Effect of water content on the fracture behaviour of hydroxypropyl cellulose films studied by the essential work of fracture method

The dependence of the fracture behaviour of hydroxypropyl cellulose (HPC) films on water content (up to 8.5%, dry basis) was investigated at ambient temperature. Two types of tensile tests at low speed (2 mm/min) were carried out: (1) using sheet-specimens to identify the changes of the main mechanical characteristics of films with respect to water content; (2) using double edge notched tension (DENT) specimens to study the fracture behaviour by means of the essential work of fracture (EWF) method. The results of these two types of mechanical test were discussed and correlated. These results showed that a transition in the fracture behaviour of HPC films occurred above 3.3% water content. This transition was related to changes in the structural and physical properties of HPC films, which occur at lower water content than less hydrophobic biopolymers.