In a multi-layer coextruded medical tubing line with a 25:1 L/D single-screw extruder, a 45 mm barrier screw and a melt pump, the Kraton G SEBS-Comp. G7723 outer layer is typically processed with barrel zone settings of 175°C, 195°C, 210°C, 215°C, and a die temperature of 220°C. The material is pre-dried at 80°C for 2 h if ambient relative humidity exceeds 50% because moisture above 0.05% by weight produces surface splay and intermittent lumen voids during vacuum sizing. The inner layer is a polypropylene or cyclic olefin copolymer carrier, and the tie layer is an olefin block copolymer selected for a peel adhesion target above 1.0 N/mm when tested under a controlled 90° peel method derived from ASTM D6862. Layer distribution is commonly 10/70/20 for the inner, tie, and G7723 outer layers, although published data for this specific configuration is limited and line trials are required to confirm gauge control. A water quenching bath with a first-stage temperature of 40°C and a second-stage temperature of 15°C permits the ethylene/butylene midblock to relax without introducing crystalline polypropylene shrinkage mismatch. The finished tubing is evaluated for tensile strength and elongation under ASTM D638-14 at 500 mm/min, for hardness under ASTM D2240-15, and for plasticizer extraction because the SEBS compound does not contain ortho-phthalates. Biocompatibility documentation for this type of fluid-transfer application is normally structured around ISO 10993-1:2018/Amd 1:2022, with additional testing under ISO 10993-5:2009 for cytotoxicity, ISO 10993-10:2010 for skin sensitisation, and USP <87> for in vitro biological reactivity. The component is then assembled into gravity IV sets, enteral feeding extension lines, and single-use suction tubing. The principal processing conflict is residence-time control at the die lip, where melt temperatures above 230°C or local residence times over 8 min can initiate crosslinking or gel speck formation that will appear as fish-eye defects in the inner bore.

What Limits Syringe Plunger Sealability After Gamma Irradiation?

The replacement of thermoset bromobutyl with a hydrogenated styrenic block copolymer in a syringe plunger tip imposes a different set of sealing and fragmentation constraints. The G7723 compound is generally evaluated under USP <381> for elastomeric closures for injections, with specific attention to fragmentation, self-sealing, and penetrability when compressed by a high-density polyethylene piston. Gamma irradiation in the range of 25 kGy to 40 kGy produces free-radical reactions in the ethylene/butylene midblock only to a limited extent because the saturated backbone has low residual unsaturation, but the styrenic domains and the stabiliser package govern long-term colour shift. Steam sterilisation at 121°C for 30 min is an alternative when the plunger assembly is not moisture-sensitive, while electron beam sterilisation at 25 kGy to 50 kGy may be used for pre-filled syringes where terminal sterilisation is selected. Injection moulding of the plunger tip uses a 16-cavity or 32-cavity cold-runner mould, a clamp force from 800 kN to 1,500 kN depending on projected area, and a melt temperature of 205°C to 220°C. The mould surface is held at 25°C to 35°C to control sink marks, and the gate geometry is a subgate or edge gate with a land length below 1.0 mm to minimise shear-induced discolouration. A sealability failure in this part is rarely a bulk elastomer failure; it is more often a surface defect caused by gas entrapment during filling, which is controlled by venting depths of 0.020 mm to 0.030 mm and by reducing injection velocity in the final 10% of stroke. Extractables and leachables testing under ISO 10993-18:2020, with the component immersed in 50% ethanol and water at 70°C for 24 h, is used to quantify residual processing oils or additives. If the plunger is used in an ophthalmic or inhalation product, more aggressive polar solvents may be included in the extraction protocol. Published data for this specific configuration is limited for long-dwell gas-sterilisation cycles; processors should request a supplier change-control statement for irradiation dose mapping.

