Biodegradable natural fiber composites : fabrication and characterization of hemp fiber with PLA powder composites

Interest in natural fiber composites has been increasing in recent years due to their environmental benefits, along with weight reduction and economic viability. The composites in some cases have proven to exceed glass fiber composites and are suitable substitutes for the same. Hemp-Polylactic acid (PLA) composites were fabricated using a novel method, wherein PLA powder is mixed with hemp fibers through a needle punching process. The composites were produced at three different fiber loading levels of 35%, 50% and 55% and showed differently finished top and bottom surfaces, the top being plastic and the bottom being fibrous. The mechanical, acoustic and thermal properties were characterized and it was found that 50% composites provided the best results. Overall, the composites performed in the range of previously documented non modified natural fiber composites, giving the fabrication process validity. The tensile and impact tests showed acceptable strengths and also demonstrated low shattering probability due to fiber entanglement. This was also seen from the high values of elongation at break. Dynamic mechanical analysis (DMA) showed the highest storage modulus for the 50% fiber loaded samples and an increased glass transition temperature compared to neat PLA. The samples showed low thermal conductivity values, comparable to asbestos, showing good thermal insulation properties. Acoustic absorption coefficients were measured using a two microphone impedance test at varying high and low frequencies. The coefficients showed high acoustic absorption even at moderate frequency levels, owing to the dampening effect of the hemp fibers.