Design of recyclable matrixes from lignin-based polymers

Abstract

1,1-Bis(aryl) propane-2-O-aryl ether-type lignin-based polymers, lignophenols (LPs) were synthesized through a phase-separation system composed of phenols and concentrated acid. LP with C1-p-cresol (LP-P) and LP-24X containing C1-2,4-xylenol had a similar phase-transition point, average molecular weight, frequency of phenols in the molecule and switching functionality (nucleophilic attack of C1-phenols to C2). LP-P, however, was hydroxymethylated (HM) at its reactive cresolic and terminal phenolic nuclei to give network-type structures on heating. On the other hand, LP-24X without a reactive point on the grafted nuclei resulted in the formation of linear-type structures. The structures of polymerized LPs were controlled by the grafting ratio of p-cresol and 2,4-xylenol in LPs. The resulting polymer chains were cleaved at the C2-aryl ether linkages to give low molecular weight subunits by the switching function of the C1-grafted unit. In order to use LPs as matrixes for various composites, HM-LP-P, HM-LP-24X, and HM-LP-P/24X, containing an equivalent amount of C1-p-cresol and C1-2,4-xylenol, were hybridized with powdery materials such as cellulose, glass, iron or talc by applying heat and pressure. The resulting HM-LP composites had a glossy surface and high dimensional stability because the polymerized HM-LPs' matrixes tightly bound fillers. Furthermore, using the switching functionality of LPs, the composites were re-separated into LP fractions and fillers. The physical and recycling properties of the composites were controlled by the structure of the LPs matrixes and/or the density, the morphology and the accessibility for reagents of the powdery materials.