High-heat polylactic acid compounds occupy a narrow formulation window between standard amorphous PLA and petroleum-based engineering resins. The product designated PLA Blend C Impact Modified High Heat PLA Blend is supplied as cylindrical pellets for injection moulding, sheet extrusion, and thermoforming feedstock. Its melt mass-flow rate is specified at 8–14 g/10 min under 2.16 kg at 210 °C according to ISO 1133-1:2022. After annealing at 90 °C for 60 min, the heat deflection temperature under 0.45 MPa flexural stress reaches 85–100 °C when measured by ISO 75-2:2013 Method B. Notched Izod impact strength at 23 °C on injection-moulded 4 mm specimens is typically 18–24 kJ/m² under ISO 180/A:2019. These values distinguish the compound from standard PLA, which commonly exhibits notched Izod impact strengths below 4 kJ/m² and heat deflection temperatures near 50 °C unless annealed. Density is 1.20–1.26 g/cm³ by ISO 1183-1:2019. The supplied form is opaque and pregranulated to a bulk density of 0.70–0.85 g/cm³ by ISO 60:1977.

Material Constitution and Thermal Classification of PLA Blend C

The compound comprises a PLA continuous phase, a dispersed impact-modifier phase, and a high-heat nucleation package. Differential scanning calorimetry performed at 10 K/min under nitrogen in accordance with ISO 11357-1:2016 and ISO 11357-3:2018 indicates a glass transition temperature of 58–62 °C, a cold-crystallisation exotherm between 95 °C and 110 °C, and a melting endotherm peak at 165–175 °C. The annealed degree of crystallinity is typically 30–38% when specimens are held at 90 °C for 60 min. The nucleating agent promotes lamellar growth without requiring filler reinforcement; however, the crystalline fraction remains lower than that of fully annealed unmodified high-heat PLA homopolymer, which can exceed 45%. Tensile yield strength is 45–55 MPa with elongation at break of 6–20% tested to ISO 527-2:2012. Flexural modulus is 2.4–3.0 GPa tested to ISO 178:2019. Oscillatory shear at 210 °C in a parallel-plate rheometer with 25 mm plates and 1 mm gap shows complex viscosity of 500–800 Pa·s at 10 rad/s and 250–400 Pa·s at 100 rad/s. These values place the material between rigid high-heat PLA and ductile impact-modified PLA in terms of stiffness-toughness balance.

What Distinguishes Impact-Modified High-Heat PLA from Standard PLA?

Standard PLA has a narrow processing and service window. The unannealed HDT-B at 0.45 MPa is typically 50–55 °C, and notched Izod impact strength is usually 2.5–4.0 kJ/m². Impact-modified grades raise toughness but sacrifice temperature resistance; commercial impact-modified PLA often shows HDT-B values below 60 °C unless annealed and notched Izod values of 15–30 kJ/m². High-heat PLA grades use nucleation or crystallinity enhancement to reach annealed HDT-B values of 80–105 °C, but notched Izod strength often remains below 6 kJ/m², which limits demoulding and drop-impact durability. PLA Blend C combines the two modifications by dispersing an impact modifier in a nucleated PLA matrix. The resulting comparative profile is summarised in the table below. The compromise is not cost-free: tensile modulus is lower than unmodified high-heat PLA, and melt viscosity is higher than standard PLA at equivalent melt temperatures. Processors requiring tight flatness or low creep must account for post-mould shrinkage and lower modulus than mineral-filled PLA compounds.

On a 120-tonne hydraulic injection moulding machine with a 30:1 L/D general-purpose screw, PLA Blend C has been used to mould thin-wall hot-fill cup lids with a nominal wall thickness of 2 mm. The mould temperature is held at 95 °C for 30 s to develop crystallinity before ejection. Shortened hold times produce parts that eject cleanly but exhibit lower heat resistance until post-annealed at 80 °C for 30 min. Dimensional shrinkage after 24 h at 23 °C is 0.4–0.7% in the flow direction and 0.5–0.8% transverse on 2 mm plaques. Hot-fill performance is limited to filling temperatures up to 85 °C for short contact times; sustained contact at 100 °C causes distortion. Published data for this specific configuration is limited; the above parameters are representative of nucleated high-heat PLA compounds and must be confirmed by production tool trials.

