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The role of carboxyl functional groups in acrylic latex employed to fabricate an organic-inorganic composite material based on magnesium phosphate cement has been investigated. The acidic nature of the latex aqueous medium enhanced the dissolution of the magnesium oxide in the first stages of the cement reaction. The following increase in pH promoted the deprotonation of the carboxyl groups, which became involved in surface adsorption effects. Adsorption processes were found to control the nucleation and growth of the reaction products. The resulting overall hindering effect slowed down the reaction rates and delayed the precipitation of the solid phosphates with beneficial consequences, namely, the retardation of setting time and the modulation of the heat released. Modification in the morphology of the formed crystals, with the prevalence of platelet-like over prismatic habit, along with a decrease in their average size, was obtained. The crystals formed in higher amounts with respect to the neat cement because the reaction proceeds closer to equilibrium. The obtained microstructure is strengthened because of a more effective intermingling between crystals and the amorphous phase. Furthermore, the synergistic combination of polymer and phosphate cement improved the elastic properties, and reduced the water absorption, impacting positively on the durability of the composite. [ABSTRACT FROM AUTHOR]

Geopolymers offer increasingly better physico-mechanical properties concerning thermal exposure at high temperatures compared to ordinary Portland cements (OPC). This paper aims to comprehensively study the use of different types of fillers with different particle size distributions in terms of type (silica sands and cordierites) and surface area, loaded at different temperatures and dwell times (30 min and 180 min). After thermal exposure in the temperature range of 100–1000 °C, geopolymer samples were evaluated regarding physico-mechanical properties compared to samples without thermal exposure, using OPC as a reference material. Geopolymer samples were found to have a denser microstructure than OPC, supporting their better resistance to elevated temperature conditions. In addition, the influence of different filler compositions on the resulting internal structure and porosity was demonstrated. Samples containing fillers in two particle size ranges showed better densification than samples with one particle size range. Conversely, OPC samples showed the least favourable results. In addition, the mechanical behaviour of the geopolymers under static loading, especially in bending and compression tests, showed that the prepared geopolymers exhibited better properties than Portland cement at elevated temperatures, especially in the range of 500–1000 °C. In conclusion, appropriately designed geopolymer compositions have the potential to be a sustainable material, a high-performance alternative to traditional building materials. • Geopolymers (GP) with cordierite and silica sand exposed to 100–1000 °C were studied. • The physico-mechanical properties of the samples after thermal loading were investigated. • The results of the GP samples were compared with ordinary Portland cement (OPC) ones. • GP results suggest solid phase reactions and/or partial sintering at higher temperatures. • GP show better overall properties than OPC in the 500–1000 °C range. [ABSTRACT FROM AUTHOR]

A novel ceramic composite has been obtained by introducing polyvinyl alcohol in magnesium-based chemically-bonded ceramics and exploiting the cross-link reaction with glutaraldehyde during setting. The properties of the obtained material and the interaction of the polymer with the cement reaction have been investigated. Several beneficial effects were observed. Namely, an extension of the working time, a reduction in the water sensitivity, a decrease in the rate of the heat evolution during hardening. The latter has been ascribed to the intervention of surface adsorption processes, which hindered the dissolution of MgO, as well as the nucleation and growth of the magnesium phosphate products, in concert with the film forming ability of the polymer. Thanks to the complementarity of their mechanical properties, the cement and the additive operated in a synergistic fashion, allowing for the obtainment of a material possessing higher strength and better elastic properties. Three-dimensional quantitative image analysis from synchrotron X-ray microcomputed tomography evidenced the development of a more compact microstructure, comprising a higher number of crystals of smaller size. As a consequence, the pore network exhibited a higher fraction of small pores and lower pore connectivity. These characteristics contributed to hinder the water absorption, as confirmed by the fluid transport simulations within the volume. The observed correlation between the solution pH and the polymer cross-link density offers the way to effectively modulate the material performance by acting on the chemical environment thanks to its compatibility with the cross-link reaction. [ABSTRACT FROM AUTHOR]

