ELVANOL 51-05

ELVANOL 51-05 is a partially hydrolysed polyvinyl alcohol granular resin with a 4 wt% aqueous solution viscosity of 5.0–6.0 mPa·s at 20 °C and a hydrolysis degree of 87.0–89.0 mol%. The product is supplied as a white to off-white free-flowing granulate and is assigned CAS number 9002-89-5. Because the polymer retains a portion of its original acetyl groups, it dissolves more readily in cold-to-warm water than fully hydrolysed grades and yields lower solution viscosity than medium-chain partial grades at equal solids. These properties make it suitable for emulsion polymerisation protective colloid systems, remoistenable adhesives, paper surface sizing, and water-soluble packaging intermediates where low solution viscosity is a processing requirement.

The residual acetate content also reduces the degree of crystallinity after film casting. For comparison, fully hydrolysed polyvinyl alcohol with hydrolysis above 98 mol% develops a more ordered hydrogen-bonded network, which raises tensile strength and lowers equilibrium moisture under high-humidity exposure. The partially hydrolysed structure of 51-05 retains greater chain flexibility, which is useful where film re-wetting or rapid dissolution is required.

Product Data Adjacent to ELVANOL 51-05 in the Kuraray Range

Specifications below are taken from supplier technical data for the neat granular resin and from the general test framework of JIS K6726 where indicated. The viscosity measurement uses a 4 wt% aqueous solution equilibrated in a water bath at 20 °C and evaluated with a Brookfield rotational viscometer. Solution pH is measured with a glass electrode after complete dissolution and cooling to 20 °C.

For continuous solution make-up, a recirculating eductor is configured with a low-shear centrifugal pump. The granulate is drawn into a cold water stream at 15 °C, then passed through a plate heat exchanger to raise the temperature to 90 °C. The mixture is held in a jacketed tank with a turbine mixer for 30 min. Solution is transferred through a 100-mesh duplex filter before use. The pressure drop across the filter is monitored; an increase above 0.5 bar indicates incomplete dissolution or gel formation. This arrangement prevents fisheyes and reduces batch-to-batch viscosity variation.

Dissolution of ELVANOL 51-05 is conducted by pre-slurrying the granulate in cold water at 10–25 °C under mechanical agitation with a sawtooth impeller, followed by indirect heating to 90–95 °C. At concentrations above 10 wt% the solution phase forms gel networks during cooling; therefore storage and transfer lines are maintained above 30 °C. If dry granulate is added directly to hot water without cold water pre-slurry, partially dissolved particles gelatinise on particle surfaces and form agglomerates. The low molecular weight of the grade permits dissolution in 30–45 min at 90 °C at 5 wt%, compared with 60–90 min for medium-viscosity partially hydrolysed grade ELVANOL 52-22.

In vinyl acetate ethylene emulsion polymerisation, ELVANOL 51-05 is typically charged at 1.5–4.0 wt% on total monomer as a protective colloid, with the lower end used for coarse seed lattices and the upper end for fine particle size and high mechanical stability. Because the grade has a low molecular weight, dissolved colloid viscosity drops more rapidly with temperature than that of ELVANOL 52-22; this difference can be quantified by rotational viscometry according to ASTM D2196-20. Reactor charge viscosity limits often govern colloid selection in jacketed glass-lined vessels equipped with pitched-blade impellers. When a plant must raise total latex solids from 55 wt% to 60 wt% without exceeding a high-shear viscosity threshold of 1,000 mPa·s at 20 rpm, a low-viscosity grade such as 51-05 is used in place of a medium-viscosity partial grade at equal protective colloid concentration.

The 51-05 grade also contributes to latex particle size control. Dynamic light scattering measured under ISO 22412:2017 indicates that increasing the colloid concentration from 2.0 wt% to 4.0 wt% on total monomer generally shifts the final particle size distribution toward finer average diameters, while the low molecular weight prevents the excessive thickening observed with higher-viscosity grades. For systems containing vinyl acetate and ethylene, the grafted polyvinyl alcohol content influences shear stability and coagulum formation. Reactor operators monitor coagulum on a 100-mesh discharge filter; accumulation above 0.05 wt% of batch weight triggers corrective adjustment of initiator feed rather than colloid replacement.

What Limits Shelf-Life Stability in Partially Hydrolysed PVOH Granulate?

Moisture uptake is the main storage boundary for ELVANOL 51-05. At 25 °C and 80% RH, dry granulate becomes cohesive within 24 h, and caked layers can form at the base of bulk silos. Closed storage at <40 °C and <60% RH is recommended; under these conditions the supplier suggests a shelf life of 24 months from manufacture in sealed packaging. Pneumatic conveying should be conducted with dried air at a dew point below 5 °C. Fine dust from the granulate is combustible; explosion prevention measures follow IEC 60079-10-2:2015, with bonding and grounding in transfer equipment.

