Platinum-catalysed addition-cure silicone elastomer RH-SEB-9061 is evaluated for short-term implantable and medical fluid-path components where peroxide decomposition residues are unacceptable and leachable profiles must remain below the analytical evaluation thresholds of ISO 10993-18:2020. Compliance documentation for this downstream category normally references ISO 10993-4:2017 for haemolysis, ISO 10993-5:2009 for cytotoxicity, ISO 10993-10:2021 for skin sensitisation, and USP Class VI systemic injection tests under <88>; fabrication sites are expected to operate under ISO 13485:2016 process controls. In a representative addition-cure formulation, 100 parts of RH-SEB-9061 Part A and 100 parts of Part B are combined at a 1:1 volumetric mixing ratio, with platinum catalyst content maintained between 6 ppm and 10 ppm by total compound mass and a 1-ethynyl-1-cyclohexanol inhibitor charge of 0.20–0.40 phr to extend pot life. The downstream production process is liquid silicone rubber injection moulding on a screw machine with a 20:1 L/D feed section, static mixing loop, and closed-loop injection pressure from 300 bar to 800 bar; mould temperature is held at 160–185 °C with a tolerance of ±5 °C because below 155 °C cure retardation lengthens demould times above 120 seconds, while above 190 °C thermal expansion mismatch with thin-wall stainless steel cores raises flash and tearing. Post-curing in a forced-air convection oven at 200 °C for 4 hours is imposed to reduce volatile condensables below 0.5 % by weight before packaging. Terminal finished product types emerging from this route include endotracheal cuff membranes, peristaltic pump tubing, wound contact layers, respiratory mask sealing lips, and septum seals for injection ports. Published product-specific data for RH-SEB-9061 under ISO 10993-18:2020 extractables testing is limited; the above parameters reflect typical platinum-cured 40 Shore A silicone elastomer technology and must be verified on production lots.
High-Voltage Cable Accessory Insulation and Interfacial Tracking Resistance
For separable connector bodies, bushing insulation, and stress-control sleeves operating at 6 kV to 36 kV, RH-SEB-9061 is processed as a high-consistency silicone rubber with peroxide cure where electrical performance is controlled under IEC 60243-1:2013 for electric strength, ASTM D149-20 for dielectric breakdown voltage, and IEC 60811-501:2012 for mechanical properties after thermal ageing. The formulation addition ratio is 100 phr RH-SEB-9061 with 0.8–1.5 phr 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and 15–30 phr hexamethyldisilazane-treated fumed silica; the peroxide level is adjusted downward when insulated line speeds exceed 20 m/min to avoid surface scorch competing with transverse crosslink uniformity. The downstream production process begins with two-roll milling at 25–40 °C, followed by preform strip feeding into a cooled screw extruder fitted with a cable crosshead; barrel wall temperature is maintained at 30–50 °C, head temperature at 55–70 °C, and die temperature at 80–100 °C to prevent dicumyl peroxide decomposition before the die. Continuous hot-air vulcanisation at 200–250 °C completes the cure, with a final post-cure of 4 hours at 200 °C to remove peroxide by-products. A processing threshold exists at stock surface temperature above 110 °C: dicumyl peroxide decomposition generates visible scorch nodules within 8–10 minutes and increases gel particle defects that lower partial discharge inception voltage. Terminal finished product types include medium-voltage separable connectors, surge arrester housings, bushing insulators, stress-cone adapters, and cable-joint sleeves. Metal particulate contamination from cable conductor drawing operations must be excluded from the compound because conductive inclusions above 50 µm create interfacial tracking paths under ASTM D2303-20 inclined-plane testing.
Does Self-Bonding RH-SEB-9061 Maintain Adhesion to Polyamide Connector Substrates When the Overmold Processing Window Narrows Below 165 °C?
