The use of amines and the application of mechanical force (shear) in rubber devulcanization have been reported in the literatures. In this paper, the devulcanization of ethylene propylene diene rubber (EPDM) is conducted in a Brabender batch mixer using hexadecylamine (HDA) as the devulcanizing agent. Considering the complexity of the compound and the limitations of the analyses techniques for crosslinked systems, an engineering approach to model a devulcanization process of EPDM material is proposed. An engineering kinetic model has been derived by fitting a large number of experimental data with several models based on simple kinetic considerations. Rate determining parameters such as temperature, shear rate, reactant concentrations and time are included in the model. The model obtained covers all the phenomena happening during the devulcanization, without distinguishing them on the molecular level. ᭧

An engineering kinetic model is applied to EPDM devulcanization in an extrusion process. Parameters that were included in the model are crosslink density, devulcanizing agent concentration, time, shear rate, and temperature. The extruder is considered as a series of plug flow and stirred tank reactors. The residence time is calculated using solid flow or liquid flow model, depending on the degree of decrosslinking. The model can accurately predict the decrosslinking degree inside the temperature boundary defined by the applied experimental conditions. Outside this boundary, the effect of chemical degradation on the measured conversion becomes more significant. ᭧

Two types of ethylene-propylene-diene monomer (EPDM) rubbers, namely an efficient vulcanized (EV) and a semiefficient vulcanized (SEV), have been used to produce devulcanizates in a continuous setup. The devulcanizates are re-cured using the same recipes as for the virgin rubber. The influence of mixing it with virgin rubber compound, the addition of extra sulfur, the operating devulcanization conditions, and the excess of devulcanizing agent on the mechanical properties (hardness, tensile strength, and compression set) of the reclaim rubbers are studied. Most of the reclaims produced show slightly inferior mechanical properties compared to the virgin rubber. Surface imperfection was observed on the devulcanizate with high devulcanizing agent content. Excellent mechanical properties (all above the standards) of the reclaim were found when the devulcanized profile material was used (EV-EPDM) to replace the virgin one for application as a roofing sheet material (SEV-EPDM).

Since the past few decades, environmental issues have become a serious concern in society. It is a requisite for the industry to minimize waste, in order to protect the environment from being polluted. The term waste here comprises processing waste and post-consumer waste. The amount of processing waste should not be underestimated since it might consist of approximately 10% of the total production. The recycling of EPDM rubber is an interesting topic, especially if considered in connection with the continuous market growth of EPDM. This paper is a summary of efforts that have been taken so far on this subject. Studies done on EPDM recycling include reusing EPDM as filler in new rubber products and chemical, thermal, and mechanical devulcanization of EPDM in order to achieve a material that resembles the virgin one and could be revulcanized. Such studies on EPDM recycling are discussed extensively and in the conceptual frame of more general rubber recycling processes.

This paper presents the use of statistical analysis for studying the responses of two continuous devulcanization processes (of the EPDM roofing sheet and the EPDM profile) in the extruder. The response is represented by the reaction conversion, which is denoted as the relative decrease in crosslink density. Experimental design is considered as a useful tool when the kinetic data for the physical modeling are not available. The models derived show similar tendency of both processes with respect to the temperature and the screw speed. A difference is observed in their responses to the feed rate, which might be the consequence of their different devulcanization rates.