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In this paper, woven wearable metamaterials are developed. For this purpose, several frequency selective surface (FSS) textile absorbers are proposed. The main structure of the FSS consists of a fabric with different patch shapes, a back ground plate (conductive layer) and a textile substrate. Firstly, the effect of the substrate used on the S-parameters and absorbance in order to detect the best substrate is analyzed. Then, once selected the best substrate, the effect of the patches’ shape on the performance of the wearable metamaterial is analyzed. It was found that the fabric that gives the best results is the one composed of 65% polyester and 35% cotton and the best patches are the cross-shaped ones. The developed FSS can be used in wearable textiles to protect the human body from microwave radiation emissions.

Within the building construction sector, fiber cement boards have attracted interest as facade cladding materials in the last ten years, especially those that incorporate –for reinforcing purposes– natural and/or recycled synthetic fibers (i.e, from the textile industry). So far, the design-governing parameters of facade cladding panels have been mechanical strength, durability, constructability, aesthetics, insulation capacity, and fire resistance. From the sustainability perspective, the impact of the facade on the economic and energy efficiency performance is most often the parameter that leads the decision-making process. Within this context, the quantification of the sustainability performance of the facade –accounting for economic, environmental, and social indicators– is unfrequently carried out in design and project phases, this being attributed to the lack of methodologies that allow considering and quantifying some relevant indicators representative of the facade sustainability performance. As consequence, decisions made based on solely economic and on some of the environmental indicators might lead to solutions with lower sustainability performance than that required (or expected). Recycled textile waste fabric-reinforced cement board as a facade-cladding material for building envelopes is the focus of this research. In order to characterize the fire resistance, and thermal and acoustic insulation –as relevant serviceability parameters– of this material, an experimental program was carried out. Likewise, the sustainability performance of this facade-cladding is assessed through a method based on the Integrated Value Model for Sustainability Assessment (MIVES). This multi-criteria decision making (MCDM) model relies on the value function concept and the multi-disciplinary participation of experts to identify and quantify the relevant indicators of the facade sustainability performance and the relative importance of indicators and requirements. The MIVES-based model generated for this research can be straightforwardly used for assessing the sustainability performance of facade-cladding techniques made of any material and for any type of building (and location). The application of the MIVES model led to the sustainability index of this new material for facade-cladding ranging from 0.68 to 0.71 (/1.00) for different weighting scenarios. The authors express their gratitude to the Spanish Ministry of Economy, Industry, and Competitiveness for the financial support received under the scope of the projects CREEF (PID2019-108978RB-C32) and RECYBUILDMAT (PID2019-108067RB-I00).

The aim of this work was to develop and characterize polyurethane-based shape memory polymer filament yarns of a suitable diameter and thermo-mechanical performance for use in tailored multi-sectorial applications. Different polymer compositions – pure shape memory polyurethane and shape memory polyurethane composites with 0.3 and 0.5 wt.% of multi-walled carbon nanotubes or carbon black as additives – were studied. Filaments were obtained using a melt spinning process that allowed the production of the permanent and temporary shape of the shape memory polyurethane filament. Two drawing speeds (20 and 32 m/min) were studied. Characterization techniques such as the tensile test, differential scanning calorimetry, and dynamic mechanical analysis were used to investigate the shape-memory effect of the filaments. Pure and additive shape memory polyurethane filament yarns of a controlled diameter were produced. The results indicated that the pure shape memory polyurethane on the temporary shape had the highest tensile strength (234 MPa). Filaments with carbon black revealed a significant strain (335%) in the permanent shape with respect to the other filaments. The melt spinning process influenced the soft segment glass transition temperature (Tgs) significantly, with a decrease in the temporary shape (first heating) as compared to the permanent shape (second and third heating). However, only the 0.5% multi-walled carbon nanotubes additive clearly influenced the filament, increasing the Tgs by 10°C. The additives also influenced the shape-memory effect, obtaining an increased fixity ratio (up to 97%) with the multi-walled carbon nanotubes additive and an increased recovery ratio (up to 86%) with the carbon black additive.

In recent years, great efforts have been made to research and develop advanced thermodynamic textiles that can change their thermal behavior in response to external stimuli. More specifically, shape memory alloys and shape memory polymer coatings have used for thermal comfort applications. However, the use of shape memory polymers in the form of filament yarns integrated in the fabrics has not yet reported. These fabrics have some advantages related to versatility in shape design. The aim of this study was to develop woven SMPU-based fabrics with reversible thermodynamic properties induced by weft SMPU filament yarns interlaced into polyester (PES) fabrics. To this end, PES woven fabrics with different ratios of weft SMPU filament yarns (PES/SMPU 1:0; 3:1; 1:1; 1: 3, and 0:1) were developed and their thermodynamic properties (thermal resistance, water vapor resistance, and permeability index), shape memory effect, and mechanical performance were evaluated and compared to the 100% PES reference fabric. All the SMPU-based fabrics developed were classified as extremely breathable (water vapor resistance