Adhesion of liquid silicone rubber to polyamide 66 containing 30 weight-% glass fibre is a threshold-controlled interface problem because the polyamide surface must remain above its glass transition temperature during crosslinking while the silicone must not cure so rapidly that trapped air at the interface reduces bonded area. Automotive qualification for this segment references SAE J200 and ASTM D2000-18 material classification, and connector-level performance follows USCAR-2 for terminal retention, thermal shock, and humidity cycling. The formulation addition ratio is 100 parts RH-SEB-9061 with 0.8–1.2 phr dicumyl peroxide and 1.0–2.0 phr of an epoxy-functional silane adhesion promoter; the silane loading is the controlling variable for retention of adhesion after 85 °C and 85 % relative humidity ageing for 1000 hours. The downstream production process is two-shot injection moulding in which the nylon substrate is either plasma-pretreated or moulded with a surface temperature of 80–120 °C, followed immediately by overmoulding of RH-SEB-9061 at 165–180 °C mould temperature and clamp force from 1500 kN to 3000 kN depending on cavitation. When mould surface temperature drops below 160 °C, 90-degree peel strength on polyamide falls below 1.0 N/mm and cohesive failure converts to adhesive failure; this failure mode is observed on production tooling where peripheral cavity cooling causes edge lifting after thermal shock. Terminal finished products include sealed automotive connectors, sensor housings, grommets, and battery-pack vent seals. Published multi-lot peel-strength data for RH-SEB-9061 on 30 % glass-filled nylon 66 is limited, so first-article validation should include peel testing according to ASTM D6862-11 after thermal shock from 150 °C to −40 °C.
Food-contact transfer tubing fabricated from RH-SEB-9061 is constrained by extraction limits under FDA 21 CFR 177.2600, EU Regulation 1935/2004, and BfR Recommendation XV; volatile organic compounds must be below 0.5 % after post-cure as measured by headspace gas chromatography according to ISO 17714:2007. In this application the elastomer is processed with a platinum addition-cure system at a 1:1 mix ratio by volume, with Pt catalyst concentration held between 6 ppm and 10 ppm and no organic peroxide residue; RH-SEB-9061 addition level is 96–99 % of the compound, with the balance being a fumed silica masterbatch and approved pigment paste. The downstream production process is single-screw extrusion through a cooled barrel at 25–45 °C into plain or braid-reinforced tubing profiles using a crosshead die, followed by continuous hot-air vulcanisation at 180–220 °C and a mandatory post-cure of 4 hours at 200 °C. Terminal finished products include beverage dispenser tubing, dairy transfer hose, laboratory culture-medium tubing, and cosmetic fluid-transfer lines. Published extractables data for RH-SEB-9061 under food-contact conditions is limited; converters should verify lot-specific leachable profiles against FDA 21 CFR 177.2600 chloroform-extract limits before shipment.
When Silicone Elastomer Is Calendered onto Fiberglass Cloth for Flexible Heater Dielectric Layers
Flexible heater insulation demands a dielectric layer that maintains volume resistivity above 1014 Ω·cm after 1000 hours at 180 °C; RH-SEB-9061 is processed as a high-consistency elastomer with a peroxide-cure package to produce 0.5 mm to 1.5 mm calendered sheets on 0.18 mm silane-pre-treated fiberglass cloth. Compliance references include UL 94 V-0 flammability at 1.5 mm thickness, UL 746B relative thermal index for electrical properties, and ASTM D149-20 dielectric strength. Formulation addition ratio is 100 phr RH-SEB-9061, 0.8–1.2 phr 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 5–15 phr treated fumed silica, and 1.0–2.0 phr vinyl-specific silane coupling agent; for UL 94 V-0 compliance, 3–8 phr antimony trioxide may be incorporated but this can reduce elongation at break below 300 %, so the addition ratio must be verified against ASTM D412-16 tensile properties. The downstream process starts with two-roll milling at 25–40 °C to incorporate filler and peroxide without exceeding 100 °C stock temperature, followed by three-roll calendering onto the fiberglass cloth with nip forces from 40 N/mm to 80 N/mm; vulcanisation occurs in a hot-air tower at 200–230 °C for 5–10 minutes, with a final post-cure of 4 hours at 200 °C. Terminal products include drum heaters, medical warming blankets, battery-pack heating films, mirror defoggers, and outdoor telecommunications enclosure heaters. A batch-to-batch variance risk occurs when calendering speeds exceed 8 m/min because entrapped air becomes visible as surface pinholes that lower dielectric breakdown voltage below 20 kV/mm.
