Polylactic Acid (PLA) REVODE213T is a pelletized poly(L-lactic acid) homopolymer marketed under the REVODE trademark by Zhejiang Hisun Biomaterials Co., Ltd. The grade is designated for injection moulding of rigid, transparent parts with wall thicknesses from 0.8 mm to 2.5 mm. Its manufacturer-reported melt mass-flow rate is 10–30 g/10 min at 190 °C under 2.16 kg, tested according to ISO 1133-1:2022. Solid-state density is 1.24 g/cm³ by ISO 1183-1:2019. The grade is not intended for blown film or extrusion blow moulding because melt strength is insufficient for sustained bubble stability under normal blow-up ratios.

The material is processed with a barrel temperature range of 180–220 °C and a mould temperature of 20–35 °C when maximum optical clarity is required. Under these conditions the resin remains largely amorphous, producing glass-like transparency, but the heat deflection temperature remains tied to the PLA glass transition. The product requires pre-drying before melt processing. Residual moisture above 250 ppm hydrolyzes the ester backbone and is observed on production lines as gate splay, falling melt cushion, and brittle part ejection. A dehumidifying dryer with a dew point of -40 °C or lower at 80 °C for 4–6 h is used. At ambient relative humidity above 60 %, exposure of dried pellets to plant air should be kept below 30 min.

What separates REVODE213T from an unmodified PLLA homopolymer?

The principal differences are rheological and optical. An unmodified PLLA homopolymer of similar molecular weight may exhibit a melt mass-flow rate of 6–20 g/10 min; REVODE213T is positioned at the higher-flow end to reduce injection pressure in thin-wall tooling. The grade also carries a low residual lactide specification, commonly below 0.5 wt%, which reduces plate-out on mould vents during runs longer than 8 h. Because the D-lactide fraction is low, the resin shows a melting peak in the range 165–175 °C by ASTM D3418-15, whereas fully amorphous PLA grades may not display a distinct melting endotherm. In cold-mould processing, haze for a 2 mm plaque is reported below 3 % by ASTM D1003-13, but the value depends on mould polish, gate geometry, and hold pressure.

Compared with a nucleated high-heat PLA grade, REVODE213T gives lower haze without annealing but lower heat deflection at 0.45 MPa. Compared with an extrusion-grade PLA, the material has higher flow and lower melt strength, making it unsuitable for cast film or thick-section extrusion profiles. Published data for direct comparison with every REVODE series grade is limited; the manufacturer’s current specification sheet should be consulted for lot-specific values.

Drying is the first critical processing boundary. A vacuum dryer at 100 mbar and 80 °C for 4 h is an alternative to desiccant drying, but hopper residence time must be validated because dried PLA can bridge in a non-jacketed hopper throat. On injection moulding machines, the failure mode from wet material is often first observed at the gate as silver streaks and at the part surface as a loss of gloss. Hydrolysis is not reversible by drying after the melt has degraded.

Injection Moulding Thermal Boundaries and Screw Configurations

The melt processing window is bounded below by incomplete plastication and above by thermal degradation. Barrel settings from rear to nozzle are typically 180 °C, 195–205 °C, 200–210 °C, and 210–220 °C. Nozzle melt temperature should not exceed 230 °C. Above 240 °C, thermal degradation of PLA follows rapid molecular weight reduction, with lactide, acetaldehyde, and carbon monoxide as principal volatile products. Screw configurations with an L/D ratio of 24:1 and a compression ratio of 2.0:1 to 2.8:1 are preferred. An 18:1 L/D general-purpose screw may produce unmelted pellets or excessive shear heating. Back pressure is maintained at 0.5–1.0 MPa. Screw surface speed of 0.15–0.30 m/s is used on a 40 mm screw. Residence time above 5 min at melt temperature produces measurable viscosity loss and brown streaking.

Injection pressure of 80–120 MPa is typical, with hold pressure at 50–70 % of injection pressure. For a 2 mm wall, a gate diameter of 0.8–1.2 mm prevents jetting and excessive shear. Cooling time is 8–12 s at a mould temperature of 20–35 °C. Cavity pressure at the end of fill should be 40–70 MPa. Peak cavity pressure above 80 MPa causes overpacking and increases molecular orientation. In a cold runner with a 2 mm wall, overpacking can increase tensile elongation in the flow direction from 5 % to 7 % while reducing transverse elongation to 3 %, producing anisotropic brittle failure. Gate seal time for a 2 mm wall and 0.8 mm gate generally requires 4–6 s of hold. A cushion of 3–5 mm prevents nozzle decompression and air entrapment. Screw decompression of 2–4 mm reduces drool, but excessive decompression draws air into the barrel.

