KURARAY POVAL 4-88

Polyvinyl alcohol (PVOH) having varying degree of polymerization and hydrolysis.

Kuraray Poval™ resin as an adhesive promoter

Kuraray Poval™ resin as an adhesive raw material used similarly to natural products such as casein, starch, and its degraded derivatives (for example, dextrins) as raw material for the production of aqueous adhesive solutions. Compared to dextrins and casein, Kuraray Poval™ resin has the advantage of a more uniform chemical structure and greater adhesion, being obtained with minimum raw material requirements.

Water-activated Adhesives

Remoistenable adhesives are employed mainly in the paper processing industry. Very familiar uses are the gumming of paper on the reverse side (e.g. postage stamps and labels) and the application of gum to the flaps of envelopes and Jiffy®-type bags. Partially saponified Kuraray Poval™ grades with low to medium viscosity, e.g. Kuraray Poval™ 5-88 are particularly suitable for this function. To produce the adhesive, Kuraray Poval™ solutions of up to 30% are applied according to the viscosity requirements, these solutions containing additions of preservative and defoamer if necessary. The open time of the adhesive depends on the grade of Kuraray Poval™ employed.

Increasing viscosity of a 4% Kuraray Poval™ solution is generally accompanied by decreasing open time. An applied quantity of some 10 g Kuraray Poval™ 5-88 solid per m² allows the production of coatings with very good remoistening properties and the following advantages

• High degree of flatness during storage under fluctuating air humidity
• Colorless, flexible coatings
• Minimal blocking tendency, even in high air humidity
• Fast setting after reactivatio

Modification of Emulsion Adhesives 

Aqueous solutions of Kuraray Poval™ resin can be added to polymer emulsions already stabilized with polyvinyl alcohol.

These emulsion adhesives affect the

• Extension of the open time
• Increase the setting speed
• Influence on the rheology

The open time is very important in such operations as the manual or mechanical bonding of wood and paper. In a number of polymer emulsions, the addition of Kuraray Poval™ solution increases the bonding speed considerably. Additions of up to 10% of an approx. 15% solution of Kuraray Poval™ resin to the polymer emulsion have proved to be suitable for this purpose. The choice of Kuraray Poval™ grades is primarily dependent on the viscosity required in the ready-to-use adhesive. Generally speaking, preference should be given to partially saponified Kuraray Poval™ grades on account of their faster solubility at lower temperatures. In emulsion adhesives suitable for application by dip wheel or roll-on applicator machines, the addition of a Kuraray Poval™ solution has the advantage of largely preventing skin formation during processing.

Kuraray Poval™ resin as a protective colloid 

Kuraray Poval™ grades, preferably of the partially hydrolyzed range, are used as protective colloids in the polymerization of polymer emulsions. Because of their ability to anchor to the surface of the polymer particles that form, they help to stabilize the polymer emulsion during and after the polymerization. Those Kuraray Poval™ types influence not only particle size distribution but also the application properties such as viscosity, stability to stirring, the freeze/thaw stability, pigment compatibility, electrolyte stability and open time of the emulsion.

The characteristics of PVOH make it well suited for an extensive range of applications in products that individuals use every day. From an emulsion polymerization aid to a binder for pigments in paper applications, the versatility of PVOH is widespread.

Preparation of PVOH Solutions

In the adhesives sector, PVOH is processed as an aqueous solution as it is in most other fields of application. The solutions should be prepared in corrosion-resistant vessels. In the case of Fully and Medium hydrolyzed PVOH, the PVOH is sprinkled into cold water during stirring and heated to 90 - 95°C in a water bath or by the use of live steam. In the case of Partially hydrolyzed PVOH, the PVOH is sprinkled into cold water during stirring and heated to 70 - 95°C in a water bath or by the use of live steam. The solution should be stirred during cooling to prevent skin formation.

The speed of dissolution increases with increasing temperature. For both partially and fully hydrolyzed PVOH grades the speed of dissolution decreases with increasing molecule size (increasing viscosity of the 4 % aqueous solution). The dissolving process is also made more difficult when there is a transition to higher concentrations. As a result, even more highly concentrated PVOH solution, (e.g. 30 % solution of Kuraray Poval™ 5-88), should be produced at temperatures of 90–95°C. Polyvinyl alcohol solutions may produce foam during stirring or transporting in pipelines, but this can be largely prevented by using a suitable stirrer design such as a low-speed anchor stirrer or by avoiding steep downward gradients in the pipelines.

Suitable defoamers are offered by numerous suppliers such as Dow Corning, Air Products and Chemicals, Inc., Emerald Performance Materials, Munzing Chemie GmbH, etc. Please check regulatory compliance if the application requires such status. Polyvinyl alcohol solutions which have been stored for lengthy periods may show increases in viscosity. This is especially true of fully hydrolyzed grades in high concentrations and at low temperature. The original viscosity can be restored by heating and stirring.

Polyvinyl alcohols are water-soluble polymers manufactured by alcoholysis of polyvinyl acetate. The properties of the various grades are mainly governed by the molecular weight and the remaining content of the acetyl groups.

Under certain conditions, aqueous solution PVOH can be attacked by micro-organisms. The main organisms that can reproduce in the acidic pH range are the fission fungi, whilst bacteria grow most readily in a neutral to weakly alkaline medium. The PVOH solutions can be preserved from any microorganism attack by the addition of preservatives. Suitable preservatives are offered by numerous suppliers such as Dow Chemical, Bayer Chemicals, Troy Corporation, Thor Specialties, Inc. etc. The dosage depends on the concentration of the solution, the storage temperature and the nature and intensity of the infection. Quantities of about 0.01 - 0.2% by weight preservative, relative to the PVOH solution, are generally sufficient. Compatibility and efficiency must be tested. Information on the quantity to be used is available directly from the suppliers.

It is advisable for the PVOH solution to be prepared and stored in clean containers. Considering the resistance that is shown by some micro-organisms to the preservatives employed, the dissolving vessel in particular, together with the filling equipment (pipes, valves, tubing, etc.), needs to be kept clean. Any skins or incrustations should be removed. In the event of complications, the possibility of changing to a different preservative must be considered.

Kuraray Poval™ resin can be stored for an unlimited period of time under appropriate conditions that is in its original packs in closed, dry rooms, at room temperature. Kuraray would recommend that our product is used within 12 months from the shipment date as given on the certificate of analysis.