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 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     

Rheology,cure characteristics,physical and mechanical properties of tire tread reclaimed rubber/natural rubber compounds

This work aimed to examine the effect of addition of tire‐tread reclaimed rubber on the properties of two natural rubber (NR) compounds with respect to the reclaimed rubber concentration and mastication time, the properties of interest including rheological and cure characteristics, physical and mechanical properties. The results under the test conditions suggested that Mooney Plasticity and shear viscosity increased with reclaimed rubber content, but decreased with mastication time. The greater the molar mass of the natural rubber the higher the sensitivity to the change in compound viscosity due to mastication and reclaimed rubber content. The die swell was more dependent on the reclaimed rubber than the molar mass of the rubbers. The cure rate and scorch time were found to increase and decrease with reclaimed rubber content, respectively, whereas the cure time was independent of the reclaimed rubber content. For vulcanized rubbers, it was also observed that 100% modulus of the rubber increased with reclaimed rubber content, but this was not the case for tensile stress and elongation at break. The hardness and heat buildup properties of the vulcanizates increased with reclaimed rubber content whereas the tear strength became independent of the reclaimed rubber. The findings in this work suggested that the variations in the rheological and cure characteristics for the unvulcanized rubber were very much dependent on the molar mass of the rubber whereas the mechanical properties for the vulcanized rubber were influenced by crosslink density. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1723–1731, 2003     

Quantifying and comparing the selectivity for crosslink scission in mechanical and mechanochemical devulcanization processes

Devulcanization processes have potential to increase the economic value of ground tire rubber (GTR) derived from waste tires, although the chemistry of the devulcanization process is still poorly understood. This article presents a method, based on sol extraction and swelling measurements, for quantifying the selectivity for crosslink scission over main chain scission, and applies it to extrusion‐based mechanical and mechanochemical devulcanization processes at various operating conditions. The mechanochemical devulcanization process, using diphenyl disulfide and process oil, resulted in a higher selectivity for crosslink scission than the mechanical devulcanization process. Furthermore, it was shown that the process oil, along with lower reaction temperature, in the mechanochemical devulcanization process was responsible for the increased selectivity, rather than the presence of diphenyl disulfide. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43932.     

Balancing mechanical properties and processability for devulcanized ground tire rubber using industrially sized single‐screw extruder

Devulcanized ground tire rubber (DGTR) samples were produced using an independently developed industrially sized single‐screw extruder. The DGTR was further revulcanized to produce revulcanized DGTR (RDGTR) samples. The structure and properties of the produced samples were investigated via tests and characterization of sol fraction, crosslink density, Fourier transform infrared spectroscopy spectra, X‐ray photoelectron spectroscopy spectra, Mooney viscosity, curing characteristics, dynamic rheology, tensile properties, and surface morphology. The results demonstrate that the extruder can effectively break up crosslinked structure of ground tire rubber to achieve high devulcanization level (characterized by sol fraction and crosslink density), which is mainly associated with its moderate shear strength. The balance between mechanical properties and processability for the DGTR samples was analyzed. Lower ratios of main‐chain to crosslink scission and good processability (mainly characterized by modest Mooney viscosity) for the DGTR samples, and high tensile strengths and elongations at break for the RDGTR samples are obtained via appropriately combining the barrel temperature and screw speed. High quality DGTR sample with tensile strength and elongations at break of up to 11 MPa and 370%, respectively, is prepared under the conditions used in this work. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43761.     

影响废旧轮胎胶粉热-机械剪切脱硫再生效果的因素

利用自行研制的长径比为60/1的强剪切型双螺杆挤出机对废旧轮胎胶粉进行热-机械剪切脱硫,用傅里叶变换红外光谱对脱硫胶粉进行了表征,考察了胶粉粒径和喂料螺杆转速与主机转速之比对脱硫胶粉凝胶含量、交联密度及再生胶力学性能的影响,以及脱硫过程中胶粉相对分子质量及其分布的变化。结果表明,随着胶粉粒径的增大,胶粉所受到的剪切力增强,脱硫效果也越好。随着转速比的增加,胶粉的脱硫程度提高;脱硫过程的第1个阶段是交联网络的破坏,第2个阶段除交联网络的破坏外分子主链也发生降解,再生胶的力学性能先增大后减小;当转速比为1.4时再生胶的扯断伸长率和弹性最好,拉伸强度也相对较高。     

