Polymer Grafting onto Cellulose

Abstract

The proposed work investigates the potential utilization of poly (ethylene-alt-maleic anhydride) (PEMA) as linkers for grafting alkane and PEG chains onto cellulosic fibres. Alkyl-amines and PEG-amines were introduced on the PEMA backbone, forming comb polymers. These comb polymers can be grafted onto cellulose with as low as 12-14% anhydride moieties remaining. The investigation is structured into three main sections as follows: The behaviour of comb polymers in aqueous solutions was investigated. Specifically, PEMAc-alkyl exhibited a pH-induced conformation transition, primarily influenced by the alkyl chain length. In the case of alkyl chains ranging from 6 to 10 carbons, the comb polymers exhibited a hypercoil to expanded coil transition with increasing pH. Notably, comb polymers with pendant decyl (C10) chains formed stable unimolecular nanogels at pH of 7-9, and this behaviour remained insensitive to the degree of substitution (DS) in the range of 25-75%. PEMAc derivatives were grafted onto bleached softwood pulp fibres through an aqueous impregnation method. High yields (>90%) were achieved when polymer dosages were below 13 g/kg (dry polymer/dry fibre) for PEMAc-alkyl and 38 g/kg for PEMAc-PEG The maximum wet tensile index (WTImax) of the grafted pulp sheets fit in a power-law model represented as WTImax~βΓru0.54–0.62. However, at high polymer doses, the WTImax values deviated from the model due to the lubricating effect of the ungrafted polymers. PEMAc and its derivatives were grafted onto cellulose nanofibrils (CNF) using DMAP-catalyzed esterification in acetone. High yields were obtained when the PEMA dosages were below 0.125 g/g (dry polymer/dry CNF). Aggregated structures, consisting of individualized nanofibrils, microribbons, and flocs, were formed in acetone first and then preserved by the grafted polymer. Changes in polymer dosage and DS influenced the floc content. The structure of microribbons was affected by the DS values of PEMA-PEG3 derivatives, with helical structures observed for DS values below 75% and flat structures when DS values exceeded 75%.