Thermomechanical Devulcanisation of Ethylene Propylene Diene Monomer (EPDM) Rubber and Its Subsequent Reintegration into Virgin Rubber

Fully tuneable ethylene-propylene elastomers using a supported permethylindenyl-phenoxy (PHENI*) catalyst

Using a highly active supported permethylindenyl-phenoxy (PHENI*) titanium catalyst, high molecular weight ethylene-propylene (EPM) and ethylene-propylene-diene (EPDM) elastomers are prepared using slurry-phase catalysis. Final copolymer composition was found to reflect the monomer feed ratio in a linear fashion, to access a continuum of material properties with a single catalyst. Post-polymerisation crosslinking of EPDM was also demonstrated in a model sulfur vulcanisation system.

Insights into the Structural and Dielectric Behavior of Composites Produced from EPDM Waste Processed through a Devulcanization Method and SBR

Ethylene propylene diene monomer (EPDM) is one of the most used polymers in the world. It is an elastomer, which means that the existing cross-linking between the main chains of the polymer created during the vulcanization process makes its recycling difficult. In this paper, a possible solution to this issue is studied. The devulcanization of EPDM is achieved by a thermomechanical process followed by microwave irradiation. These combined treatments suppress the cross-linking, yielding a material (EPDMd) that can be successfully blended to form composites. A common elastomer, styrene butadiene rubber (SBR), has been selected as the matrix. The new SBR/EPDMd composites can be useful as elastomeric dielectric materials and can contribute to the recycling of the discarded EPDM. To provide a better understanding of their microstructure and its relationship with their micro- and macroscopic behavior, samples containing 20 and 40% of EPDMd have been tested by thermogravimetric and dielectric analysis, focusing on variables such as the thermal properties of the blends, permittivity, electric modulus, conductivity, and activation energies. The results show interesting changes linked to the presence of EPDMd in the SBR matrix, such as the displacement of the β dielectric relaxation toward higher frequencies. The correct integration between the two phases is confirmed by the absence of any Maxwell-Wagner-Sillars type relaxation in their dielectric behavior. The presence of additives in the EPDMd samples has an effect on the conductivity, mainly due to the conductive aluminum silicate present in the EPDMd, which acts toward increasing some key dielectric features like conductivity and permittivity and decreasing the insulation of the final SBR/EPDMd materials. The inclusion of EPDMd also affects the α relaxations (low frequencies) and suppresses the β relaxations (high frequencies). The samples showed a non-Debye dielectric behavior. In short, a compact and well-integrated material with a dielectric behavior is created, which exhibits interesting differences from the reference SBR matrix. Finally, it is concluded that the compounds tested are suitable for applications as electrical insulators.

4R of rubber waste management: current and outlook

Excessive accumulation of rubber waste necessitates the need to revisit the effectiveness of the existing rubber waste management system. This review provides an overview of the legislative frameworks, techniques, challenges, and trends of rubber waste management in various countries. The 4R (reduce, reuse, recycle and recover) framework applied in waste management system in some countries appears to be viable for the processing of rubber waste. Certain countries especially some of the European Union (EU) members have implemented extended producer responsibility (EPR) system to manage the collection of rubber waste, particularly used tires. The processing of rubber waste in each level of the 4R hierarchy was then discussed, with detailed elaboration on the most practiced 'R', recycling which encompasses the direct recycling of products, as well as material recycling via physical and/or chemical means. The challenges faced in the implementation of rubber waste management system in different countries were highlighted and recommendations for a more sustainable rubber consumption were provided at the end of this review.

Recycling of EPDM via Continuous Thermo-Mechanical Devulcanization with Co-Rotating Twin-Screw Extruder

Devulcanization represents the recycling of choice for a homogenous rubber waste stream because it allows revulcanization of samples previously devulcanized, making the life of the rubber virtually endless, according to the principles of circular economy. Among the many devulcanization processes, the thermo-mechanical one is the most appealing because it is a continuous process, easy to be industrialized. In this paper a comprehensive set of analyses (FTIR, TGA, DSC, elemental analyses, Py-GC/MS, swelling tests) were carried out on a post-industrial ethylene propylene diene monomer (EPDM), thermo-mechanical devulcanized in a co-rotating twin-screw extruder with different process parameters (thermal and screw profile, rpm). Results of the swelling test according to the Flory-Rehner theory and Horikx analyses show that the higher the thermal profile and the higher the rpm, the higher is the percentage of devulcanization. The quality of the devulcanized sample in terms of sol fraction and percentage of random scissions depends on the process conditions. The screw profile concurs to the efficiency of the devulcanization: the different number of kneading elements and more in general the screw profile composition affects the percentage of devulcanization, making the results in some tests more dependent on the screw speed.

Electrical Conductivity of Rubber Composites with Varying Crosslink Density under Cyclic Deformation

Studies addressing electroconductive composites based on rubber have attracted great interest for many engineering applications. To contribute to obtaining useful materials with reproducible behavior, this study focused on understanding the mechanism of conductivity changes during mechanical deformation for rubber composites based on styrene-butadiene rubber (SBR) or ethylene-propylene-diene terpolymer (EPDM) vulcanized for various times. The composites were characterized by static electrical conductivity, tensile testing, dynamic mechanical thermal analysis (DMTA), and crosslink density measurements. The tensile strength and Young’s modulus were found to increase significantly with rising vulcanization time. Higher static conductivity values of the composites were observed with the increase in vulcanization time. The most important aspect of this investigation consisted in the electrical current measurement online with recording the stress-strain curves, revealing the details of the uniaxial cyclic deformation effect on changes in the structure of conductive pathways indirectly. The electrical conductivity during five runs of repeated cyclic mechanical deformations for SBR composites increased permanently, although not linearly, whereas EPDM composites showed a slight increase or at least a nearly constant current, indicating healing of minor defects in the conductive pathways or the formation of new conductive pathways.

Efficient synthesis of thermoplastic elastomeric amorphous ultra-high molecular weight atactic polypropylene (UHMWaPP)

The synthesis of amorphous ultra-high molecular weight atactic polypropylene (UHMWaPP), with molecular weights (Mw) up to 2.0 MDa and narrow polydispersities is reported using remarkably efficient permethylindenyl-phenoxy (PHENI*) titanium complexes.