Concentrated Hydrophilic Silicone Oil for Towel RH-NB-962G-5GS

Model RH-NB-962G-5GS is a concentrated hydrophilic silicone oil formulated for the finishing of terry towelling and loop-pile cellulosic substrates. The -5GS suffix denotes a five-gallon supply unit, while the base code identifies the hydrophilic silicone chemistry. In production-scale towel finishing, the product is diluted with demineralised water to working concentrations between 5 g/L and 30 g/L in pad baths or 0.5–2.0% on weight of fibre in exhaust processes. Unlike conventional amino-functional silicone softeners that generate surface hydrophobicity, this class of concentrate retains sufficient water transport through the terry loop structure to allow AATCC TM 79 rewet times of ≤3 s on bleached cotton after curing. The product is also expected to minimise the post-wash hydrophobic rebound that occurs when hydrophobic polydimethylsiloxane films reorient at the fibre surface; however, published data for this specific configuration is limited, and the supplier’s certificate of analysis should be used to fix incoming quality windows.

Physicochemical specification and raw material quality windows

The concentrated product is typically a translucent to slightly opalescent fluid with a nonionic or weakly cationic character. Incoming inspection at textile chemical warehouses should include measurement of active solids by ISO 3251 at 105 °C ± 2 °C, pH of a 10 wt% aqueous dilution by ISO 976, and Brookfield viscosity at 25 °C by ISO 2555. Typical acceptance bands for hydrophilic silicone concentrates in this category are 55–65 wt% solids, pH 6.0–7.5, and viscosity 1000–5000 mPa·s. Density at 20 °C is generally 0.98–1.03 g/cm³ when measured by ISO 2811. The emulsion particle size after dilution to 10 wt% should remain below 500 nm as determined by laser diffraction per ISO 13320, because larger particles can deposit unevenly on cotton fibre and reduce laundering durability. Storage at 5–40 °C in sealed containers is required; freeze-thaw cycling above 3 cycles may split the emulsion phase and is not covered by the supplier’s stability warranty.

When an incoming batch falls outside viscosity or particle-size limits, it should be isolated and not fed into automated dosing lines, because high-viscosity lots can produce flow meter drift and uneven pick-up on padding mangles.

Compared with standard amino silicone softeners, RH-NB-962G-5GS is differentiated by the presence of hydrophilic polyether blocks or equivalent hydrophilic segments grafted onto the siloxane backbone. The practical consequence is that treated terry cloth retains capillary wicking and can be certified by AATCC TM 79 as absorbent; standard aminofunctional silicones often produce rewet times above 10 s after a single padding pass, whereas the hydrophilic product is targeted to remain below 3 s at comparable application levels. Hydrophobic softeners also reduce dyehouse re-wetting during repair operations and can induce uneven blotching if garments are re-dyed. The polyether modification reduces the contact-angle hysteresis associated with post-bath drying, but it also lowers softness efficiency per unit of applied silicone; consequently, application doses are usually 5–20% higher than those used for hydrophobic aminofunctional fluids to reach the same handle ranking under AATCC TM 202.

How does the polyether modification alter rewetting and washfastness after curing?

The polyether side chains act as internal hydrophilic channels that reduce the interfacial energy of the cured silicone film. During stenter curing at 120–150 °C for 60–120 s, the siloxane matrix crosslinks and anchors to the cotton surface through condensation with cellulosic hydroxyl groups. The polar segments remain partially oriented toward the aqueous phase during use, allowing water droplets to penetrate the terry loops rather than sitting on the pile surface. In standard hydrophobic silicones, the methyl groups of polydimethylsiloxane dominate the outer monolayer after heat treatment, and the resulting surface resists rewetting even though the fibre bundle interior remains hydrophilic. Washfastness testing according to AATCC TM 61, test method 2A, with an alkylene-bridged detergent compresses this difference: hydrophobic silicone films show restored surface hydrophobicity after 5 wash-dry cycles, whereas the hydrophilic concentrate is formulated to retain AATCC TM 79 rewet values below 5 s through 20 cycles on bleached cotton terry. Published data for this specific product under full-scale wash testing is limited, so the supplier’s recommended add-on should be validated on plant-processed articles.

In exhaust application on rope dyeing or jet machines, the product is fed after the final cold rinse and prior to unloading. Typical machine parameters are liquor ratio 1:8–1:12, bath temperature 30–40 °C, and circulation time 20–30 min at pH 5.5–6.5. The bath pH is maintained with acetic acid to promote attraction between the weakly cationic emulsion particles and the anionically charged cotton surface. If the temperature exceeds 45 °C, the emulsion may destabilise and deposit on reel or guide surfaces; if pH falls below 5.0, cellulose degradation can occur, measurable as a loss of tensile strength according to ASTM D5034. The concentrate should be pre-diluted in a side tank to 5–10 wt% before injection into the jet machine to prevent localised high-shear demulsification at the addition port. Production reports from textile chemical application teams indicate that dosing undiluted concentrate directly into turbulent main circulation loops can produce batch-to-batch variability of ±15–20% in final fabric absorbency.

