Page 462 - Handbook of Materials Failure Analysis

460 CHAPTER 17 Application of pyrolysis

FIGURE 17.11
SEM image of a fracture surface of the damaged car tire, indicating the brittle nature
of the component failure.

around in the grooves were investigated. Figure 17.11 shows the SEM image of a
fracture surface of the damaged car tire, indicating the brittle nature of the compo-
nent failure. Figure 17.12 shows the pyrograms of the examined rubber samples from
the tire treads pyrolyzed at 700 °C. Both samples were identified as SBR.
The detailed identification of the pyrolysis products of SBR was described in previ-
ous publication of the author (P. K.) [2]. In the meticulous examination of all
detected compounds in Figure 17.12a and b and with the help of the mass spectral
library NIST 05, it was found that the investigated SBR samples included the vulca-
nization accelerator, antioxidants, and a plasticizer but the corresponding content of
the additives was not the same in both samples [10]. The identified benzothiazole
(Figure 17.13,RT¼26.73 min) had been formed by the thermal degradation of
MBT. MBT is used as an accelerator for the vulcanization of rubber and as an anti-
oxidant. The content of the component measured by peak area ratio was two times
greater in the damage tire tread when compared to the new car tire. The sulfur content
from MBT increases the hardness and weakens the elastic properties of the rubber.
This can lead to brittle cracking of the tire. The peak of p-tert-butylphenol was only
seen in the chromatogram of the broken car tire tread (Figure 17.13,
RT¼27.93 min). The substance was probably generated from the antioxidant
BHT. The plasticizer p-isopropenylphenol was only detected in the broken car tire
tread (Figure 17.14,RT¼28.13 min). The content of the antioxidant allyl cresol was
about 2.5 times greater in the damaged tire tread compared to the new tire tread
(Figure 17.14,RT¼29.43 min). However, the content of the identified N-phenyl-
1,4-benzenediamine (Figure 17.12,RT¼37.48-37.49 min) was about 2.75 times