Two masterbatch suppliers claim to have found effective ways to make polyethylene and polypropylene products degrade like paper or wood while remaining cost-competitive with conventional LDPE or PP. Willow Ridge Plastics and ECM Biofilms incorporate proprietary additives into polyolefin carriers. Their masterbatches are said to make polyolefin products fully degrade in five years or less.
Both companies claim a cost advantage for their approach as compared with inherently biodegradable polymers (see PT, March '02, p. 50; Sept. '02, p. 66). On a cost-per-cubic-inch basis, they say, biodegradable copolyester and polylactic acid polymers are at least 10 times more costly than polyolefin additive masterbatches.
"Ours is the only approach that makes degradability viable in large-volume film, sheet, and molding applications," asserts Robert Sinclair, president of ECM. His company supplies a proprietary biodegradable additive that is compounded at a 1% level into masterbatches with an LDPE carrier. Sinclair says ECM masterbatch pellets fully biodegrade PE and PP products in nine months to five years, depending on the disposal conditions.
Sinclair draws an analogy between the way ECM's masterbatches biodegrade and how wood breaks down into CO2 and water in nature. He says wood decomposes after a long period of interaction between successive groups of micro-organisms. Sinclair says ECM's active ingredient initiates a similar chain of events that degrades the entire polyolefin composition in a reasonable timeframe for products bound for landfills or likely to end up as litter.
ECM is a relatively new firm that tailors a range of biodegradable masterbatches for PE and PP films, extruded sheet, bottles, and injection moldings. ECM plans to expand its line to include PET and PVC carriers. The masterbatch pellets cost $3.50 to $5.00/lb and are used at a 1% level. The end product contains 0.5% to 0.6% active ingredient, which raises its overall cost by around 5%, Sinclair calculates.
The first commercial uses reportedly will emerge shortly and will include garbage bags in Ireland, bread wrap in New Zealand, milk pouches in India, and food-packaging films in the U.S. Sinclair also sees interest in using ECM products in agricultural films (with the addition of a photodegradation promoter), blow molded shampoo and motor-oil bottles, and protective overwrap used in shipping new cars.
Meanwhile, Willow Ridge Plastics has offered degradable masterbatches since the early 1990s, though its recent thrust has been toward synergistic combinations of additives promoting multiple degradation mechanisms. The firm offers biodegradable, photodegradable, and thermal-oxidative degradable additives—as well as combinations—in LDPE, HDPE, and PP masterbatches. These are said to make finished products break down in less than five years. Degradation rates can be tailored for specific applications.
One of the three main Willow Ridge products is PolyStarch N, a masterbatch of 55% cornstarch in LLDPE. It is typically let down to 12.5% or 25% starch level. The product includes a processing aid and 3% to 10% levels of a desiccant (trade-named Aquanil) that ensures moisture control prior to use. PolyStarch N is suitable for LDPE and LLDPE trash bags, agricultural films, and injection and blow molded parts intended for disposal in conditions able to sustain microbes. Pellet cost is $1.10/lb.
A second Willow Ridge additive is PDQ, a proprietary non-starch masterbatch that simultaneously triggers photodegradation and thermal-oxidative breakdown in PE and PP. The product is typically used at a 3% level and costs $2.25/lb. For agricultural markets, this additive is offered in versions for black or dark-colored mulch films and clear solar films. Other current applications include garbage bags and injection molded flower pots and golf tees.
Willow Ridge also supplies a photodegradable masterbatch designated UV-H that accelerates uv degradation by creating free radicals that sever the polymer chains into smaller fragments that can be consumed by microbes. UV-H costs $1.50/lb and is typically used at a 2% level. It can be combined into a triple-acting system with PDQ, called PDQ-H, which costs $2.25/lb.
Willow Ridge's additives are effective alone or in synergistic blends of additives that exploit different degradation mechanisms. Thermal-oxidative effects of PDQ, for instance, boost the temperature of disposed products and accelerate biodegradation activity. And when starch biodegrades it creates micro-voids in plastics products, exposing more surface area to attack by photodegradable agents. The company's PolyStarch Plus products use starch and other ingredients to exploit such synergies.
Backing up claims
"Clearly defined criteria for biodegradabilty and scientifically valid test methods are essential to the success of this concept in plastics markets," comments Prof. Ramani Narayan, who is scientific chairman of the Biodegradable Products Institute (BPI) in N.Y.C., a trade group representing compostable polymer suppliers.
Both ECM and Willow Ridge bolster their degradability claims with test data. For example, ECM has hired certified consultants to perform controlled composting tests on garbage bags and microscopic examination of the residues. "Our masterbatch fully biodegrades in home composts, commercial composts, buried in the ground or landfills, tilled into soil, or littered on land or sea," ECM's Sinclair claims. Willow Ridge offers extensive data showing physical-property losses that are said to correlate with biodegradation.
William Hogan, president of Willow Ridge, says the 12-week requirement for full biodegradation laid down in current ASTM composting standards is relevant only when the goal is disposal in an engineered composting facility—very few of which exist in the U.S. Hogan argues that nine months to five years is a meaningful time frame for degradation in most real-world situations.
Both suppliers claim that their additives do not impair recycling efforts. Hogan says markets for degradability invariably are not ones where significant recycling is likely to occur. He also says rates of incidental "recapture" of degradable products are far too low to adversely affect recycled feedstock quality.