KURARAY POVAL 56-98 LA

KURARAY POVAL 56-98 LA is a fully hydrolysed polyvinyl alcohol supplied as a white to off-white granular powder with CAS Registry Number 9002-89-5. The grade designation encodes two key rheological and compositional properties: the first segment places the nominal dynamic viscosity of a 4 wt% aqueous solution at 20 °C near 56 mPa·s, and the second segment corresponds to a degree of hydrolysis of 98.0–99.0 mol%. The suffix LA identifies a low-ash variant in which residual sodium acetate and inorganic ash are controlled below the tolerances commonly assigned to the standard 56-98 grade. Viscosity and degree of hydrolysis are measured according to JIS K6726 or ISO 15023-2, with exact lot-release values reported on the certificate of analysis. The polymer is produced by controlled alcoholysis of polyvinyl acetate and therefore carries a linear carbon backbone substituted with hydroxyl groups; the fully hydrolysed structure exhibits strong interchain hydrogen bonding, limited cold-water solubility, high film tensile strength, and reduced moisture swell relative to partially hydrolysed grades. Bulk density, volatile content, pH, and residual acetyl content are lot-dependent and should be taken from the manufacturer’s lot-specific documentation rather than generic datasheet values. The powder is not classified as dangerous goods under GHS criteria in the as-supplied form, but plant-scale handling must control combustible dust formation through local exhaust ventilation, antistatic bonding, and housekeeping limits. The low-ash attribute is the principal specification difference that directs this grade into ceramics, high-purity binders, and electronics-adjacent process streams where sodium residues from polymerisation catalysts are considered process-relevant variables.

How Does the 56-98 LA Grade Differ from Standard and Partially Hydrolysed Grades?

The selection boundary between KURARAY POVAL 56-98 LA and other Poval grades is established by three factors: molecular weight reflected in 4% solution viscosity, degree of hydrolysis, and ash residue. Fully hydrolysed grades such as 56-98 LA require elevated-temperature dissolution but yield dried films and binders with high water resistance and cohesive strength. Partially hydrolysed grades with hydrolysis near 88 mol% dissolve in cold water and are suited to low-viscosity protective colloid duties, but their films show increased water uptake and lower shear strength after drying. Compared with 28-99, 56-98 LA raises solution viscosity at equal solids, thus increasing wet adhesion and green-body mechanical properties while increasing mixing torque and limiting the solids level that can be pumped through standard coating equipment. The LA suffix does not alter the primary polymer architecture but signals a reduced ash ceiling; this is operationally significant when the dried binder must disappear without leaving sodium-bearing defects. Film tensile properties may be compared through ASTM D882-18, and water resistance can be ranked through equilibrium water absorption tests referenced in supplier technical bulletins; the exact numerical values depend on plasticiser content, film thickness, and drying history.

The values in the table are supplier-nominal midpoints or published grade designations. They are not substitutes for certificate-of-analysis data when qualifying a production lot.

During vinyl acetate and vinyl acetate–ethylene emulsion polymerisation, KURARAY POVAL 56-98 LA is pre-dissolved in a dedicated make-down vessel before it is metered into the reactor as a protective colloid. The powder is slurried in cold demineralised water, then heated to 85–95 °C under low-shear agitation until optical clarity is achieved; direct powder addition to a cold latex charge produces fisheyes and can obstruct reactor transfer lines. Once dissolved, the fully hydrolysed polymer participates in grafting reactions with vinyl acetate radicals and sterically stabilises latex particles. The resulting latex exhibits pseudoplastic flow, so transfer pumps and coating stations are selected for shear-sensitive viscosity rather than simple centrifugal delivery. In adhesive compounding, the grade contributes water redispersibility after drying and improves heat-seal strength in coated paper structures. Viscosity measurements on compounded adhesives are usually made with a Brookfield rotational viscometer at controlled spindle speeds because Newtonian assumptions fail for these systems. The main operational boundary is viscosity drift: solutions of fully hydrolysed grades can build viscosity on standing, particularly below 40 °C. Therefore, hold time, temperature, and agitation history must be fixed in batch records to keep adhesive coat weights reproducible. Production lots should be qualified by comparing final latex particle size distribution and cake filtration behaviour, because lot-to-lot ash variation may influence emulsion electrical stability.

Aqueous Solution Preparation and Viscosity Behaviour Under Plant-Scale Mixing

The make-down procedure for 56-98 LA is governed by the polymer’s tendency to form unhydrated gel aggregates if the powder is added too rapidly to hot water. A production-scale vessel equipped with a side-entering propeller or an eductor is charged with ambient demineralised water, and the powder is fed gradually into a well-formed vortex at moderate impeller speed. After wetting, the batch is heated with saturated steam or jacketed hot water to 90 °C and held for 30–60 min with continued low-shear agitation. High-shear rotor–stator devices may be used for dispersion during powder addition but should be stopped during the hydration phase to prevent polymer chain scission. The finished solution is filtered through a 100–200 µm bag or cartridge filter and deaerated by vacuum or centrifugal degassing before use. At 4% solids and 20 °C, Brookfield viscometry returns a nominal viscosity in the region of 56 mPa·s; at 10% solids, the solution is a sluggish gel at room temperature and should be maintained above 60 °C for metering into coating baths. Preservatives are added only after cooling below 40 °C to avoid thermal degradation of the biocide. Borate ions, glyoxal, and certain multivalent metal cations create strong physical crosslinks that can raise viscosity sharply or form irreversible gels; these additives must be segregated or buffered before incorporation. When the solution is stored, the tank should be blanketed or sealed to prevent skinning, and recirculation should be gentle to avoid shear-induced viscosity loss. The solution temperature should not be allowed to fall below 30 °C during transfer; otherwise gelation in unheated pipework can occur, especially at solids above 6%.

