TEREZ NatureGran PO1000 is a semi-transparent injection-molding grade of polylactic acid supplied as cylindrical or spheroidal pellets. The resin is intended for rigid, thin-walled articles in which partial light transmission, high stiffness, and renewable carbon content are combined. The material belongs to the class of unmodified, un-nucleated PLA injection compounds; it contains no impact modifier, mineral filler, or processing oil, which distinguishes it from opaque PLA grades formulated with talc, calcium carbonate, or acrylic core-shell rubber. Because the grade is unfilled, its density remains near 1.24–1.26 g/cm³ measured according to ISO 1183-1. The semi-transparent appearance results from low crystallinity after rapid injection molding: fast cooling suppresses spherulite growth, so visible light is transmitted rather than scattered. Plaque measurements using ASTM D1003 on 2 mm specimens typically show total luminous transmittance between 85% and 92% and haze between 5% and 10%. These optical values are lower than those of cast PLA film because injection-molded surfaces replicate tool roughness and flow fronts create visible weld lines. Published data for TEREZ NatureGran PO1000-specific lot values is limited; therefore, the numeric ranges in this document are class-typical values for semi-transparent PLA injection grades and should not be interpreted as supplier release limits.

Before melt processing, the moisture content of PO1000 must be reduced below 250 ppm. PLA is hygroscopic and reaches equilibrium moisture above 0.25% at 50% RH. A desiccant dryer with air dew point below -40 °C and hopper temperature of 80 °C for a minimum of 4 h is standard. Drying air leakage or extended residence above 100 °C causes pellet aggregation in the hopper; bridging then produces feed voids and shot-weight drift. The screw is a general-purpose three-zone configuration with L/D ratio 20–24, compression ratio 2.5–3.0, and non-return valve clearance maintained below 0.05 mm. Barrel set points are rear 160–170 °C, middle 180–200 °C, front 190–205 °C, and nozzle 185–200 °C, producing a nozzle melt temperature of 190–210 °C. Mold temperature is held at 15–40 °C for cycle-time reduction; a higher mold temperature of 50–60 °C improves weld-line tensile strength but increases cycle time and haze. Injection pressure at the material is commonly 800–1200 bar on a 80–120 t toggle machine for wall thickness 1 mm. Screw rotation speed should not exceed 200 rpm on a 30 mm screw; typical settings are 100–200 rpm with back pressure 5–10 bar. Decompression after plastication of 2–5 mm minimizes nozzle drool.

What Limits Melt Residence Time and Hot-Runner Hold in PO1000?

Residence time governs thermal degradation in semi-transparent PLA. At melt temperatures exceeding 220 °C, ester backbone scission accelerates and generates lactide, carbon dioxide, and low-molecular-weight fragments. On production-scale injection molding machines with screw diameters from 25 mm to 35 mm, total barrel residence time should remain below 8 min; 5 min is preferred for small shot weights or multi-cavity molds with hot-runner hold. Hot-runner systems require internally heated tips and no dead-end channels, since stagnant melt at 210 °C degrades within 10–15 min and yellows the transparent melt stream. Shear heating also contributes to temperature rise: at apparent shear rates above 100,000 s^-1 in gates, viscous dissipation can raise local melt temperature by 5–15 °C and must be subtracted from barrel set points. The frozen skin forms early at the wall and limits pressure transmission; packing pressure from 60% to 80% of injection pressure, applied for 0.5–2.0 s, is used to compensate gate seal and reduce sink. Nozzle temperature stability is critical: fluctuations above ±5 °C shift viscosity and cause inconsistent fill in tools with wall thickness below 0.8 mm. Residual moisture above 0.02% produces surface silver streaks and reduces knit-line strength by more than 20% relative to well-dried granulate tested under ISO 527-1/-2.

Mechanical and thermal data generated under ISO 291 conditioning

Laboratory evaluations of PO1000 should use injection-molded Type 1A tensile bars produced at 190–200 °C melt temperature and 25 °C mold temperature. Specimens are conditioned at 23 °C and 50% RH for 88 h according to ISO 291 before testing. Class-typical values for semi-transparent PLA with melt flow rate 6–15 g/10 min are summarized in Table 1. Tensile strength is measured at 5 mm/min with ISO 527-1/-2; flexural modulus uses ISO 178 at 2 mm/min; notched Charpy impact is obtained on 80 mm × 10 mm × 4 mm bars with ISO 179-1/1eA. The amorphous structure of PO1000 yields elongation at break between 2% and 5%, which is lower than that of impact-modified PLA grades but similar to general-purpose polystyrene. Heat deflection temperature under 0.45 MPa is 50–60 °C measured by ISO 75-2/B, and Vicat A/50 is 55–65 °C measured by ISO 306. These thermal limits mean PO1000 is not suitable for hot-fill containers, autoclaving, or dishwasher-safe components. The direction of flow affects tensile strength by less than 10% when processing is optimized, but excessive melt temperature or moisture can reduce strength by 15–25% due to molecular weight reduction. Product-specific certificate of analysis values from TEREZ NatureGran PO1000 may differ from the class ranges; the ranges are provided for initial tooling and simulation input, not for production lot release.