This study was performed to study the effects of the cement paste composition (calcium aluminate cement—CAC and a geopolymer in comparison to Portland cement—OPC) on bamboo pulp and nanofibrillated cellulose (NFC). The changes in the composition and chemical structure of the fibers were analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The changes in the mechanical strength were evaluated through tensile tests on the fibers after immersion on the cement pastes, in the form of sheets. The XPS results showed that the immersion of the pulp and NFC in the different pastes (CAC, geopolymer and OPC) modified the chemical surface of these fibers: it was found removal of lignin and extractives and some degradation of hemicellulose and cellulose. The FTIR analysis indicated modifications in the hydrogen bonds energy. The tensile strength of pulp sheets decreased in 70% and 34% after immersion in OPC and geopolymer, respectively. The tensile strength of the NFC sheets decreased 36%, 68% and 54% after immersion in OPC, CAC and geopolymer, respectively. Thus, the response of the bamboo pulp and NFC immersed in different cement pastes was different due the inherent characteristics of such fibers, and not only the Portland cement should be considered as harmful to lignocellulosic fibers. Although CAC and geopolymer are free of calcium hydroxide, the high alkalinity of these pastes also accelerated the degradation process of lignocellulosic fibers.

Fiber reinforced mortars (FRM) are growingly used in several fields of building technology (e.g., façade panels, roofing, raised floors and masonry structures) as building elements. One of the promising type of fiber for these composite materials can be textile waste originated from cloth wastes. The use of this sort of recycled materials and wastes as cement reinforcement within the building sector can play a relevant role in sustainability, both the environmental, economic and social perspectives. In this paper, the design mechanical properties (flexural and compressive strengths at 7, 28 and 56 days as well as toughness and stiffness) together with durability properties of cement pastes reinforced with short Textile Waste Fiber (TWF) in contents ranging from 6 to 10 % by weight fraction cement was investigated. The results were compared with those obtained from Kraft Pulp pine Fiber (KPF), taken as reference. The main conclusion is the feasibility of using this type of fiber as potential reinforcement in construction materials with the optimum dosage of 8%. Although the flexural resistance and toughness of the TWF composite are lower than KPF control by almost 9%, the compressive strength and stiffness together with durability properties have proven to be enhanced respect to the reference composite. The authors express their gratitude to the Spanish Ministry of Economy, Industry and Competitiveness for the financial support received under the scope of the projects RECYBUILDMAT (PID2019-108067RB-I00) and CREEF (PID2019-108978RB-C32).

In this work, the hydrophobization of lignocellulosic jute fibers was achieved via the laccase/TEMPO-mediated grafting of octadecylamine (OA) on their surface, with the aim to improve the interfacial compatibility with nonpolar polylactic acid (PLA) resins in fiber-reinforced composites. The modified jute fibers were analyzed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The characteristic vibrations of methylene groups and the increase in the surface C/O ratio of the jute fibers after the enzymatic treatment indicated that OA molecules were successfully grafted onto the jute fiber surface mediated by the laccase/TEMPO system. It was shown that the grafted jute fibers had increased surface hydrophobicity and reduced polarity with water contact angle of 124.2 °, diiodomethane contact angle of 94.1 ° and surface free energy of 11.44 mJ/m2, which were attributed to the presence of the OA nonpolar alkyl chains on their surface. The tensile, bending, and dynamic mechanical properties of the hydrophobized jute/PLA composites were enhanced, which suggested stronger interfacial adhesion between the jute fibers and the PLA matrix. The mechanical stability was investigated by water immersion measurements and it was found that the modified jute/PLA composites were better in this regards than the control jute/PLA composites. Therefore, this enzymatic hydrophobic modification could be used as an effective and eco-friendly method to produce natural lignocellulosic fiber-reinforced composites with excellent performance.

In this work, several fabrics with different composition and structure have been used as the substrate for the production of wearable textile-embroidered dipole antennas. The performance of the antennas has been determined by measuring their resonance frequency, return loss and bandwidth. To determine their durability as wearable fabrics, the performance has been assessed before and after subjecting the antennas to washing and abrasion cycles. The results revealed that the woven fabrics presented a good washing fastness, even in fabrics having elastic fibers or low-crimp structures. In all cases, a good performance of the antennas was maintained after 30 washing cycles. For the abrasion cycles, the substrates with higher stability (measured as the crimp ratio) presented a higher wear fastness, whereas a higher variability was observed for the substrates with lower stability.

This paper examines the influence of weaving variables such as yarn count, number of layers, warp and weft ratio, materials of the top layer, weft density and interlocking cell shape, and size on the thermal performance of multilayer interlocked woven fabrics. A split-plot design was used to construct a total of 64 fabric structures, which were assessed for thermal performance in terms of resistance to convective, conductive, and radiative heat. It was found that, for equal weft density and yarn number, protective performance improved with the number of fabric layers and with the presence of air cells between these layers, especially if air was not trapped within and could rather pass freely between the cells. An optimal combination of factors for the thermal response to the three types of heat was established via a Derringer–a much needed desirability function. The results of this paper are useful for identifying the interaction between configuration parameters and thermal performance, and hence for the design of improved heat protective clothing.

