PURAPOL LX175 is supplied as a high-viscosity amorphous poly(lactic acid) resin in cylindrical pellet form. The polymer is classified under ISO 1043-1 as PLA and carries CAS registry number 26100-51-6. The amorphous character is controlled by a D-lactide comonomer content commonly reported in the range of 4–8 mol% on the supplier certificate of analysis. This comonomer level suppresses chain ordering, reduces spherulite nucleation density, and lowers the crystallization rate compared with semicrystalline PLA. Melt flow rate at 210 °C and 2.16 kg load is typically below 6 g/10 min when tested in accordance with ISO 1133-1:2022. The low MFR corresponds to elevated molecular weight, increased melt elasticity, and higher melt strength than standard extrusion or injection PLA grades. Nominal density of amorphous PLA is approximately 1.24 g/cm³ under ISO 1183-1, and water absorption of a 1 mm plaque after 24 h immersion is generally below 0.5% under ISO 62. The resin remains amorphous after quench cooling, so contact clarity in thick sheet is higher than for nucleation-grade PLA, but the heat deflection temperature under load remains below that of deliberately crystallized PLA. Published data for this specific grade’s lot-to-lot rheological spread is limited; processing parameters should be set from the certificate of analysis and incoming thermal analysis rather than from generic PLA datasheets.

Why Is Thermal Degradation Rather Than Crystallization the Controlling Processing Limit?

Because the amorphous architecture suppresses rapid crystallization, the practical processing envelope for PURAPOL LX175 is limited primarily by thermal degradation rather than by solidification kinetics. Hydrolytic chain scission accelerates when residual moisture exceeds 250 ppm at melt temperatures above 200 °C; therefore desiccant drying at 80–100 °C for 4–6 h is required before extrusion. On single-screw extruders with 28:1–40:1 L/D barrels, the melt pressure can decline by 0.5–2.0 MPa during the first hour of processing if moisture specification is not met, followed by increased screw amperage as degraded material accumulates in the compression zone. Typical barrel settings for sheet and film are 180–220 °C, with adapter and die zones held at 190–210 °C. Melt temperatures above 230 °C should be avoided because residence-time-dependent molecular weight loss produces volatile lactide and oligomer fractions; on vented corotating twin-screw extruders with 0.06–0.08 MPa vacuum, vent condenser fouling increases when the melt remains above 225 °C for more than 5–10 min. These values are production observations for amorphous high-viscosity PLA and should be validated on the specific screw geometry and throughput.

Capillary rheometry by ISO 11443 using a 1 mm diameter, 30 mm length die at 200 °C is recommended for incoming lot differentiation. At apparent shear rates below 500 s⁻¹, the melt exhibits pronounced shear thinning; the power-law index for high-viscosity amorphous PLA is normally in the range of 0.5–0.7. The melt also shows strain hardening under extensional deformation, which is less pronounced in low-molecular-weight linear PLA and is the primary reason for reduced draw resonance in film converting. Melt strength measured on a capillary rheometer with a haul-off wheel at 200 °C in air is typically in the range of 0.1–0.3 N for high-viscosity amorphous PLA; lower-viscosity grades often fall below 0.05 N. These are comparative ranges and not lot-specific specifications for LX175. Differential scanning calorimetry under ISO 11357-2 generally reports a glass transition between 55 °C and 62 °C; no significant melting endotherm is present as supplied unless the resin is annealed above the cold-crystallization onset. Annealed films may show a melting endotherm near 145–155 °C under ISO 11357-3, but as-supplied pellets remain amorphous. The practical window is therefore narrow on the high-temperature side and wide on the low-temperature side; barrel temperatures below 170 °C may cause excessive torque on a 30:1 L/D single-screw extruder and poor melt homogeneity, particularly at specific throughput below 0.3 kg/h per rpm for 90 mm screws.

