Effect of Molecular Modification on PCL Foam Formation and Morphology of PCL

Poly(ƒÕ-caprolactone) was chemically modified by using dicumyl peroxide from 0.125 to 2 % (w/w) and the effects of branching on the density and morphology of PCL foams were examined. The polymer was first blended with dicumyl peroxide at low temperature (80¢XC), in order to avoid premature branching reaction. The peroxide modification was then performed at different temperature conditions, from 110¢XC to 150¢XC. The reaction kinetic was followed by measuring the dynamical rheological properties of the melt in isothermal experiments by using a plate-plate rheometer. The evolution of the macromolecular structure during the chemical reaction was followed by analyzing time evolution of complex viscosity. Foams were prepared from the reacted polymeric matter with the batch foaming process by using nitrogen as foaming agent in different process conditions. As expected, the increase of the degree of branching led to a shift towards higher temperatures of the foaming window. Moreover the degree of branching influenced the viscoelastic behavior of the expanding polymeric matrix and, therefore, the final foam properties.