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This study investigates the hygrothermal aging effect on the tensile and impact behavior of flax/PLA biocomposites. Specimens underwent up to four weeks of conditioning at 40°C in a climate chamber with water. Analysis covered porosity, moisture diffusibility, and transversal microstructure, enabling assessment of tensile strength, tensile modulus, and impact performance in relation to moisture uptake and fiber orientation. The study of tensile properties revealed that at approximately 12% moisture content, stiffness and yield stress decrease, while strength remains constant. Moisture diffusivity is higher in warp and weft yarn directions than the out‐of‐plane direction. Tensile testing at environmental equilibrium moisture reveals greater stiffness in the weft direction, correlated with lower crimp percentage and yarn angle. The main contribution of the paper is the study of the influence of moisture on the impact behavior, the results show that energy absorption capability of flax/PLA biocomposite increases with moisture content. Highlights: Fully biodegradable composite material by heat‐compression molding subjected to hygrothermal aging conditions for up to four weeks.The moisture diffusivity in both the warp and weft yarn directions registered higher values in comparison to the out‐of‐plane direction.Tensile testing at environmental equilibrium moisture revealed that the stiffness in the weft direction presented higher values.At 12% of moisture uptake, the stiffness and yield stress reached their lowest values, while strength remained constant.However, the low‐velocity impact properties of the composites exhibited improvement with moisture. [ABSTRACT FROM AUTHOR]

The main goal of this study is the comparison of different reinforcement architectures on the low-velocity impact behavior of green composites. The study includes the comparison of unidirectional, basket weave, and twill weave flax/PLA composites, they are subjected to unidirectional tensile tests, drop-weight impact tests, and after-impact compression tests. Results show that the unidirectional composite demonstrates superior tensile strength and initial modulus due to reduced fiber crimp, while basket weave exhibits the highest energy absorption capability and strain capacity attributed to its higher fiber–weight ratio and fiber crimp. Unidirectional composite also shows a larger impacted damage area compared to basket weave and twill weave, attributed to its internal architecture. Residual compressive strength across all composites decreased by 40% compared to the reference sample. However, the reduction in stiffness after impact was different, UD/PLA composite stiffness was reduced by 30% while the reduction in BW/PLA and T/PLA composites was about 20%. [ABSTRACT FROM AUTHOR]

Since natural fibers is a combination of different materials, this are classified as a composite material, where the cellulose microfibers are the reinforcement and the lignin and the hemicellulose are the matrix, which hold the microfibers. Raw fibers, generally present a low density and with this, low cellulose content; however, after the alkali treatment, cellulose proportion increase and the other constituents were reduced as expected, except the ashes. Since the true density of the cellulose, hemicellulose, lignin, extractives and ashes are different; true density measurement can be an alternative to determine the composition of the fibers (cellulose, lignin and extractives), as long as, fibers belong to the same family (species). Since the density of cellulose is higher than the other constituents, alkali treated fiber will have a higher density than raw fibers. [Extracted from the article]

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Natural fibers are a renewable resource that has become an economic alternative to replace synthetic fibers as reinforcement in composite materials. In this study, the aim was to characterize physical and thermal properties of the Andean Stipa obtusa and Jarava ichu leaves (grasses known as ichu) before and after the alkaline treatment. Energy dispersive spectrum identified external phytoliths on the surface of nontreated raw leaves. With the alkaline treatment, improvement on the thermal stability and increment in the crystalline index and size was observed. Additionally, raw leaves present a hydrophobic behavior; however, with the treatment this hydrophobicity was lost for Stipa obtusasignificantly but not for the Jaravaichu. Furthermore, low surface energy was observed for the nontreated raw leaves and increasing consistently for the treated fibers. According with these results, these grasses are quite interesting materials from which fibers can be extracted for engineering applications such as composite materials. [ABSTRACT FROM AUTHOR]

The mechanical properties of the glass fiber reinforced Polyamide (PA6) composites made by prepreg tapes and commingled yarns were studied by in-plane compression, short-beam shear, and flexural tests. The composites were fabricated with different fiber volume contents (prepregs-47%, 55%, 60%, and commingled-48%, 48%, 49%, respectively) by using vacuum consolidation technique. To evaluate laminate quality in terms of fiber wet-out at filament level, homogeneity of fiber/matrix distribution, and matrix/fiber bonding standard microscopic methods like optical microscopy and scanning electron microscopy (SEM) were used. Both commingled and prepreg glass fiber/PA6 composites (with Vf ∼ 48%) give mechanical properties such as compression strength (530-570 MPa), inter-laminar shear strength (70-80 MPa), and transverse strength (80-90 MPa). By increasing small percentage in the fiber content show significant rise in compression strength, slight decrease in the ILSS and transverse strengths, whereas semipreg give very poor properties with the slight increase in fiber content. Overall comparison of mechanical properties indicates commingled glass fiber/PA6 composite shows much better performance compared with prepregs due to uniform distribution of fiber and matrix, better melt-impregnation while processing, perfect alignment of glass fibers in the composite. This study proves again that the presence of voids and poor interface bonding between matrix/fiber leads to decrease in the mechanical properties. Fractographic characterization of post-failure surfaces reveals information about the cause and sequence of failure. POLYM. COMPOS., 36:834-853, 2015. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]