Roto gives new materials a spin

Rotational molding’s markets and applications are largely defined by the limited material portfolio—polyethylene, polyethylene, and more polyethylene. But a new custom compounding company is urging rotomolders to think of new materials including acetal, nylon, and polyesters.

Most rotomolders are going to look at what they already do and try to figure out how [new materials] can work for them,” Michael Gehrig says. “What we’re trying to tell them is, ’Don’t look at what you already do—look at what you can’t do. Look at the people that have come to you and said they want something that will take an extra 30-40 degrees and you had to turn that job down. Look at jobs where maybe you’re needed to sterilize parts and you couldn’t do it.’”

Gehrig, who started his plastics consulting business, Gehrig & Associates, in 1983, has had a developmental material division called Aardvark Plastics going back 20 years, which took on one-off jobs to develop materials for specific jobs.

Last year, after completing a project to expand the material portfolio for thermoforming, Gehrig saw similarities in rotomolding that cried out for more diverse materials. “They’re both low-pressure processes, and they have very distinct advantages on tooling,” Gehrig says of thermoforming and rotomolding. “They’ve never really had a good shot of high-performance and engineering materials before.”

Broadening the material palette

Launching Aardvark Polymers (Lambertville, NJ) last year, the company upped its material manufacturing capacity in August to 2 million lb for production of five grades of acetal. By November, in conjunction with the Assn. of Rotational Molders International’s (ARM; Oak Brook, IL) fall conference in Washington DC, Gehrig hopes to announce a more than doubling of capacity to 5 mm lb/yr, as well as the addition of two more acetal grades, a nylon 6/6, and a polyester. The company is working with copolymer acetals from Ticona, homopolymer Delrin from DuPont, and a variety resins from other material suppliers, including BASF and Bayer.

Gehrig says the rotomolding grades of acetal could largely serve markets where it’s applied in injection molding and extrusion, including medical, automotive, and housewares. One instance where it could displace PE is in fuel systems, since acetal meets all current and pending emission regulations of the California Air Resources Board (CARB) with a permeability rating of 1.2g/m2/day (for more, see MPW July 2006 Tech Trends).

Impact resistance and cost could pose a problem, but in hot-oil applications, like hydraulic tanks, which run from 200 to 210°F, acetal’s ability to withstand 230°F compared to around 175°F for PE, makes it more attractive. Aardvark has also been working on electrostatic dissipative grades.

On the advice of friends in the pharmaceutical sector, last year Gehrig purchased a variety of grinders used in that industry, including rotor beat, small-hammer, and jet mills, working on new formulations of resins and additives featuring a different consistency than the pulverized materials created by the opposed-face grinders typically used. Aardvark also brought in two lab-scale rotomolding machines at the start of the year to undertake material trials.

Global interest

Gehrig says half the inquiries it fields are from North America, with India next, and then Europe, with the bulk there generated by the UK. Gehrig hopes in three years that engineering material sales will be in the range of 10 million lb, with high-performance materials, which will include sulfones, polyphenylene sulfide, polyetheretherketone, and liquid crystal polymers, coming in at 2 million lb. The company is also working with different additives, including glass reinforcements, ceramics, minerals, antimicrobials, and electrostatics, pushing rotomolders to pursue new markets.

“It takes a really inventive rotomolder to say, ’I’m going to do this with something new and different—even my tooling style is going to be a little bit different. I’m going to make ducts and shrouds and things like that rather than being into a tank market,’” Gehrig says.

Tony Deligio • [email protected]