Ecoplant HRS High Heat Resistant Flexible Modified Polylactic Acid is a nucleated, impact-modified polylactic acid compound supplied as cylindrical pellets. The product is specified for flexible component geometries where standard PLA homopolymer fails by brittle fracture but where conventional plasticized PLA or PLA/polybutylene adipate terephthalate flexible blends cannot retain dimensional stability above 60 °C under low-load heat exposure. The grade contains a semi-crystalline PLA matrix, a flexible polymeric modifier, and an inorganic nucleating package. The manufacturer-nominated melt volume-flow rate is 4 cm³/10 min at 210 °C and 2.16 kg when measured in accordance with ISO 1133-1:2022. The specified density is 1.27 g/cm³ according to ISO 1183-1:2019. The model designation HRS denotes high heat resistance combined with reduced rigidity relative to mineral-filled PLA; it is differentiated from standard flexible PLA principally by a higher heat deflection temperature and a shorter cycle time in heated tooling due to rapid nucleation.

What Distinguishes the HRS Grade from Conventional Flexible PLA?

The primary difference is the crystalline morphology obtained during molding. Conventional flexible PLA compounds typically contain a high proportion of biodegradable polyester soft segments that lower flexural modulus to 1.2–1.6 GPa but reduce heat deflection temperature below 60 °C at 0.45 MPa per ISO 75-2:2013. Ecoplant HRS incorporates a nucleating system that promotes growth of PLA crystallites during cooling at mold temperatures between 90 °C and 110 °C, producing a heat deflection temperature of 115 °C at 0.45 MPa and 78 °C at 1.8 MPa under ISO 75-2:2013 methods A and B. Tensile modulus is nominally 2.5 GPa per ISO 527-2:2012, which is higher than flexible PLA but substantially below a 30 wt% talc-filled PLA grade at approximately 4.5 GPa. Notched Izod impact strength is 9 kJ/m² at 23 °C per ISO 180:2023. This combination places the material between flexible biodegradable blends and rigid high-heat PLA, with an elongation at break above 50% but below the 200–300% elongation typical of a high-modifier PLA/PBAT blend. Stereocomplex PLA and nucleated rigid PLA can achieve heat deflection temperatures above 130 °C, but their notched impact values are commonly below 4 kJ/m². The HRS grade therefore trades approximately 15 °C of heat deflection for a higher deformation capacity.

Moisture control before melt processing is the dominant variable affecting molecular weight retention. Pellets should be dried with desiccant air at 80 °C for 4 h to a residual moisture level below 250 ppm by Karl Fischer titration. Dew point of the drying air should not exceed −40 °C. At lower moisture levels, hydrolysis-induced viscosity loss during extrusion remains below 5% over a 6 min residence time. For continuous extrusion, a co-rotating twin-screw extruder with L/D 44:1 and segmented screw elements has been used at screw speed 200 min⁻¹ and a barrel profile of 165–195 °C. Melt temperature at the die should be limited to 205 °C; above 210 °C, random chain scission of the PLA backbone increases and melt strength degrades. The compounding step is not a simple dilution: dispersion of the impact modifier requires moderate shear, but excessive shear can raise local melt temperature and deactivate the nucleating package. On a 50 mm twin-screw line, a screw design with two kneading blocks of 45° forwarding angle is reported to maintain melt temperature below 210 °C while achieving pellet-to-pellet viscosity deviation of less than 2%.

