Kraton™ G1654 E is a linear styrene-ethylene/butylene-styrene triblock with a polystyrene content near 30 wt% and a specific gravity of 0.91. It is processed as a formulating base polymer rather than as a finished compound. Downstream routes are selected according to oil tolerance, thermal shear history, end-use compliance requirements, and the need for a non-polar elastomer phase that can be diluted, filled, or chemically modified without sacrificing process stability. The following application segments are separated by processing equipment, additive chemistry, and final article specifications.

Medical tubing compounds are formulated without phthalate plasticizers because the SEBS matrix provides elastic recovery and flex fatigue resistance without migrating monomeric additives. A typical peristaltic pump tubing compound contains 45–60 wt% Kraton™ G1654 E, 10–15 wt% polypropylene homopolymer, 25–35 wt% white mineral oil selected for low aromatic content, and 0.1–0.3 wt% hindered phenolic antioxidant. Compounding is performed on a co-rotating twin-screw extruder with an L/D ratio of 40:1 and a barrel profile of 170–200°C; the melt is strand-pelletized and subsequently extruded into tubing on a single-screw medical extruder with an L/D of 25:1 at a melt temperature of 185–215°C. Mechanical acceptance follows ISO 37:2017 for tensile strength and elongation at break, with unaged control values typically exceeding 8 MPa and 500%; hardness is measured under ISO 868:2003 at 60–75 Shore A. Biocompatibility is controlled through ISO 10993-1:2018 evaluation, and repeated-use articles may be supported under USP 88 Class VI or FDA 21 CFR 177.1810. Ethylene oxide sterilization is preferred because gamma irradiation above 50 kGy can raise gel fraction and reduce elongation at break. When the compound contains more than 30 wt% free oil, autoclave exposure at 121°C for 30 min may produce surface oil bloom; therefore steam-sterilized tubing lines require lower oil content or a higher polypropylene fraction. Production articles include peristaltic pump tube sets, enteral feeding tubing, and vacuum manifold lines. The controlling factors are the absence of ortho-phthalates, low total extractables in aqueous media, and retention of flex-fatigue life after sterilization cycling.

What governs co-molded soft-touch adhesion on glass-filled polypropylene?

The controlling variable in overmolding Kraton™ G1654 E onto a rigid substrate is the melt-interface temperature of the glass-filled polypropylene at the moment the TPE reaches the cavity. If the substrate surface temperature falls below 130°C, molecular interdiffusion across the melt boundary is insufficient and delamination occurs under a 90° peel at loads below 4 N/mm. A production-grade soft-touch compound for a power-tool grip uses 30–45 wt% Kraton™ G1654 E, 20–35 wt% polypropylene random copolymer, 20–30 wt% paraffinic process oil, and 0.1–0.3 wt% antioxidant package. When the rigid substrate is a polyamide rather than polypropylene, 3–6 wt% maleic anhydride grafted SEBS is added to the soft phase to create interfacial bonding. The two-shot injection molding machine is set with barrel zone temperatures of 200–230°C, mold temperatures of 30–50°C, and clamp force of 120–180 t depending on tool size. Vent depth is held at 20–30 µm to prevent gas marks on high-gloss tool surfaces. Hardness is specified at 45–70 Shore A under ASTM D2240-15, tensile properties under ISO 527-1:2019, and notched impact under ISO 180:2019. Scratch resistance on visible automotive surfaces is assessed with VDI 2019, and oil-free formulations are used when low fogging is required for cabin interiors. The practical boundary is that free oil content must remain below 30 wt% for glass-filled substrates because oil migration into the interfacial layer suppresses peel strength after thermal aging at 80°C for 168 h. Finished components include power drill housings, electric toothbrush handles, and automotive interior grab handles. In all cases, cohesive failure within the TPE layer is the acceptance criterion; adhesive failure at the bond line is treated as a processing fault.

Solvent-free hot-melt pressure-sensitive adhesives formulated with hydrogenated tackifier resins

Hot-melt pressure-sensitive adhesives based on Kraton™ G1654 E use the styrene endblocks as physical crosslinks that solidify on cooling. A standard tape-lamination formulation contains 20–30 wt% Kraton™ G1654 E, 40–55 wt% fully hydrogenated aliphatic tackifier resin, 15–25 wt% naphthenic process oil, and 0.1–0.5 wt% hindered phenolic antioxidant. Mixing is performed in a jacketed sigma-blade mixer at 160–180°C under nitrogen; the final hot-melt viscosity is below 25,000 mPa·s at 175°C when measured by ASTM D3236-15. The molten adhesive is transferred to a slot-die coating head and applied to polyester film or nonwoven at 165–175°C. The selectivity of the tackifier is critical: hydrogenated aliphatic resins associate with the ethylene/butylene midblock and reduce plateau modulus, whereas aromatic resins enter the styrene domains and lower tensile strength. Standard testing follows ASTM D3330/D3330M-04(2018) for loop tack, ASTM D3654/D3654M-06(2019) for static shear, and ASTM D4498-07(2013) for hot shear. The closed-cup flash point of the mixed system exceeds 220°C, which permits hot-melt operation without solvent recovery or explosion-proof coating equipment. End uses include diaper elastic attachment, medical-tape lamination, and automotive interior trim bonding. The service-temperature boundary is 70–80°C because the styrene domains begin to soften above that range and shear resistance falls. For indirect food-contact adhesive layers, FDA 21 CFR 175.105 applies to the finished adhesive article, not to the polymer alone; extractives testing is carried out on the full laminate. Aromatic tackifiers are generally excluded from medical-tape laminates to reduce the risk of skin sensitisation. This segment is chosen when low halogen content, low odour, and solvent-free processing are simultaneous constraints.