• Acrylic latex additives were produced with and without keto-hydrazide crosslinking from standardly available low-cost raw monomers. • The results indicate that the highest effect on heat flow evolution changes has been detected in the case of latexes without crosslinking. • An important mitigation of liquid water transport properties of latex-modified composites has been achieved. • The developed latex cement-based composites may find utilization as special materials for structures or products for water-loaded constructions. Polymer-modified Portland-based composites are of interest for specific applications, in reason of their properties. There are different types of commercial additives and waste polymer-based materials applied to cement-based composites, however, their impacts on the environment are debatable. This work has prepared new acrylic latex additives with and without keto-hydrazide crosslinking from standardly available low-cost raw monomers. The influence of their incorporation into Portland cement-based fine-grained mortars has been investigated. The obtained results indicate that the highest effect on heat flow evolution changes has been detected in the case of latexes without crosslinking. The incorporation of both latex types into produced cement composites resulted in a significant increase in open porosity connected with the gradual decrease in mechanical resistance, especially the compressive strength. On the other hand, an important mitigation of liquid water transport properties of latex-modified composites has been achieved, and such properties can be tuned according to the used latex type and its concentration. The developed latex cement-based composites may find utilization as special materials for structures or products for water-loaded constructions or in areas with high concentrations of water-soluble salts or other pollutants. [ABSTRACT FROM AUTHOR]

3D printing of reinforced polymeric materials, which provides products of excellent physical and mechanical properties, is at the forefront of interest in the field of additive technologies. To ensure material, time, and financial savings, 3D objects having reduced filling density are frequently prepared. The presented work aims to study the effect of different levels of filling density (18, 42, and 62% using a honeycomb filling pattern) in contrast to 100% solid fill of carbon fiber-reinforced polyamide 6.6 materials processed by Fused Filament Fabrication on their flammability and mechanical properties. Concurrently, the effect of a commercial flame retardant additive concerning the filling density was also evaluated. The flammability and mechanical properties of the 3D printed materials were evaluated according to cone calorimeter measurements, and tensile and bending tests, respectively. It was found that the reduction in the filling density led to a pronounced decrease in mechanical properties (of about 40–50% for tensile and bending stress) and also to the deterioration of flame resistance (of about 50–70% shorter burning time), with no unambiguous correlation with the respective filling density level used. If significant economic savings are preferred, 3D objects designed with low levels of filling density (18 or 42%) are advantageous to be manufactured from nylon stabilized with a flame retardant additive, resulting in acceptable fire-resistant properties. • Preparation and testing of various honeycomb fillings with regard to properties. • With increasing filling density, the samples show better mechanical properties. • With decreasing filling density, the samples release less smoke during burning. • Optimization of filling density ensures favorable fire performance and economic savings. [ABSTRACT FROM AUTHOR]

• Innovative latex nanodispersions were employed for the consolidation of porous stone. • Their effectiveness to improve mechanical properties of Prague sandstone was proved. • Consolidation can be tuned according to type of applied latex and its concentration. This investigation aims at assessing the potential of polyacrylate latex nanodispersions as consolidation agents for sandstones. Four different latex types, implementing polymer fluorination and chemical crosslinking, have been synthesized at the scope and fully characterized. The Prague sandstone employed in this study has been selected as an example of highly porous stones used as building materials for many historical monuments. Two different concentration levels of nanodispersions have been adopted. The consolidated stone samples have been tested using a combination of physical-mechanical tests and microscopic observations. Compared to the non-treated samples, significant increments of mechanical properties (e.g. up to 3.3 times higher bending strength) have been detected after the consolidation treatment with concentrated products. Moreover, when 10 times diluted latex nanodispersions have been applied, the improvement of mechanical properties has still been significant, while moisture transport properties, such as water absorption, have been found to be comparable with those of the untreated sample. Fluorinated polymers imparted better hydrophobic properties with a contact angle above 100°. Observations using a scanning electron microscope revealed the good filling and bridging capacity of the applied consolidation agents. As demonstrated, by acting on the polymer structure, that is, by tuning the degree of crosslinking, polymer fluorination and gel content, the properties of these novel polyacrylate latex nanodispersions can be tailored to the specific stone and type of decay in order to improve the effectiveness of the treatments and obtain the desired final properties. The flexibility of their chemistry offers new opportunities for preserving objects of cultural heritage that are also at risk due to the ongoing climate change. [ABSTRACT FROM AUTHOR]

