Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1118-1123  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal web link:  
Significant Factors Affecting the Thermo-Chemical  
De-vulcanization Efficiency of Tire Rubber  
Anuwat Worlee , Sitisaiyidah Saiwari , Wilma Dierkes , Siti Salina Sarkawi  
Department of Rubber Technology and Polymer Science, Faculty of Science and Technology, Prince of Songkla University, Pattani, 94000, Thailand.  
Department of Mechanics of Solids, Surfaces and Systems, Elastomer Technology and Engineering, University of Twente,  
500AE Enschede, the Netherlands  
Rubber Research Institute of Malaysia, Malaysian Rubber Board, P.O. Box 10150, 50908 Kuala Lumpur, Malaysia  
Received: 13/05/2020  
Accepted: 09/07/20xx  
Published: 20/09/2020  
In this study, the influence of the molecular structure of the rubber, the carbon black loading and de-vulcanization time and temperature  
on the thermo-chemical de-vulcanization efficiency of whole tire rubber was investigated by correlating sol fraction and crosslink density  
(Horikx-Verbruggen method). Differences in molecular structure influence the de-vulcanization mechanisms of rubbers as well as the  
efficiency. Increasing carbon black loadings result in higher crosslink densities due to a deactivation of the de-vulcanization aid. Variation  
of de-vulcanization temperature and time results in different degrees of heat accumulation in the rubber during de-vulcanization and thus  
leads to different de-vulcanization efficiencies.  
Keywords: Tire rubber; De-vulcanization; Recycling; Carbon black  
comparable de-vulcanized and virgin rubbers due to the  
uncontrolled polymer scission which occurs during the reclaiming  
process. De-vulcanization targets at the sulfuric crosslinks in the  
vulcanized rubber, to selectively cleave C-S and S-S bonds. These  
strength of these bonds differs: -C-S-C (285 kJ/mol), -C-S-S-C-  
When mentioning the environmental pollution problems that  
almost every country is facing today, it is inevitable to discuss the  
issue of non-biodegradable waste like vulcanized elastomers and  
plastic. The molecular structure of these materials results in  
outstanding water resistance and in-conduciveness to growth of  
microbes. In addition, elastomers have a very strong network. As  
a result, these materials when becoming waste are difficult to  
decompose: some types may take more than 100 years to  
biodegrade completely in the environment.  
Used tire rubber is one of polymer materials that is difficult to  
decompose. It is a durable material made of complex components  
consisting of various types of rubbers, reinforcing fillers and  
fabric. Therefore, disposal in the environment or usage of  
inappropriate methods of removal may cause environmental  
pollution in the future. Recycling and re-utilization of used rubber  
pose a great challenge. For end-of-life tires, incineration is  
currently the main outlet, impeding the re-use of this valuable raw  
material in new rubber products. Two recycling processes of end-  
of-life tires are well known: reclaiming and de-vulcanization.  
These two methods are often referred to as similar processes, but  
they are fundamentally different concerning the chemical reaction  
to break sulfur crosslinks, the ratio of crosslink scission to  
network breakdown, and the molecular structure of the polymeric  
material (Fig. 1). Reclaiming is usually accompanied by  
considerable scission of the polymeric chains resulting in a lower  
molecular mass fraction and poorer mechanical properties than  
(268 kJ/mol) or C-S -C- (251 kJ/mol). This can be one way to  
selectively break sulfur bonds in a crosslinked elastomer (1). A  
considerable share of material recycling can only be achieved if  
tire material can be used in real recycling loops: tires back into  
tires. This requires high-quality recycled rubber products, which  
can only be produced by a tailored de-vulcanization process.  
Within this study, vulcanized rubber was de-vulcanized and  
its efficiency was investigated concerning the tendency for  
crosslink versus main-chain scission. Thermo-chemical de-  
vulcanization using the optimum conditions proposed by Saiwari  
and co-workers (2) was applied to rubbers used in passenger ca  
tires: styrene-butadiene rubber (SBR), brominated butyl rubber  
(BIIR), natural rubber (NR) and butadiene rubber (BR). The goal  
of this project was to elucidate the influence of the molecular  
structure of the elastomer on the de-vulcanization efficiency, and  
to understand the influence of carbon black in a thermo-chemical  
de-vulcanization process of the tire rubbers. The effect of carbon  
black loading (i.e., 30, 60, 90 phr) and de-vulcanization time and  
temperature on the de-vulcanization efficiency were also studied.  
The mechanisms behind the rubber network breakdown of the  
carbon black filled single rubbers will be investigated and  
discussed. The understanding of the factors affecting the de-  
Corresponding author: Sitisaiyidah Saiwari, Department of Rubber Technology and Polymer Science, Faculty of Science and Technology,  
Prince of Songkla University, Pattani, 94000, Thailand. Email: