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.

The study evaluated the possibility of using natural fibers as a reinforcement of bio-polyethylene. Flax, coconut, basalt fiber, and wood flour were used in the work. Strength tests like static tensile test, three-point flexural test, or impact strength showed a positive effect of reinforcing bio-polyethylene-based composites. The effect of water and thermal ageing on the mechanical behavior of composites was assessed. In order to analyze the structure, SEM microscope images were taken and the effect of natural fibers on the change in the nature of cracking of composites was presented. Composites with natural fibers at a content of 12% by weight, resulting in increase of strength and rigidity of materials. The greatest strengthening effect for natural fibers was obtained for the composite with basalt fibers.

Due to the ubiquity and single-use character of plastic products, their production represents a burden to the environment. Therefore, an increasing interest in biodegradable and bio-compostable materials has been observed in the recent years. Bio-based materials are becoming more and more popular, especially in applications where biodegradability provides an advantage for customers and environment. However, biodegradable materials are more expensive compared with durable plastic materials, so to reduce costs and in order to improve their mechanical properties, biocomposites are created by reinforcement with natural fibers: cellulose, hemp, jute, cotton, etc. This paper is focused on the investigation of the selected group of biocomposites based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate) with the addition of 15 wt% of various fillers (nanocellulose, walnut shell flour, eggshell flour, and tuff). Thus far, there is limited information concerning comparison of the different natural fillers introduced into the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) matrix. Here, the following mechanical properties were evaluated: the tensile strength, modulus of elasticity, strain at break, flexural modulus, and flexural stress at 3.5% strain. The tensile test was performed at various temperatures (− 24, + 23, and + 60 °C), followed by samples conditioning in water and compost. Thermal behavior of the biocomposites was studied by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The study showed that the value of the elasticity modulus of each composite was higher in comparison with neat poly (3-hydroxybutyrate-co-3-hydroxyvalerate), at each of the above temperatures. The factor responsible for the enhancement of the mechanical properties of composites (enhancement of the stiffness of the material) was the increase in crystalline phase content in composites. Interestingly, at − 24 °C, all of the analyzed composites exhibited over twofold increase in tensile strength which was accompanied by an almost 30% increase in elastic modulus. This phenomenon likely resulted from an increase in tensile strength and an increase in internal stress at interfaces within the components of the composites during tests. It was also observed that both conditioning in water and degradation in the compost heap led to a considerable decrease in mechanical properties of the examined composites. The scanning electron microscopy analysis, carried out to assess the distribution of particles and the adhesion of fillers to the matrix, revealed that the size and the shape of the particles affected the mechanical properties of the composites.