Asahi Kasei Tuftec™ H1272 is a hydrogenated styrenic block copolymer of the poly(styrene-ethylene-butylene-styrene) family, classified under ISO 1043-1 as TPS-SEBS and identified by the general SEBS CAS registry number 66070-58-4. The polymer chain consists of terminal polystyrene blocks and a saturated ethylene-butylene midblock. At service temperature the polystyrene domains are glassy and function as physical crosslinks, while the ethylene-butylene segments provide elastic recovery. The hydrogenation step converts the polybutadiene midblock of the precursor SBS into an ethylene-butylene structure, removing most carbon-carbon double bonds and the associated allylic hydrogen positions. This structural difference alters thermo-oxidative stability, ultraviolet ageing behaviour, solubility, and compatibility with process oils relative to unsaturated SBS. The designation H1272 denotes a medium-high hardness grade within the Tuftec line, supplied as porous pellets with bulk density typically in the range 0.30–0.50 g/cm³. The porous pellet morphology supports oil absorption during compounding but can increase feed throat floating in high-speed gravimetric feeders if the feed hopper is not fitted with a positive discharge aid.

The values in the table are representative data from the manufacturer technical datasheet and are not unconditional lot acceptance limits. The current datasheet revision should be confirmed before design calculations or production tooling decisions. The hardness of 72 Shore A indicates a higher polystyrene block fraction than is found in low-hardness Tuftec grades such as H1221, which is published at approximately 42 Shore A. The higher brittle-fraction content increases room-temperature stiffness, tensile modulus, and dimensional stability but reduces low-temperature elasticity and raises melt viscosity compared with softer SEBS grades.

How Does the Hydrogenated Midblock Differentiate H1272 from Unsaturated SBS Grades?

In unsaturated styrene-butadiene-styrene block copolymers, the butadiene midblock contains allylic double bonds that are susceptible to ozone attack, radical-driven chain scission, and ultraviolet-induced embrittlement. Ozone resistance can be ranked by ASTM D1149, and weathering performance is commonly assessed by ASTM G154 or ISO 4892-2. For SEBS, the saturated ethylene-butylene midblock eliminates the most reactive double-bond sites. The remaining degradation pathways are principally thermo-oxidative attack at tertiary carbon positions and chain scission at the phase boundaries between polystyrene domains and the elastomeric matrix. These degradation routes are managed with hindered phenolic antioxidants, phosphite process stabilizers, and, where necessary, thioester secondary antioxidants rather than by stabilizer systems designed for unsaturated rubber.

The replacement of unsaturated SBS with Tuftec H1272 is therefore most relevant where the application involves prolonged outdoor exposure, contact with ozone-generating equipment, or thermal processing above 180 °C. The trade-off is that the hydrogenated midblock is less compatible with highly aromatic process oils and may require paraffinic or naphthenic oil extension rather than aromatic oil. Published quantitative UV retention data for H1272 under ASTM G154 is limited; component qualification for exterior applications should therefore be based on tested compounds rather than on extrapolation from the neat polymer chemistry.

Within the Tuftec range, the comparison with lower-hardness SEBS grades is primarily rheological and mechanical. H1272 produces compounds with higher scratch resistance and lower rubbery compliance than H1221. The difference of approximately 30 Shore A points indicates a significant shift in the physical crosslink density associated with the polystyrene domains. The practical consequence is that a compound based on H1272 can achieve a given hardness with less filler or less polypropylene than a softer SEBS, but it may require plasticization or blending with a softer grade for applications requiring 50 Shore A or below.

In polypropylene-rich compounds, Tuftec H1272 is metered into a co-rotating twin-screw extruder with an L/D ratio of 40:1 to 44:1. The PP homopolymer or block copolymer is dry-blended with the SEBS and a hindered phenolic antioxidant at 0.05–0.15 wt%. Processing aids such as zinc stearate may be added at 0.05–0.20 wt% to reduce die build-up and strand tack. Barrel set points are generally maintained between 180 °C and 210 °C, while the melt temperature at the die is held below 230 °C. When screw speed exceeds 400 min⁻¹, dispersion quality becomes sensitive to residence time and local shear heating. If the SEBS phase viscosity is reduced excessively, the dispersed morphology can coarsen; notched impact strength should be verified via ASTM D256 or ISO 180 because the morphology directly controls impact performance.

Paraffinic white oil is frequently used as an EB-phase plasticizer. Addition levels of 10–30 wt% lower the effective hardness of an H1272-based compound from 72 Shore A into the 45–60 Shore A range. The oil is preferentially absorbed by the ethylene-butylene midblock. Aromatic oils are less suitable because the hydrogenated midblock has weaker affinity for aromatic species, which can lead to exudation during service life. On production lines, strand pelletizing requires water-bath temperatures below 25 °C to prevent strand blocking. Porous pellets can absorb surface moisture if stored in humid ambient conditions; desiccant drying is required before injection moulding when surface moisture content exceeds 0.05 wt%.

