Evolution of Tissue Softening Agents

For many years, the term “tissue softeners” referred to a simple class of products that could be more accurately described as “debonders”. Debonding chemistries do have the impact of creating a softer sheet in most instances, but this is achieved via the destruction of strength. Tissue softness is well understood to be inversely proportional to base sheet strength which is what made the original debonding softeners popular with tissue makers who had excess strength that they were not able to drive down to their desired target.

This paradigm was a function of the main production platforms of the time, namely the pressure formers, inclined pressure formers and even twin wire designs of the day that most tissue producers had access to and used.

These production platforms necessitated heavier basis weights in order to be able to successfully traverse the pick-up stage and to do so without holes and other defects.
Many North American and European tissue producers were also using more local fiber sources and recycled materials which have higher inherent strengths than today’s eucalyptus pulps. For some producers, the combination of higher basis weight and stronger pulps meant that using a debonding softener was an effective solution for improving handfeel.

Connected to innovative technology

With the expiration of the patents surrounding the crescent former, the industry underwent a steady conversion of their existing platforms to the crescent former machines.
These offered higher speed, lower basis weight and improved overall sheet formation and appearance than the older light-dry-crepe platforms. With the proliferation of eucalyptus pulps, most tissue producers could make tissue to their strength targets with creping and refining adjustments, negating any need for debonding softeners. As base sheet eucalyptus content increased to ever higher levels, up to even 100%, tissue makers found themselves often in need of more strength. Trying to improve softness via debonding softeners was no longer a viable solution. Debonding softeners are sometimes still used in machines with stratified headboxes, allowing tissue makers to debond only the top layer of the sheet, or they spray the debonding chemistry onto the sheet while it is carried by the felt to the Yankee. These approaches allow for reduced impact on tensile while giving the outer layer of the sheet a softer feel.

These approaches have their drawbacks however. Debonding the Yankee side layer on a stratified headbox can result in higher dusting and pilling which produced customer complaints. Spray applications created sheet handling issues and reel build problems that hurt runnability and produced converting plant complaints. These issues and constraints are well understood by tissue makers, and they have been clear that they want a chemical alternative that:

• Could be fed easily to the wet end of the process.
• Did not impact Yankee coating or sheet handling.
• Did not cause uneven reel build or corrugation.
• Did not reduce the strength of the sheet.
• Provided a substantial boost in handfeel, as measured by the TSA and/or panel.

Early on attempts were made to use converting-type silicones in the wet end. The first product iterations attempted in this area suffered from a lack of dispersibility and fiber substantivity which both increased the amount that had to be fed and often resulted in machine deposition and high costs. Benefiting from the potential softness boost of silicones required significant chemistry and formulation work to circumvent the problems associated with amino silicone use in the wet end. The most recent successes in this area have been achieved by creating custom formulations of water dispersible silicones that are also fiber substantive.

The result is a clean wet end system and lower addition rates which reduce cost. The application of these sort of wet end softening products have provided up to 10 points of increased TSA to the tissue base sheet.
When replacing an existing debonding-type chemistry, tissue makers benefit from significant cost reductions in refiner energy and dry strength resin use as well increased caliper.
Other ROI streams customers are leveraging include:

• Substituting for less expensive pulp while maintaining softness targets.
• Improving machine runnability by eliminating the spray-on softener application.
• Accessing private label contracts for higher softness products.

The industry is making use of these chemistries and we can expect that their adoption will continue to spread given their benefits over the older approach of debonding chemistries.