In continuous warp sizing, the comparison of PVA vs Starch & CMC in Textile Sizing is made on the basis of film mechanical properties, size-box viscosity control, and desizing effluent behaviour. Polyvinyl alcohol grades used in slashers are partially hydrolysed, typically 86.0–89.0 mol% hydrolysis, with a 4% aqueous solution viscosity of 4.0–40.0 mPa·s at 20°C. Starch is applied as native, oxidised, or esterified corn or tapioca starch; CMC is used as technical-grade sodium carboxymethyl cellulose with a degree of substitution between 0.7 and 0.9. The functional distinction is not price alone: PVA forms a tough, extensible film; starch forms a brittle, high-friction film that is easy to remove; CMC forms a hygroscopic film with high size-bath viscosity at low concentration. These properties determine size add-on, size-box stability, shed cleanliness, warp hairiness, and the desizing chemistry required before dyeing and finishing.

Does Film Elongation Rather Than Tensile Strength Control Weaving Stops?

Cast films of partially hydrolysed PVA measured according to ASTM D882 at 23±2°C and 50±5% relative humidity typically exhibit tensile strength of 39–55 MPa and elongation at break of 150–250%. In contrast, modified corn starch films exhibit 20–32 MPa tensile strength and 2–6% elongation; CMC films with DS 0.7–0.9 fall between 28–40 MPa tensile strength and 10–20% elongation. The elongation difference is critical in shed cycling because a size film with low elongation fractures under repeated bending and inter-yarn abrasion at lease rods and drop wires. Starch-size films fail cohesively at low strain, generating powder and fibre pull-out; PVA-size films deform without rupture, but high elongation can increase blocking under high humidity. CMC film elongation is intermediate, but its hygroscopicity reduces glass transition and may increase yarn tackiness unless formulated with lubricants.

On sized yarn, ISO 13934-1 tensile strength retention of 9.0–12.0% size add-on on 20 Ne cotton warps is common for starch; PVA-based sizes are typically applied at 5.0–8.0% add-on because the higher film toughness permits lower add-on. However, too low an add-on below 4.0% fails to cover protruding fibres and increases warp stops on air-jet looms. Published loom-stop data for every yarn count and loom configuration is limited; direct comparisons require identical yarn lots, size-box settings, and shed geometry.

Size-box viscosity control differentiates the three polymers more sharply than film data alone. Starch pastes cooked at 85–95°C undergo retrogradation when the liquor temperature falls below 60°C, causing apparent viscosity to rise by 30–70% over 6 h in unjacketed storage. This drift changes wet pickup at the squeeze roll and produces uneven size add-on across the warp sheet. Carboxymethyl cellulose solutions exhibit pronounced pseudoplasticity: viscosity under high shear in a size box can fall by 10–20% from the low-shear Brookfield value, and prolonged circulation may cause irreversible chain scission, reducing thickening efficiency. Partially hydrolysed PVA at 75–80°C is more stable; supplier technical bulletins report viscosity variation within ±5% over 8 h in closed circulation. The operational boundary for PVA is therefore a narrower solids window: too high a PVA concentration at 10.0 wt% or above can produce sheet-splitting and sticky size boxes, while too low a concentration below 6.0 wt% may not deliver adequate film coverage. Wet pickup is controlled at 70–100% for cotton and 50–80% for polyester/cotton warps; the actual pickup depends on roll hardness and linear nip load.

Comparative Film, Adhesion, and Desizing Data for Slasher Formulations

The following ranges are compiled from polymer supplier technical bulletins and textile auxiliary handbooks. Values are indicative and must be verified against the specific grade and slasher configuration.

The most decisive table value for downstream processing is hot-water desizing efficiency. Starch without enzymatic desizing leaves residual size on cotton; PVA and CMC are removed more completely in hot water, but PVA’s low BOD₅/COD ratio shifts the effluent burden to COD rather than BOD. In mills with an anaerobic-aerobic biological treatment plant, starch-based size is preferred because of rapid degradation; PVA may pass through conventional activated sludge and require extended aeration or oxidative pretreatment.

Adhesion to hydrophobic polyester fibre differentiates PVA from starch. Native starch films show poor interfacial adhesion to polyester, producing fibre-to-fibre bonding failure and size shedding. Formulations for 65/35 polyester/cotton warp yarns therefore replace part or all of the starch with PVA at 5.0–8.0 wt% solids, often with an acrylic co-binder at 5–10 wt% of total solids. CMC is added at 5–15 wt% of total solids to control size-box viscosity and improve film uniformity, but its sensitivity to hard water above 200 ppm as CaCO₃ requires softened or conditioned water. Published comparative adhesion values for every slasher formulation are limited; size selection is normally confirmed by warp-weaving trials rather than by film peel tests alone.

When Desizing Effluent Load Dictates Polymer Choice in Continuous Processing

Continuous desizing on an open-width washer requires size removal above 90% before bleaching and dyeing. PVA sizes are desized with hot water at 80–90°C and oxidative agents such as persulphate or hydrogen peroxide; CMC desizing uses hot water with nonionic detergents and soda ash; starch requires enzymatic desizing with alpha-amylase at 60–80°C and pH 6.0–7.5. In mixed PVA-starch sizes, a two-stage desizing process is typical: enzymatic starch conversion followed by hot-water PVA removal. The effluent from PVA-containing desizing baths has high COD, commonly 5,000–20,000 mg/L depending on bath carryover and add-on, with BOD₅/COD ratios below 0.15. Starch desizing effluent exhibits BOD₅/COD ratios of 0.5–0.7 and is more readily mineralised. CMC effluent is intermediate. These ranges are process-specific; sampling and mass balance are required for compliance with discharge permits. COD is measured by ISO 6060, and BOD₅ by ISO 5815-1 or equivalent methods.

Storage and formulation boundaries are equally specific. PVA powders should be pre-mixed in cold water before heating to 85–95°C to prevent lump formation; extended cooking above 95°C under high shear can reduce viscosity. CMC should be dissolved in cold, soft water to avoid gel particles; hard water above 200 ppm as CaCO₃ can reduce viscosity and cause precipitation. Starch size must be used before retrogradation, or a thermostable size box must maintain the liquor above 60°C. These limitations prevent direct substitution without reformulation.