processability considering their properties and possibilities for their incorporation into existing thermoforming lines, whereas CAP material can compete the commercial materials on the basis of product shape, production speed, and energy requirements in thermoforming. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA) plastics are biodegradable materials manufactured from PLA resin by melt spinning and solvent spinning methods. PLA is widely applied in textile fabric, non-woven, masks and sanitary napkins applications due to excellent safety, environmental protection and good mechanical properties. The process of 3D printing is continuous and able to produce complex three-dimensional structures. PLA/ZnO composite samples were fabricated by a 3D printer. ZnO acts as filler in PLA/ZnO composites to obtain the excellent properties like specific tensile properties and density. However, ZnO agglomeration occurred at higher concentration when viewed via SEM. Printing parameters such as infill density, raster orientation and infill pattern can influence the mechanical properties of 3D samples as well. The objective of this paper is to determine the effect of infill density with different ZnO concentration on the mechanical properties of 3D printed PLA/ZnO composites. Tensile and density measurement were carried out to determine the mechanical properties of composites. The influence of 80%, 90%, 100% infill rate and ZnO concentration varied by 1 and 5 mol. As a result, higher infill rate (100%) and optimum filler concentration (1 mol ZnO) give the excellent properties thus can be used for future applications. [ABSTRACT FROM AUTHOR]

Plastics that are renewable and biodegradable have become increasingly popular in the quest for greener and more sustainable food packages. These so-called bioplastics are designed to replace traditional petrochemical polymers with renewable natural resources. To be a viable alternative to these oil-based resources the material must be successfully integrated into existing mass-manufacturing processes that transform material sheets into three-dimensional products. The purpose of this study was to examine the effect of process parameters, particularly moulding temperatures, on the 3D-formability of bioplastics during thermoforming. A numerical/visual comparison was conducted between thermoformed tray packages and reference packages made of petrochemical polymers focusing primarily on product geometry and stiffness. Three bioplastic materials were selected based on their availability and suitability for the process: Polylactic Acid (PLA) and Cellulose Acetate Propionate (CAP). The sample materials were formed to specimen trays using a custom-designed sheet-forming chamber on a commercial Form-Fill-Seal (FFS) thermoforming line. Material changes necessitated separate optimizations of the process parameters for each material. It was found that the material properties of bioplastics set certain limits to the formed geometric shapes, but these limits can be addressed during the packaging design phase, making bioplastics a viable material for environmentally friendly yet economically feasible packages. [ABSTRACT FROM AUTHOR]

Polylactide (PLA) is one of the most important bioplastics on the market with a permanent growth in production capacity. Due to its good mechanical properties, it is comparable to polystyrene. But in terms of foaming the melt strength and extensibility of commercial polylactide are rather low. Therefore such commercial grades often need to be chemically modified to induce crosslinking, chain extension or grafting by means of reactive extrusion on a twin-screw extruder. In this work different polylactide grades were used, to better understand the influence of the molecular characteristics, such as molecular weight, acid value and D-content, not only on the modification mechanism, but also on the foam properties. [ABSTRACT FROM AUTHOR]

Biodegradable plastics find more and more applications. In addition to biodegradable packaging, the number and type of products also being used in medical applications is increasing. The goal of the presented research is development technique for preparation of microcellular foams based on biodegradable polylactic acid (PLA) and its co-polymers for biomedical applications. The goal is to understand the influence of microblowing agents on the course and efficiency of microcellular process of injection molding biodegradable polymer compounds as well as on the properties of the obtained products. Polylactide (PLA) under the trade name NatureWorks Ingeo 2002D modified with chemical blowing agents having an exothermic and endothermic character of the distribution was used during the tests. The blowing agents used in the injection molding process were inserted into polymers processed in the following amounts: 0.5%, 1.5% and 3.0% wt. The article presents the characteristics of the process of injection of biodegradable plastics and the study of selected physical properties of the materials produced. The research on the structure of manufactured materials, density and the degree of porosity, mechanical strength, impact resistance and hardness are presented. It was found that as a result of the increased temperature in the plasticizing system, the blowing agents decompose and the resulting numerous microcells, due to pressure and surface development, immediately mix with the plastic. The resulting microcells are filled with both air and gases, increasing the volume of PLA. There was a change in the examined physical properties of the tested materials, mainly mechanical strength of the tested PLA compositions. [ABSTRACT FROM AUTHOR]

