Evonik Vestamid E62-S3 is a heat- and light-stabilized polyether block amide (PEBA) thermoplastic elastomer in which nylon 12 hard segments provide semicrystalline mechanical strength and polyether soft segments depress low-temperature modulus. The material is specified for fiber optic jacketing, including loose-tube, tight-buffered, and microduct cable constructions where a Shore D hardness of 62 per ISO 868 is required to balance jacket stiffness, crush resistance, and minimum bend radius. The reported melt-state density is 1.01 g/cm³ per ISO 1183-1, which is lower than many filled polyamide and PBT jacketing compounds and reduces cable weight per unit length. The S3 designation identifies a stabilizer package for oxidative and UV-induced chain scission during melt processing and outdoor service; the full additive composition is not disclosed in public supplier literature.

Compared with polyamide 12 homopolymer jacketing grades, the polyether soft blocks in E62-S3 depress the flexural modulus to a representative range of 110–180 MPa under ISO 178, while retaining the nylon 12 hard-segment melting endotherm at approximately 165–170°C under ISO 11357-3. This combination supports reduced bending force at sub-zero installation temperatures and higher melt processing latitude than unmodified PA12. The product is also distinguished from TPU jacketing elastomers by lower equilibrium water uptake near 1.0–1.5 wt% at 23°C saturation under ISO 62, which limits hydrolytic softening in wet outdoor cable environments.

What Distinguishes Vestamid E62-S3 from Semicrystalline PA12 and Polyolefin Jacketing Grades?

A semicrystalline PA12 homopolymer with Shore D hardness near 70 commonly exhibits flexural modulus above 900 MPa, whereas the 62 Shore D PEBA class reduces modulus by roughly an order of magnitude and permits tighter coiling without exceeding the critical microbend strain of the optical fiber. Under notched impact at −40°C, unfilled PA12 can maintain ductile behavior, but the block copolymer architecture of Vestamid E62-S3 lowers the embedding stress on the fiber by reducing jacket wall stiffness. Against HDPE jacketing grades with density near 0.950–0.960 g/cm³, the E62-S3 density of 1.01 g/cm³ is higher, but the nylon 12 hard segment provides superior resistance to cut-through and abrasion when tested on thin-wall cable jackets under IEC 60794-1-2 mechanical methods. Against PBT, the PEBA structure avoids the rapid hot-wet hydrolysis associated with aromatic polyesters and offers higher elongation at break, typically above 300% per ISO 527-2.

These differences become relevant in loose-tube designs where waterblocking gels, filling compounds, and outer jacketing layers contact the PEBA surface. Unlike plasticized PVC jacketing compounds, E62-S3 does not rely on external plasticizer migration for flexibility, so softening and shrinkage caused by plasticizer extraction into cable gels are reduced. Published data for fiber optic cable components under combined gel and thermal cycling are limited; qualification should be performed on the finished cable construction rather than on the raw compound alone.

Before extrusion, pellets of Vestamid E62-S3 should be dried in a desiccant dryer to residual moisture below 0.10%, preferably below 0.05%, with an inlet-air dew point of −40°C or lower. When storage relative humidity has exceeded 60%, drying at 80°C for 4–6 h is normally required. Single-screw extruders with 24:1 to 30:1 L/D ratio, gradual-compression screws, and screen packs of 80/120/80 mesh are suitable. A barrel profile from 180°C in the feed throat to 225°C in the metering section and melt temperature of 210–230°C at the die are typical for fiber optic jacket tubing. Published melt flow rates for the 62 Shore D PEBA class at 230°C/2.16 kg are generally in the range of 10–30 g/10 min under ISO 1133-1; lot-specific values should be taken from the certificate of analysis. Tee-head or spiral-mandrel crossheads deliver the most uniform wall thickness around optical fiber bundles, while melt pressures above 300 bar on small crossheads indicate insufficient screen-pack area or low melt temperature.

Thermal Oxidation and UV Aging Response of the S3 Stabilizer Package

The S3 stabilizer package is designed to suppress melt-phase discoloration and long-term oxidation of the polyether soft segment. For outdoor fiber optic cable jackets, accelerated weathering is typically assessed under ISO 4892-2 xenon-arc conditions with a 0.51 W/m² irradiance at 340 nm and a black panel temperature near 65°C. Retention of tensile strain at break and surface gloss is evaluated after 1000–2000 h exposure, but published data specific to E62-S3 are limited; validation must be carried out on finished jacketing because additives, carbon black, and drawing history alter UV stability. Heat aging is commonly assessed at 100°C or 120°C in circulating-air ovens using tensile property retention per ISO 188. The grade is not formulated as a cross-linked thermoset and should not be used as a load-bearing sheath at continuous temperatures above the supplier-recommended upper service limit.

The stabilizer package does not provide inherent flame retardance. If the cable construction must meet IEC 60332-1-2, IEC 61034, or NFPA 262, a separate flame-retardant jacket layer or an FR concentrate must be evaluated. The base nylon 12/PEBA chemistry is halogen-free by formulation, but compliance with IEC 60754-1 acid gas emission is a finished-cable property and depends on all layer components and printing inks.

Representative physical property values for the 62 Shore D PEBA class are listed in Table 1. These values are not specification limits and may vary by production lot, test specimen preparation, and conditioning.

When Jacketing Is Coextruded with PBT or HDPE Inner Layers

Coextrusion of Vestamid E62-S3 with PBT or HDPE inner layers requires thermal and rheological matching to prevent layer thickness fluctuation and interfacial delamination. Because the melting endotherm of E62-S3 is 165–170°C, direct coextrusion with HDPE can overheat the polyolefin layer unless the die adapter is thermally separated and the HDPE melt is kept below 200°C. With PBT inner layers, the PEBA melt temperature should be held near 220–230°C to provide adhesion and avoid PBT crystallization defects. Peel strength under ISO 11339 is often below 1.0 N/mm without a functional tie resin, so an acid-modified olefin tie layer is required for reliable structural adhesion in multi-layer jacketing. Moisture in the PEBA layer must be below 0.05% before coextrusion because residual steam can form interfacial voids and reduce adhesion in the die-lip region.

The shear-thinning behavior of the PEBA melt results in lower pressure drop in the adapter than PBT at equal throughput. Separate melt pumps or independently trimmed extruder speeds are recommended when the layer ratio exceeds 3:1 between PEBA and PBT. If die temperatures exceed 235°C, volatile evolution from the polyether soft segment can produce surface defects and reduce the continuity of the jacket inner wall. Processing trials on production-scale lines with 20–30 mm extruders have shown that ovality control for loose-tube jackets below 0.3 mm wall thickness becomes sensitive to air gap length, which should be set between 100–150 mm depending on cone stability.

The S3 stabilizer package does not convert the grade into a flame-retardant material, and the raw polymer should not be represented as compliant with IEC 60332-1-2 unless tested in the final cable design. Storage should be in sealed containers below 50°C, protected from direct sunlight and high ambient humidity. Regrind addition above 30 wt% is not recommended for thin-wall fiber optic jacketing because repeated melt processing can increase melt viscosity variance through polyether segment degradation, leading to unstable cone dimensions at line speeds above 600 m/min. Avoid melt hold-up times longer than 10 min at 230°C and melt temperatures above 250°C, because the nylon 12 hard segment may undergo chain extension or gel formation in the presence of acidic processing aids. Published data for jacket wall thickness below 0.2 mm at line speeds above 1000 m/min are limited; pilot trials are required to confirm bubble collapse, cold-set shrinkage, and fiber excess length control.