As with flame retardants and plasticizers, there are environmental issues for heat stabilizers, and, because of these issues, different additives are favored around the world.
The global heat stabilizer market is valued at about $1.8 billion, representing volumes of between 1.1 billion and 1.2 billion lb, according to Gastrock. The growth of heat stabilizers, at 4% per year, tracks the PVC market. Almost all heat stabilizers are used in either rigid or flexible PVC. The main kinds of heat stabilizers are organotins; lead; mixed metals such as barium/cadmium, barium/zinc, and calcium/zinc; and organic materials that companies are beginning to introduce. In North America, lead is only found in wire and cable applications. Instead of lead, organotins are dominant in North America in rigid PVC applications, such as pipe. On the other hand, lead is used in all sorts of rigid applications in Europe, and some plastics converters and governments are phasing it out. Asian markets are somewhere in between North America and Europe in the predominance of lead.
In mixed metals, Ca/Zn has a better image than Ba/Zn or Ba/Cd, but it doesn't perform as well in many applications. "Ca/Zn will probably do better in the market than the others down the road," Gastrock says, adding that global growth in Ca/Zn and organotins will be more than 4% in the long run, while growth in lead and other mixed-metal classes will remain flat or decline. In North America, on the basis of volume, tin and mixed metals each accounts for about 40% of the heat stabilizer market and lead accounts for less than 20%, according to Gastrock's figures. In Europe, lead accounts for nearly 70% of the market, while mixed metals represent about 20%, and organotins, a mere 10%.
Crompton Corp. , one of the largest players in heat stabilizers, exited cadmium- and lead-based heat stabilizers a decade ago, according to John Hamilton, market manager of vinyl additives for Crompton's Witco polymer additives group. The move was part of the company's push to convert these markets to Ba/Zn and Ca/Zn.
"A lot of the conversion took place several years ago, so today cadmium is pretty small," says Sally Lenhart, Ferro Corp.'s worldwide business director for polymer additives. "It is only used today when there are no alternatives."
As they phase out lead, Europeans will probably skip organotins altogether and opt for Ca/Zn instead, says William Hrubik, PolyOne's director of sourcing. "In Europe, all of the heavy metals have perception issues that are much greater than in the U.S. Rather than going to tin, they are trying to see if they can use Ca/Zn stabilizer technology in rigid applications," he adds.
Crompton's Hamilton agrees. "Throughout Europe, pipe is stabilized with lead, and they want to knock out heavy metals completely," he says. "In Europe, Ca/Zn is what they are going to. They look at organotin as an interim solution," he adds. Crompton has been developing a Ca/Zn replacement for lead in rigid applications for the European market and is currently working on getting approvals for drinking-water pipe and food contact uses.
Crompton is also working on a Ba/Zn stabilizer for wire and cable. Lead, Hamilton says, is difficult to replace in this market because it is perfect for the applications. Lead has been the only heat stabilizer good enough to allow electrical wiring to pass stringent standardization tests. "Lead is the best stabilizer you can possibly use," he says.
Ferro is working on the development of organic stabilizers, Lenhart says, noting that, in the long run, they could solve the lead problem in Europe. But it will take time for them to catch on, she admits. "Nobody is clamoring for organic stabilizers, but we have to be prepared," she adds.