There are several different meanings to the term “bioplastics” being used today including medical plastics, natural polymers (like collagen), biodegradable plastics, oxo-degradable plastics and plastics from renewable sources. In North America the latter is the primary designation, whereas in Europe the compostable and biodegradable materials have been more highly rated. Each continent has set up its own standards and labelling protocols to aid purchasing managers and consumers in understanding what they are buying into. A market study in 2009 by Utrecht University in Holland predicted a bio-based plastics market size of 2.3 million tonnes in 2013 including conventional polymers from renewable sources.
In the first half of 2011, Applied Market Information LLC organized an international conference in Miami, Florida for the plastics industry to discuss practical aspects of bioplastics use and disposal, Bioplastics Compounding and Processing 2011. The program covered primarily the relatively new plastics derived from plants including PLA and polyesters like PHA, and suitable additives and processing technology, as parameters and performance have to be tailored for different applications. The technology to produce these materials has been available for several decades, but polymer supplies have been limited and relatively expensive. With the current focus on sustainability coupled with the rise in oil prices and increasing output, there is now greater market interest.
Professor Ramani Narayan of Michigan State University is the leading US academic in this field with research on renewable carbon content, life cycle analysis (LCA), processing and degradability. He is the Scientific Chair of the Biodegradable Products Institute (BPI) in North America, and chairs the American standards ASTM committee on Environmentally Degradable Plastics and Biobased Products. Narayan gave the keynote address at the Bioplastics Compounding and Processing conference and outlined the value proposition for plant-origin plastics: the reduction in CO2 emissions, renewable feedstocks, and the economic development of rural areas. Crops and residues can be processed to give monomers, sugars and oils, which can be converted to PLA, PHA or conventional ethylene/propylene (via ethanol). It is the carbon origin that gives environmental value, not the production processes. It takes more than a million years to fix the carbon in fossil sources like oil, whereas it only takes 1-10 years to fix carbon in plants, thus giving a sustainable carbon cycle. The current buzz in the industry is in the use of algae as sources, because of the rapid growth and short life cycle.
The standard ASTM D6866 gives test methods for determining the biobased carbon content of a product using radiocarbon analysis. The principle behind this is the carbon cycle where radiation generates C14 from N14 in the atmosphere. This C14 is present in plants, but has decayed to C12 in fossil fuels, so by determining the C14 content of a polymer the percentage of renewable origin can be measured. This is the primary standard in use in the USA today. The US government has set up a Biopreferred procurement system and the US Department of Agriculture (USDA) has a “Certified Biobased Product” labeling program to guide purchasing.
Biodegradability is also subject to standards and testing. The time frame should be short and the polymer should be completely used up by microorganisms to qualify. There are different standards for different settings including industrial and home composting (ASTM D6400, D6868, D7021; EN 13432; ISO 17088) and marine biodegradability (ASTM D7021).
For brand owners the issue of sustainability is high on the agenda. Procter and Gamble is a leader in this area with the guiding principle “to touch and improve lives, now and in the generations to come”. The aim is to switch to sustainable sources of materials in products and packaging including recyclate, and to replace 25% of petroleum-based materials by 2020. The solutions should be affordable to consumers, who want to be “green” but can’t pay a premium, and also practical at a social level, for example, not requiring a separate waste bin. The company prefers bio-identical resins like the Braskem bio-sourced polyethylene from sugar cane feedstock, which provides a drop-in solution and can enter the existing recycling stream. However this comes at a premium cost and Dr Emily Boswell commented that consumers expect the same packaging and price. Biodegradable renewable plastics may be useful in emerging markets without recycling facilities.
Japan leads the world in its application of bioplastics with Fujitsu and Sony using PLA in mobile technology in 2002. The NEC Corporation has an environmental action plan to use bioplastics in most of its hardware products by March 2018. It has developed materials specifically for electronic products, including flame-retardant polylactic acid (PLA), which is modified with aluminum hydroxide and other additives, giving a V-0 rating at 1.8-13 mm thickness. This PLA is in use in the housing of business PCs. NEC has also developed a new cellulose-based material bonded with cardanol, which is extracted from cashew nut shells. The inventor Michio Komatsu of Nissei has developed an injection molding system for PLA and a Mucell foaming system can be added. It includes tools to optimise the cycle to provide the required crystallinity.
