Bioplastics are not a marketing trend: they are materials with real properties, specific technical constraints and applications where they deliver measurable value. They are also widely misunderstood, often mis-specified and sometimes mis-processed. This guide covers the main grades (PLA, PHA, bio-PE, bio-PA), their injection constraints (moisture, drying, temperatures, shrinkage) and the applications where bioplastic injection makes sense in 2024.
What exactly is a bioplastic?
The term covers two distinct realities that must not be confused. Bio-based plastics are made from renewable raw materials (corn starch, sugar cane, castor oil) but are not necessarily biodegradable. Biodegradable plastics degrade under controlled conditions (industrial composting per EN 13432) but are not necessarily bio-based.
A plastic can be both (PLA is bio-based and compostable), one without the other (bio-PE is bio-based but not biodegradable; PBAT is fossil-based but biodegradable) or neither (recycled ABS: not bio-based, not biodegradable, but circular). For accurate product communication, you must specify which property is actually certified.
PLA: the most common, the most misused
PLA (polylactic acid) is the most widespread bioplastic in injection moulding. It is bio-based (fermentation of plant sugars), compostable in industrial composting (EN 13432), and offers a surface gloss and hardness close to ABS. This is why it is often proposed as a direct substitute.
The problem: standard PLA has a low softening point, between 55 and 65 degrees C depending on grade (compared to 95-110 degrees C for ABS). A PLA part in a car interior in summer (60-80 degrees C), in a dishwasher (55-65 degrees C) or near a heat source will deform. This is the most common cause of failure in bioplastic projects: incorrect thermal specification.
Reinforced PLA grades (PLA with mineral fillers, PLA with natural fibres, or modified PLA such as PDLA/PLLA blends) raise heat resistance to 100-120 degrees C. These grades exist, but they are less common, more expensive and require cycle adaptation (higher mould temperatures, longer cooling times).
PLA injection constraints: drying and hygroscopy
PLA is highly hygroscopic. A damp pellet injected into a hot barrel undergoes hydrolytic degradation: polymer chains break under the combined effect of heat and moisture, producing brittle parts, surface defects (strings, bubbles, marks) and irreversible molecular weight loss.
Standard drying protocol for PLA: 4 to 6 hours at 80 degrees C in a desiccant dehumidifying dryer. A simple hot-air dryer is insufficient when ambient humidity is high. After drying, PLA must be processed within 2 to 4 hours to prevent moisture re-absorption. Target moisture level is below 200 ppm.
PLA injection parameters: melt temperature 170-210 degrees C depending on grade, mould temperature 20-60 degrees C (cold mould for fast cycle, hot mould for better crystallinity), moderate injection pressure (PLA is less viscous than ABS at equivalent temperature), longer cooling time than ABS for the same wall thickness.
PHA: the promise of marine biodegradation
PHA (polyhydroxyalkanoate) is a family of bioplastics produced by bacterial fermentation. Its advantages over PLA: biodegradable in marine conditions (unlike PLA which only degrades in industrial composting), and slightly higher heat resistance depending on grade.
PHA injection constraints are significant. The processing window is narrow: degradation temperature is close to melt temperature, making machine setup delicate. Insufficient purging or excessive machine downtime causes irreversible degradation in the screw and barrel. PHA is also moisture-sensitive and requires careful drying (protocols close to PLA).
PHA shrinkage rates: variable by grade, between 0.5% and 2%, with a stronger crystallisation tendency than PLA. This makes mould design more complex for tight-tolerance parts.
Bio-PE and bio-PA: bio-based but not biodegradable
Bio-PE (bio-based polyethylene, notably bio-HDPE and bio-LDPE) is produced from sugar-cane ethanol. Its chemical structure is identical to conventional PE: same mechanical properties, same thermal resistance, same recyclability. The only difference is raw material origin. Processing parameters are identical to standard PE.
Bio-PA (bio-based polyamide: PA6.10, PA10.10, PA11) is produced from castor oil. PA11 (Arkema Rilsan) is the most mature bio-based grade for industrial injection: high mechanical strength, good chemical resistance, thermal range -40 to 130 degrees C, lower moisture absorption than standard polyamides. Its use in injection is well documented.
