Comparative analysis of ultrasonically devulcanized unfilled SBR,NR, and EPDM rubbers

The comparative study of the continuous ultrasonic devulcanization of various unfilled rubbers [natural rubber, styrene–butadiene rubber (SBR), ethylene–propylene–diene rubber (EPDM)] is carried out by means of a ultrasonic reactor. The power consumption, gel fraction, crosslink density, cure behavior, and physical properties of devulcanized rubbers were measured. The glass transition temperatures of virgin, vulcanized, and devulcanized rubbers were determined in order to characterize the difference in the mobility of rubber molecules for each rubber before and after devulcanization. Thermogravimetric analysis was also used to determine thermal stability of the various rubbers. A unique correlation between gel fraction and crosslink density indicated significant differences in the efficiency of devulcanization of various rubbers. Under certain devulcanization conditions, the mechanical properties of revulcanized SBR and EPDM rubbers were found to improve compared to those of the original rubbers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 434–441, 2003     

Effects of shear stress and subcritical water on devulcanization of styrene–butadiene rubber based ground tire rubber in a twin‐screw extruder

The devulcanization reaction of styrene–butadiene rubber (SBR) based ground tire rubber (GTR) in GTR/ethylene–propylene–diene monomer rubber (EPDM) blend was investigated through a compound‐induced reaction by increasing screw rotation speed and being in the presence of subcritical water. The effects of temperature, pressure, screw rotation speed, or promoting agents on the gel content, Mooney viscosity, and Fourier transform infrared spectra of the sol of the devulcanized blends (devulcanized ground tire rubber (DGTR)/EPDM) were measured, and the mechanical properties and microstructures of the revulcanized blend ((DGTR/EPDM)/SBR) were characterized. The results show that subcritical water as a swelling agent and reaction medium promotes the devulcanization reaction, increases the selectivity of the crosslink breakage, keeps the extrusion material from oxidative degradation, reduces the gel particle size of the devulcanized blends, and significantly improves the mechanical properties of the revulcanized SBR/(DGTR/EPDM) blends. In subcritical water, the suitable promoting agents (alkylphenol polysulfide 450, hydrogen peroxide H₂O₂, or 450/H₂O₂) accelerate the devulcanization reaction, keep the double bond content, and lead to further decrease of the gel content and Mooney viscosity of the devulcanized blends and further increase of the mechanical properties of the revulcanized SBR/(DGTR/EPDM) blends. Especially the compound promoting agent (450/H₂O₂) improves the selectivity of the crosslink breakage in devulcanization of SBR‐based GTR. When 450/H₂O₂ is added as a compound promoting agent at the best reaction condition in subcritical water (200°C, 1.6 MPa and 1000 rpm), the tensile strength and elongation at break of the revulcanized SBR/(DGTR/EPDM) blends reach to 85.4% and 201% of vulcanized SBR (24.0 MPa, 356%), respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1845–1854, 2013     

Continuous ultrasonic devulcanization of unfilled NR vulcanizates

Sulfur-cured unfilled natural rubber (NR) is successfully devulcanized in a continuous extrusion process under the application of high-power ultrasonic energy. The die characteristics and ultrasonic power consumption are measured. A unique correlation is found between the crosslink density and gel fraction of the devulcanized NR. This correlation is independent of the processing parameters, such as barrel temperature, die gap, flow rate, and amplitude of ultrasound. However, these parameters do influence the degree of devulcanization. In most cases, the degree of devulcanization is found to pass through a maximum at an intermediate level of ultrasonic energy. It is hypothesized that simultaneous breakup and reformation of crosslinks occur during the devulcanization of NR, with the relative contribution of each being determined by the process parameters. The cure curves and mechanical properties of the revulcanized NR are studied. The mechanical properties are found to depend on the revulcanization recipe. On optimizing it, tensile strength as high as 14.2 MPa is achieved, which is about 70% of that of the virgin NR vulcanizate. Ultimate elongation as high as 670% is obtained, which is the same as that of the virgin NR vulcanizate. Such stress–strain behavior is an indication that the devulcanized NR maintains the strain-induced crystallization characteristics inherent to the virgin NR vulcanizates. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2007–2019, 1998     