North American compounders are seeing increased demand for bioplastics materials as brand owners and processors look to the next stage of development. RTP Company is engineering compounds for demanding applications. For example, PLA has low impact properties and is very brittle if unmodified; compounding with a copolymer can raise the notched Izod impact strength to comparable levels to HIPS giving a 90% bio-content. The heat distortion temperature (HDT) is low at around 120F; this can be raised by alloying, increasing the crystallinity, or by adding glass fiber or mineral. PLA is not recommended for areas of high heat and humidity such as dishwashers, because as with other thermoplastic polyesters it undergoes hydrolysis degradation, which in turn is a necessary precursor to biodegradation. The company is also working with nylons synthesized from castor oil giving up to 100% bio content, the product is around 3-5 times more expensive than conventional polyamide.
In Germany FKuR Plastics started as a research institute project and now it produces a total of 10,000 MT/year of bioplastics (the third largest bio-resin producer in Europe). It has several products including a PLA for extrusion and injection molding and a cellulose material. The company’s main application markets are hygiene film, bags and pouches, general injection molding and automotive, with a lesser percentage going into mulch film and specialty areas. The PLA is compounded to improve properties so that it can be used as a drop in replacement for petroleum based plastics such as PE, PP and PS. There is a new 3-layer film with high clarity and 30-50% renewable content for applications including the back film of diapers, frozen McCain food bags and form-fill-seal.
Additives corporations have studied the appropriate agents for PLA. Clariant International has found that the light stabilizers and anti-blocking agents used for polyesters such as benzotriazoles and fatty acid esters respectively, can be used for PLA as well. There are also special masterbatches like the CESA-extend chain extender for melt stabilization. In terms of mineral fillers, talc and calcium carbonate can be used as nucleating agents and to increase stiffness. Clariant also has a premium range of naturally sourced pigments and additives which are “OK Compost” certified including a beeswax, a pale yellow color from fruit and an antioxidant based on vitamin E.
Charlie Martin of Leistritz in New Jersey is well-known for his expertise in twin screw extrusion and he has applied his extensive knowledge to the compounding of and the machine should be of stainless steel to avoid the corrosive effects of PLA. There should be provision for devolatilization of undried PLA. The material is heat-sensitive, so cooling systems are important. The torque should be increased, for example by changing the shaft design to include more splines and asymmetric geometry, as well as by upgrading the gearbox. Gala Industries as worked on pelletizing systems for bioplastics.
Natureworks LLC is probably the best known supplier of PLA worldwide. It produces three lactide monomers from corn, L-lactide, meso-lactide and D-lactide, and these are polymerized using a catalyzed ring-opening process. The monomer ratio can be used to develop different properties. There are film, fiber, thermoforming, injection molding and injection stretch blow molding grades. The Ingeo 3801X injection molding materials is compounded with a core-shell impact modifier from Arkema, a dioctyl adipate crystallization accelerant from HallStar, mineral reinforcement from Specialty Minerals and a nucleating agent from Takemoto Oil & Fat Co. The company is currently developing improved injection molding and higher performance materials.
Another company that is working on new PLA compounds is Techmer PM. The company has molding and film grades, some of which are compostable and have FDA food contact approval. It has worked with talc as a natural mineral filler and with a yeast filler, which adds bio-based content. Its PLA masterbatches have applications in nonwoven fabrics.
Brand owner Kimberly-Clark is “weaving environmental sustainability into its products” and has been named as a leader in the Dow Jones Sustainability Indexes. Current projects include testing high percentage bio-based materials to replace 100% petrochemical plastics. This includes polyethylene-starch blends to manufacture films., which requires plasticizers and compatibilisers for processing, and gives films that have a suitable modulus for flexible packaging.
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.