Super Soft and Smooth Silicone Oil RH-NB-8602

Super Soft and Smooth Silicone Oil RH-NB-8602 is a tertiary amine-functional polydimethylsiloxane fluid supplied as a clear to slightly turbid viscous liquid for exhaust and pad finishing of cotton, regenerated cellulose, polyester/cellulosic blends, and synthetic knit structures. The model designation RH-NB-8602 identifies a linear aminoalkyl-modified dimethylsilicone that is non-ionic in concentrated form and develops weakly cationic bath behavior after acidification at pH 5.5–6.5. Manufacturer batch certificates list an active content of ≥98 % by mass according to ISO 3251 and a rotational viscosity at 25 °C of 800–1500 mPa·s when measured by ISO 2555. The product is typically diluted to a 10–30 g/L pad liquor or applied at 0.5–2.0 % o.w.f. in exhaust equipment; curing is carried out at 150–170 °C on a stenter frame. Representative specifications are consolidated in Table 1. Published independent data for this specific configuration is limited; the entries below derive from manufacturer batch certificates and should be confirmed against each delivered lot.

What Process Variables Govern Bath Stability and Deposition Uniformity on Cellulosic Substrates?

Bath stability for RH-NB-8602 is controlled by pH, water hardness, shear history, and the order of addition in the finishing liquor. In a jet dyeing machine or overflow softener operated at a liquor ratio of 1:8 to 1:15, the bath is adjusted with 0.5–1.0 g/L acetic acid 60 % to reach pH 5.5–6.5. At pH values above 8.0, the aminoalkyl groups remain insufficiently protonated and bath substantivity decreases; at pH values below 4.5, over-protonation increases cationicity to the point where fibre rewet time may exceed 10 s in AATCC TM79 vertical wicking and residual anionic dyes in the bath may coacervate.

Water hardness above 150 ppm CaCO3 destabilizes the emulsion because divalent cations bridge anionic groups present in sizes and cellulosic surfaces. Production lines using hard water should add a polycarboxylate sequestrant before the silicone is introduced; the sequestrant dose is determined by complexometric titration, and the final bath is checked for sedimentation after 30 min at 40 °C. High-shear pumping above 1500 rpm during stock emulsion preparation can also reduce particle size below the target range and create a viscous inversion that deposits on pad mangle rollers.

The addition sequence on a range with multiple chemical stations should place RH-NB-8602 after the acid but before any cationic fixative; anionic softeners, acrylic binders, and high-electrolyte antistats are withheld from the same bath unless a compatibility trial with a 100 mL jar test shows no phase separation after 24 h. In padding lines, wet pickup is maintained between 65 % and 80 % on a horizontal two-roll padder with roller hardness 70–75 Shore A; lower pickup produces uneven deposition on dense cotton twill and higher pickup extends drying time and migrates the silicone film toward the fabric surface.

In unmodified polydimethylsiloxane, the absence of amine anchoring groups limits exhaustion onto cotton and produces poor wash durability under ISO 6330 machine washing at 40 °C. RH-NB-8602 contains tertiary aminoalkyl side chains that become positively charged at pH 5.0–6.5, permitting electrostatic deposition onto negatively charged cellulosic fibres. The same charge mechanism distinguishes this product from conventional dimethylsilicone oils that require external emulsifiers and from primary aminopropyl silicones that exhibit stronger protonation but also greater thermal yellowing. After padding and curing, the fluid forms a low-surface-energy film; fabric handle is assessed by panel evaluation after five ISO 6330 washes, bending hysteresis by Kawabata KES-FB2, and whiteness retention by ISO 105-B02 daylight exposure.

Stock emulsions are prepared by charging water at 20–30 °C to a stainless steel or high-density polyethylene mixing vessel, adding acetic acid to pH 5.5–6.0, and then feeding RH-NB-8602 under a propeller mixer at 300–500 rpm. The mixture is stirred for 15–20 min and passed through a 150 µm filter before entering the pad trough. A concentric-tube homogenizer is not required and may impart excessive shear; if an inline rotor-stator mixer is used, the tip speed should not exceed 5 m/s. Batch-to-batch variation is controlled by measuring the pad bath pH and viscosity at 25 °C before the first lot and after each 4 h of running time.

In exhaust application on softflow or overflow jets, the fibre load is wetted at 40 °C, the bath is set to pH 5.5–6.5 with acetic acid, and RH-NB-8602 is added at 0.5–2.0 % o.w.f. over 10 min. The bath is circulated for 20–30 min; exhaust of the silicone is monitored by measuring residual turbidity at 600 nm. Residual turbidity above 50 NTU after 30 min may indicate insufficient bath substantivity, high hardness, or anionic interference. The fabric is hydro-extracted and dried at 110–130 °C; no additional curing is required for exhaust application unless durable press resins are present.