Creep Relaxation in Silicone Charge-Air Duct Cuffs Reaches a Sealing-Force Cliff Below 0.4 N/mm² at 230 °C
Turbocharger charge-air duct cuffs require resistance to hot air at 200–230 °C with intermittent excursions to 250 °C and simultaneous exposure to blow-by gases containing nitrous oxides and unburned diesel hydrocarbons; RH-SEB-9061 is used at the bellows cuff interface between stainless steel or PA66 pipes. Compliance includes ASTM D2000-18 material classification, SAE J200, and FMVSS 302 flammability for underhood components. The formulation addition ratio is 100 phr RH-SEB-9061, 0.8–1.5 phr 1,3-bis(tert-butylperoxyisopropyl)benzene or 0.5–1.0 phr dicumyl peroxide, 20–35 phr treated fumed silica for tensile strength above 8 MPa, and 2.0–5.0 phr cerium oxide or iron oxide heat stabiliser. Compression moulding is used with preforms loaded into multi-cavity tools, press platens heated to 165–185 °C, clamping pressure from 20 MPa to 40 MPa on projected part area, and demould time of 3–6 minutes depending on cross-section; flash is removed cryogenically at −196 °C. Terminal products are charge-air duct cuffs, exhaust gas recirculation connector sleeves, crankcase ventilation diaphragm seals, and turbo oil drain seals. A processing threshold exists at 260 °C: above this temperature, depolymerisation of the polydimethylsiloxane chain accelerates and tear strength per ASTM D624-20 drops below 15 kN/m after 500 hours; published data for RH-SEB-9061 at continuous 250 °C exposure is limited, so long-term sealing-force retention above 0.4 N/mm² must be validated on production moulded cuffs.
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Silicone Elastomers RH-SEB-9061 is a platinum-catalyzed, addition-cure high-consistency silicone rubber (HCR) supplied as a pre-catalyzed base with a separate methylhydrogen siloxane crosslinker. The grade is formulated to a nominal hardness of 40 Shore A after post-cure according to ASTM D2240-15. Representative cured properties include specific gravity 1.12 (ASTM D792-20), tensile strength 10.5 MPa (ASTM D412-16 Die C), elongation at break 620% (ASTM D412-16 Die C), tear strength 35 kN/m (ASTM D624-00 Die B), and compression set 18% after 22 h at 177°C (ASTM D395-18 Method B). Typical uncured Mooney viscosity ML(1+4) at 100°C is 45 MU (ASTM D1646-15). Linear shrinkage after post-cure is 2.1% when measured by an internal optical comparator method. The material is translucent and is supplied in 20 kg polyethylene-wrapped slabs. RH-SEB-9061 is used in transfer molding, compression molding, and ram extrusion for medical patient-contact parts, pharmaceutical closures, food-contact seals, and automotive electrical connector gaskets.
When Post-Cure Ovens Fall Below 200°C, Compression Set Drift Accelerates
In a three-zone forced-air post-cure tunnel, the surface temperature of parts must remain at 200°C ± 5°C for 4 h until residual silanol condensation is suppressed. Air exchange is maintained at 6–10 chamber volumes per hour. Below 195°C, cyclic siloxane oligomer removal slows and compression set after 22 h at 177°C rises from 18% to 24%. Above 220°C, visible amber discoloration may occur due to oxidation of pendant methyl groups. The operational boundary should not be exceeded; a continuous tunnel with three independently controlled zones minimizes batch-to-batch variation caused by part wall thickness changes of 1 mm to 6 mm. Production-scale observations show that densely packed wire baskets can create local thermal shadowing, producing under-post-cured regions with elevated extractables. Tray loading should not exceed 2.5 g/cm² of tray surface area when parts are smaller than 10 mm in cross-section.
