Melting and nonisothermal crystallization behavior of polypropylene/hemp fiber composites

Abstract

Melting and nonisothermal crystallization behaviors of polypropylene (PP) and PP/hemp fibers (HFs) composites was investigated by differential scanning calorimetry (DSC) technique. The results show that the incorporation of HFs increases both the melting temperature ( Tm) and crystallization temperature ( Tc) of PP. Moreover, in comparison with PP/HF(70/30) composite, the addition of maleic anhydride-grafted PP (PP-MAH) results in a slight decrease in Tm but a significant increase in Tc of PP. The higher Tc of PP in the composites implies that HFs could act as nucleating agents for the crystallization of PP. Nonisothermal crystallization kinetics analysis was performed using Avrami and Mo models. The values of half-time ( t1/2) and rate constant indicate that the crystallization rate increases with the increasing of cooling rate for all the specimens. However, the crystallization rate of PP/HF(70/30) composite is found to be lower than that of PP at a certain cooling rate. Additionally, the composite containing PP-MAH has the lowest crystallization rate. Lower overall crystallization rate of PP/HF composites compared to PP is probably due to sufficiently high density of nuclei, which hinders the transport of PP molecular chains to crystal surface during nonisothermal crystallization. The crystallization activation energies (Δ E) determined by Kissinger method are 207.4 KJ/m2, 218.5 KJ/m2, and 220.4 kJ/m2 for PP, PP/HF(70/30), and PP/HF/PP-MAH(70/30/5), respectively.