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Two routes to RIM recycling.

Two Routes to RIM Recycling

Dow Plastics, Midland, Mich., and Mobay Corp., Pittsburgh, went public in late January with the first details on their separate R&D programs on how to recycle RIM molding scrap that is currently being landfilled. This technology will be shared with industry via the Polyurethanes Recycle & Recovery Council (PURRC), formed within SPI's Polyurethanes Div. last fall (see PT, Nov. '90, p. 13).

The two firms have developed quite different methods to recycle RIM scrap back into automotive parts. Dow's method, a three-stream recycling process, allows as much as 10% regrind to replace virgin material in new RIM parts. Mobay's solution to the problem is a compression molding process that company representatives say can produce nonappearance parts from 100% regrind.

The two companies, normally rivals in the RIM materials and machinery business, said they decided to team up in announcing their recycling solutions because they agree this problem is the most pressing issue currently facing the RIM business. Representatives of both companies said they felt assured that their processes could handle all of the in-plant RIM scrap being produced today. PURRC says that amounts to about 10% of the 120-160 million lb/yr of RIM processed in the U.S. Dow and Mobay spokesmen estimated their processes may take three to five years to find their way into automotive parts production, but they hope the techniques will be utilized sooner in other applications such as parts for golf carts or lawn mowers.

SCRAP AS A THIRD STREAM

Because amine chain extenders such as DETDA tend to swell regrind particles, the Dow system puts RIM regrind into a third stream feeding into the mixhead to keep it separate from the amine as long as possible. The system consists of one stream made up of DETDA, IMR, catalyst and filler (if necessary); an isocyanate stream; and a polyol/regrind slurry stream, all fed into a single three-stream head. The regrind consists of sprues, runners and fascia that have been rejected due to molding or painting flaws. This scrap is granulated into 3/8-in. chips and then pulverized into a fine (-80 mesh) powder. Up to 10% of this powder by weight is added back into the system, reducing the amount of virgin material that must be used.

Tests of the resulting products showed little if no changes in physical and mechanical properties and in all cases met OEM specifications, Dow says. For example the OEM specification for minimum tensile strength for unfilled RIM fascia is 2828 psi. In Dow's tests, fascia produced with no regrind had a tensile strength of 3610 psi. Fascia made with 10% unfilled and unpainted regrind came in at 3620; parts made with unfilled and painted regrind registered a tensile strength of 3770; and fascia produced with filled and painted regrind had a tensile strength of 3640 (Table 1).

Dow reports that surface finish on the recycle-containing parts was only slightly affected--to a degree not detectable to the naked eye after the parts had been painted.

Dow estimates the cost of installing such a system to be about $550,000, using equipment readily available from a variety of suppliers. The company estimates that for a typical fascia, the 10% increase in capital cost per part and a 3% boost in energy costs are more than offset by the lessened material requirement. Taking into account labor and tooling costs, Dow estimates this material reduction can result in a 5% overall decrease in manufacturing cost per part. (CIRCLE 25)

MOLDING 100% REGRIND

Mobay's approach to recycling RIM scrap is quite different. While Dow's three-stream approach is aimed at putting scrap right back into the exterior auto panels from which it came and is, therefore, limited in the amount of regrind it can use, Mobay is directing its method at nonappearance parts in order to maximize scrap-reuse capability.

Like the Dow process, Mobay's technique starts with rejected fascias and other RIM scrap being chopped into 1/8-in. to 1/4-in. granulate. This is then preheated to 350 F for 5-15 min and compression molded for 3 min in a 375 F mold at 4400 psi. Under high shear and high temperature, the thermoset bonds break and the material becomes what a Mobay spokesman describes as a "psuedo thermoplastic" with limited flow. When the pressure and heat is removed the bonds reform. Under these conditions the particles of cured polyurethane, although a thermoset, will fuse into a single mass. Initial applications include parts such as seat bases and trunk liners. As the size of the parts made increases, the necessary clamping force of the compression press also goes up. For instance, a 400-sq-in. part requires about 800 tons of clamp force while a 2000-sq-in. part needs 1600 tons.

Some compromise of mechanical properties is expected in the remolded parts. Mobay's data, comparing five mechanical properties of fascia-grade, unreinforced polyurethane with material that has gone through one recycling, show a slight drop in flexural modulus and greater drops in tensile strength and elongation (Table 2).

Like the Dow method, no radically new equipment is needed to compression mold RIM scrap, Mobay says. Among the items the company suggests using are a scrap granulator capable of chopping 200 lb/hr; a conveyor to transport the granulate to a storage container; a balance to weigh the scrap for each molding; a 28,000-Btu/hr oven that can heat 50 lb of material to 390 F within 15 min; a hydraulic press; and a heated steel mold with a shear edge. Mobay did not provide a cost estimate for setting up such a system. (CIRCLE 26)

Both companies said that while some RIM processors and auto companies have been interested in these systems, no one is yet using one.

PHOTO : Because the amine fillers in RIM parts tend to swell regrind particles, Dow Chemical Co. has developed a three-stream process for RIM recycling where the amines are kept separate from the regrind. [Tabular Data 1 Omitted] TABLE 2--COMPRESSION MOLDED URETHANE FASCIA SCRAP (UNREINFORCED)
Typical Properties Original Recycled
Density, lb/cu ft 63 75
Flexural Modulus, psi 46,000 42,000
Tensile Strength, psi 3200 1800
Elongation, % 240 110
Hardness, Shore D 60 53


(Source: Mobay)
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Title Annotation:molding scrap
Author:Monks, Richard
Publication:Plastics Technology
Date:Mar 1, 1991
Words:1033
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