Thermal stability boundaries apply during processing. Polyvinyl alcohol decomposes at temperatures above 200 °C, releasing acetic acid and unsaturated decomposition products. Therefore extrusion of compounded films should be limited to melt temperatures below 200 °C unless a plasticiser is present. Contact with strong oxidising agents and transition-metal salts that catalyse oxidation should be avoided. Aqueous solutions are susceptible to microbial degradation; for storage longer than 48 h, preservation or refrigerated hold at 5–10 °C is needed.

Because polyvinyl alcohol complexes with borate ions, aqueous 51-05 solutions should not be blended with alkaline borate buffers unless controlled crosslinking is intended. In adhesive and coating plants, product changeover from a borated starch or borate-crosslinked polyvinyl alcohol formulation requires flushing with hot water at 80 °C to remove gel deposits.

Remoistenable envelope adhesives based on ELVANOL 51-05 are prepared at 15–25 wt% solids. The solution is applied by gravure wheel or slot applicator at 20–30 g/m² dry coat weight. Drying tunnels operate at 80–120 °C for 5–15 s. The low viscosity of the grade allows uniform transfer at line speeds up to 300 m/min without stringing; wet coat thickness is controlled by gravure roll speed ratio. Rewetting of the dried adhesive is rapid because of the residual acetate content. The rewetted bond must develop fibre tear within 10–15 s under 20 °C, 50% RH conditions; adhesion is assessed by ASTM D1876-08 T-peel testing.

Formulation limits apply below 10 °C. Plasticiser addition is necessary to prevent brittleness; glycerol or polyethylene glycol at 5–15 wt% on PVOH solids is used. Excess plasticiser above 20 wt% reduces fibre tear by lowering cohesive strength and increasing re-wet tack after ageing at 40 °C, 75% RH. These effects are evaluated by ASTM D1876-08 T-peel testing and by accelerated ageing in a humidity cabinet.

When Surface Sizing Formulations Are Limited by Press Roll Viscosity

At the size press of a paper machine, starch surface sizing formulations containing ELVANOL 51-05 are prepared at total solids of 8–12 wt%. The low molecular weight of the grade permits addition of 1–3 parts PVOH per 100 parts starch without exceeding the viscosity envelope of the metering size press. Surface strength of dried paper is assessed according to ISO 3783:2006; the PVOH component increases pick resistance relative to pure oxidised starch at equal coat weight. The resin also reduces dusting and improves film continuity on sized paper. However, because 51-05 is partially hydrolysed, it retains greater water sensitivity than fully hydrolysed PVOH; paper intended for high-humidity packaging may require blending with a fully hydrolysed grade or with a crosslinker.

The primary differentiation between ELVANOL 51-05 and medium-viscosity partially hydrolysed grades such as ELVANOL 52-22 is the magnitude of solution viscosity. At 4 wt% solids and 20 °C, 51-05 produces a viscosity of 5.0–6.0 mPa·s; 52-22 produces a viscosity of 20–26 mPa·s. This difference corresponds to a reduced chain length and lower molecular weight, not to a significant difference in hydrolysis degree. Both grades carry approximately 87–89 mol% hydroxyl functionality, but 51-05 dissolves more quickly and develops lower solution elasticity. Conversely, fully hydrolysed grade ELVANOL 70-06 is similar in solution viscosity to 51-05 but has hydrolysis above 98 mol%. As a result, it requires higher dissolution temperature, forms a more crystalline film, and gives better water resistance and oxygen barrier after drying. The partially hydrolysed 51-05 grade is preferred when low temperature dissolution or re-wetting is required, for example in remoistenable adhesives and water-soluble packaging used for dry detergents. In barrier film applications, 51-05 is not the optimum choice because residual acetate groups reduce crystallinity and increase water permeability; grades with hydrolysis above 98 mol% are specified for films measured under ISO 15106-1:2007 oxygen transmission rate testing. Specific oxygen transmission rate values for a 51-05 monolayer film are not provided in the supplier datasheet; published data for this specific configuration is limited to comparative statements against fully hydrolysed grades.

Regulatory and Safety-Critical Compliance Checklist

ELVANOL 51-05 is a candidate resin for water-soluble packaging film when combined with plasticiser and processing aids. The low molecular weight reduces melt pressure during twin-screw extrusion. Extruders with L/D 30:1 to 40:1 and barrel temperatures of 150–190 °C are used; venting at the vacuum port removes residual moisture. The partially hydrolysed grade dissolves at 10–20 °C within 60–120 s when cast film thickness is 50–70 µm, but dissolution rate data should be confirmed with end-use machinery because water temperature, agitation, and film orientation influence the result. Packages for alkaline detergents may require a fully hydrolysed grade if reduced cold-water solubility is needed to prevent premature dissolution in humid storage.