Abstract
Cellulose nanofibrils (CNFs) have been used as reinforcing elements in optically transparent composites by combination with polymer matrices. In this study, strong, optically transparent, and thick CNF/epoxy composites were prepared by immersing two or four layers of CNF sheets in epoxy resin. The morphology of the CNF, the preparation conditions of the CNF sheet, and the grammage and layer numbers of the CNF sheets were controlled. The solvent-exchanged CNF sheets resulted in the production of a composite with high transparency and low haze. The CNF with smaller width and less aggregated fibrils, which are achieved by carboxymethylation, and a high number of grinding passes are beneficial in the production of optically transparent CNF/epoxy composites. Both the grammage and number of stacked layers of sheets in a composite affected the optical and mechanical properties of the composite. A composite with a thickness of 450–800 μm was prepared by stacking two or four layers of CNF sheets in epoxy resin. As the number of stacked sheets increased, light transmittance was reduced and the haze increased. The CNF/epoxy composites with two layers of low grammage (20 g/m2) sheets exhibited high light transmittance (>90%) and low haze (<5%). In addition, the composites with the low grammage sheet had higher tensile strength and elastic modulus compared with neat epoxy and those with high grammage sheets.
Highlights
The use of petroleum-based plastics has caused serious environmental problems, increasing the need for alternative eco-friendly materials
Hardwood bleached kraft pulp (HwBKP) for cellulose nanofibrils (CNFs) preparation was supplied by Moorim P&P (Ulsan, Korea)
ResultCs oamndpoDsiitsecsuosfsUio-nCNF sheets and epoxy were prepared by stacking two layers of dried and solvent-exchanged Untreated CNF (U-CNF) sheets, which were immersed into epoxy resin, respectively
Summary
The use of petroleum-based plastics has caused serious environmental problems, increasing the need for alternative eco-friendly materials. The preparation of the composites by mixing CNF with transparent resins such as acrylic resin or epoxy resin has drawn much interest [18,21,24,25,26]. As these resins have a similar refractive index to that of CNF, the light scattering of the composites could be minimized [13,24]. This study aimed to prepare thick and optically transparent CNF/epoxy composites by controlling the properties of the CNF and CNF sheets. The key factors in preparing thick, strong, and transparent CNF/epoxy composites were determined
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