Design and Characterization of Lignin-Based, Thermoresponsive Soft Composites with Improved Mechanical and Transport Properties

In this study, two series of thermoresponsive soft biocomposites were fabricated and their mechanical and transport properties were characterized. Specifically, soft biocomposites of poly(vinyl alcohol) (PVA), poly(N-isopropylacrylamide) (PNIPAm), and a sustainable biopolymer, lignin, were fabricated at mass ratios of 1:1:1 to 2:2:1 (lignin:PNIPAm:PVA). Further, the concentration of crosslinkers for both the PVA and PNIPAm were varied between 5 and 15 mass %. Specifically, the compression and tensile Young’s moduli increased with an increase in temperature, while the 2:2:1 lignin:PNIPAm:PVA membranes also showed an increase in compression moduli with an increase in lignin MW. The permeability of methylene blue and diffusivity of caffeine through the network were seen to decrease with the incorporation of lignin, where, most notably, the diffusivity decreased by approximately two orders of magnitude and permeability by a factor of 45:1. Finally, the hydrated network structure was characterized via both structure via small-angle neutron scattering and scanning electron microscopy.