Milkweed floss-reinforced thermoplastics: interfacial adhesion and related mechanical properties

This research aimed to evaluate the improvement of the mechanical properties of composites and their reduction of weight induced by milkweed floss (MW). As MW is severely affected by surface treatments, a good inherent affinity with the matrix is required for efficient reinforcement. Thus, composites made of MW and polyamide (PA11) (or polypropylene (PP) for reference) were studied, as PA11 should have a good physical interaction with natural fibers. The interfacial adhesion between MW and both matrices was determined by single fiber fragmentation tests (SFFTs) and composites with different MW amounts were produced. The length of MW, the density of the composites and their mechanical properties were measured. SFFT results revealed a better affinity between MW and PA11, with a critical length of 85 mu m compared to 335 mu m in PP. This had a direct impact on the fiber length efficiency factor, which was found to be lower in PP than in PA11. The addition of 2.5 wt.% of MW fibers in PA11 led to an increase of 29% of Young's modulus but only 4% in PP. However, the density decrease was limited for all the composites as the lumen of the fibers was partially filled (80-100% filling rates).