A review of vinyl technology



This is a review of PVC technology from chlorine and ethyle, to PVC polymerization, to melt processing, to properties, to recycling and environmental concerns. It is written in terms for understanding by even non-scientists in the industry.

PVC has a large sales volume, second only to polyethylene. Its high chlorine content provides it with a very high level of combustion resistance for building products, electrical enclosures, and wire & cable insulation. PVC has a unique ability to be compounded with a wide variety of additives, making it possible to produce materials in a range from flexible elastomers to rigid compounds, materials that are weatherable such as for siding and windows, compounds that have stiff melts and little elastic recovery for outstanding dimensional control useful in profile extrusion, or low viscosity melts, which compete effectively with ABS and PC/ABS in thin walled injection molding parts such as computer monitor housings.

Some of PVC's properties are attributed to unique structures. The polymer precipitates from its monomer and grows into primary particles, which are later the melt flow units. Fusion into larger structures and product strength are controlled by break-down of the grains into primary particles, by the choice of additives, by the amount of melting (temperature), and by the number of tie molecules (molecular weight).

The main type of polymerization is the suspension process, with significant polymerization made by the mass process and emulsion process. In the suspension process, the polymerization takes place in droplets of monomer suspended in a water.

PVC is environmentally sound. With over 50% chlorine content, chlorine makes PVC one of the most energy efficient polymers, makes PVC inherently flame retardant, and acts as a marker, enabling automated equipment to sort PVC containers from other plastics in the waste stream. Analysis from 155 large-scale, commercial incinerator facilities found no relationship between the chlorine content of waste nor the addition of PVC, and dioxin emissions from combustion processes. New requirements from the U.S. EPA make scrubbers mandatory on all incinerators and are necessary whether or not PVC is present in the waste feed.