Abstract
In this study, the effects of the devulcanization process realized by an intermeshing co-rotating twin-screw extruder (ICTSE) on three vulcanized Natural Rubber (NR) composites with different crosslink densities (CD) have been investigated. The extrusion parameters were fixed, as well as the initial material granulometry and auxiliary thermoplastic added to the process. After composites vulcanization, they were characterized accordingly their soluble fraction (SF), crosslink density (CD), mechanical properties and thermogravimetry (TGA). The extrusion was performed on the vulcanized elastomers pursuing selectively crosslink rupture and the same characterization previously cited was conducted on the devulcanized material, except the mechanical properties analysis. The extrusion demonstrate effective devulcanization, evidenced in the increasing of soluble fractions, reduction in crosslink density and thermal stability gain. These results are directly affected by preliminary differences on materials structure and presence of ethylene vinyl-acetate (EVA) on extrusion.
Highlights
The growing demand for natural rubber (NR) has been of concern to various sectors of society
This study aims to evaluate the process of NR devulcanization by intermeshing co-rotating twin-screw extruder (ICTSE) using three NR compositions with different crosslinking densities, adding ethylene vinyl-acetate (EVA) to promoting swelling and optimizing the stress distribution in the threedimensional elastomeric network
It is known that the amount of sulfur is essential for the crosslinking process, the sulfidic bond type/length is more closely correlated with the accelerator/sulfur ratio (A/S) and the curing conditions
Summary
The growing demand for natural rubber (NR) has been of concern to various sectors of society. Regarding the methods used to recycle the NR contained in automotive tires, is observed that few devulcanization or regeneration processes, defined by selective breaking of cross-linked rubber networks, demonstrate productive, economic and qualitative capacity. The researchers found that shear stress acting on the material during the extrusion has directionality, promoting better breaking of the bonds perpendicular to the main chain, in this case the sulfidic crosslinks Another point mentioned is the possible compatibilization effect that can be realized by the thermoplastics when they stabilize, through chemical bonds, the macrorradicals produced by rubber network breakdown, optimizing extruded material compatibility and mechanical properties. They observed a better interfacial adhesion between the devulcanized and virgin rubber when mixed (blend), occasioned by the compatibility promoted when using thermoplastics added to the extrusion process
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