KURARAY POVAL 44-88

How Does Surface Sizing with 44-88 Modify Cobb Values and IGT Pick Velocity on Recycled Linerboard?

Surface sizing on recycled linerboard and white-top testliner with a size press formulation based on partially hydrolyzed poly(vinyl alcohol) and oxidized corn starch addresses both liquid penetration resistance and surface fiber bonding. The addition of KURARAY POVAL 44-88 to a size press feed at 1–2 wt% dry solids in a total solids range of 3–8% and temperature 55–65°C produces a film that reduces 60-second Cobb values per ISO 535 from 55–70 g/m² to 25–35 g/m² on recycled furnish; the degree of improvement depends on the starch-to-PVOH dry-weight ratio, which is normally set between 2:1 and 5:1. The partially hydrolyzed grade specified with 87.0–89.0 mol% hydrolysis retains enough residual acetyl groups to reduce film brittleness and improve adhesion to high-ash recycled fiber, while its 4.0–5.0 mPa·s viscosity at 4% solids and 20°C avoids excessive back-flow on high-speed applicator rolls. On a rod-metering film press running at 800–1,200 m/min, size solution viscosity is maintained at 20–60 mPa·s at 60°C using Brookfield spindle 2 at 100 rpm; metering rod pressure and film thickness are adjusted so that dry pick-up stays within 0.8–1.8 g/m² per side. Higher pick-up on recycled linerboard leads to film splitting at the dryer cans and dusting at the blade coater, while lower pick-up produces uneven fiber coverage and poor IGT pick velocity. The IGT pick velocity measured with medium-viscosity oil and 20 mm strips per ISO 3783 typically increases from 1.5–2.0 m/s to 2.8–3.5 m/s after size press application, with the larger gains recorded on furnish containing recovered corrugated fibers. Published data for this specific configuration is limited where high levels of anionic trash are present; mill trials usually include a cationic scavenger at 0.05–0.2% active solids before the size press to prevent filler adsorption onto the PVOH film. Partial hydrolysis at 88 mol% limits water resistance compared with fully hydrolyzed grades; therefore 44-88 is not recommended as the sole surface-sizing polymer for high-humidity frozen-food packaging where wet stiffness after 24-hour immersion is specified. For those grades, a fully hydrolyzed grade or a combination with styrene-acrylate surface size is required. If the size press bath contains calcium carbonate from the wet end, PVOH can adsorb onto filler surfaces and increase foaming; defoamer addition at 0.05–0.2% active and pH buffering to 6.5–7.5 with citric acid prevents film defects visible under oblique lighting.

During continuous or semi-batch emulsion polymerization of vinyl acetate homopolymers and vinyl acetate-ethylene (VAE) copolymers, KURARAY POVAL 44-88 functions as a steric and electrostatic protective colloid when the charge is maintained at 2.5–6.0 wt% on total monomer. The grade is specified with a degree of hydrolysis of 87.0–89.0 mol%, a dynamic viscosity of 4.0–5.0 mPa·s in 4% aqueous solution at 20°C, and pH 5.0–7.0 per JIS K6726 solution methods. In a typical VAE polymerization, a jacketed stainless-steel reactor of 6–15 m³ fitted with a wall-wiped anchor impeller rotating at 55–75 rpm is operated at 65–75°C under an ethylene partial pressure of 20–40 bar. The aqueous phase is prepared by cold-water slurrying of the powder at 8–12°C, followed by heating to 85–90°C for 30–45 minutes and cooling to the reaction temperature before initiator metering. The persulfate initiator, typically potassium or ammonium persulfate at 0.05–0.2 wt% based on total monomer, is fed as an aqueous solution over 3–5 hours; the redox residual monomer finishing step uses 0.02–0.08 wt% sodium metabisulfite at 70–75°C to reduce free vinyl acetate to <0.1% measured by ISO 13741-1. The partially hydrolyzed 87–89 mol% structure retains sufficient residual acetyl groups to provide lower interfacial tension than fully hydrolyzed PVOH grades, while the 4.0–5.0 mPa·s viscosity range maintains workable dispersion rheology at final solids of 50–60%. Brookfield viscosity of the finished dispersion is typically reported at 2,000–8,000 mPa·s using spindle 3 at 20 rpm and 23°C per ISO 2555, with solids controlled by ISO 3251. At 44-88 levels below 2.0 wt%, coagulum formation in VAE batches with high ethylene content (15–25 wt%) is observed on baffles and reflux condenser walls; above 7.0 wt%, the finished dispersion commonly exceeds 12,000 mPa·s and dried films show excessive whitening after 4-hour water immersion at 23°C. The residual acetyl content introduces a controlled hydrophilic/hydrophobic balance that reduces the wetting angle on low-surface-energy substrates such as corona-treated polypropylene; the same balance limits water resistance in wood adhesives unless a crosslinker such as glyoxal or a blocked isocyanate is added at 0.5–2.0 wt% on dispersion solids. Batch-to-batch variability in the protective colloid's ester group distribution influences grafting efficiency and dispersion particle size. When VAE dispersions are measured by dynamic light scattering, the Z-average particle diameter commonly falls between 350 nm and 900 nm; coagulum is filtered through a 40 µm mesh and reported as <200 mg/kg for paper and film applications. Additions of 44-88 must not be combined with borate salts, borax, or sodium tetraborate in the stabilization package because diol-borate complexation produces a reversible but strong gel network that raises reactor torque and can block heat-transfer surfaces. For adhesive formulations requiring post-thickening, hydroxyethylcellulose or fumed silica is preferred; if borate is unavoidable as a pH buffer, the concentration must remain below 0.1 wt% of the aqueous phase and the colloid must be pre-blocked with glycerol or sorbitol at 5–10 wt% on PVOH. Particle size distribution is monitored by laser diffraction, and residual PVOH in the serum is tracked by gravimetric methanol extraction; a free PVOH content above 0.5% of dispersion mass signals overcharging or insufficient grafting. Equipment experience shows that the most frequent processing failure is not reactor initiation but post-polymerization adsorption of unconverted monomer onto the protective colloid sheath, which raises taint and odor in food-packaging adhesives if the monomer stripping column is not held at 50–60°C under −0.85 bar for at least 45 minutes.