CM和HDPE对再生橡胶物理机械性能的影响

研究CM和HDPE对再生橡胶物理机械性能的影响。结果表明,再生橡胶的门尼粘度随着CM用量的增加而降低,随着HDPE用量的增加而增加。再生橡胶的拉伸强度和拉断伸长率随着CM和HDPE用量的增加逐渐增加;扫描电镜研究表明,添加CM的再生橡胶硫化胶的拉伸断面相对平整,断层更均匀。综合比较当CM用量为8phr时,再生橡胶的综合性能最佳。     

连续机械剪切对废旧轮胎胶粉脱硫效果的影响

利用自行研制组装的剪切型双螺杆挤出机对废旧轮胎胶粉进行连续机械剪切脱硫,考察了螺杆转速和加工温度对胶粉脱硫效果的影响。结果表明,在螺杆转速为120 r/min,螺杆部分加热输送区、多段压缩和分段剪切区、混炼剪切区3个区段的加工温度分别为250,230,200℃的条件下,胶粉的凝胶质量分数由脱硫前的97.71%最低可下降到67.57%,交联密度由脱硫前的5.00×10-4mol/mL最低可下降到1.08×10-4mol/mL,具有很好的脱硫效果。     

The effect of UV‐irradiation and molten medium on the mechanical and thermal properties of polystyrene–polycarbonate blends

Polymer materials with improved properties can be obtained through polymer blends. As a polymer mixture is generally immiscible and incompatible, it is necessary to develop new methods to improve the interfacial adhesion. The aim of this work is to find formulations and associated processes to upgrade engineering polystyrene (PS) and polycarbonate (PC) polymer blends with the objective of using the best “process‐formulation” couple. In this study, blends of PS/PC were prepared in molten medium using reactive extrusion after UV‐irradiation. The effects of UV‐irradiation on some properties of blends under molten medium were investigated by differential scanning calorimetry (DSC), fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The data showed that the presence of polycarbonate in the blend increased the tensile strength and elongation at break with respect to pure PS. The mechanical properties of the blends were improved after irradiation. All irradiated blends are thermally more stable than those nonirradiated. Chemical changes can be clearly seen in FTIR spectra through two bands assigned to C?O and OH groups. The mutual influence between the PS/PC polymer blends compositions during UV‐irradiation was studied. PS and PC have different photo‐mechanisms due to the larger UV absorption of polystyrene and formation of more stable tertiary carbon radicals. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical and dynamic mechanical properties of natural rubber blended with waste rubber powder modified by both microwave and sol–gel method

Waste rubber powder (WRP) was modified by microwave, sol–gel method, and both microwave and sol–gel method, respectively. The mechanical and dynamic mechanical properties of natural rubber (NR)/modified WRP composite were investigated. The influence of bis‐(3‐(triethoxysilyl)‐propyl)‐tetrasulfide (TESPT) content on curing characteristics and mechanical properties of vulcanizate was also studied. The results showed that NR/WRP modified by both microwave and sol–gel method composite owned the best mechanical properties. Rubber processing analyzer was used to characterize the interaction between silica and rubber chains and the dispersion of silica. With increase of TESPT content, the Payne effect decreased. Scanning electron microscopy indicated the coherency and homogeneity of in situ generated silica filled vulcanizate. Dynamic mechanical analyzer showed that NR/WRP modified by both microwave and sol–gel method composite with 5 phr TESPT exhibited the lower tan δ at temperature range of 50–80°C, compared with composite without TESPT and the higher tan δ at temperature of 0°C, compared with the conventional modification of WRP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Cure characteristics and physical properties of ground‐rubber‐filled natural rubber vulcanizates: Effects of the curing systems of the ground rubber and rubber matrix

Recycling discarded rubber is important for both environmental and economic reasons. One of the most attractive methods of recycling rubber waste is to use ground rubber (GR) as a compounding ingredient or as a replacement for raw polymers. In this study, ground natural rubber was prepared with different curing systems and compounded into the parent compounds. The cure behaviors and physical properties of the GR‐filled vulcanizates were investigated, and they were largely affected by the curing systems of the rubber matrix and GR. GR‐filled vulcanizates with GR and the rubber matrix, having a conventional curing system, showed the largest changes in the cure characteristics. The greatest decrease in the physical properties was observed for peroxide‐cured‐GR‐filled vulcanizates. The addition of GR decreased the crosslink density of the GR‐filled vulcanizates. This was thought to be the main reason for the reduction of the mechanical properties of the GR‐filled vulcanizates. However, the adhesion between the GR and rubber matrix may also have caused the differences in the physical properties of the GR‐filled vulcanizates with respect to the curing systems of the rubber matrix and GR. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

