Mechanochemical devulcanization of ground tire rubber and its application in acoustic absorbent polyurethane foamed composites

The use of recycled rubber in preparation of acoustic absorbent materials will help to combat the existing environmental problems of both waste disposal and noise pollution. The focus of this work is to investigate the influence of mechanochemical pretreatment of ground tire rubber (GTR) on the acoustic absorption properties of polyurethane (PU)/GTR foamed composites. GTR subjected to pan‐milling could be mechanochemically devulcanized by breaking up the crosslinked structures through inducing fairly strong shearing and compressing forces. The significant increase in sol fraction of GTR confirmed the partial devulcanization during pan‐milling. Moreover, thermal gravimetric analysis indicated that rubber content in the soluble part of GTR was also remarkably increased. The devulcanization increased flexible chains of the GTR particles, which could help to improve damping properties as well as acoustic absorption ability of the PU/GTR foamed composites. Dynamic mechanical analysis and acoustic absorption measurements well confirmed this hypothesis. The loss modulus and sound absorption coefficient of PU/GTR foamed composites were remarkably increased through the mechanochemical pretreatment of GTR. The mechanochemical pretreatment also enhanced foamability of the composites as revealed by cell morphology. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of thermoplastic vulcanizates based on waste crosslinked polyethylene and ground tire rubber through dynamic vulcanization

An environmental‐friendly approach called high‐shear mechanical milling was developed to de‐crosslink ground tire rubber (GTR) and waste crosslinked polyethylene (XLPE). The realization of partial devulcanization of GTR and de‐crosslinking of XLPE were confirmed by gel fraction measurements. Fourier transform infrared spectral studies revealed that a new peak at 1723.3 cm^?1 corresponds to the carbonyl group (? C?O) absorption was appeared after milling. The rheological properties showed that the XLPE/GTR blends represent lower apparent viscosity after mechanical milling, which means that the milled blends are easy to process. Thermoplastic vulcanizates (TPVs) could be prepared with these partially de‐crosslinked XLPE/GTR composite powders through dynamic vulcanization. The mechanical properties of the XLPE/GTR composites increased with increasing cycles of milling. The raw XLPE/GTR blends could not be processed to a continuous sheet. After 20 cycles of milling, the tensile strength and elongation at break of XLPE/GTR (50/50) composites increased to 6.0 MPa and 185.3%, respectively. The tensile strength and elongation at break of the composites have been further improved to 9.1 MPa and 201.2% after dynamic vulcanization, respectively. Re‐processability study confirmed the good thermoplastic processability of the TPVs prepared. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Short sisal fiber‐reinforced tire rubber composites: Dynamic and mechanical properties

The world tendency toward using recycled materials demands new products from vegetable resources and waste polymers. In this work, composites made from powdered tire rubber (average particle size: 320 μm) and sisal fiber were prepared by hot‐press molding and investigated by means of dynamic mechanical thermal analysis and tensile properties. The effects of fiber length and content, chemical treatments, and temperature on dynamic mechanical and tensile properties of such composites were studied. The results showed that mercerization/acetylation treatment of the fibers improves composite performance. Under the conditions investigated the optimum fiber length obtained for the tire rubber matrix was 10 mm. Storage and loss moduli both increased with increasing fiber content. The results of this study are encouraging, demonstrating that the use of tire rubber and sisal fiber in composites offers promising potential for nonstructural applications. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 670–677, 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%.     

Enhancement of processability and foamability of ground tire rubber powder and LDPE blends through solid state shear milling

The foamed composites made from low-density polyethylene(LDPE) and ground tire rubber(GTR) powder using azodicarbonamide as chemical blowing agent have been investigated. Solid state shear milling was used to enhance the processability and foamability of LDPE/GTR blends by a pan-mill type mechanochemical reactor. First the blends of LDPE/GTR were prepared by co-milling, then the samples were melt-mixed in a Brabender Plasti-Corder, saturated with blowing agent, crosslinking agent and blowing co-agent, and finally the saturated specimens were expanded during the pressure-quench process. The results indicated that the mechanical properties of the LDPE/GRT foamed composites were improved, and the blends of co-milled GTR and LDPE powder showing better processability and foamability than those obtained in a conventional melt-mixing manner, as indicated by the rheological and morphological studies.     