In suspension polymerization of vinyl chloride, the droplet–particle transition and grain morphology are governed by the competitive adsorption of two partially hydrolyzed PVOH grades differing in hydrolysis and molecular weight. KURARAY POVAL 44-88 is employed as a secondary or co-dispersant in formulations where the primary dispersant is a 70–74 mol% hydrolyzed grade with a lower viscosity. The addition window for 44-88 is normally 0.06–0.15 parts per 100 parts vinyl chloride monomer, and the primary-to-secondary ratio is held between 60:40 and 40:60 depending on the target K-value and particle porosity. In a typical 105 m³ steam-jacketed stainless-steel autoclave fitted with a two-blade Pfaudler impeller and baffle plate, the aqueous phase is charged at 45–55% of total volume, the mixed suspending agents are added as a 4% aqueous solution, and the reactor is brought to 56–72°C before vinyl chloride is loaded. The oil-soluble initiator system, usually di(2-ethylhexyl) peroxydicarbonate or cumyl peroxyneodecanoate at 0.03–0.08 phr, decomposes with a half-life tuned to the polymerization temperature. Agitation speed is maintained at 75–120 rpm in the early stage and reduced by 10–15 rpm after the pressure drop begins to preserve grain morphology. The pressure is held at 8–12 bar until monomer conversion reaches 65–75%; then the reactor is degassed and the slurry is transferred to strippers operated at 55–65°C under vacuum. With 44-88 in the formulation, the median particle size measured by low-angle laser light scattering typically shifts from 160–180 µm to 120–150 µm as the secondary ratio increases, while the fraction retained on a 250 µm sieve falls below 0.1% per ISO 4610. Bulk density rises from 0.48–0.53 g/cm³ to 0.52–0.58 g/cm³ when the 44-88 fraction is increased; cold plasticizer absorption per ISO 4608 declines by 3–6 parts per 100 parts resin, which narrows the processing window for high-porosity flexible PVC.

Reactor experience indicates that increasing the 44-88 fraction too rapidly causes transient foam at the monomer/water interface during the early polymerization stage, which accelerates scale on the reactor crown if the freeboard is less than 15%. The partially hydrolyzed 88 mol% grade also raises the cloud point of the aqueous suspending phase; if the polymerization temperature exceeds 75°C, the combined dispersant system can undergo phase separation and lead to coarse particles. For target K-values above 70, published data for this specific configuration is limited; most production runs restrict 44-88 to K-values 57–68 to avoid bimodal distributions and residual surfactant effects on fused dry blends.

