TABLE OF CONTENTS The history of polyvinyl chloride (PVC) formulating is based on enhancing the properties derived from the starting raw material. The influence of impact modifiers and plasticisers has already been covered. This chapter focuses on work carried out to expand PVC, a so-called commodity plastic, into the property performance areas given by some engineering plastics, such as acrylonitrile butadiene styrene (ABS), and so on.
Crosslinking of PVC results in the improvement of a number of properties, particularly at elevated temperatures. Investigative work has been carried out on both unplasticised-PVC (PVC-U) and plasticised-PVC (PVC-P) formulations.
Chemical crosslinkable formulations need to generate a sufficient crosslinked portion or gel content (up to 50%) with satisfactory processing stability (usually a conflict) and should not, of course, crosslink during processing. Crosslinking is achieved hydrolytically.
For some PVC-P formulations, mercaptosilanes and aminosilanes grafted by nucleophilic substitution during processing appear to be more suitable than organic peroxides in achieving improved solvent and abrasion resistance [1, 2].
Organic peroxide crosslinking of PVC foam formulations (based on emulsion-grade resin) has shown the positive benefit of a trimethylolpropane trimethacrylate (TMPTMA) compound as co-agent, with good thermal stability and a very dense crosslink network. In the presence of the peroxide, radical reactions occur and the TMPTMA is grafted onto the PVC chains with a resultant network formation [3].
The use of a reactive plasticiser, triallyl cyanurate, has also been shown to improve the high-temperature creep resistance of organic peroxide-crosslinked plastisols [4].
The chemical crosslinking of PVC-U formulations...
