"External Plasticizing" and "Internal Plasticizing"

Manufacturer: We are manufacturer of water-based adhesives using polyvinyl acetate emulsion (latex). Please explain the meanings of "External Plasticizing" and "Internal Plasticizing".

John Woon (Senior Latex Consultant): These terms are used quite frequently in plastic technology, where rigid plastics are rendered soft by adding a plasticizer (softener). A good example is the rigid PVC used of making rigid PVC pipes. The same PVC material can be softened by adding plasticizers for the manufacturing of soft and flexible hoses. Such plasticizing effect is known as "External Plasticizing". However, the addition of "external" plasticizer could lead to "sweating", where the plasticizer migrates and bloom on the surface of the plastic products. As a result, the products concerned become more rigid again.

Another more permanent method of making the polymer/plastic softer is through "co-polymerization". In one case, rigid Polystyrene can be made softer by co-polymerization with another monomer, butadiene. This is known as "Internal Plasticizing".

Same principle also applies to polyvinyl acetate homopolymer and co-polymers.