Characterization of EPDM Vulcanizates Modified with Gamma Irradiation and Trichloroisocyanuric Acid and Their Adhesion Behavior with Natural Rubber

Abstract

The adhesion strength between surface-modified vulcanized ethylene propylene diene methylene (EPDM) rubber and unmodified natural rubber (NR) was investigated by a 180° peel test. Surface modification of EPDM vulcanizate was carried out by two different techniques: (a) irradiation of the surface by gamma radiation in the presence and absence of trimethylol propane triacrylate (TMPTA) as a sensitizer and (b) chemical treatment of the surface with trichloroisocyanuric acid (TCICA). The modified EPDM surface was thoroughly characterized by attenuated total reflection infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray sulfur mapping (EDX), surface energy measurements, and free sulfur and gel content analysis. The joint between the modified vulcanized EPDM and the unmodified unvulcanized NR was prepared by a co-curing method. The adhesion strength between these two surfaces was found to depend on the nature of oxidation, roughness of the joining surfaces, and extent of blooming of sulfur on the modified surface. Surface modification of EPDM sample with 1 kGy of gamma irradiation in the presence of 10 wt% TMPTA resulted in a good increase in the adhesion strength between EPDM and NR (∼76% improvement over the untreated sample). On the other hand, for the trichloroisocyanuric acid modified sample, maximum improvement of adhesion strength was observed at 0.5 wt% of TCICA (∼29% improvement in comparison with the untreated sample).

Keywords:

• 180°-Peel test
• Adhesion
• Co-curing
• EPDM vulcanizate
• Gamma irradiation
• Trichloroisocyanuric acid

ACKNOWLEDGMENT

The author would like to acknowledge the financial assistance provided by the Department of Atomic Energy (DAE), and the Board of Research in Nuclear Sciences (BRNS) Mumbai vide sanction no. 2005/35/4/BRNS/516 dated 8 June 2005.

Notes

∗phr—parts per hundred grams of rubber.

∗EP= EPDM rubber, EP _0kGy = EP _0TCICA means untreated vulcanized EPDM rubber surface.

^@ EP _{xkGy/0 (c)} -NR _(UC) , Here EP _xkGy/0(c) means cured modified EPDM rubber vulcanizate with varying irradiation dose (0 to 3 kGy) and EP _{xkGy/10TM (c)} implies cured modified EPDM rubber vulcanizate with varying irradiation dose (0 to 3 kGy) in presence of 10 wt.% TMPTA.

Similarly EP _z(c) in ^$ EP _z(c) -NR _(UC) means vulcanized surface modified with TCICA (trichloroisocyanuric acid). Here, Z stands for concentration of TCICA and C means cured EPDM rubber.

NR _(UC) =designation of uncured rubber.

N.B.—Free sulfur of EPDM _3kGy is 2.016 mg.

∗TCICA modified sample.