HOW BRITTLE ARE GELS

Gels of different polysaccharide concentrations were cracked quasi-sta tically by driving a 40-degrees included angle wedge into intact speci mens in order to determine their fracture toughness. This could not be determined for some of the gels tested, gellan gum and xanthan gum bl end. The work to fracture of alginate and apr gels, calculated without respect to energy loss due to viscoelastic or frictional effects betw een gel and wedge, varied from 4-32 J m-2. The magnitude of fracture t oughness values were found to be agar >high guluronic acid alginate> h igh mannuronic acid alginate. Agar gels were found to behave in a mann er typical of starch gels; as gels became firmer their toughness incre ased, whereas the reverse appeared to hold for alginate gels.