Polyamides from renewable sources as matrices of short fiber reinforced biocomposites Summary -At present, in production of commercially available biopolyamides, castor oil is used as one of raw materials. In this paper possibilities of processing biocomposites based on biopolyamide (commercially delivered by Chinese company Suzhou Hipro Polymers) filled with 10 or 20 wt. % of glass, carbon or flax fibers were presented. Tensile properties (tensile strength, modulus of elasticity and elongation at break) of the composites in their conditioned state and after water soaking were discussed. As the results showed, a strong effect of reinforcement was obtained for all of the composites. The composites with glass and flax fibers have a great elongation and impact resistance. To evaluate fatigue stress of tested materials, simplified shortened Lehr's method was used. The results of this work can be used in the designing process of structural materials with varying stiffness and ability to dissipate energy depending on the expectations of the recipient.

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In the study, polylactide-based (PLA) composites modified with natural particles (wood, bamboo, and cork) and with different levels of infilling (100%, 80%, and 60%) obtained by fused deposition modeling were tested. The effect of fiber type, infill level and crystallization rate on the mechanical properties were investigated by using tensile, flexural, and impact tests. The materials were subjected to mechanical tests carried out at 23 and 80 °C. Differential scanning calorimetry were employed to analyze crystallization behavior of composite. Furthermore, hydrothermal degradation was performed, and its effect on the properties was analyzed. The addition of natural fillers and different levels of infilling result in a similar level of reduction in the properties. However, the addition of natural fillers resulted in a slightly lower drop than the lowered infilling rate − 40% and 50% for tensile strength, respectively. Moreover, it was found that, composites made of PLA are more sensitive to high temperatures than to water. The decrease in Young's modulus of PLA at 80 °C was 90%, while after 28 days of hydrodegradation ~ 9%. The addition of fibers reduced this decrease at elevated temperatures. Importantly, in the case of a brittle material such as PLA, the impact strength has been improved by 50% for composites with cork particles and other lignocellulosic composites remained at the same level as for resin. Generally, the thermal treatment of composites increased the degree of crystallinity of the materials, as reflected in the higher results of mechanical tests.

In this study, biodegradable biocomposites based on polylactide with basalt fibres (BFs) or wood fibres (WFs) of 7.5 or 15 wt% were prepared by injection moulding. Various tests, including tensile test, bending test and impact test, were carried out to investigate the mechanical properties of the composites. Additionally, the samples were tested at different temperatures. Depending on the type of fibre, differences were noted in their mechanical properties; the addition of WF caused a decrease in strength and the higher the fibre content, the higher the decrease was noted from 18% up 25% in the case of tensile strength. However, the Young modulus was improved by 45% for composites with 15 wt% of WF. The addition of BF improved all the properties, especially Young modulus was improved by over 45%. Despite the low strength observed in neat polylactide at high temperatures-394 MPa, the addition of WF or BF improved the flexural strength more than twofold up to 1684 MPa (PLA/15BF). Moreover, the addition of natural fibres caused an increase in dimensional stability as shown by the decrease of the coefficient of thermal expansion which dropped over 50% for composites with 15 wt% of BF, which significantly expands the areas of use of materials. After 4 weeks of biodegradation, only a slight decrease approximately 5% was observed in the mechanical properties together with an increase in crystallinity. Overall, the results confirm that the prepared composites can be successfully used in engineering applications with long-term operation.