For transfer molding, the compound is loaded into a cold pot at 25°C to 30°C and injected into cavities held at 140°C to 160°C. Mold clamping force is set at 0.5–1.0 tons per square inch of projected area. Moving die rheometer data at 150°C show scorch time ts2 of 35 s and cure time tc90 of 4 min 20 s. Injection speed is ramped from 15 mm/s to 35 mm/s over the first 20 mm of stroke to prevent gate freeze and flow-line formation. The material must not remain in a barrel above 80°C for more than 15 min; extended residence triggers premature hydrosilylation and produces hard particles in the molded part. Mold fouling after 500–1000 cycles appears as a transparent oligomeric film on vents. A mold surface temperature of 150°C and vent depth of 0.02 mm reduce deposit accumulation. Demolding force on polished P20 steel without external release agent is typically 4.2 N/mm. Silicone oil release agents can reduce crosslink density at the surface and should be avoided when post-mold bonding is required.
Uncured storage stability is temperature-dependent. In sealed original packaging below 30°C, shelf life is 12 months. Pot life after addition of the crosslinker is 8 h at 23°C and drops to 3 h at 40°C. The base does not require pre-drying at relative humidity above 60%; moisture uptake is negligible. However, condensation from chilled slabs should be allowed to dissipate before molding to prevent surface voids. Contact with sulfur-containing compounds, amines, and organotin salts must be avoided because platinum catalyst inhibition can occur at part-per-million levels. Nitrile rubber residues, amine-based mold release agents, and sulfur-bearing O-rings are known incompatibilities on shared production lines.
How Does RH-SEB-9061 Differ From Peroxide-Cured HCR in Closure and Gasket Production?
Peroxide-cured HCR grades release acidic residues from dicumyl peroxide or 2,4-dichlorobenzoyl peroxide decomposition, whereas RH-SEB-9061 cures by hydrosilylation and generates no acidic volatile byproducts. The addition-cure grade shows lower compression set, reduced extractables, and no post-cure bloom. Table 1 lists representative property values for the two cure chemistries. Published independent comparative data for this exact grade remains limited; the following distinctions derive from cure chemistry and supplier technical bulletins.
| Property | RH-SEB-9061 addition cure | Typical 40 Shore A peroxide-cured HCR | Test method |
|---|
| Hardness | 40 Shore A | 40 Shore A | ASTM D2240-15 |
| Tensile strength | 10.5 MPa | 9.0 MPa | ASTM D412-16 |
| Elongation at break | 620% | 560% | ASTM D412-16 |
| Compression set, 22 h/177°C | 18% | 25% | ASTM D395-18 |
| Volatile content after post-cure | 0.3% | 0.8% | internal gravimetric |
| Post-cure acid residue | none | possible benzoic acid or chlorobenzoic acid traces | ion chromatography |
Unlike single-component tin-condensation RTV silicones, RH-SEB-9061 does not rely on ambient moisture for crosslinking, which eliminates thick-section reversion in closed molds. The hydrosilylation reaction follows first-order consumption of vinyl-functional polydimethylsiloxane at 140°C, with an apparent activation energy of approximately 86 kJ/mol. A 5°C increase in mold temperature reduces tc90 by roughly 18%. This narrow activation window requires documented mold temperature mapping; cold spots below 135°C can leave tacky surfaces even after the nominal cure timer has elapsed.
In comparison to liquid silicone rubber of the same hardness, RH-SEB-9061 has much higher uncured viscosity, requiring a screw-ram injection unit rather than a piston pump. The higher green strength allows unsupported extrusion of profiles up to 8 mm diameter without slumping. It is not suitable for automated direct liquid injection without preforming. Meter-mix systems designed for liquid silicone rubber below 1000 Pa·s cause cavitation and inconsistent mixing when used with this HCR grade.