Morphology and physical properties of composite foams based on low‐density polyethylene and ground tire rubber

Low‐density polyethylene (LDPE)/(ground tire rubber) (GTR) composite foams with an average cell size smaller than 100 µm were produced by compression molding. The effects of the mechanochemical pretreatment of the LDPE/GTR blends and their GTR content on the cell morphology and physical properties were investigated. The results indicated that the pretreatment of LDPE/GTR blends by using a pan‐mill type of mechanochemical reactor made in our laboratory improved the dispersion state and thereby enhanced the foamability of the blends. The average cell size of the composite foams decreased from 64.0 to 42.3 µm with an increase in GTR content from 0 to 50 phr (parts by weight per hundred parts of resin). Moreover, the addition of 20–40 phr of GTR into the LDPE foams increased their rebound resistance and decreased their compression set. J. VINYL ADDIT. TECHNOL., 19:105–112, 2013. © 2013 Society of Plastics Engineers     

Thermoplastic elastomers based on recycled high‐density polyethylene,ethylene–propylene–diene monomer rubber,and ground tire rubber

High‐performance thermoplastic elastomers (TPEs), based on recycled high‐density polyethylene (HDPE^R), olefinic type ethylene–propylene–diene monomer rubber (EPDM), and ground tire rubber (GTR) treated with bitumen, were prepared by using dynamic vulcanization technology, and their structure–property relationships were investigated. It was established that special pretreatment of GTR by bitumen confers outstanding mechanical properties on the resulting TPEs. TPEs, containing GTR pretreated by bitumen, exhibit thermal behavior similar to that of the HDPE^R/EPDM basic blend in the temperature region up to about 340°C. Rheological measurements showed that bitumen acts as an effective plasticizer for the GTR‐containing TPEs. SEM, DSC, and DMTA results revealed improved adhesion between the particles of GTR treated by bitumen and the surrounding thermoplastic matrix, compared to that of the untreated GTR particles. It was concluded that bitumen acts as an effective devulcanizing agent in the GTR treatment stage. In the following steps of TPE production, bitumen acts simultaneously as a curing agent for the rubber components (EPDM/GTR) and as a compatibilizer for the blend components. GTR‐containing TPEs, prepared by extrusion technology, were reprocessed (by passing through the extruder six times) without any observable changes in their tensile properties, thermal stability, and melt viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 659–671, 2005     

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     

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.     

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.     

Aramid‐short‐fiber reinforced rubber as a tire tread composite

Mechanical and dynamic‐mechanical properties of a typical tire tread compound reinforced with one part aramid short fibers were investigated in order to predict the effects of fibers on tire tread performances such as rolling resistance and traction. Rubber processing, including mixing and extrusion, was performed in an industrial scale. Fiber orientation as a result of extrusion was evaluated quantitatively and qualitatively using mechanical anisotropy in swelling and scanning electron microscopy, respectively. Unidirectional tensile tests revealed higher modulus, but slightly lower strength and elongation at break for the composites stretched in the longitudinal (orientation) and transverse directions than those for the isotropic reference compound with no fiber. Dynamic mechanical thermal analysis showed that relative values of loss factor for the longitudinal and transverse composites and the reference compound depended on the state of polymer as glassy or rubbery. Therefore, a high loss factor at lower temperatures and a low loss factor at higher temperatures predicted a balanced improvement of tire traction and rolling resistance as a result of fiber addition. Heat build‐up and abrasion experiments showed that addition of fiber did not deteriorate other performances of tire tread. Also, the fibers had negligible effects on processing and vulcanization characteristics of the composite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

Thermomechanical reclaiming of ground tire rubber via extrusion at low temperature: Efficiency and limits

Thermomechanical reclaiming of ground tire rubber (GTR) was performed at different temperatures (60, 120, and 180°C) using a co‐rotating twin‐screw extruder. Obtained samples were used in styrene‐butadiene rubber (SBR) blends. As reference samples, SBR compounds containing untreated GTR were used. Curing characteristics, static and dynamic mechanical properties, and morphology of the obtained blends were determined. The results show that the increase of barrel temperature during the thermomechanical reclaiming of GTR has a positive effect on the decrease of screw torque (lower machine load) and decrease of Mooney viscosity (better processing characteristics). However, mechanical properties and crosslink density of rubber revulcanizate decreased with increasing barrel temperature during the reclaiming process. SBR blends with 50 phr of reclaimed rubber showed increasing phase compatibility between SBR matrix and the reclaimed rubber, which was confirmed by mechanical properties and morphology measurements. J. VINYL ADDIT. TECHNOL., 22:213–221, 2016. © 2014 Society of Plastics Engineers     

Mechanical properties of surface‐modified ultra‐high molecular weight polyethylene fiber reinforced natural rubber composites

The mechanical properties of ultra‐high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were determined, and the effects of fiber surface treatment and fiber mass fraction on the mechanical properties of the composites were investigated. Chromic acid was used to modify the UHMWPE fibers, and the results showed that the surface roughness and the oxygen‐containing groups on the surface of the fibers could be effectively increased. The NR matrix composites were prepared with as‐received and chromic acid treated UHMWPE fibers added 0–6 wt%. The treated UHMWPE fibers increased the elongation at break, tear strength, and hardness of the NR composites, especially the tensile stress at a given elongation, but reduced the tensile strength. The elongation at break increased markedly with increasing fiber mass fraction, attained maximum values at 3.0 wt%, and then decreased. The tear strength and hardness exhibited continuous increase with increasing the fiber content. Several microfibrillations between the fiber and NR matrix were observed from SEM images of the fractured surfaces of the treated UHMWPE fibers/NR composites, which meant that the interfacial adhesion strength was improved. POLYM. COMPOS., 38:1215–1220, 2017. © 2015 Society of Plastics Engineers     

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.     

