Effect of vulcanization systems and antioxidants on discoloration and degradation of natural rubber latex thread under UV radiation

The effect of accelerator combinations and antioxidants on UV radiation degradation of natural rubber (NR) latex thread with a conventional and efficient vulcanization system is presented. Zinc diethyl dithiocarbamate (ZDEC), zinc dibutyl dithiocarbamate (ZDBC), zinc mercaptobenzothiazole (ZMBT), and tetramethyl thiuram disulfide (TMTD) were used as accelerators. The antioxidants used were reaction products of butylated p-cresol and dicyclopentadiene (Wingstay-L), Tris-nonylated phenyl phosphite (Crystol EPR 3400), styrenated phenol (SP), and polymerized 1,2-dihydro 2,2,4-trimethyl quinoline (HS). The thread samples were exposed to UV radiation and the appearance and physical properties of the thread were examined. The results indicated that the threads having ZDBC + ZDEC and ZDBC + ZMBT combinations as accelerators are more resistant to UV radiation than the thread having the ZDEC + ZMBT combination. The antioxidants Wingstay-L and SP + HS are effective in retaining the physical properties of the thread after UV exposure, and Crystol EPR 3400 is better in reducing discoloration. (C) 2000 John Wiley & Sons, Inc.