Polymerization compounding of hemp fibers to improve the mechanical properties of linear medium density polyethylene composites

Improved mechanical properties play an important role allowing the expansion of natural fiber composites in automotive interior parts and construction industries. Unfortunately, their hydrophilic nature leads to incompatibility with hydrophobic matrices limiting their full potential. But this can be overcome by fiber surface modification. So the objective of this work was to modify hemp fibers by an advanced process called surface‐initiated catalytic polymerization and to evaluate its effect in terms of morphological, rheological, and mechanical properties for linear medium density polyethylene (LMDPE) composites. The results showed that catalytic polymerization of hemp fibers was successful as the fibers were coated with grafted polymer chains (polyethylene). This was confirmed by an increase of the C‐H and C‐C groups by FTIR on the fibers surface, as well as the presence of an extra peak in DTG curves between 400 and 500°C. This was also confirmed by SEM pictures and density change owing to the presence of these grafted PE molecules. The composites morphology (SEM) and mechanical properties in the solid (E' and tan δ) and melt (van Gurp‐Palmen plot, complex and transient viscosity, and activation energy) state showed that, the presence of PE molecules on the surface of treated hemp fibers led to a significant improvement of the fiber‐matrix interfacial quality producing significant increases of the composite's (30% wt.) Young's modulus (8%) and tensile strength (43%) with respect to the composite based on untreated fibers, which represents a 125% and 58% increases with respect to the neat polymer. POLYM. COMPOS., 39:2860–2870, 2018. © 2017 Society of Plastics Engineers