Two new families of starch-based bioplastics are being introduced in the US market- as extension of the line of products supplied by Cereplast. Cereplast, offering 14 grades of compostable products based on polylactic acid (PLA) or a thermoplastic starch mixed with some PLA, has introduced Cereplast Hybrid polymers, which are blends of plant starch with conventional polymers. Because they are made with up to 50% conventional thermoplastics, Hybrids overcome what has been a limitation of most biobased materials so far —limited heat resistance in use and heat stability in processing. These hybrids are different as they are not biodegradable, but a way for processors to reduce their reliance on oil and gas and increase use of renewable resources.

Cereplast plans to launch Biopropylene grades with 60% and 70% starch, followed by Hybrids based on LDPE and HDPE. The first Hybrid product in the market is Biopropylene CP Bio-PP-50, a patented mixture of polypropylene homopolymer with 50% starch and a blend of plasticizers or processing aids. It is an end-product of reactive twin-screw compounding in which a chemical coupling occurs between the starch and PP matrix, which accounts for the material’s excellent properties. Biopropylene has higher stiffness, strength and heat resistance than un-filled PP but also has lower elongation and impact toughness. Biopropylene is easy printability, unlike standard PP. And unlike most biopolymers, it needs little or no drying. The price of Biopropylene and pue PP is almost similar, though its 16% higher density will raise its cost in use.
Biopropylene can be tailored for different uses, and the blend of starches can be varied for both properties and economics. It can be formulated with any PP polymer and various starches— corn, tapioca, wheat, and/or potato. This product has been aimed at durable goods rather than disposable packaging. Considerable interest is evinced in the automotive field. It is also targeted for houseware and other consumer products, toys, consumer electronics, cell-phone and computer housings, medical products, cosmetics packaging, CD/DVD cases, furniture and building construction. Biopropylene has been tested in sheet extrusion, thermoforming, blow molding and injection molding, though not yet in blown film. It runs on conventional equipment in similar cycle times, but generally at lower temperatures. Processing requires low-shear screws and temperatures below 200 C. It is opaque and can be colored with standard PP masterbatches or colorants specifically designed for biopolymers. Though not intended to be compostable, Biopropylene is being tested for biodegradability and compostability. The starch component is expected to break down, leaving small fragments of PP. The resin has already passed toxicity tests required for composting in the U.S. (ASTM D6400-04), Canada and Western Europe. Cereplast is also seeking FDA approval for food contact.

Dupont will introduce a second new family of starch-based materials that is fully biodegradable and compostable in collaboration with Plantic Technologies of Australia. Plantic has been making thermoformable sheets and injection mouldable pellets of thermoplastic starch since 2003. Plantic uses high-amylose cornstarch that has been chemically modified by hydroxy-propylation to make it behave as a thermoplastic. The starch is mixed with other polymeric and non-polymeric ingredients, plasticizers and processing aids. The material densities range from 1.35 to 1.62. The formable sheet is fairly rigid but the molding pellets come in both rigid and flexible grades.