螺杆结构对轮胎胶粉超声波脱硫工艺及性能的影响

采用负载超声波发生装置的同向旋转双螺杆挤出机对40目废旧轮胎胶粉（GTR）进行超声波脱硫,考察了两种不同结构螺杆对脱硫过程中的口型压力和功率消耗、脱硫GTR（DGTR）的外观形貌、流变性能、硫化特性及DGTR硫化胶力学性能的影响。结果表明,在13 μm超声波振幅和含较多捏合块部件螺杆的作用下得到的DGTR的凝胶含量、黏度及储能模量较低,说明含捏合元件的螺杆剪切作用更强,能使GTR获得更高程度的脱硫。该条件下所制得的DGTR硫化胶的拉伸强度和100%定伸应力较低,扯断伸长率较高。     

Influence of compatibilizers and processing temperature on microcellular injection‐molded polypropylene/(waste tire powder) composites

Nowadays the economic recycling of waste tires has become a global challenge. The use of waste tire powder as a dispersed elastomeric phase in a polypropylene (PP) matrix offers an interesting opportunity for recycling of waste tire rubber. Compatibilized PP/(waste tire powder) composites are microcellularly processed to create a new class of materials with unique properties. Recent studies have demonstrated the feasibility of developing microcellular structures in PP/waste ground rubber tire (WGRT) composites. Microcellular PP/WGRT composites are prepared by an injection‐molding process using a chemical blowing agent. In this study, cell sizes, cell density, void fraction, and mechanical properties of the composite foams were measured, as well as the shear viscosity of the unfoamed composites. The influence of various compatibilizers and processing temperatures on cell morphology and the mechanical properties of injection‐molded PP/WGRT composites were investigated. It was seen that the addition of maleic anhydride‐grafted styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) increased the shear viscosity of the composites. The void fraction and cell density of the PP/WGRT composites increased with addition of compatibilizers, whereas the average cell sizes decreased. A processing temperature range of 180–195°C gave finer microcellular structure and regular cell distribution. The SEBS‐g‐MA enhanced the elongation properties and acted as an effective compatibilizer in this particular system. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

The effect of EVA content on the processing parameters and the mechanical properties of LDPE/ground tire rubber blends

In this work, thermoplastic elastomers were prepared based on low‐density polyethylene (LDPE) and ground tire rubber (GTR). To improve the adhesion and achieve better rubber‐like properties, ethylene vinyl acetate copolymer (EVA) was selected and used as a compatibilizer. The GTR and EVA content were varied between 0–45 and 0–20 wt%, respectively. Blends with different composition were produced from the raw materials on a twin screw extruder. Tensile and instrumented falling weight impact (IFWI) specimens were injection molded from the granulated blends. Injection pressure and the shrinkage of the IFWI specimens were measured. Besides the tensile and IFWI tests, the cut cross‐sections were inspected with a scanning electron microscope. Based on the results, it can be stated that the application of EVA as a compatibilizer is essential for even lower weight percentage to ensure the rubber‐like properties, but as the EVA content is increased, only less additional improvement can be detected. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Reinforcement of acrylonitrile butadiene rubber with waste rubber ash using ionizing radiation

Composites of acrylonitrile butadiene rubber with waste rubber ash (WRA) were prepared in the laboratory by a two‐roll mill. Gamma radiation at different doses (0 to 150 kGy) was applied to curing of acrylonitrile butadiene rubber composites loaded with reinforcement filler (ash powder, 5–40 parts by weight per hundred parts of rubber [phr]). WRA was characterized by Fourier‐transform infrared spectroscopy and X‐ray diffraction. Mechanical and thermal properties of prepared composites were investigated. The results show that the concentration of WRA up to 40 phr and irradiation dose up to 100 kGy improve the mechanical properties of composites. On the other hand, the thermal stability of the composites improved by adding 40 phr of WRA. J. VINYL ADDIT. TECHNOL., 23:117–124, 2017. © 2015 Society of Plastics Engineers     

Mechanical and viscoelastic properties of short fiber reinforced natural rubber composites: effects of interfacial adhesion,fiber loading,and orientation

The effect of a two-component dry bonding system consisting of resorcinol and hexamethylene tetramine on the mechanical and viscoelastic properties of short sisal fiber reinforced natural rubber composites has been studied. The studies were conducted with chemically treated and untreated short sisal fibers. Treated fibers impart better mechanical properties to the composites. By mixing with short fibers, the dynamic storage modulus (E') of natural rubber composites was improved. The effects of fiber-matrix adhesion on the mechanical and viscoelastic properties of the composites were investigated. The storage moduli and mechanical loss increased continuously with an increase in fiber loading but decreased with an increase of temperature. The influence of the fiber orientation on the mechanical and viscoelastic properties is discussed.