Smooth Silicone Oil Especially for Cotton RH-NB-663G

Product RH-NB-663G is a linear amino-functional polydimethylsiloxane emulsion formulated for cotton and cotton-dominant textile constructions. The supplied form is a nonionic, water-dilutable macroemulsion containing no alkylphenol ethoxylates. Pad application at 10–30 g/L on bleached cotton knit develops a smooth surface tactility and a dry, elastic hand without the hydrophobic film associated with high-viscosity dimethylsilicone oils. In this grade, the amino side-chain substitution is positioned to limit hydrogen-bonding interference with cellulose fibrils while permitting film formation at 130–160°C. Manufacturer control limits specify active silicone content of 15–20% by gravimetric method according to ISO 3251, pH at 25°C of 5.5–6.5 according to ISO 976, and Brookfield viscosity below 500 mPa·s at 25°C according to ISO 3219. The product is classified as nonionic and is intended for pad-dry-cure and exhaust processes on cellulosic substrates. Batch certificate values should be confirmed for each delivery; the listed ranges are control limits, not all-batch guarantees.

The silanol-reactive component in RH-NB-663G is supplied as a hydrolytically stable emulsion at pH 5.5–6.5. Cellulose zeta potential at neutral pH is moderately negative; the protonated secondary amino groups in the polymer backbone provide charge-driven adsorption. Laboratory padding of bleached cotton at 20 g/L bath concentration and 70% wet pick-up deposits approximately 0.3–0.5 g/m² silicone on the fiber surface. Fiber friction reduces by 20–35% compared with untreated cotton when measured with a friction meter under 50–100 g load. Because the product is nonionic, deposition depends less on bath conductivity than cationically charged softeners; however, high electrolyte content above 10 g/L compresses the electrical double layer and reduces adsorption uniformity.

What Distinguishes RH-NB-663G from Conventional Dimethylsilicone and Amino-Silicone Softeners?

Standard polydimethylsiloxane fluids impart high surface slip but reduce absorbency because of a continuous hydrophobic methyl layer. Conventional amino-functional silicones improve softness and durability but often increase yellowing at curing temperatures above 150°C because primary amine groups undergo oxidative chromophore formation. RH-NB-663G differs through control of amino side-chain density and absence of primary amine groups, which permits film orientation on cotton with a measured wicking time below 5 s after one pad-dry-cure cycle. In parallel, the product uses a shear-stable emulsion with D50 particle size between 0.5–1.5 µm when measured by laser diffraction according to ISO 13320-1. A smaller particle fraction is not used to avoid excessive penetration into fiber capillaries, which would reduce surface smoothness. The product does not contain silicone resin, fumed silica, or wax extenders.

Under production conditions, the difference in yellowing is most visible on optical-brightened cotton. AATCC 110-2015 whiteness index values on bleached mercerized cotton after curing at 150°C for 90 s typically show a shift of < 2.5 units for RH-NB-663G, while conventional primary-amino silicones can shift 3.0–5.0 units. The lower yellowing is not a complete thermal stability guarantee; curing above 170°C remains restricted.

Unlike wax-extended softening systems, RH-NB-663G does not contain fatty wax or polyethylene emulsion. Wet crocking fastness on cotton after treatment remains within 0.5 grade of the blank when evaluated according to ISO 105-X12, whereas wax-based softeners can reduce wet crocking by more than 1.0 grade. This distinction is important for dark reactive-dyed cotton, where surface wax increases color transfer under moisture.

In pad application on mercerized cotton poplin at 40 m/min through a two-roll pneumatic padder with wet pick-up of 65–75%, the recommended working concentration is 15–25 g/L at bath pH 5.0–6.0, adjusted with 0.5–1.0 g/L acetic acid. Liquor temperature is maintained at 25–35°C. Drying at 110–120°C to residual moisture of 20–30% precedes curing at 150–160°C for 60–90 s. On an 8-chamber Brückner stenter with a 30 m hot-air zone, chamber exhaust temperatures are set to 150°C in chambers 1–4 and 160°C in chambers 5–8. Fabric width is set 3–5% below greige width to prevent cellulose relaxation shrinkage. Replenishment of the pad trough is set at 0.5–1.0 L/min per 100 L working volume; this maintains pH drift below 0.3 units and prevents edge-to-edge softener imbalance.

Exhaust application on cotton jersey in jet or winch equipment uses 2–4% on weight of fabric. The bath is set at 30–35°C, pH 5.0–5.5, and run for 15–20 min. The product is added as the final component after dyeing and rinsing, and before extraction. Because the emulsion is nonionic, it is broadly compatible with residual anionic dyes but can precipitate when concentrated cationic dye-fixing agents are present without intermediate draining.

Hydrophilicity retention is a differentiating parameter against standard dimethylsilicone fluids. On 100% cotton single jersey treated with 25 g/L RH-NB-663G and cured at 150°C for 90 s, vertical wicking height after 30 min according to AATCC 79-2019 remains above 6 cm, whereas dimethylsilicone-treated fabric typically drops below 2 cm. This property is relevant for activewear and toweling where water absorption must be preserved. The film is not durable to strong alkaline hydrolysis; repeated industrial laundering at pH 11.0 and 85°C for 20 cycles reduces silicone deposition by 30–40%. Under household washing conditions of AATCC 61-2020 test 1A, retained smoothness after 5 cycles is 60–70%.

Specifications, Storage Stability, and Shear Limits

Storage in sealed polyethylene or stainless-steel vessels at 5–40°C is required. Frozen material must not be used; freeze-thaw cycling damages the emulsion, causing creaming and D50 agglomeration above 5 µm. The product is stable for 12 months from production date when stored in original sealed containers. In production, high-shear recirculation through gear pumps at speeds above 1,200 rpm can reduce emulsion stability; positive-displacement diaphragm pumps with low shear are preferred. Avoid contact with strong acids below pH 2.0 and strong alkali above pH 9.0. The product should not be mixed with high-electrolyte solutions above 20 g/L of magnesium chloride without gradual dilution and agitation, because local osmotic shock can destabilize the dispersion.

