Continuous Devulcanization Research Articles

Upscaling of a Batch De-Vulcanization Process for Ground Car Tire Rubber to a Continuous Process in a Twin Screw Extruder.

As a means to decrease the amount of waste tires and to re-use tire rubber for new tires, devulcanization of ground passenger car tires is a promising process. Being an established process for NR and EPDM, earlier work has shown that for ground passenger car tire rubber with a relatively high amount of SBR, a devulcanization process can be formulated, as well. This was proven for a laboratory-scale batch process in an internal mixer, using diphenyl disulfide as the devulcanization aid and powder-sized material. In this paper, the devulcanization process for passenger car tire rubber is upscaled from 15 g per batch and transformed into a continuous process in a co-rotating twin screw extruder with a capacity of 2 kg/h. As SBR is rather sensitive to devulcanization process conditions, such as thermal and mechanical energy input, the screw design was based on a low shear concept. A granulate with particle sizes from 1–3.5 mm was chosen for purity, as well as economic reasons. The devulcanization process conditions were fine-tuned in terms of: devulcanization conditions (time/temperature profile, concentration of devulcanization aid), extruder parameters (screw configuration, screw speed, fill factor) and ancillary equipment (pre-treatment, extrudate handling). The influence of these parameters on the devulcanization efficiency and the quality of the final product will be discussed. The ratio of random to crosslink scission as determined by a Horikx plot was taken for the evaluation of the process and material. A best practice for continuous devulcanization will be given.

The influence of feed rate and shear forces on the devulcanization process of ground tire rubber (GTR) conducted in a co-rotating twin screw extruder

The search for new ways to recycling of rubber waste has been the aim of many studies conducted by research centers and companies worldwide. The results of our investigations on the process of continuous thermomechanical devulcanization of ground tire rubber using a twin screw extruder are presented. We used a co-rotating twin screw extruder with a special configuration of plasticizing unit, enabling generation of considerable shear forces. Various properties were characterized, such as the influence of the ground tire rubber feed rate and screw speed (shear forces) on the screw torque, acetone extract, sol fraction, and the degree of devulcanization in the resulting products. The effect of a secondary vulcanization on the vulcametric curves was determined, and the mechanical properties (tensile strength, elongation at break, hardness, resilience and abrasion resistance) of the revulcanized material were studied. It has been determined that the devulcanization process depends on the values of shear force and residence time acting on ground tire rubber. The devulcanization degree increases with increasing screw speed and feed rate. The results of repeatability of continuous devulcanization process of ground tire rubber were also determined. Obtained products possess the quality comparable to that of reclaim rubber available on the market.

Continuous devulcanization of waste tires by using a Co‐rotating twin screw extruder: Effects of screw configuration, temperature profile, and devulcanization agent concentration

Recently, for reasons both economical and environmental, recycling of waste tires based on (styrene butadiene rubber)/(natural rubber) (SBR/NR) has been widely considered. Response surface methodology (RSM) has been used to predict SBR/NR devulcanization behavior in a co‐rotating twin screw extruder. In this study, variable parameters were barrel temperature, screw configuration, and content of devulcanization agent. A Box‐Behnken design for the three variables, at three levels, was chosen. The sol fraction of devulcanized rubber, Δtorque (difference between maximum and minimum curing torque), and mechanical properties of revulcanizate samples were considered as the responses. The results indicated that an increase of devulcanization agent content at a certain temperature caused the sol fraction to increase. Samples including a higher sol fraction showed a lower cross‐link density. Sol fraction for high shear rate screw configuration was lower than that for other screw configurations. Tensile strength of revulcanized rubber showed a decrease with a rise of devulcanization temperature. Moreover, a relationship connecting the residence time in the extruder with stagger angle and length of different kneading blocks were obtained. J. VINYL ADDIT. TECHNOL., 19:65–72, 2013. © 2013 Society of Plastics Engineers

The use of experimental design to study the responses of continuous devulcanization processes

AbstractThis paper presents the use of statistical analysis for studying the responses of two continuous devulcanization processes (of the EPDM roofing sheet and the EPDM profile) in the extruder. The response is represented by the reaction conversion, which is denoted as the relative decrease in crosslink density. Experimental design is considered as a useful tool when the kinetic data for the physical modeling are not available. The models derived show similar tendency of both processes with respect to the temperature and the screw speed. A difference is observed in their responses to the feed rate, which might be the consequence of their different devulcanization rates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5028–5038, 2006

Modelling a continuous devulcanization in an extruder

An engineering kinetic model is applied to EPDM devulcanization in an extrusion process. Parameters that were included in the model are crosslink density, devulcanizing agent concentration, time, shear rate, and temperature. The extruder is considered as a series of plug flow and stirred tank reactors. The residence time is calculated using solid flow or liquid flow model, depending on the degree of decrosslinking. The model can accurately predict the decrosslinking degree inside the temperature boundary defined by the applied experimental conditions. Outside this boundary, the effect of chemical degradation on the measured conversion becomes more significant.

Recycling of roofing membrane rubber by ultrasonic devulcanization

AbstractThe recycling of vulcanizates based on EPDM roofing membrane rubber using a new ultrasonic devulcanization reactor with a grooved barrel was carried out. This reactor provided continuous devulcanization at an output as high as 2.52 g/s. Die pressure and ultrasonic power consumption were measured as a function of processing conditions. The mechanical properties of virgin vulcanized and revulcanized roofing membranes were measured. Tensile strength of the revulcanized rubber was found to be similar to that of the virgin vulcanizate. Gel fraction, crosslink density, and dynamic properties of the virgin vulcanizate, the ultrasonically devulcanized rubber, and the revulcanized rubber were determined. Also, dynamic properties and the cure behavior of the virgin compound and of the devulcanized roofing membrane were investigated. All these properties were found to be dependent on processing conditions during devulcanization. The thermal stability of the virgin compound, virgin vulcanizate, and devulcanized and revulcanized rubbers were studied by means of TGA. It was found that the thermal stability of all the vulcanizates in air and nitrogen environments remained practically intact, while that of devulcanized rubber in air environment was a function of processing conditions.