When Processing Temperatures Exceed 230 °C

Thermal degradation of PLA proceeds by random chain scission, lactide reformation, and hydrolysis. Barrel zone setpoints should be arranged to produce a homogeneous melt without exceeding 220 °C at the nozzle. If hot-runner manifold temperatures exceed 230 °C, molecular weight reduction can occur within 5 min, observed as a viscosity drop and unstable cushion position. The maximum recommended residence time at 220 °C is 8 min; at 240 °C the safe residence time is 3 min. Spiral-flow testing on a 2 mm cavity at 800 bar injection pressure and 210 °C melt temperature yields flow lengths of 180–220 mm for this type of compound, but tool-specific results must be established. Screw rotation should be set to a peripheral speed of 0.2–0.4 m/s with back pressure between 5 bar and 10 bar. High-shear gates exceeding 50,000 s⁻¹ produce shear heating; melt temperature should be measured by insertion pyrometer rather than inferred from zone setpoints. Purging with unfilled PLA or a dedicated purging compound after production reduces carbonised residue in hot-runner channels.

Desiccate the Pellet Feed Before Melt Processing

Residual moisture above 250 ppm hydrolyses PLA during melt processing, producing surface splay and a reduction in tensile strength of 15–30% at 23 °C under ISO 527-2:2012. Pellets are dried at 80 °C for 4–6 h in a desiccant dryer with a dew point of −40 °C. The hopper should be sealed and purged with dry air when relative humidity exceeds 60%. Opened material exposed to 50% RH should be consumed within 8 h or resealed with desiccant. Vacuum drying is an alternative if the resin temperature is maintained below 90 °C to avoid pellet bridging from surface sticking. The dried granules are fed through a throat cooled to 30–50 °C to prevent premature pellet softening and feed-throat blockages. Moisture content can be verified by coulometric Karl Fischer titration to ISO 15512:2019 or loss-on-drying at 80 °C to constant mass. Failure to dry consistently is observed on production lines as batch-to-batch tensile variation and intermittent screw slippage.

In extrusion of sheet for thermoformed food-service trays, the dried compound is processed on a 45 mm single-screw extruder with 25:1 L/D and a barrel profile of 180 °C to 210 °C. The melt is filtered through a 60 mesh screen pack and cast onto a roll stack at 40–60 °C. The unannealed sheet remains ductile enough for trimming, but the final article must be annealed at 80 °C for 20–40 min to achieve the target HDT-B. Thermoforming depth-draw ratios above 0.5 require plug-assisted forming to avoid wall thinning below 0.8 mm.

Assessing Compliance Across Food-Contact, REACH, and RoHS Scope

Regulatory compliance for the pellet grade is supported by documentation for REACH and RoHS Directive 2011/65/EU Annex II; declared SVHC content is below 0.1% w/w in the supplied form. Food-contact suitability requires article-specific validation under EU Regulation 10/2011 and applicable United States FDA food-contact notifications for the additive package, because total migration and organoleptic behaviour depend on final wall thickness, crystallinity, and contact time. The material should not be specified for continuous immersion in water above 85 °C, boiling-water sterilisation at 100 °C, or steam autoclave cycles, because hydrolysis of PLA accelerates above the glass transition. Alkaline cleaning solutions with pH above 10 at 60 °C cause surface etching and reduce impact strength after 24 h immersion. Storage in sealed moisture-barrier bags at 10–30 °C preserves pellet feed performance for 12 months from the date of manufacture when unopened. The product is not intended for implantable medical devices requiring ISO 10993-1:2018 biological evaluation unless the converter independently validates the final device. Drying and processing conditions must be revalidated after any blend of regrind above 20% because regrind lowers melt viscosity and can shift cold-crystallisation onset.