Used by papermakers for more than 40 years, Kymene® Wet Strength Technology is a range of water-soluble polymer products that provide wet strength to paper.  The most common paper grades that utilize this technology include tissue and towel, liquid packaging, unbleached packaging board, and specialty grades such as label paper. 

The most commonly used Kymene® products utilize polyamide-epichlorohydrin (PAE) resin chemistry at alkaline pH.  PAE resins provide specific paper properties, have the highest level of wet strength permanence, and improve machine efficiency.

Recent development work has focussed on improving the wet strength efficiency of Kymene® products while increasing product solids and decreasing organic chlorine content.  Today, there are many new Kymene® products available that offer these benefits.   

Mode of Action

During the curing process, the cationic functional groups on the Kymene® polymer react with cellulose fiber to form a covalent bond.  The polymer molecules cross-link forming a network in the cellulose web that provides strength when the paper becomes wet.  Additionally, Kymene® resins can reinforce existing fiber-to-fiber bonds, which also enhances the strength of the paper when it is wet.

Product Selection

Your Hercules representative can assist you with the selection of the most appropriate Kymene® resin.  Selection is based on several important criteria:

Paper grade and required levels of wet strength
Paper machine conditions (e.g., pH, fiber furnish, conductivity, and drying conditions)
Other additives present (e.g., size, dry strength, creping aids, dyes, and debonders)
Shipping distance and product turn-over at the customer site
Regulatory requirement of finished paper product

Application Technology

Kymene® Wet Strength Technology is most effective over a stock pH range of 4 to 9; however, since Kymene® PAE resins are alkaline curing, the best performance is obtained at pH 6.5 to 8.5.  Optimum results are obtained by adding diluted Kymene® resin to the high-consistency stock either before or preferably after refining.  Wet strength addition rates generally range from 0.2% to 1.2% dry basis and occasionally dosages outside this range are used for specific wet strength paper grades.

Hercobond® polyacrylamide anionic dry strength additive can be used to enhance the performance of Kymene® Wet Strength Technology.  Normally added after Kymene® Wet Strength Resin to the thickstock, wet and dry tensile performance can be increased by up to 20%.  The Hercobond® polyacrylamide additives are especially useful for improving Kymene® performance at the upper end of the addition range.   Hercobond® polyacrylamide addition rates are determined by system chemistry, especially ionic demand and conductivity, as well as the furnish composition.  The usual addition strategy is to balance system charge in the wet end of the machine. Your Hercules representative can advise on the best optimization strategy.  Additional benefits include control of excessive cationic charge in the short loop, improving drainage, formation; foam control and press felt cleanliness.

When Kymene® Wet Strength Technology is used with sized grades, generally, the sizing chemicals are added before the wet strength resin.  This may require the wet strength to be added to thin stock before the fan pump since the sizing chemicals may be added to high consistency stock.

Recorded Benefits

In addition to providing wet strength in paper, Kymene® Wet Strength Technology has been shown to provide additional benefits.  Not all benefits are realized for all applications.

Improved retention and drainage
Improved wet end charge control
Enhanced creping control
Enhanced dry strength
Reduced chemical costs
Improved runnability