Influences of thermal aging on properties and pyrolysis products of tire tread compound

Due to variation on waste tires as raw materials for pyrolysis process in terms of mileage leading to varied extents of degradation, the effects of time-governed thermal aging were investigated on two properties of tire, and on pyrolysis product yields and product distribution. Samples of a tire tread compound originally cured to 90% crosslink were aged in an environment-controlled oven for 0–4 weeks. Pyrolysis was performed on all samples. It was found that aging time had the influence over the crosslink density and hardness in steps during the course of aging due to the different response of the rubber constituents toward aging as well as changes on the tire molecules occurring in different stages upon aging. These affected the product yields and component distribution of products obtained from pyrolysis process. At the earlier stage of aging for 1–3 weeks, gas yield decreased with the aging time in accordance with the increase in liquid yield. The gas component distribution and carbon number distribution in liquid products insignificantly altered. However, the amount of gas oil in liquid products slightly decreased with aging time while the other commercial fractions remained practically constant. After 4 weeks of aging, sudden changes in opposite direction on the pyrolysis products occurred. The gas product rapidly increased along with the abrupt decrease in the liquid yield. The carbon number distribution in liquid product shifted to lower numbers, and the shape was narrower. The gas oil amount suddenly increased after reaching the lowest value at about 3 weeks of aging. An aging model was finally proposed in order to explain the observations.