Materials resulting from incorporation of solid waste incineration fly ash into phosphate-based geopolymers, to partially replace metakaolin (up to 50% wt), were studied. X-ray diffraction, scanning electron microscopy, solid-state nuclear magnetic resonance spectroscopy and infrared spectroscopy were adopted to describe the mineralogical changes and the structural modifications of the geopolymer networks which impacted on the mechanical performance (compressive strength) of the materials. The results indicated that fly ash displays a different reactivity compared with metakaolin, behaving preferentially as a source of alkali that compete with the aluminosilicate metakaolin fraction by precipitating crystalline and amorphous phosphates. At 10 wt% of metakaolin substitution with fly ash, the extent and reticulation of the amorphous geopolymer matrix is preserved, and the mechanical properties are retained. At higher waste content (30–50% wt), the fast kinetics of the acid-base reactions involving the fly ash reactive phases prevail over the metakaolin dealumination, and the nature of the material shifts to an alkali-phosphate cement/phosphate-geopolymer composite. This behaviour, together with the development of porosity and presence of low-strength phases in the ash, led to a decline in the mechanical performance with increasing amount of substitution. All in all, this work provides fundamental information in the direction of a sustainable employment of phosphate-based geopolymers, which is limited by the relatively high cost of both metakaolin and phosphoric acid. Moreover, it indicates a recycling opportunity for this type of fly ash. [ABSTRACT FROM AUTHOR]

Flexible polyurethane foams (FPUF) are common plastic materials used in industry or consumer goods (heat and sound insulation, washing sponges, car seats). FPUF wastes are frequently taken to landfills and incineration, which causes environmental problems. The current method of physical recycling for rebound foams seems to be efficient, however, with limited usage in the structure of mattresses or construction insulations. Disadvantages of the current chemical recycling methods of FPUF consist of the slow reaction process, high energy consumption, and production of secondary waste by-products. This article deals with the special technique of the controlled depolymerisation of the studied FPUF. FPUF was depolymerised in an ambience of non-reactive liquid at a temperature of 130 °C, only giving liquid products. The depolymerisation process and the final product was characterised by titration methods, Fourier Transform-Infrared Spectroscopy (FT-IR), Gas Chromatography/Mass Spectrometry (GC/MS), and Gel Permeable Chromatography (GPC). The recycled polyol (product of depolymerisation) was tested in model polyurethane adhesive formulations and evaluated for shear tensile strength on spruce wood test pieces. [Display omitted] • Wastes from flexible polyurethane foam are taken to landfills and incinerated, causing environmental problems. • The traditional recycling approach was related to the generation of by-products requiring a significant energy input. • The new recycling approach is energy favorable and all products recovered can be processed and re-used. • The research proposes the use of recovered polyol in adhesive formulations for wood specimens. [ABSTRACT FROM AUTHOR]

• Designed eco-friendly polymer emulsions improved the properties of Magnesium cements. • Self-crosslinking is beneficial and exhibits synergistic effect with cement reaction. • More crystals, lower porosity, higher toughness, lower reaction rates, were obtained. In the context of reducing the environmental impact of cement manufacturing, magnesium phosphate cements raise interest as alternative binders in construction, for immobilization of wastes, and recycling purposes. Their use in applications is somehow limited by short setting time, brittleness and low water resistance; this calls for the use of additives. Two polymer additives were designed adopting emulsion polymerization, an environmentally friendly solution to make available polymers as water-based latex dispersions. The composites containing 5 wt% of polymer, exhibited better elastic behaviour, with up to twice the toughness of the reference sample and of a sample produced with commercial styrene-butadiene rubber latex. Moreover, the additives reduced the apparent porosity, promoted phosphate crystallization, modified the size and shape of crystals, and effectively retarded the reaction, extending working time. The acrylic emulsion developing keto-hydrazide self-crosslinking reaction imparted better properties to the composite, thanks to the synergistic effect with the MPC setting reaction. [ABSTRACT FROM AUTHOR]

The cementitious properties of natural Mg-rich olivine when reacted with a phosphoric acid solution are investigated, as a function of acid concentration and liquid/solid mass ratio. The obtained cements are composed of residual olivine crystals and amorphous silica nanoparticles dispersed in a dense and compact newberyite (MgHPO 4 ∙3H 2 O) matrix. The latter was mostly formed by packed micrometric tabular crystals, although evidence of the presence of a fraction of amorphous MgHPO 4 was also found. Water content in the raw mix was observed to play a pivotal role on the reaction pathway, either promoting porosity or hindering the crystallization of the products. Up to 57 % of olivine reactivity, whose dissolution was promoted by the curing temperature (60 °C) and low pH, was achieved. All in all, these results indicate that the industrial mineral olivine may serve a viable source of Mg for the production of phosphate cements. [Display omitted] • Mg-olivine is tested for the first time as raw material in the production of MPC. • The cements are made of amorphous silica dispersed in a dense newberyite matrix. • The precipitated Mg-phosphates are mostly crystalline. • Water plays a pivotal role in defining the reaction pathways. • Up to 75 MPa of compressive strength is reached. [ABSTRACT FROM AUTHOR]

