Characterization of the amino silicone fluid supplied by Ningbo Runhe Chemical Industry Co., Ltd. for textile soft finishing begins with the siloxane backbone in which polydimethylsiloxane chains carry pendant aminoalkyl groups, most commonly aminopropyl or aminoethylaminopropyl substituents. The fluid is ordinarily supplied as a clear to slightly hazy liquid with an active silicone content above 95 wt% before emulsification. The amine value is typically controlled within 0.1–0.9 meq/g, and the bulk viscosity at 25°C ranges from 500 mPa·s to 5000 mPa·s when measured by rotational viscometry under ISO 2555. Conversion to an aqueous dispersion is carried out in a 500 L stirred vessel using nonionic emulsifier blends with a hydrophilic-lipophilic balance between 10.5 and 13.5, with inversion from oil-continuous to water-continuous phase occurring at controlled stirring speeds of 300–800 rpm. The resulting emulsion is adjusted to 20–30 wt% silicone active content and a final pH of 5.0–7.0 using dilute acetic acid. Hard water above 150 mg/L CaCO₃ should be avoided during dilution because divalent cations compress the surfactant electrical double layer and destabilize the dispersion. In bulk storage, the emulsion should be kept in sealed HDPE containers between 5°C and 35°C; viscosity drift beyond ±20% of the initial reading under ISO 2555 indicates hydrolysis or progressive condensation of residual silanol groups.
How Does Amine Content Modulate Inter-Fiber Lubrication and Handle?
The amine value directly controls the degree of protonation at acidic bath pH, which determines the affinity of the emulsified polymer for negatively charged cotton, viscose, and wool surfaces. In exhaust processing on cotton knit, the silicone emulsion droplets shift from a neutral or weakly negative zeta potential to a positive zeta potential upon acidification with acetic acid, promoting electrostatic attraction and deposition. Typical exhaust bath conditions use pH 5.5–6.5, a liquor ratio between 1:8 and 1:12, and a temperature of 35–45°C for 20–30 min. At low amine values of 0.1–0.3 meq/g, the cured film is dry and elastic, and the kinetic surface friction measured by a KES-FB4 surface tester gives mean coefficient of friction values in the range 0.14–0.20. At 0.5–0.9 meq/g, the finish becomes softer but more hydrophilic after protonation, and yellowing under thermal stress increases. The influence of amine value on handle and whiteness is not linear; plant trials on 190 g/m² cotton interlock have shown that softness improvement beyond 0.6 meq/g is often accompanied by a measurable whiteness loss after stenter drying at 150°C for 60 s. Because published data for narrow amine value increments in this specific configuration is limited, optimization is best performed by systematic pad trials with fixed drying conditions and fabric construction.
| Parameter | Amine value 0.1–0.3 meq/g | Amine value 0.4–0.6 meq/g | Amine value 0.7–0.9 meq/g | Test method |
|---|---|---|---|---|
| Handle character | Dry, elastic, low greasy drape | Balanced softness and surface fullness | Strong softness, higher greasy drape | KES-FB4 surface tester |
| Bending stiffness reduction on 190 g/m² cotton interlock vs untreated | 20–30% | 30–45% | 40–60% | ISO 9073-7 cantilever |
| Whiteness index after 150°C for 60 s | ΔWI below 1.0 | ΔWI 1.0–2.0 | ΔWI 2.0–3.5 | AATCC 110-2015 |
| Retained softness after 5 cycles at 40°C | 30–40% | 40–60% | 50–70% | ISO 6330:2021 Type 3A then ISO 9073-7 |
| Typical emulsion particle size | 50–150 nm | 50–200 nm | 50–250 nm | ISO 22412:2017 |
Exhaust application on cotton and cotton-polyester blends is conducted in jet or soft-flow dyeing machines with a liquor ratio between 1:8 and 1:12. The amino silicone emulsion is injected into the bath after dyeing and clearing, and the bath is acidified with acetic acid to pH 5.5–6.5. After running at 35–45°C for 20–30 min, the bath is dropped without rinsing when maximum exhaustion is required. Rope processing in a jet creates high turbulence and foam; therefore a foam-control agent based on organosiloxane or polyether-siloxane chemistry is preferred over mineral-oil defoamers, which can deposit as spots on dark shades. Pad application is performed on a 2-roll or 3-roll pad mangle with roller Shore A hardness 65–75, linear pressure 20–40 N/cm, and expression 65–80% on cotton. The pad bath is prepared at 10–30 g/L of the commercial emulsion and adjusted to pH 5.0–6.0. If crosslinking is required for improved washing durability, 1–2 g/L of magnesium chloride hexahydrate can be added; however, the exact addition must be validated because excess electrolyte can cause emulsion creaming. In a continuous range running 60–100 m/min, bath pH and turbidity are monitored every 2 h; a turbidity increase above 50 NTU indicates that shear or ionic contamination has initiated coalescence.
