Testing Adhesive Performance in the Absorbent Hygiene Core

Whether designed for babies or incontinent adults, the core of a diaper is a dynamic, complex system. Inside, there are many individual components that must work together. Each plays a role in preventing leaks and keeping the skin dry. The construction adhesive used to bond these different parts helps ensure core integrity and performance. Adhesive can also provide structure in the core. As manufacturers explore newer options, the adhesive can take on additional tasks. But every adhesive does not work in every core, and consumer satisfaction depends on making the right choices for your product.
 

Testing procedures and equipment vary

There is no industry-wide standard to ensure that cores retain their integrity and perform as designed. Although manufacturers may use similar tests, the exact details may vary. Differences can include speed, time, and other specifics. Some use expensive equipment, whilst others rely on manual alternatives. Methods chosen may be a function of resources available, experience, or simple preference.

This article outlines a number of procedures used to test the core adhesive’s performance. Other methods, such as absorption, retention, or rewet, can be used to evaluate overall core performance. At Bostik, we take a holistic approach to achieving and testing the desired impact of the adhesive.
 

Adhesive testing in the traditional core 

Although exact details may vary, certain types of evaluation are fairly common for the traditional core. 

• Core Cracking. Qualitative test: After insult, the core is subjected to movement (typically some form of dropping, shaking, or spinning) until cracking is observed. May be performed manually or on a machine.
• Visual Test for SAP/Fluff Remains. Qualitative analysis: After insult, the core wrapping material is peeled back to observe retention of SAP/fluff. More retention indicates better wet strength.
• Wet Peel. Quantitative test: Used to demonstrate the effectiveness of adhesive bonds when wet. A tensile tester records average peel after simulated insult.

Bostik’s holistic approach means we continually look for ways to improve testing, especially opportunities to gain additional or more accurate information. Our Conditioned Core Cracking test, for example, takes the typical core cracking test a step further. In addition to evaluating a fresh diaper, we add a preconditioned component to the procedure. This allows us to simulate the impact of a baby, toddler, or incontinent adult moving around before the insult occurs. 
 

Channel adhesive testing: will it hold or release?

Because of their differing structure, core cracking is not a concern in channel cores. Instead, adhesive tests focus on the performance of the adhesive used to create the channels. This is necessary to ensure they perform as expected when the SAP absorbs insult and swells. 

• Dynamic Peel Test: Quantitative test: The top and bottom layers of a dry diaper are pulled apart at a consistent speed to determine the amount of force needed to separate the layers. This may be done under wet and dry conditions.
• Immersion Test: Qualitative test: The diaper is immersed in a saline solution and allowed to absorb for a set period of time. (Typically, a 0,9% NaCl solution is used.) The diaper is then observed at set intervals to determine if the channels have broken open. 
• Centrifugation Test: Qualitative test: The diaper is immersed in saline solution, then centrifuged for a set period of time. The diaper is then observed to determine if the channels have opened.

Compound/pre-Compound core testing

Manufacturers testing their early compound cores learned they do not crack. However, they do have other weaknesses, which manufacturers have been working to improve. The primary aspects tested today include absorption (speed, volume, and rewet) and SAP movement. These tests can also help determine how the adhesive can best be used to positively impact performance. We have found that using a variation on our Conditioned Core Cracking Test is useful in determining how much SAP shifts in use. 
 

Bostik testing and solutions

Bostik offers a variety of informative tests to measure product performance and integrity. Take advantage of our additional specialty services, such as product audits. Bostik’s trained professionals will thoroughly test finished articles taken from your lines. We can also provide recommendations to overcome any integrity and performance issues we find. 

CODE: CO-22A09