• MSWI-FA is tested as either inert or reactive component in MKPC. • In both conditions, dissolution reactions involving Ca, Mg, S, Al, Si and Zn occur. • The precipitated secondary products are mostly amorphous phosphates. • The heavy metals leaching is below the Italian legal limits. • A 60% compressive strength increase is observed for the reactive formulation. In this study, the behaviour and reactivity of Municipal Solid Waste Incineration Fly Ash (MSWI-FA), introduced in the formulation of magnesium potassium phosphate cement (MKPC), was investigated by considering the waste either as fully inert or reactive. MSWI-FA induced structural and compositional modifications in MKPC as a consequence of dissolution/precipitation processes which involved many MSWI-FA elements (e.g., Ca, Mg, Al, Si, Zn) and led to the formation of mostly amorphous phosphate secondary products. The reaction path has been described in terms of the early fast dissolution of MSWI-FA, with precipitation of very low solubility phases, and subsequent late precipitation due to pH changes and water subtraction during MKPC gelification. The increase in amorphous content peaked to 50 wt.% and it has been related to the improved behaviour with respect to the leaching of heavy metals (reduced by 70-99%), pointing to this cement as an excellent matrix for their chemical stabilization. The obtained MKPC microstructure exhibited better mechanical performance, with an improvement of up to 60% in compressive strength. All in all, the results indicated that the incorporation in MKPC is a viable recycling opportunity for MSWI-FA, although, for an effective cement formulation, its reactivity must be taken into account. [ABSTRACT FROM AUTHOR]

Citric acid modulates the release of heat and the rates of reaction in magnesium phosphate cements, chemically-bonded ceramics employed in biomaterials, for the encapsulation of nuclear wastes and in civil engineering. To gain knowledge on the mechanism of action of citric acid and, therefore, help in the effective material design, the reaction was studied in-situ to address molecular issues. The results indicated that citric acid enhances dissolution of MgO by promoting surface ligand-exchange reaction which leads to a net acceleration of the first reaction step. The Mg2+ ions released in solution are complexed by citrates. The degree of supersaturation is therefore reduced, delaying the nucleation of phosphates. The growth of stable nuclei, the crystal growth, and the amorphous-to-crystalline transformation are hindered due to citrate adsorption. The formed surface complexes are prevalently inner-sphere complexes exhibiting the combined coordination of hydroxyl and carboxylate groups. The mutating chemical environment dictates the coordination modes of citrate, the competition with phosphates, and the stable forms of phosphate products. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of PA12 recycling on the hygroscopicity of SLS printed parts was tested. • The sintered particles were found in the post-industrial recycled powder. • Molar mass increase was found in the post-industrial recycled powder. • Secondary crystallization was found in the post-industrial recycled powder. • Parts from the post-industrial recycled powder were less moisture sensitive. The ageing and recycling of polyamide 12 (PA12) powder are key issues in selective laser sintering (SLS) processing, while hygroscopicity is an important defect of PA12 products during use. This paper aims to correlate PA12 powder recycling with changes in the hygroscopicity of printed parts, which is significant for a comprehensive understanding of the impact of ageing on the performance of PA12 parts. PA12 powder was utilized in different grades: virgin, post-industrial recycled, and virgin-post-industrial recycled mixture (virgin-to-post-industrial recycled powder weight ratio of 25/75). The mutual effects of the powder grade, print orientation used in the building process, and absorbed moisture on the properties of printed parts were evaluated. Molar mass increase and secondary crystallization have been demonstrated in the post-industrial recycled powder, being responsible for the worse sintering quality in the SLS process. Therefore, the printed parts made from the post-industrial recycled powder or the virgin-post-industrial recycled powder mixture exhibited worse mechanical strength, a higher porosity, and hence a higher level of hygroscopicity in terms of moisture absorption and wettability. On the contrary, the printed parts made from the virgin powder were found to be more moisture-sensitive in terms of the decline in mechanical strength in the wet state because of the higher content of the amorphous phase holding the plasticizing water. [ABSTRACT FROM AUTHOR]

