Effect of Alternate Heating and Cooling on the Breaking Strength and Elongation of Cotton and Rayon Tire Cords

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Abstract
Six different tire cords, including one mercerized and two unmercerized cottons, and three rayons, were subjected to alternate heating for 16 hours at 265°F and then cooling for 8 hours in a room temperature of 70°F and 65 percent relative humidity. The effects of these treat ments on the tenacity (grams per denier) and elongation were determined at the end of 1, 24, 36, and 48 heating periods. Tests were conducted on the cords in the oven-dry state, and also after conditioning in a standard atmosphere of 65 percent relative humidity at 70°F. Elonga tions at breaking load were read from the charts measuring from the point where the pen first registers and also from the point where it leaves the axis. In all tenacity tests the mercerized cotton cord showed the greatest resistance to change, and was generally followed by one of the rayons. The unmercerized cotton cords gave better re tention of tenacity than the other two rayon cords under standard conditions of test, but this order was reversed under oven-dry conditions. All the rayons exhibited higher initial elonga tions and, with one exception, greater losses on heating and cooling than did the cottons. The two methods of measuring elongation gave a slightly different order of rankings of the cords. The degrees of polymerization of the cellulose changed after 48 heating and cooling cycles from 2400 to 385 for Wilds 13 unmercerized cotton cord, from 2360 to 310 for the Wilds 13 mercerized cotton cord, and from 430 to 129 for the rayon cords.

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