Silicone Softener Rhsoft 110

Silicone Softener Rhsoft 110 is supplied as an amino-functional polydimethylsiloxane emulsion for pad–dry–cure and exhaust finishing of cotton, regenerated cellulosic and polyester/cellulosic blended textiles. The product is weakly cationic in acidified finishing baths and develops a low-friction silicone film on fibre surfaces after thermal fixation. Because lot-specific certificate-of-analysis data for this exact trade designation is limited, the following values are class-typical commercial tolerances for this silicone category rather than lot-specific data: pH of 5.0–7.0 in 10% aqueous dispersion measured according to ISO 4316:1977, non-volatile solids of 20–30 wt% by ISO 3251:2019, Brookfield LV2 viscosity at 60 rpm and 25 °C of 500–1500 mPa·s per ASTM D2196, and median particle diameter ≤0.5 μm by dynamic light scattering per ISO 22412:2017. The product is dispersible in demineralized water at 20–30 °C and should be stored in sealed containers at 5–35 °C; freeze–thaw cycles produce irreversible oil separation.

Incoming inspection should include pH, solids, viscosity, and particle size against the certificate of analysis. A laboratory pad–dry–cure trial on the same substrate as bulk production is conducted before warehouse release. The trial should compare the finish against a retained reference sample and report bending length by ASTM D1388, drop absorbency by AATCC TS-018, and whiteness index by AATCC 110. Because silicone hand is surface-sensitive, the trial must use identical pad pressure, drying rate, and cure dwell; otherwise the correlation to bulk production is not reliable.

What Limits Pad–Dry–Cure Reproducibility on Continuous Stenters?

In continuous pad–dry–cure finishing, the limiting process variable is the curing-window control on multi-compartment stenters. The product is typically applied at 10–30 g/L in a pad bath adjusted to pH 5.0–5.5 with acetic acid, with wet pickup of 65–80% on knitted cotton. Drying in the first two chambers at 110–130 °C removes unbound water before film coalescence. Curing in the final chambers at 150–160 °C for 45–60 s is sufficient for fixation; the acceptable curing range narrows to ±5 °C when optical brightener stability and whiteness retention are critical. At temperatures above 170 °C, amino-functional silicone films undergo oxidative yellowing that may shift whiteness index by more than 2–3 units under AATCC 110; below 150 °C, the film remains water-extractable and the softness fails to survive laundering. Production-scale thermocouple surveys on 8-compartment stenters running 180 cm wide cotton knit show selvedge-to-centre temperature differences of 10–15 °C when circulation air dampers are not calibrated, producing visible hand and shade variation. The bath should therefore be metered continuously and the wet pickup held within ±3% of target to avoid over-application.

On production-scale softflow machines, bath preparation begins with a rinse cycle at pH 5.0–5.5. Rhsoft 110 is pre-diluted 1:3 with demineralized water and introduced through the side addition tank after the bath reaches 40 °C. Circulation pump pressure is kept below 0.5 bar during addition to limit shear-induced coalescence. Exhaustion on cotton at 1–3% owf with a liquor ratio of 1:8 to 1:12 is completed within 20 min at 40–50 °C. Longer contact does not increase softness and may increase hydrophobic surface character and yellowing. After draining, the substrate is hydroextracted and dried at 70–80 °C; high-temperature tumble-drying after exhaust application can produce local film migration and should be evaluated by ISO 105-X18 for phenolic yellowing before bulk approval. Residual hydrogen peroxide from bleaching is a common cause of poor exhaustion; residual peroxide should be reduced below 0.1 mg/L before addition of the softener.

Comparative Performance Against Hydrophilic Silicone and Fatty Acid Systems

Unlike fatty acid amide softeners, Rhsoft 110 develops hand through a continuous polydimethylsiloxane film rather than through surface wax adsorption. This produces lower kinetic friction coefficient and higher drape, but also reduces surface wettability. On bleached cotton knit, pad application above 15 g/L typically raises drop absorbency time beyond 5 s under AATCC TS-018; therefore the product is not recommended for towelling, medical absorbent textiles, or interlining grades requiring rapid wicking. Compared with hydrophilic amino silicone alternatives, Rhsoft 110 is positioned as a high-lubricity rather than moisture-transport finish. Compared with reactive trialkoxy amino silicones, Rhsoft 110 is non-reactive and relies on ionic attraction and film coalescence; this facilitates re-processing and removal but reduces durability after repeated home laundering. When wash fastness is evaluated by ISO 105-C06, non-reactive silicone films may show progressive hand loss after 5–10 launderings, whereas reactive grades retain more of the original hand. The selection between these chemistries should be based on final-use laundering exposure and acceptable absorbency loss. Published data for this specific product configuration is limited; comparative assessments should use the same substrate construction and the same finish add-on solids rather than equal g/L doses.

