Safer accelerators

Presented at the International Latex Conference 2021,
by Dr Boyd Grover - Senior Polymer Chemist
at Robinson Brothers. 

Title: Replacement of zinc dibutyldithiocarbamate by safer accelerator(s) for nitrile latex glove formulation

Abstract

Primary accelerators are relatively slow and have a delayed onset of cure. Secondary accelerators activate primary accelerators and increase speed of vulcanisation but they are well known contact sensitizers (Type IV allergy) and can pose serious health implications, and therefore can be major problem in nitrile latex applications like gloves. In order to overcome the concerns relating to health issues, a cure system based on safer chemical accelerators such as bis[bis(3,5,5-trimethylhexyl)dithiocarbamate-S,S’]zinc and di-isopropyl xanthogen polysulfide were investigated for use in the nitrile rubber latex. It is more commonly known as zinc diisononyldithiocarbamate or Robac Arbestab Z and Robac AS100 respectively. These accelerators are nitrosamine safer compared to more traditional accelerators like zinc diethyldithiocarbamate (ZDEC) and zinc dibutyldithiocarbamate (ZDBC).

Our work investigated the contribution of these secondary accelerators in nitrile latex glove formulation from a rheological point of view and mechanical testing of dipped films. This aimed to substitute ZDBC with a safer secondary accelerator. ZnO was used as an activator for sulphur vulcanisation to improve cross-link efficiency. However, a cure system with ZnO alone takes three times longer to cure latex compared to an accelerated system. Our findings showed that ZDNC in combination with Robac AS100 resulted in superior cure profile to ZDBC and therefore, could potentially work as a replacement for ZDBC from a rheological point of view. The initial tensile and heat aging properties of the dipped films using ZDNC in combination with Robac AS100 appear to be comparable to ZDBC cure. However, the accelerator loading is critical and has to be optimised, prior to use in latex glove dripping, to maximise prevulcanisation and glove defects. The accelerator compositions must also be such that it does not give rise to irritant dermatitis, Type IV allergy or form carcinogenic N-nitrosamine and N-nitrosatable substances, after vulcanisation cure, in the final product.

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