On knit cotton, rope marks and crease formation are controlled by reducing loading per chamber to 80 % of nominal capacity and maintaining fabric speed below 300 m/min in overflow machines. Softening with RH-NB-8602 at 1.0–1.5 % o.w.f. lowers cross-machine bending rigidity but does not fully replace mechanical compacting or resin stabilization. Fabric width is checked by AATCC TM135 or the buyer’s dimensional stability protocol; the finish contributes less than 2 % weight change at normal dosage.

Deposition Uniformity and Tertiary Amine Substantivity on Cotton/Polyester Blends

On cotton/polyester blends, differential deposition can occur because the cellulosic component carries anionic hydroxyl groups while polyester exhibits a lower surface charge. RH-NB-8602 is typically applied at 10–20 g/L on 65/35 polyester/cotton shirting weight and 15–30 g/L on cotton-heavy knits to compensate for the hydrophobic polyester surface. The pad-dry-cure cycle is set at 110–130 °C for moisture removal followed by 150–170 °C for 45–90 s. Curing below 150 °C leaves an incompletely coalesced film that is removed by subsequent ISO 6330 washing; curing above 180 °C may increase the yellowness index of the finish, particularly on optical brightened cotton.

Deposition uniformity is checked by dyeing the finished fabric with a drop of 0.5 % methylene blue solution; uneven areas appear darker because cationic dye binds preferentially to exposed cellulose. This method is qualitative and is supplemented by measuring silicone add-on through inductively coupled plasma optical emission spectrometry after extraction with xylene; the acceptable add-on range for woven cotton shirting is 0.5–1.0 % silicon on mass of fabric.

Because the tertiary amine in RH-NB-8602 is less nucleophilic than primary aminopropyl groups, the product exhibits lower thermal yellowing in high-temperature cure cycles. Primary amino silicones can undergo amine oxidation at 170–180 °C, producing chromophoric imine and azomethine species; RH-NB-8602, with an amine value of 0.15–0.40 meq/g, limits this pathway. Textile mills that cure at 170 °C for 90 s report whiteness retention values that are acceptable under ISO 105-B02 when optical brightener is applied in a separate step; however, visible yellowing must still be checked on each fibre/dye combination because residual high-temperature processing oils can migrate from polyester and react with amino groups.

Hydrophilic silicone softeners based on polyether-modified siloxanes maintain a wicking time of 3–5 s by AATCC TM79 but typically exhibit lower surface smoothness than aminoalkyl grades. RH-NB-8602 is not selected when the fabric must retain high absorbency; its low-surface-energy film can increase vertical wicking time to 10–20 s. Where both softness and absorbency are required, a blend of RH-NB-8602 with a hydrophilic silicone is evaluated at a ratio of 1:1 to 1:3 by mass, with the mixture checked for clarity after 24 h to rule out phase separation.

When Low-Yellowing Performance Is Required in High-Temperature Cure Cycles

When the finishing range operates above 175 °C to accommodate durable-press resins or pigment printing binder crosslinking, the low-yellowing character of the tertiary amine group becomes the primary selection criterion. The product can be co-applied with dimethyloldihydroxyethyleneurea resin at 30–60 g/L and magnesium chloride catalyst at 6–12 g/L, provided the pad bath is cooled below 30 °C and used within 4 h because acid catalysis can slowly protonate the amino groups and raise bath viscosity. The fabric is cured at 160–170 °C for 60–90 s; extended dwell above 120 s should be validated against ISO 105-B02 and ISO 105-X18 phenolic yellowing because yellowing from amine oxidation becomes time-dependent beyond 180 s.

For bright white goods, a two-stage pad sequence with optical brightener in the first pad and RH-NB-8602 in the second reduces yellowing compared with single-bath co-application. The whitening agent is fixed at 120–130 °C, then the silicone is padded at 5–10 g/L and dried at 130–150 °C. This separation prevents quenching of the optical brightener by the amino groups. Whiteness retention is assessed by ISO 105-B02 daylight exposure and phenolic yellowing by ISO 105-X18. A tertiary amine grade is recommended when the same fabric will be stored in polyethylene film for periods exceeding 90 days.

Storage at 5–35 °C in sealed high-density polyethylene or stainless steel vessels prevents moisture ingress and gel formation. Freeze-thaw cycles below 0 °C may increase haze; the product should be remixed at 20–25 °C before use. Containers opened for partial withdrawal should be purged with nitrogen if storage exceeds 30 days. Diluted emulsions are not self-preserving; prepared pad baths should be consumed within 24 h to avoid microbial growth and shear-induced coalescence. The fluid is incompatible with strongly alkaline solutions above pH 10, concentrated hypochlorite bleach, and anionic silicone emulsions; contact with such materials in mixing lines can form a rubbery precipitate that blocks filters with base diameter less than 75 µm.