On mercerized cotton poplin, the dosage required to reach equivalent surface smoothness is lower than on ring-spun carded cotton knit because mercerization already reduces fibre surface roughness. For polyester-cotton blended shirting, Rhsoft 110 reduces the rough handle caused by polyester fibrils, but it also lowers absorbency; permanent press resin catalyst systems containing magnesium chloride may interact with the weakly cationic emulsion and should be evaluated for bath stability before use. On dark shades, silicone film formation can increase apparent depth, but uneven film deposition can cause frosty patches. Visual assessment should be supplemented by spectrophotometric reflectance with specular excluded geometry; shade variation above 0.5 DE CMC should be investigated as a sign of uneven film formation or chemical interaction with unfixed dye.

Combination of Rhsoft 110 with anionic fluorescent brightening agents, anionic dyestuff fixing agents, or high-charge anionic softeners produces turbidity and may reduce exhaustion. If the process requires an anionic auxiliary, the bath should be buffered at pH 5.0–5.5 with 0.5–1.0 g/L acetic acid, and the anionic component should be dosed first through a separate line before Rhsoft 110 is introduced. Residual alkalinity from hydrogen peroxide bleaching must be neutralised below 0.05 g/L NaOH equivalents; otherwise the amino-functional emulsion can destabilise and deposit on rollers. The product is not recommended for continuous application with high levels of glyoxal resin at pH <4.0, because strong protonation of amino groups reduces bath stability. Foaming in high-speed pad troughs can be controlled by reducing circulating pump speed and by avoiding air induction at the suction line; defoamers should be tested for compatibility because some silicone-based defoamers can form surface spots.

When Hard Water and High Shear Destabilize Silicone Emulsions

During high-turbulence circulation in jet dyeing machines or high-speed padder troughs, the emulsion particle size distribution determines whether the product remains stable or separates as a tacky deposit. Hard water above 200 mg/L CaCO₃ equivalent can screen the electrostatic repulsion of weakly cationic particles and cause coagulation; therefore, water hardness should be measured and softened if necessary. In-line 50 μm filters on circulation lines should be monitored for pressure drop; an increase above 0.2 bar indicates coalesced silicone oil and requires bath discharge and machine cleaning. Storage below 0 °C causes freeze–thaw separation, while storage above 40 °C accelerates emulsion creaming and microbial growth. Under normal storage in closed HDPE or stainless-steel vessels at 5–35 °C, the product remains usable for 12 months from the date of manufacture. When the product is diluted, the dilution water should be below 30 °C; hot water addition can shock the emulsion and raise particle size. The product should not be mixed under high-shear propeller agitation exceeding 1500 rpm. If the final finish bath is to be filtered, a 100 μm upstream filter is preferred over fine filtration to avoid removing the silicone phase.

Bulk handling uses diaphragm pumps rather than high-speed centrifugal pumps to limit shear. Transfer lines should be flushed with demineralized water before and after Rhsoft 110 movement to prevent cross-contamination with anionic auxiliaries. Totes and drums should be resealed immediately after sampling. If the product is pre-diluted for metering, the dilution batch should be used within 24 h because microbial growth in non-sterile water can alter pH and reduce stability. Spray application is restricted to low-shear nozzle systems and requires final dilution to 0.5–1.0% solids. Nozzle clogging is a function of coarse particles; if the D50 exceeds 0.5 μm after dilution, filtration or re-emulsification is required. Foam finishing is not a standard application route for Rhsoft 110 unless the foam generator is specifically designed for low-shear silicone emulsion dosing. Published data for that specific configuration is limited; the low surface tension of silicone may cause foam collapse or uneven distribution.

Softness evaluation should not rely on a single panel test. Bending length measured by ASTM D1388 and kinetic coefficient of friction measured by a horizontal plane method may be combined with compressional resilience. Kawabata KES-FB4 surface friction parameters are available in textile research literature and are suitable for quantifying the surface smoothness effect of silicone films. Published data correlating Kawabata parameters to Rhsoft 110 specifically is limited; therefore, finishing plants should establish internal correlation between silicone solids add-on and bending length reduction. The median particle diameter of the emulsion determines penetration into fibre bundles and shear resistance. A D50 below 0.5 μm allows the product to penetrate yarn capillaries and produce internal softness; emulsions above 1.0 μm remain on the fabric surface and can build up on padder rollers. Particle size distribution should be checked by ISO 22412:2017 after dilution and after 24 h standing; any increase in D90 above 1.0 μm indicates destabilisation.