Polyurethanes Get Greener, More Productive

Polyurethanes (PUR) are a bigger segment of the industry than many realize, with a global consumption in 1998 of approximately 15 billion pounds. Europe and North America each account for 35 percent of the total, and the compounded growth rate for PUR is estimated at four to five percent per year. The versatile material is used primarily as flexible slabstock and rigid foams in construction and transportation applications.

When environmental issues launched the recycling industry in thermoplastics, the intrinsic properties of commodity resins made the task easy; the biggest challenge today is finding a market for the regrind. Recycling, however, is only one avenue toward profitable “green” processing. The polyurethane community has introduced processes which use non-traditional materials to produce goods that meet the green processing paradigm at the front end of the product life cycle.

Wheat straw seems an unlikely material for high performance building products, but Kansas City-based Harvest Board International, Inc. has launched three new plants to produce agrifibre-based particleboard. The straw is bonded into a matrix of Dow ISOBIND (145), a polymeric methylene diphenyl diisocyanate (PMDI). The binder is also used in the production of oriented strandboard and medium-density particleboard. The resulting board is strong and moisture-resistant, while transforming wheat straw from farm waste into a valuable raw material.

Another new polyurethane technology is ready to bring green materials into auto interiors. Hennecke’s NafpurTec process (146) allows the use of natural fibres such as flax, sisal, and hemp in loadings as high as 65 percent in large surface area thin-wall parts such as door panels, parcel shelves, and luggage compartment floors. When molded with Bayer’s Baypreg F (147), the resulting composite door panels can save as much as 2.5 kg per vehicle.

What’s the most widely used polymer in automobiles? Polyurethanes, are currently the leading class by weight, accounting for 15 to 25 kg per vehicle. Foam for seating accounts for two-thirds of the total. Foams derive much of their mechanical properties from the voids left by blowing agents, and in the past, CFC’s were the compound of choice. The foam industry, however, was well ahead of Montreal Protocol requirements as carbon dioxide and dimethyl chloride (DMC) have replaced CFC’s as blowing agents, although DMC is under regulatory pressure as well. The flexible foam sector has responded through the Canadian Flexible Foam Manufacturers Association with a set of voluntary guidelines based on Environment Canada’s ARET (Accelerated Reduction and Elimination of Toxics) program. Current plans call for DCM emission reductions of 50 percent by 2002, with total phaseout by 2007. Of the four major foamers represented by the Association, one has switched from DMC, and the other three have announced their intention to meet the voluntary guidelines. The phaseout recommendation is designed to force new technology, which at the present centres on carbon dioxide as a blowing agent. In the meantime, foam softening agents are reducing the quantities of DCM needed for some grades of foam.

The changeover, however, will be expensive.

Mel Himel, president of the Canadian Flexible Foam Manufacturers Association, says: “Cost issues are serious, and could be up to two million dollars a plant”. Himel, who is also secretary/treasurer of Vitafoam Products Canada Ltd. (Toronto, Ont), feels that the voluntary measures won’t leave Canadian firms at a competitive disadvantage compared top US foamers: “Many American states have already passed similar legislation, so it will be a level playing field in this area.”