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

Waste rubber cannot be reprocessed by melting because of its three‐dimensionally crosslinked molecular structure. Mechanical size reduction is the most common method for recycling and reusing waste rubber. The modified solid‐state shear extrusion (SSSE) process developed at the Illinois Institute of Technology was used for mechanical size reduction of rubber in a continuous process. In this work, an extended screw was used in conjunction with the original design of the SSSE apparatus to achieve greater rubber pulverization with a higher throughput rate and lower power consumption. The operating conditions of the modified SSSE apparatus were optimized to produce finer rubber particles that could be further used in a wide variety of applications. Controlling the residence time of rubber particles inside the pulverization section was crucial for producing a fine powder without agglomeration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of rubber composites from ground tire rubber reinforced with waste‐tire fiber through mechanical milling

Composites made from ground tire rubber (GTR) and waste fiber produced in tire reclamation were prepared by mechanical milling. The effects of the fiber content, pan milling, and fiber orientation on the mechanical properties of the composites were investigated. The results showed that the stress‐induced mechanochemical devulcanization of waste rubber and the reinforcement of devulcanized waste rubber with waste‐tire fibers could be achieved through comilling. For a comilled system, the tensile strength and elongation at break of revulcanized GTR/fiber composites reached maximum values of 9.6 MPa and 215.9%, respectively, with 5 wt % fiber. Compared with those of a composite prepared in a conventional mixing manner, the mechanical properties were greatly improved by comilling. Oxygen‐containing groups on the surface of GTR particles, which were produced during pan milling, increased interfacial interactions between GTR and waste fibers. The fiber‐filled composites showed anisotropy in the stress–strain properties because of preferential orientation of the short fibers along the roll‐milling direction (longitudinal), and the adhesion between the fiber and rubber matrix was improved by the comilling of the fiber with waste rubber. The proposed process provides an economical and ecologically sound method for tire‐rubber recycling. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 4087–4094, 2007     

Thermomechanical devulcanization of ethylene propylene diene monomer rubber and its application in blends with high-density polyethylene

The recycling of ethylene propylene diene monomer (EPDM) rubber remains a challenge, as its cross-linked structure cannot be broken down reversibly. Devulcanization may offer a breakthrough; however, a 100% decrease in cross-link density (CLD) with no chain degradation has never been reported. In this research, sulfur- and peroxide-cured EPDM rubbers of known compositions were devulcanized on a two-roll mill and in an internal mixer. The CLD of both rubber samples decreased by around 85%, while the sol content of the peroxidic devulcanizate was considerably higher than that of the sulfuric devulcanizate (23% vs. 3%). Horikx's theory revealed that sulfur-cured samples showed excellent selectivity for cross-link scission, while peroxide-cured samples suffered degradation. Uncured, cured, and devulcanized rubber samples were mixed into high-density polyethylene at various compositions. Large EPDM rubber contents impaired the mechanical properties of the blends, indicating insufficient adhesion between the two phases. Compounds containing originally uncured rubber mixtures had the most beneficial mechanical properties.     

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.     

Sulfuric acid treatment of ground tire rubber and its effect on the mechanical and thermal properties of polypropylene composites

Ground tire rubber (GTR) was modified by sulfuric acid in order to improve its compatibility with and reinforcement of a polypropylene (PP) matrix. Polymer composites PP/GTR were prepared by melt mixing at different concentrations, with a maximum of 50 wt % of GTR. Studies by Fourier transform infrared spectroscopy (FTIR), surface specific area by BET (Brunauer, Emmett, and Teller), and scanning electron microscopy were used to characterize the untreated GTR and treated GTR, while the mechanical and thermal properties of the PP/GTR composites were assessed to understand how the surface treatment of GTR affected the mechanical and thermal properties of the composite PP/GTR. FTIR revealed the presence of sulfonic groups on the surface of sulfuric acid–treated GTR, and BET analyses showed an increase of about 625% in the specific surface area as a result of the high porosity produced by the treatment. In all composites containing treated GTR, a higher Young's modulus was obtained than for composites containing untreated GTR. Particularly, an increase of about 275% in the Young's modulus was obtained in composites with treated GTR (40 wt %) against that containing untreated GTR. However, a more significant reduction of the elongation at break was observed in composites containing treated GTR than in those containing untreated GTR. Also, an increase of the crystallization temperature of PP as a function of GTR was observed by differential scanning calorimetry, but the crystallinity of the composites was reduced by the addition of both untreated and treated GTR. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44858.     

Complete devulcanization of sulfur‐cured butyl rubber by using supercritical carbon dioxide

Sulfur‐cured butyl rubber was devulcanized completely in supercritical CO₂ by using diphenyl disulfide (DD) as a devulcanizing reagent. The optimum devulcanizing conditions were studied and the sol fraction of the reclaimed rubber obtained was up to 98.5%. The possible devulcanizing mechanism was investigated. Then, the sol component of reclaimed rubber was characterized by gel permeation chromatography, ¹H‐NMR, and differential scanning calorimetry, and the reclaimed rubber was characterized by TGA. Because of the substitution of a large portion of allylic hydrogen by sulfurated functional groups during vulcanization, the signal of the olefinic proton shift. As a result of the numerous decreases in the active crosslinking sites and the remaining DD, reclaimed rubber could not be cured by sulfur. At last, the blends of virgin butyl rubber and different contents of reclaimed rubber were revulcanized and their mechanical properties investigated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Die‐swell behavior during the short‐tube flow of rubber compounds

In this study, the flow properties and die‐swell ratios (B's) of two kinds of rubber compounds (SI was a calcium carbonate filled natural rubber compound, and SII was a carbon‐black‐filled natural rubber/butadiene–styrene rubber/cis‐1,4‐butadiene rubber compound) in a short‐tube extrusion flow were measured by means of a capillary rheometer under test conditions with a temperature of 90°C and an apparent shear rate varying from 10 to 4000 s^?1 to identify the effects of extrusion conditions on the rheological behavior of the materials and to estimate B. The shear flow roughly obeyed the power law, whereas B increased nonlinearly with increasing extrusion rate. Under the same shear rates, the viscosity of SII was higher than that of SI, whereas the values of B of SI were higher than those of SII. Furthermore, B of the rubber compounds was estimated by means of an extrudate swell equation published in a previous work. The results show that the predictions of B were close to the measured data from the experiments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Structure and performance of reclaimed rubber obtained by different methods

Four different reclaiming methods involving important reclaiming factors such as temperature, shear force, and atmosphere were used to reclaim ground tire rubber. The structure and performance of the reclaimed rubber were investigated. The reclaimed samples were all found to be mixtures of three parts: the sol part, a loosely crosslinked gel part, and low molecular substances. For a reclaimed product to have both good processability and mechanical properties, the ideal structure should be that the sol fraction and its molecular weight (M_n) are as high as possible. However, the high sol fraction and high M_n cannot be reached at the same time because of the nonselective scission of the main chain and crosslink bonds. Thus, for a reclaimed rubber to have high quality, the presence of some amount of gel fraction is essential. Our preliminary results showed that the recommended reclaiming method would be a process under oxygen‐free atmosphere, without severe shear force, and at relative low temperature. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Vulcanization characteristics and mechanical properties of natural rubber–scrap rubber compositions filled with leather particles

Scrap rubber recycling combined with waste leather particles in natural rubber compounds has been studied. The effect of leather and scrap rubber loading on vulcanization characteristics of natural rubber compounds has been evaluated. The presence of leather was found to reduce the scorch time and increase the maximum and minimum torque. While reversion was not observed in the absence of leather at 150 °C, it was more prominent when leather was incorporated. Mechanical properties such as tensile strength, elongation at break, tear strength, modulus and hardness were found to increase on increasing the scrap rubber loading in the absence of leather. Compounds containing leather exhibited higher tensile strength, modulus, hardness and tear strength values but the modulus and hardness values were found to decrease as the scrap rubber loading increased. All the vulcanizates exhibited only limited swelling in different media as the swelling of one phase of the composite was found to be restricted by the other phase. Copyright © 2004 Society of Chemical Industry