Transparent composites with high impact strength are used in a variety of areas of application such as in windshields, protective glazing, or transparent armor. Typically, silica-based glass has been used when a high level of impact protection is required, which comes with the drawback of its high weight. The work here focuses on creating alternative transparent composites of impact-modified acrylic (IM-acrylic) and polycarbonate (PC) reinforced by bacterial nanocellulose (BC) for improved impact performance. BC is grown in a three-dimensional intermeshing network of cellulose fibers, leading to both high stiffness and fracture toughness in the dried nanopaper. Inherently, the BC nanopaper is both brittle and opaque. To improve its value as reinforcement for impact-resistant and transparent composites, an alkaline treatment is employed to improve the transparency and ductility of the nanopaper. Two types of BC nanopapers were prepared, neat BC, press-dried from the pellicle without further treatment, and BC-20, for which the pellicle was immersed in a 20 wt.% NaOH solution for 30 min prior to neutralization and press-drying. The nanopapers were subsequently impregnated with a liquid, UV-curable resin and sandwiched in between two layers of either IM-acrylic or PC, followed by UV-curing. After the alkaline treatment, the total light transmittance of the nanopaper increased from 40 % to 80 % at 550 nm, and the fracture toughness was increased by 50 %. All of the laminated composites are transparent with a total light transmittance of 74 - 77 % at 550 nm. The impact resistance of the IM-acrylic-based composites was measured by Charpy impact testing, where the impact was 16.7 kJ m-2 when reinforced with the neat BC and increased to 19.5 kJ m-2 with the BC-20 nanopaper. In the PC-based composites, the bending stiffness and strength were increased by 21 % and 16 % respectively when reinforced by the BC-20 compared to the neat PC. When subjected to an impact energy of 100 J by a falling weight impactor the PC+BC-20 composites were able to absorb 13 % more energy than the pristine PC.

Transparent armor reinforced by mercerized bacterial nanocellulose

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