Thermal Yellowing and Storage Stability Limits in Amino Silicone Finishing
Thermal yellowing occurs because primary and secondary amino groups in the silicone side chain undergo oxidative chromophore formation at stenter temperatures above 150°C, particularly on optically brightened white goods. The yellowing tendency is lower when the amino group is tertiary or cyclohexylamino-modified, because primary amino functionalities are more susceptible to nitrosation and carbonyl condensation during heat exposure. In a typical 8-chamber stenter with zone temperatures of 120, 130, 150, 160, 160, 150, 140, and 130°C and a dwell time of 45–90 s, the whiteness loss of a 0.5 meq/g amino silicone finish can be held below ΔWI 2.0 under AATCC 110-2015 if the final two chambers are kept below 145°C. At temperatures above 160°C, the amine oxidation accelerates, and the silicone film can also develop a harder, less elastic hand because of oxidative crosslinking. Bulk emulsion storage at 25°C is typically stable for 6–12 months; however, freeze-thaw resistance is not intrinsic and requires 5–10 wt% propylene glycol if transport below 0°C is anticipated. Strong oxidizing agents, hypochlorite bleaches, and anionic optical brighteners should be avoided because they oxidize the amino group or precipitate the cationic dispersion. Published data for extended storage under high-humidity and high-temperature warehouse conditions is limited, so each mill should perform container-specific stability checks under local climate exposure before committing to bulk inventory.
When combining amino silicone emulsions with optical brighteners or finishing auxiliaries, the order of addition and the ionic character of the co additives determine bath stability and final fabric appearance. Nonionic optical brighteners can be added before the silicone emulsion, but anionic stilbene-based brighteners may cause heterocoagulation at pH below 6.0 unless an amphoteric protective colloid is used. For durable press finishes, dimethyloldihydroxyethyleneurea resin catalyzed by magnesium chloride can reduce silicone film strength if the resin crosslinking is completed before silicone deposition; therefore the amino silicone is often applied as a separate after-wash top finish. Quaternary ammonium antistatic agents can enhance electrostatic dissipation, while polyethylene glycol ester nonionic antistats increase surface hydrophilicity and partially reduce the silicone hand. Residual hydrogen peroxide from bleaching must remain below 0.5 mg/L in the finish bath because peroxide promotes oxidation of amino groups and accelerates yellowing. In a plant run of 40,000 m of cotton sheeting, pH variation of ±0.5 units around a target of 6.0 produced visible shade variation in the final handle; automated pH dosing and in-line monitoring are therefore recommended for continuous ranges. Water hardness above 150 mg/L CaCO₃ should be softened before emulsion preparation because calcium ions destabilize the surfactant boundary layer and can form precipitates with anionic co additives.
When Pad-Mangle Application Requires High-Shear Stability and Low Foaming
Roller pad mangles generate local shear rates above 10,000 s⁻¹ in the nip gap, which can destabilize macroemulsions with particle sizes above 150 nm unless a high-molecular-weight emulsifier or a small molecule co-stabilizer protects the droplets. In continuous operations running at 60–100 m/min, the pad bath is recirculated and filtered through 50 µm screens; emulsions with a droplet size below 80 nm show higher shear stability and less tendency to deposit on rubber rollers. Foam formation is lower in microemulsion systems because the mixed surfactant layer reduces air entrainment; if foam appears, 0.1–0.3 g/L of a polyether-siloxane defoamer added continuously at the circulating line gives adequate control without modifying the fabric hand. Roller hardness influences pickup and penetration: harder rollers of Shore A 80–85 produce lower pickup and more surface finish, while softer rollers of Shore A 65–70 produce higher pickup and deeper penetration into terry loops and pile structures. The finishing bath temperature should be kept between 20°C and 30°C; above 40°C the emulsion viscosity drops and pickup decreases, while below 15°C surfactant crystallization can occur. Published engineered data for amino silicone emulsions in high-speed pad applications is limited; however, filter blocking frequency and nip deposit formation are reliable plant indicators that the selected emulsion is outside its shear tolerance.
After padding or exhaustion, the amino silicone finish is dried and fixed on a stenter frame with controlled air flow and residual moisture. The degree of film formation depends on the actual fabric temperature, not the nominal chamber temperature, because evaporative cooling delays the fabric reaching the target. On a 190 g/m² cotton interlock, a 6-chamber stenter with fan speed 1200 rpm, air flow 15,000 m³/h, and set temperature 150°C gives a fabric temperature of 120–130°C at a speed of 25 m/min. Dwell times shorter than 30 s can leave residual water that hydrolyzes the silicone film and reduces durability, while times longer than 90 s increase yellowing. Crosslinking on cotton occurs mainly through hydrogen bonding of protonated amino groups to carboxylate groups; covalent links are not formed unless an external crosslinker such as trimethoxymethylsilane or an epoxy-functional silane is added at 1–3 wt% of the silicone active content. The crosslinked film retains 60–80% of the initial softness after 5 cycles under ISO 6330:2021 Type 3A washing at 40°C, whereas an uncrosslinked film retains only 30–50%. If the stenter is also used for durable press curing at 160–170°C, the amino silicone should be applied after the resin cure to prevent amine-formaldehyde interactions and minimize whiteness loss.