In low-smoke zero-halogen cable jacket compounds, the elastomer phase supplied by Kraton™ G1654 E compensates for the ductility loss caused by high mineral-filler loading. A production-scale formulation for internal appliance wiring uses 18–25 wt% Kraton™ G1654 E, 15–20 wt% polypropylene, 40–55 wt% magnesium hydroxide with a specific surface area of 5–10 m²/g, 4–8 wt% zinc borate, 5–10 wt% paraffinic oil, and 1–3 wt% silicone processing aid. The compound is mixed in a Buss kneader at a screw temperature of 170–190°C or in a co-rotating twin-screw extruder with an L/D of 44:1. Because the filler level exceeds 40 wt%, the filler is side-stuffed downstream and the process oil is injected at 60°C to prevent cold-viscosity spikes. After underwater pelletizing, the compound is extruded on a 90 mm single-screw cable line with a barrel profile of 160–190°C and a compression ratio of 2.5:1. The resulting jacket is tested according to IEC 60754-1:2011 for halogen acid gas content, IEC 60754-2:2011 for pH and conductivity, and IEC 61034-2:2005 for smoke density. The compound is designed to fall within the performance limits of EN 50363:2018 for low-smoke zero-halogen cable sheathing. Typical unaged jacket hardness is 88–92 Shore A, and tensile strength is above 10 MPa under ISO 37:2017. The limiting condition is that magnesium hydroxide content must remain below 60 wt%; above this threshold, melt fracture becomes severe and elongation at break falls below 150% at line speeds above 50 m/min. Final parts include internal appliance wiring, data-cable jackets, and flexible appliance cords where IEC halogen limits and smoke density are mandatory.

Chemical foaming process windows for lightweight insole compounds

A foamed insole formulation using Kraton™ G1654 E as the load-bearing phase combines 25–35 wt% Kraton™ G1654 E, 10–20 wt% polypropylene homopolymer, 15–25 wt% white oil, 5–15 wt% precipitated silica, 0.5–1.5 wt% azodicarbonamide blowing agent, 0.2–0.5 wt% zinc oxide activator, and 0.3–0.5 wt% stearic acid internal release. The compound is injection-molded on a machine with a shut-off nozzle and a clamp force of 80–150 t. Barrel temperatures are held between 180°C and 200°C because the azodicarbonamide decomposition onset lies in the 195–205°C range under dynamic shear. Mold temperature is set at 40–50°C to stabilize gas-cell walls against premature rupture. Foaming ratios between 1.5 and 2.5 lower apparent density to 0.5–0.7 g/cm³ while retaining compression set below 35% after 22 h at 70°C under ISO 815-1:2020. Hardness is specified at 20–45 Shore A depending on oil content; tear strength under ISO 34-1:2015 is above 10 kN/m for the unfoamed base compound and is proportionally reduced after expansion. The critical process window is that gas counter-pressure is required when the density target is below 0.45 g/cm³; without counter-pressure the cellular structure collapses during pack-out and the part exhibits surface sink marks. Production parts include running-shoe midsoles, sandal footbeds, and thermoformed orthotic shells. The melt strength of Kraton™ G1654 E prevents bubble coalescence, but compounds containing more than 20 wt% free oil may show die build-up during extended molding runs.

When the same SEBS is extended with high oil loadings for medical gel cushions

At oil loadings above 70 wt%, Kraton™ G1654 E forms a physically crosslinked gel network with low elastic modulus and high energy absorption. A cushioning gel composition of 10–15 wt% Kraton™ G1654 E, 80–90 wt% white mineral oil, and 0.1–0.3 wt% antioxidant is compounded in a hot-melt vessel at 150–170°C until the polymer fully solvates; the resulting melt is cast into open molds and cooled to form a solid gel. The oil phase is selected from severely hydrotreated petroleum distillates with a kinematic viscosity between 20 cSt and 50 cSt at 40°C to limit migration from the network. Gel hardness is typically 5–25 Shore OO under ASTM D2240-15, and the block-copolymer network reduces oil leaching below 3 wt% in a 24 h compression extraction test according to ISO 10993-12:2021. Applications in medical seating and anti-decubitus pads are evaluated for cytotoxicity under ISO 10993-5:2009 and for skin irritation under ISO 10993-10:2021. Production-scale casting requires a vacuum degassing step at −0.08 MPa to remove air bubbles before gelation; otherwise voids create fatigue-initiation sites under repeated load. The operational boundary is that the maximum oil uptake of Kraton™ G1654 E is finite. Published data for this specific configuration at oil loadings above 90 wt% is limited, and batch-to-batch oil absorption must be verified before a production recipe is fixed. Parts produced from this system include wheelchair seat cushions, bicycle saddle pads, and vibration dampers in industrial seating. In these applications, oil retention, hardness stability after repeated compression, and the absence of leachable plasticisers are the primary design constraints.