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     

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%。     

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.     

不同胶粉在丁苯橡胶中的使用性能研究

系统研究了采用常温粉碎、水射流粉碎、湿法粉碎和冷冻粉碎等工艺制备的4种胶粉基本性质及其在丁苯橡胶(SBR)中的应用性能。结果表明,4种胶粉(GTR)的表面形貌和组成以及在丁苯橡胶中的使用性能均有较大差异,其中湿法胶粉比表面积较大,冷冻法胶粉表面形貌光滑。将4种胶粉分别加入到丁苯橡胶中,相应混炼胶的t90和t10均缩短;随着胶粉用量的增大,t90和t10均持续缩短。在实验范围内,湿法胶粉硫化胶拉伸强度均优于其他胶粉硫化胶。胶粉表面形貌粗糙,比表面积较高,其SBR硫化胶拉伸强度较高。     

Mechanical and Viscoelastic Properties of Natural Rubber/ Reclaimed Rubber Blends

Summary Addition of reclaimed rubber affected mechanical properties, processing and rheological behavior of rubber compounds. Sulfur left in reclaimed rubber affected curing process of NR/reclaimed rubber blends. The most suitable curing was achieved with ratio 1:1 of natural rubber and reclaimed rubber which was used in this study. Presence of fillers in reclaimed rubber, non-homogeneity of phases, non-uniform filler dispersion and lower molecular weight of reclaimed rubber due to chain scission in reclaiming process caused diminishing of mechanical properties of NR/reclaimed blends, particularly dynamic-based properties. Reclaimed rubber also affected rheological behavior of natural rubber. In a strain sweep viscoelastic test, it could be observed that NR/reclaimed blend show more non-linear viscoelastic and viscous behavior than predicted one which was due to non-homogenized phases. This non-homogenized morphology was detected using scanning electron microscopy (SEM) and the blend with ratio 1:1 had the most homogenized morphology.     

Curing characteristics,mechanical properties and morphology of butyl rubber filled with ground tire rubber (GTR)

The results on testing application of ground tire rubber (GTR), as potential filler for butyl rubber, are presented. The GTR content variation, within the range of 10–90 phr, was studied with respect to the vulcanization process, static mechanical properties (tensile strength, elongation-at-break, hardness and resilience), dynamic mechanical properties and the morphology of the obtained vulcanizates. Butyl rubber was characterized by its low compatibility to other elastomers [i.e., natural rubber and styrene–butadiene rubber (SBR)—the main ingredients of tires] and low degree of unsaturation. To evaluate the impact of these factors on curing characteristics and mechanical properties of butyl rubber vulcanizates filled with GTR, the same compositions of SBR compounds, cured under identical conditions, were used as reference samples. Based on the obtained data, it can be stated that butyl rubber vulcanizates containing 30 phr of GTR as filler revealed the highest tensile strength and elongation-at-break. The microstructural analysis of a sample containing 30 phr of GTR revealed strong interactions between the butyl rubber matrix and GTR. This phenomenon resulted mainly from two factors. First, the cross-link density of the butyl rubber matrix was affected by its competition against GTR for cross-linking agents. Secondly, the migration of carbon black particles from GTR into the butyl rubber matrix had a significant impact on properties of the obtained vulcanizates.     

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     

Styrene–butadiene rubber/natural rubber blends: Morphology,transport behavior,and dynamic mechanical and mechanical properties

Blends of styrene–butadiene rubber (SBR) and natural rubber (NR) were prepared and their morphology, transport behavior, and dynamic mechanical and mechanical properties were studied. The transport behavior of SBR/NR blends was examined in an atmosphere of n‐alkanes in the temperature range of 25–60°C. Transport parameters such as diffusivity, sorptivity, and permeability were estimated. Network characterization was done using phantom and affine models. The effect of the blend ratio on the dynamic mechanical properties of SBR/NR blends was investigated at different temperatures. The storage modulus of the blend decreased with increase of the temperature. Attempts were made to correlate the properties with the morphology of the blend. To understand the stability of the membranes, mechanical testing was carried out for unswollen, swollen, and deswollen samples. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1280–1303, 2000     

