New applications breed more ways to process TPOs.

Having firmly established themselves in injection molding of exterior automotive parts such as bumper fascias and claddings, thermoplastic olefin elastomers are breaking into new areas of processing. Film and sheet extrusion and thermoforming appear to be the primary new processing opportunities for TPOs. Applications are in development for interior automotive components and medical uses. Also promising are extrusion and calendering of TPOs for geotextiles, pond and landfill liners, roofing membranes, and heavy-gauge industrial packaging. Extrusion of wire and cable insulation and jacketing, as well as hose and corrugated tubing for appliances, are also on the way.

The injection molding arena is also widening for TPOs to include two-shot and low-pressure molding processes for applications ranging from interior car parts to lawn/garden and sports/recreational equipment.

Although at an earlier stage of development, applications in bottle blow molding and rotomolding are being actively explored by some resin suppliers and compounders.

FILM & SHEET PROCESSING

A flurry of developmental activity is aimed at extruding or calendering TPO sheet for thermoforming to replace PVC skins on "soft-feel" auto interior parts such as door and instrument panels. New-generation TPOs tailored for soft-feel applications can get very soft indeed. For example, Montell Polyolefins, Wilmington, Del., now offers a super-soft grade of its HiFax in-reactor TPO with a flexural modulus of 8000 psi, compared with 120,000 psi for conventional TPOs.

Also being explored are TPO flooring - another PVC replacement - and auto headliners, in which a TPO substrate is extrusion laminated to a PP cloth.

Extruded or calendered TPO film and sheet also appear to have large-volume potential in medical markets, at the potential expense of PVC in most cases. Virtually all TPO resin suppliers and compounders have active programs in this arena, aimed at applications from I.V. bags to hose and tubing. For these applications, TPOs reportedly offer autoclave and radiation sterilizability, soft feel, and good tear and impact strengths.

For example, Quantum Chemical Co. in Cincinnati foresees in-reactor TPOs making entry into cast and blown films for medical-waste/biohazard bags, according to marketing manager John Denzer. He says TPOs could also compete with PP copolymer and LLDPE in heavy industrial bags.

Edwin Tamm, v.p. at compounder J-Von L.P., Leominster, Mass., sees a fit for very thin (less than 10-mil) TPO sheet made by a proprietary extrusion process for use in disposable surgical drapery or surgical gowns.

Andre Fritz, president of another compounder, Multibase, Inc., in Copley, Ohio, reveals that in the next few months his company will introduce medical-grade TPOs for cast film, aimed at replacing non-plastic materials.

Montell marketing manager John Cowperthwait says that while PP film and sheet cannot normally be extruded in air-quenched film lines used for PE films because of PP's high crystallinity, blending at least 30% TPO with PP reduces crystallinity enough to permit using standard PE equipment. Resulting products can be targeted to applications requiring good tear strength and creep resistance, such as industrial films, geotextiles, pond liners, and agricultural sheeting.

Ron Price, marketing manager at Exxon Chemical Co.'s Automotive Business Group in Southfield, Mich., reveals that work is under way to replace extruded LLDPE landfill liners with a TPO or blends of TPO with a metallocene polyolefin.

Extruded TPO sheeting is also expected to make its mark in building and construction. One application, commercialized first in Europe and more recently in North America, is replacing EPDM in roofing membranes. Weatherability and heat sealability that eliminates the need for adhesives are major advantages, according to Montell's Cowperthwait.

In addition, Multibase's Fritz says his company has focused on replacing PVC sheet with TPO in roof-ridge vents or flashing. TPOs are said to offer excellent uv resistance, low-temperature impact strength, and ability to produce dark colors.

NEW INJECTION APPROACHES

A new alternative to thermo-forming for "soft-feel" car-interior applications is low-pressure injection molding, a more capital-intensive process but one that eliminates further processing of finished parts and needs no adhesives. Says Exxon's Price, "You get a door panel, for example, that is essentially pre-skinned."

With this process, a laminated composite of TPO skin and poly-olefin foam are fitted into the mold and PP is then injected behind it under low pressure. When the mold opens, you have a finished part, explains Ermanno Ruccolo, market-development specialist with Montell's automotive group in Troy, Mich. Tamm says J-Von has one customer that is trying out this process with TPO.

Overmolding PP or PE with TPO is another area where TPOs are considered likely to find a fit due to good adhesion between the layers. An example is caster wheels for hospital carts, says J. Von's Tamm. The wheel hub could be PP and the tire TPO, resulting in a cost advantage over caster wheels made of metal, nylon over rubber, or urethane over rubber.

Exxon's Price says his company is focusing on two-shot molding for applications such as instrument panels, whereby a rigid substrate such as glass-filled PP is overmolded with a TPO to achieve a soft feel.

Work on two-shot injection molded TPO air-bag covers is also well under way, according to sources at Multibase and J-Von. Multibase, says Fritz, is exploring overmolding an inner hard shell made of new TPOs that have good toughness at low temperature (-40 F) with an outer shell of a soft styrenic TPE. The company is also looking at the potential of coinjecting TPO with the styrenic TPE in one shot.

TRY TUBING & PROFILES

Extrusion of profiles for construction uses such as extension joints or door seals is another promising processing area for TPOs, where they can bridge the gap between PVC and TPVs, according to Tamm.

Some suppliers are also actively exploring appliance uses such as beverage tubing, conduit, and flaps. In these applications, TPOs' broad service-temperature range reportedly spans those of currently used rubber, PVC, and other polyolefins.

There is also activity in wire and cable extrusion. Montell, for one, is already selling in-reactor TPOs to compounders of jacketing and primary insulation for replacement of PVC or crosslinked PE.

BLOW MOLDING BECKONS

Blow molding of TPOs is still in the early stages of development. TPOs have a soft feel that's attractive for squeeze bottles, as well as good ESCR and heat resistance. But because of their higher cost, TPOs are not expected to replace PP or HDPE containers except in niche applications. For example, some medical containers are already blow molded from TPOs, and Quantum's Denzer sees a fit in bottles for industrial and household cleaners and other aggressive chemicals. To address the cost issue, Quantum is investigating coextrusion blow molding, which can combine the ESCR of TPO with the economy and column-crush resistance of HDPE. Such coextruded bottles could have many uses in packaging aggressive household and industrial cleaners where storage and shipping conditions require stacking.

Other potential blow molded applications include bellows-type automotive steering-column covers and industrial dust covers. In these cases, TPOs are less expensive than rubber and TP urethanes.

A NEW SPIN ON ROTOMOLDING

As in blow molding, niche opportunities are anticipated for TPOs in roto-molding, where these resins cannot compete with lower-cost materials for most high-volume applications like toys and playground equipment. For example, Exxon is seeking to replace PVC powder slush molding with rotocast TPO in soft-feel applications such as auto armrest covers and other interior applications. For this process, the TPO is cryogenically pulverized into a fine powder.

Quantum has introduced what is believed to be the only standard TPO grade for rotomolding currently available. Microthene MT-4390HU is an unpigmented 35-mesh powder targeted for 55-gal indoor chemical-storage tanks. Compared with currently used PP and other resins, TPO offers higher heat and chemical resistance, along with better low-temperature impact, according to Denzer.