Polylactic Acid REVODE201

When Screw Recovery Time Exceeds Cooling Time in Thin-Wall PLA Cutlery Moulding

Processors of REVODE201 for single-use forks, knives, spoons and stirrers must hold screw recovery time below the mould cooling time to maintain a cycle under 6.5 s for nominal wall thickness of 1.2–1.8 mm. Before sustained processing, residual moisture must be reduced to 250 ppm in a dehumidifying hopper dryer at 70°C for 4 h; ambient regrind at relative humidity above 60% can exceed 0.05% moisture within 4 h and produce hydrolysis splay. PLA homopolymers in this viscosity range show a stable flow plateau between 195°C and 215°C; each barrel zone heated above 230°C accelerates random chain scission and generates lactide odour. A general-purpose screw with L/D 20:1–24:1 and compression ratio 2.0:1–2.5:1 provides sufficient shear uniformity without excessive residence time. Extended mixing sections are not required for unfilled cutlery grades and can raise melt temperature by 8–12°C from shear heating alone. Hot runner manifolds with internally heated nozzles should be avoided where local residence time may exceed 5 min; cold runner pin-point gates of 0.8–1.2 mm diameter reduce dead spots and gate blush. Injection speed is profiled in two stages: 100–150 mm/s for the first 70% of fill, followed by 30–50 mm/s to avoid vent blockage and flash. Cavity pressure peaks between 600 bar and 900 bar are typical for flow lengths up to 120 mm. Holding pressure is set at 50–70% of injection pressure for 0.5–1.0 s; longer holding times do not improve filling but produce gate blush. Mould temperature is held at 15–30°C with turbulent water flow above 2.5 m/s. The rapid quench yields an amorphous part with a heat deflection temperature near 55°C under ISO 75-2 Method B. Cutlery used with food above 60°C may show permanent deformation; this boundary must be stated in technical specifications. Food-contact conformity requires overall migration below 10 mg/dm² under Regulation (EU) No 10/2011, and neat PLA produced under a U.S. FDA Food Contact Notification is acceptable without further additive review. End products include injection-moulded forks, knives, teaspoons, soup spoons, stirrers, and airline meal cutlery, usually packed in compostable cellulose films.

Why Do Dairy Cup Moulders Shift from Hot-Runner to Cold-Runner Systems for PLA?

For single-serve dairy cups with wall thickness of 0.5–0.8 mm and flow length-to-thickness ratios above 180:1, shear heating in hot runner drops becomes the dominant defect source. PLA melt exhibits pseudoplastic behaviour with power-law index approximately 0.35–0.55 between 50 s⁻¹ and 1000 s⁻¹. Shear heating in a hot runner nozzle of 2.5 mm diameter can raise local melt temperature by 12–20°C above the set point. When local melt temperature exceeds 235°C, molecular weight decreases and surface haze develops at the gate. Cold-runner edge gates eliminate this localised overheating at the expense of runner regrind. Tunnel gates of 1.0–1.5 mm diameter are preferred over three-plate stacked systems for cups with a rim diameter below 75 mm. Barrel temperature settings are 175–190°C rear, 185–200°C centre, 195–210°C front and 200–215°C nozzle. The melt must be forced into the cavity with a two-stage injection profile: 120–160 mm/s initial fill, then 35–50 mm/s for the final 20%. Clamp force per projected area is approximately 3–5 kN/cm². Vent depth is fixed at 0.015–0.025 mm around the cavity perimeter to prevent burn marks and acidic odour. Mould temperature is kept at 15–25°C to avoid thick-skin crystallisation. For cold-filled dairy desserts, the cup side wall must survive drop impact at 4°C; Charpy notched impact values for unmodified PLA are often 2–3 kJ/m² by ISO 179-1, so low-temperature abuse testing is mandatory. Compliance for dairy cups includes Regulation (EU) No 10/2011 with simulant 3% acetic acid for acidic dairy desserts, Regulation (EC) No 1935/2004, and Regulation (EC) No 2023/2006 for good manufacturing practice. End products include single-serve espresso cups, dessert cups, condiment cups, and lid-compatible rims used in chilled food service.

Thermoforming of extruded PLA sheet for fresh produce punnets requires a narrow sheet temperature window of 85–105°C at the forming station. Below 85°C, the sheet tears at corner radii below 2 mm; above 110°C, sheet sagging causes wall thickness variation exceeding ±15% across a 250 mm × 180 mm fruit punnet. The sheet extruder uses a 35:1 L/D barrier screw with a melt pump operated at 40–80 bar differential pressure to dampen positive displacement variation. Chill roll temperatures are set at 15–25°C to quench the sheet into an amorphous state with less than 5% crystallinity. Oven reheating is staged at 70°C, 90°C, and 100°C for a sheet thickness of 0.35–0.50 mm before the forming station. Plug-assisted forming with syntactic foam plugs reduces contact mark depth below 0.05 mm; aluminium plugs tend to chill the sheet and produce stress whitening at the plug walls. Perforation geometry is executed with 2–4 mm diameter holes spaced 20–30 mm apart; edge tear resistance after perforation is tested according to ISO 6383-2. A post-forming lip rolling station needs sheet temperature above 60°C to prevent rim cracking; this is achieved with an additional short-wave infrared heater bank placed before the lip roller. Compliance for fresh produce packaging includes Regulation (EU) No 10/2011 for food contact, EN 13432 for compostability in organic waste collection, and ASTM D6400 for North American compost claims. End products include vented punnet trays for berries, hinged salad bowls, mushroom tills, and bakery clamshells. Low-temperature impact brittleness below 5°C should be evaluated by ISO 179-1 Charpy impact; PLA punnets are not recommended for frozen fruit with sharp ice crystals because impact failure occurs with limited deformation.

