ELVANOL 71-30

ELVANOL 71-30 is a fully hydrolysed polyvinyl alcohol resin supplied as white to off-white granules. The polymer is identified by CAS 9002-89-5. The manufacturer specifies a 4 % aqueous solution viscosity of 27.0–33.0 mPa·s at 20 °C and a degree of hydrolysis of 99.0–99.8 mol%. These values place the grade in the high molecular weight, fully hydrolysed segment of PVOH homopolymers. The resin is used in aqueous solution systems where high film tensile strength, controlled water resistance, and high binder efficiency are required. It is not a plasticised compound and contains no intentionally added plasticizer.

Because the degree of hydrolysis is specified at 99.0–99.8 mol%, the residual acetate content is low, typically 0.2–1.0 mol%. This increases crystallinity and the melting endotherm, commonly reported above 220 °C by differential scanning calorimetry. The material is not cold-water soluble; full dissolution requires heating under agitation. These properties distinguish it from partially hydrolysed grades in the same product family and from lower molecular weight grades with identical hydrolysis.

What Does the Specification Set Control in Downstream Processing?

The 27.0–33.0 mPa·s range is not a cosmetic specification. It controls solution handling and dry film strength simultaneously. At a fixed solids concentration, a higher 4 % viscosity indicates higher molecular weight and a longer main chain. In solution preparation, this gives a nonlinear increase in apparent viscosity above 8 % solids. Metering pumps and tank agitators must be designed for this behaviour. Positive displacement diaphragm or screw pumps are used in preference to centrifugal pumps at addition rates below 1 m³/h to maintain stable flow.

Batch-to-batch viscosity variation within the specification can change size press pickup at constant rod pressure. Production experience indicates that a shift of 1.0 mPa·s in the 4 % inspection viscosity can be visible as a change in surface holdout when the size press is operated above 500 m/min. The hydrolysis limit matters because residual acetate groups influence water sensitivity and crystallisation rate. At 99.0–99.8 mol%, the dried film has lower equilibrium water absorption than partially hydrolysed grades, but the solution requires more heat input and longer dissolution time.

For food-contact applications, the formulated article must comply with the applicable conditions of 21 CFR 176.170 for paper and paperboard components or 21 CFR 175.105 for adhesives. The polymer itself is covered by REACH registration for polyvinyl alcohol; the supplier should be consulted for the current registration number and any restriction. No chlorinated solvents or aromatic plasticizers are present in the resin as supplied.

In a production-scale solution preparation area, the granular resin is first dispersed in cold water at 20–30 °C to prevent lump formation. The dispersion is then heated under low-shear agitation to 90–95 °C and held for 20–30 min. A jacketed mixing vessel with baffles and a turbine impeller is used. If the resin is added too quickly, partially swollen granules form agglomerates that require extended heating and can blind a 100 µm screen. Downstream filtration through 100–200 µm is recommended before the solution enters a size press or adhesive coating head.

Storage conditions require sealed bags and silos below 40 °C. At relative humidity above 60 %, the granules take up moisture, flow behaviour in a rotary screw feeder deteriorates, and bridging may occur. Pre-drying is not normally required for aqueous solution use, but for any melt-processing trial the powder should be dried to ≤0.5 % moisture because residual moisture accelerates hydrolysis and viscosity loss above 180 °C.

In melt-processing trials without plasticizer, the onset of thermal decomposition is near 200 °C; the polymer cannot be processed as a conventional thermoplastic without external plasticizer or water. Twin-screw compounding with glycerol or sorbitol is performed with barrel temperatures below 190 °C and a vent-port vacuum to remove water. The fully hydrolysed grade has higher melt viscosity than partially hydrolysed grades at the same plasticizer content, which increases torque and requires a machine with sufficient specific torque. Published data for this specific configuration is limited; compounding trials should start at 10–15 % plasticizer and 150–180 °C barrel temperature.

