Super Soft and Fluffy Silicone Oil Especially For Cotton RH-NB-665G

RH-NB-665G, identified commercially as Super Soft and Fluffy Silicone Oil Especially For Cotton, is an amino-functional polydimethylsiloxane fluid supplied for textile wet finishing of cotton and cotton-rich knits and wovens. The material is not a ready-to-use emulsion; it is a 100 % active silicone fluid that requires controlled emulsification before application by pad or exhaust routes. The primary technical function is the development of a soft, bulky, dry-surface handle without the high yellowing tendency associated with high-amine silicone fluids on white goods. In plant trials, the product is typically compared with reference amino silicone fluids using Kawabata KES-FB bending and shear hysteresis measurements, AATCC Test Method 110 whiteness indices after hot-air curing, and ISO 6330 washing durability protocols. Published product-specific data for RH-NB-665G are limited; consequently, processing recommendations are derived from the general behaviour of aminofunctional siloxane fluids in cotton finishing and should be confirmed with lot-specific certificates of analysis.

Product Identity and Physicochemical Specification

Table 1 summarizes the typical physicochemical envelope reported for this product class. The values are provisional and should be read against the manufacturer's certificate of analysis for each batch.

Emulsion preparation at plant scale uses a 200 L stainless-steel vessel fitted with a rotor-stator homogeniser. The oil phase comprising RH-NB-665G and nonionic emulsifier is charged at 25–35°C; deionized water is added slowly under 3000 rpm, followed by 10 min at 5000 rpm. The resulting stock emulsion should be checked for D90 by laser diffraction; a D90 above 5 µm correlates with pad roll build-up and softener spots on red and black reactive-dyed cotton. If the stock emulsion is stored longer than 48 h, mild stirring at 50–100 rpm should be maintained to prevent creaming; freezing and reheating are not recommended. In high-speed continuous pad lines above 60 m/min, emulsion shear stability can be evaluated by recirculating through a centrifugal pump for 30 min at 40°C and rechecking D90; an increase of more than 20 % indicates insufficient emulsifier level. Batch-to-batch variation in viscosity of ±10 % can shift the required emulsifier HLB by 0.5–1.0 units, so a single-point emulsifier package is not always optimal.

Exhaust application on cotton knits in softflow or overflow machines is performed after dyeing and neutralization. The silicone fluid is first converted into a 10–15 % stock emulsion using deionized water at 25–35°C and a nonionic emulsifier with hydrophile-lipophile balance between 10.5 and 12.5. The emulsion is added to the exhaust bath at 0.5–2.0 % o.w.f. The bath pH is maintained between 5.0 and 6.0 with acetic acid, and the temperature is held at 35–40°C. Under these conditions the protonated amino-functional siloxane exhausts onto cotton by ionic attraction to residual anionic groups. Treatment time of 20–30 min is common; machine operators should monitor baginess and filter clogging as early indicators of emulsion instability. Batch-to-batch variation in silicone fluid amine value may shift optimum pH by ±0.3 units, so compatibility trials with cationic fixatives and residual dyes are required when the softener is combined with post-dyeing auxiliaries.

Residual reactive-dye hydrolysis products and salt from the dyeing cycle can interfere with silicone exhaustion. Bath conductivity above 3000 µS/cm reduces electrostatic attraction between protonated amino groups and the cotton surface, and residual anionic dyestuff can form coloured coacervate spots on pale shades. A thorough drop-fill-rinse cycle is therefore recommended before the softener bath is prepared. On production machines with limited rinsing, the addition of 0.5–1.0 g/L nonionic dispersant has been used to reduce coacervate formation, but this reduces softener efficiency and must be validated in advance. The bath should not be circulated through high-shear pumps at maximum speed during the entire treatment because prolonged shear above 500 s⁻¹ may induce coalescence; softflow pump speed should be reduced to the minimum consistent with fabric rope movement.

How Does RH-NB-665G Differ from Conventional Amino Silicone Fluids on White Cotton?