When H1272 Is Chosen for Soft-Touch Overmoulding onto Polypropylene

Two-component injection moulding of a polypropylene substrate with an H1272-based overmoulded layer relies on melt-interface diffusion between the polyolefinic EB phase and the PP substrate. The interface temperature is a more important variable than melt temperature alone. When the interface temperature remains above 160 °C, the overmoulded layer typically achieves cohesive failure in peel testing rather than adhesive delamination. Melt temperatures for the SEBS layer are commonly set between 200 °C and 230 °C, with mould temperatures at 30–50 °C. Surface contamination, mould release agents, or excessive condensation on the PP substrate can reduce peel strength. ISO 2411 or ASTM D903 are used to validate peel or bond performance for production acceptance.

The elimination of sulfur or peroxide cure is a fundamental processing difference from vulcanized rubber and from rubber-modified polypropylene TPVs. Tuftec H1272 does not require vulcanization kinetics, scorch control, or post-cure handling; it can be reground and reprocessed. However, the absence of a covalent crosslink network results in higher compression set at elevated temperatures. Published ISO 815 data for H1272 is limited, but SEBS compounds generally exhibit higher compression set after 22 h at 70 °C than crosslinked EPDM or TPV materials. The material is therefore not a direct replacement for EPDM in sealing applications with continuous service above approximately 100 °C or where low compression set is the controlling specification.

Because the EB midblock is saturated, the compound is more resistant to reversion and surface tack during high-shear processing than unsaturated SBS. However, the polystyrene domains soften near 100 °C, so dimensional stability under load at elevated temperature depends on the compound formulation and is not defined by the neat polymer alone. Applications such as automotive interior soft-touch elements, power-tool grips, and appliance overmoulding can use H1272 when the continuous service temperature is below the threshold at which the physical crosslink network loses mechanical integrity.

For extrusion of wire and cable jacketing, strain-relief grommets, and flexible profiles, H1272-based compounds are run on single-screw extruders with 25:1 to 30:1 L/D and compression ratios of 2.5:1 or lower. Melt temperature is not permitted to exceed 240 °C for extended residence time because thermal gel formation may occur. Screen packs with 100–200 μm openings can trap char or crosslinked particles. Since the polymer is nonpolar, adhesion to copper conductors, aluminum substrates, or polar engineering thermoplastics is minimal without a coextruded tie layer, a maleated polyolefin primer, or a chlorinated polyolefin surface treatment. This limitation is a key difference from polyurethane elastomers, which exhibit higher inherent adhesion to polar substrates but generally have lower long-term hydrolytic stability.

Rheological response and drying boundary conditions

The melt mass-flow rate of 12 g/10 min at 230 °C and 2.16 kg is a single-point, low-shear measurement. It does not define the pseudoplastic response required for mould-filling simulation. At injection moulding shear rates of 10³–10⁴ s⁻¹, SEBS viscosity decreases substantially from the zero-shear value. Capillary rheometry per ISO 11443 is required to generate shear-viscosity curves for a specific H1272 compound. Complete rheological master curves are not published in all regional manufacturer datasheets; therefore, simulation users should measure the specific compound.

Drying is required when pellets have been exposed to relative humidity above 60% for more than 24 h or when surface moisture is visible. A desiccant dryer with dew point below −20 °C and a chamber temperature of 80 °C for 2–3 h is typically sufficient for neat H1272. Compounds containing hygroscopic fillers such as mineral flame retardants may require longer drying. Residual moisture causes splay, surging, and reduced overmould adhesion. Mould shrinkage for SEBS-rich compounds is commonly in the range 1.0–1.8% after 24 h; the value must be measured on a standard plaque, such as a 150 mm × 150 mm × 2 mm plaque per ISO 294-3, because shrinkage is strongly affected by PP content, filler type, gate geometry, and packing pressure.

Thermo-oxidative ageing limits the upper continuous service temperature of SEBS compounds

Continuous service above 120 °C accelerates antioxidant consumption and can lead to chain scission, tensile loss, and yellowing. Heat-ageing per ISO 188 should be performed at the intended continuous service temperature, with retained tensile strength and elongation at break measured after aging intervals appropriate to the service life. Applications requiring retention above 80% of initial properties at temperatures above 120 °C for extended time may require TPV or EPDM rather than an H1272 compound. The saturated midblock is not biologically or hydrolytically unstable, but strong oxidizing acids, hypochlorite solutions, and chlorinated solvents can attack or swell the polymer. Continuous immersion in aromatic solvents, esters, or halogenated hydrocarbons is not recommended because the ethylene-butylene phase is miscible or partially miscible with many nonpolar and moderately polar solvents.

Under the U.S. Code of Federal Regulations, styrene block copolymers intended for food contact are referenced in 21 CFR 177.1810, but the finished compound containing H1272 must be tested separately because oil extension, colorants, fillers, and process stabilizers can change extractive and migration behaviour. Under REACH Regulation (EC) No 1907/2006, the polymer itself is generally exempt from registration, although imported monomers and additives used in compounds must satisfy relevant registration and authorization obligations. Under RoHS Directive 2011/65/EU, the base SEBS polymer does not contain intentionally added lead, mercury, cadmium, hexavalent chromium, PBB, or PBDE; however, a finished compound certificate is required for each shipping lot rather than relying on the generic polymer composition. For medical, food-contact, or potable-water applications, the grade-specific regulatory status must be verified with Asahi Kasei before compounding.