ELVANOL 80-18

Surface Sizing of Recycled Containerboard and Fine Paper

ELVANOL 80-18 is introduced at the size press as a 4–8% aqueous solution prepared in an atmospheric or jet cooker. The grade’s 4% aqueous viscosity of 16.0–20.0 mPa·s at 20 °C, measured by Brookfield rotation in accordance with ASTM D2196-20, permits stable puddle or metering-film transfer when mixed with oxidised starch. For recycled containerboard, a starting blend of 1 part PVOH solids to 4 parts oxidised starch solids at 6.0–8.0% total solids is circulated at 55–65 °C through a pond-type size press; for fine paper using a rod-metered or blade-metered film press, the PVOH fraction is often raised to 2–3 parts per 4 parts starch. The fully hydrolysed 98.0–98.8 mol% structure reduces thermoplasticity and re-wetting on subsequent corrugator heating, while maintaining fibre-to-fibre bond contribution measured by Scott bond TAPPI T569 or tensile energy absorption. Surface strength is typically assessed by IGT pick test ISO 3783:2014; oil- and water-holdout is monitored by Hercules Size Test TAPPI T530 at 60% reflectance. Mills operating closed water loops should control size press pH between 6.5 and 7.5, because residual alum below pH 5.0 can precipitate PVOH and increase cleaned-up blade wear. External size press additions of 1.5–4.0 kg PVOH per dry metric tonne are common when replacing a fraction of starch in high-performance liner and white-top grades. Because ELVANOL 80-18 is fully hydrolysed, dissolution requires 30–45 min at 90–95 °C under low shear; undissolved microgel particles from short cook cycles cause coating streaks and lower opacity in subsequent flexo printing.

Prepared as a jet-cooked size liquor at 8.0–12.0% solids for cotton and cotton-rich warp yarns, ELVANOL 80-18 is blended with thinned starch or polyacrylic acid size at a PVOH solids ratio of 20–40% depending on loom type and yarn count. The medium-viscosity profile maintains a size-box viscosity of 40–120 mPa·s at 85 °C, allowing wet pick-up between 8% and 12% on ring-spun Ne 20–40 yarns. Warp abrasion resistance is measured with a Zweigle G552 abrasion tester or by DSM cycling to failure; sizing efficiency is indirectly evaluated by loom stop rate per 100,000 picks. The fully hydrolysed grade gives tensile strength and elongation responses consistent with ISO 13934-1:2013 when cast as an unsupported film; a typical conditioned film exhibits tensile strength of 40–60 MPa and elongation at break of 150–250% after conditioning at 23 °C and 50% RH. Because ELVANOL 80-18 is not cold-water soluble, desizing of pure PVOH size is performed with 80–90 °C water containing 0.5–1.0 g/L nonionic wetting agent; starch-sized blends are desized with commercial α-amylase at pH 6.5–7.0 and 70–75 °C before hot wash. Residual PVOH on finished fabric is detected by iodine staining in accordance with internal mill methods; a blue complex persists above approximately 0.1% surface add-on. High-humidity weaving rooms benefit from the grade’s low equilibrium moisture sensitivity relative to starch-only size films, but size-shedding can increase when the size film is overdried below 5% moisture. Addition of 5–10 parts glycerol or polyethylene glycol 400 per 100 parts PVOH resin reduces brittleness for high-twist yarns, though excessive plasticiser lowers size film cohesion and raises warp breakage on air-jet looms.

What Limits Green Strength in Alumina Substrates Bound with ELVANOL 80-18?

In tape-casting and dry-pressing operations for technical ceramics, ELVANOL 80-18 functions as a temporary organic binder at 2.0–6.0 wt% of dry ceramic powder. The fully hydrolysed backbone provides higher green tensile strength than partially hydrolysed grades at equivalent binder loading, but it also raises slip viscosity, which is controlled by maintaining the aqueous slurry at 45–55 °C during tape casting. For a 40 vol% alumina slip containing 3.0 wt% ELVANOL 80-18 and 0.5 wt% ammonium polyacrylate dispersant, typical Brookfield viscosity at 20 rpm falls between 3000 and 8000 mPa·s, measured with spindle 4; this range supports doctor-blade gap settings of 0.5–1.5 mm on a continuous tape caster. Green sheet strength is evaluated by three-point flexure using ASTM C1161-18 for advanced ceramics or equivalent in-house bar tests; values are reported on ready-to-sinter tape after drying at 60 °C for 20–30 min to a residual moisture content below 0.5%. Binder burnout is designed around thermogravimetric analysis at 5 °C/min heating rate; ELVANOL 80-18 decomposes predominantly between 250 °C and 480 °C in air, with total ash contribution below 0.5% of ceramic mass when the grade meets standard ash specifications. Sintering profiles for alumina substrates typically include a 60–120 min hold at 450–500 °C before ramp to 1500 °C, preventing carbon residue and through-thickness delamination. The addition of 10–30 parts glycerol per 100 parts PVOH solids plasticises the binder film and lowers the glass transition of the dried matrix, but excessive glycerol delays burnout and can produce pinholes in tape-cast layers above 100 µm dry thickness. Published data for this specific configuration is limited at high tape thicknesses; operators commonly adjust plasticiser ratio by iterative green density measurements rather than relying on fixed nominal values.