Particle Size Distributions in Microemulsion and Macroemulsion Systems
Particle size controls the optical clarity, penetration, and adhesion of amino silicone finishes on different fiber assemblies. Microemulsions with particle sizes below 50 nm, measured by dynamic light scattering under ISO 22412:2017, appear transparent to translucent and penetrate into tightly woven cotton and microdenier polyester because the droplet diameter is smaller than the interfiber capillary diameter. Macroemulsions with particle sizes between 100 nm and 300 nm appear milky and deposit more on the fiber surface, producing higher bulk softness but lower washfastness. On cotton woven fabric with a pore size distribution dominated by 10–30 µm capillaries, the actual penetration difference is small; on microdenier polyester and synthetic leather substrates, microemulsion is required because macroemulsion droplets can bridge small pores and create uneven surface films. In pad application, microemulsion tends to reduce fabric bending stiffness more than macroemulsion at the same total silicone add-on because it spreads over a larger interfacial area. Stability is evaluated by accelerated aging at 50°C for 14 days; a mean diameter increase above 20% under ISO 22412:2017 indicates droplet coalescence. When the emulsion is diluted to 1% solids and allowed to stand for 24 h, a sediment layer below 0.5 mL in a 100 mL graduated cylinder is acceptable. The choice between microemulsion and macroemulsion is therefore based on fabric construction, required handle, cost constraint, and washing durability target rather than on a single universal performance criterion.
Compliance status for amino silicone oil in textile finishing is assessed against multiple standards. The substance is generally classified as a polymer under REACH and does not require monomer registration if the silicon-containing monomers have been registered under the applicable provisions. For Oeko-Tex Standard 100, the finish should meet the applicable annex limits for extractable heavy metals and total tin compounds, and the fabric should be tested under the latest published version of the standard before certification. ZDHC MRSL conformance requires absence of alkylphenol ethoxylates, perfluorinated compounds, cyclic siloxanes above prescribed thresholds, and specific amine biocides. Volatile organic compounds emitted during stenter drying can be measured by GC-MS according to ISO 16000-6; typical emissions from amino silicone emulsions are below 50 mg/m³ at 150°C when the emulsion contains less than 1% volatile methylcyclosiloxane. Wastewater discharge depends on local permits, but emulsifiers should be biodegradable under OECD 301B, with a pass level above 60% conversion in 28 days. The amino silicone fluid itself is not readily biodegradable and is removed from wastewater predominantly by adsorption to sludge. Since the exact compliance status of the Ningbo Runhe Chemical Industry Co., Ltd. grade depends on the supplied Safety Data Sheet section 15 and buyer-specific restricted substance lists, each textile mill should validate the product against its own certificate of compliance and local discharge permit before use.
What Operational Boundaries Apply to High-Shear Mixing of Amino Silicone Fluids?
High-shear mixing during emulsion preparation imposes operational boundaries because the amino silicone fluid can undergo irreversible viscosity loss if the siloxane chain is mechanically degraded. A rotor-stator homogenizer operating at 5,000–10,000 rpm for 30–60 min can reduce base fluid molecular weight by chain scission when tip speed exceeds 20 m/s; therefore lower speed planetary mixers or counter-rotating anchor stirrers are preferred for initial dilution. Once the emulsion is formed, high-shear recirculation across a pad mangle can be tolerated only if the particle size distribution remains monomodal and the pressure drop across the filters remains stable. Incompatibilities include anionic surfactants, sulfonated dyes, and strong acids below pH 3.0, which protonate the siloxane oxygen and promote siloxane bond cleavage. Alkaline conditions above pH 8.0 accelerate condensation of residual silanol groups and can cause viscosity increase or gelation in bulk storage. The operational window for a typical amino silicone emulsion is pH 4.5–7.5 in the finish bath, temperature 10–35°C, and water hardness below 200 mg/L CaCO₃. If the fabric carries residual alkali from mercerization, it must be neutralized to pH 6.0–7.0 before silicone application. At relative humidity above 60% during warehouse storage of dried finished fabric, absorbed moisture can plasticize the silicone film and slightly increase softness, but no additional chemical change occurs. Published data for siloxane depolymerization under extreme mechanical shear in textile mills is limited; therefore inline filter blocking and viscosity drift are the most reliable diagnostics for shear damage in continuous production.
