Effect of bamboo powder fibers on the crystalline and impact properties of polyhydroxy fatty acid ester composites

PHA/bamboo powder fiber composites were prepared by melt blending process using polyhydroxy fatty acid ester (PHA) as the matrix material to study the effect of different content of bamboo powder fiber on the crystalline and impact properties of PHA composites. The results show that: (1) the addition of bamboo powder fiber reduces the impact strength of PHA/bamboo powder fiber composites. The main reason is that the compatibility between bamboo powder fiber and PHA is not good, and it does not transfer and disperse the impact load well during the impact process, but becomes the stress concentration point, inducing more and longer cracks, and macroscopically resulting in the reduction of the impact performance of PHA composites. (2) Adding different content of bamboo powder fiber can improve the crystallization temperature and crystallization speed of PHA. On the one hand, it makes PHA composites start to crystallize rapidly at higher temperatures, and it is easy to produce larger size crystals, which increases the large-size crystals equivalent to the rigid group in the PHA matrix, resulting in a decrease in the impact strength; on the other hand, bamboo powder fibers in the matrix can hinder the movement of molecular chains, which can also cause a decrease in impact strength. Bamboo powder fiber can reduce the crystallinity of PHA composites, mainly because it changes the PHA’s original regularity and order, resulting in decreased crystallinity. (3) Adding bamboo powder fibers of different contents can increase the energy storage modulus, loss modulus, and viscosity of PHA composites, which is mainly because the addition of bamboo powder fibers hinders the movement of molecular chains, allowing the material to store more elastic strain energy. Meanwhile, it increases internal friction, leading to an increase in energy loss. With the increase of bamboo powder fiber content, the melt index of PHA/bamboo powder fiber composites decreases to varying degrees, but the processing performance is better.