(A heavy reliance on film-forming polymers for warp sizing, particularly on high-speed weaving machinery operating above
800 picks per minute, has driven the adoption of polyvinyl alcohol (PVA) across cotton, polyester-cotton, and filament yarn processing. The material is supplied as a dry granular resin differentiated by two primary attributes: degree of hydrolysis, reported as mol% residual acetate groups, and 4 % solution viscosity at
20 °C per
ISO 15023-1:2017. In slasher sizing kitchens, the selection between partially hydrolyzed (typically
86–89 mol%) and fully hydrolyzed (
98–99 mol%) grades defines film solubility, tensile elongation, and adhesion to hydrophobic fibers. A consistent limitation observed across all PVA handling is the requirement for pre-dissolution
≥85 °C with high-shear mixing to prevent microgel formation; moisture content of incoming granules must remain below
5 wt% to avoid lumping in the make-up kettle.)
Why Does Partial Hydrolysis Dominate Warp Sizing Formulations?
Partially hydrolyzed grades such as the
5-88 type (viscosity
4.5–6.5 mPa·s, hydrolysis
86–89 mol%) exhibit dry film elongation values between
150 and
250 % when tested per
ASTM D882. This extensibility is critical for yarns subjected to cyclic whip-lash on air-jet and rapier looms, where film brittleness generates shedding dust that increases loom downtime and compromises reed cleanliness. The residual acetate groups depress crystallinity and lower the glass transition temperature to approximately
65–70 °C, allowing the size film to deform plastically without micro-cracking under instantaneous tension spikes exceeding
3 cN/dtex. Adhesion to mercerized cotton warps, measured as pulling force in a Zweigle G 552 yarn-to-yarn separation test, typically falls between
0.8 and
1.2 N/mm for
5-88 films, rising to
1.5–1.8 N/mm for
17-88 grades (viscosity
20.5–24.5 mPa·s) that deposit a heavier size add-on. Fully hydrolyzed polymers with
98–99 mol% hydrolysis, exemplified by
20-99 resin (viscosity
28–32 mPa·s), deliver higher film tensile strength of
60–80 MPa but elongation rarely exceeds
80 %, making them unsuitable for staple-fiber yarns yet valuable as a protective film for zero-twist continuous filament nylon where rigidity is desired.
Slasher Sizing Conditions and Film Morphology
Standard industrial slashers equipped with
12-cylinder drying sections apply PVA size liquor at solids concentrations of
6–10 wt% in the size box, maintained at
85–90 °C. Viscosity drift in the size box is minimal when pH is buffered between
6.5 and
7.5; contact with borax or alkaline persulfate desizing agents must be avoided as they induce crosslinking and a rapid viscosity climb that defeats penetration. Drying cylinder surface temperatures are typically profiled from
120 °C on the wet-end cans to
140 °C on the dry-end. Exceeding a peak metal temperature of
145 °C causes water to boil beneath the film, producing blush defects and a measurable reduction in film clarity—quantified as haze above
12 % per
ASTM D1003. Warp break monitoring on a Toyota JAT810 air-jet loom weaving
20 Ne cotton at
850 rpm shows break rates of
0.5–1.0 breaks per
100,000 picks when sized with
5-88 at
8 % add-on, providing a baseline for economic benchmarking against starch.
In the finishing of woven cotton sheeting and polyester-cotton blend shirting, a fully hydrolyzed PVA grade with viscosity
5.0–7.0 mPa·s and ash content below
0.5 wt% is padded as a hand-building finish that imparts a crisp, non-foaming handle. The finish bath is applied on a two-roll padder at a wet pick-up of
65–80 % followed by drying on a stenter at
110–130 °C. Circular bend stiffness measured per
ASTM D4032 increases linearly with PVA add-on up to
3 % on-weight-of-fabric, after which stiffness plateaus and the risk of surface marring on subsequent calender rolls becomes apparent. Unlike polyvinyl acetate homopolymer emulsions, PVA does not introduce tack or block under humid conditions because of its lower surface energy and complete cold-water re-solubility, yet this same solubility means that uncrosslinked finishes survive fewer than
5 home laundry cycles as defined by
AATCC TM135.
If PVA is Applied via Pad-Dry-Cure as a Permanent Finish, What Crosslinker Chemistry Prevents Laundering Loss?
Reactive PVA systems for durable press or soil-release finishes require co-application with a crosslinking agent such as dimethyloldihydroxyethyleneurea (DMDHEU) or a low-formaldehyde glyoxal resin. A representative formulation contains
40 g/L PVA (
5-88),
60 g/L DMDHEU (
45 % solids), and
12 g/L magnesium chloride hexahydrate catalyst, padded at
70 % expression and cured at
160 °C for
3.5 minutes. The resulting interpenetrating network raises the fabric bending rigidity from an initial
120 mg·cm (Shirley stiffness tester) to
220–260 mg·cm with retention above
80 % after
20 launderings. A documented processing conflict arises when oxalic acid catalysts are substituted for magnesium chloride: the liberated acid hydrolyzes the acetate ester residuals on partially hydrolyzed PVA, generating acetic acid vapor that corrodes tenter-frame rails and reduces fabric tensile strength by
8–12 % as measured by
ASTM D5034 grab test. To circumvent this, fully hydrolyzed PVA (
98–99 mol%) is preferred in acid-catalyzed systems, though its lower hydroxyl reactivity demands a cure temperature increase of
10–15 °C.
