Hot-Fill Injection Moulding Requires Either In-Mould Crystallisation or a Post-Annealing Step

Luminy D120 High Heat Medium Viscosity PLA Homopolymer is run as a neat resin or with a PLA-carrier colour masterbatch at 2–4 wt% in rigid food-serviceware applications where short-contact hot-fill exposure, dishwasher steam, or warm stacking is required. The granulate is pre-dried in a desiccant drier with a dew point of −40 °C to −50 °C at 80 °C for 4–6 h, targeting residual moisture below 250 ppm. Moulding is performed on a three-zone general-purpose screw with an L/D ratio of 20:1 to 24:1 and a compression ratio of 2.5:1 to 3:1. Barrel set points are generally rear 170–185 °C, middle 185–200 °C, and nozzle 195–210 °C. At these temperatures, the medium melt viscosity of D120 fills thin-wall cutlery handles, bowl rims, and lid seating features without the extreme shear heating observed in high-flow PLA grades.

Two thermal strategies are available. For maximum heat resistance, the mould is heated with pressurised water or oil to a cavity surface temperature of 95–105 °C. This allows isothermal crystallisation to proceed inside the closed tool. Published crystallisation half-time data for high-purity PLA near 100 °C range from 20–40 s depending on nucleating additives and wall section. D120-derived articles crystallised in the mould can withstand short contact with water at 80–90 °C without gross deformation, but ejection must be controlled because the material remains soft above the glass transition of 55–60 °C until sufficient crystallinity develops. The alternative cold-mould route uses a surface temperature of 20–30 °C to produce an amorphous part, followed by free-air or jig-assisted annealing at 100–110 °C for 20–40 min. Annealed parts shrink 0.5–2.0% depending on orientation, filler content, and annealing restraint, so mould dimensions must include shrink compensation or the annealed article will fail dimensional checks.

The critical processing boundary is thermal degradation. Sustained melt temperatures above 230 °C or residence times above 10 min regenerate lactide, reduce molecular weight, and produce yellowing, screw deposits, and acrid odour. The machine should be purged with a medium-viscosity PLA purge grade, not with polypropylene or polycarbonate, because residual incompatible carrier layers will delaminate at the gate and reduce weld-line strength. Clamp force requirements for multi-cavity cutlery production are calculated from projected area. A 150 t machine can normally hold a 4-cavity cutlery mould with a projected area of 400 cm² when cavity pressure is 400–600 bar, but actual values depend on wall thickness, melt temperature, and gate diameter. Terminal articles include reusable cutlery, hot-fill salad bowls, deli containers, lids, and institutional serviceware tested for heat deflection according to ISO 75-2 and for migration under EU 10/2011.

Thermoformed fruit punnets, dairy portion cups, and modified-atmosphere ready-meal trays produced from D120 begin with cast sheet extrusion rather than injection moulding. The resin is dried to the same moisture specification and fed to a 75 mm single-screw extruder with an L/D ratio of 30:1, barrier screw geometry, and a melt gear pump to suppress surging. A screen changer with 60/80/100 mesh packs removes char particles. Melt temperature at the flex-lip die is held at 185–205 °C. The melt curtain is cast onto a three-roll stack with polished rolls at 40–60 °C, producing a transparent amorphous sheet of 0.5–1.5 mm. If roll temperature exceeds 70 °C, uncontrolled crystallisation begins, creating haze and sheet brittleness. If roll temperature is below 30 °C, static cling and winding-tension defects increase.

Thermoforming is performed on a plug-assisted pressure former with sheet surface temperature of 90–110 °C and forming air pressure of 4–6 bar. D120 sheet has a narrow forming window because it must be heated above the glass transition but below the onset of rapid crystallisation. Tool temperature is normally 40–60 °C. Higher tool temperatures accelerate crystallisation but can cause the sheet to stick to aluminium female cavities. The base formulation uses no external plasticiser, but a PLA-carrier antiblock masterbatch may be added at 0.5–1.0 wt% to reduce nesting of stacked trays. For dairy and ready-meal applications, migration testing under EU 10/2011 is required with overall migration below 10 mg/dm². Acidic products are tested in 3% acetic acid for 10 days at 40 °C, while aqueous products use 10% ethanol. Terminal articles include clear deli cups, insert trays for fresh pasta, fruit punnets, and shallow ready-meal bases. Thermoformed D120 parts remain largely amorphous unless a secondary annealing step is added, so hot-fill above 60 °C is not recommended for unannealed sheet.

Can D120 Homopolymer Maintain Shelf Life in Single-Serve Espresso Capsules?

Single-serve espresso capsule bodies are thin-wall injection moulded from D120 because the medium-viscosity melt fills the conical sidewall and bottom filter geometry at wall sections of 0.6–1.0 mm. The capsule body is normally moulded in a 16–32-cavity hot-runner tool with valve gates to reduce gate vestige and flange fibre formation. Melt temperature is 195–210 °C, cavity surface temperature is 95–105 °C, and cycle time is 15–25 s. The body formulation is often 98.5 wt% D120, 1.5 wt% PLA-carrier colour masterbatch, and 0.2–0.5 wt% internal slip additive. The exact slip package must be migration-compliant for coffee contact and must not interfere with flange heat-sealing. During extraction, water at 90–93 °C contacts the capsule for 20–30 s. Crystallised D120 bodies maintain flange flatness and do not soften inside the espresso machine basket.

