Optically transparent pectin/poly(methyl methacrylate) composite with thermal insulation and UV blocking properties based on anisotropic pectin cryogel

Bioderived polysaccharide-based cryogels prepared via freeze-casting method not only mimic the highly aligned anisotropic pore structure of plant stems but also offer other benefits as compared to biological structures, such as lower density, higher porosity, better permeability, and lower thermal conductivity. However, the application of polysaccharide cryogels to fabricate multifunctional composites is still at its infancy. In this study, a novel class of optically transparent pectin/poly(methyl methacrylate) (PMMA) composite (with optical transmittance as high as 84% and haze of 38% -73%) combined with thermal insulation outperforming conventional glass has been prepared by using freeze-casted pectin cryogel as template. The final pectin/PMMA has comparable optical transmittance and comparable or lower haze as contrasted with most reported studies on transparent wood/ bamboo. Astonishingly, this type of composite has very good UV blocking ability both as compared to glass and nanocellulose-based polymer composites. Overall, the optical properties of these composites can be optimized via controlling the pectin concentration and freeze-casting temperature. Furthermore, pectin/PMMA composites can reach much lower thermal conductivity (0.110 -0.126 W/(m.K)) than glass. Therefore, these multifunctional pectin/PMMA composites could be beneficial in many applications, such as optically transparent materials, solar cell substrates, and UV protective displays.