Mechanism and kinetics of free-radical degradation of xyloglucan in aqueous solution

Abstract

Free-radical degradation of xyloglucan (XG) in aqueous solution initiated by 4,4′-azobis-(4-cyanopentanoic acid), potassium persulfate (KPS), hydrogen peroxide (H 2O 2) and H 2O 2 with ascorbic acid at 75–80 °C has been investigated using gel permeation chromatography. XG degradation behaviour is similar to that of hydroxyethylcellulose with carbon-centred radicals causing little degradation and oxygen-centred radicals producing significant degradation. Based on the observations, the predominant mode of degradation is believed to be random chain scission of sterically unhindered glycosidic main-chain linkages, with an increasing contribution from side-group scission as the degree of polymerization reduces and the relative concentration of side-group linkages increases. The rate coefficient for random chain scission degradation by KPS at 75 °C was 3.98 × 10 −6 s −1.