The tensile strength of a nonwoven web is measured by die cutting the test samples from the web and pulling these samples in the tensile test machine. The tensile test machine pulls the ends of the sample apart at a uniform speed while continuously measuring the force on the sample. The "peak" or maximum force sustained by the web is commonly called the tensile strength. The RK roll is not made with layers of nonwoven web and no tensile values for RK rolls are presented in this report.

All samples tested were a single layer of web and the strengths were normalized to compensate for the various web weights. The strengths under the "Dry" column were measured on samples that were cut and stored at typical indoor temperature and humidity conditions. The "Wet" samples were submerged in tap water at room temperature for 3 days. Before the tensile test,, these samples were simply removed from the water and tested. No effort was made to wring out or dry off any excess water.

With nonwoven webs, the downwebs and crossweb strengths are usually different from each other due to the specific way the web is produced and the pulling of the web as it moves through the making process and is wound up into a roll. The 3M webs were tested in both the downweb and crossweb directions and the values were averaged to provide more of a random or average value on the comparison chart. The competitive webs were obtained as cut sections ready to be made into a roll. Thus, the web orientation is unknown and the web direction of these samples was truly random.

Another factor of web manufacture that affects the web tensile strength is needling. The 3M Neutral web is not a needled construction. We are uncertain if the Toho web is needled, but the URB web appears to be needled. The 3M C web is a needled construction and the 3M Acid web is heavily needled. The needle punch process results in higher tensile strength values compared to the same web without needling.

The included chart presents a summary of the relative tensile strengths of the various webs. The 3M Neutral web is presented as the baseline at 100%. The tensile strengths of the other webs are shown as a percent value compared to the 3M Neutral web. Typically, only differences of 15% or more are considered significant due to the high variability of nonwoven webs.

Perhaps what stands out the most are the extremely low values of the Toho web. The Toho web is simply the lowest strength web we have tested. The Freudenberg/URB web and the 3M Neutral web are quote comparable. (Recall that values within 15% are considered within the random nature of nonwoven webs.)

The 3M Acid and 3M Type C webs have dry strengths in the neighborhood of the URB and 3M Neutral webs, but the wet strengths are significantly higher than the other webs. The 3M Acid web is stronger than the 3M Type C web due to the very heavy needling used during manufacture. More importantly, there is a basic difference that the Nylon webs all lose strength when saturated in water while the polypropylene webs gain strength when saturated in water.

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