Are bio-based plastics suitable for injection molding?

The short answer

Bio-based and biodegradable are two different questions

Buyers routinely treat these as one word, and that is where specifications go wrong. Bio-based means the carbon came from a plant rather than from oil or gas. Biodegradable means the material can be broken down by micro-organisms under stated conditions. A bio-based polymer can be non-biodegradable, and a fossil-based polymer can be compostable. Bio-polyethylene and bio-PET are chemically identical to their petrochemical versions and will persist in the environment exactly as long as they always have. PLA is both bio-based and compostable, but only industrially. PHA is bio-based and degrades in home compost, soil and marine environments. If the requirement is a lower carbon feedstock, ask the first question. If the requirement is end-of-life, ask the second, and ask where the degradation has to happen.

The drop-in options: bio-PE, bio-PET and bio-PA

These are the easiest route into a bio-based part because nothing about the mould, the machine or the processing window changes. Bio-polyethylene is made from sugar-cane ethanol and is a drop-in replacement for fossil PE at the same density, shrinkage and melt behaviour. Bio-PET substitutes bio-based monoethylene glycol and, in some grades, bio-based purified terephthalic acid. Bio-polyamides from castor oil replace PA6, PA11 or PA12 in technical parts with comparable or better properties, including lower moisture uptake than PA6 in the case of the long-chain grades. The trade-offs are commercial rather than technical: a price premium over fossil equivalents, and a supplier base that is smaller, so lead time and minimum order quantity have to be checked before a programme depends on it.

The new polymers: PLA, PHA, PBS and starch blends

These are the materials that behave differently, and each has a distinct position.

• PLA. The volume leader in rigid compostable parts. It is stiff and strong, with tensile strength around 60 MPa, close to polystyrene, and it is transparent. Its glass transition sits between 55 and 65 C and its heat deflection temperature around 55 to 60 C, which is the single biggest constraint: a PLA container distorts in a hot car or under hot food. Its melting range is roughly 170 to 180 C and it moulds between about 170 and 210 C, with mould temperatures of 80 to 120 C and often a hot runner or hardened, chromium-plated tooling to avoid sticking.
• PHA. Produced by bacterial fermentation, it is the most versatile of the degradable family, ranging from stiff to rubbery depending on copolymer, with heat resistance that can reach around 120 C in some grades and genuine home-compost, soil and marine certification. The obstacles are cost, around USD 8,500 to 9,940 per tonne or roughly twice PLA, a narrow melt window in the region of 130 to 180 C with degradation risk at the top of it, shorter shelf stability, and a moulding cycle about 4 to 6 seconds longer than polypropylene on comparable parts.
• PBS and PBAT. PBS behaves much like polypropylene, with a melting point around 115 C, a heat deflection temperature near 100 C and tensile strength around 40 MPa, and it moulds on conventional equipment. PBAT is the flexible member of the group, with elongation above 700 percent, and is used where toughness or film behaviour is needed. Both are usually blended rather than used alone.
• Starch blends. Cheap and genuinely compostable, but mechanically weak and moisture sensitive. They mould thick, short-flow parts such as disposable cutlery and trays, with starch contents above 60 percent, and they need careful drying because the material takes up water readily.

Where bio-based plastics sit in the market

The market is real but still small, and knowing the scale helps set expectations on supply. Bio-based plastics production capacity was around 2.31 million tonnes in 2025, against roughly 431 million tonnes of plastics produced worldwide, or about 0.5 percent of the total, and it is forecast to reach about 4.69 million tonnes by 2030. Industry capacity utilisation was about 72 percent in 2025, which means the constraint is demand and cost more than technology. Packaging is the largest segment at about 41 percent of capacity, or 0.95 million tonnes, followed by textiles, consumer goods and automotive at roughly 0.24 million tonnes. PLA alone accounts for around a quarter of capacity, and polyamides, PTT and bio-PE follow. The practical consequence for a programme is that a bio-based grade may carry a longer lead time and a higher minimum order quantity than the commodity resin it replaces, and that only a few suppliers will hold stock.

The limits you have to design around

• Heat is the first limit for PLA. Softening near 60 C rules out hot-fill, dishwashers, vehicle interiors and anything near a heat source unless the part is crystallised or annealed, which changes the tool and the cycle.
• Composting needs infrastructure. PLA is certified for industrial composting to EN 13432 and ASTM D6400, requiring temperatures of about 58 C or more, and it degrades very slowly in home compost, soil or landfill. A part labelled compostable that goes to landfill behaves like a conventional plastic.
• Degradable grades can contaminate recycling. A compostable item wrongly placed in the PET recycling stream degrades the recyclate. That is a labelling and collection problem as much as a materials one, and it is a reason some brand owners choose bio-based but non-degradable drop-ins instead.
• Impact resistance is usually lower. PLA is brittle, with elongation at break of only a few percent, so anything that is dropped, snapped or hinged needs a blend, a rubbery grade, or a different polymer.
• Drying and thermal control are strict. PHA and starch blends take up water quickly and are sensitive to shear heat. Desiccant or vacuum drying and controlled residence time are not optional extras.
• Regulatory approval is per grade. Food contact and medical status depend on the specific grade and the migration limits that apply, not on the polymer family. Compostability claims also have to name the standard and the environment.
• Tooling may differ. The higher mould temperatures PLA wants, and the sticking tendency of some grades, can mean hardened and polished tool steel rather than the plain P20 used for a commodity resin.

How to specify a bio-based part without a surprise

Tell us which requirement is driving the change: a lower-carbon feedstock, a compostable end-of-life claim, a specific regulatory target, or a consumer-facing label. Then give the service temperature, whether the part is hot-filled or dishwasher-cleaned, the impact and drop requirement, the required compostability standard and the disposal environment, the food-contact status, the expected annual volume and the acceptable price premium. With that we can say whether a drop-in bio-grade keeps the existing tool and settings, or whether a new polymer is needed and what it changes in mould temperature, drying, cycle time and tooling. See plastic injection molding for the process, FDM 3D printing for the prototyping route that runs PLA best, and surface finishing for decoration and texture on bio-based parts.