Surface Sizing and Warp Sizing Under Mill Conditions

On a rod-metering or film-press size press, ELVANOL 71-30 is co-applied with oxidized or modified starch at total solids of 4–8 %. The PVOH fraction is usually 10–30 % of the dry size. Size press roll temperature is held at 60–70 °C. The benefit is evaluated by paper surface porosity and water absorption using ISO 535:2014, dry pick resistance on an IGT tester, and surface strength. Because the fully hydrolysed film is insensitive to water after drying, the Cobb value is lower than that of an all-starch control at comparable pickup. The high molecular weight contributes to film toughness and fold crack resistance, but it also forces the size press to operate at lower solids than a low-viscosity grade to maintain the same blade or rod pressure.

The size press can be run at higher machine speed when the starch fraction is increased, but that reduces water resistance. A practical upper limit for the PVOH/starch dry blend is 30 % PVOH because higher fractions may cause doctor blade chatter and build-up. Surface size solids above 12 % can lead to viscosity instability at the return pan due to evaporation; online refractive index or solid-state viscosity monitoring is used to hold solids within ±0.5 %.

In textile warp sizing, the size box is run at 80–85 °C with solids from 6–12 % depending on yarn count and weaving speed. The high molecular weight film protects warp yarns by reducing hairiness and abrasion at high-speed looms. Weaving performance is measured as loom stops per 100,000 picks; published data for this specific configuration is limited because mill conditions vary widely. Size box viscosity stability is affected by starch addition and water evaporation; level controls are required to keep solids within ±0.5 % of target.

For aqueous adhesive compounding, ELVANOL 71-30 is dissolved at 10–20 % solids and compounded with plasticizers such as glycerol, sorbitol, or trimethylolpropane. Drying at 80–110 °C produces a clear film. The 99.0–99.8 mol% hydrolysis gives the dried adhesive lower cold-water rewetting than partially hydrolysed grades; remoistenable adhesive formulations based on this grade therefore require a rewetting agent to achieve acceptable tack development. If borate-based insolubilizers are used, the pH must be controlled below 8 before borate addition because borate ion complexation with polyvinyl alcohol produces a reversible gel and a sharp viscosity increase. The solution should not be held at high temperature for more than 24 h; microbial growth can reduce viscosity and produce odour.

Heated jacketing of transfer lines at 60 °C is used to reduce viscosity relative to ambient and to prevent gelling. If the solution is left in an unheated line, skinning occurs at the air interface. The dried film can be crosslinked with dialdehyde or other insolubilizers; the reaction is pH-dependent and should be validated with a viscosity profile and water resistance test per ISO 535:2014 or ISO 62.

Compared with lower molecular weight fully hydrolysed grades such as ELVANOL 70-03, which is specified at 2.5–3.5 mPa·s, ELVANOL 71-30 provides higher tensile strength and greater adhesive film toughness but lower permissible solids at equal coating viscosity. The choice between the two grades is therefore a balance between mechanical performance and maximum coatable solids.

When Partially Hydrolysed Grade 52-22 Is Substituted Uncritically

ELVANOL 71-30 is not a direct drop-in replacement for partially hydrolysed grades used as protective colloids in vinyl acetate emulsion polymerization. ELVANOL 52-22 is specified at 20.0–26.0 mPa·s and 86.5–89.0 mol% hydrolysis; the residual acetate groups provide interfacial activity and lower aqueous dissolution temperature. Substitution with 71-30 increases aqueous phase viscosity, reduces cold-water solubility, and can alter particle size distribution. If substitution is evaluated, the particle size distribution should be measured according to ISO 13320:2020 and the emulsion viscosity determined on a Brookfield or equivalent rotational viscometer. Published data for this specific substitution is limited; bench trials are required.

The dissolving temperature difference is measurable: partially hydrolysed grades can be solubilised at 40–50 °C, whereas fully hydrolysed 71-30 requires heating above 85 °C. This affects energy input and jacket steam load in a solution plant. In applications requiring cold-water rewetting or low temperature coating, the partially hydrolysed grade is preferred. In applications requiring lower water sensitivity after drying and higher film strength, the fully hydrolysed 71-30 is used. The substitution decision must be made against the target film water resistance, tested on paper with ISO 535:2014 or on film with ISO 62 as appropriate.