The PVA film vs PE film water-soluble packaging shift is observed in unit-dose detergent sachets, agrochemical water-soluble pouches, dye transfer control bags, and pharmaceutical containment. The substitution is driven not by mechanical property parity or raw-material cost equivalence, but by a binary end-of-use event: complete dissolution of the package in water. Polyethylene film cannot provide that event, and the conversion therefore re-orders packaging line design around moisture protection, seal geometry, and film handling.

Commercial cold-water-soluble polyvinyl alcohol grades are partially hydrolyzed polyvinyl acetate with hydrolysis degree between 86 mol% and 89 mol% and 4 % aqueous solution viscosity from 20 mPa·s to 30 mPa·s at 20 °C per JIS K6726. Fully hydrolyzed grades above 98 mol% enter solution only at elevated temperature, typically 70–85 °C, and are specified where hot-water triggering is required. Polyethylene film, by contrast, is usually a blown or cast LLDPE/LDPE structure with a melt index of 0.5–2.0 g/10 min at 190 °C and 2.16 kg per ISO 1133-1:2022. It remains insoluble in neutral aqueous media below its melting region because the semicrystalline polyethylene backbone lacks hydrolyzable functional groups.

What Limits Cold-Water Solubility in High-Crystallinity PVA Film Grades?

Cold-water solubility is controlled primarily by the fraction of residual acetyl groups and the crystalline sequences developed during drying. In partially hydrolyzed PVA, acetate units interrupt hydrogen-bonded sequences and reduce crystallite size. At hydrolysis degrees below 86 mol%, dissolution in water at 10 °C is rapid, but film blocking and creep under load increase on roll stock. At hydrolysis degrees above 92 mol%, dissolution time for a 38 µm film in 750 mL agitated water at 20 °C can exceed 120 s, which is outside the acceptable range for most unit-dose detergent machine cycles. Because no single ISO method covers film dissolution time, converter specifications typically use an internal agitated immersion method; published data for a standardized dissolution method is limited.

Plasticizer selection shifts the dissolution window. Glycerol, sorbitol, and trimethylolpropane at 10–20 wt% reduce glass transition temperature and hydrogen-bond density. Glycerol-rich films absorb atmospheric moisture and lose dimensional stability above 60 % RH. The processing conflict is that soft, rapidly dissolving film blocks more easily, while stiff, low-plasticizer film can shatter during cold forming. Equilibrium moisture content at 25 °C and 50 % RH for a 25 µm cold-water PVA film is typically 8–12 %; at 75 % RH it rises to 15–20 %. Tensile strength falls by 30–50 % as moisture content moves from 10 % to 20 %, which makes sealed overwrapping mandatory in high-humidity distribution. PE film under identical conditions absorbs less than 0.01 % water per ASTM D570 and retains its mechanical properties.

Mechanical and Barrier Trade-Offs in PVA Film Formulation

Direct substitution of PE by PVA cannot be designed on thickness equivalence alone because the unstabilized mechanical response differs by more than a factor of two in elongation and by more than an order of magnitude in water-vapour transmission. The ranges below are representative for 25–40 µm films; film-grade verification is required because plasticizer content, hydrolysis degree, and molecular weight shift the PVA data set more than the PE data set.

The data explain the packaging shift: PVA is specified for the dissolution event, not for barrier permanence. A PVA pouch containing a hygroscopic powder must be placed inside a secondary PE or foil pouch to prevent premature moisture gain. In contrast, PE is selected where the film must resist water ingress and maintain seal integrity for months under uncontrolled humidity.

On a production-scale PVA solution-casting line, the film is formed by coating a 20–30 wt% aqueous PVA solution onto a stainless-steel carrier belt through a slot die with a die gap of 0.5–1.2 mm. The solution is degassed under vacuum at 50–150 mbar to eliminate microbubbles that produce pinholes in the dried film. Drying-zone temperatures typically step from 80 °C to 120 °C, and the residual moisture target for winding is 8–12 %. Below 8 % the film becomes brittle and slitting edge cracks increase; above 14 % blocking between adjacent layers causes unwind tension spikes on sachet form-fill-seal machines.

PE blown film manufacture operates in a different processing window. LLDPE is extruded through a die gap of 1.5–2.5 mm at a blow-up ratio of 2.0–3.0 and a frost-line height controlled within ±50 mm on lines with a screw length-to-diameter ratio of 24:1 to 30:1. The PE line is less sensitive to ambient humidity but more sensitive to melt-temperature uniformity; gauge variation above ±5 % produces seal-pressure variability on high-speed sealing jaws. PVA film on form-fill-seal equipment requires precise jaw temperature control, commonly 120–160 °C, dwell from 0.2 s to 0.8 s, and pressure from 2 bar to 4 bar. Above this window, film shrinkage and burn-through occur; below it, seal strength remains below 2 N/15 mm in peel-mode testing.

When Polyethylene Film Retains Packaging Dominance in High-Humidity Logistics

In distribution chains where relative humidity exceeds 70 % for more than 48 h, PVA film without an overwrap absorbs atmospheric moisture and exhibits blocking, seal softening, and premature partial dissolution at folds. The operational boundary is therefore set by moisture ingress, water activity of the fill, and the presence of secondary containment. PE film retains dominance for dry food, medical devices, and industrial parts where package integrity must survive condensation cycles and hydrostatic head. Its water-vapour transmission rate below 8 g/(m²·day) under ISO 15106-2 conditions prevents the contained product from hydrating, while PVA film at 200–600 g/(m²·day) actively transmits moisture.

Polyethylene also demonstrates superior puncture and tear resistance. Elmendorf tear strength for a 40 µm LLDPE film typically falls between 400 mN and 800 mN in the machine direction per ISO 6383-2. PVA film tear values after conditioning at 50 % RH are often 100–300 mN. This difference becomes critical for heavy or sharp-edged fill contents, where PVA film requires thicker gauge or reinforcement. The water-solubility shift is therefore not a universal replacement; it is confined to applications where the dissolution value outweighs puncture and moisture-barrier requirements.

The environmental fate of PVA after dissolution is a further operational boundary. In wastewater treatment, PVA can be biodegraded by acclimated sludge; OECD 301B testing has reported degradation above 60 % in 28 days under optimized conditions, while PE remains below 5 % in the same test. However, cold water and short hydraulic retention times can release dissolved PVA through municipal treatment if sludge acclimation is absent. PVA film intended for food-contact applications is evaluated under FDA 21 CFR 177.1670 or EU Regulation (EU) No 10/2011 where applicable, with specific migration limits depending on plasticizer type and residual vinyl acetate monomer content. Because PVA film is not a drop-in replacement for heat-sealable PE in all packaging, converters typically qualify each film grade with sachet dissolution time at 10 °C, 20 °C, and 40 °C, seal strength after conditioning at 50 % RH and 75 % RH, and blocking resistance under 0.5 kPa load at 40 °C for 24 h.