Published: August 25th, 2016
A simple two-step approach involving rubber modification and cross-linking yields fully reworkable, elastic rubber products.
A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ethylene-propylene rubber, grafted with maleic anhydride, is thermo-reversibly cross-linked in two steps. The pending anhydride moieties are first modified with furfurylamine to graft furan groups to the rubber backbone. These pendant furan groups are then cross-linked with a bis-maleimide via a Diels-Alder coupling reaction. Both reactions can be performed under a broad range of experimental conditions and can easily be applied on a large scale. The material properties of the resulting Diels-Alder cross-linked rubbers are similar to a peroxide-cured ethylene/propylene/diene rubber (EPDM) reference. The cross-links break at elevated temperatures (> 150 °C) via the retro-Diels-Alder reaction and can be reformed by thermal annealing at lower temperatures (50-70 °C). Reversibility of the system was proven with infrared spectroscopy, solubility tests and mechanical properties. Recyclability of the material was also shown in a practical way, i.e., by cutting a cross-linked sample into small parts and compression molding them into new samples displaying comparable mechanical properties, which is not possible for conventionally cross-linked rubbers.
Sulfur vulcanization and peroxide curing are currently the main industrial cross-linking techniques in the rubber industry, yielding irreversible chemical cross-links that prevent melt reprocessing.1, 2 A 'cradle to cradle' approach to recycle cross-linked rubbers requires a material that behaves similar to permanently cross-linked rubbers at service conditions, while having the processability and complete recyclability of a thermoplastic at high temperatures. An approach to achieve such recyclability uses rubbery networks with reversible cross-links that respond to an external stimulus, such as temperature (most feasible from the viewpoint of futur....
1. Rubber Modification
The successful modification of EPM-g-MA into EPM-g-furan and the cross-linking with the bismaleimide is shown by Fourier transform infrared spectrometry (FTIR) (Figure 2). The presence of furan groups in the EPM-g-furan product can be deduced from the splitting of the CC aliphatic stretching peak ( = 1,050 cm-1) into two furan peaks (
A commercial EPM-g-MA rubber was thermo-reversibly cross-linked in a simple two-step approach. The maleated rubber was first modified with FFA to graft furan groups onto the rubber backbone. The resulting pending furans show reactivity as Diels-Alder dienes. An aliphatic BM was used as cross-linking agent, resulting in a thermo-reversible bridge between two furan moieties. Both reactions were successful with good conversions (> 80%) according to infrared spectroscopy, elemental analysis. Cross-linking was shown by sw.......
|LANXESS Elastomers B.V.
|LANXESS Elastomers B.V.
|Vacuum oven for one hour at 175 °C
|Freshly distillated before use
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