Silicone Wax RH-C2402

Silicone Wax RH-C2402 is supplied as a solid alkyl-modified polysiloxane wax. The model designation RH-C2402 identifies a non-emulsified, high-solids additive intended for melt-compounding, solventborne coating, and external release applications in which a controlled low-surface-energy film is required but gross surface oiliness is unacceptable. Unlike linear polydimethylsiloxane fluids, the alkyl substitution in RH-C2402 modifies solubility in hydrocarbon and olefinic matrices and retards the rapid bloom that ordinarily causes print-adhesion loss and die plate-out in polyolefin extrusion. Incoming material is normally released against a quality-control card that includes congealing behaviour, melt viscosity, and volatile content. The values in the following table are representative supplier specification ranges; the lot certificate of analysis supersedes these figures for any individual production batch.

Specification compliance is determined on the solid pastille without pre-drying unless the storage environment has exceeded 60% relative humidity. In that condition, a brief vacuum drying step at 40 °C for 4 h prevents condensation-induced microvoid formation when the wax is fed into a heated compounding throat. RH-C2402 contains no intentionally added water and is not classified as an emulsifiable silicone wax; attempts to dilute it with water or low-boiling alcohols produce unstable dispersions.

Why does RH-C2402 exhibit lower die plate-out than linear dimethyl silicone fluids at the same active silicone loading?

The behavioural difference arises from the alkyl side chains bonded to the polysiloxane backbone. Linear polydimethylsiloxane fluids migrate rapidly to the thermoplastic surface because their solubility parameter is low relative to polyolefin matrices. At loadings above 0.5 wt%, these fluids can form a continuous oily boundary layer at the die lip, especially on cast-film chill rolls and blown-film collapsing frames. RH-C2402 retains siloxane character but presents a higher molecular-weight solid at ambient temperature. During melt processing at 170–220 °C, the wax drops below its melt viscosity and disperses as a high-viscosity lubricating phase rather than a low-viscosity oil. The result is a slower, more controlled surface bloom that reduces gross accumulation at the die exit while still lowering coefficient of friction after migration.

In a comparative production trial on a 40:1 L/D co-rotating twin-screw extruder processing a 20 wt% talc-filled polypropylene homopolymer, the substitution of 1.0 wt% of a 1000 mm²/s polydimethylsiloxane oil with 1.0 wt% RH-C2402 reduced die-plate accumulation sufficiently to extend uninterrupted run time from 6 h to 22 h before manual wiping was required. The specific improvement is equipment-dependent; published data for this exact formulation is limited, and lot-to-lot variation in filler moisture can shift the plate-out threshold by several hours. The underlying mechanism is consistent with reduced free-oil fraction at the metal-polymer interface.

RH-C2402 also differs from ethylene bis stearamide and paraffin waxes in its thermal-oxidative behaviour. Thermogravimetric analysis under nitrogen at 10 °C/min typically shows the onset of significant mass loss above 250 °C, which places the wax within the processing window of polyethylene and polypropylene but below the upper melt-temperature range of some engineering resins such as polycarbonate and polysulfone. In formulations processed above 280 °C, fuming and brown discolouration may occur, and a higher-temperature silicone gum or polyphenylene-siloxane grade should be evaluated. The use of RH-C2402 with amine-based additives should also be approached with caution because residual moisture and amine-functional stabilizers can promote siloxane rearrangement at elevated temperatures, altering release character.

Melt rheology and screw-configuration boundaries in twin-screw compounding

The melt viscosity of RH-C2402 is strongly temperature-dependent. At 80 °C the wax behaves as a pourable liquid with a kinematic viscosity of 35–45 mm²/s, but at 25 °C it is a solid with sufficient hardness to be handled as pastilles. This phase transition is significant for side-feeding. When the wax is added through the main feed hopper with polyolefin pellets, the screw heat generated in the first barrel zone must be high enough to melt the wax before the kneading blocks begin intensive dispersive mixing. If the first barrel is set below 50 °C, the pastilles can survive into the melt-conveying section and create localized viscosity striations. On a 40:1 L/D co-rotating twin-screw extruder, barrel temperatures of 60 °C in zone 1, 90 °C in zone 2, and 180–220 °C downstream are typical when the polymer matrix is a polypropylene homopolymer.

Powdered RH-C2402 can be introduced through a loss-in-weight side feeder after the polymer has melted. Side-feeding after the first kneading section reduces the residence time of the wax at high temperature and preserves its migration character. However, side-feeding a solid wax can produce localized torque spikes if the feeder output is not synchronized with the extruder screw speed. In one production-scale trial, a 10% overshoot in side-feeder mass flow produced a transient die-pressure fluctuation of 0.6 MPa over 45 s before the control loop corrected the setpoint. The observed fluctuation did not affect pellet quality but did indicate that gravimetric feed control is required when the wax is side-fed at loadings above 2 wt%.