Biocomposite from natural rubber toughen polylactic acid (PLA) and kenaf core powder (KF) was prepared by melt blending method. The effect of kenaf loading on the biocomposite was studied based on the processability, tensile properties and morphological study. Processing and stabilization torque of biocomposite increased with increasing kenaf loading attributed from more resistance to shearing action generated by kenaf particles in the biocomposites. Addition of kenaf core powder was found to deteriorate the tensile strength and elongation at break of biocomposite due to poor interfacial adhesion as proven by FESEM micrograph. However, the tensile modulus was enhanced gradually with kenaf loading because of the rigidity and stiffness of kenaf core powder itself. [ABSTRACT FROM AUTHOR]

Polylactide (PLA) is the most important bioplastic on the market due to its good mechanical properties and a permanent growth of the production capacity. But in terms of extrusion foaming the melt strength and extensibility of commercial polylactide is too low. Therefore such commercial grades need to be modified to induce crosslinking, chain extension or branching by means of reactive extrusion on a twin-screw extruder. In this work different modifiers (chemical as well as physical modifiers) were used. The most effective results were achieved with organic peroxide. With this modifier the molecular weight, the melt viscosity, the melt strength and the crystallization rate were improved leading to foams with a closed-cell structure and improved compression behavior. Furthermore, the modifier was found to be more effective than a commercial modifier. [ABSTRACT FROM AUTHOR]

One of the most perspective directions of tissue engineering development is the use of synthetic biodegradable polymers based on polyurethane, polycaprolactone, polylactic and polyglycolic acids structures and their co-polymers. Electrospinning was shown to be an optimal way to produce nanofibers suitable for building biodegradable and highly biocompatible scaffolds. This study is devoted to the preparation of various polymer nanofilaments used as a substrate for cell therapy of cardiovascular diseases. [ABSTRACT FROM AUTHOR]

Our study aims to investigate the behavior induced by multiple injections molding cycles on the properties of olive husk flour reinforced poly lactic acid composites. The effect of the chemical treatment was studied. Biocomposite compounds (20wt% of OHF) are manufactured by twin-screw extrusion. Then, multiple injections and grinding cycles were performed (up to 8 cycles) to obtain normalized samples. Mechanical properties were performed at a macro-scale using tensile tests. The results show that the Young modulus of the composites has slightly decreased with the number of cycles and a slight reduction in the elongation at break was noticed. [ABSTRACT FROM AUTHOR]

The main objective of the presented work is to evaluate the thermal behavior of Poly-lactic acid (PLA) parts made with a Fused Deposition Modelling (FDM) process. By using a robust framework for the testing sequence of PLA parts, with the aim of establishing a standard testing cycle for the optimization of the part performance and quality. The research involves study the materials before and after 3D printing. Two biodegradable PLA polymers are investigated, characterized by different colors (one black and the other transparent). The study starts with the examination of each polymeric material and measurements of its main thermal properties. [ABSTRACT FROM AUTHOR]

The disposal of polymeric waste is increasingly becoming an issue of international concern. The use of biodegradable polymers is a possible strategy to face most of the problems related to the disposal of the durable (nonbiodegradable) polymers. Among biodegradable polymers, PLA (obtained from renewable sources) is a very attractive one, due to its good processability, biocompatibility, interesting physical properties. Hydrolysis is the major depolymerisation mechanism and the rate-controlling step of PLA biodegradation in compost. The propensity to degradation in the presence of water significantly limits specific industrial applications such as automobile, biomedical, electronic and electrical appliances, agriculture. Therefore the control of biodegradation rate is somewhat even more important than the characteristic of biodegradability itself. This is the reason why it is critical to find additives able to modulate the biodegradation rate of biodegradable polymers in relationship to the expected lifetime. Since the kinetics of hydrolysis strongly depend on the pH of the hydrolyzing medium, in this work some fillers able to control the pH of water when it diffuses inside the polymer were added to PLA. In particular, fumaric acid, a bio- and eco-friendly additive, was used. In order to control the dispersion of this molecule inside the polymer, it was intercalated in a biocompatible nanofiller: layered double hydroxides (LDH). These fillers were added to the material using meltcompounding technique, suitable for industrial application. The preliminary results obtained are encouraging toward the possibility of effectively controlling the degradation rate. [ABSTRACT FROM AUTHOR]

