Plasticizer migration from cross-linked flexible PVC: Effects on tribology and hardness

Uses of flexible poly(vinyl chloride) (PVC) are restricted by plasticizer migration affecting material properties. Moreover, the use of phthalate-based plasticizers is being questioned worldwide because of their potential toxicity to humans and environment. Chemical modification of PVC structure is one of the most effective tools for reduction of plasticizer diffusion. In this work, a flexible dry blend based on cross-linked PVC was obtained using a difunctional amine, namely isophoron diamine (IPDA) as the cross-linking agent. The gel fraction was evaluated from insoluble portions obtained by means of solvent extraction; the efficiency of cross-linking in reducing the plasticizer leaching was evaluated by migration tests. Effects of addition of IPDA on PVC thermal stability were determined by thermogravimetric analysis (TGA). The cross-linking reaction turned out to be responsible for accelerating thermal degradation. Tribological properties of flexible uncross-linked, cross-linked and rigid PVC were determined. Flexible formulations were held in contact for 32 days with rigid PVC sheets. Plasticizer migration towards the interface caused an increase of dynamic friction compared to that of the reference rigid PVC.Vickers microhardness h Vickers values of rigid PVC sheets decreased due to plasticizer surface absorption.