The thermal and fire behaviour of calcium aluminate cement-based composites with a variable metakaolin content (from 0 to 40 wt% addition) reinforced with nonwoven flax fabrics has been examined. The fire behaviour was assessed using epiradiator and small-scale fire testing. The composites did not emit smoke or generate flames, nor did they produce spalling. Their integrity was maintained above 1000 ¿C. Samples having a higher metakaolin content revealed a delay in the temperature of the unexposed surface until reaching 760 ¿C. The effect of exposure to high temperatures (250 ¿C, 450 ¿C, and 950 ¿C) on bending behaviour was examined. The fibres were found to maintain their reinforcing capacity up to 250 ¿C, while the matrix maintained its performance up to 450 ¿C. The addition of metakaolin reduced conductivity and diffusivity. The results of the thermal and fire behaviour of the tested composites indicated that they may be suitable for façade panels for outdoor applications Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables

Large amounts of nonrenewable resources are depleted by the construction industry in addition to the generation of million tons of mineral waste and carbon dioxide gas every year. For the sake of a more sustainable consumption pattern of building materials, as well as for reducing the waste flux to landfills, the use of recycled materials and wastes should be researched and motivated. In this sense, textile waste (TW) nonwoven fabric from residues of the garments and textile industries are investigated as internal reinforcement for cement-based matrices to enhance ductility and cracking control. To this end, an extensive experimental program was carried out to characterize both the mechanical and durability properties of the composite. The results were compared with those obtained from flax nonwoven fabric, taken as a reference (FNH and FH composites). All the composites showed a remarkable improvement in terms of toughness and post-cracking stress-bearing capacity, six being the optimum number of TW reinforcing layers. Through the analysis of the results obtained, the feasibility of using TW composite as a potential construction material in non-structural applications was confirmed. The extension to structural applications of low-medium responsibility is still required further research; nonetheless, the results are promising to this respect. The authors express their gratitude to the Spanish Ministry of Economy, Industry and Competitiveness for the financial support received under the scope of the projects RECYBUILDMAT (PID2019-108067RB-I00) and CREEF (PID2019-108978RB-C32).

The aim of this work was to develop strain hardening cementitious composites (SHCC) and durable composites based on calcium-aluminate cement (CAC) with variable metakaolin (MK) content (from 0 to 50 wt%) and flax nonwoven natural textile reinforcement. For this purpose, three experimental packages were performed in order to: a) evaluate the effect of MK content on the mechanical performance and cement mixture microstructure of the matrix, b) analyze the effect of the cement mixture on the performance of the natural fibers, and c) determine the bending behavior and durability of the composites. It was found that the strength and modulus of the 28 days cured cement paste under compression and bending modes decreased with MK content. Low degradation of the natural fibers on the CAC-MK matrix was found and this degradation was lower for higher MK content. The developed composites presented a ductile behavior and high tensile strength and maintained this performance after subjecting them to a 250 cycles of accelerated aging. The authors acknowledge Prof. Claret Verdú and Prof. Maite Más from the DEAB-UPC for their help on the statistical analysis of the results in this study. This work was supported by the Ministerio de Economía, Industria y Competitividad (MINECO) of the Government of Spain [project BIA2014-59399-R]. The author Heura Ventura is a Serra Húnter Fellow

The aim of this paper is to evaluate the influence of sustainable surface treatments —performed on flax nonwoven fabrics as textile reinforcement— on the durability of calcium aluminate cement (CAC) based composites. Two treatments are considered: an alkaline treatment (for increased stability and adhesion), and a treatment with soybean oil (to reduce fiber degradation). The cement hydration was studied by analysis of back-scattered scanning electron microscopy images, which revealed variations nearby the fibers owing their capacity for water absorption and presence of oil on the surface. A retarding effect on cement hydration was observed on the composites prepared with the oil-treated fabrics. The composites containing the alkali treated fabrics had better mechanical properties and also the highest durability. For these composites it was found an optimized fiber-matrix adhesion and penetrability of the cement to the fabric.

The enzymatic functionalization of lignocellulosic fibers using oxidoreductases was successfully achieved by targeting lignin moieties as grafting sites on the surface. In this study, a novel strategy for hydrophobization of lignocelluloses was investigated, which involved the laccase/TEMPO-mediated grafting of octadecylamine (OA) onto both lignin and cellulose components of jute fabrics. The results showed that OA monomers were successfully grafted onto jute fabric surface using the laccase/TEMPO system with the grafting percentage and efficiency values of 0.712% and 10.571%, respectively. The primary hydroxyl groups of cellulose were oxidized by laccase/TEMPO to carbonyl groups, which were then coupled with amino-contained OA monomers via Schiff base reaction. The phenolic hydroxyl groups of lignin were transformed by laccase to radicals, on which OA molecules were grafted via Michael addition reaction. Consequently, grafted jute fabrics showed a considerable increase in the surface hydrophobicity with a contact angle of 125.9° and a wetting time of at least 2 h. Furthermore, there was an acceptable decrease in the breaking strength of jute fabrics by 13.60%, and the color of fabrics turned yellowish and reddish. This eco-friendly enzymatic process provides a new strategy for grafting hydrophobization and even functionalization of lignocellulosic fiber materials using amino compounds.