Biodegradable polylactic acid nanocomposites for orthopaedic implants require optimum particle dispersion and high molecular weight in load bearing applications. Novel coated hydroxyapatite nanoparticles can offer new opportunities for enhanced dispersion during melt compounding. Nanocomposites compounded with a Minilab recirculating twin screw extruder have improved flexural strength when compared to the pure polymer. Dispersion of particles within the matrix was determined from transmission electron micrographs. Chromatography revealed that the polymer matrix of nanocomposites compounded over dry nitrogen had a higher molecular weight than that over air, and hence should exhibit delayed degradation within the body. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the effect of reactive agents on the rheological behaviors, morphology and mechanical properties of two biodegradable polyesters; poly(lactic acid) (PLA) and poly(butylene succinate) (PBS) reinforced with eucalyptus fiber. Two types of reactive agents, chain extender (Joncryl®) and peroxide (Perkadox® 14), were selected. Biocomposites consisting of a constant fiber loading of 10 wt% with and without reactive agents were prepared by one-step melt-mixing methods via an internal mixer with the rotational speed of 60 rpm and the temperature of 150 and 190 °C for PBS and PLA, respectively. The biocomposite samples were then compression-molded for tensile testing. Rheological and morphological properties of the biocomposites were also investigated by means of dynamical mechanical analysis (DMA) and scanning electron micrograph (SEM). The results revealed the presence of Joncryl® in PLA biocomposites caused the increase of mixing torque, complex viscosity, storage modulus and mechanical properties when compared to the addition of peroxide. The increase of complex viscosity of PLA biocomposites added Joncryl® was due to the increase in the population of the higher molecular weights as confirmed by GPC analysis. In the case of PBS biocomposites, it showed a dramatic increase in the complex viscosity and storage modulus with decreasing crossover frequencies when adding peroxide rather than adding Joncryl®. The SEM micrographs demonstrated that the compatibility between the polymer matrix and fiber was improved when adding a small amount of Joncryl® and peroxide for both polymers, except for 0.5 phr peroxide loading, leading to an improvement of their modulus and tensile strength. [ABSTRACT FROM AUTHOR]

Poly (lactic acid) (PLA) has been known as an excellent candidate for developing the future bioplastic due to its biodegradability and competitive price. However, inherent brittleness and low thermal stability of PLA have limited its applications. Considerable studies have been developed to improve the flexibility of PLA, in which blending PLA with various plasticizers has been identified as a cost-effective way to lower glass-transition temperature (Tg) and thus improve its elongation property. In this study, PLA was modified by incorporating poly(ethylene glycol) as a plasticizer with different molecular weights (*w 400, 1000, and 6000, called respectively as PEG 400, PEG 1000, and PEG 6000) via a solvent-casting blend method. FTIR was used for analyzing the chemical interaction while TGA and DSC measured the thermal behavior of PLA/PEG. The results indicated that the addition of lower *w (PEG 400 and PEG 1000) could reduce the Tg due to the enhancement of chain mobility of PLA with PEG and so driving into a more amorphous states resulted reduction of melting temperature (Tm) compared to the neat PLA. Further, at a higher *w of PEG 6000, the longer chain of ethylene glycol, in contrast, resulted a gradual increase in the Tg as well as Tm where the value went back to the point of neat PLA compared to the other lower molecular weight of PLA. This was due to the decrease in polymer miscibility with the increasing of *w. In terms of thermal stability, the addition of PEG exhibited two step degradation behavior while the neat PLA only possessed single step degradation. The presence of PEG could act as a protective barrier layer that could hinder the permeability of the volatile compound and product during decomposition reaction and thus could eventually delay and slower the degradation process. It was observed that the addition of PEG at higher *w (PEG1000 and PEG 6000) exhibited a higher second degradation temperature up to 380 °C. [ABSTRACT FROM AUTHOR]

Stretch blow moulding process has been used for the manufacture of bioresorbable vascular scaffold (BVS) made by poly (l-lactic acid) (PLLA) to improve its mechanical performance. In order to better understand the process, thermomechanical properties of PLLA were investigated by experimental method. Extruded PLLA sheets were biaxial stretched under strain rate of 1s-1, 4s-1 and 16s-1 to simulate the deformation process applicable in the blow moulding process. Both the equal-biaxial stretch and constant-width stretch were conducted by an in-house developed equipment. By differential scanning calorimeter (DSC), thermal analysis for materials before and after stretch were compared to evaluate the microstructural change of PLLA materials in the deformation process. A constitutive model based on glass rubber model was presented to simulate the mechanical behaviour of PLLA above glass transition under biaxial deformation. [ABSTRACT FROM AUTHOR]