When pad application requires a stable concentrated dilution under high shear

Padding operations with vertical or horizontal mangles impose high shear at the nip and in the trough circulation line. The diluted emulsion must be shear-stable enough to survive pumping through a gear pump or diaphragm metering system without particle coalescence. Typical pad-bath concentrations are 5–30 g/L, wet pick-up is held at 70–85% on cotton terry, and the mangle nip pressure is set to 2–4 bar. The pad bath should be prepared by adding the silicone concentrate to demineralised water under moderate stirring; softened water containing polyvalent metal ions should be tested for electrolyte stability because calcium and magnesium can compress the electrical double layer and accelerate creaming. Compatibility with pad-bath additives used for towel finishing—optical brighteners, anti-slip agents, and low-formaldehyde or formaldehyde-free crosslinkers—is generally acceptable when the final bath pH is kept below 7.5. High aldehyde resin systems may require a preliminary jar test because methylol-containing compounds can react with residual amino groups in the silicone and reduce absorbency after curing.

On continuous stenter frames with automatic dosing, the diluted silicone is often metered into the trough via magnetic flow meters. The presence of gel particles larger than 1 mm can obstruct narrow-gap valves and produce streaks along the fabric width; therefore, in-line filters of 100–200 µm are recommended. If the concentrate is pumped from drum to day tank, avoid gear pumps with recirculation bypass lines that impose repeated mechanical shear above 10 000 s⁻¹, because this can split the emulsion and lead to oil spots on finished goods. Stenter temperature must be held within ±5 °C of the target curing window: lower temperatures leave the film insufficiently fixed, while higher temperatures increase the risk of yellowing on bleached white towels.

Evaluating laundering durability under alkaline detergent stress

Durability of the hydrophilic finish is assessed by launderometer protocols rather than single-position immersion tests. AATCC TM 61, test method 2A, uses 150 ml wash liquor, 50 steel balls, and 45 min at 49 °C; the protocol imposes mechanical abrasion that removes loosely bound silicone and exposes the underlying cotton surface. After 5 launderometer cycles, the treated towel should still show AATCC TM 79 rewet times below 5 s and a handle retention of at least 80% compared with the unwashed finished article as measured by AATCC TM 202. Yellowing on white goods is evaluated after 180 °C hot pressing or after storage under polyethylene film at 60 °C for 7 days; standard amino silicone oils often produce discernible yellowing under these conditions due to oxidation of aminopropyl groups, while the hydrophilic product’s reduced amino content is intended to limit whiteness loss to ΔE*ab <0.5 when assessed according to AATCC TM 110.

Not all resin systems tolerate concentrated hydrophilic silicone in the same pad bath

Because the silicone molecule may contain secondary amino groups, reactive resin systems based on dimethyloldihydroxyethyleneurea or N-methylol acrylate derivatives can consume the hydrophilic segment under acidic curing and leave a hydrophobic surface. When the pad bath includes a cellulosic crosslinker at 30–60 g/L, the bath should be kept at pH 4.0–5.0, and the silicone addition should be made last. If visible gelation occurs within 30 min at room temperature, the bath should be rejected. Similarly, addition of anionic wetting agents in the same bath can form coacervates with weakly cationic emulsions; a jar test with 0.5 g/L anionic surfactant at cure temperature reveals whether phase separation occurs. Do not combine with amine-reactive fluorocarbon extenders in the same bath, as fluorocarbon film formation can disrupt the hydrophilic channels and produce an inconsistent surface energy.

Under REACH Regulation (EC) No 1907/2006, the product must be used in accordance with the safety data sheet and not discharged undiluted into municipal wastewater without treatment. The weakly cationic emulsion can bind to suspended solids in biological treatment; textile mills discharging under integrated pollution prevention and control permits should conduct jar settling tests to verify that residual COD does not exceed the site consent. RoHS Directive 2011/65/EU restrictions are not implicated for textile use, but compliance with the brand’s restricted substance list should be verified for finished article claims.

In mills processing high-pile terry constructions with dense loop height above 3 mm, the wet pick-up required to achieve uniform silicone deposition can rise beyond 85%. Under these conditions, the pad bath concentration should be reduced to the lower end of the range, and a second extraction pass may be necessary to avoid overloading the pile tips. Failure to control nip pressure and emulsion stability simultaneously can produce edge-to-centre absorbency differences exceeding 2 s in AATCC TM 79 testing, which is unacceptable for split-lot export programmes to buyers specifying uniform rewet performance across the full fabric width.