This paper focuses on the preparation of two types of hydrophobic nanolayers using electrospinning technology. The first synthetic approach consists in direct fiberizing of polymeric phenyl-methyl-polyphosphazene Ph-Me(p) with the aim to preparing nanolayers that have significant hydrophobicity and thermal stability. The preparation of Ph-Me(p) is a multi-step reaction which produces a relatively low amount of the product. The second area of our interest was the creation of nanofibers formed from a mixture of some commercially available organic polymers and a cyclo -phosphazene derivative. In this case, tri(phenyl)-trimethyl- cyclo -triphosphazene, Ph-Me(t), whose synthesis is less complicated than its polymeric form, was used as an additive. The influence of the Ph-Me(t) additive in the nanofibers on the affinity to water was compared with the affinity of nanolayers made from a pure commercial polymer, i.e. without any phosphazene additive. It was also shown that the hydrophobic properties of fibers formed from Ph-Me(p) dissolved especially in THF are better than those of the nanofibers composed of a commercial polymer with the addition of Ph-Me(t). [ABSTRACT FROM AUTHOR]

[Display omitted] • The role of carbonized bio-based aggregate in the preparation of advanced lightweight concretes was investigated. • Honeycomb-like structure of BA particles was observed. • Lower BA additions up to 50 vol% allow to make concretes with sufficient strength for structural applications. • Highly thermal and acoustic insulating composites, suitable for building claddings, were prepared with BA content above 25 vol%. Concrete is the most utilized man-made building material and its global production reaching 25 billion tons per year represents a huge burden on our environment. Unsurprisingly, a lot of effort is dedicated to searching for suitable replacing materials of concrete constituents, e.g. of mineral aggregate that usually forms 70–80 vol% of fresh concrete mix, not only to reduce the depletion of our natural resources, but, at the same time, to improve some of the concrete properties. For example, dense building materials are not very effective in acoustic-insulation performance. In this context, renewable resources can provide a possible solution in the preparation of advanced concrete composites that will help to reduce noise originating in high populated urban and/or industrialized areas. This paper is focused on the application of carbonized lightweight bio-based aggregate (BA), having about 63 % lower thermal conductivity compared to the traditional ones, in the manufacturing of lightweight concretes which, related to BA quantity in mixes, dispose with considerably mitigated thermal transport properties and enhanced acoustic-insulation function. Traditional dense aggregate was replaced with the bio-based alternative in the amount of 0–100 vol% and the batch water content was adjusted to keep similar consistency (class S4) of fresh concrete mixes. After 28 days of water curing, the development of dry bulk density, open porosity, flexural and compressive strengths as well as thermal and acoustic performance in the dependence on bio-based aggregate content were determined on hardened specimens. Experimental investigation revealed significant lightening effect of BA particles having a honeycomb-like porous structure and thus promoting the high thermal and acoustic performance of developed concretes. Accordingly, hardened concrete samples with alternative aggregate content only showed 7.5 times lower thermal transport and about 16.2 % improved acoustic performance compared with ordinary dense concrete. In addition, lower BA dosages (up to 50 vol%) allowed to produce concretes disposing sufficient strength parameters – average flexural strength about 6.5 MPa and compressive strength about 27.0 MPa maintaining their usage for structural purposes. Furthermore, bio-based aggregates are sorted among renewable resources that may mitigate environmental impacts connected with the quarrying of traditional filling materials, and thus contribute to higher sustainability of concrete production. [ABSTRACT FROM AUTHOR]

• The waste incorporation up to 25 vol.% allows structural application of concrete. • Considerable lightening and high thermal performance of composites were observed. • Designed concretes may find usage for special filling and flooring applications. • The waste application mitigates negative environmental impacts. Intensive quarrying of natural non-renewable resources belongs to the actual topics related to the dynamically developing construction industry worldwide. However, at the same moment, an appreciable quantity of construction and demolition waste (CDW) is generated, from which the primacy to concrete, ceramic and masonry derived materials is attributed. These are already traditionally applied in concrete manufacturing as supplementing and filing materials due to their good recycling ability. Nevertheless, a number of material blends which separation is complicated or highly financial demanding still remain and thus burden our environment. This work has been aimed at the effective application of lightweight blended building waste (LBW) in the manufacturing of eco-friendly concretes. Concrete mixtures with the volumetric content 0–100% of the waste blend have been prepared. The influence of LBW on 28 days' water cured samples has been investigated with the application of a wide range of experimental procedures and various instrumental techniques. Performed tests revealed a substantial lightening effect of LBW – leading to hardened concretes with a unit weight of about 760 kg·m−3. On the other hand, a high rate of lightening caused considerable decrease in strength properties of produced composites. However, application of LBW up to 25% can be used to preserve usage of these blended concretes for construction applications. Other performed tests showed excellent thermal performance of waste aggregate enriched concretes, and thus these materials may find usage for special filling and flooring applications with minimum loading of bearing structures. [ABSTRACT FROM AUTHOR]