Structure and Properties of Extensively Degraded Rubber Vulcanizates

Abstract

Chemical stress relaxation is a unique technique to study the degradation of vulcanized natural rubber (NR).It is well-known that the relationship between the initial stress, f(0), and the initial network chain density, n(0), is given by eq. (1).f(t)=n(t) RT(α-α-2) at t=0 (1)at t =t (2)Thus far, eq. (2) has been used for degraded vulcanized NR. However, we have assumed that eq. (2) cannot be applied in the case of extensive degradation, and introduced a new method relating the netwark chain density with the number of scission in thermo-oxidative degradation of NR.Then, we have compared the network chain density calculated from relative stress with that calculated from the number of scission based upon the thermo-oxidative degradation of uncured-NR under the same degradative condition for DCP cured-NR.The values of the network chain density determined by the above two methods agreed with each other only in the early stage of degradation. However, it was found that eq. (2) is not valid as the degradation proceeds extensively. Consequently, a correction of eq. (2) has been advocated experimentally which is represented by f(t)-C·exp{-D·f(t)}=n(t)RT(α-α-2)