In oxide and non-oxide ceramic processing, the low-ash profile of KURARAY POVAL 56-98 LA becomes the controlling variable for binder selection. Tape-casting formulations combine ceramic powder, solvent, dispersant, plasticiser, and binder; the fully hydrolysed grade contributes green tape tensile strength through high molecular weight chain entanglement and interfacial hydrogen bonding. Binder demand is formulation-dependent, but laboratory evaluations often begin near 2–5 wt% of dry ceramic mass and are adjusted until the dried green tape reaches the required handling strength. The LA variant is specified when sodium acetate residues from standard PVOH grades would otherwise survive burnout and contaminate dielectric layers or create pinholes in fired ceramic sheets. In continuous doctor-blade casting, the slurry is applied to a carrier film, and the wet-film thickness is controlled by the blade gap and casting speed; high solution viscosity reduces slurry settling but may require vacuum deairing to prevent bubbles in the green film. Burnout of the binder in air is typically completed before 500 °C, and the low-ash composition leaves less inorganic residue. Published data for exact green-strength values with this specific LA lot are limited; manufacturers must run fixture-based three-point bend or tensile measurements on their own green tape because strength is sensitive to particle size distribution, solvent system, and plasticiser type. The dried green sheet should be tested with a universal testing machine using a three-point bend fixture adapted from ASTM C1161 or internal protocols; no universal green-strength specification exists.

In ceramic injection moulding feedstocks, KURARAY POVAL 56-98 LA is compounded as a temporary organic backbone in low-pressure injection moulding machines equipped with heated tanks and planetary mixers. The feedstock consists of ceramic powder, binder, and minor plasticiser; mixing is carried out at temperatures that keep the PVOH fluid without inducing thermal decomposition. The high viscosity of the grade produces green parts with sufficient handling strength for demoulding, while the low-ash profile reduces residue after solvent debinding and thermal burnout. Thermal debinding profiles are developed to avoid skin formation; hold steps are typically introduced below the decomposition onset of fully hydrolysed PVOH. Published data for this specific configuration is limited; processors should establish debinding profiles by thermogravimetric analysis rather than relying on generic supplier curves.

In textile warp sizing, the film-forming properties of fully hydrolysed PVOH can be exploited when water resistance is required in finishing steps. The 56-98 LA grade is generally too high in viscosity for high-speed single-end sizing unless diluted, but it can serve in formulations requiring high abrasion resistance. Size boxes must be maintained at controlled temperature and concentration; viscosity control by automatic refractometer or viscometer is common. The low-ash profile is beneficial in dyeing operations where sodium residues can shift dye uptake. Production-scale trials should include weaving efficiency and desizing residue checks.

When the Grade Is Deployed as Paper or Fibre Surface Size

If KURARAY POVAL 56-98 LA is applied at a size press or film press, the full molecular weight of the polymer raises surface strength and oil holdout but also limits the solids level that can be pumped and metered. Size-press trials with fully hydrolysed PVOH are typically run at solution temperatures between 50 °C and 70 °C to maintain sufficient flow without excessive drying load. The polymer forms a continuous film on the fibre surface and reduces porosity; when a crosslinker such as glyoxal is used, the wet strength of the dried coating increases but the open time of the size-press formulation decreases because of progressive crosslinking. Air-knife and roll misting may occur at high machine speeds if the solution viscosity is too high, so the grade is often diluted below the viscosity ceiling of the coater. Surface sizing response can be measured by the IGT pick strength test and TAPPI T 459 wax pick method, while grease resistance is commonly screened with TAPPI T 559 and oxygen transmission with ASTM D3985. In barrier papers, the dried PVOH layer contributes oxygen and grease resistance but remains sensitive to liquid-water penetration unless insolubilised. Published data for the exact speed limits of specific paper machines with this LA variant is not available; a pilot-scale trial is required before full-width commercial runs. The low-ash designation is less important in standard paper sizing than in ceramic or electronics applications, but it still reduces the ionic load introduced into the mill water circuit.

Regulatory Status and Food-Contact Compliance Boundaries

For indirect food-contact applications, polyvinyl alcohol may be used as a component of paper and paperboard under 21 CFR 176.170 and as an adhesive component under 21 CFR 175.105, provided the finished article meets the applicable extractives limitations and use restrictions in those sections. Compliance is not conferred by the polymer alone; it depends on coating weight, substrate, food type, and end-use temperature. Direct addition to food is outside the scope of this grade. In the European Union, the material is subject to REACH registration duties and should be checked against the supplier safety data sheet for the current registration status. The powder absorbs moisture from ambient air; storage areas must be kept below 35 °C and below 60% RH, with bags re-sealed immediately after use because caking can occur under humid conditions. Dust from the powder is combustible when suspended in air; housekeeping must prevent accumulation on hot surfaces and electrical equipment. The LA low-ash specification does not remove all inorganic matter from the polymer, but it lowers the sodium residue available for migration into process water or sintered ceramic bodies. For applications requiring a specific ash limit, the certificate of analysis must be verified against the internal specification before the lot is released to production.