Enhancing Poly(lactic acid) Composites with Polymer-Modified Bleached Softwood Kraft Pulp Before and After Fibrillation

Utilizing modified bleached softwood kraft pulp (BSKP) in polylactic acid (PLA) composites offers a promising approach to enhance mechanical properties and advance sustainable material applications. This study investigates PLA composites reinforced with either polymer-grafted BSKP or after its fibrillation to yield modified cellulose nanofibers (CNFs). The dispersive and polar surface energies of the dried reinforcements could be varied by a grafting-through polymerization to yield either polyacrylamide (PAM) or poly(methyl methacrylate) (PMMA) modifications. Spray drying the polymer-modified CNF suspensions produced dry powders with significantly increased specific surface areas compared with unmodified CNFs. The surface modification of BSKP and its subsequent fibrillation and spray-drying to produce modified CNFs enhanced the tensile strength of PLA composites over the unmodified materials: a 16% increase for the BSKP modified with PMMA and an 11% increase for the spray-dried CNFs modified with PAM at 20% reinforcement loading. These increases were attributed to the improved dispersion and stronger interfacial adhesion of the modified fibers in the matrix. The significant improvements in mechanical properties for the polymer-modified BSKP and comparable results to the refined and spray-dried materials demonstrate the potential to improve biobased composites without the high energy processes of refining and spray drying. Furthermore, these results underscore the potential of these modified materials to develop high-performance composites for applications ranging from packaging to automotive components.