A remoistenable seam adhesive based on ELVANOL 80-18 is formulated by dissolving 15–20 parts resin in 80–85 parts water at 90–95 °C, then adding 3–5 parts glycerol or sorbitol as humectant and 0.5–1.0 part defoamer. The resulting adhesive is applied by wheel or nozzle at 10–20 g/m² dry coat weight onto paper envelopes, paper tape, or label stock; drying is performed on a steam-heated drum at 90–110 °C for 5–15 s. The fully hydrolysed grade yields a non-tacky film at 23 °C and 50% RH, which is evaluated by block resistance test TAPPI T477 or an inclined-plane tack method; adhesion is reactivated by passing the coated side over a water wheel or sponge with 0.2–0.5 g/m² moisture. T-peel adhesion to recycled paper and kraft paper is measured according to ASTM D1876-08 with a crosshead speed of 300 mm/min; typical remoistening peel values fall between 1.0 and 3.0 N/mm on 80 g/m² kraft. Borax is sometimes added at 0.1–0.3 wt% of wet adhesive to increase tack wet-out and shift rheology through didiol complexation, but borax levels above 0.5 wt% cause gelation and irreversible viscosity build in fully hydrolysed PVOH. The 98.0–98.8 mol% hydrolysis degree reduces cold-water tack development relative to 88 mol% grades, making ELVANOL 80-18 suitable for applications requiring moisture-resistant dry film but rapid bonding after remoistening. Because the grade’s 4% viscosity of 16.0–20.0 mPa·s is higher than low-viscosity remoistening grades, transfer-coating head pressure should be maintained above 1.5 bar for engraved roller coaters; lower pressure causes skips on highly calendered substrates.

When PVA Film Replaces Non-Dissolvable Laminate in Unit-Dose Agrochemical Packaging

The conversion of ELVANOL 80-18 into cast film for agrochemical unit-dose packaging follows a solution-casting or tape-casting sequence rather than blown extrusion, because dry granules must be first dissolved at 90–95 °C for 45–60 min to form a 10–15 wt% dope. Plasticiser content is normally 15–25 parts per 100 parts PVOH solids, with glycerol or trimethylolpropane selected to meet cold-water disintegration targets. Wet film is cast at 300–800 µm onto a polyester carrier and dried at 70–95 °C to a residual moisture content of 8–12%; final film thickness is controlled between 35 and 75 µm. Mechanical performance is measured according to ISO 527-3:2018 for plastics film; typical unsupported film values for ELVANOL 80-18 with 20 phr glycerol are tensile strength 35–55 MPa and elongation at break 150–350% after conditioning at 23 °C and 50% RH, but published data for this specific configuration is limited and producer trials should verify. Disintegration time in water at 10 °C, 20 °C, and 30 °C is assessed by a 1 L stirred beaker method using a 50 mm × 50 mm film swatch. Fully hydrolysed 98 mol% grade requires warm water for rapid dissolution, so agrochemical packages designed for cold-water release below 15 °C often blend ELVANOL 80-18 with 10–30 wt% of an 88 mol% grade. Contact with strong oxidising agents, high-pH alkaline formulations above pH 9, or borate-containing tank-mix adjuvants can produce gelation or accelerated hydrolysis; compatibility tests after 7-day accelerated ageing at 40 °C and 75% RH are therefore required before approving a formulation. Sealing of water-soluble film pouches is performed by heat sealing at 120–150 °C, 0.2–0.5 s dwell time, 2–4 bar jaw pressure; excessive sealing temperature above the crystalline melt range reduces toughness at the seal edge and promotes pinholes.

How Fully Hydrolysed PVOH Governs Particle Size and Shear Stability in Vinyl Acetate Dispersions

In vinyl acetate emulsion polymerisation, ELVANOL 80-18 is employed as a high-molecular-weight protective colloid at 2.0–5.0 wt% of the aqueous phase. The hydrolysis degree of 98.0–98.8 mol% produces a lower cloud point and less blocky branching than partially hydrolysed grades, yielding polyvinyl acetate dispersions with medium to high Brookfield viscosity and strong shear stability. Batch or semi-batch reactor charging is performed by pre-dissolving the resin at 90 °C for 30–60 min, cooling to reaction temperature of 60–70 °C, and adding as a 10% stock solution; initiator is typically hydrogen peroxide/tartaric acid or persulphate redox at 0.05–0.2 wt% of monomer. Particle size distributions measured by laser diffraction typically shift to smaller volume mean diameters when PVOH concentration increases from 2.0 to 5.0 wt%; residual PVOH on particle surfaces contributes to wet-tack and water resistance trade-offs. The resulting dispersion is characterised by viscosity per ISO 2555:2018 at 23 °C, pH, and lump content after 100 µm filtration; coagulum is weighed after reactor discharge and after 30 min of mechanical shear at 5000 rpm in a laboratory dissolver. Fully hydrolysed grades such as ELVANOL 80-18 can gel at lower temperatures and are less tolerant of methanol-rich feeds than 88 mol% grades; therefore feed systems using methanol/water mixtures above 15 wt% methanol should be avoided unless compatibility testing confirms stability. The high molecular weight of the grade also increases particle bridging and may require a delayed addition profile to avoid thickening before monomer conversion reaches 90%. End-use adhesives based on these dispersions are tested for wet strength and water resistance under DIN EN 204 classifications D1–D4; limit values depend on formulation, not on PVOH alone.