API Megol AM SEBS-Comp. DP2433/50PBT is a ready-to-process thermoplastic elastomer compound based on a styrene-ethylene/butylene-styrene triblock copolymer matrix modified with polybutylene terephthalate hard segments. The alphanumeric designation identifies the product family, the 50 Shore A nominal hardness node, and the PBT coupling target for overmoulded polybutylene terephthalate substrates. The grade is supplied as pellets for injection moulding and extrusion; because the specification sheet remains the normative source for lot-specific values, the following sections describe the class-typical test regime and processing envelope rather than substitute for the manufacturer’s certificate of analysis.

Feedstock Architecture and Phase Morphology

The compound consists of a hydrogenated styrenic block copolymer soft phase and a polyester hard phase. The SEBS midblock provides elastomeric recovery below the styrene glass transition; the PBT domains act as high-melting reinforcing nodes that raise heat resistance relative to unmodified SEBS. Phase morphology in this class is controlled by the melt viscosity ratio between the SEBS and PBT fractions. If the melt viscosity of the PBT phase exceeds the SEBS continuous phase by more than approximately one order of magnitude, domain coalescence and gross phase separation can occur in the hot runner. The compatibilizer system is therefore critical. Lot-to-lot variation in phase size is commonly assessed by scanning electron microscopy after selective extraction of the PBT phase; published morphology data for this specific grade is limited, but general SEBS/PBT compatibilized blends show PBT domain diameters in the 0.5–2.0 µm range when properly compounded.

At the 50 Shore A hardness node, the product is classified as a soft-touch material rather than a structural thermoplastic. Durometer measurement according to ISO 868 or ASTM D2240-15 should be performed on a conditioned 6 mm plaque with a 15 s reading delay; lot-specific values for DP2433/50PBT are reported on the manufacturer’s certificate of analysis. Tensile properties are tested according to ISO 37:2017 using type 1A dumbbells at 200 mm/min. Tear resistance is evaluated by ISO 34-1:2015, method B, procedure (a). Compression set is measured under constant deflection per ISO 815-1:2019 at 23 °C and 70 °C. The following matrix summarizes the primary incoming inspection parameters and the corresponding test methods.

During injection moulding trials on 80–120 t clamp machines, the main observable failure mode for PBT-modified SEBS is not short shot but delamination at the PBT interface when the mould surface temperature falls below the crystallization threshold of the PBT phase. Therefore substrate temperature is a more sensitive parameter than melt temperature alone.

How Does the 50PBT Designation Modify Compression Set and Solvent Resistance?

The presence of PBT hard domains raises the upper service temperature compared with unmodified SEBS of equivalent hardness. Compression set at 70 °C is the critical control property because excessive set causes seal leakage in dynamic applications. SEBS/PBT compounds at 50 Shore A generally exhibit compression set values in the 35–55% range after 24 h at 70 °C; however, published data for this specific configuration is limited, and the manufacturer’s datasheet value should be used for design calculations. Solvent resistance is governed by the semicrystalline PBT phase. Resistance to aliphatic hydrocarbons improves relative to pure SEBS, while ketones, chlorinated solvents, and strongly polar fluids remain aggressive. The material should be considered for applications involving intermittent contact with mineral oil, but not for continuous immersion in aromatic solvents unless validated under the actual fluid and temperature profile.

Processing equipment selection for this grade should prioritize consistent melt temperature over aggressive shear. Reciprocating-screw injection moulding machines with a compression ratio of 2.5:1 to 3.0:1 and a non-return valve with low dead volume are suitable. Barrel temperature profiles are normally flat to slightly reverse; typical settings begin at 170–190 °C in the feed zone, rise to 200–220 °C in the metering zone, and hold the nozzle at 210–230 °C. These ranges are class-typical for 50 Shore A SEBS/PBT compounds and must be adjusted using the grade-specific melt viscosity curve. Excess residence time at melt temperatures above 240 °C accelerates thermal degradation of the styrenic block copolymer, visible as yellowing and a drop in tensile elongation.

