Comparative Performance of Flax Fibers and Ramie Fibers Reinforced Functionalized Polypropylene Composites

Flax fiber (FLX) and ramie fiber (RMI) reinforced chemically functionalized polypropylene (CF-PP) composites (FLX/CF-PP and RMI/CF-PP) have been developed by extrusion followed by injection molding. Composites with 10, 20, and 30 wt.% fiber content were fabricated and characterized for both composite systems. FE-SEM and FTIR analysis confirmed good reinforcement-matrix adhesion in both systems, attributed to the formation of ester bonds and hydrogen bonds, formed between the reinforcements and the matrix by the Palsule process. The 30/70 FLX/CF-PP composition showed the best overall performance with approximately 49% higher tensile strength, 71% higher tensile modulus, 42% higher flexural strength, and 118% higher flexural modulus compared to the pristine CF-PP matrix. The same composition also demonstrated 57% higher impact strength than the matrix. All FLX/CF-PP composite compositions show higher mechanical properties compared to respective RMI/CF-PP composite compositions; despite, both, FLX and RMI having similar holo-cellulose contents. This superior performance is attributed to the higher aspect ratio of flax fibers. Water absorption increased with fiber content for both composites, with the 30/70 compositions of FLX/CF-PP and RMI/CF-PP showing maximum absorption of approx. 0.79% and 0.76% respectively after one week. Thermo-gravimetric analysis showed both composites exhibit thermal stability between the CF-PP (380 °C) matrix and reinforcing FLX or RMI (281–290 °C). 30/70 FLX/CF-PP offers the most promising performance and sustainability, amongst all the compositions.