The proliferation of new vinyl technology is one of the best-kept secrets in the plastics industry. While emotionally charged issues like the soft-toy controversy capture the headlines, researchers are hard at work pushing the boundaries of PVC performance outward in all directions.
Far from being just an incremental improvement, what's happening is a transformation of vinyl capabilities, often creating new types of material that are economical replacements for more-expensive polymers.
So much innovation may come as a surprise to many in the industry. First commercialized in the 1930s, PVC is commonly perceived as an old-line commodity resin family that once upon a time grew very big, very quickly, as an inexpensive substitute for metal and cloth.
There is a grain of truth in this: the word inexpensive. Vinyl continues to offer a cost advantage over other plastics, because PVC is based on a molecule that is only half-derived from petrochemicals. But it is not low price in itself that has made vinyl the world's second-largest thermoplastic in terms of annual tonnage. The real driver is the high level of performance that vinyl delivers for the price. Manufacturers of flexible vinyl medical products do not specify ``cheap commodity substitutes'' as raw materials, nor do producers of rigid vinyl pipe that must distribute municipal water under pressure over a use life of decades.
And now come new frontiers of performance. You can get a glimpse of these frontiers by considering the vinyl research projects launched last fall by the Edison Polymer Innovation Center, a partnership between the University of Akron and Case Western Reserve University in Cleveland. Funding for the program, amounting to $1 million, comes from nine U.S. and international companies which are basic in PVC resin, plus Teknor Apex Co., which is a flexible vinyl compounder.
The following are new types of vinyl which EPIC and other research programs aim to develop:
PVCs whose polymer structures can be precisely controlled through use of metallocene polymerization catalysts, yielding new types of vinyl resins. Among the possibilities are highly crystalline resins for use in producing fibers and filter media with outstanding heat and chemical resistance; vinyl resins with unusual gas-barrier properties; vinyl co- and terpolymers incorporating comonomers that, by conventional polymerization techniques, cannot be used in combination with vinyl chloride; and possibly even PVC with inherent flexibility, avoiding the need for liquid plasticizers. In addition, metallocene catalysis may make it possible to tailor analogs to standard vinyl resins that are less susceptible to heat degradation.
Vinyl thermoplastic elastomers of various types, achieved by means of copolymerization, modification by new types of plasticizers, and blending with elastomeric materials. Such elastomers could compete with today's TPE workhorses, the widely used olefinic and styrenic compounds, while retaining vinyl benefits such as lower cost, inherent flame retardance, chemical resistance, and transparency.
Functionalized vinyls that raise application-tailoring to a whole new level of specialization. In the medical area, for example, we can expect to see compounds with long-term nonthrombogenic (resistance to clotting) properties, eliminating the need for expensive coatings that have limited shelf life. Also under study are oxygen-barrier vinyls, containing additives or comonomers that react with oxygen and limit its transmission; containers made with such compounds would extend the shelf life of oxygen-sensitive drugs or foodstuffs.
While these developments are still in the works, a wide range of new vinyl materials already have entered the marketplace. These include new alloy combinations made possible by advances in compatibilizer technology, PVC resins partially cross-linked during polymerization, and rubberlike vinyls vulcanized during compounding.
In addition, the introduction of ultrahigh-molecular-weight PVC resins earlier in this decade has led to whole new families of vinyl TPEs with dramatically improved performance.
This does not exhaust the list of innovations being developed through advances in polymerization and compounding. Many of the new PVC-based formulations are improved versions of existing materials, providing better performance or reducing conventional trade-offs between properties and cost. The real surprise is that so much potential remains for creating new and valuable types of vinyl different from any that we have seen thus far.
Brookman is PVC business manager for Teknor Apex Co.