Abstract
Polymeric xylan can be reacted with propylene oxide (PO) in aqueous alkali homogeneously. Since xylan is isolated from biomass in aqueous alkaline solution, an ‘in-line’ modification with PO as part of the isolation protocol, is most practical. Hydroxypropyl xylan (HPX) is a low molecular weight, branched, water-soluble polysaccharide with low intrinsic viscosity and thermoplasticity. Following peracetylation of HPX in formamide solution, water-insoluble acetoxypropyl xylan (APX) is formed that is also thermoplastic but no longer water soluble. The glass transition temperature (T g) of APX varies in relation to degree of substitution with hydroxypropyl groups (DSPO), and this is found to decline from 160 to 70°C as DSPO rises from 0.2 to 2.0. At a temperature above the T g of HPX a molecular reorganization is noted, and a faint transition due to melting (T m) is observed at 205°C. HPX thermally degrades with a weight loss maximum at 317°C, or approximately 60°C below that of a corresponding cellulose derivative. HPX forms clear films when solvent cast from aqueous solution. Films are higher in ultimate tensile strength and lower in toughness than corresponding cellulose derivative films. The properties of HPX and APX derivatives qualify this material as a potential biodegradable and thermoplastic additive to melt-processed plastics. Blend characteristics with polystyrene reveal a shear-thinning effect in melt and a plasticization effect in solid state.
Published Version
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