Ostomy Barrier Film Core-Skin Viscoelastic Requirements

An ostomy barrier flange manufactured from G7723 as the skin-contact layer is combined with a breathable nonwoven and a polymeric barrier core to resist stomal effluent penetration. The SEBS compound provides the required skin adhesion through surface melt lamination rather than through solvent-borne adhesives. Cast film extrusion is preferred over blown film for a 0.25 mm to 0.50 mm monolayer skin layer because the melt strength of SEBS at 200°C is lower than that of high-pressure LDPE, and a chill roll at 30°C is necessary to reduce surface tack. The core layer is ethylene vinyl acetate or polyvinylidene chloride, and the pouch film is sealed at 135°C to 155°C using a jaw sealer with a dwell time of 0.8 s to 1.5 s. Because SEBS has a wide sealing window and no PVC, the finished pouch is assessed under ISO 10993-23:2021 for skin irritation and under ISO 10993-10:2010 for delayed-type hypersensitivity. Odour containment is measured according to a puncture-and-seal challenge method derived from ASTM F88/F88M-21, with seal strength targets of at least 2.5 N/15 mm width after a 24 h contact period. The viscoelastic requirement is strict: the film must deform to follow abdominal contours but must not cold-flow under a 0.5 kg load at 40°C. Testing under ISO 6721-1 dynamic mechanical analysis can be used to verify that the storage modulus crosses into the rubbery plateau above 60°C, which is a practical predictor of dimensional stability during body contact. A production bottleneck occurs in the lamination nip, where pressure above 4 bar can cause blocking and pressure below 2 bar can create tunnelling at the nonwoven interface. Batch-to-batch variance in the midblock viscosity, measured by melt index at 230°C/2.16 kg under ISO 1133-1:2022, should be held within a producer-specified limit to avoid gauge drift during long runs.

Peristaltic pump tubing extruded from a single-layer G7723 formulation must survive repeated compression cycles between a roller and a rigid track without spallation, bore occlusion loss, or fatigue cracking. In this application, the compound is processed on a 25:1 L/D single-screw extruder with a polished nitrided screw, a screen pack of 60/100/60 mesh, and a crosshead die calibrated to a 0.8 mm to 1.6 mm wall thickness. The absence of silicone oil provides a clean inner surface for bioprocess fluid transfer; the tube is evaluated for protein adsorption using a bovine serum albumin challenge under a method adapted from ISO 10993-4:2017. Compression set after 22 h at 70°C, tested under ASTM D395-18 Method B, is the main predictor of pump life, and SEBS materials of this class normally fall within 25% to 40% depending on oil content and hardness. Lower compression set is obtained by using a higher styrene-block weight fraction, but this raises modulus and increases current draw on the pump motor. The service conflict is therefore between fatigue resistance and pumping torque. In production, the critical quality issue is inner-bore roughness, which is controlled by keeping the tip and die set at 215°C and by maintaining melt filtration at 100 mesh minimum. Trapped volatiles from insufficient drying produce microvoids that nucleate flex fatigue cracks and reduce operational life. The extruded tube is cut under filtered air, washed with deionised water, and double-bagged after testing under ISO 10993-12:2021 for sample preparation consistency. Published data for this specific configuration is limited for high-peristaltic speed above 600 rpm; users should validate tubing life on the target pump head because roller geometry and occlusion ratio are dominant variables.

When a Two-Shot Mould Replaces Adhesive Bonding of a Polypropylene Grip

When a two-shot injection mould replaces an adhesive-bonded polypropylene handle with a soft G7723 overshoe, the process window is governed by the solidification of the polypropylene substrate and the interdiffusion of the ethylene/butylene midblock across the interface. The substrate is moulded first in a polypropylene homopolymer at a mould temperature of 30°C to 50°C and then transferred to the second station within 60 s to maintain surface temperature above 80°C at the interface. The G7723 overshoe is injected at a melt temperature of 200°C to 215°C, an injection pressure of 60 MPa to 90 MPa, and a holding pressure of 30 MPa to 40 MPa. A chemflow path or the second-shot gate is located on a non-cosmetic edge so that flow fronts meet at the parting line and not at the grip surface. Adhesion is tested by a peel fixture based on ISO 34-1:2015 trouser tear, but because the joint is not an adhesive bond, the acceptance criterion is expressed as cohesive failure of the G7723 layer rather than interfacial peel strength. The main defect mode on production lines is short shots in the distal thumb pad when the wall thickness drops below 1.5 mm; this is corrected by increasing the second-shot barrel temperature only after verifying that the compound does not exceed 220°C at the nozzle. Oil migration from the G7723 layer into the polypropylene substrate can reduce surface friction and alter perceived tack; this is controlled by limiting the oil content in the formulation and by using a 48 h post-mould ageing step at 23°C before packaging. Flammability for consumer portable appliances may be assessed under UL 94 HB, while toys or childcare articles require migration limits under EN 71-3 or the relevant regional standard. The absence of ortho-phthalate plasticisers supports documentation for REACH SVHC declarations.

