Bacterial cellulose enhanced optically transparent composites for impact protection

Abstract

Bacterial cellulose (BC) nanopaper exhibits both high strength and stiffness and is widely regarded as a promising reinforcing material for polymer matrix composites. This thesis reports the mercerisation of BC nanofibrils as a route to produce ductile BC nanopaper, and the impregnation of (mercerised) BC nanopaper with an acrylated urethane resin, followed by lamination with sheets of impact-modified acrylic producing optically transparent BC nanopaper reinforced acrylic composites. At a BC loading of 8 wt.-%, the mercerised BC nanopaper acrylic composite possessed an increase in flatwise and edgewise Charpy impact strength of 62% and 22% respectively over “gold-standard” monolithic acrylic. This thesis further investigates the reinforcing capabilities of ultra-low grammage BC nanopaper in multi-layered BC/acrylic composites. Ultra-low grammage BC nanopaper is laminated with several acrylic sheets, to create composites reinforced with one, three and five layers of BC nanopaper. In Charpy impact testing, the impact strength of the optically transparent BC nanopaper reinforced acrylic composites was increased by up to 130% compared to the monolithic acrylic at a cellulose loading fraction of only 1.6 wt.-%. In this thesis the viscoelastic properties of the (mercerised) BC nanopaper and BC nanopaper reinforced poly(acrylated urethane) composite films are further evaluated as they pose an important design factor for laminated structures designated for impact protection. The reinforcing capabilities of (mercerised) BC nanopaper were further studied under falling weight impact testing of optically transparent polycarbonate laminated composites reinforced with BC nanopaper. It was shown that at the same loading fraction of BC, 4 wt.-%, the composite reinforced with mercerised BC nanopaper was able to absorb more of the impact energy compared to the composite reinforced with neat BC nanopaper while both composites outperform the monolithic PC. This thesis demonstrates the potential of BC nanopaper as reinforcement for optically transparent laminated composites.