Formation of bubbles during ultrasonic treatment of cured poly(dimethyl siloxane)

A static ultrasonic treatment device was used to investigate the effect of ultrasound on degradation of unfilled poly(dimethyl siloxane) (PDMS) vulcanizate in the absence of shearing effect. The effects of pressure, ultrasound intensity and thickness of the disks upon ultrasonic treatment were investigated. The power consumption was measured as a function of sample thickness, ultrasonic amplitude, and applied pressure. The dynamics of bubble (nucleation, growth and coalescence) was also studied with respect to applied pressure and amplitude. An increase in thickness of the sample was observed during ultrasonic treatment. The unique correlation between gel fraction and crosslink density obtained in the present static experiments was compared with those of continuous devulcanization studied earlier.

Recycling technology of tire rubber

Material recycling technology for automotive tire rubber waste was developed by the continuous devulcanization method. The deodorization during the recycling process has become possible by the newly developed method. The devulcanized rubber obtained by these methods from tire rubber waste, generated from both the manufacturing products and scrap tires, shows excellent mechanical properties applicable to the new tire rubber compounds in engineering practice. Furthermore, it was confirmed by actual road tests that a test truck tire containing 10 wt % of the devulcanized rubber in the tread might exhibit tread wear behavior almost equal to that for the standard type with the new rubber compound.

せん断流動場反応制御技術によるゴムの連続再生 第８報 過酸化物架橋ＥＰＤＭの再生条件と加硫再生ゴム物性

Continuous devulcanization by the shear flow stage reaction control technology for vulcanized rubbers has been developed. This technology has been applied to sulfur-crosslinked rubbers such as EPDM, NR/SBR (used tire waste) and IIR (used for tube). In this study, this technology has also been applied to peroxide-crosslinked EPDM. The obtained reclaimed rubber was found to be a mixture of two components; one is a linear chain which is soluble in toluene and whose average molecular weight is one third of that of the original raw rubber, and the other is a very loosely crosslinking network whose effective network chain density is about one fiftieth of that of the peroxide-crosslinked virgin rubber. The ratio of linear chain component and loosely crosslinking network component was approximately 3 to 2. The reclaimed rubber can be cured with sulfur- accelerator curing system. The sulfur-crosslinked reclaimed rubber shows good mechanical properties nearly equal to those of sulfur-crosslinked virgin one.

マレイン酸変性を伴う加硫ゴムの脱硫反応

Continuous devulcanization technology by the shear flow stage reactor for sulfur cured rubber has been developed. As an application of this technology, chemical modification with maleic anhydride (MAH) of sulfur cured EPDM and IIR has been performed in the devulcanizing process. MAH was able to be grafted onto both kinds of rubber. The degree of grafting of MAH was 0.05 to 0.06wt% for EPDM, 0.06 to 0.09wt% for IIR, respectively. These values correspond to 1/2 to 1/10 for some commercial acidic modified EPR or EPDM. As sol fraction and the degree of swelling, the MAH grafted devulcanized rubber (EPDM-g-MAH, IIR-g-MAH) was comparable to those of the unmodified rubber. The resulting EPDM-g-MAH has been used to binary nylon-6/EPDM-g-MAH blend by melt mixing. The EPDM-g-MAH dispersed micrometer order in the blend.

新脱硫技術の提出

Continuous devulcanization by shear flow stage reaction control technology for vulcanized rubber has been developed. Screw geometry and alignment, screw rotation, reaction temperature, internal pressure, and addition of process oil and devulcanizing agent are the most important factors for this process. This process can be applied to sulfur vulcanized rubbers such as EPDM, NR, SBR and IIR. This paper described the results of the devulcanization of EPDM rubber. The obtained devulcanized rubber was found to be even mixture of two components; one is linear chain which is soluble in toluene and whose average molecular weight is nearly equal to that of the original raw rubber, and the other is very loosely crosslinking network whose effective network chain density is about one twentieth of that of the virgin vulcanized rubber. The devulcanized rubber can be revulcanized by conventional curing process with sulfur-accelerator vulcanizing system. The revulcanized rubber exhibited excellent mechanical properties and formability nearly equal to virgin vulcanized one.

せん断流動場反応制御技術によるゴムの連続再生 ５ 廃タイヤの脱硫反応条件と再加硫ゴム物性

Continuous devulcanization by shear flow stage reaction control technology for sulfur vulcanized EPDM rubber has been developed. In this study, this technology has been applied for the devulcanization of rubber tire consisting of NR/SBR which has been used in practice. By optimizing devulcanization conditions such as reaction temperature, screw rotation and addition of process oil, devulcanized rubber can be extruded continuously. The devulcanized rubber can be revulcanized by conventional curing process with sulfur-accelerator vulcanizing system. The revulcanized rubber shows good mechanical properties which meet JIS K6313 standard.

せん断流動場反応制御技術によるゴムの連続再生 ６ 廃ブチルチューブの脱硫反応条件と再加硫ゴム物性

せん断流動場反応制御技術によるゴムの連続再生 ６ 廃ブチルチューブの脱硫反応条件と再加硫ゴム物性