Abstract
AbstractA systematic study was performed to understand the effects of the devulcanizing agent dibenzamido diphenyl disulfide (DBD) on the vulcanization and devulcanization process of a sulfur‐cured ethylene‐propylene‐diene monomer (EPDM) rubber. The influence of DBD on vulcanization was investigated by mixing DBD with virgin rubber and curative system. The devulcanization of rubber waste was achieved with varying amounts of DBD ranging from 0.4 to 13.8 wt% and temperatures from 150 to 200°C. The quality of vulcanizates and devulcanizates was evaluated by rheometer tests, temperature scanning stress relaxation measurements, and analysis of mechanical properties. During vulcanization, DBD acts as an accelerator in the presence of sulfur. When accelerators are added, the scorch time increases, and the cure rate decreases. Thus, DBD acts as a retarder. In the presence of activators, DBD leads to a significant reduction of crosslink density. This results in composites with high elongation at break and poor compression set values. The efficiency of the devulcanization of rubber waste depends strongly on DBD concentration and temperature. The monosulfidic crosslinks are cleaved by low concentrations of DBD, while polysulfidic crosslinks require higher concentrations. These results show that DBD is effective as a devulcanizing agent and degrades the network below 200°C.
Highlights
The recycling of rubber waste is still considered a challenge due to its chemically cross-linked three-dimensional structure
DBD acts as a retarder or pre-vulcanization inhibitor when the accelerator is added, which is observed by an increase in scorch time and a decrease in cure rate
The efficient vulcanization system (EV) curative system leads to low crosslink density and predominantly PS bonds formation in the presence of DBD
Summary
The recycling of rubber waste is still considered a challenge due to its chemically cross-linked three-dimensional structure. Intensive studies have been carried out in the last decades to break down the crosslinked rubber network by devulcanization. This involves treating rubber waste thermo-mechanical,[1,2] chemically,[3,4,5] biologically,[6,7,8] with ultrasound[9,10] and microwaves,[11,12] or by a combination[13] of such methods to achieve selective cleavage of C-S and. A melt-processable material is obtained after devulcanization, which can later be used to produce new industrial rubber goods and composites.[14,15] Despite all efforts in current rubber waste recycling research, the selectivity of S-S cleavage is challenging to achieve. Side reactions and crosslinks can occur depending on the DA and the devulcanization parameters.[17,18,21]
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