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     

Partial replacement of EPR by GTR in highly flowable PP/EPR blends: Effects on morphology and mechanical properties

This research analyzes the effect of ground tire rubber (GTR) and a novel metallocene‐based ethylene–propylene copolymer (EPR), with high propylene content, on the morphology and mechanical behavior of ternary polymer blends based on a highly flowable polypropylene homopolymer (PP). The PP/EPR blends morphology, with very small domains of EPR dispersed in the PP matrix, indicates a good compatibility among these materials, which leads to a significant improvement on elongation at break and impact strength. The incorporation of EPR on the rubber phase of thermoplastic elastomeric blends (TPE) based on GTR and PP (TPE^GTR) has a positive effect on their mechanical performance, attributed to the toughness enhancement of the PP matrix and to the establishment of shell‐core morphology between the rubber phases. The mechanical properties of the ternary blends reveal that TPE^GTR blends allow the upcycling of this GTR material by injection molding technologies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42011.     

Mechanical and aging properties of cross‐linked ethylene propylene diene rubber / styrene butadiene rubber blends

The mechanical properties and aging characteristics of blends of ethylene propylene diene monomer (EPDM) rubber and styrene butadiene rubber (SBR) were investigated with special reference to the effect of blend ratio and cross‐linking systems. Among the blends, the one with 80/20 EPDM/SBR has been found to exhibit the highest tensile, tear, and abrasion properties at ambient temperature. The observed changes in the mechanical properties of the blends have been correlated with the phase morphology, as attested by scanning electron micrographs (SEMs). The effects of three different cure systems, namely, sulfur (S), dicumyl peroxide (DCP), and a mixed system consisting of sulfur and peroxide (mixed) on the blend properties also were studied. The stress‐strain behavior, tensile strength, elongation at break, and tear strength of the blends were found to be better for the mixed system. The influence of fillers such as high‐abrasion furnace (HAF) black, general‐purpose furnace (GPF) black, silica, and clay on the mechanical properties of 90/10 EPDM/SBR blend was examined. The ozone and water aging studies also were conducted on the sulfur cured blends, to supplement the results from the mechanical properties investigation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2606–2621, 2004     

Characterization and properties of LDPE/(ground tire rubber)/crosslinked butyl rubber blends

In recent years, interest in used rubber recycling, mainly focusing on the utilization of end‐of‐life tires, has heightened. This interest, is owing to the activities related to environmental protection and economic factors, which both stimulate companies to reuse the high‐quality rubber present in ground rubber scrap. In this study, the application of crosslinked butyl rubber in thermoplastic compositions of low‐density polyethylene and ground tire rubber (GTR) is presented. The static and dynamic mechanical properties and morphology of obtained products were studied. The addition of crosslinked butyl rubber to the investigated blends increased the compatibility between the low‐density polyethylene and the GTR particles. It was found that the mechanical properties of thermoplastic compositions containing higher amounts of elastomers (i.e., GTR and crosslinked butyl elastomer) displayed the same behavior, whereas the samples with GTR had worse respective parameters. Depending on their composition, the obtained new polymer blends can be applied to automotive parts, be adapted to pavement surfaces, and become parts of antivibration systems. J. VINYL ADDIT. TECHNOL., 20:237–242, 2014. © 2014 Society of Plastics Engineers     

Curing characteristics,morphology, thermal stability,mechanical properties,and irradiation resistance of methylethylsilicone/methylphenylsilicone rubber blends

Methylethylsilicone rubber (MESR)/methylphenylsilicone rubber (MPSR) blends were cured with 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy)hexane. The curing characteristics, morphology, thermal behaviors, mechanical properties at different temperatures, radiation resistance, and thermal aging resistance of the MESR/MPSR blends were investigated. The results show that a high MPSR content could decrease the optimum curing time and improve the scorch safety. Dynamic mechanical analysis revealed that the glass‐transition temperature of the blends increased slightly with the addition of MPSR. Scanning electron microscopy showed that MESR and MPSR had good compatibility in the blends. Thermogravimetric analysis indicated that the thermal stability of the blends increased with increasing quantity of MPSR. The blends had excellent mechanical properties at low temperatures. However, these properties were significantly reduced when the temperature was increased. Moreover, changes in the mechanical properties decreased with increasing MPSR content at high temperatures, especially at temperatures higher than 100°C. In addition, the radiation resistance and thermal aging resistance of the blends increased with increasing MPSR content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40529.     