Bioplastic shrinkage and tolerances
Shrinkage is a critical variable for mould design. PLA: 0.3-0.5% (close to PS, relatively low). PHA: 0.5-2% (variable by grade and cooling conditions). Bio-PE: 1.5-3% (identical to conventional PE). Bio-PA (PA11): 0.5-1.5% depending on flow orientation.
Mould design for bioplastics must integrate these material-specific shrinkage values. A mould designed for ABS cannot be directly used for PLA injection without risk of out-of-tolerance parts, particularly for geometries with tight functional tolerances.
Applications where bioplastics deliver real value
Non-thermal packaging (ambient temperature only): cosmetic jars, bottles, lids, caps. PLA is competitive here as long as the industrial composting collection chain is in place at end-user level. Belgium Chocolatiers, one of our clients, is exploring food-contact PLA packaging applications for premium product lines.
Unheated toys and childcare items: PLA offers recognised chemical safety (no bisphenol A, no phthalates, no heavy metals in certified grades), making it a strong argument for parent and child market segments.
Promotional items and point-of-sale displays: short lifecycle, CSR communication argument, no thermal constraint. This is currently the most developed segment for injected PLA.
Single-use medical components (e.g. internal sterile packaging): PLA meets some biocompatibility requirements, but regulatory validation is lengthy and field experience limited for critical applications.
9. Comparing bioplastics for injection: a practical decision matrix
PLA: choose it for packaging, promotional items, ambient-temperature articles where compostability matters. Avoid it above 60 degrees C. Bio-PE: choose it for standard PE applications where bio-based origin is required; no performance trade-off. Bio-PA (PA11): choose it for technical structural parts replacing PA11 or PA12; excellent all-round performance. PHA: choose it for marine-biodegradability requirements; be aware of narrow processing window.
The common mistake is choosing a bioplastic grade based on commercial availability rather than application requirements. The right sequence is: define thermal, mechanical and end-of-life constraints first, then identify which grade meets them, then assess availability and processability.
10. What we do with bioplastics in practice
We injection-mould PLA and bio-PA in small and medium runs. We carry out drying to the specific protocols for each grade. DFM analysis integrates the shrinkage values specific to the chosen material. Our equipment covers the temperature and pressure ranges for common bioplastics.
We advise clients on grade selection based on the thermal, mechanical and regulatory requirements of their application. A PLA project with a thermal constraint above 60 degrees C is resolved by changing grade (reinforced PLA) or changing material (PHA, bio-PA) depending on budget and required certifications.
FAQ
FAQ
Can PLA be injected on the same presses as ABS?
Yes, provided that processing parameters are adapted (lower melt temperature, mandatory pre-drying) and the screw is correctly purged before and after production. The PLA temperature range (170-210 degrees C) is compatible with standard presses. The main risk is contamination by ABS or other material residues if purging is insufficient.
Is PLA dishwasher-safe?
No, standard PLA does not withstand dishwasher temperatures (55-65 degrees C in a normal cycle). A PLA part in a dishwasher will deform. Reinforced PLA grades (mineral-filled or PDLA blends) can hold up to 100-120 degrees C, but this is not standard. If dishwasher resistance is required, consider PP, HDPE or a bio-PA depending on requirements.
What is the difference between compostable PLA and recyclable PLA?
Compostable PLA (per EN 13432) degrades in industrial composting within 12 weeks under controlled conditions. It is not recyclable through standard plastics streams (mixed with other plastics it contaminates them). Recyclable PLA exists in dedicated streams, but collection infrastructure is still limited. The two properties are not interchangeable.
Does bio-PE have the same properties as conventional PE?
Yes, identically. Bio-PE is chemically identical to conventional PE: same mechanical properties, same thermal resistance, same injection behaviour, same recyclability in existing PE streams. The only difference is the renewable origin of the raw material. No mould or machine cycle adaptation is required.
Which bioplastics are suitable for structural technical parts?
For structural parts with significant mechanical and thermal requirements, the options are bio-PA (PA11 or PA10.10: good mechanical strength, range -40 to 130 degrees C), reinforced PLA (mineral fillers or natural fibres, heat resistance up to 120 degrees C) and PHA depending on grade. Standard PLA is not suitable for load-bearing structural parts or temperatures above 55 degrees C.
