Ingeo™ Biopolymer 6302D is an amorphous poly(L-lactide-co-D-lactide) resin specified for conversion into staple fiber on conventional short-staple spinning lines. The grade is characterized by a glass transition temperature of 55–60 °C measured by differential scanning calorimetry according to ISO 11357-2:2020 and by the absence of a measurable melting endotherm under ISO 11357-3:2018. This thermal signature separates 6302D from semi-crystalline PLA fiber grades such as 6202D, which exhibit a crystallization exotherm and a melting endotherm above 160 °C. The amorphous chain packing is obtained through a controlled D-lactide fraction that interrupts stereochemical regularity and suppresses lamellar crystallization; the melt therefore remains amorphous after quench and yields a broad softening window rather than a sharp solid-to-liquid transition. Resin density is supplied as 1.24 g/cm³ per ASTM D792-20, with a melt flow rate within the fiber-grade range of 15–30 g/10 min at 210 °C and 2.16 kg per ASTM D1238-20. As-shipped moisture content is specified at ≤0.25 % by weight per ISO 15512. The high-flow, low-crystallinity position of 6302D within the Ingeo fiber portfolio supports low-temperature thermal bonding, sheath-core binder formulations, and fiberfill where lower calender energy input is required.

What Distinguishes an Amorphous Staple Fiber Grade from Semi-Crystalline PLA?

The critical structural difference is the absence of a crystalline reinforcement phase after fiber formation. Semi-crystalline PLA staple fiber develops oriented crystallites during drawing and heat-setting, producing a melting endotherm normally between 160 °C and 180 °C and a heat of fusion in the range of 30–50 J/g when tested by ISO 11357-3:2018. Amorphous 6302D does not develop this crystalline network; its mechanical and thermal-load response is controlled primarily by chain entanglement and the proximity of the use temperature to the glass transition. The practical consequence is a lower hot-air bonding threshold. Published thermal-bonding data for amorphous PLA fiber grades indicate calender bonding can be initiated in the 90–120 °C range, whereas semi-crystalline PLA binders require temperatures near 130–150 °C. Single-fiber tenacity for amorphous PLA typically falls between 2.0 cN/dtex and 3.0 cN/dtex, below the 3.5–5.0 cN/dtex range typical of oriented semi-crystalline PLA staple fiber, because the amorphous phase lacks load-bearing crystallites. The amorphous grade also exhibits lower shrinkage resistance above 50 °C and should not be selected for applications requiring sustained dimensional stability above its glass transition.

On production-scale staple fiber conversion equipment, 6302D is processed through single-screw extruders with barrier screws and an L/D ratio of 24:1 to 30:1. The melt temperature at the spinneret is maintained between 210 °C and 230 °C, lower than many semi-crystalline PLA fiber grades because the amorphous resin reaches acceptable spinline viscosity at reduced barrel temperatures. Quench air velocities are typically held at 0.3–0.6 m/s, and spinneret hole diameters of 0.25–0.40 mm are used for staple fiber production. Draw ratios between 2.5:1 and 4.0:1 are applied across the take-up and draw stand; the suppressed crystallization rate of 6302D permits lower draw temperatures than semi-crystalline PLA, although excessive draw stress produces melt fracture and filament break. In high-humidity environments above 60 % RH, pre-drying in a desiccant dryer at 80 °C for 4–6 h to reach a melt moisture level of ≤0.025 % by weight is required. Moisture-induced chain scission is observable as spinneret drips, reduced drawability, and a measurable drop in apparent melt viscosity, which compromises fiber uniformity and increases end-break frequency on the spin beam.

When Thermal-Bonding Calender Gaps Fall Below the Softening Plateau of 6302D

Calender bonding of 6302D requires control of nip pressure and roll gap because the amorphous softening plateau is broad and the fiber begins to flow under pressure at temperatures only 30–60 °C above its glass transition. Excessively narrow calender gaps produce film-like bond points, squeeze the binder phase out of the nonwoven structure, and reduce bond-point peel strength measured by ISO 9073-3. Insufficient gap pressure at low roll temperature yields weak bonds with delamination under tensile loading. The operational boundary is therefore set by the softening plateau rather than a crystalline melting point. Above 130 °C, the amorphous fiber loses fibrous geometry and can adhere to the calender rolls; below 90 °C, adequate bond formation is not achieved on high-speed nonwoven lines. Because the amorphous phase has no reinforcing crystallites, continuous exposure near 50 °C or above can induce progressive shrinkage and compression set. Finished products should not be specified for autoclave sterilization or for service environments exceeding 60 °C, and dimensional stability should be verified according to ISO 17052 for any application with elevated-temperature exposure.

Wet processing of 6302D staple fiber must avoid alkaline scouring baths above pH 9; alkali-catalyzed hydrolysis cleaves the polyester backbone and reduces molecular weight. Melt-phase reprocessing with additives that release free amines at process temperature should likewise be avoided because amine groups can accelerate chain scission. The fiber is supplied in baled form with a cut length commonly between 38 mm and 64 mm, and linear density can be selected from 1.5 denier to 6.0 denier depending on downstream carding and nonwoven formation. Fiber finish is applied during spin finish application or top-coating; the finish type and level must be specified for the intended thermal-bonding process because excess finish reduces bond strength and creates roll contamination. A finish level of 0.20–0.40 % by weight is typical for staple fiber entering carded nonwoven lines, but published data for a single standard finish chemistry is limited and finish selection should be confirmed through bond-strength testing.

Regulatory and Bio-Based Carbon Compliance Matrix

In thermal-bonded nonwoven structures, 6302D is most frequently used as the binder component in sheath-core fibers, where a high-tenacity core such as PET or PP provides load-bearing capability while the amorphous PLA sheath bonds at reduced calender temperatures. The grade is also converted into low-melting staple fiber for needle-punched filtration media, absorbent hygiene material, and compressed fiberfill for insulated garments and mattress pads. In filtration media, the amorphous PLA binder contributes to low-energy bonding but limits maximum service temperature; published data for high-temperature filter performance of 6302D-based needle-punched fabrics is limited. In hygiene applications, the bio-based carbon content and lower bonding energy are relevant selection factors, but migration and extractables testing under the intended food-contact or skin-contact regulatory framework must be completed on the finished nonwoven because the resin alone does not constitute a regulatory clearance. Compared with semi-crystalline PLA fiber grades, 6302D offers a lower activation temperature for bonding and reduced crystallinity-driven stiffness, but the trade-off is reduced thermal resistance, lower tenacity, and a narrower service envelope above ambient temperature.