Composite materials have attracted the attention of some industrial fields due to their lightness and relatively good mechanical properties. One of these properties is impact strength, essential to ensure the processability and application of these materials under impact conditions. In addition, it is known that water absorption has a plasticizing effect in polymers and polymer composites which can change the properties of such materials and limit their use. Moreover, this effect worsens when hydrophilic reinforcement is used. In this work, the impact and water uptake behavior of totally bio-based composites from polyamide 11 (PA11) and lignocellulosic pine fibers mechanically processed as stone groundwood (SGW) were studied. The impact resistance of PA11 and its composites was higher than expected, obtaining better results than those of polyolefin-based materials. The evaluated mechanical properties and the micrographs showed an adequate interface. The water uptake test showed that PA11 and its composites had non-Fickian and Fickian case I behaviours, respectively. It was found that the maximum water absorbance was similar to that of SGW reinforced polypropylene.

In this study, we present an analysis of the rheological behaviour of calcium aluminate cement (CAC) based pastes with variable metakaolin (MK) contents (0–50%), with and without superplasticizer (SP) and at different water/cement ratios. Viscosity tests were performed under variable shear rate to analyze the macroscopic flow behaviour of the pastes. Furthermore, the penetrability of the pastes into natural fiber nonwoven fabric was examined using optical microscopy. The penetrability results were assessed to determine the suitability of the pastes for production of textile-reinforced composites. It was found that increased metakaolin content and decreased water/cement ratio both led to reduced viscosity. The addition of SP led to a reduction in viscosity, although this effect was lessened at high MK contents. Penetrability tests indicated that the paste viscosity significantly influenced the ability of the pastes to flow through the nonwoven structure, with more viscous pastes showing reduced penetrability.

In this paper, the compositions of commercial lead and non-lead X-ray protective materials were investigated by material analysis methods as FTIR-ATR, SEM/EDS, and density measurement to estimate the content of the structures, which were not declared explicitly by the manufacturers. Moreover, Monte Carlo simulations were carried out with the estimated weight ratio of the element amounts and actual densities. Hypothetical compositions were also generated and all the compositions were evaluated in terms of weight per area values versus dose transmission values. The results show that non-lead materials are basically composed of antimony and bismuth. The commercial material with the lowest density showed insufficient attenuation performance, hence it should not be proposed for lightweight apron production. The simulation results indicated also that non-lead compositions that contain adequate amount of radiopaque elements can be environmentally friendly alternatives for lightweight aprons at 60 kV and 90 kV. Besides, at higher levels as 120 kV, non-lead compositions lose their weight advantage against lead compositions.

In this article, with the aim of promoting sustainability, contributing to the circular economy and the fight against climate change, the production of composite materials from Bio-polyethylene reinforced with corn stover fibers has been studied. The behavior of the materials obtained has been studied experimentally and by mathematical models of micromechanics. The composite materials were produced by extrusion and then injection with from 10 to 50 wt.% of fibers. The creation of a good fiber-matrix interface was studied by the incorporation of coupling agent between (0&ndash, 8 wt.%). Increase of 131.2% on tensile strength for 40wt.% reinforcement was achieved by adding 6 wt.% of coupling agent. The correct interface was demonstrated by a correlation of 0.99 between the experimental results and the results of the mathematical models used.

Most of the decisions taken during the early design and development steps of a new product compromise a large part of its cost, including its environmental footprint and energy consumption. This is of special interest for the automotive industry that has made an effort to increase its sustainability. Adjectives like bio-based, recyclable or biodegradable are commonly used as synonyms of greener; nonetheless, such materials must achieve the requirements of the industry. This paper researches the use of alternative materials instead of glass fiber reinforced polypropylene, a commodity material. The authors propose using a wood fiber reinforced polyamide 11 composite as replacement. The research discussed the mechanical properties of such composites, obtaining values similar to the currently used materials. Moreover, a case study was performed to assess the behavior of the composites when used to manufacture a door car handle. The materials with reinforcement contents ranging from 40 to 60% showed its ability to replace the commodity materials. Furthermore, a preliminary LCA analysis was performed to evaluate the environmental footprint of the researched materials. In was found, that, in terms of energy and carbon footprint, the PA11 composites were penalized by the energy cost of the PA11 monomer production.

The replacement of commodity polyolefin, reinforced with glass fiber (GF), by greener alternatives has been a topic of research in recent years. Cellulose fibers have shown, under certain conditions, enough tensile capacities to replace GF, achieving competitive mechanical properties. However, if the objective is the production of environmentally friendlier composites, it is necessary to replace oil-derived polymer matrices by bio-based or biodegradable ones, depending on the application. Polyamide 11 (PA11) is a totally bio-based polyamide that can be reinforced with cellulosic fibers. Composites based on this polymer have demonstrated enough tensile strength, as well as stiffness, to replace GF-reinforced polypropylene (PP). However, flexural properties are of high interest for engineering applications. Due to the specific character of short-fiber-reinforced composites, significant differences are expected between the tensile and flexural properties. These differences encourage the study of the flexural properties of a material prior to the design or development of a new product. Despite the importance of the flexural strength, there are few works devoted to its study in the case of PA11-based composites. In this work, an in-depth study of the flexural strength of PA11 composites, reinforced with Stoneground wood (SGW) from softwood, is presented. Additionally, the results are compared with those of PP-based composites. The results showed that the SGW fibers had lower strengthening capacity reinforcing PA11 than PP. Moreover, the flexural strength of PA11-SGW composites was similar to that of PP-GF composites.