Continuous ultrasonic devulcanization of unfilled butadiene rubber

The devulcanization of sulfur‐cured unfilled butadiene rubber (BR) with a grooved‐barrel ultrasonic reactor under various processing conditions was carried out. The experiments indicated that BR had a narrow devulcanization window. Outside this window, significant degradation or no devulcanization occurred. Gel permeation chromatography (GPC) measurements were carried out with the sol part of virgin and devulcanized samples to study the breakdown of the polymeric chains. The GPC data showed a significant molecular weight reduction and a broadening of the molecular weight distribution upon devulcanization, indicating that the devulcanization and degradation of BR occurred simultaneously. The rheological properties showed that devulcanized BR was more elastic than the virgin gum. The vulcanizates of the blends of virgin and devulcanized BR showed a considerable enhancement of the mechanical properties. The thermal behaviors of the virgin and devulcanized BR were found to be different. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1166–1174, 2004     

Properties of natural rubber vulcanizates containing mechanochemically devulcanized ground tire rubber

The devulcanization of ground tire rubber (GTR) was carried out with a self-designed pan-mill type mechanochemical reactor. Gel fraction and crosslink density measurements confirmed the occurrence of stress induced mechanochemical devulcanization of GTR. The partially devulcanized GTR (dGTR) was blended with virgin natural rubber (NR) at different ratios. The curing characteristics and mechanical properties of these composites were investigated and compared with those composites of raw ground tire rubber (rGTR) and NR. The results showed that the tensile properties of the dGTR/NR vulcanizates were much better than those of the rGTR/NR vulcanizates, which are comparable to or even better than the virgin vulcanizate, indicating the significant benefit of mechanochemical devulcanization. At the GTR content of 10%, the tensile strength of the dGTR/NR blends increased to 23.2 MPa from 13.7 MPa of the rGTR/NR blends, enhanced by 69% through partial devulcanization of GTR, and the elongation at break increased by 47%.     

Recycling of unfilled polyurethane rubber using high‐power ultrasound

This investigation deals with the recycling of polyurethane rubber by the application of high‐power ultrasound in a continuous ultrasonic coaxial reactor. The cured rubber has been devulcanized at various feed rates and various gap sizes and then revulcanized again with certain adjustments in the curing recipe. The die pressure and the total power consumption have been recorded as a function of the processing conditions. The rheological and mechanical properties, hardness, gel fraction, and crosslink density of the original, devulcanized, and revulcanized samples have been measured and compared in an attempt to determine the optimum condition for devulcanization. Gel permeation chromatography (GPC) has been carried out with the sol part of the devulcanized samples to study the devulcanization and degradation. The results show that at low flow rates and narrow gaps, the material is degraded very quickly and, therefore, exhibits very poor mechanical properties. However, increasing the feed rate results in an improvement of the mechanical properties. Measured values of the crosslink densities and gel fractions indicate the processing conditions under which greater devulcanization and degradation of the samples take place. The lower molecular weights of the sol, extracted from the devulcanized samples, obtained in the GPC experiments in comparison with polyurethane gum indicate a breakdown of the polymeric chains as a result of devulcanization. The devulcanized samples show a higher activation energy of viscous flow, possibly because of the formation of branched structures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 980–989, 2003     

Continuous ultrasonic devulcanization of unfilled butyl rubber

The devulcanization of resin‐cured unfilled butyl rubber with a grooved‐barrel ultrasonic reactor under various processing conditions was carried out. The experiments indicated that, because of the lower unsaturation and good thermal stability of butyl rubber, its devulcanization could be successfully accomplished only under severe ultrasonic‐treatment conditions. Gel permeation chromatography measurements were carried out for the virgin gum and sol part of devulcanized samples to study the changes in the rubber network during the devulcanization process. The obtained data showed a significant molecular weight reduction and a broadening of the molecular weight distribution upon devulcanization, which indicated that the devulcanization and degradation of butyl rubber occurred simultaneously. The rheological properties showed that devulcanized butyl rubber was more elastic than the virgin gum. The vulcanizates of the devulcanized butyl rubber showed mechanical properties comparable to those of the virgin vulcanizate. The thermal behaviors of the virgin and devulcanized butyl rubber were different and were correlated to the double‐bond content. The structural characteristics of the devulcanized butyl rubber were simulated with the Dobson–Gordon theory of rubber network statistics. A fairly good agreement between the experimental data and theoretical prediction was achieved. The simulation of devulcanized butyl rubber indicated that the rate of crosslink rupture was much higher than that of the main chain. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1316–1325, 2004     