Nonwoven binder applications demand low-ash PVA with a hydrolysis degree of
98–99 mol% and a viscosity range of
18–25 mPa·s, designated as
17-99 or
20-99 types. These grades are spray-applied onto carded polyester-viscose webs at
2–5 g/m
2 dry add-on, then thermally bonded through calendar rolls heated to
160–180 °C. Dry tensile strength of the bonded web measured according to
ISO 9073-3 achieves
45–60 N/5 cm in the machine direction, exceeding that of ethylene-vinyl acetate binder of comparable add-on by approximately
20 %, while maintaining a soft drape absent from styrene-butadiene latex-bonded fabrics. Ash content is controlled to
≤0.3 % to prevent discoloration on contact with oxidative bleaching chemistries downstream.
Desizing Effluent Biodegradability and COD Load
Dissolved PVA size contributes a chemical oxygen demand (COD) load of
1,600–1,800 mg O₂/g resin, while its inherent biochemical oxygen demand after
5 days (BOD₅) under
OECD 301F conditions typically falls below
10 mg O₂/g. This BOD₅/COD ratio of
≤0.01 classifies the polymer as poorly biodegradable in standard domestic wastewater treatment, although specialized activated sludge acclimated to PVA-containing desize effluent can achieve removal efficiencies exceeding
90 % within a hydraulic retention time of
24 hours. Membrane-based size recovery systems operating with
0.1 µm ultrafiltration modules achieve PVA recoveries of
92–98 % from hot desize wash water, directly reducing COD discharge and representing the primary abatement strategy in integrated mills subject to ZDHC Wastewater Guidelines Version
2.1. Quantitatively, the COD of desize bath effluent after UF recovery can be driven below
3,000 mg/L, permitting downstream biological treatment without inhibition of nitrifying bacteria.
Comparative Film Properties and Warp Breakage Rates
The following table, derived from mill-scale slashing trials and laboratory film testing, positions PVA grades against other sizing agent chemistries on mechanical performance and environmental load criteria.
| Property /Test Method | PVA 5-88 (partial) | PVA 20-99 (full) | Oxidized Corn Starch | Sodium CMC | Acrylic Copolymer Binder |
|---|
| Film tensile strength (ASTM D882), MPa | 40–55 | 60–80 | 22–34 | 50–70 | 8–15 |
| Film elongation (%), ASTM D882 | 150–250 | 50–80 | 2–5 | 10–20 | 400–650 |
| Adhesion to cotton, N/mm (EN 13780) | 0.8–1.2 | 0.3–0.6 | 1.5–2.0 | 1.0–1.5 | 0.5–0.8 |
| BOD₅ (OECD 301F), mg O₂/g | 5–10 | 5–10 | 400–600 | 10–30 | <5 |
| COD (ISO 6060), mg O₂/g | 1,600–1,800 | 1,600–1,800 | 800–1,200 | 1,200–1,500 | 1,500–2,000 |
| Warp breaks /100,000 picks, 20 Ne cotton, 850 rpm air-jet | 0.5–1.0 | not recommended | 2.0–5.0 | 1.0–3.0 | <0.5 |
In weaving sheds where scratchy handle and high loom dust generation from oxidized starch cause operator discomfort and elevated warp stops, conversion to a
5-88 size formula offers reductions in atmospheric dust concentration below the
3 mg/m
3 inhalable fraction threshold specified by the UK Health and Safety Executive EH40/2005 workplace exposure limit, provided size shed exhaust ventilation meets
15 air changes per hour. Acrylic copolymers, while yielding the lowest warp break rates owing to extreme film elongation, carry a price premium of
2.5–3.5 times over PVA and demand solvent-based desizing that conflicts with ZDHC detox commitments.
Regulatory Compliance Matrix for Textile Auxiliaries
PVA grades manufactured under controlled hydrolysis and containing residual methanol below
0.5 % consistently pass the conformance requirements of major eco-label and chemical management systems.
| Regulation /Standard | Test Method or Clause | PVA Compliance Status |
|---|
| ZDHC MRSL Version 3.1 | Substance detection in raw material | Meets all limits; PVA not listed as restricted |
| OEKO-TEX Standard 100, Annex 4 | Extractable heavy metals, formaldehyde | Certifiable for product class I (infants) when ash <0.3% |
| REACH (EC) No 1907/2006 | SVHC candidate list, Annex XVII | No restrictions; registration as polymer under Article 2(9) |
| FDA 21 CFR 177.1670 | Polyvinyl alcohol film for food contact | Compliant with extractives <4 % in water and heptane |
| EC 10/2011 Plastics FCM | Migration limits for vinyl acetate monomer | Monomer <2 mg/kg food simulant (10x below SML) |
| GOTS Version 7.0 | Chemical inputs criteria | Approved for sizing and finishing with biodegradation plans |
The ash content ceiling of
0.3 % is a recurring specification driven not by polymer performance but by metallic catalyst residues (predominantly sodium as sodium acetate) that interfere with reductive bleaching processes and can form pinhole defects in downstream polyurethane laminations.
