Determination Of The Effect Of Accelerator Type And Accelerator/Sulfur Ratio On The Vulcanization Kinetics And Aging Properties Of Natural Rubber/Chloroprene Based Rubber Compounds

Abstract

In the scope of this thesis it has been tried to clarify the effects of different types of accelerators and the effects of accelerator/sulfur ratio also known as vulcanization system on mechanical, thermo mechanical and stress relaxation properties, crosslink density and network structure of the NR/CR vulcanizates. In addition, it has been tried to clarify effects of accelerator type and vulcanization system on accelerated weathering behavior of NR/CR based elastomers method has been chosen to investigate aging behavior in conditions closer to open air, where NR based materials are more vulnerable to aging. So far, such relationship has not been established to identify the effects of type and ratio of accelerator used in preparation of NR/CR based elastomers on crosslink density and aging properties of the resulting vulcanizates using pulse-NMR technique and spin-echo method and the role of dynamic relaxation after accelerated weathering. It has been planned to fill this gap in the literature and provide detailed scientific data related to structural differences of sulfur vulcanizates and their thermo mechanical response to different cure systems. The ultimate goal of this thesis is to determine optimum accelerator, and accelerator/sulfur ratio for not pre-scorched but fast vulcanized, minimum reversion vulcanizates, which possess stable mechanical properties and crosslink density even after curing. For this purpose, keeping all the other chemicals in a fixed amount, we have prepared a series of compounds in an internal mixer using tetramethyl thiuram disulfide (TMTD), 2-Mercaptobenzothiazole (MBT), diphenyl guanidine (DPG), Zinc dibutyl dithiocarbamate (ZDBC) and N,N' Diethylthiourea (DETU) from different types of accelerators and also different accelerator to sulfur ratios. The vulcanization of the compounds has been examined by using moving die rheometer (MDR); crosslink densities have been determined by pulse-NMR technique; stress relaxation properties have been analyzed using temperature scanning stress relaxation (TSSR) method; and mechanical properties have been determined by universal testing machine. To determine weathering effect, the prepared vulcanizates have been aged using accelerated weathering machine. Changes in thermal, mechanical and thermo-mechanical properties have been analyzed using the same standard methods in order to maintain a good comparison base. At the end of all these experimental work, the relations between each accelerator group and each cure system and mechanical, thermal and thermo mechanical properties of the NR/CR based vulcanizates have been clarified. This will fill the literature gap in this field and provide valuable information for the researchers, students and engineers who are trying to prepare NR/CR based formulations with optimum thermal, mechanical, thermo-mechanical and aging properties.