What are biodegradable plastic mulches made of? Are all components biobased?

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The specific composition of biodegradable mulch products is proprietary information retained by the manufacturers. The composition of biodegradable plastic mulch is not all biobased (derived from plant sources). Commercially available products vary in their bio-based content and range from less than 10% bio-based up to 20% biobased. Generally, the products are composed of some combination of polyesters (a group of polymers, distinguished because they contain an ester bond that is readily broken by microorganisms, sunlight, and water; they may be derived from synthetic or natural sources) and starches. Polyesters commonly used to make biodegradable plastic mulch include:

  • Polybutyrate adipate terephthalate (PBAT): a synthetic random copolyester of adipic acid, terephthalic acid, and 1,4-butanediol. The ester bonds contribute to PBAT’s biodegradation.
  • Polylactic acid (PLA): a thermoplastic polyester, derived from starch (e.g., corn, sugar beet, tapioca, or sugar cane) fermented by microorganisms to produce lactic acid, which is then polymerized synthetically through a series of reaction steps. PLA can be produced relatively inexpensively in large quantities compared to other biobased biopolymers.
  • Polyhydroxyalkanoate (PHA): a polyester created by a natural, one-step bacterial fermentation of plant sugars and/or lipids.