Effects of processing parameters on the properties of microwave‐devulcanized ground tire rubber/polyethylene dynamically revulcanized blends

This work aimed to evaluate the effects of processing parameters on properties of dynamically revulcanized blends based on 60 wt % of devulcanized ground tire rubber (GTR) and 40 wt % of high density polyethylene (HDPE). Devulcanization of the GTR was carried out in a system comprised of a conventional microwave oven adapted with a motorized stirring system with speed control. The resulting devulcanized GTR contained 26 wt % soluble in toluene. It was processed with HDPE in a twin screw extruder to produce a dynamically revulcanized blend. Processing parameters such as screw speed and feeding mode were varied. Their effects were evaluated based on tensile, dynamic mechanical, thermal and rheological properties, as well as on morphology. The results show the importance of the processing parameters involved in the production of blends with dynamically revulcanized rubber phase in the extruder, and good match between the residence time of the rubber and its revulcanization kinetics. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43503.     

Thermoplastic dynamic vulcanisates containing LDPE,rubber, and thermochemically reclaimed ground tyre rubber

Abstract

Thermochemically devulcanised ground tyre rubber (GTR^DL) was added to fresh rubber compositions, which were then melt blended with low density polyethylene (LDPE). Styrene/butadiene rubber (SBR), natural (NR), and ethylene/propylene/diene (EPDM) rubbers were selected as the fresh rubbers. During blending, dynamic curing was achieved using sulphuric, phenolic, and peroxide curing agents. Some of the GTR was decomposed in the presence of 6 phr Regen^TM Agent-S reclaiming compound before being incorporated into the blends. The resulting thermoplastic dynamic vulcanisates had constant compositions, namely LDPE/rubber/GTR=50:25:25. Sulphuric and phenolic curing agents proved to be most suitable for dynamic curing. The thermoplastic dynamic vulcanisates with the best mechanical performance contained SBR and EPDM rubbers. The observed improvements in mechanical performance were attributed to chain entanglement and co-crosslinking in the interphase between the GTR^DL particles and the surrounding matrix (i.e. with the fresh rubber and/or LDPE). The phase morphology, which was assessed using scanning electron microscopy on the etched surfaces of cryogenically fractured thermoplastic dynamic vulcanisate compositions, is discussed.     

Curing Characteristics and Mechanical and Morphological Properties of Styrene Butadiene Rubber/Virgin Acrylonitrile-Butadiene Rubber (SBR/vNBR) and Styrene Butadiene Rubber/Recycled Acrylonitrile-Butadiene Rubber (SBR/rNBR) Blends

Curing characteristics and mechanical and morphological properties of styrene butadiene rubber/virgin acrylonitrile-butadiene rubber (SBR/vNBR) and styrene butadiene rubber/recycled acrylonitrile-butadiene rubber (SBR/rNBR) were investigated. Results indicated that the curing characteristics, such as scorch time, t₂, and cure time, t₉₀, of SBR/vNBR and SBR/rNBR blends decreased with increasing vNBR and rNBR content. At similar blend ratios, particularly up to 15 phr, SBR/rNBR blends exhibited higher t₂ and t₉₀ compared with SBR/vNBR blends. Minimum torque (ML) and maximum torque (MH) of SBR/vNBR blends significantly increased with increasing vNBR content. For SBR/rNBR blends, ML increased with increasing rNBR content, but MH exhibited the opposite trend. Tensile strength, elongation at break (E_b), resilience, and fatigue decreased with increasing virgin and recycled NBR content in both blends. Up to 15 phr, the tensile strength, E_b and fatigue life (Kc) of SBR/rNBR blends were higher than in SBR/vNBR blends. The M100 (stress at 100% elongation), hardness, and cross-linking density of both blends also showed an increasing trend with increasing vNBR and rNBR content. The scanning electron microscopy study indicates that rNBR exhibited a weak rNBR-SBR matrix interaction particularly when more than 15 phr of rNBR was used, thus decreasing the mechanical properties of SBR/rNBR blends.     