A new approach for the modification of polylactic acid (PLA) materials using atmospheric pressure plasma (APP) is described. PLA films plasma exposure time was 20, 60, 120 s. The surface morphology and wettability of the obtained PLA films were investigated by atomic force microscopy (AFM) and the sitting drop method. The atmospheric pressure plasma increased the roughness and surface energy of PLA film. The wettability of PLA has been improved with the application of an atmospheric plasma surface treatment. It was shown that it is possible to obtain PLA films with various surface relief and tunable wettability. Additionally, we demonstrated that the use of cold atmospheric pressure plasma for surface activation allows for the immobilization of bioactive compounds like hyaluronic acid (HA) on the surface of obtained films. It was shown that composite PLA-HA films have an increased long-term hydrophilicity of the films surface. [ABSTRACT FROM AUTHOR]

A trifunctional aziridine linker, trimethylolpropane tris(2-methyl-1-aziridinepropionate) (TTMAP), was melt blended with linear polylactic acid (PLA) to make star branched PLA. Adding pyromellitic dianhydride (PMDA) led to long chain branched (LCB) PLA. Mixing torque evolution during melt processing revealed high reactivity of aziridine with the carboxyl end group on PLA and an incomplete reaction of PMDA with the hydroxyl end group. Star-shaped PLA exhibited higher viscosity but no strain hardening in extensional flow while LCB PLA showed significant extensional hardening. Excess TTMAP in the branching reaction resulted in gel formation, which led to failure at low strain in extension. PMDA conversion was estimated based on gelation theory. The strain rate dependence of extensional hardening indicated that the LCB PLA had a low concentration of long chain branched molecules with an H-shaped topology. Unlike current methods used to branch PLA, free radical chemistry or use of an epoxy functional oligomers, our branching strategy produced strain hardening with less increase in shear viscosity. This study provides guidelines for design of polymers with low shear viscosity, which reduces pressure drop in extrusion, combined with strong extensional hardening, which enhances performance in processes that involve melt stretching. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA) is a thermoplastic biodegradable polymer that can be made from annually renewable resources. Lignin is a natural amorphous polyphenolic macromolecule inexpensive and easily available. In the present study PLA and acetylated lignin biocomposites were prepared by casting from chloroform solution. PLA can crystallize from the melt in the α and α' forms, depending on the adopted crystallization conditions. The presence of the lignin in the biocomposites can interfere with the crystal formation process. Isothermal crystallizations were performed at different temperatures, the presence of lignin causes an increase of the time of crystallization, while the overall crystallization rate and the spherulite radial growth rate decrease with enhancing the lignin content in the biocomposites. [ABSTRACT FROM AUTHOR]

A study on physical and mechanical properties of PLA/PCL polyesters reactive blends, obtained by adding LTI was made with the aim to apply these blends in biomedical field, for example for absorbable suture threads or scaffolds for cellular growth. Polyesters based reactive blends were obtained by internal mixing, and it was find out the possibility of finely control the characteristic properties of those materials by varying the weight fraction of the two components and the amount of reactive agent. Blends of different composition were characterized by torque measurements, uniaxial traction test and wet-ability. [ABSTRACT FROM AUTHOR]

Blending of ductile poly(-caprolactone) (PCL) and rigid polylactic acid (PLA) is a promising way to tailor biodegradable materials with broad range of properties. But the mutual incompatibility of both polyesters leads to compromised behaviour only. Alternative to PCL/PLA blends is application of PLA in the form of short fibres, however, difficult dispergation of flexible fibres including their poor adhesion and limited processing is a significant restriction. More effective is in situ formation of polymeric fibre-reinforced materials using microfibrillar composites (MFC) concept based on melt- or cold-drawing of a polymer blend. Important advantage of MFC is efficient dispersion and bonding of in-situ formed reinforcing fibres This work deals with combination of structure-directing and reinforcing effects of montmorillonite (oMMT) and halloysite nanotubes (HNT) in the PCL/PLA 80/20 blend with in-situ formation of PLA fibrils in the PCL matrix. In the resulting microfibrillar composite, reinforcement by rigid PLA fibrils is combined with strengthening of both components by the nanofiller (NF). Moreover, PLA fibrils formation via melt-drawing is only possible after nanofiller addition due to favourable affecting of rheological parameters of the polymer components. The structure-properties relationship and complex effect of NF on microfibrillar composite performance, causing e.g., quite comparable parameters of both microfibrillar composites in spite of lower reinforcing effect of halloysite nanotubes on components, are discussed. [ABSTRACT FROM AUTHOR]