When Residence Time Exceeds 15 Minutes in Hot-Runner Tooling

For hot-runner injection molding, residence time is the main boundary. At melt temperatures above 200 °C, holding material in the hot runner for more than 15 min produces a measurable reduction in melt viscosity and an increase in yellowness index. A blocked or imbalanced manifold should not be operated in production; startup purges should use unmodified PLA or a purging compound that does not contain amine-based additives. The grade is incompatible with amine-based thermal stabilizers because amine groups accelerate transesterification in the PLA ester backbone. In a 1200 kN clamp force reciprocating screw machine, the recommended melt temperature is 185–200 °C, mold temperature 95–105 °C, and injection speed 50–100 mm/s. The practical melt-temperature processing window is ±5 °C around 190 °C: below 185 °C, the nucleated compound viscosity increases and gate pressure may exceed 160 MPa; above 200 °C, the impact modifier phase may coalesce. Cycle time for a 1.5 mm wall thickness is governed by crystallization. The part should be held under 60 MPa packing pressure until the gate freezes; otherwise, sink marks and dimensional variation appear. Ejection at a surface temperature above 60 °C can lead to hinge whitening because amorphous skins that have not crystallized remain flexible and may tear at the gate.

Injection molding of thin-wall hinged food containers with a nominal wall thickness of 1.2 mm has been carried out in a two-plate cold-runner tool with a valve gate. The observed total cycle time was 14–18 s depending on cooling water temperature; the greatest cycle-time reduction compared with rigid high-heat PLA was obtained by reducing mold temperature from 120 °C to 100 °C. Flexural fatigue testing per ASTM D7774-22 at 1 Hz and 0.5% outer-fiber strain yielded no hinge cracking at 5,000 cycles; failure initiated at 12,000 cycles in molded parts with incomplete crystallization. The failure mode was localized stress whitening at the gate, where flow-line crystallite size gradients were greatest. Processing at the low mold-temperature boundary did not reproduce the full heat deflection of the compound, confirming that the high HDT-B value depends on mold temperatures above 95 °C rather than on post-mold annealing.

Migration Behavior and Food Contact Boundaries

Ecoplant HRS in its supplied form is manufactured from monomers and additives that have been evaluated for certain food-contact uses. The supplier limits overall migration to 10 mg/dm² under food simulants A, B, C, D1, and D2 according to EU 10/2011 when tested on 1 mm plaques. For repeated-use articles, the appropriate time-temperature conditions—commonly 70 °C for 2 h with simulant D1—must be validated because migration of low-molecular-weight PLA oligomers increases with processing history. Compliance with FDA 21 CFR 175.300 applies only to resinous and polymeric coatings used in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food; finished-article compliance must be established by the converter. Heavy metals and phthalates are below the limits in REACH Regulation (EC) No 1907/2006, Annex XVII, and the product is formulated without substances listed in RoHS Directive 2011/65/EU, Annex II. The material does not contain polyvinyl chloride, bisphenol A, or intentionally added per- and polyfluoroalkyl substances. Industrial compostability of the final article remains dependent on part thickness and surface area; the base compound is aligned with the testing frameworks of ASTM D6400-23 and EN 13432:2000, but the HRS grade itself may not be certified for every converted shape.

What Creep and Hydrolysis Boundaries Limit Load-Bearing Service?

Creep behavior diverges sharply from polyolefin systems above 50 °C. Under a constant tensile stress of 10 MPa at 23 °C, the tensile creep modulus at 1,000 h remains above 1.8 GPa per ISO 899-1:2017; at 60 °C and 10 MPa, creep strain accelerates and dimensional recovery after unloading is incomplete. Continuous load-bearing service above 60 °C is not recommended unless the part is mechanically supported or the stress is below 2 MPa. Hydrolysis is the second boundary: at 40 °C and 85% relative humidity, PLA molecular weight decreases through chain scission; molded parts should not be stored or used in contact with aqueous solutions at pH below 4 or above 9 for prolonged periods. The material is not recommended for hot-fill liquids above 80 °C under pressure. For dry, non-load-bearing parts, intermittent service temperature can be as high as 95 °C, but dimensional stability should be confirmed with a constrained-specimen test rather than a standard heat-deflection value. Published data for long-term hydrolysis of this specific configuration is limited; the boundary conditions given are extrapolated from PLA homopolymer and nucleated PLA blend studies.