In polypropylene homopolymer, addition of RH-C2402 at 0.5–1.5 wt% reduces lubricated coefficient of friction after a conditioning period of 24 h at 23 °C and 50% relative humidity. The measurement is commonly performed according to ASTM D1894 on compression-moulded plaques or cast film. The full slip effect is not immediate because the wax must migrate from the bulk to the polymer-air interface. If online reduction in coefficient of friction is required within minutes of extrusion, a low-viscosity silicone fluid or a surface-applied release coating is more appropriate.

When RH-C2402 is used in rigid PVC extrusion, the loading is typically 0.3–0.8 phr. At these levels the silicone wax functions as an external lubricant and contributes to metal release without the excessive plateau effect observed with some oxidized polyethylene waxes. The migration of silicone wax to a PVC surface can reduce the gloss level of the extrudate, which may be a processing advantage in profile extrusion but a limitation in high-gloss sheet. Addition above 1.2 phr in rigid PVC can produce a persistent surface bloom that interferes with subsequent printing or hot-foil blocking. No additional vinyl stabilizer adjustment is normally required because silicone wax does not contain labile chlorine or acid-accepting metal soaps.

When RH-C2402 replaces amide wax in polypropylene cast-film formulations

In cast-film lines, amide waxes such as erucamide and oleamide are often used to reduce film-to-film blocking and lower coefficient of friction. Their action depends on the formation of a polar surface layer after migration. RH-C2402 does not form the same hydrogen-bonding network as a primary amide and therefore does not produce the same magnitude of blocking-force reduction at equal loading. A direct substitution without formulation adjustment may result in higher blocking force when measured by ASTM D3354. The preferred approach is to use RH-C2402 as a partial replacement for a portion of the amide slip agent, or to combine it with a secondary amide at reduced amide loading. Production trials on a 3-layer cast-film line indicated that replacing 50% of the erucamide in the skin layer with RH-C2402 maintained acceptable film-to-film separation while reducing the visible bloom haze after 72 h of storage at 40 °C. The haze value, measured by ASTM D1003, was 1.2% lower than the all-amide control at the same total slip-agent loading of 0.3 wt%. Published data for this specific formulation configuration is limited, so these results should be treated as equipment-sensitive rather than as a universal performance guarantee.

In solventborne coating applications, RH-C2402 is introduced by pre-dissolution in an aromatic or aliphatic hydrocarbon solvent at 40–60 °C. The solution is added during the let-down phase after the main resin and pigment dispersion are combined. The wax changes the surface tension of the dried film and can improve mar resistance and block resistance. The effect is concentration-dependent: below 0.2 wt% on total formulation solids, the influence on surface slip is marginal; above 1.0 wt%, surface haze and intercoat adhesion loss become risks. Crosslinking systems that rely on isocyanate or melamine-formaldehyde cure should be checked for surface cure interference because the migrating silicone wax can create a low-energy surface layer that inhibits mechanical and chemical intercoat bonding. Adhesion testing by ISO 2409 cross-cut tape pull after 7 days of ambient cure and 24 h water soak is a useful screening tool for these systems.

In polyamide injection-moulding compounds, RH-C2402 can be used as an internal mold-release additive at 0.2–0.5 wt%. Because polyamide processing temperatures commonly exceed 260 °C, the wax is near the upper limit of its thermal stability. Short residence times below 3 min and tight melt-temperature control are required to avoid degradation-induced brown specks and a drop in mould release efficiency. The use of RH-C2402 in polycarbonate, polysulfone, or other resins processed above 300 °C is not recommended without pre-screening because siloxane degradation products can generate volatile low-molecular-weight species and contaminate vent lines and vacuum pumps.

Storage conditions for RH-C2402 are also a processing constraint. The product should be kept in sealed containers below 30 °C and protected from direct sunlight. Re-warming a container from cold storage to ambient temperature should be performed without opening the liner until the wax has equilibrated for at least 12 h. Condensation on cold pastilles can introduce moisture into the hopper and reduce the efficiency of gravimetric feeding. In high-humidity environments above 60% relative humidity, pre-drying at 40 °C for 4 h or the use of a hopper dryer set at 50 °C is advisable. Failure to control surface moisture can be mistaken for poor dispersion when the observed defect is actually steam-induced microporosity in the finished part or film.