Pulverization of rubber using modified solid state shear extrusion process (SSSE)

Abstract

ABSTRACT:The challenge of reusing scrap rubber material is mainly due to its crosslinked/vulcanized structure, which prevents the material from melting and from being melt processed into new items. The most feasible recycling approach is believed to be a process in which the vulcanized rubber is first pulverized into a fine powder and then incorporated into new products. Solid state shear extrusion (SSSE), developed at Illinois Institute of Technology, is a process for continuous pulverization of rubber materials into a fine powder (Aratoopour, H. U.S. Pat. 5,704,555 (1998); Arastoopour, H.; Schocke, D. A.; Bernstein, B.; Bilgili, E. U.S. Pat. 5,904,885 (1999); Ivanov, G. Polym Eng Sci 2000, 40, 676). In this work, the design of the SSSE apparatus was modified to overcome heat generation due to pulverization and the limitation from the torque/feeding rate relation and, thus, to increase the efficiency of the process in the production of finer particles at higher throughput. The modification was achieved by separating the original process into the extrusion section and the pulverization section. The extrusion section is dedicated to convey material to the pulverization section, which consists of a cylindrical housing and a rotatable cylindrical element that rotates independent of the extruder's screw. The rotatable cylindrical element can be treaded or flightless. Both sections are connected with an adapter. This new approach to the design allowed us to apply a more efficient cooling system, capable of removing the heat of pulverization and, in turn, results in the production of finer rubber particles. Furthermore, separation of the conveying process from the pulverization process resulted in a reduction in extruder's torque and a significant increase in the throughput.

Devulcanization of Elastomers and Applications

“…The literature presents several works that discuss the different methods used to devulcanize rubbers, as mechanical and chemical mechanical method [10][11][12], microwaves method [9,[13][14][15][16][17][18][19], ultrasound method [20][21][22], chemical method [23,24], microbial method [25,26], and still other methods as bioreactor and spraying for solid-state shear [27,28]. Subsequently, when the goal is to use the recycled elastomer in the production of a blend, the role of devulcanization is to increase the interaction between the raw and recycled material, reducing the degradation of the properties of the finished product, and making it possible to increase the amount of recycled elastomer in the compound raw phase/recycled phase [29].…”

Studying the pulverization mechanism of rubber with a modified design of the solid‐state shear extrusion process

“…In 1935, Bridgman4 used the effects of compression and shear force to pulverize metal in an instrument known as the Bridgman anvil. The Bridgman anvil was initially used at the Center of Excellence in Polymer Science and Engineering (Illinois Institute of Technology) to study the pulverization of polymer particles 2, 3, 5, 6. Pulverization with the Bridgman anvil is achieved by the application of hydrostatic pressure to a particle placed between a fixed anvil and a rotating anvil 4.…”

“…The SSSE process has been shown to be effective in pulverizing rubber particles with high shear stress and compression forces. However, in this work, the throughput and efficiency of such a system were significantly improved with a modified SSSE apparatus using a separate screw at the end of the extruder and in a separate assembly 5. Shahidi et al5 investigated the effect of the pulverization of rubber particles with a modified SSSE design with a 28–76‐mm cylindrical housing.…”

“…However, in this work, the throughput and efficiency of such a system were significantly improved with a modified SSSE apparatus using a separate screw at the end of the extruder and in a separate assembly 5. Shahidi et al5 investigated the effect of the pulverization of rubber particles with a modified SSSE design with a 28–76‐mm cylindrical housing. On the basis of their study, we investigated the use of the pulverization of rubber with a 14–28‐mm cylindrical housing to increase the throughput of rubber particles and to reduce the erosion of the extended screw.…”

“…We used a 1.5 : 1‐CR screw for most of the experimental work. The shift of the pulverization phase of the recycling process to the extended section of the extruder provides higher cooling efficiency, reduced maintenance costs, and lower power requirements 5…”