Compatibility studies on some polymer blend systems by electrical and mechanical techniques

Systematic electrical and mechanical studies were carried out on natural rubber (NR) blended with different types of synthetic rubber such as styrene‐butadiene rubber (SBR), polybutadiene rubber (BR), and ethylene‐propylene‐diene monomer (EPDM) as nonpolar rubbers and nitrile‐butadiene rubber (NBR) and chloroprene rubber (CR) as polar rubbers. The NR/SBR, NR/BR, NR/EPDM, NR/NBR, and NR/CR blends were prepared with different ratios (100/0, 75/25, 50/50, 25/75, and 0/100). The permittivity (ε′) and dielectric loss (ε″) of these blends were measured over a wide range of frequencies (100 Hz–100 kHz) and at room temperature (∼ 27°C). The compatibility results obtained from the dielectric measurements were comparable with those obtained from the calculation of the heat of mixing. These results were confirmed by scanning electron microscopy and showed that NR/SBR and NR/BR blends were compatible while NR/EPDM, NR/NBR, and NR/CR blends were incompatible. To overcome the problem of phase separation (incompatibility) between NR and EPDM, NBR, or CR, a third component such as SBR or poly(vinyl chloride) (PVC) was added as a compatibilizing agent to these blends. The experimental data of dielectric and mechanical measurements showed that the addition of either SBR or PVC could improve the compatibility of such blends to some extent. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 60–71, 2001     

废旧轮胎胶粉应力诱导脱硫反应影响因素的研究

在废旧轮胎胶粉/EPDM的熔融挤出过程中,以仲丁醇为脱硫反应促进剂,研究螺杆转速和挤出反应温度对脱硫共混物凝胶质量分数(w)、凝胶分子链结构以及SBR/脱硫共混物再硫化材料物理性能的影响。结果表明:在废旧轮胎胶粉/EPDM的熔融挤出过程中,随着螺杆转速和挤出反应温度的升高,废旧轮胎胶粉颗粒所受的机械剪切应力作用增强,引起废旧轮胎胶粉中交联网络的断裂、降解或解交联反应,导致脱硫共混物w显著减小以及SBR/脱硫共混物再硫化材料中凝胶粒子尺寸明显减小;添加仲丁醇有利于脱硫反应的进行,并具有抑制交联副反应和保护脱硫产物中双键的作用,使脱硫共混物的w进一步减小;在螺杆转速为1 000 r.min-1、挤出反应温度为240℃的条件下,SBR/脱硫共混物(添加仲丁醇)再硫化材料的拉伸强度和拉断伸长率分别为19.3 MPa和567%。     

Continuous ultrasonic devulcanization of carbon black‐filled NR vulcanizates

The continuous ultrasonic devulcanization of natural rubber (NR) filled with various concentrations of carbon black (CB) indicated a minimum of crosslink density and gel fraction at an intermediate amplitude, which is independent of CB content. An attempt was made to improve the efficiency of devulcanization by use of various chemicals (1,3 Diphenylguanidine, 2‐Mercaptobenzothiazole, Thianaphthene). However, these experiments did not indicate any improvement in comparison with devulcanization without chemicals. An idea of adding fresh CB into devulcanized compound, which has been shown to improve mechanical properties in the case of styrene–butadiene rubber (SBR), was tested in the present study for CB filled NR compound. The obtained result indicated that an addition of fresh CB to devulcanized CB‐filled NR did not lead to an improvement in mechanical properties upon revulcanization. The revulcanization recipe was optimized to improve the mechanical properties of revulcanized CB‐filled NR vulcanizates. It was found that CB‐filled NR upon revulcanization retained its strain‐induced cystallizability with the tensile strength and elongation at break at about 50 and 70% level of the virgin vulcanizates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2340–2348, 2001     