This work focused on the evaluation of the kinetics of dyeing polyester fabrics with high molecular weight disperse dyes, at low temperature by solvent microemulsion. This study also compared the effect of two non-toxic agro-sourced auxiliaries (o-vanillin and coumarin) using a non-toxic organic solvent. A dyeing bath consisting of a micro-emulsion system involving a small proportion of n-butyl acetate was used, and the kinetics of dyeing were analysed at four temperatures (83, 90, 95 and 100 °C). Moreover, the dyeing rate constants, correlation coefficient and activation energies were proposed for this system. It was found that o-vanillin yielded higher dye absorption levels than coumarin, leading to exhaustions of 88% and 87% for Disperse Red 167 and Disperse Blue 79, respectively. K/S values of dyed polyester were also found to be higher for dye baths containing o-vanillin with respect to the ones with coumarin. In terms of hot pressing fastness and wash fastness, generally no adverse influence on fastness properties was reported, while o-vanillin showed slightly better results compared to coumarin.

Producción Científica, The aim of this study is to propose and explore a novel approach for the production of cellular lightweight natural fibre, nonwoven, fabric-reinforced biocomposites by means of gas dissolution foaming from composite precursors of polyhydroxybutyrate-based matrix and flax fabric reinforcement. The main challenge is the development of a regular cellular structure in the polymeric matrix to reach a weight reduction while keeping a good fibre-matrix stress transfer and adhesion. The viability of the process is evaluated through the analysis of the cellular structure and morphology of the composites. The effect of matrix modification, nonwoven treatment, expansion temperature, and expansion pressure on the density and cellular structure of the cellular composites is evaluated. It was found that the nonwoven fabric plays a key role in the formation of a uniform cellular morphology, although limiting the maximum expansion ratio of the composites. Cellular composites with a significant reduction of weight (relative densities in the range 0.4–0.5) were successfully obtained., Ministerio de Educación y Formación Profesional (grants FPU12/05869 and EST14/00273), Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (grants BIA2014-59399-R and MAT2015-69234-R), Junta de Castilla y Leon (grant VA011U16)

In the last few years, an increase in interest has been given to the use of cellulose fibers as alternatives for conventional reinforcements in composites. The development of commercially viable environmentally friendly and healthy materials based on natural resources is on the rise. In this sense, cellulosic fibers as reinforcements for cement mortar composites constitute a very interesting option for the construction industry. This paper presents a review of the research done during the last years in the area of the cement-based composites reinforced with cellulose fibers. The fibers used, processing methods, mechanical behavior and durability are presented. The main achievements found have been the development of durable cement composites with optimized fiber–matrix adhesion. Moreover, the recently developed textile composites will allow obtaining high performance materials reinforced with vegetable fibers.

The incorporation textile fabric reinforcements made of vegetable fibers on fragile cement based matrix can lead to new sustainable construction materials with high strength under flexural and tension forces. However, one of the main problems of the cement composites reinforced with vegetable fibers is their low durability to accelerated aging, mainly due to the presence of calcium hydroxide (Portlandite) on the cement Portland matrix. The degradation of the fibers in this matrix is mainly due to its high alkalinity and the presence of calcium cation, which catalyzes the breakage of cellulose polymer chains. Less studied is the use of other cement based matrix free of Portlandite, like calcium aluminate based cements.

The aim of this paper is to explore the potential of oil palm frond fibers (OPFf) for technical applications such as composite reinforcement. For this purpose, fibers obtained from frond wastes were subjected to various chemical treatments with NaOH and chemically and morphologically characterized. Afterward, composites of poly-lactic acid matrix and nonwoven matts made with the treated and the untreated OPFf were prepared and the mechanical properties tested. It was found that the alkaline treatment was effective for increasing the wettability of the fibers leading to composites with a good-balanced between lightness and toughness for potential applications in packaging or automotive industries.

This research analyses the effect of hydrothermal aging on the water uptake and mechanical performance of biocomposites based on a polyhydroxyalkanoate matrix and flax fibre reinforcement in the form of nonwoven (NW) fabrics. The effectiveness of various surface treatments—wet/dry cycling (C), argon plasma (Ar), ethylene plasma and combinations—of these NW in the improvement of the mechanical properties of the composites is also evaluated. The water uptake during aging is analysed at both room temperature and 65 °C. Moreover, the composites are characterised before and after the aging to determine its effects on the morphology, thermal behaviour and tensile properties. It is found that the water diffusion is mainly influenced by the fibre content, and no significant differences are found in the effects of the NW treatments. Although the highest tensile stiffness and strength was found for the composites prepared with the Ar-treated NW, the C treatment is the most effective to prevent the loss of tensile performance after aging.

