Hyoung Jin Kim

Principles of Developing a Softness Evaluation Technology for Hygiene Paper

In developing objective tissue softness evaluation methods, reliable and reproducible subjective evaluation data are a prerequisite. A trade-off relationship generally exists between the relevance to a consumer’s in-use situations and the test variability. At present, sensory panel test (SPT) has been most widely used. It provides the least variable data, but it has the problem of being the least relevant to the real world. Recently we have developed a new sensory panel test which is referred to as new sensory panel test (NSPT). It performs like a HUT (home-user-test) for the relevance and like a physical test for the test variability. Since the pioneering work by Hollmark, it is now widely accepted that subjective tissue softness should primarily consist of the bulk softness component and the surface softness component. The bulk softness component can be determined by the tissue flexibility. The surface softness component can be determined by measuring the surface roughness and the surface friction. In the present study, the NSPT was performed on 7 commercial bathroom tissue products. For subjective softness evaluation, the Thurstone interval scale values have been determined for the 7 products. For the bulk softness component, the flexibilities of these samples were measured using a tensile tester (Criterion model-41, MTS, U.S.A.). For the surface softness component, the surface roughness and the surface friction were measured using the surface roughness/friction tester (KES-SESRU, Kato Tech., Japan). The result validates the hypothesis that the bulk flexibility and the surface roughness/friction should be sufficient for developing an objective tissue softness evaluation method.

A New Subjective Softness Evaluation Method for Hygiene Paper

Hygiene paper belongs to a category of consumer products whose properties need to be evaluated subjectively by users. For hygiene paper (e.g., tissues and towels), softness, absorbency, and strength are the three most important attributes. These attributes are most frequently evaluated by Sensory Panel Tests (SPTs). Subjective evaluation methods employ ranking, rating, and/or the percentage (%) of the preferences between two products in collecting the data. However, none of these methods provides linear and continuous scale values such as physical measurements which have many benefits. Such a linear and continuous scale is also referred to as the Thurstone interval scale. When more than two products are to be compared, a round-robin paired-comparison test would be required for each pair. In the present study, several subjective tests had been conducted with 100 panelists. They were not trained and minimal instruction was provided for evaluating softness of seven commercial bathroom tissues. Each panelist was asked to rank and rate the seven tissue samples and to select the softer on between two samples in paired-comparison tests. The results showed that the paired-comparison test method was the most discriminating. The method, however, has also the problem that it does not generate linear-scale numbers and the required number of round-robin tests increases dramatically as the number of products for testing increases. To solve this problem, a new SPT (NSPT) was developed. It was concluded that the NSPT would be much easier and faster than the conventional SPT while being more relevant to the consumers. The NSPT is expected to play a critical role in developing an objective test method which can be used to predict subjective tissue softness evaluation.