A gasket cut from 2.0 mm G7723 sheet for a single-use bioreactor port is tested for seal strength under ASTM F88/F88M-21 and inspected for particulate generation after die cutting. The sheet is produced by calendering or flat-die extrusion; calendering temperatures of 175°C to 185°C are used because the compound must release cleanly from polished rolls without the use of external release agents. Steam sterilisation at 121°C for 30 min is the default validation condition, and the gasket must maintain dimensional change below 2.0% in length after one autoclave cycle. Water vapour transmission is measured under ASTM E96/E96M-22 at 38°C and 90% RH, with SEBS compounds in this class exhibiting low transmission relative to silicone but higher than butyl rubber. The gasket is assembled into a polycarbonate or polysulfone port, and compression set under 25% strain at 70°C for 22 h per ASTM D395-18 Method B is used as a screening test. A production concern is the die-cutting process, where the sheet must be conditioned at 20°C to 25°C for 24 h before cutting to avoid dimensional springback. The cut edges are inspected under 10× magnification for delamination or particulate generation. Extractables testing under USP <661.1> may be required for plastic packaging components, and the supplier's drug master file or medical-grade certificate is referenced for change control. For single-use assemblies that contact process fluids, the final component is evaluated under ISO 10993-18:2020 and ISO 10993-12:2021 with buffer and ethanol extraction protocols. The boundary condition is the seal compression force: excessive torque on the port can cause the gasket to extrude into the flow path, so a torque limit of 0.5 N·m to 1.2 N·m is commonly specified for a 25 mm port diameter.

Compounding for Halogen-Free Wire Jackets Involves Trade-Offs in Oil Migration and UL 94 Performance

Halogen-free cable jacket compounds based on G7723 require a balance between flame retardancy, oil migration, and elongation retention after thermal ageing. The SEBS compound is let down with 40 wt% to 65 wt% magnesium dihydrate or aluminium trihydroxide in a 40 mm co-rotating twin-screw extruder with an L/D ratio of 28:1 to 40:1 and a screw speed of 250 rpm to 400 rpm. The process temperature must remain below 200°C in the mixing zones when using aluminium trihydroxide because dehydration begins near 180°C to 200°C; magnesium dihydrate allows a slightly higher threshold but reduces elongation retention more quickly at high loading. The diluted jacket compound is tested for flame spread under IEC 60332-1-2, with the vertical burn test used for cable certification under UL 1581, and the moulded slab flammability under UL 94 V-0 is not sufficient for wire because the cable geometry and copper conductor heat sink change the burn behaviour. Elongation retention after 7 days at 136°C is measured under ISO 188:2011 or UL 1581. The mineral filler raises Shore A hardness from the unfilled G7723 value to a jacket range of 75 A to 90 A, and the tensile strength may decline by 20% to 40% depending on filler particle size and surface coating. Oil migration from the SEBS midblock to the filler surface is assessed by a 70°C oven ageing test followed by visual inspection for bloom; the use of a high-molecular-weight ethylene/butylene midblock delays this effect. The production bottleneck is dispersion: agglomerates larger than 50 µm will cause spark-test failures at the wire insulation voltage test. A two-pass compounding route is used when the filler content exceeds 55 wt%; the first pass produces a masterbatch, and the second pass lets down with a coupling-agent-modified polypropylene or an olefin block copolymer to recover tensile energy to break. Published data for this specific configuration is limited for high-speed thin-wall extrusion below 0.2 mm jacket thickness; line trials are required to validate screw recovery and die pressure.