Melt Filtration and Barrel Temperature Profile for PLA Masterbatch Carrier Systems

REVODE201 is used as a carrier resin in compounded masterbatches for biodegradable packaging and agricultural films. A co-rotating twin-screw extruder with L/D 32:1–44:1 and 25–50 kg/h output rate provides sufficient dispersive mixing for pigments and nucleating agents. The screw profile uses two high-shear kneading blocks at 90° offset after the feed zone, followed by a distributive mixing element before vacuum venting. Melt temperatures at the die are maintained between 180°C and 205°C; thermocouples in zones 4 through 8 are set 5–10°C lower than the die to offset shear energy. Vacuum venting at -0.08 MPa to -0.09 MPa strips residual lactide and moisture after the kneading blocks. Filtration through a slide-plate screen changer with 50–120 mesh stainless steel screens removes agglomerates from pigments and inorganic fillers; differential pressure across the screen pack should not exceed 80 bar. If pressure exceeds 80 bar, screen change frequency must be reduced below every 45 min or the pigment dispersion is judged inadequate. Twin-screw torque above 85% of drive capacity indicates viscosity rise from chain extension or excessive filler addition. Masterbatch let-down ratios are 2–5 wt% for white TiO₂ concentrates in opaque PLA packaging, 1–3 wt% for slip/antiblock combinations, and 4–8 wt% for mineral-filled nucleated compounds. The carrier resin must have a melt flow rate within 10–30 g/10 min at 210°C/2.16 kg as measured by ISO 1133-1. A narrower MFR spread between the carrier and the let-down resin of less than 15 g/10 min prevents surface streaks and weld-line visibility. End products include coloured masterbatch granules, mineral-filled compounds for cutlery, impact-modified PLA alloys, and nucleated high-crystallinity rigid packaging.

PLA injection moulded caps and cosmetic jars are produced with wall thicknesses of 1.0–2.5 mm and an internal thread profile that is stripped from the core before the part cools below 50°C. For a 45 mm diameter closure, core rotation speed is 200–400 rpm during unscrewing; forced ejection before the part reaches 25°C may deform the thread flanks. PLA closures exhibit a static coefficient of friction against glass and PET in the range 0.25–0.45. Thread torque retention after 10 closures is evaluated by applying 2.0 N·m and measuring back-off torque; PLA closures typically show a 20–30% decrease after repeated application. This is a known limitation for reusable closures and should be stated in product specifications. To improve dimensional stability, the PLA may be compounded with 2–5 wt% talc or nucleating agent; this reduces shrinkage anisotropy but lowers clarity from 90% transmittance to below 70% at 1 mm thickness. For clear cosmetic jars, clarification additives and low mould temperatures of 10–20°C preserve light transmittance above 88% measured by ASTM D1003. For opaque jars, titanium dioxide added at 2–4 wt% provides CIELAB L* above 94. Compliance for cosmetic packaging includes Regulation (EC) No 1223/2009 for cosmetic safety, REACH Article 33 for SVHC communication, and Directive 94/62/EC for heavy metal limits. End products include eye cream jars, serum bottles, lip balm tubes, jar caps, and airless pump collars.

Unmodified REVODE201 Cannot Withstand Bending Angles Above 10° in Drinking Straw Extrusion

Extrusion of PLA drinking straws from unmodified REVODE201 is constrained by an elongation at break below 5% measured under ISO 527-2. A straight drinking straw with 0.15–0.25 mm wall thickness will crack when bent more than 10–15° without impact modification. Compounding with an approved biodegradable flexibiliser at 5–15 wt% raises elongation at break to 20–50% and reduces flexural modulus from 3000–3500 MPa to 1200–1800 MPa, making bendable straw sections possible. A single-screw extruder with L/D 30:1, barrier flighted screw, and 2.0:1–2.5:1 compression ratio operates with barrel zones 165–175°C, 175–185°C, 185–195°C, and die temperature 195–205°C. Die pressure is maintained between 80 bar and 120 bar through a gear pump connected to the extruder; pressure fluctuation exceeding ±3 bar creates wall thickness variation visible as stripe haze. The melt is drawn through a calibrator with vacuum at -0.04 MPa to -0.06 MPa and water bath temperature 20–30°C; line speed is set to achieve a draw-down ratio of 3:1–6:1 from die gap to final wall. Bendable straws are scored with radial notches spaced 5–7 mm apart; notch depth is 0.05–0.10 mm and must not exceed 40% of wall thickness or circumferential cracking occurs in use. Food-contact compliance follows Regulation (EU) No 10/2011; compostability claims require EN 13432 for products sold in Europe. End products include straight straws, bendable straws, cocktail straws, and individually wrapped straws for beverages below 45°C.