Nowadays, the most used construction solutions for building envelopes are “ventilated facade” systems, which have continuity between the thermic and impermeable envelopes, avoiding thermal bridges and consequently avoiding energy loss and the presence of water vapor condensation. The sheets or panels of this envelope system should fulfill certain requirements such as strength, flexibility, ductility, lightness, permeability, thermal insulation, and durability. In this sense, it is of practical importance to develop new materials with the maximum characteristics aforementioned, primarily strength, ductility, flexibility, and durability, using environmentally friendly and low-cost raw materials and processes. Over the last few years, many interesting works have been published describing the use of natural fibers as reinforcements for cement matrix composites. These fiber–cement composites exhibit improved toughness, ductility, flexural strength, and crack resistance. Nonetheless, in most of the research done the fibers are used in pulp or staple forms, limiting the improvement of the flexural strength and ductility of the composites due to the short length of the fibers and the maximum content that it is possible to mix with the cement matrix (around 4–8 wt.%). One possible solution to overcome these problems is the incorporation of the fibers in the form of textile structures, such as nonwovens. However, as far as we know, the incorporation of textile structures made of vegetable fibers in the form of nonwovens on cement-based matrix has been scarcely reported. This chapter focuses on the processing and characterization of high-performance cement-based composites reinforced with nonwoven flax fabrics intended for application in sheets for ventilated facades.

In this work, polyamide 11 (PA11) and stone ground wood fibres (SGW) were used, as an alternative to non-bio-based polymer matrices and reinforcements, to obtain short fibre reinforced composites. The impact of the reinforcement on the thermal degradation, thermal transitions and microstructure of PA11-based composites were studied. Natural fibres have lower degradation temperatures than PA11, thus, composites showed lower onset degradation temperatures than PA11, as well. The thermal transition and the semi-crystalline structure of the composites were similar to PA11. On the other hand, when SGW was submitted to an annealing treatment, the composites prepared with these fibres increased its crystallinity, with increasing fibre contents, compared to PA11. The differences between the glass transition temperatures of annealed and untreated composites decreased with the fibre contents. Thus, the fibres had a higher impact in the composites mechanical behaviour than on the mobility of the amorphous phase. The crystalline structure of PA11 and PA11-SGW composites, after annealing, was transformed to α’ more stable phase, without any negative impact on the properties of the fibres.

The aim of this study is to develop a process to produce high-performance cement-based composites reinforced with flax nonwoven fabrics, analyzing the influence of the fabric structure—thickness and entanglement—on mechanical behavior under flexural and tensile loadings. For this purpose, composite with flax nonwoven fabrics with different thicknesses were first prepared and their cement infiltration was evaluated with backscattered electron (BSE) images. The nonwoven fabrics with the optimized thickness were then subjected to a water treatment to improve their stability to humid environments and the fiber-matrix adhesion. For a fixed thickness, the effect of the nonwoven entanglement on the mechanical behavior was evaluated under flexural and direct tension tests. The obtained results indicate that the flax nonwoven fabric reinforcement leads to cement composites with substantial enhancement of ductility.

This experimental research analyzes the mechanical performance and durability of facade pieces based on Portland cement matrix and flax nonwovens as reinforcement. Two types of pozzolanic additions (silica fume and metakaolin) combined with nonwovens subjected to different treatments to decrease their water absorption are analyzed as potential materials for fiber-cement sheets for building envelopes with high strength and durability. For this purpose, on the one hand, the mechanical performance and chemical composition of various ternary compositions were studied. On the other hand, various treatments were performed on the nonwovens and the nonwoven–matrix adherence was also analyzed. Finally, composites were prepared from some selected treated nonwovens and matrix mixtures, and their mechanical properties and durability were evaluated under four-point bending tests after 28 days of curing in a humidity chamber and after accelerated aging. The composites developed with the treated nonwovens presented very high performance combined with enough durability to be potential candidates for the development of sustainable materials for building envelopes.

Producción Científica, This research analyzes the effects of different treatments on flax nonwoven (NW) fabrics which are intended for composite reinforcement. The treatments applied were of two different kinds: a wet/dry cycling which helps to stabilize the cellulosic fibers against humidity changes and plasma treatments with air, argon and ethylene gases considering different conditions and combinations, which produce variation on the chemical surface composition of the NWs. The resulting changes in the chemical surface composition, wetting properties, thermal stability and mechanical properties were determined. Variations in surface morphology could be observed by scanning electron microscopy (SEM). The results of the X-ray photoelectron spectroscopy (XPS) showed significant changes to the surface chemistry for the samples treated with argon or air (with more content on polar groups on the surface) and ethylene plasma (with less content of polar groups). Although only slight differences were found in moisture regain and water retention values (WRV), significant changes were found on the contact angle values, thus revealing hydrophilicity for the air-treated and argon-treated samples and hydrophobicity for the ethylene-treated ones. Moreover, for some of the treatments the mechanical testing revealed an increase of the NW breaking force., Ministerio de Educación y Formación Profesional (grants BIA2014-59399-R and FPU12/05869)

One of the actual trends in polymer foams consists in the development of new materials by combining density reduction through foaming with the incorporation of functional fillers. This would enable to obtain materials with improved specific properties and added functionalities. There is also a growing interest in the use of environmentally-friendly materials obtained from renewable sources, thus coming as a logical step to combine both in order to create novel biocomposite foams. This work presents an overview of our recent results regarding the preparation and structural and thermo-mechanical characterizations of rigid polypropylene-based composite foams, with the main goal of developing new lightweight materials with tailor-made properties (multifunctional foams). Several reinforcements have been considered, from renewable cellulose fibres to nanometric-sized reinforcements such as silicate-layered nanoclays and carbon nanofibres.