酚硫化物/醇复合促进剂对废轮胎胶应力诱导脱硫反应的影响

在废轮胎胶(GTR)与三元乙丙橡胶(EPDM)熔融挤出过程中添加多烷基苯酚二硫化物(简称420)或/和仲丁醇作为脱硫促进剂,考察了在不同螺杆转速和挤出反应温度下脱硫促进剂对GTR与EPDM脱硫共混物(DGTR/EPDM)凝胶含量和溶胶分子链结构的影响,研究了DGTR/EPDM/丁苯橡胶(SBR)再硫化胶的相态结构及物理...     

Effect of dicumyl peroxide and phenolic resin as a mixed curing system on the mechanical properties and morphology of TPVs based on HDPE/ground tire rubber

Thermoplastic vulcanizates (TPVs) are a special group of thermoplastic elastomer with the characteristic that consists of rubber elasticity and the processability of thermoplastic polymers. TPVs based on high density polyethylene (HDPE)/ground tire rubber (GTR) with phenolic resin (HY‐2045) and dicumyl peroxide (DCP) as vulcanizing agents are prepared through dynamic vulcanization in this article. The blends consisting of 40/60 HDPE/GTR are melt‐mixed in an internal mixer and then pressed with a compression molding machine. The aim of this experiment is to study the influence of a compound curing agent system on the mechanical properties of the HDPE/GTR composites. The results indicate that the mechanical properties of the HDPE/GTR blends are improved significantly by adding 4 phr HY‐2045 and 0.3 phr DCP than those of TPVs without any vulcanizing agents after dynamic vulcanization. The X‐ray photoelectron spectroscopy study and the FTIR‐ATR analysis confirmed that the crosslinking phenomenon occurred in the preparation of TPVs; and the gel fraction analysis indicates that the GTR components and the HDPE components of the HDPE/GTR blends are all moderately crosslinked. In addition, the morphology of the HDPE/GTR blends has been investigated by scanning electron microscopy. POLYM. COMPOS., 36:1907–1916, 2015. © 2014 Society of Plastics Engineers     

热剪切对聚乙烯/胶粉共混物结构演变及性能的影响

研究了聚乙烯(PE)/胶粉(GTR)共混物中GTR在不同热剪切加工条件下结构形态的演变过程及其对共混物力学性能、流变性能和溶胀行为的影响。结果表明,PE/GTR共混物中GTR受到热剪切作用后,体系中会出现大量几微米的小颗粒,且几微米的小颗粒随温度的升高和加工时间的延长而增多,但即使在220℃下连续剪切25 min,仍有100μm以上的大颗粒存在。随着加工温度的升高和加工时间的延长,共混物的力学性能、流变性能略有下降;而溶胀比随温度的升高先减小后增大,随时间的延长则略有减小。     

Partial replacement of NR by GTR in thermoplastic elastomer based on LLDPE/NR through using reactive blending: Its effects on morphology,rheological, and mechanical properties

Attempts have been made to use different amount of ground tire rubber (GTR) powder as a partial substitute for natural rubber (NR) in thermoplastic elastomer based on linear low‐density polyethylene (LLDPE, 60 wt%) and NR (40wt%). Maleic anhydride (MA) and dicumyl peroxide (DCP) were used, during melt mixing of the compound, to modify GTR and vulcanize the rubber phases of the blends. Morphology of the blends was studied by scanning electron microscopy and rheological behavior investigated through rheomechanical spectroscopy. Mechanical properties of the blends were also measured, and the effect of GTR concentration on properties was evaluated. Obtained results showed that modification of GTR with MA and using DCP in the blends containing GTR improves the bonding between GTR and matrix. This leads to a distinctive rheological behavior and enhances tensile strength and elongation at break compared to its corresponding simple blend. It can be said that using of MA and DCP during melt mixing of thermoplastic elastomers based on LLDPE/NR containing GTR, concludes to a better dispersion of GTR and formation of morphology similar to that of a dynamic vulcanized thermoplastic elastomer, which improves interfacial bonding between phases and causes a dramatically increase in mechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010