Tissue Testing Primer

Good standards ensure date objectivity, fair trade, and good decision making.

TODD POPSON, DAVID LOEBKER, JESSICA CARETTE, COLLEEN WALKER

In today’s worldwide paper industry, there is a lot of activity related to tissue. A recent market research study shows that between 2018 and 2024, annual growth in the tissue and hygiene areas is expected to reach 3.8 percent in North America, and even higher in less developed countries1. Due to increased trade and new product development, there has been an increased attention to standardization and harmonizing methods for testing tissue products. Luckily, TAPPI has a committee specifically devoted to this task.

Checking the thickness (caliper) of towel, tissue, napkin, and facial products.

The Tissue Properties Testing Subcommittee, which is part of the Process & Product Quality Division, generates new work items as potential standards, reviews existing standards, periodically updates methods, and submits standards to ANSI to be considered National Standards. The committee, currently chaired by Jessica Carette, is comprised of mill personnel, technical professionals, suppliers and members from allied industries. Here are the existing TAPPI Test Methods that are specific to paper tissue and towel:

T 432 Water absorbency of bibulous papers;
T 580 Thickness (caliper) of towel, tissue, napkin and facial products;
T 581 Dry tensile properties of paper towel and tissue products (using constant rate of elongation apparatus).

There are many other TAPPI methods that are inclusive and applicable to tissue and towel paper, but as is often the case, important method deviations are often required to make the test results more meaningful and/or reproducible when applied to tissue’s relatively high bulk, flexible, and low strength properties (compared to most other paper grades).

Some of the important attributes of tissue/towel paper are: absorbency, thickness (bulk), softness, dry strength, wet strength, optical (e.g., brightness, opacity), and various properties related to flushability. Each of these attributes is a function of the fibrous structure, chemical, and material properties that can be measured in an infinite number of ways, with the goal of predicting consumer desirability and/or process runnability.

Have an idea for a new method or standard? Anyone can propose a new work item. And by joining and participating in the TAPPI Tissue Properties Subcommittee, a wealth of testing knowledge and experience can be easily accessed to help develop the test method into a potential standard. The committee works together to ensure:
1. Widely accepted and scientifically sound testing equipment/procedures;
2. Unbiased, objective, and quantitative results (i.e., not “pass or fail”);
3. Repeatability and reproducibility of measurements;
4. Results that provide value to the tissue paper and related industries.

Sometimes a new test method isn’t needed or required, but rather technical guidance and other information on how to best measure a specific property. In this case, TAPPI Technical Information Papers (aka TIPs) may be a more appropriate means to disseminate information.
In addition to TAPPI, standardization work is also performed in ISO (International Standards Organization). Within the technical committee #6 (TC 6: paper, board and pulps, with Todd Popson leading the US/ANSI delegation) resides working group #27 (WG 27: Tissue Test Methods, Convenor: David Loebker), which is responsible for following ISO Standards:

ISO 12625-1
Tissue paper and tissue products—Part 1: General guidance on terms
ISO 12625-3
Tissue paper and tissue products—Part 3: Determination of thickness, bulking thickness and apparent bulk density and bulk
ISO 12625-4
Tissue paper and tissue products—Part 4: Determination of (dry) tensile strength, stretch at maximum force and tensile energy absorption
ISO 12625-5
Tissue paper and tissue products—Part 5: Determination of wet tensile strength
ISO 12625-6
Tissue paper and tissue products—Part 6: Determination of grammage
ISO 12625-7
Tissue paper and tissue products—Part 7: Determination of optical properties—Measurement of brightness and colour with D65/10° (outdoor daylight)
ISO 12625-8
Tissue paper and tissue products—Part 8: Water-absorption time and water-absorption capacity, basket-immersion test method
ISO 12625-9
Tissue paper and tissue products—Part 9: Determination of ball burst strength (dry)
ISO 12625-11
Tissue paper and tissue products—Part 11: Determination of wet ball burst
ISO 12625-12
Tissue paper and tissue products—Part 12: Determination of tensile strength of perforated lines—Calculation of perforation efficiency
ISO 12625-15
Tissue paper and tissue products—Part 15: Determination of optical properties—Measurement of brightness and colour with C/2° (indoor daylight) illuminant
ISO 12625-16
Tissue paper and tissue products—Part 16: Determination of optical properties—Opacity (paper backing)—Diffuse reflectance method

Also, there are new work item proposals and ongoing development projects related to the following topics:

Absorbency: The rate of fluid uptake, as well as the maximum capacity of tissue and towel, are important consumer product attributes. A TAPPI method from the 1990s (T 561) was withdrawn for a variety of reasons, but there is renewed interest to redevelop and standardize the GATS (gravimetric absorbency test system) technique created by M/K Systems, as the need for a commercially available standardized test still exists.

The makers of the Emtec TSA instrument are proposing a TAPPI TIP document to give background and guidelines for how to best use their instrument to generate results that effectively correlate to subjective surface and bulk softness feel.

Disintegration: The ability of tissue and towel paper to disintegrate in water into smaller fragments is important for repulping broke from the paper machine, toilet flushability, and drain line clearance, and other consumer uses and process functions. A laboratory disintegration test method was proposed to ISO last year by Dr. Sylvie Moreau-Tabiche (France), and is being further studied in round robin testing as of this writing.

Tensile stiffness: The aim of this method (from Dr. Young Chan Ko, Korea) is to determine tensile stiffness of tissue paper, which he has shown in various publications to have correlation to bulk softness (as opposed to surface softness, discussed below). This new work item proposal is currently in the ISO ballot voting process.

Tissue softness: Although the human perception of softness will never be fully replicated by analytical instruments, measuring certain physical properties can often produce a useful result that correlates very well to subjective softness paneling results. The makers of the Emtec TSA instrument are proposing a TAPPI TIP document to give background and guidelines for how to best use their instrument to generate results that effectively correlate to subjective surface and bulk softness feel. Friction measurement (COF) is another measurement topic that also comes up in the softness conversation, and a new work item has recently been proposed by Dr. Young Ko (currently in ISO ballot).

In summary, tissue and towel are a specialized subset of paper products that require specialized test methods and standards. TAPPI and ISO offer several test methods for tissue and towel paper products; however, there are still other important properties that do not have standardized methods associated with them. Good standards ensure data objectivity, fair trade, and good decision making. Therefore, it is important that companies and organizations of every type be involved in the development process.

Reference
1. “Global Market Study on Tissue and Hygiene: Asia Pacific to Beat North America to the Top Position by 2025 End,” Report from: Persistence Market Research, Sept. 2017. URL: https://www.persistencemarketresearch.com/market-research/tissue-and-hygiene-market.asp