Before melt processing, PURAPOL LX175 should be dried in a desiccant dryer with a dew point below -30 °C, using pellet bed depth and residence time calibrated to achieve residual moisture below 250 ppm by Karl Fischer titration under ISO 15512. If ambient relative humidity exceeds 60%, resin from an opened container should be redried even if the original moisture barrier packaging was intact. Continuous drying is preferred for cast-film and sheet lines because re-exposure to humid air for more than 1–2 h can reabsorb enough surface moisture to generate die-lip deposits and optical haze. Dried pellets should be conveyed with dry air, not ambient plant air, to prevent moisture pickup in hoppers. These requirements are derived from extrusion-grade PLA handling practice; lot-specific drying curves may shift with pellet geometry and residual crystallinity.

When a Semicrystalline PLA Is Replaced in Thermoforming and Injection Stretch Blow Molding

During reheating and forming, PURAPOL LX175 changes the failure behavior of extruded sheet. Semicrystalline PLA sheet can develop crystallinity during roll-stack cooling or reheating, producing a distinct yield point and reducing sag; the amorphous grade remains rubbery above 60 °C and sags without a crystalline network unless the sheet is intentionally annealed. On a form-fill-seal thermoformer with quartz infrared heating banks, the sheet surface temperature should be controlled to 75–95 °C for LX175, which is lower than the 90–115 °C zone often used for nucleated PLA. The lower setpoint compensates for the absence of a crystalline phase and reduces variability in plug-assisted forming. Because the high viscosity of the polymer resists localized thinning, deep-draw containers with a draw ratio above 2:1 may be produced with more uniform wall thickness than standard extrusion PLA, provided that plug speed and plug temperature are optimized. Production data from amorphous PLA sheet extrusion indicate that die temperatures within 190–210 °C and a polish stack roll gap of 0.4–0.8 mm are suitable starting values, but published data for LX175 in specific thermoforming tools is limited.

Injection molding and injection stretch blow molding are not primary application areas for this grade because the melt flow rate below 6 g/10 min requires high clamp force, elevated barrel temperatures, or enlarged runner diameters to fill thin-wall cavities. If the grade is used as a blend component with a higher-MFR PLA, the amorphous fraction can retard crystallization and reduce stress whitening, but the heat deflection temperature of the blend will remain low unless nucleation and annealing are applied. For injection stretch blow molding preforms, the lack of crystallites improves sidewall haze, but the preforms may require longer conditioning times because the high-viscosity backbone retains more orientation memory after injection. These differences should be evaluated using ASTM D638-14 tensile data and ISO 6603-2 puncture data on finished articles, not on resin pellets alone.

Cast film and sheet extrusion with PURAPOL LX175 typically uses 90–120 mm single-screw extruders at 30:1–36:1 L/D, a coat-hanger die with a lip gap of 0.5–1.2 mm, and a polished chrome roll held at 15–30 °C. The high melt strength reduces neck-in and edge bead irregularity at film thicknesses below 50 µm; lower-viscosity amorphous PLA grades may require wider die lips or lower draw ratios to achieve the same final width. For a 1.2 m die on a pilot cast line, stable web formation has been maintained up to 80–100 m/min when the melt temperature is held below 220 °C and the air gap is kept under 100 mm. These are production observations for high-viscosity amorphous PLA and are not lot-specific guarantees for LX175. Chill-roll plate-out and die-lip build-up increase when the polymer is processed above 230 °C, when regrind use exceeds 30 wt%, or when moisture is not controlled. Film produced from the amorphous grade retains a low haze level after quench cooling because spherulite formation is suppressed; quantitative haze must be measured under ASTM D1003-13 on the final film thickness. The roll surface temperature directly affects winding and blocking because the amorphous surface softens above 55 °C; contact rolls and slitting equipment should be checked for surface temperatures below the glass transition to avoid picking and stretching.