In comparison with opaque PLA compounds containing 10–30 wt% talc or calcium carbonate, PO1000 shows different mold-filling, shrinkage, and surface-gloss behavior. Mineral fillers increase thermal conductivity and reduce shrinkage anisotropy, but they also scatter light; opaque grades typically show total transmittance below 50% at 2 mm under ASTM D1003, while PO1000 remains above 85%. The filler-free formulation gives lower viscosity at identical temperature; however, the unfilled melt stores less heat, so it is more sensitive to cold runner and gate freeze. Comparative injection molding on a 100 t electric toggle press shows that PO1000 requires injection speeds from 50 mm/s to 150 mm/s for wall thicknesses between 0.6 mm and 2.0 mm. Below 50 mm/s, the gate freezes before packing; above 150 mm/s, shear heating increases the risk of burn marks. Cavity-to-cavity weight variation in an 8-cavity cold-runner tool is typically held below 0.3% after balancing. The dimensional stability of PO1000 supports closures and rigid packaging, but the moisture regain of PLA at high humidity can increase final part dimensions by 0.1–0.2% after 48 h at 85% RH.

Shrinkage is not uniform across the part because the amorphous orientation freezes unevenly. In a rectangular plaque 120 mm × 80 mm × 2 mm injection-molded with a film gate at one short edge, post-mold shrinkage measured by ISO 294-4 is typically 0.3–0.5% in flow direction and 0.3–0.5% transverse after 24 h at 23 °C. Warpage is promoted by differential cooling between the moving and fixed mold halves; mold temperature difference above 5 °C causes bowing in thin plaques. Annealing semi-transparent PLA at 80–100 °C for 30–60 min increases crystallinity and raises HDT B above 80 °C, but the article loses translucency and develops dimensional change of 0.5–1.0%. Therefore, annealing is not recommended when optical transparency is required. Mold filling simulation inputs should use Cross-WLF viscosity coefficients derived from capillary rheometry at 190 °C, 210 °C, and 230 °C with shear rates from 100 s^-1 to 10,000 s^-1; simulation without crystallization kinetics is acceptable for short cycle times below 30 s.

When Semi-Transparent PO1000 Replaces GPPS in Thin-Walled Rigid Packaging

Substitution of GPPS with PO1000 requires a different thermal and rheological boundary. GPPS exhibits a Vicat A/50 near 95–105 °C and a higher melt strength; PO1000 exhibits Vicat A/50 of 55–65 °C and must be demolded with more attention to surface drag. Draft angles below 0.5° are not recommended for cavity depths above 20 mm. The flow length of semi-transparent PLA at 190 °C and 1000 bar is approximately 20–30% shorter than that of GPPS with MFR 8 g/10 min at 200 °C; therefore, wall thickness below 0.8 mm may require additional gates or a change from cold runner to hot runner. Pressure drop across a 1 mm by 50 mm cavity path is reported to be 15–25% higher for this PLA class at equivalent apparent shear rate. Molders replacing GPPS typically reduce nozzle temperature by 10–20 °C and increase screw retraction to reduce drool. The lower heat deflection temperature of PO1000 means that a thin-walled lid stored in a vehicle in summer can approach the deflection temperature; design loads must be below 0.45 MPa if the temperature exceeds 50 °C. For cold-chain packaging, however, PO1000 retains stiffness down to -20 °C because the amorphous PLA remains below its glass transition. This cold-chain advantage is offset by low impact resistance; notched Charpy values of 2–4 kJ/m² require careful handling of snap-fit closures.

Regulatory and compliance matrix for renewable injection-molding feedstocks

Biobased carbon content may be measured by ASTM D6866-22 or ISO 16620-2:2019. PLA derived from corn, sugarcane, or cassava feedstock typically contains 95–100% biobased carbon. Industrial compostability claims for a specific article should be verified under EN 13432 or ASTM D6400; these standards require disintegration, biodegradation, heavy-metal limits, and ecotoxicity tests. Food-contact suitability is not automatic and must be confirmed by a supplier declaration referencing FDA 21 CFR 175.300, EU 10/2011, or a national equivalent. Electrical and electronic applications require separate evaluation of UL 94 flame class, comparative tracking index under IEC 60112, and surface resistivity under ASTM D257. RoHS obligations under 2011/65/EU and REACH SVHC screening should be documented in the supplier’s material compliance certificate. Neat PLA is not inherently flame retardant and is not recommended for enclosures requiring V-0 ratings unless a halogen-free flame-retardant system is added. No conclusion is drawn from this compliance summary; the responsible molder must obtain lot-specific regulatory documents from the TEREZ NatureGran PO1000 supplier before commercial use.