When High-Speed Shuttleless Weaving Requires Low Add-On and High Filament Abrasion Resistance

Warp sizing for air-jet and water-jet weaving lines running at 600–900 rpm requires a film former with sufficient cohesive strength to bind surface fibers without producing brittle splits at the reed. A size mix formulated with 15–30% of the dry solids as 44-88 and the balance as oxidized corn starch, acrylic ester, or wax is applied at 6–10% total solids in a single-end size box at 75–85°C. The resulting add-on on spun cotton or polyester/cotton yarns is held at 8–12% for ring-spun and 5–8% for rotor yarns; add-on is calculated per ISO 2060 linear density and dry mass after desizing. The film properties of the partially hydrolyzed grade give an elongation at break measured on solvent-cast films of 100–170% per ISO 527-3, which is sufficient to absorb cyclic tensile stresses in the weaving zone, while the tensile strength of 35–50 MPa is lower than that of fully hydrolyzed grades and must be compensated by the starch component when high starch replacement rates are attempted. The size box nip pressure is set to 0.25–0.45 MPa and drying cylinder surface temperatures are limited to 95–115°C; above 125°C the PVOH film develops crystalline domains that resist desizing and can create loom dust. Desizing with hot water at 80–85°C and a non-ionic wetting agent at 0.5–1.0 g/L removes the film from cotton warps in 10–15 minutes; polyester blended warps require 20–30 minutes in a continuous wash box. Weaving efficiency on air-jet looms is generally evaluated by warp breaks per 100,000 picks; size formulations containing 44-88 typically maintain breaks below 6 when the size film is intact, but breaks increase when the size-box solids fall below 6% or when wet-on-wet splitting reduces film thickness below 0.5 µm. The grade is not recommended for yarns that must be stored longer than 30 days under uncontrolled humid conditions after sizing because the residual acetate groups increase moisture pickup and can soften the film enough to lower abrasion resistance at the back rest.

Water-activated gummed tapes, envelope flap adhesives, and label stocks require a dry polymeric film that remains non-blocking at 35°C and 75% relative humidity but rewets rapidly when moisture is applied. 44-88 is dissolved at 10–25% solids in water and combined with dextrin or maltodextrin at 40–60% of total solids, glycerol or sorbitol plasticizer at 5–15% on PVOH, and a release agent such as calcium stearate at 1–3% of wet formulation. The resulting solution is coated by roller, slot die, or Meyer rod onto kraft paper, then dried at 60–90°C to a residual moisture of 3–6%. The open time after water application on a gumming machine is measured by the time required for the adhesive film to reach a tack value sufficient to retain a paper strip under a 20 g peel load; typical values are 2–5 seconds at 22°C and 50% relative humidity. Blocking resistance is assessed by stacking coated sheets under 0.2 kg/cm² for 24 hours at 35°C and 75% RH; 44-88-based films can pass if the plasticizer content is below 10% and calcium stearate or talc is uniformly dispersed, but above 12% plasticizer the dry film becomes tacky and causes sheet-to-sheet adhesion in unwind stands. Adhesive performance of water-activated tapes is tested by TAPPI T 463 and ISO 1924 tensile strength; the paper substrate often fails before the adhesive bond at peel angles above 45°. Because 44-88 contains 11–13 mol% residual acetate groups, film hygroscopicity is higher than fully hydrolyzed grades; storage in uncoated polypropylene envelopes at 40°C and 90% RH leads to visible film softening within 24 hours. For applications requiring tropical moisture resistance, a small addition of crosslinker such as glyoxal at 0.5–1.5% on PVOH solids improves water resistance but reduces rewet speed, so the crosslinker level must be balanced against activation time on the packaging line.

Cementitious Dry-Mix Aqueous-Phase Retention and Open-Time Extension in Tile Adhesives

Dry-mix cementitious tile adhesives classified as C2TE under ISO 13007 use small amounts of partially hydrolyzed PVOH powder to increase water retention and extend open time without significantly altering rheology after water addition. 44-88 is dry-blended at 0.3–1.0 wt% of total formulation into a ribbon mixer or ploughshare mixer at 40–70 rpm for 5–10 minutes; the powder particle size is controlled to <250 µm to prevent segregation. The water demand at 23°C to reach a mortar slump of 140–160 mm per EN 13454-2 increases by 2–4% compared with the same formulation without PVOH; this is associated with a water retention of 98–99% measured by vacuum capillary method. Open time measured by the wetting method per ISO 13007-2 is extended from 20–25 minutes to 30–40 minutes at 23°C and 50% RH when 44-88 is present, but early tensile adhesion strength after 28 days is normally 0.1–0.3 MPa lower than unmodified controls due to air entrainment and plasticizing action in the cement matrix. The effect is acceptable when original designs exceed 1.0 MPa; below 0.8 MPa the powder level must be reduced or a defoamer such as tri-butyl phosphate at 0.1–0.3% on liquid additives is used. In formulations containing calcium sulfate or high-alumina cement at pH above 12.5, 44-88 undergoes alkaline hydrolysis and loses molecular weight over 30–90 minutes after mixing; published data for this specific configuration is limited. Therefore, the grade is not recommended for spray-applied renders with prolonged pot life or for steam-cured precast concrete where sustained rheology is required.