Conventional amino silicone oils often provide strong surface softening but develop visible yellowing when cured above 150°C on optically brightened cotton. The yellowing mechanism is associated with oxidation of primary amino groups and the formation of chromophoric imine or amide species. RH-NB-665G is formulated to reduce the concentration of primary amino sites relative to sterically hindered secondary amine functionality. This substitution pattern requires a slightly altered curing profile: durability to ISO 6330 washing may remain acceptable when a 160–170°C cure interval of 60–90 s is used, but yellowing under AATCC Test Method 110 is generally lower than that observed for standard amino fluids. Compared with hydrophilic polyether silicones, RH-NB-665G provides greater bulk and dry-surface fluffiness but higher contact-angle hysteresis, reducing water drop absorption speed. Compared with non-reactive dimethylsilicone oils, it has substantially better durability to machine washing because the amino functionality anchors to cotton. The material is supplied as a fluid rather than a pre-emulsified product, which gives formulators direct control over particle size and concentration but requires plant emulsification equipment.

On continuous stenter finishing lines, RH-NB-665G is usually applied from a deaerated pad emulsion at 10–40 g/L depending on fabric weight and residual moisture. The foulard nip expression is set between 60 % and 80 % for cotton knit goods; lower pickup below 55 % tends to produce handle stripes because the silicone fluid does not uniformly coat fiber bundles. Foam build-up in the pad trough is controlled by using defoamer only after compatibility testing, as some defoamers reduce shear stability of amino silicone emulsions. The padded fabric enters a stenter with infrared pre-drying at 110–130°C for 20–40 s, followed by hot-air curing at 150–170°C for 60–120 s. Dwell times below 50 s at 150°C may result in poor wash-fastness; temperatures above 180°C increase yellowing and can degrade optical brighteners on white goods.

When Stenter Curing Is Operated Outside the 150–170°C Window

On multi-pass stenter frames with chamber temperature control tolerance of ±5°C or wider, edge-to-centre differences in fabric temperature create handle non-uniformity. The silicone film forms less crosslinked deposits at the edges if local temperature falls below 150°C; over the centreline, temperatures above 180°C can cause premature oxidative yellowing and loss of bulk. For a 24 m stenter running at 30 m/min, total dwell time is approximately 48 s, which is insufficient for full cure at 150°C; line speed must be reduced to 15–20 m/min to achieve 72–96 s. Production scheduling with 80–100 % cotton fleece and French terry should therefore validate chamber profile with contact thermocouples or infrared pyrometer each shift. Variations in exhaust humidity above 70 % can increase fabric moisture and lower actual fabric temperature by 5–8°C due to evaporative cooling; pre-drying with infrared panels is required when residual moisture after padder exceeds 75 %.

Laboratory evaluation for cotton interlock knits treated at 20 g/L uses AATCC Test Method 61 condition 2A after 5 wash cycles; handle retention is assessed by ring tensile and Kawabata KES-FB4 surface friction. Water absorbency is measured according to AATCC Test Method 79, with a drop absorption time below 2 s reported for untreated reference cotton; treated RH-NB-665G samples may show 5–15 s depending on finish loading and cure. Whiteness retention after cure is quantified by AATCC Test Method 110 under D65 illuminant and CIE WI values. Published product-specific data are limited, so each mill laboratory should generate control charts from a minimum of 20 batches before setting final limits.

Anionic auxiliaries, including residual dye-fixing agents and some optical brighteners, should be removed before exhaust application because electrostatic coacervation leads to stable silicone/anionic complexes that deposit on machine walls and cause spotting. Water hardness above 200 mg/L CaCO₃ may reduce emulsion stability; dilution with softened water is strongly preferred. Direct mixing with concentrated acids or alkalis should be avoided because hydrolysis of the siloxane chain is accelerated below pH 3.0 or above pH 9.5 at ambient temperature. Storage in unopened containers at 5–35°C is recommended; freezing may break the fluid into gel fractions, and prolonged storage above 40°C may increase amine oxidation and shift viscosity. During bulk handling, nitrogen blanketing of day tanks is not required if the product is used within 12 months, but prolonged air exposure should be avoided. Because RH-NB-665G is an amino-functional fluid, it is not recommended as the sole finish for towelling where drop absorption by AATCC Test Method 79 below 3 s is required; a hydrophilic silicone or emulsion blend should be used for that application.