ELVANOL 71-30

In woodfree paper production on machines running 800–1,200 m/min, ELVANOL 71-30 is introduced at the size press as a cooked aqueous solution. The granules are dispersed in cold water at ambient temperature, then heated to 90–95 °C under low-shear agitation for 30 min. The solution is pumped through a 150 µm bag filter to remove fisheyes before entering the run tank. Bath solids are maintained between 8.0 wt% and 12.0 wt%. The blend ratio with oxidized starch is commonly 75:25 on a dry basis for fine paper grades requiring high surface strength. Metering rod pressure is set between 80 kN/m and 120 kN/m depending on base sheet absorbency. Total size pickup is controlled between 1.0 g/m² and 2.5 g/m² dry add-on per side.

The fully hydrolysed structure of ELVANOL 71-30 contributes oil and grease resistance after the sheet reaches equilibrium moisture. This resistance is measured with TAPPI T 559 cm-12 at a Kit value of 8–12 on a one-side coat of 6–10 g/m². Printing surface strength is measured with ISO 3783 IGT pick velocity. Water absorption is measured by Cobb 60 according to ISO 535. At equal pickup, ELVANOL 71-30 raises IGT pick velocity more than oxidized starch alone because the dried film has higher tensile strength. However, Cobb 60 values increase if the size film is not insolubilised with a suitable crosslinker or if internal sizing is below 2.0 kg/tonne alkylketene dimer. The limiting operational boundary is viscosity drift in the size press run tank. Because the product specification spans 27.0–33.0 mPa·s for a 4.0 wt% solution at 20 °C, a batch at the upper limit requires lower rod pressure to maintain target pickup. Failure to compensate leads to overapplication and reel-edge blocking. At sump temperatures above 60 °C, solution viscosity drops measurably. Operators should control sump temperature at 55–65 °C and record Brookfield viscosity at 20 rpm every 60 min. Published plant-scale data for this specific configuration are limited. Most mills qualify the grade through a two-level pickup trial rather than extrapolating from laboratory viscosity alone.

Table 1 summarises the powder and aqueous solution parameters relevant to the size press runnability limits described above.

Why Is Fully Hydrolysed 71-30 Selected Instead of Dextrin in Repulpable Envelope Front-Seam Adhesives?

The front-seam adhesive on remoistenable envelopes is applied as a thin aqueous film that must remain non-blocking in storage yet develop tack within 1–3 s after contact with water. ELVANOL 71-30 provides higher dry-film tensile strength than dextrin and a narrower rewet activation window. A typical formulation consists of 18–25 wt% solids in water, with 2–6 parts glycerol or polyethylene glycol 200 per 100 parts dry PVA. The solution is cooked at 90–95 °C and held at 60 °C in a jacketed supply tank. Direct gravure application is made at 8–12 µm wet film thickness on 80 g/m² wove envelope stock. Drying is carried out with hot air at 95–120 °C for 1.5–3.0 s.

The rewet behaviour is controlled by the degree of hydrolysis. At 99.0–99.8 mol% hydrolysis, the film swells more slowly than a partially hydrolysed grade would. This property is evaluated by applying a 5 mm wide water stripe with a contact-time applicator, then measuring peel resistance on a tensile tester at 180° peel angle. For correlation with end-use runnability, repulping assessment is performed according to a mill-specific screening procedure aligned with TAPPI T 275 sp-12. The adhesive layer must disperse without tacky agglomerates after 30 min of repulping at 45 °C in tap water.

A major operational boundary is borate incompatibility. Sodium tetraborate or boric acid should not be used as a tackifier or pH buffer in this adhesive. The 1,3-diol units in fully hydrolysed PVA react with borate ions to form a monodiol-borate crosslink. This raises viscosity sharply and can produce an irreversible gel in the coating pan. If pH adjustment upward is required, dilute sodium carbonate or sodium hydroxide solution should be used. The lowest-viscosity portion of the specification, near 27.0 mPa·s, may require a solids increase of 0.5–1.0 wt% to hold coat weight constant on a direct gravure line.

Desizing Requires a Temperature Above 70 °C After Air-Jet Slashing

In cotton and cotton-polyester warp sizing, ELVANOL 71-30 is used as a high-strength film former in size formulations. A typical size box formula for 14.8 tex 100% cotton yarn is 70:30 PVA-to-thinned starch at 8.0–10.0 wt% total solids. The size box temperature is held at 88–92 °C. Squeeze pressure is set to produce a size add-on of 10–14% dry on yarn mass. The sized warp is dried on a multi-cylinder contact dryer with first cylinder surface temperature not above 130 °C to prevent skinning. Yarn tensile properties are measured per ISO 2062. Abrasion resistance is measured with a loom-shed simulator rather than extrapolated from single-yarn tensile data alone.

The critical desizing threshold for this grade is temperature. Because fully hydrolysed PVA has a crystalline phase that dissolves slowly below 70 °C, desizing is run in caustic or oxidative baths at 80–90 °C. In enzyme desizing for starch-containing blends, the PVA portion remains as a film unless hot-water washing follows the enzyme stage. In oxidative desizing, 2.0–4.0 g/L hydrogen peroxide and 2.0–3.0 g/L sodium hydroxide at 85 °C for 20 min are typical. Residual PVA on the fabric is checked with iodine-boric acid solution, which produces a blue-green complex.

The operational boundary is add-on. Above 14–16% add-on, the film becomes excessively stiff and shedding increases on air-jet looms at 700–1,000 rpm. Shedding is observed as white deposits in the reed and heald frames. If shedding occurs, formulation adjustment is made by reducing PVA solids by 1.0–2.0 wt% or by adding a liquid acrylic size at 1.0–2.0 wt% to improve film flexibility. The viscosity span of 27.0–33.0 mPa·s is narrow enough that size box pickup at constant squeeze pressure remains steady within ±0.5% on a modern two-box slasher.

