Super Smooth Clear and Elastic Silicone Oil RH-NB-8068-8

Super Smooth Clear and Elastic Silicone Oil RH-NB-8068-8 is a linear polydimethylsiloxane fluid manufactured without reactive terminal hydroxyl or vinyl groups and supplied as a clear, solvent-free liquid. The model designation RH-NB-8068-8 identifies a non-reactive dimethyl fluid with a target viscosity of 8000 mm²/s at 25 °C; the NB designation separates it from amino-functional and vinyl-functional grades in the same product family. In bulk handling, the fluid is transferred at 30–40 °C through stainless-steel lines and metered with positive-displacement gear pumps rather than centrifugal pumps because the high viscosity promotes air entrainment and pump cavitation. The material is used in textile finishing, fibre lubrication, internal modification of silicone rubber compounds, and as a non-reactive elasticising component in solventborne coatings. Compared with standard dimethyl silicone oils of 350 mm²/s or 1000 mm²/s, the grade develops a more coherent elastic film after shear deformation; compared with amino-functional fluids, it contains no amino groups and therefore avoids the yellowing pathway associated with aminopropyl oxidation at stenter temperatures. These differences are controlled by the supplier through molecular weight distribution and residual volatile content rather than by filler addition.

The elastic behaviour arises from the high average chain length of the dimethylsiloxane polymer. Under low-shear conditions the fluid exhibits Newtonian behaviour: when measured on a cone-and-plate rheometer in accordance with ISO 3219-1:2021, the viscosity remains within ±5 % of the zero-shear value over a shear-rate range from 0.1 s⁻¹ to 100 s⁻¹. The supplier does not publish an absolute weight-average molecular weight on the certificate of analysis; control is exerted through kinematic viscosity, polydispersity, and residual volatile content. The narrow chain-length distribution is important because low-molecular-weight fractions above 1.5 % act as migrating oils that reduce film cohesion and create tack in downstream converting. The fluid is supplied with a specified volatile content of ≤ 1.5 % by ISO 3251:2019, water content of ≤ 200 mg/kg by ISO 760:1978, and an acid number of ≤ 0.05 mg KOH/g by ASTM D974-22. These limits are batch-release parameters and are intended to prevent hydrolytic chain extension and catalyst interference in downstream silicone compounding.

The batch release specification is summarised in Table 1. Batch-to-batch variation is controlled by multi-point viscosity and volatile testing; the certificate of analysis reports viscosity, density, refractive index, flash point, and water content for each production batch. Published data for this specific grade in fully formulated consumer articles is limited, and downstream qualification should include film ageing at the intended maximum processing temperature.

The comparative behaviour of RH-NB-8068-8 against other silicone fluid classes is summarised in Table 2. The difference is most significant in elastic recovery and long-term storage colour under thermal load, rather than in bulk viscosity alone.

When RH-NB-8068-8 Is Run Through High-Shear Dispersion and Stenter Frame Equipment

On production lines, the fluid is conditioned to 30–40 °C before entry into the high-shear mixing unit. In a rotor-stator emulsifier running at 3,000–5,000 rpm, local viscous heating typically raises the temperature by 8–12 °C; the vessel jacket is therefore set to maintain a bulk temperature below 45 °C. Sustained shear above 60 °C causes mechano-chemical chain scission in linear polydimethylsiloxane, and the resulting low-molecular-weight fragments no longer contribute to elastic film recovery. The scission event is not visible as a colour change, but it can be detected as a drop in the high-molecular-weight fraction measured by gel-permeation chromatography and as a reduction in film recovery behaviour. In stenter frame finishing, an emulsion prepared at 20–30 wt% silicone content is applied by foulard at wet pick-up of 60–80 %; drying is conducted at 150–170 °C for 45–90 s. At these temperatures the methyl groups remain stable, but residence above 200 °C in open air begins to generate silanol and carbonyl oxidation products that increase surface energy. The non-amine composition eliminates the chromophore pathway that causes aminopropyl-functional fluids to yellow when exhaust ducts are restricted or when stenter dwell times are extended. However, the high viscosity of RH-NB-8068-8 requires continuous agitation of the pad bath to prevent creaming of the emulsion; static pad baths show separation within 20–30 min, and film build-up on rollers becomes non-uniform if agitation is interrupted.

