K.A.J. Dijkhuis

A Mechanistic Approach to EPDM Devulcanization

Abstract The extensive utilization of rubber in a wide variety of products causes a problem in terms of waste. Reclaiming of end-of-life products or production scrap is a potential solution. A high quality reclaim would preferably be obtained by devulcanization, to leave the polymer chains intact. Reclaiming of natural rubber is common practice, although the fundamental knowledge about de- and re-crosslinking is rather limited. EPDM-based rubber is even more unexplored in terms of reclaiming and re-utilization. This paper gives a mechanistic insight into the thermal reclaiming of two differently vulcanized EPDM compounds, using hexadecylamine (HDA) as devulcanization agent. Reclaim from conventionally vulcanized EPDM, mainly polysulfidic of nature, shows the largest decrease in remaining crosslink density with increasing HDA concentration and at lower reclaim temperatures. After reclaiming at the lower limit of the experimental temperature window applied: 225 °C, the concentration of remaining di- and pol...

Improved Aging Performance of Virgin EPDM Roof-Sheeting Compounds with Amine-Devulcanized EPDM Weatherstrip Material

Sulfur-cured EPDM building-profile material was reclaimed in a co-rotating twin-screw extruder using hexadecylamine as reclaiming aid. This reclaim was blended with increasing amounts of a virgin EPDM roof-sheeting masterbatch and cured at temperatures allowing for a reversion-free vulcanization. The trends in cure characteristics showed that increasing amounts of reclaim employed in the blends lowered the reversion-free cure temperature and the maximum torque values, while the vulcanization speed was increased. The insoluble fraction and crosslink density both decreased, while the ratio of mono- to di- and polysulfidic crosslinks increased with growing reclaim contents. A SEM-EDX morphology study of the blends, in order to evaluate the dispersion of the reclaim into the virgin rubber matrix showed, that even large amounts of reclaimed material resulted in homogeneous and smooth compounds. Tensile strength, modulus at 300% strain and hardness decreased, while elongation at break, tear strength and compression set at 70 degrees C increased with increasing reclaim ratios. Irrespective of the blend ratios, the mechanical properties all fulfilled the most stringent UEAtc specifications for EPDM roof-sheeting. Increasing reclaim contents improve the aging resistance and prolong the time before a practical limiting value for elongation at break of 250% for EPDM roof-sheeting purposes is reached.

State of the art : Recycling of EPDM rubber vulcanizates

Abstract 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.

Designing of Cradle-to-cradle Loops for Elastomer Products

ABSTRACT Reuse of devulcanisates in virgin rubber compounds is the shortest loop in cradle-to-cradle cycles for elastomers. Due to the enormous complexity of these loops, the technology still stands in its infancy. Two elastomer types, EPDM (Ethylene–Propylene-Diene Terpolymer) and SBR (Styrene–Butadiene Rubber), are compared as to their ease of devulcanisation with an optimized devulcanisation aid. EPDM is relatively easy to devulcanise into a quality which allows for reuse of large amounts till 50% in virgin compounds for applications like roofing sheets and others. This is already being done on industrial scale. SBR is more difficult to devulcanise due to re-crosslinking under the influence of oxygen. Furthermore, tyre scrap is a mix of compounds and elastomers, which are impossible to segregate before devulcanisation. A lot more research and development is needed to bring this to a success.