Semi-batch vinyl acetate and vinyl acetate-ethylene polymerisation employs ELVANOL 71-30 as the primary protective colloid at 2.0–6.0 parts per hundred parts monomer by mass. The grade is dissolved in demineralised water at 10.0–12.0 wt% solids in a jacketed pre-dissolver at 90–95 °C before transfer to the polymerisation reactor. The solution is then mixed with initiator and monomer feed. The reactor is typically a stainless steel 316 vessel with a dual pitched-turbine agitator running at 150–300 rpm. Tip speed is held below 2.5 m/s after nucleation to avoid shear-induced coagulation of the growing particles.

The high degree of hydrolysis at 99.0–99.8 mol% gives the latex a larger average particle size than a partially hydrolysed colloid would at the same concentration. For target particle sizes below 0.5 µm, a secondary surfactant is often required. The latex viscosity at 55–60% solids is monitored by ISO 2555 and controlled by adjusting the colloid-to-monomer ratio. Residual vinyl acetate monomer is measured by headspace gas chromatography with a flame ionisation detector.

The main processing conflict is between dispersion stability and water resistance of the finished film. Increasing the ELVANOL 71-30 concentration above 6.0 phr improves reactor stability but raises the hydrophilic character of the coalesced film. For wood glue applications, the increase in wet-bond strength may be acceptable. For exterior coatings, the formulator must separately crosslink or reduce the colloid content. Plant experience shows that pH drift below 4.0 accelerates reactor fouling because the fully hydrolysed colloid can precipitate under strongly acidic conditions. Alkali addition should be made as a 5% sodium hydroxide solution and never as concentrated alkali.

When Self-Leveling Cementitious Underlayments Need Controlled Water Release Under Forced-Air Drying

In self-leveling underlayment dry blends, ELVANOL 71-30 is added at 0.3–0.8 wt% of the dry mix. The powder is dry-blended with cement, calcium aluminate, sand, and dispersing agents before water addition. Mixing is performed in a planetary paddle mixer at 140 rpm for 3 min. Flow is measured per EN 12706. Water retention is measured according to DIN 18555-7. The polymer dissolves during mixing and increases the viscosity of the aqueous phase, reducing surface bleed and controlling water release to the absorbent substrate.

The primary process conflict is between flow and set retardation. Addition above 1.0 wt% delays initial set and may reduce 28-day compressive strength because polymer film bridges cement hydration products. Below 0.3 wt%, water retention on absorbent substrates is insufficient and plastic shrinkage cracks can occur. The addition window is therefore narrow. Forced-air drying should not exceed 35 °C surface temperature during the first 4 h. High early air temperature skins the surface and traps water vapour, leading to delamination.

Borated setting accelerators must be avoided. The same borate-gel reaction described for adhesives occurs in the highly alkaline cement pore water. If an accelerator is required, lithium carbonate at 0.1–0.3 wt% of cement is preferred. Batch-to-batch viscosity differences within 27.0–33.0 mPa·s are less significant than dispersion quality, which is improved by pre-dissolving the PVA in mixing water at 50–60 °C before adding cement.

Ceramic Pressing Binder Requirements in Spray-Dried Granulate Lines

Porcelain stoneware and technical ceramic bodies use ELVANOL 71-30 as a temporary organic binder for spray-dried pressing granulate. The PVA is pre-dissolved as an 8.0–12.0 wt% aqueous solution and added to the ceramic slurry at 0.5–1.2 wt% of dry body mass before spray drying. The spray-drier inlet temperature is typically 200–250 °C and outlet temperature 90–110 °C. The resulting granulate is controlled for d50 250–350 µm, moisture 6.0–8.0%, and bulk density 0.85–1.05 g/cm³.

Green strength is evaluated by three-point bending on compacted bars according to ASTM C674-13. Large-format tiles with side length above 600 mm require higher binder dosage to survive robot handling before the kiln. Low ash content at max 0.5% is specified to limit sodium oxide contamination in the fired body. Binder burnout is a critical firing stage. The fully hydrolysed grade decomposes in an oxidising atmosphere between 350 °C and 550 °C. The kiln profile must allow at least 15 min within this band to avoid black core. Published data for this specific grade in fast-firing porcelain stoneware cycles are limited. Trials are run with a minimum of three pressings per binder level and measured green strength after drying at 110±5 °C to constant mass.

During solvent-free barrier coating of paper for wrapping and food-service uses, a 10 wt% aqueous solution of ELVANOL 71-30 is applied by smooth-roll coater or blade coater at 6–10 g/m² dry coat weight. The base paper is typically 35–80 g/m² machine-glazed or bleached kraft. Drying is carried out in an infrared-air float dryer at web surface temperature below 110 °C. Above 120 °C, moisture blistering and skinning occur because the film forms a surface skin before internal water is removed.

Oil and grease resistance is assessed by TAPPI T 559 cm-12. A one-coat application on a dense base sheet commonly achieves a Kit rating of 8–12. Water vapour transmission is measured by ISO 2528 at 23 °C and 50% relative humidity. The fully hydrolysed structure gives lower hot-water sensitivity than a partially hydrolysed grade, but the coated sheet is not waterproof. Direct contact with liquid water reduces film integrity after prolonged immersion.

The operational boundary is the presence of calcium carbonate in the base sheet. High-alkalinity board can reduce rewetting of the dried PVA film at the coater and cause pinholes. If pinholes are observed under transmitted light, the pH of the coating solution should be adjusted to 6.0–7.0 with dilute acetic acid. Plant-scale data for this specific grade in single-coat food-service barrier applications are limited to customer trials because optimum coat weight depends heavily on base sheet smoothness and porosity.