Vapor-grown carbon nanofibers (VGCNFs)/trifunctional epoxy resin composites were prepared by directly mixing the VGCNFs and the epoxy resin using ultrasounds to improve dispersion. Different weight fractions of VGCNFs were studied, from 0.05 to 2 wt.%. The dispersion degree of the VGCNFs was analyzed in the uncured stage by optical microscopy and after the curing reaction by Scanning Electron Microscopy (SEM). The electrical conductivity of the epoxy composites, measured by means of surface electrical conductivity, increased with the addition of VGCNFs content, reaching a conductivity value of around 10 −6 S/cm at 2 wt.% loading, which is an increase of eight orders of magnitude over the pure epoxy matrix. A very low critical weight fraction corresponding to the formation of a tunneling conductive network was found. To identify the effect of adding VGCNFs on the mechanical properties of epoxy resin, flexural tests were performed on neat epoxy and the composites. The highest improvement in flexural modulus was obtained with 0.1 wt.% loading of VGCNFs.

The use of vegetable fibers to reinforce a cement-based matrix has its weakest point in terms of durability. The alkalinity of the matrix and the volumetric instability of the fibers are the main causes of the loss of resistance of vegetable fiber-reinforced cement mortar composites. The aim of this study was to determine the effects of the previous hornification of the vegetable fibers on the mechanical performance and durability of softwood kraft pulp and cotton linters cement mortar composites. For this purpose, composites containing 4 wt.% of the hornificated fibers and the untreated ones were prepared with both fiber types. The mechanical performance of these composites was tested after 28 days of cure treatment and after aging with four wet–dry cycles. Results indicated that the previous treatment of fibers had beneficial effects on the mechanical performance and durability of the resulting cementitious composites.

In this paper, polymer foams based on a benzoxazine resin have been successfully prepared using azodicarbonamide (ADC) as a chemical blowing agent and have been characterized regarding their foaming behavior, cellular structure, and physical properties. The effect of the ADC on the curing process of the resin was analyzed using differential scanning calorimetry and blowing agent decomposition was followed by thermogravitmetric analysis (TGA). The characterization of the cellular structure of the foamed samples was done using scanning electron microscopy. The mechanical properties of the foams were determined using compression tests and the thermal conductivity was assessed using the transient plane source method. The results indicated that the curing process and gas release took place in a similar time interval. The foams showed an isotropic cellular structure with relative densities in the range 0.35–0.60, and showed compressive strengths and compressive moduli in the range of 10–70 MPa and 400–1100 MPa, respectively. Thermal conductivities were in the range of 0.06–0.12 W m−1K−1. The findings in this paper demonstrate the possibility of producing polybenzoxazine foams using a simple process in which curing and foaming take place simultaneously. In addition, the mechanical characterization of these materials indicates that they are suitable for structural applications. Copyright © 2011 John Wiley & Sons, Ltd.

Layered Double Hydroxide (LDH) particles intercalated with dodecylsulfate anions were prepared following different methods and analysed by thermogravimetry (TGA) and X-ray diffraction (XRD). Two commercial grades of MgAl LDH particles were used as LDH precursors. Two-step reconstitution was found to be the most effective route to prepare dodecylsulfate intercalated LDH particles. The obtained particles were melt blended with polypropylene at a 10 wt.% loading. The thermal stability and flame retardant behaviour of the resultant nanocomposites were studied with TGA and limiting oxygen index tests. The mechanical properties were also characterized. The experimental results reveal the potential of these organic modified LDH particles to improve both the thermal stability of polypropylene matrix and the mechanical properties.

With the aim of gaining a better understanding of the phenomena responsible of the loss of durability of cement mortar composites reinforced with vegetable fibers, this paper focuses on the analysis of the fiber-matrix interactions. More specifically we analyze the effects of the vegetable fibers on the cementitious matrix after their mixture for different periods of time and vice versa. Three kinds of cellulosic fibers with differences on its physic-chemical properties were studied: bamboo fibers, kraft pulp and cotton linters. The results show that the cellulosic fibers modify the total amount of heat released during the hydration process in the cement paste, this effect differing depending on the purity of the fibers. The high alkalinity of the cementitious matrix causes the partial dissolution of chemical components of the fibers and a harmful precipitate of the inorganic particles on its surface and/or lumen, damaging the fibers and hence decreasing its reinforcement capacity.