Ultrasonic properties and morphology of devulcanized rubber blends

The ultrasonic properties of two devulcanized rubber (DR) blends with a styrene‐butadiene‐styrene (SBS) copolymer compound (ACE) are investigated using a transmission method. The DR materials are obtained from commercial rubber crumbs (RC) by a proprietary devulcanization technique. Measurements on the acoustic attenuation and travel velocity are conducted on the samples with different sample thicknesses in the pulsed mode. Attenuation coefficients of the materials are obtained by changing the frequency of the ultrasound in the tuned tone‐burst mode. The two DR/ACE blends show marked differences in the attenuation and attenuation coefficient, although the ultrasonic velocities are similar. These differences arise from the variation of the remaining degree of crosslinking in the DR materials. The acoustic velocities in the three materials are similar. The morphologies of the DR/ACE blend samples, observed using scanning electron microscopy (SEM) with different staining agents, explain their similarities and differences. There are two crops of rubber particles: larger ones belong to the original rubber crumbs that survived devulcanization; the smaller ones are fragments of partially DR. These crosslinked particles contribute to the overall degree of crosslinking in the blends. The devulcanized fractions of the DR materials are dispersed in the ACE matrix. Scattering at the interface accounts for the differences in the acoustic attenuation of the samples. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Devulcanization of waste tires using a twin‐screw extruder: The effects of processing conditions

During recent decades, for both economic and environmental reasons, recycling of waste tires that are based on SBR/NR has been widely considered. In this study the devulcanization process of the tread section of waste tires was carried out by using a twin‐screw extruder. The effects of barrel temperature and screw speed were investigated. Percent of devulcanization, sol fraction, and curing behavior of devulcanized samples were studied. After the addition of curing agents into the devulcanizates, the general behavior of the rheometry test for rubber compounds was observed. Percent of devulcanization and sol fraction depended on the screw speed and barrel temperature, respectively. The devulcanized samples were formulated with virgin rubber (15/85 wt% ratio) and re‐cured successfully. Tensile strength, elongation at break, compression set, hardness, and resilience were evaluated. It was found that the mechanical properties of the compound containing devulcanizates were slightly inferior to those of the virgin compound. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

The effect of adding devulcanized rubber on the thermomechanical properties of recycled polypropylene

This work aims to investigate the effect of adding vulcanized or partially devulcanized rubbers on recycled polypropylene (PPr), considering thermomechanical and morphological properties. The study proposes to better understand how structural changes underwent by rubber (after the devulcanization) contributed to improving the mechanical properties of the PPr. The PPr/rubber blends were prepared by a co-rotating twin-screw extruder and then were injected. The blends composed of the most devulcanized rubbers by microwaves with refined microstructure showed higher values of elongation at break and toughness. Data showed that the devulcanization process applied to the rubber interfered positively in its adhesion to the PPr. Data from dynamic mechanical analysis and atomic force microscopy indicated that the most devulcanized rubbers presented an interface more connected to PPr. These chemical interactions possibly impacted the mechanical properties of the PPr. Moreover, dilatation processes favored the fracture mechanisms of the PPr when rubber was added to it.     

Recycling of roofing membrane rubber by ultrasonic devulcanization

The 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.     

Friction and wear behavior of styrene butadiene rubber‐based composites reinforced with microwave‐devulcanized ground tire rubber

In this work, the tribological properties of a new material obtained by revulcanization with styrene butadiene rubber (SBR) and devulcanized ground tire rubber (GTR) were investigated. GTR was devulcanized using the microwave method at a constant power while varying the microwave exposure time. Devulcanized rubber (DV‐R) and untreated GTR were revulcanized by mixing with SBR at different rates (10, 30, 50 phr). To determine friction and wear characteristics of the samples, pin (ball) on disc and abrasion tests were conducted. Scanning electron microscopy (SEM) was employed to observe the worn surfaces of the composites to correlate the experimental test results to the wear mechanisms. All of these tests and experiments were performed on original vulcanized rubber samples for comparison. The composites exhibited different friction and wear behavior due to morphology, dispersion behavior and devulcanization functionalization of ground tire rubber. In general, DV‐R/SBR composites exhibited improvement in both mechanical and tribological properties. However, the enhanced compatibility of DV‐R resulting from the specific chemical coupling of DV‐R with SBR was crucial for the mechanical, friction and wear properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42419.     

Improved properties of blends of ultrasonically treated unfilled polyurethane rubber

The aim of this investigation is to improve the properties of the polyurethane rubber that has been devulcanized using the coaxial ultrasonic reactor. After devulcanization of the cured rubber under varying gap sizes and amplitudes, blends of the devulcanized and virgin rubber at different ratios are prepared. Rheological and mechanical properties, hardness as well as gel fraction and crosslink density of the vulcanized blends have been investigated. Results show that compared to the vulcanizates of the devulcanized samples, the vulcanizates of the blends show a remarkable improvement in properties, which are sometimes comparable to or even better than the virgin vulcanizate. Blends have also prepared using different proportions of ground samples and virgin rubber, and a comparison of properties between these blends and the blends of the devulcanized rubber has been carried out. The results show that compared to the ground samples, the blends of the devulcanized samples are easier to mix and exhibit enhanced and more uniform properties. Polym. Eng. Sci. 44:794–804, 2004. © 2004 Society of Plastics Engineers.     

