Surface treated pollen performance as a renewable reinforcing filler for poly(vinyl acetate)

Pollen grains have the potential to be effective plant-based biorenewable reinforcing fillers for polymers due to their high mechanical strength, chemical stability, and unique micro- and nano-structured surfaces. Pollen polymer composites could form the basis for a new class of light-weight, high strength sustainable materials if compatible polymer filler systems can be engineered. The exine shell of pollen, composed of sporopollenin, offers opportunities for surface functionalization to provide for compatibility between the pollen and the polymer matrix, but this idea has been previously unexplored. We present the first demonstration of surface functionalization of sporopollenin to enable, incorporation of pollen as a reinforcing filler, using ragweed pollen in poly(vinyl acetate) (PVAc). Composites prepared with 'as received', untreated ragweed pollen displayed interfacial voids, degraded mechanical properties, and a decreased glass transition width with increased pollen loading, relative to neat PVAc. Composites prepared with pollen treated via an acid base surface preparation displayed improved interfacial morphology and increasing modulus with pollen loading (29% increase). Interfacial adhesion was optimal for pollen functionalized with vinyltrimethoxysilane (VTMS), followed by in situ free radical polymerization of PVAc. In situ polymerization of functionalized pollen resulted in simultaneous stiffening and strengthening of composites (80% increase in tensile strength). Films containing treated and functionalized pollen also displayed a wider glass transition regions in the presence of pollen filler relative to neat PVAc.