The preparation and characterization of cellulosic fibre-reinforced polypropylene composite foams is presented. The cellulose fibres were isolated from a barley straw obtained from local sources. They were compounded with the polymer in the melt state to obtain composites with nominal concentrations of 10 and 20% by weight. After compression-moulding the composite samples were foamed in a high-pressure batch-process employing CO2 as foaming agent. The effects of the fibre loading on the basics characteristics of the foams was investigated.

The changes produced in cellulosic fibres when they are subjected to successive drying and rewetting cycles could have an important impact on the resistance and durability of cement mortar composites based on these fibres. In this paper, unbleached, oxygen delignificated, semi-bleached, and fully bleached softwood pulps have been subjected to drying and rewetting cycles and the corresponding dried pulps characterized. The morphological structures and thermal stabilities were investigated with X-ray diffraction and thermogravimetric analysis. While the water retention values decrease significantly with drying and rewetting cycles, an overall increase in the crystallinity index and in the thermal stability was found in the hornificated pulps. Natural fibres from cotton linters were also studied and the results compared with the fibres from these softwood pulps.

High-density polyethylene (HDPE)/hydrotalcite nanocomposites were prepared and characterized with a partially neutralized sodium ionomer of poly(ethylene-co-methacrylic acid) (EMAA) as a compatibilizer. Moreover, nanocomposites based on this ionomer were characterized as patterns to analyze the interactions between the hydrotalcite sheets and the methacrylic groups on the ionomer. Hydrotalcite particles were organically modified with sodium dodecyl sulfate ions. Their presence in the interlayer space was confirmed by means of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Morphological analysis carried out with XRD and transmission electron microscopy (TEM) revealed the partially exfoliated/intercalated structure achieved in the nanocomposites. The mechanical properties of the HDPE nanocomposites mainly depended on the nature of the polymer matrix. Higher values of the tensile strength and Young's modulus were found in the EMAA nanocomposites. Thermogravimetric analysis (TGA) showed that hydrotalcite particles improved the thermal stability and delayed the onset decomposition temperature of both HDPE and EMAA nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The non-isothermal crystallization behaviour of Mg–Al layered double hydroxide (LDH)/polypropylene (PP) nanocomposites prepared by melt-dispersion was investigated through differential scanning calorimetry and discussed in comparison with that of montmorillonite (MMT)/PP ones. Combined effects of the LDH interlamellar modification and blending the PP with maleic anhydride-grafted PP (PP-g-MAH) and maleic anhydride-grafted poly(styrene-co-ethylenebutylene-co-styrene) (SEBS-g-MAH) were analysed. Different approaches were applied to determinate the crystallization kinetic parameters. The nucleation activity parameter indicated that LDH particle resulted active for heterogeneous nucleation of PP. Overall; the crystallization rate constant of the PP increased in presence of LDH in a similar extension that in presence of MMT nanoparticles. By applying an isoconversional method to the calorimetric data it was found that the effective activation energy decreased because of the effect of the nanoparticles and its value displayed different growing trends with the crystallization degree depending of the nanocomposite composition.

Bacterial polyesters such as polyhydroxyalkanoates (PHAs) are of great interest for a large number of applications both because of their properties and because they come from renewable resources, despite having a higher cost than commodity polymers. Their foaming—although it presents some difficulties—could be an option to increase their competitiveness. In this work, two strategies have been studied to enhance the poly(3-hydoxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) foamability by extrusion foaming. The effect of the cooling system (water-quenching or air-cooling), chain extender (CE) addition and chemical blowing agent (CBA) amount were evaluated. Density, cellular morphology, mechanical and thermal properties were studied. Optimal density reduction was achieved with use of CE and 3–4 wt.% of CBA masterbatch. The most effective strategy on density reduction was the addition of CE, while the water quenching had only a slight influence on the samples in which CE was not present. CE addition decreased the viscosity and the degradation rate of the polymer, thus leading to lighter foams with larger cells but with equal or even slightly better resistance to compressive and tensile stress, in general terms.

The effect of modifying the particle/matrix interfacial region on the morphology and tensile behaviour of glass bead-filled polypropylene (PP) composites was studied. The interface modification was promoted by blending PP with a small concentration (5% by weight) of poly(ethylene terephthalate-co-isophthalate) (co-PET). Ten different PP/co-PET/glass beads ternary composites were prepared, characterized and compared with the homologous PP/glass beads binary ones. Maleic anhydride-grafted PP was added as a compatibilizing agent for PP and co-PET in some of the studied formulations, and its effect studied. Furthermore, four different silane-treated glass beads were used to prepare the composites (50 wt.%). Results showed that three different interfaces, corresponding to three different levels (low, middle and high) of particle/matrix adhesion, could be obtained in these composites by varying the matrix composition and the silane coupling agent on the glass bead surface, which resulted in a wide range of tensile properties, from ductile composites with low tensile strength and high elongation to brittle ones with high tensile strength. It was found that co-PET embeds glass bead surface independently of the silane coupling agent employed. Finally, the adhesion degree differences between the different composite phases seemed to be the main cause to explain the differences found in the sensitivity of the composite tensile characteristics to the strain rate.