Free-radical degradation of xyloglucan (XG) in aqueous solution initiated by 4,4'-azobis-(4-cyanopentanoic acid), potassium persulfate (KPS), hydrogen peroxide (H2O2) and H2O2 with ascorbic acid at 75-80 degrees 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 degrees C was 3.98 x 10(-6) s(-1). (C) 2010 Elsevier Ltd. All rights reserved.