When PBT Domains Enter the SEBS Matrix: Processing Boundaries

Processing boundary conflicts arise because the SEBS phase requires lower processing temperatures than the PBT phase. If the melt temperature is set below 200 °C, the PBT domains may remain partially unmelted, producing surface roughness and anisotropic shrinkage. If the melt temperature exceeds 240 °C, the hydrogenated midblock can undergo chain scission and the styrene, ethylene, and butylene segments may oxidize in the presence of residual oxygen. For hot-runner systems, especially valve-gated configurations, the thermal history in the manifold is decisive. Drool formation at the gate is common when the nozzle temperature is kept above the PBT crystallization onset for too long. To minimize drool, the nozzle should be set at the lower end of the melt window and the hot-runner manifold should be purged with material at the start of each shift.

Adhesion to PBT substrates in two-shot moulding is evaluated on production-scale injection moulding cells rather than on laboratory-scale specimens alone. A typical validation sequence uses a 100 t two-shot machine with a rotary platen, a PBT substrate thickness of 2 mm, and an overmoulded TPE layer of 1–2 mm. Peel specimens are cut to 25 mm width and pulled at 50 mm/min according to ISO 813. The failure mode is recorded as cohesive or adhesive. For this grade, the PBT substrate should be moulded with a surface temperature of 80–120 °C prior to TPE injection; if the substrate temperature falls below 60 °C, interfacial adhesion drops markedly because the PBT skin crystallizes before the TPE melt can wet it. Published adhesion strength values for this specific configuration are limited, but the qualitative failure-mode requirement is cohesive failure within the TPE rather than clean adhesive separation.

Chemical Incompatibilities and Moisture Management

Contact with amine-based process aids, alkaline mould-release agents, or copper-containing stabilizer packages should be avoided because amines can catalyze transesterification in the PBT phase and destabilize the SEBS endblock. The material is not recommended for continuous contact with strong acids, strong bases, or chlorinated hydrocarbons. Moisture management follows polyester drying practice: hygroscopic PBT segments require pre-drying in a desiccant dryer to a residual moisture concentration below 0.05%. At ambient relative humidity above 60%, pellets left in open hoppers for more than 30 min can absorb sufficient moisture to produce hydrolysis during melt processing. Drying at 80–100 °C for 2–4 h with a dew point of −30 °C or lower is typical for this compound class; lot-specific drying instructions should be taken from the manufacturer’s technical bulletin.

Regulatory compliance for EU markets is assessed under Regulation (EC) No 1907/2006 (REACH) and Directive 2011/65/EU (RoHS). The manufacturer’s safety data sheet should be consulted for candidate-list SVHC content above 0.1%. No food-contact statement is made for this grade unless the certificate of compliance explicitly references EU Regulation 10/2011 or FDA 21 CFR 177.1810. The presence of the AM suffix in the product designation is associated with the adhesion-modified line for multi-component moulding, but the exact adhesion promoter chemistry is proprietary and should be verified against the current technical data sheet.

Compared with an unmodified 50 Shore A SEBS grade, the PBT-modified material lifts the continuous-use temperature and provides a more rigid hard phase for creep resistance. Compared with a 50 Shore A TPU, the SEBS/PBT compound generally offers lower density, lower moisture uptake, and easier colourability, but lower abrasion resistance under ISO 4649 test conditions. Compared with a TPV of similar hardness, the SEBS/PBT compound may exhibit better adhesion to PBT but higher compression set at 100 °C. The selection boundary is therefore defined by the substrate material, the chemical exposure, and the dynamic mechanical load. When the application requires bonding to PBT with a soft-touch surface, the DP2433/50PBT designation addresses that specific material pair; when the substrate is polypropylene or polyamide, the producer’s alternative coupling grades should be evaluated instead.