On a 120-ton hydraulic injection moulding machine with a 40 mm screw and 22:1 L/D ratio, a melt-flow variation of ±10 % between batches shifts fill time in a 1.5 mm plaque tool by approximately 0.2–0.5 s. Transfer position should be set after a short-shot study. Melt cushion monitoring is more sensitive for higher-flow PLA than for amorphous PET because the fill-time curve against transfer position is steeper. Hot-runner drops should be individually controlled below 220 °C; valve-gate tip temperature above 240 °C causes gate blush and acetaldehyde formation.

Flow length in a spiral test mould at 220 °C and 1200 bar injection pressure is typically 120–150 mm per 1 mm wall thickness for high-flow PLA. At a shear rate of 100 s⁻¹ and 200 °C, melt viscosity is in the range 200–400 Pa·s. At 1000 s⁻¹, viscosity falls to 40–80 Pa·s, indicating strong shear thinning. This behaviour allows filling of thin walls but also produces jetting if the gate is undersized. Flow marks can be reduced by locally raising the mould surface temperature to 40 °C, though holding the part too long at that condition can increase haze.

When optical clarity competes with thermal resistance in service

The heat deflection temperature of amorphous PLA is limited by its glass transition at 55–60 °C. Under 0.45 MPa flexural load by ISO 75-2:2013 method B, an unannealed specimen typically deflects at 55 °C. If the service environment exceeds this, the part must be annealed or crystallized. Annealing at 100–120 °C for 30–60 min raises heat resistance but reduces light transmission and causes anisotropic shrinkage of 1.5–2.5 % in the flow direction. This is a property cliff-edge: once crystallinity exceeds approximately 25–30 %, haze increases rapidly, and the part can no longer be used as an optical component. Cold crystallization of PLA occurs between 90 °C and 140 °C with a peak near 110 °C. Parts ejected above 60 °C and stacked may post-crystallize, producing haze and warpage. For REVODE213T specifically, published data for the annealed configuration is limited; converters must measure shrinkage and optical change on their own tooling.

Table 1 summarizes the manufacturer-reported typical values for REVODE213T against the broad range observed for unmodified PLLA homopolymers. These values are not to be used as specifications.

Table 2 lists critical processing boundaries observed in injection moulding practice. Exceeding a bound does not necessarily create immediate part failure, but the failure mode becomes visible over a production run.

Chemical exposure boundaries are driven by the ester backbone. Aqueous alkali solutions at pH above 10 and temperatures above 50 °C initiate surface hydrolysis within 24 h. Concentrated mineral acids such as hydrochloric acid at 1 mol/L reduce tensile strength rapidly. Ketones, esters, and chlorinated solvents swell or dissolve PLA. Oxygenated fuel constituents and hand sanitizers containing more than 60 % ethanol are incompatible for load-bearing parts; environmental stress cracking can occur below the tensile yield stress. The material should not be melt blended with polycarbonate or PET because transesterification and haze develop at standard PLA melt temperatures. Amine-based additives such as certain slip masterbatches or chain extenders can accelerate aminolysis of the ester backbone and must be avoided unless melt viscosity retention after 5 min residence time is validated.

Compliance statements for food-contact packaging require migration testing under EU 10/2011 or the applicable FDA 21 CFR section. The resin supplier may provide a Declaration of Compliance, but the finished part must be tested under intended use conditions because migration depends on crystallinity, residual lactide, wall thickness, and food simulant. Industrial compostability claims require evaluation under EN 13432; material certification alone is insufficient. Heavy-metal and hazardous-substance declarations should reference REACH and 2011/65/EU. The product is biologically derived, but it should not be assumed to be home-compostable or marine-biodegradable without specific test data.

Failure modes when drying and residence-time limits are ignored

Ignoring the moisture limit produces splay first at the gate, then a progressive loss of melt cushion, followed by ejection of parts with low elongation and visible surface streaks. The hydrolysis reaction is accelerated by melt temperature; a melt at 220 °C containing 400 ppm moisture degrades faster than the same melt at 200 °C with 250 ppm moisture. The molecular weight loss is not recoverable by remelting. Ignoring residence-time limits produces yellowing and acetaldehyde, with a measurable shift of 1.0–2.0 in the CIE b* colour coordinate after 5 min. In a 16-cavity hot-runner mould for 1.5 mm wall containers, batch-to-batch melt-flow variation of ±10 % can shift injection pressure by 8–12 bar. Regular purging and shot-weight verification reduce variability.