At the California State University at Chico, Joe Greene has been examining the potential for bioplastics to reduce the effects of debris in the ocean. The US has a good system for large waste cleanup along the shore line, which means that the main contaminant is smoking-related materials like cigarette butts (35%), plastic bags (6%), food wrappers (10%) and plastic bottles (5%). The ASTM standard D6691 is a test used to simulate degradation in ocean waters – a Mirel carrier bag showed 70% disintegration after 12 weeks in this test, and Mirel PHA behaved like cellulose in marine water under ASTM D7081. The university has been trying to blow mold biodegradable bottles with only limited success.

Mirel is a trade name of the Telles company and is a PHA made by fermenting corn sugar. The production facility in Iowa has a production capacity of 50,000 tons per year. There are grades for injection molding, sheet, film, thermoforming, coating, foam and fiber.

Novamont is the producer of Mater-Bi polymer and is owned by the largest merchant bank in Italy, Banca Intesa-Sanpaolo. The biorefinery has capacity of 80,000 tons per year. This biodegradable plastic is used in films including agricultural mulch and although it has a high water vapor transmission rate (WVTR), it can be treated to improve this.

PLA can be biaxially-oriented in films using technology similar to that used for polypropylene (BOPP). One of the companies leading this new industry is Toray Plastics. The BOPLA is said to have good mechanical properties lying between those of OPP and PET and can be used as a print web or seal web. The metallized PLA can be used as a foil or to replace other metallized films according to Toray Plastics. The film has moderate oxygen and moisture transmission rates and should be converted at temperatures below 180F.

The technology for processing these new bio-sourced plastics is advancing. Reifenhauser has worked on film and sheet extrusion equipment for cellulose, starch, PLA and PHA materials.

As one example, the major use it has seen for PLA is in extruded sheet for thermoforming. The PLA should be pre-dried prior to extrusion and it is important to avoid sag using various adjustments such as a duck-bill die design to minimise the gap between the die exit and the primary roll.

As consumers look to a “green agenda” it is important to give accurate information about products. Companies such as Beta Analytic quantify the biobased content of materials using ASTM D6866 methods by measuring the carbon-14 content.

The test result is given as a percentage of renewably sourced carbon compared to the total organic carbon. Carbon-14 is formed from nitrogen-14 reacting with cosmic neutrons in the atmosphere and it undergoes radioactive decay with a half-life of 5730 years.

This is taken up by plants and incorporated into biomass. Due to the decay rate there is no carbon-14 in fossil fuels. Hence, the carbon-14 levels indicate the biobased content of a material, which can be listed on the USDA BioPreferred voluntary labelling program.

What about waste disposal of biodegradable plastics?

Organic Waste Systems, Inc. designs and constructs anaerobic digestion plants for organics and is involved in compostability certification and standards in the USA and Europe. Composting takes place in stages: biodegradation at a chemical level, followed by disintegration at a physical level.

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