Dielectric Breakdown Strength and Volume Resistivity in Electrical Insulation
For electrical insulation, at 2.0 mm thickness the dielectric strength is 21 kV/mm per IEC 60243-1. Volume resistivity is 1.2 × 1015 Ω·cm per IEC 62631-3-1. The base polymer is not formulated for conductive filler loading; carbon black above 5 phr disrupts platinum catalytic activity and can prevent cure. Extruder pressure fluctuations above ±8% at 60 rpm correlate with melt fracture in 1.5 mm wall cable insulation. Die land length must be at least 12 mm to reduce elastic memory at the die exit. For high-voltage connector boots and insulator sleeves, the grade is tested under dry heat aging according to IEC 60216-1 at 180°C for 1000 h. Tensile strength retention is 85% and elongation retention is 72%. The material can be used in low-voltage applications below 600 V where creepage distances follow IEC 60664-1. Inserts made of brass or copper do not affect cure, but zinc-plated steel inserts may liberate amines at molding temperatures and must be passivated before overmolding.
For short-term patient-contact devices, the cured elastomer is tested according to ISO 10993-5:2009 and ISO 10993-10:2010. A post-cure of 4 h at 200°C is mandatory to reduce cyclic siloxane oligomers below 0.05 mg/kg in isopropanol extract. Extracts prepared at 37°C for 72 h in 0.9% saline show no evidence of cytotoxicity in L-929 mouse fibroblast cell culture. The grade contains no phthalate plasticizers, bisphenol A, or organic peroxide decomposition fragments. It is not recommended for prolonged implantation beyond 30 days unless additional systemic toxicity testing is performed under the intended use. For pharmaceutical closures, the material is evaluated under USP <381> elastomeric closure requirements; the supplier recommends a challenge test with the specific drug product because silicone oil migration and stopper fragmentation are formulation-dependent. The product should not be autoclaved repeatedly in sealed bags above 121°C without allowing steam penetration, as trapped condensate can create surface discoloration.
Thin-wall tubing extrusion demands careful thermal management of the hydrosilylation reaction. On a 44:1 L/D co-rotating twin-screw extruder, barrel zones are set at 40°C, 50°C, 55°C, 60°C, and the die head at 70°C. Screw speed is limited to 80–120 rpm to avoid excessive shear heating above 90°C. At 120 rpm, the compound temperature at the die should not exceed 88°C; otherwise, scorch occurs inside the head. Output rates are highly tooling-dependent, but pressure before breaker plate typically ranges from 4.0 MPa to 7.5 MPa for a 25 mm screw diameter. Online diameter monitoring with laser gauges at ±0.03 mm tolerance reduces dimensional drift during start-up. Melt fracture in thin-wall tubing occurs when the wall shear stress exceeds the critical value for this compound; reducing die land temperature below 65°C worsens surface roughness because the elastomer does not relax fully before exit. A heated extension die with a 10 mm parallel land improves surface finish.
Regulatory compliance for RH-SEB-9061 is summarized in Table 2. The grade is intended for industrial processors that maintain controlled post-cure and contamination barriers. Table 2 includes the principal standards and conditions that govern food-contact and medical use. Compliance is not self-certified by the supplier; processors must verify finished-article compliance under their own processing conditions and final part geometry.
| Standard / regulation | Scope | Condition / result |
|---|
| FDA 21 CFR 177.2600 | Rubber articles for repeated food contact | Post-cure 4 h at 200°C; extractable limits per regulation |
| ISO 10993-5:2009 | Cytotoxicity, L-929 fibroblasts | No cytotoxic effect at 72 h extract |
| ISO 10993-10:2010 | Skin irritation | No erythema or edema at 48 h |
| RoHS 2011/65/EU | Restricted substances | Pb, Hg, Cd, Cr(VI), PBB, PBDE below limits |
| REACH SVHC | Candidate list substances | Below 0.1% w/w |
| USP <381> | Elastomeric closures for injectables | Challenged with intended drug formulation |
