Passage III

The tensile strength of a paper towel (PT) is the force per unit width required to break the PT when it is clamped and stretched (see diagram).

Dry strength is the tensile strength of a dry PT, and wet strength is the tensile strength of a PT that has been submerged in water. The wet strength can be increased by treating the PT with certain chemicals.

Students conducted 2 experiments to study the wet strengths of identical PTs, each 20 cm x 20 cm, treated with glutaraldehyde (GLA)or with GLA and zinc nitrate.

Experiment 1

First, the dry strengths of 5 PTs were measured, in newtons per meter (N/m), and the average of the measurements, D, was calculated. Then, Steps 1-5 were performed on each of 100 other PTs:

1. A PT was submerged for 30 sec in water (if the PT to be a control) or in a test solution containing GLA.

2. The PT was dried on a hot plate at 85°C for 4 min.

3. The PT was heated in an oven for 3 min at a certain temperature—25°C for a control PT and 25°C, 110°C，120°C, 130°C, or 140°C for a treated PT.

4. The PT was submerged in water for 10 min, 2 hr, or 24 hr.

5. The wet strength of the PT was measured in N/m.

The wet strengths of PTs that had been subjected to identIcal conditions were averaged. Each average wet strength, W, was divided by D and then multiplied by 100. The resulting values are shown in Figure 1.

Experiment 2

Steps 1-5 were repeated with 100 other PTs, except that the test solution contained both GLA and zinc nitrate (see Figure 2).

Figures 1 and 2 adapted from Gordon Guozhong Xu, Charles Qixiang Yang, and Yulin Deng, "Applications of Bifunctional Aldehydes to improve Paper Wet Strength"©2002 by John Wiely & Sons,Inc.