Impact of gamma irradiation on virgin styrene butadiene rubber blended with ultrasonically devulcanized waste rubber

This investigation focused on the opportunity of devulcanizing waste Rubber (WR) by ultrasonication to study the possibility of utilized as an added substance to replace with styrene‐butadiene rubber (SBR) in preparation process with the final aim of preparation new composites. The present work expects to compare the ultrasonic technique and the previous work on devulcanization by mechano‐chemical method. The influence of the ultrasonication treatment on the WR was explored by Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy analysis revealed that ultrasonication was observed to be the best factor impacting the devulcanization procedure, this procedure suggests that use of specific levels of ultrasonic waves to the vulcanized rubber with a specific aim to accomplish a particular breaking of compound connections: scission of C‐S and S‐S bonds without break carbon–carbon (C‐C) bonds. Various blends of devulcanized WR with SBR was treatments with gamma ray then investigated and compared with find out the rubber giving the highest compatibility for compounding and revulcanization. In addition, a comparison of these results was made with the ones of raw SBR rubber compound. POLYM. ENG. SCI., 59:807–813, 2019. © 2019 Society of Plastics Engineers     

亚临界流体挤出法复合诱导SBR基轮胎胶脱硫化及 再硫化材料力学性能

在SBR基轮胎胶(GTR)与三元乙丙橡胶（EPDM）混合物的熔融挤出过程中,采用改变亚临界流体品种和提高螺杆转速的方法,研究了亚临界流体（水,乙醇,丙醇）、螺杆转速、烷基酚多硫化物促进剂（450）以及温度对脱硫共混物（DGTR/EPDM）凝胶含量、门尼粘度、溶胶红外光谱及脱硫共混物共混丁苯橡胶（SBR）再硫化材料（SBR/(DGTR/EPDM)）力学性能的影响,对再硫化材料的试样断面形貌也进行了SEM观察。实验结果表明：亚临界流体（水,乙醇,丙醇）作为一种溶胀剂和反应性介质能够很好地促进脱硫反应,提高交联键断裂的选择性,降低脱硫产物的凝胶含量和凝胶颗粒尺寸并明显提高脱硫共混物共混丁苯橡胶再硫化材料的力学性能,其中亚临界乙醇的作用最显著。当450作为一种脱硫促进剂,在最优亚临界乙醇挤出反应条件（200℃,1.6 MPa,600 rpm）下,脱硫共混物共混丁苯橡胶分别达到丁苯生胶混炼硫化材料拉伸强度（24.0MPa）和断裂伸长率（356%）的99.6%和209%。     

Development of novel elastomeric blends containing natural rubber and ultra-low-density polyethylene

This study sought to develop novel elastomeric compounds using natural rubber (NR) and ultra-low-density polyethylene (ULDPE). Blends were prepared by means of a two-roll mill for three ratios (70/30, 60/40, and 50/50 NR/ULDPE). Conventional vulcanization was performed in a compression mold. The physical and mechanical properties of the blend were determined according to ASTM standards. The results were compared with those obtained from NR blended with styrene-butadiene rubber (SBR). The morphological examinations with scanning electron microscopy indicated that ULDPE was compatible with NR; thus, the addition of a compatibilizer was not necessary. The cocontinuous phase was dominant in the NR/ULDPE blend containing 50 and 60 wt % NR. The tensile properties, tear resistance, and aging resistance of the NR/ULDPE blends were found to be superior to those of NR/SBR blends. On the other hand, the abrasion and flex cracking resistances of the NR/ULDPE blend were inferior to those exhibited by SBR blends but the Mooney viscosity and resilience of both blends fell in the same range. However, the addition of dicumyl peroxide appeared to have caused crosslinking of the ULDPE phase in the blend, which in turn increased the tensile properties and abrasion and aging resistance. The properties of the tertiary NR/SBR/ULDPE blend were investigated as well. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 650–660, 2001     

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