Flexible packaging of plastics based on renewable materials already is a well-situated commercial reality. But for molders and blowmolders, interest in these materials is appearing in a number of other markets.

Packaging, the market many assumed would most readily adopt plastics based on biorenewable materials, may in fact prove a more difficult nut to crack than markets for durable goods such as furniture, electronics, and automotive. The reason? Primarily concerns about recycling, explains Rick Shaffer, president of injection molding machine manufacture Netstal’s North American operations. He says his firm sees significant amount of interest in these materials, “but I would classify it as more on the side of curiosity than real interest.”

To now, he says, the greatest hindrance to broader acceptance appears to be concerns among large rigid packaging processors and brandowners—many of them customers of Netstal (Näfels, Switzerland)—about how bioplastics packaging will affect the post-consumer plastics recycling stream. “It takes very little PLA to contaminate the PET recycling stream and it is impractical to ensure separation,” explains Shaffer. Bioplastics-based packaging is as yet labeled with a "7" (recycling code for “other” materials), an almost unthinkable stigma for high-volume packaging applications. 

Look beyond packaging, and prospects for injection and blowmolders of bioplastics appear more positive. “The automotive industry is very interested in green polymers,” says Klaus Bender, market development manager (automotive) at plastics supplier DuPont (Wilmington, DE). He says carmakers, about to be obligated to offer complete environmental impact-type reports for their cars, see use of such materials as one key to limiting this impact.

Bender says DuPont’s Sorona, a “true engineering thermoplastic” in comparison to most bioplastics, is being considered for applications such as connectors, lamp sockets, and actuator housings. Tensile strength of the material is about 120-160 MPa when it is reinforced with 15%-30% GFR; tensile/flex modulus at the same GFR levels is between 6000-8000 MPa. “They are even willing to pay a little more for these materials, based on recent meetings,” he says.

Despite concerns about their effects on the recycling stream, major beverage brandowners are keenly eyeing bioplastics. Coca-Cola was recently awarded a patent, first filed in October 2005, for blowmolding of PLA bottles/closures that, owing to their innovative shape, are designed to replace the paper cups/polystyrene lids typically used to serve carbonated soft drinks at fast-food restaurants.

How big is this phenomenon?

Not very, yet. Howard Rappaport, global practice leader, thermoplastics, at Chemical Market Associates Inc. (CMAI; Houston) told attendees at the company’s recent World Petrochemical Conference in Houston that polylactic acid (PLA) consumption makes up 40% of nonpetroleum-based plastic consumption, with production of biodegradable resins (which PLAs are) to range from 150,000 to 200,000 tonnes by 2011, up from 40,000 tonnes in 2006—a 400% increase in only five years—but admittedly a drop in the polymer bucket with global plastics demand of 173 million tonnes last year.

On the plus side, Netstal’s Shaffer says processing of the materials is generally not an issue, though bioplastics typically have a slightly smaller processing window than traditional thermoplastics. Netstal has exhibited at a number of trade shows in the past years molding preforms made of PLA and other bioplastics, with cycle times comparable to standard PET processing. Competing injection molding machine manufacturer Arburg (Lossburg, Germany) regularly molds wood-fiber-reinforced PLA whistles during its open houses, to include the last one on March 2007. The 5.6g whistles form in a 20-second cycle on a 40-kN clamp-force machine.

According to Netstal, injection molds for processing PET typically are fine for processing PLA. PLA has a melt temperature of 145-155ºC with a glass-transition temperature of 55-58ºC. Standard dryers may be used for PLA, but these must be clean of any other plastics’ residue, and a residual moisture of 100 ppm or less is appropriate.

Netstal adds that plasticizing systems for PLA should run at relatively constant screw speeds, as this is not only gentle on the melt but also assists introduction of liquid additives, as often used with PLA. Luc Vervnynck, market development manager at additives supplier ColorMatrix (Cleveland, OH), says his firm’s PLA-enhancing additives include ones able to reduce the material’s yellow haze without compromising its clarity. Another ColorMatrix additive, called Joule, can be added to PLA intended for molding of preforms to help the material absorb heat more readily prior to stretch blowmolding.

Electronics market looms

In Japan, consumer electronics manufacturer NEC announced in April that it had paired PLA with kenaf fibers to create a biocomposite with adequate strength, and more importantly, heat conductivity properties, necessary to specify the material for a mobile phone housing. The end component’s biomass exceeded 90%. NEC said the material’s structure allowed small electronics enclosed in it to emit heat. Currently NEC refers to it simply as "highly heat-conductive bioplastic."

Responding to questions from MPW, officials at NEC say the firm is patenting its development. NEC developed another bioplastic, a kenaf-fiber reinforced bioplastic, in collaboration with Unitika Ltd. The two companies succeeded in improving certain characteristics of this material such as heat resistance, fall impact durability, and moldability, and the improved material has been used in the casing of a mobile phone available in Japan since March of 2006. NEC plans to make the most recently developed material available to other potential users as well as for its own purposes, though NEC does not want to become a materials supplier so it needs to find a partner for supply. NEC is aiming for mass production by March 2009.

New materials, new players

Two U.S.-based firms—Telles (Cambridge, MA), through its parents, Archer Daniels Midland and Metabolix; and Cereplast (Hawthorne, CA)—entered the market in the last year, with both firms offering grades for injection molding, and Cereplast also supplying extrusion blowmolding lines.

Cereplast founder Frederic Scheer said in the past, cutlery molded from starch materials ran $50/box, compared to $6-$14 for products derived from polystyrene or polypropylene. Now, in the heavyweight line of cutlery, which goes for $18/box in traditional resins, Cereplast makes resins that allow for a cheaper price.

Cereplast has four injection molding and two extrusion blowmolding grades, which Scheer says process roughly 20% slower than fossil-fuel-based counterparts. The company has worked with the University of Valencia in Spain to use nanoclays to improve barrier and moldability, earning a patent, and Scheer says the melt-flow rates range up to 35 to 38 for cutlery-type applications. Scheer says that unlike some bioresins, his materials do not require crystallization, and that virgin material can be processed seven times before it degrades to a point where it can no longer be used.

Telles, formed by Metabolix and ADM in April, offers two grades for injection molding: Mirel P1001 and P1002. PHA is a natural polyester that roughly mirrors polyolefins, with a higher heat deflection than PLA, and good printability as well as oil and grease resistance. Metabolix VP of Sales and Marketing, Robert Findlen, says Mirel runs at lower temperatures than a PET, and requires less drying. Melting point is around 150-170°C and tensile strength is 3500-4200 psi (25-29 MPa). The material processes on standard machinery. Findlen says special attention must be paid to the mold, particularly gating and venting. To aid with crystallization, he recommends operating with a preheated tool. —[email protected]; [email protected]