Continuous pad trough recirculation with a centrifugal pump at 1,450 rpm over 8 h was monitored; D50 remained below 1.5 µm, but at 2,900 rpm D50 increased to 4.2 µm after 6 h, causing visible creaming and reduced deposition on fabric edges. This defines a shear limit: recirculation should use a low-shear pump with tip speed below 10 m/s. In contrast, microemulsions resist shear but penetrate too deeply, reducing surface smoothness. This is a processing conflict specific to the product.

Compatibility jar tests with 10% sodium dodecylbenzene sulfonate at 1:1 volume ratio caused phase separation within 30 min. Dilution before mixing avoids this. In pad formulations that include anionic optical brighteners, the brightener should be prediluted 1:10 with water before addition. If not, flocculation at the brightener feed point can produce visible deposits on fabric edges.

Viscosity of a 10 g/L working bath is below 50 mPa·s at 25°C, permitting use in low add-on foam finishing equipment with blow ratio 1:4 to 1:8. The diluted liquor is Newtonian; no yield stress is observed. This is relevant for metering pumps that require consistent flow at low shear rates of 50–100 s⁻¹.

During stenter curing at 150–170°C, amino-functional silicone film formation proceeds by condensation of silanol groups after water evaporation. At temperatures above 180°C or dwell times beyond 120 s, oxidative yellowing on cotton becomes measurable. On bleached cotton, AATCC 110-2015 whiteness shift can move from 1.5–2.5 units at 150°C for 90 s to more than 4.0 units at 170°C for 180 s. This defines a critical processing window: cure setpoints above 175°C are outside the intended use range. Batch-to-batch variation in residual peroxide from cotton bleaching intensifies this yellowing, because free radicals accelerate amino oxidation. Production practices therefore require a catalase or reducing rinse before softener application when bleached cotton residual hydrogen peroxide exceeds 5 mg/L. In a production trial on an 8-chamber stenter, fabric temperature at the exit was measured at 148–153°C with an infrared pyrometer across a 72-inch width; edge regions were 2–4°C hotter than center and showed AATCC 110-2015 shift values 0.5–1.0 units higher, which required chamber airflow adjustment to reduce side-to-side temperature delta below 3°C.

This thermal behavior differs from standard dimethylsilicone oils, which do not yellow but create water repellency and lower seam slippage. It also differs from primary-amino functional silicone fluids, which can develop yellowing at lower temperatures because primary amine groups form azomethine chromophores. The secondary amino group content in RH-NB-663G is controlled to keep whiteness shift below 2.5 units at the specified cure, as verified by AATCC 110-2015 on bleached cotton. Published data for this specific formulation is limited beyond the manufacturer technical bulletin and in-house testing; independent reproduction of the thermal yellowing limit should follow ISO 105-B02 for light fastness and AATCC 92 for perspiration-induced yellowing where downstream exposure conditions are severe.

Low add-on application by foam coating has been evaluated on cotton twill using a Gaston Systems CFS foam generator. At a blow ratio of 1:5 and wet add-on of 15–20%, RH-NB-663G at 30–40 g/L in the foam liquor produced surface smoothness comparable to a 65% wet-pick-up pad application at 15 g/L. Foam stability was maintained for 30–45 s half-life, sufficient for transfer from parabolic foam distributor to the substrate. The lower wet add-on reduced drying energy by 40–50% in this configuration. This is an operational difference from low-viscosity dimethylsilicone fluids, which typically require higher surfactant loading to form stable foam. However, foam finishing narrows the curing window because residual water content is lower; fabric surface temperature reaches 150°C within 15–20 s of entering the stenter, whereas full wet pad application requires 30–45 s. That faster heating is beneficial for film formation but increases the risk of overdrying at chamber temperatures above 165°C.

When RH-NB-663G Is Co-Applied with Glyoxal Resins and Optical Brighteners

Co-application with dimethyloldihydroxyethyleneurea-based glyoxal resins and magnesium chloride acid donor requires sequencing adjustment. The softener emulsion should be added after the resin and catalyst have been diluted, at a bath pH of 4.0–5.0. Direct addition of concentrated RH-NB-663G into a high-acidity resin premix at pH below 3.0 can produce localized coagulation. Optical brighteners should be added before the softener, because the silicone film can trap brightener at the fiber surface and increase apparent unlevelness. In pad-dry-cure finishing of cotton shirting with 60 g/L glyoxal resin, 12 g/L magnesium chloride hexahydrate, 0.8 g/L stilbene-derived optical brightener, and 20 g/L RH-NB-663G, the finished fabric shows reduced formaldehyde release if tested according to ISO 14184-1, with values below 20 ppm, provided curing is complete. Incomplete cure at 140°C for 30 s can raise formaldehyde release above 75 ppm and also reduce silicone durability to AATCC 61-2020 accelerated washing. Durable smoothness after 5 washing cycles according to AATCC 61-2020 test 1A is retained at 60–70% of the initial handle improvement when cure is complete, whereas under-cure drops retention below 40%.

Compatibility with cationic fixing agents is limited. In dyeing house sequences, residual cationic fixative from dyeing should be drained and rinsed before softener exhaust. If not, bath turbidity increases and deposit on fabric edges can appear as greasy spots. Emulsion destabilization in the bath is assessed by measuring D50 particle size before and after 5 min of circulation; an increase above 1.0 µm from the initial D50 indicates early coagulation and requires pH or sequence correction.