The main technical conflict is oxygen and moisture barrier. PLA has higher oxygen permeability than PET or PVDC. A neat D120 capsule may allow unacceptable oxidative rancidity of ground coffee over 6–12 months. Commercial structures therefore co-inject a barrier layer or apply an internal EVOH liner representing 5–10% of the wall cross-section. The barrier layer must be encapsulated because EVOH is moisture-sensitive, and the layer ratio must be adjusted to retain the compostability claim. European compliance requires EU 10/2011 migration testing in coffee simulant and specific lactide migration below the applicable limit. If the capsule is marketed as industrially compostable, EN 13432 requires 90% biodegradation within 180 days and 90% disintegration after 12 weeks. D120 homopolymer alone can meet the polymer carbon criterion, but barrier layers, tie resins, and printing inks must also be certified for compostability.

Processing boundaries for capsules include gate stringing at high hot-runner temperatures, flange warpage when ejection is too hot, and start-up scrap from crystallisation variability. Published data for D120 in high-cavity capsule tooling is limited. Validation on production-scale equipment is required because the effective shear rate at the gate can exceed 10,000 s⁻¹, causing local viscosity reduction and flash if clamp tonnage is below the required value. Mould protection should be adjusted to detect short shots below 1 mm because PLA flash can be recompressed into the parting line and damage the shut-off surface.

When a Filament Extrusion Line Is Configured for High-Heat PLA

Filament production from D120 uses a single-screw extruder with an L/D ratio of 24:1 and a metering pump to maintain diameter stability at 1.75 mm ± 0.05 mm. The pellets are dried to ≤250 ppm moisture and extruded at 190–210 °C through a 1.6–1.8 mm die. The melt strand passes through a 40–50 °C water bath, an air stripper, and a dual-axis laser gauge. Haul-off speed is trimmed automatically to control diameter. D120 homopolymer filament is brittle if wound below its glass transition in a tight coil, so spooling tension is kept below 2 N and spools are conditioned at room temperature before vacuum sealing. The resulting filament is used in fused filament fabrication where high heat resistance is realised only after printing and annealing. Printing is typically performed with nozzle temperature 200–220 °C, bed temperature 50–60 °C, and no enclosure. This suppresses warping relative to ABS but leaves the printed part amorphous. Annealing in a fan oven at 80–100 °C for 30–60 min increases crystallinity and raises heat deflection temperature under ISO 75-2 method B into the 85–100 °C range. Annealing shrinkage of 1.5–2.5% must be compensated in CAD or the dimensional accuracy of printed fixtures fails.

Mechanical property testing of printed D120 test specimens follows ASTM D638-14 Type IV for tensile properties and ISO 178 for flexural properties. Layer adhesion remains the limiting factor. Z-axis tensile strength is typically 30–50% lower than XY-axis strength because interdiffusion across the cooled previous layer is incomplete. Published data for D120 filament specifically is limited. Generic high-purity PLA filament data cannot be transferred directly because molecular weight and crystallisation kinetics differ. Printed high-heat PLA parts should not be autoclaved repeatedly above 100 °C or exposed to strong alkaline cleaning agents, which accelerate hydrolytic chain scission. Terminal printed articles include heat-resistant jigs, dimensional inspection fixtures, vacuum-forming tools, and functional prototypes that experience brief hot-water contact.

Paperboard Hot-Cup Extrusion Coating and Melt Curtain Stability

Extrusion coating of paperboard with D120 for hot beverage cups involves a 90 mm single-screw extruder with an L/D ratio of 30:1, a coextrusion feedblock if a tie layer is used, and a die width of 2.4 m. Melt temperature is held at 200–210 °C. The molten curtain falls into the nip between the chill roll and pressure roll at a line speed of 150–250 m/min. Coat weight is controlled at 15–25 g/m² by varying pump speed and line speed. D120 medium viscosity is suited to extrusion coating because low-viscosity PLA creates edge neck-in and curtain sag, while high-viscosity grades produce poor adhesion to paperboard. The chill roll is kept at 15–25 °C to quench the PLA coating and prevent crystallinity, which would make the coating hazy and reduce heat-seal performance.

The main failure modes are pinholing, fibre tear on heat sealing, and barrier loss at creases. A neat D120 coating on paperboard has a narrow heat-seal window between 110 °C and 130 °C. Below the lower bound, seal strength is negligible. Above the upper bound, the coating shrinks and the paper may char. For hot beverage contact, the coated cup is tested under EC 1935/2004 and the plastic layer under EU 10/2011, with overall migration below 10 mg/dm². Use with beverages up to 85 °C is typical. Sustained exposure to boiling water is not recommended for quenched amorphous PLA coatings because the thin coating does not develop the crystallinity of thick injection-moulded parts. Terminal articles are double-wall hot-drink cups, soup cups, and paperboard sleeves for warm food service.

Warm-filled cosmetic jar bases and closure components from D120 are injection moulded on conventional hydraulic or hybrid machines with clamp force from 80–150 t depending on cavitation. The resin is dried to ≤250 ppm and processed at 190–210 °C. Mould temperature is 20–30 °C for glossy amorphous surfaces or 90–100 °C for heat-resistant jars that must survive filling at 45–60 °C. Thick jar bases of 4–8 mm develop sink marks and internal voids unless the gate diameter is increased to at least 25% of the nominal wall and hold pressure is maintained at 600–800 bar for a longer holding time than polyolefin parts of equivalent section. D120 does not contain phthalate plasticisers. Compliance for cosmetic packaging is managed under REACH Regulation (EC) No 1907/2006 and the Packaging and Packaging Waste Directive 94/62/EC for heavy metals. The terminal components include rigid cream jars, sifter closures, compact bases, and lip-care component shells. Amorphous D120 cosmetic jars should not be autoclaved or filled above 60 °C. Crystallised jars tolerate short exposure at 85–90 °C but may show a reduction in clarity due to spherulite formation.