Semi-interpenetrating network hydrogel films were prepared using hemicellulose and chemically crosslinked chitosan. Hemicellulose was extracted from aspen by using a novel alkaline treatment and characterized by HPSEC, and consisted of a mixture of high and low molecular weight polymeric fractions. HPLC analysis of the acid hydrolysate of the hemicellulose showed that its major constituent sugar was xylose. X-ray analysis showed that the relative crystallinity of hydrogels increased with increasing hemicellulose content up to 31.3%. Strong intermolecular interactions between chitosan and hemicellulose were evidenced by FT-IR analysis. Quantitative analysis of free amino groups showed that hemicellulose could interrupt the chemical crosslinking of chitosan macromolecules. Mechanical testing and swelling experiments were used to define the effective network crosslink density and average molecular weight between crosslinks. Swelling ratios increased with increasing hemicellulose content and mainly consisted of H-bonded bound water. Results revealed that by altering the hydrogel preparation steps and hemicellulose content, crosslink density and swelling behavior of semi-IPN hydrogels could be controlled without deteriorating their mechanical properties. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012