Transparent Poly(methyl methacrylate) Composites Basedon Bacterial Cellulose Nanofiber Networks with Improved Fracture Resistanceand Impact Strength

摘要

Cellulose nanofibers are often explored as biobased reinforcement for the production of high-performance composite materials. In this work, we fabricated transparent poly(methyl methacrylate) (PMMA) composites consisting of two-dimensional and three-dimensional bacterial cellulose (BC) nanofiber networks. Three different composite designs consisting of 1 vol % BC loading were fabricated and studied: (i) composites with a three-dimensional BC nanofiber network embedded uniformly throughout the PMMA matrix; (ii) sandwich-structured construction consisting of three-dimensional BC–PMMA sandwiched between two neat PMMA sheets; and (iii) dried and well-consolidated two-dimensional BC nanofiber network embedded in a PMMA matrix. All fabricated model BC–PMMA composites were found to be optically transparent, but PMMA composites consisting of the two-dimensional BC nanofiber network possessed higher light transmittance (73% @550 nm) compared to the three-dimensional BC nanofiber network counterparts (63% @550 nm). This is due to the higher specific surface area of the three-dimensional BC nanofibernetwork, which led to more light scattering. Nevertheless, it wasfound that both two-dimensional and three-dimensional BC nanofibernetworks serve as excellent stiffening agents for PMMA matrix, improvingthe tensile modulus of the resulting composites by up to 30%. However,no improvement in tensile strength was observed. The use of three-dimensionalBC nanofiber network led to matrix embrittlement, reducing the tensilestrain-at-failure, fracture resistance, and Charpy impact strengthof the resulting BC–PMMA composites. When the BC nanofibernetwork was used as two-dimensional reinforcement, cracks were observedto propagate through the debonding of BC nanofiber network, leadingto higher fracture toughness and Charpy impact strength. These novelfindings could open up further opportunities in the design of noveloptically transparent polymeric composite laminates based on the two-dimensionalBC nanofiber network for impact protection.