High-Viscosity Amorphous PLA: Differentiation from Standard Extrusion, Nucleated, and Copolymer Grades

The principal differences between PURAPOL LX175 and other PLA products arise from molecular weight, D-lactide content, and crystallization behavior. Standard extrusion or injection PLA grades typically have MFR values between 6 g/10 min and 30 g/10 min at 210 °C/2.16 kg, allowing thin-wall injection molding but reducing melt strength. Nucleated semicrystalline PLA grades may contain talc, boron nitride, or organic nucleators that increase crystallization speed and heat deflection temperature, but they also increase haze and stiffen the sheet below the crystallization onset. High-viscosity amorphous grades such as LX175 occupy a different region: the high molecular weight contributes melt elasticity for film, sheet, foam, and extrusion coating, while the amorphous structure maintains contact clarity and higher formability under controlled processing. The material does not offer the heat deflection temperature of a crystallized PLA article; after physical aging, the amorphous matrix remains limited to service temperatures below approximately 55 °C under load, as reflected in ISO 75-2 method B values for amorphous PLA. For applications above that threshold, a nucleated PLA or a different polyester should be selected unless the final article is annealed in a constrained mold.

The ranges shown are representative for amorphous high-viscosity PLA and standard semicrystalline PLA; lot-specific values must be verified by certificate of analysis and material-specific testing.

In extrusion foam processing, the high melt strength of PURAPOL LX175 controls cell coalescence and reduces open-cell content in low-density foam. When a chemical blowing agent is compounded into amorphous PLA on a 32:1 L/D corotating twin-screw extruder at melt temperatures below 200 °C, the high-viscosity matrix restricts cell coalescence and prevents blowing gas from escaping before cooling solidifies the foam. Lower-viscosity PLA grades may experience foam collapse under the same conditions. The processing window with endothermic blowing agents such as sodium bicarbonate/citric acid systems is narrow because decomposition must begin after the melt seal is established but before the polymer reaches 220 °C. Pilot trials on amorphous high-viscosity PLA have produced extruded foam board with density in the range of 50–80 kg/m³ and closed-cell content above 80%; specific data for LX175 with a selected blowing agent is limited and must be generated on the target equipment. Melt temperature control across the die and calibrator is more important for this grade than for lower-viscosity foam resins because the amorphous phase cannot dissipate exothermic crystallization heat. The resulting foam may be cut or thermoformed using standard equipment, but the service temperature remains below the glass transition unless crosslinking or annealing is applied.

Regulatory Status and Storage Boundaries Are End-Use Dependent

For regulatory compliance, the status of PURAPOL LX175 must be confirmed against the intended geography and final article end use. The resin is subject to REACH Regulation (EC) No 1907/2006; the supplier safety data sheet should be reviewed for SVHC Candidate List content and Annex XVII restrictions. No substance of very high concern is expected above 0.1 wt%, but this must be verified for the specific lot. For electrical and electronic equipment applications, compliance with Directive 2011/65/EU recast RoHS Annex II is generally expected for unreinforced PLA compound, with restricted substances below maximum concentration values. For food-contact use, no blanket approval can be assumed; the final article must be evaluated under Commission Regulation (EU) 10/2011 for overall migration and specific migration, and in the United States under the applicable food-contact substance notification or FDA clearance for the finished article. Industrial compostability may be assessed under EN 13432 for packaging; certification applies to the final article and not to the polymer alone. These statements do not replace a compliance certificate from the resin supplier.

Storage of PURAPOL LX175 should be in sealed, moisture-barrier packaging at 10–30 °C and relative humidity below 60%. Partially emptied containers should be resealed immediately because PLA pellets absorb atmospheric moisture over hours. The resin is incompatible with prolonged exposure to high-humidity environments, amine-based additives, and certain metal-based transesterification catalysts used in condensation polymers; these agents can shift molecular weight distribution and accelerate degradation. In unopened packaging at ambient conditions, the resin is expected to remain processable for at least 12 months from the certification date, but shelf life should be confirmed by the supplier and is not a guaranteed storage-limit specification. If incoming pellets exceed 250 ppm moisture, they should be dried before processing rather than rejected solely on moisture basis, provided that no visible clumping or hydrolytic odor is present. Physical aging of the amorphous phase at temperatures just below the glass transition can increase yield stress and reduce elongation to break; after storage at 40 °C for 7 d, tensile specimens may show measurable loss of ductility under ISO 527-2. This storage and aging behavior is characteristic of amorphous PLA and should be considered in production scheduling.