The major drawbacks of Poly(lactic acid) (PLA) bioplastic are its cost and brittleness. This study aims to reduce the cost by foaming PLA reinforced with wood flour. A series of PLA/ natural fiber (WF) composite was prepared by using WF of selected conifers up to 5 wt%; each composite formulation was then foamed using 2 wt% of Azodicarbonamide (ADC) as chemical foaming agent. ADC effectively reduced the density of PLA and the PLA/WF composite foam by about 45% to 0.64 g/cm³ from 1.24 g/cm³ of neat PLA and 1.26 g/cm3 of PLA/WF composites when 2 wt% ADC was applied. Mechanical behaviors in terms of compressive and impact properties were investigated. With the presence of WF, the compressive stress increased with the WF content due to the good interfacial adhesion between the PLA matrix and the WF. This was verified by microscopic observation, leading to efficient stress transfer at the interface between PLA matrix and the WF. The presence of WF raised the specific compressive modulus and strength of PLA/WF composites to around 0.94 GPa·cm3/g and 2.65 MPa·cm3/g but foaming the PLA or the PLA/WF composites led to a dramatic reduction of the compressive modulus to 0.2-0.4 GPa·cm3/g, implying that the PLA and the PLA/WF foams had become softened. This was evidently observed in the significant reduction of hardness coupled with the vast drop of stress required to compressively deform the foams. [ABSTRACT FROM AUTHOR]

Poly(lactic acid) (PLA) is biodegradable bioplastic with reasonably high tensile strength and modulus. However, its brittleness and low crystallinity led to low thermal stability and limited applications. This research aims to enhance crystallization of PLA by using talc and to improve toughness of PLA by compounding with silicone rubber (SR). Films of PLA/talc and PLA/SR were prepared by using a twin screw extruder with film blowing facility. Mechanical, thermal and physical properties of both PLA/talc and PLA/SR films were investigated. DSC thermograms revealed that the addition of talc raised the degree of crystallinity from 1.4% of the neat PLA to 4.7% for the PLA films with 10 wt% talc. The cold crystallization temperature (Tcc) of PLA also decreased with increasing talc content. The ductility of PLA was significantly improved by blending with SR; the addition of only 3 wt% SR enhanced the elongation at break of the PLA/SR film by about 24 folds to 179.4% compared with 7.4% observed in the neat PLA. Under tension, the PLA/SR film yielded more easily at lower stress than those nucleated with talc. In addition, the increase of talc and SR content led to enhancement of impact strength. Significant surge of impact strength to 732 J/m was found in the PLA film with 3 wt% SR while that of neat PLA film was 328 J/m. Microscopic study revealed talc and SR dispersed and adhered well to the PLA matrix. [ABSTRACT FROM AUTHOR]

The use of biodegradable polymers is certainly an excellent strategy to solve many of the problems related to the disposal of the traditional polymers, whose accumulation in the environment is harmful and damaging. In order to optimize the use of biodegradable polymers' it is very important to understand and control the transformation processes, the structures and the morphologies resulting from the process conditions used to produce the articles and, not least, the biodegradation. The latter is strictly dependent on the just mentioned variables. The poly-lactic acid, PLA, is a biodegradable polymer. Many studies have been carried out on the degradation process of this polymer. In the course of this work we performed degradation tests on the PLA, with a specific D-isomer content, having amorphous structure, and in particular of biodegradation and hydrolysis. An acid chemical, fumaric acid, was added to PLA with the objective of controlling the rate of hydrolysis and of biodegradation. The hydrolysis process was followed, as function of time, by means of different techniques: pH variation, variation of weight of samples and variation of crystallinity degree and glass transition temperature using DSC analysis. The samples were also analyzed in terms of biodegradability by means of a homemade respirometer apparatus, in controlled composting conditions. [ABSTRACT FROM AUTHOR]

In recent years, extensive studies have been conducted on the study of the poly(lactic acid) (PLA) properties, because of its being a typical biobased and biodegradable polymer, with good mechanical properties. However, its toughness and gas barrier properties are not satisfactory and can be improved by the addition of nanofillers, such as calcium carbonate (n-CaCO3). The present work PLA composites with nano-sized precipitated calcium carbonate (n-NPCC) were prepared by melt extrusion. Thermal, mechanical and flow properties of the composites were evaluated by using a factorial design. The results showed that the addition of the nanofiller in the PLA matrix didn't improve thethermal and mechanical properties of the matrix significantly. This behavior is probably due to the presence of the stearic acid that is coating on the n-NPCC particles, resulting in a weak polymer-particle interaction. Beyond this, it was also observed a decrease in MFI of the composites when nanofiller was added and at a higher screw speed. [ABSTRACT FROM AUTHOR]

