Designated as Mazda Bioplastic High Strength Heat Resistant Automotive Polylactic Acid, this material is supplied as a nucleation-modified poly(L-lactic acid) compound for injection moulding and sheet extrusion. Under ISO 11469:2016 the resin is marked as PLA, and the delivery form is cylindrical pellets with a bulk density of 0.75–0.85 g/cm³ after drying. Melt flow rate is 8–15 g/10 min at 190 °C/2.16 kg when measured to ISO 1133-1:2022, and solid density is 1.25–1.30 g/cm³ to ISO 1183-1:2019. The compound is directed at interior trim substrates, seat adjustment housings, and HVAC ducting where low-crystallinity PLA grades soften prematurely. Heat resistance is developed through stereocomplex crystallisation and mineral nucleation, not solely through post-mould annealing; this allows moulded components to retain dimensional stability above 100 °C. Bio-based carbon content measured to ASTM D6866-22 is 90–95% depending on additive fraction. The pellet is supplied with REACH 1907/2006 compliance for substances of very high concern, and RoHS 2011/65/EU restricted substances are below the permitted maximum concentration values. Published data for this specific configuration is limited; production validation is therefore performed against lot-specific certificates of analysis.

What Limits Continuous Service Temperature in High-Heat Polylactic Acid?

The continuous service temperature is not defined solely by glass transition. Unfilled amorphous PLA exhibits a Vicat A50 softening point of 55–60 °C and ISO 75-2:2013 method B HDT below 55 °C. In this formulation, heteronucleation raises crystallinity to 40–50% when the mould surface is held at 100–120 °C. Annealed specimens tested to ISO 75-2:2013 method B show HDT-B of 125–135 °C, while HDT-A under 1.8 MPa remains 75–85 °C. DSC to ISO 11357-3:2018 records a cold crystallisation exotherm between 95 °C and 110 °C and a melt endotherm between 165 °C and 180 °C. The practical upper envelope is therefore 95–120 °C for short-term exposure; sustained exposure above 120 °C produces modulus loss because the service temperature approaches the onset of crystal melting. A post-mould annealing step at 110 °C for 2 h is used where maximum HDT-B is required, but this step increases cycle time and must be excluded for thin-wall components with local stresses.

Before melt processing, moisture content must be reduced below 0.025% (250 ppm) using a desiccant-bed dryer with air temperature 80 °C and dew point -40 °C; virgin pellets require 4 h, and regrind above 20% requires 6 h at 70 °C. Injection moulding is carried out at a melt temperature of 200–220 °C, mould temperature 100–120 °C, screw speed 80–120 min⁻¹, and back pressure 5–10 MPa. Screw L/D should be 24:1 to 30:1 with a compression ratio of 2.5:1 to 3.0:1. Hot-runner systems require separately controlled nozzle temperatures within ±5 °C because local overheating triggers discolouration and splay. Holding pressure of 60–100 MPa and hold time of 8–12 s are required to complete crystallisation and minimise post-mould shrinkage. A nitrogen blanket is recommended when relative humidity exceeds 60%. Production-scale observations show that insufficient drying is the dominant cause of gate bloom and low-temperature impact failure, not the base resin itself.

Mechanical Performance Under Automotive Thermal Cycling

Tensile and flexural properties are determined on ISO 527-2 type 1A specimens conditioned at 23 °C/50% RH for 48 h; representative values are summarised in Table 1. The notched Charpy impact of 5–8 kJ/m² to ISO 179-1/1eA is higher than unmodified high-crystallinity PLA, which typically falls below 3 kJ/m². At -10 °C the impact value is 3–5 kJ/m²; values below 2 kJ/m² indicate insufficient impact-modifier dispersion or moisture degradation before moulding. The property balance is also injection-speed dependent: fill times longer than 1.5 s in thin-wall sections reduce crystallinity and depress HDT-B by up to 15 °C. Thermal cycling from -40 °C to 80 °C for 500 cycles is used to screen warpage and snap-fit retention. The moulded part must not exceed 0.6% mould shrinkage to ISO 294-4:2018 when measured along flow direction after 48 h.

When Regrind Content Exceeds 20% in the Drying Hopper

The regrind level is limited to 20% because repeated extrusion lowers molecular weight and raises melt flow rate. If regrind above 30% is processed, the notched Charpy impact at 23 °C typically falls below 4 kJ/m², and the melt may no longer meet the 8–15 g/10 min melt flow rate window. A production-scale twin-screw compounding line with L/D 40:1 and vacuum devolatilisation at -0.08 MPa was used to demonstrate that one additional heat history can reduce weight-average molecular weight by 10–18% when the melt temperature exceeds 220 °C. Regrind from annealed parts is more sensitive than unannealed sprue because the high crystallinity consumes the nucleating capacity. Blend ratio must be controlled gravimetrically; masterbatch dosing at 0.5–1.0 wt% is recommended for stabiliser packages. Published data for this specific configuration is limited, but parallel work on semicrystalline PLA recycling indicates that melt viscosity loss accelerates sharply above 230 °C.

Compared with unfilled PLA, this compound shifts service temperature upward by at least 60 °C while retaining a bio-based carbon fraction above 90%. Against talc-filled polypropylene, the material provides higher flexural modulus but lower long-term resistance to ethylene glycol-water mixtures at 80 °C; comparative data are presented in Table 2. The principal difference from ABS is the notch sensitivity at sub-zero temperatures and the moisture management required before moulding. Unlike mineral-filled high-heat PLA grades, the product uses a low-plate-out nucleating package compatible with grained mould surfaces. Solvent resistance is generally different from amorphous thermoplastics: aromatic hydrocarbons can swell the surface, while short-chain alcohols are less aggressive at room temperature but can extract low-molecular-weight additives during repeated wet-dry cycles.

Hydrolytic Degradation Is Accelerated by Alkaline Coolant and High Humidity

The ester backbone remains susceptible to hydrolytic chain scission in humid, hot environments. At 85 °C/85% RH, a 500 h ageing programme to ISO 527-2:2012 showed tensile strength retention of 70–85% for moulded bars, while unannealed specimens retained less than 50%. The difference is attributed to the barrier effect of the crystalline network, which slows water diffusion into the amorphous tie chains. Continuous immersion in water at 60 °C for 1,000 h produced weight gain of 0.8–1.5% measured to ISO 62:2008, with hydrolysis limited to surface layers. The material should not be dry-blended with amine-based slip agents or chain extenders that accelerate aminolysis; if such additives are required, they must be incorporated during compounding under controlled melt temperature. Exposure to strong alkaline cleaning agents with pH greater than 10 is not recommended because surface etching accelerates gloss loss and reduces tear resistance. Automotive screen wash containing methanol at 20–50 vol% does not dissolve the material but can extract low-molecular-weight additives over repeated wicking cycles. Published data for this specific configuration is limited; production components must be validated under the actual thermal management load case.