Kraton G1645 VO is dry-blended with a random copolymer polypropylene having a melt-flow index of 12–25 g/10 min at 230 °C/2.16 kg per ISO 1133-1:2022. The blend ratio is 25–40 wt% SEBS to 60–75 wt% PP for sealing liners. A hindered phenolic primary antioxidant is added at 0.08–0.15 phr. A phosphite secondary antioxidant is added at 0.04–0.10 phr to limit chain scission during melt processing. Compounding is performed on a co-rotating twin-screw extruder with an L/D of 40:1 and a barrel diameter of 50–75 mm. Barrel zone temperatures are set from 180 °C in the feed section to 220 °C before the die. Screw speed is maintained at 350–450 rpm. A vacuum vent in the penultimate barrel segment holds a pressure below −0.08 MPa to strip residual volatiles from the melt. The pelletised compound is injection moulded into crown-closure liner discs on a 32-cavity stack tool with a clamping force of 200–250 tonnes. Melt temperature is held at 210–225 °C. Mould temperature is kept at 20–40 °C.

Hardness is measured per ISO 868 and falls in Shore A 55–70 depending on oil content and PP crystallinity. Compression set is determined for 22 h at 70 °C under 25% deflection per ISO 815-1:2019. The finished sealing liner must meet migration limits under EU Regulation 10/2011 for plastic food-contact materials and, where applicable, 21 CFR 177.2600 for rubber articles intended for repeated contact with aqueous and fatty foods. Compliance is formulation-dependent because oil, PP, and stabiliser migration are controlled by final article thickness, contact ratio, and food simulant type.

What limits oil extension in high-torque compounding of G1645 VO?

At paraffinic white oil additions up to 50 phr, G1645 VO retains sufficient melt viscosity to generate wall shear stress above 50 kPa in a 50 mm co-rotating twin-screw extruder. Oil is injected downstream into barrel zone 5 of a 12-zone barrel so the styrene–ethylene/butylene–styrene network is dispersed before dilution. Early oil injection at the feed throat produces screw slip and reduces conveying efficiency. Observed failure modes include feed-block bridging and melt temperature variation of ±8 °C. At total oil loadings above 70 phr, phase inversion becomes likely. Tensile strength measured per ASTM D638-22 falls below 5 MPa. Surface tack increases enough to block pellets during silo storage. The high-oil processing window is ±5 °C around a melt temperature of 205 °C. Lower barrel temperatures reduce oil uptake and create visible oil striations in the strand. Higher temperatures vaporise low-molecular-weight paraffinic fractions when the oil flash point is near 240 °C, flooding the vacuum vent.

Extruder screw configuration uses two sets of 45° kneading blocks followed by a 1.5D reverse screw element to prevent downstream bypass. Throughput on a 50 mm extruder is limited to 400–600 kg/h. Die pressure is held at 2.0–4.0 MPa. Oil is metered through a heated gear pump at 80–100 °C with a rate accuracy of ±0.5%. Loss-in-weight feeders for SEBS and PP maintain an accuracy of ±0.25% to avoid hardness drift of more than ±2 Shore A points. Pellet hardness is checked every 4 h per ISO 868. Melt-flow is checked at 230 °C/5 kg per ISO 1133-1:2022. The final TPE compound is typically moulded into appliance feet, automotive mats, and ergonomic pads.

Modified binders fail elastic recovery when dosage stays below 3 wt%

High-shear mixing of G1645 VO into paving-grade bitumen is performed at 180–190 °C for 90–120 min using a rotor-stator mixer with a tip speed of 15–22 m/s. The dosage window is 3–7 wt% based on binder mass. Below 3 wt%, elastic recovery often fails to meet the ≥50% criterion of ASTM D6084-18 that appears in many highway specifications for modified binders. Above 7 wt%, the dynamic viscosity at 135 °C can exceed 3.0 Pa·s, causing pumping and mixing problems at the asphalt plant.

Softening point is measured by ASTM D36-14 or EN 1427. A 4 wt% addition may raise the ring-and-ball softening point from 45–50 °C to 70–85 °C, but the exact increment is source-dependent and published data for G1645 VO in a specific bitumen is limited. Low-temperature cracking resistance is evaluated by bending beam rheometer per ASTM D6648-16 or EN 14771. The target stiffness at −18 °C and m-value at 60 s are selected from the applicable climatic grade. Rutting resistance is assessed by multiple stress creep recovery per AASHTO T 350 or EN 16659. A formulation containing 4 wt% SEBS may require 1–2 wt% naphthenic flux to keep the percent recovery above 35% at 3.2 kPa. Long-term oxidative aging is tested by pressure aging vessel at 90 °C for 20 h per EN 14769 or ASTM D6521. Saturated midblock chemistry retards oxidative hardening, but styrenic block scission can become significant above 190 °C during extended aging simulations.

Roofing membranes use the same binder in a calender process. A typical membrane compound contains 12–18 wt% G1645 VO in the bitumen-rich phase, 25–35 wt% limestone filler, and 2–4 wt% of a styrene–butadiene–styrene compatibilizer or atactic polypropylene. The compound is processed through a multi-roll calender at 170–190 °C onto a polyester or fiberglass carrier. Cold-flex resistance is tested by the bend at low temperature method of EN 1109. Thickness control is maintained within ±0.1 mm across the sheet width.