The wall slip and melt fracture behaviour of several commercial polylactides (PLAs) and poly(?-caprolactone), (PCLs) have been investigated. PLAs with molecular weights greater than a certain value were found to slip, with the slip velocity to increase with decrease of molecular weight consistent with wall slip data reported in the literature for other systems. The onset of melt fracture for the high molecular weight PLAs was found to occur at about 0.2 to 0.3 MPa, depending on the geometrical characteristics of the dies and independent of temperature. Similarly, sharkskin and gross melt fracture was observed for the case of PCLs depending on the molecular characteristics of the resins and the geometrical details of the capillary dies. It was also found that the addition of a small amount of PCL (typically 0.5 wt.%) into the PLA and vice versa is effective in eliminating and delaying the onset of melt fracture to higher shear rates in the capillary extrusion of PLA and PCL respectively. This is due to significant interfacial slip that occurs in the presence of PCL or PLA as well as to the immiscibility of the PLA/PCL blend system at all compositions. [ABSTRACT FROM AUTHOR]

Composites were made from bio degradable polymer (poly)lactic acid and lignocellulosic materials derived from natural fibers of luffa cylindrica using injection moulding technique. Before reinforcement in the poymer, the fibers were subjected to chemical treatments like alkali treatment, bleaching and acid hydrolysis. Frequency dependence of dielectric parameters like dielectric constant, di electric loss and ac conductivity of the composites were investigated in the frequency range from 1000Hz to 1MHz. The effect of wt of fiber in the composites on the above mentioned dielectric parameters were also evaluated. The experimental results show that the values of dielectric constant, ac conductivity and loss factor increase with increase in wt of fiber in the polymer matrix. However when fibers exposed to alkali treatment, bleaching and acid hydrolysis were incorporated in to the matrix, the composites showed inferior dielectric response compared to composites having fibers exposed to alkali treatment and bleaching only. It was also found that dielectric constant and dielectric loss factor of all the composite samples decreased with increase in frequency of the applied field. However, the ac conductivity of all the samples is found to increase with increase in frequency. [ABSTRACT FROM AUTHOR]

Blends of Poly-L-Lactic Acid (PLLA) with two Poly-Lactic Acid (PLA) in different proportions (90/10 and 70/30) were utilized in order to produce biodegradable and biocompatible scaffolds for soft tissue engineering applications. The scaffolds were produced via thermally induced phase separation (TIPS) starting from ternary systems where dioxane was the solvent and water the non-solvent. Morphology was evaluated by Scanning Electron Microscopy (average pore size and interconnection). Moreover a DSC analysis was carried out on the as-obtained scaffold in order to obtain information about theirs thermal properties (enthalpy of melt and crystallization). The results showed that is possible to prepare scaffolds of PLLA/PLA via TIPS. Moreover, the PLA seems to influences the TIPS process in terms of demixing temperatures. The data confirm that the morphology and the mechanical properties of the scaffold can be tuned, starting from PLLA blends and using PLA with different molecular weights. [ABSTRACT FROM AUTHOR]

Complex dielectric permittivities of biocompatible, biodegradable and shape memory polycaprolon (PCL) and polyactide (PLA) composites with nanofillers in the form of multiwall carbon nanotubes (MWNTs) and Fe3O4 are investigated in the millimeter wave range in the temperature interval from 20 to 90°C in a. It is found that the electromagnetic-wave absorption in PCL and PLA, as well as in their nanocomposites, increases with temperature in the interval from 30°C to 45°C (PCL) and from 55°C to 90°C (PLA). The samples of PLA with MWNT prepared with melamine show much lower absorption compared with the same samples prepared without melamine [ABSTRACT FROM AUTHOR]

Polylactid acid seems to be an appropriate replacement of conventional non-biodegradable synthetic polymer primarily due to comparable mechanical, thermal and processing properties in its high molecular weight form. Biodegradation of high molecular PLA was studied in compost for various forms differing in their specific surface area. The material proved its good biodegradability under composting conditions and all investigated forms showed to be acceptable for industrial composting. Despite expectations, no significant differences in resulting mineralizations were observed for fiber, film and powder sample forms with different specific surface areas. The clearly faster biodegradation was detected only for the thin coating on porous material with high specific surface area. [ABSTRACT FROM AUTHOR]