In rubber compound mixing, the fluid is added at 5–8 phr on a two-roll mill or internal mixer. Field experience on a 75 L internal mixer with tangential rotors shows that adding the oil after black incorporation reduces mill sticking and improves compound release at nominal ram pressures of 4–6 bar. Because the grade is non-reactive, it does not consume peroxide or platinum catalyst; instead it lowers hardness and can delay scorch if it is used above 15 phr. Comparison with a 1000 mm²/s dimethyl fluid shows that RH-NB-8068-8 remains in the rubber matrix for a longer period at 100 °C, as indicated by reduced surface exudation after 72 h ageing. The migration rate is influenced by the higher chain length and by the absence of low-molecular-weight volatile fractions; however, published migration data for this specific configuration is limited, and compound-specific extraction testing should be performed before qualification.

Does RH-NB-8068-8 Act as a Non-Reactive Diluent in Tin-Catalysed Condensation Systems?

In tin-catalysed condensation curing, the terminal trimethylsilyl groups remaining on the chain end are not reactive with moisture and do not participate in silanol condensation. The fluid can therefore be used as a non-reactive plasticiser in RTV-1 silicone sealants at addition levels up to 15 wt%. At higher levels, the tack-free time increases because the curable proportion of the formulation is reduced, and the Shore A hardness falls approximately 2–4 points per 10 phr addition depending on the crosslinker system. In platinum-catalysed addition-cure systems, inhibitor and catalyst poisoning are the primary concerns. RH-NB-8068-8 is supplied without amine modifiers and with a controlled water content of ≤ 200 mg/kg, which reduces the risk of premature gelation due to moisture-borne impurities. However, it is not a substitute for vinyl-functional silicone polymers: when added above 10 wt% in high-hardness addition-cure elastomers, the non-reactive fluid increases compression set and weakens the crosslinked network. Amine-based adhesion promoters must be avoided in platinum-catalysed systems because they inhibit the catalyst and leave a tacky surface. Differential scanning calorimetry in accordance with ISO 11357-1:2023 can quantify the reduction in cure exotherm enthalpy; a loss greater than 10 % relative to the unfilled control indicates substantial network dilution. Published data for this specific configuration in addition-cure systems is limited, and formulation evaluation should include the intended thermal ageing programme.

The product is suitable for continuous open-air service up to 180 °C; above 200 °C, oxidative degradation accelerates and the fluid may build viscosity or form gel particles. Closed-system use under nitrogen extends the acceptable short-term exposure to 250 °C, but published data for this specific configuration is limited. The flash point above 320 °C does not eliminate the need for extraction ventilation in high-temperature coating lines because low-molecular-weight cyclic siloxanes may be released. Storage should be in sealed, moisture-resistant containers at 5–40 °C; drums that have been opened and partially used should be blanketed with dry nitrogen if ambient relative humidity exceeds 60 %, because absorption of atmospheric moisture can raise the water content above the 200 mg/kg release limit and introduce variability in platinum-catalysed processes.

Under the CLP Regulation (EC) No 1272/2008, the fluid as supplied is not classified as hazardous according to the safety data sheet; no substances above 0.1 % by weight are present from the REACH Annex XIV candidate list or from RoHS Directive 2011/65/EU Annex II. No generic food-contact clearance is claimed: where the fluid is intended for use in food-contact coatings or rubber articles, the formulator must verify that the overall formulation meets the migration limits of Regulation (EU) No 10/2011 or 21 CFR 175.300 as applicable. Because the product is a polymer under REACH, it is exempt from registration as a polymer; however, imported raw material monomers must be registered under the relevant REACH provisions.