9 TENSILE STRENGTH AND FOLD ENDURANCE

SOME TENSILE STRENGTH TESTS were run on random sample pages taken from treated books. The machine used was a Chatillon light capacity universal motorized test stand model LTCM. The results of these tests correlate with the findings on polymer thinning mentioned earlier. The tensile strength of the paper is greatest in the peripheral areas of each page and decreases toward the center binding edge of each page. It should be pointed out that even very thin coatings of parylene will cause the tensile strength of paper to go up. A coating as thin as 2500 angstroms can double the tensile strength. Figure 9 is a chart showing the increase in tensile strength of standard newsprint as the thickness of the parylene coating is increased.

Fig. 9. Chart showing increase (or decrease) in tensile strength depending on the level of Parylene polymer in place on the paper.