Effects of initial load levels and crosshead speed levels on viscoelastic properties of biodegradable loose fill extrudates

The viscoelastic properties of biodegradable loose fill extrudates can provide information at the structural level of the biodegradable cushioning materials used. The objective of this study was to test two rheological models of linear viscoelastic theory (generalized Maxwell with three units in parallel, and Burgers) using the results of stress relaxation tests in biodegradable loose fill extrudates. The experiments were run at 105 °C with screw speed 500 rpm and die diameter 3.92 mm. The extrudates were then submitted to tests of stress relaxation in an equipment of mechanical measurements, Instron Universal Testing Machine (Model 4464). The deformation, imposed to the extrudate, was 1%, guaranteeing the permanency in the domain of the linear viscoelasticity. The models were fitted to experimental data (stress × time) by nonlinear regression. The generalized Maxwell model with three units in parallel and the Burgers model represented the relaxation curves of stress satisfactorily. The viscoelastic properties varied in a way that they were less dependent on the initial stress levels.