Single-lumen tubing extruded from G1645 VO compounds runs on a single-screw extruder with an L/D of 24:1 and a screw compression ratio of 2.5:1. Barrel temperatures are set from 175 °C at the feed throat to 205 °C in the metering section. The head and die are held at 210 °C. The tube is quenched in a water bath at 15–25 °C and drawn at a puller ratio of 1.05:1–1.15:1 to control lumen collapse. Wall-thickness variation is held to ±0.05 mm for peristaltic pump lines by closed-loop ultrasonic or laser gauge control. Screw speed is adjusted to maintain a melt pressure of 10–14 MPa before the breaker plate. Batch-to-batch oil-absorption variance can shift wall thickness after raw-material lot changes. Gel particles in the raw SEBS powder can generate fish-eye defects in clear tubing when upstream filtration is below 100 µm.

The final device requires biological evaluation under ISO 10993-1. Cytotoxicity is tested per ISO 10993-5. Intracutaneous reactivity is tested per ISO 10993-10. Hemocompatibility is tested per ISO 10993-4 where blood contact is expected. A raw-material USP Class VI certificate must reference USP <88>, but the finished sterilised device must separately demonstrate compliance. Gamma irradiation at 25–40 kGy is generally preferred over steam autoclave at 121 °C because repeated autoclave cycles can increase compression set and extractable levels. Residual peroxide or crosslinking coagents should be avoided in the compound to minimise post-irradiation odour and pH shifts in aqueous media.

When cast film extrusion demands an elastane-free recovery above 90%

Film formulations contain 60–80 wt% G1645 VO and 20–40 wt% of a high-MFR random copolymer PP. Cast film is extruded through a coat-hanger die with a die gap of 0.5–1.0 mm onto a polished chill roll at 20–30 °C. Line speed is maintained at 30–80 m/min. Hysteresis set after 300% elongation is measured per ASTM D882-18. Immediate set values below 25% are typically achievable only when the styrenic phase remains below 15 wt% of the total formulation and draw resonance is suppressed by a die-to-nip distance below 25 mm. Tear strength is measured per ASTM D624-00, die C. Edge tear in cast film is controlled by maintaining a melt temperature of 205–230 °C and avoiding moisture above 0.02% in the feed resin.

For low gel counts, a screen changer with 100–200 µm filtration and a vacuum vent below −0.09 MPa is installed before the die. Pre-drying at 80 °C for 2 h is required when relative humidity at the feed hopper exceeds 60%. Film is used in elastic side panels, medical drapes, and laminate backing layers. If the film is intended for medical nonwoven applications, the fabricator must conduct ISO 10993-5 cytotoxicity testing on the finished laminate because the additional adhesive and nonwoven layers can alter the biological response.

Midblock-Compatible Rosin Esters and the Peel-Cohesion Balance

Hot-melt pressure-sensitive adhesive is prepared in a sigma-blade mixer at 170–185 °C under a nitrogen blanket. A starting formulation contains 25–35 wt% G1645 VO, 40–55 wt% hydrogenated rosin ester with a softening point of 85–105 °C, and 15–30 wt% paraffinic or naphthenic process oil. The order of addition is resin and oil first, followed by slow addition of the SEBS pellets to avoid agglomeration. Mixing continues for 45–60 min after the polymer has dissolved. Viscosity at 180 °C is measured with a Brookfield Thermosel using spindle 27. Acceptable slot-die coating viscosity is 10–30 Pa·s.

Coat weight on a slot-die line is 25–40 g/m². Loop tack is measured per ASTM D6195-03. Peel adhesion at 180° is measured per ASTM D3330-02. Shear adhesion failure temperature is measured per ASTM D4498-07. Resin additions above 55 wt% increase loop tack but reduce SAFT. The shear failure temperature may fall below 70 °C, which is unacceptable for high-temperature mounting applications. Oil addition above 30 wt% softens the adhesive but increases cold flow and transfer to release liners. The product is used for mounting tapes and labels where high peel strength and low odour are required. REACH and RoHS Directive 2011/65/EU compliance is managed through selection of low-halogen process oils and hydrogenated resins with low residual aromatic content.

Two-shot injection overmoulding of glass-filled polypropylene substrates with G1645 VO compounds requires a substrate surface temperature of 35–50 °C at the point of elastomer injection. The SEBS compound is processed at 200–220 °C with an injection speed of 80–120 mm/s and a packing pressure of 35–50 MPa. The soft component contains 30–45 wt% G1645 VO, 30–45 wt% paraffinic oil, and 10–20 wt% PP. Hardness is measured per ISO 868 at 55–70 Shore A. Adhesion is tested by a 90° peel fixture at 50 mm/min. Dry adhesion values above 1.5 N/mm are typical only when the substrate is free of mould release and the interface is packed for no more than 0.5 s before cooling. End uses include power-tool soft grips and appliance anti-skid feet. If the finished overmoulded part is exposed to skin for prolonged contact, a sensitisation test per ISO 10993-10 may be required by the device or consumer-product protocol.