Impact of Aqueous Grafting of Polystyrene through Methacrylate-Modified Cellulose Nanofibrils on Emulsion...

Cellulose nanofibrils (CNFs) are abundant materials limited in application by their hydrophilic nature and fibrillar collapse during drying. Herein, hydrophobic CNFs (PS-MetCNFs) were produced via the grafting of polystyrene through a methacrylate handle on modified CNFs. This modification prevented fibrillar collapse of the CNFs upon drying with as low as 3.5 wt % polystyrene. System characterization through kinetics studies and controls revealed that a surfactant-free emulsion polymerization ran parallel to the grafting-through polymerization. Polystyrene on the PS-MetCNFs was both covalently bound and noncovalently bound. This noncovalently bound polymer was due to polymerization in the monomer-swollen polymer particles on the PS-MetCNF surface. The polystyrene modification interfered with CNF Pickering emulsion behavior, instead stabilizing monomer-swollen polymer particles entangled in the CNF network. Composites of PS-MetCNFs and poly(lactic acid) showed higher maximum tensile stress and modulus at 5 wt % loading relative to composites made with unmodified spray-dried CNFs, demonstrating a route to composite reinforcement with CNFs without energy-intensive spray drying.