Mechanochemical Devulcanization Research Articles

Modified waste rubber powders filled styrene butadiene rubber toward the combination of high elasticity and low mechanical hysteresis

Waste recycled rubber (RR) powders are modified with modifier and low-temperature mechanochemical devulcanization (LTMD) method, and filled into styrene butadiene rubber (SBR) to improve its elasticity and reduce its mechanical hysteresis. The incorporation of modified RR (MRR) could accelerate SBR vulcanization, improve the crosslinking density of SBR and promote the compatibility of MRR in the matrix. Furthermore, it could also improve the tensile strength of SBR vulcanizates and weaken the Mullins effect by reducing their overall hysteresis, softening and energy loss. Such method realizes the high-value recovery of RR, reduces the mechanical hysteresis of rubber composites and improves the elasticity.

Adsorption of aqueous Pb(II) using non-devulcanized and devulcanized tyre rubber powder: a comparative study.

This study aimed to compare the adsorption of Pb(II) ions from an aqueous solution using non-devulcanized (NTR) and devulcanized tyre rubber (DTR) powder. Both types of rubber particles were prepared from used truck tyres, with DTR processed through mechano-chemical devulcanization. The adsorption experiments were conducted using 100-200µm particles, with adsorbent doses ranging from 5 to 15g/L. Effects of adsorbent dose, initial metal concentration and contact time were investigated. Characterization of both adsorbents was done using SEM-EDS, FTIR, and XRD analysis. Different adsorption isotherm and kinetic models were used to analyse the adsorption mechanisms. The results of the study showed that DTR was significantly more efficient at adsorbing Pb(II) compared to NTR. The maximum adsorption capacities estimated from the Langmuir equation were 75.1mg/g and 6.61mg/g for DTR and NTR, respectively. Among the kinetic models tested, pseudo 2nd order kinetic model was found to be the most suitable for tyre rubber adsorbents. The optimal dose and contact time were found to be 5g/L and 120min, respectively, for both adsorbents. The superior performance of DTR in Pb(II) adsorption was attributed to the change in the surface morphology of the rubber during the devulcanization process, resulting in increased surface roughness. The adsorption of Pb(II) was accompanied by the leaching of Zn from both types of rubber, suggesting that an ion exchange mechanism might be involved in the adsorption process. In conclusion, devulcanization appears to be a viable method for improving the adsorption properties of tyre rubber.

Fill two needs with one deed: Simultaneous devulcanization and silica reinforcement of waste rubber for green tyre tread compound

The proper disposal of waste rubber without disturbing the environment is one of the most challenging tasks towards the researchers and scientists in the 21st century. The existing disposal techniques other than recycling of waste rubber goods, does not add any value either on the waste polymeric material or in the raw material from which those polymeric materials are originated. The mechanochemical devulcanization of waste natural rubber by bis(3-triethoxysilylpropyl)tetrasulfide and its subsequent dispersion in fresh natural rubber-silica composites in various proportions ranging from 20% to 70% wt% are both addressed in this investigation. The mechanical performance of the composites clearly indicates that tensile strength, tear strength and elongation at break gradually increases with increasing devulcanized rubber (r-NR) content up to a certain proportion and the values are much superior to that of the control formulation. The evaluated mechanical properties clearly specify that the optimum level of r-NR in the composite is 40 phr. The developed green composites showed superior thermal behavior compared to that of its control formulation. The rubber filler interaction between devulcanized natural rubber (r-NR) and silica was further explored by measuring the fraction of immobilized polymer chains using differential scanning calorimetry. Scanning electron microscopic images (SEM) of the r-NR based NR/r-NR/SiO2 composites reveal a homogeneous and uniform dispersion of the silica filler.

Upscaling of a Mechanochemical Devulcanization Process for EPDM Rubber Waste from a Batch to a Continuous System

The present work is a comparative study of the effects of mechanical shear, temperature, and concentration of a chemical agent on the devulcanization process of post-industrial ethylene propylene diene (EPDM) rubber waste. Devulcanization was carried out in a heating press (no shear), an internal mixer (low shear), and a co-rotating twin screw extruder (high shear) at temperatures ranging from 100 to 200 °C. The efficiency of pure dibenzamido diphenyl disulfide (DBD) and a commercial devulcanizing agent, Struktol A89®, containing DBD were studied. Based on the results, the devulcanization process was upscaled from 40 g per batch to a continuous process with a capacity of 270 g/h. The parameters were fine-tuned regarding flow rate, screw speed, and temperature. Blends of virgin rubber (VR) and 25, 50, and 75 wt% recyclates were compared with blends of VR and 25, 50, and 75 wt% of untreated RWP. The quality of the recyclate was determined by rheometer tests, SEM images, TGA, and mechanical properties. The best results were obtained with 2 wt% DBD in the extruder with a temperature profile of 120 to 80 °C, 50 rpm, and 4.5 g per minute (gpm). The tensile strength and strain at break of the recyclate already met the requirements of DIN EN 681-1:2006 for the production of sealing systems. The compression set and Shore A hardness were restored by mixing recyclate with 25 wt% VR.

Effect of different devulcanization agents on the mechano-chemical devulcanization process of waste tires

Herein, the effects of two devulcanization agents, i.e., disulfide oil (DSO) and tetramethyl thiuram disulfide (TMTD), byproducts of gas refineries, on the mechano-chemical devulcanization process of waste tires were investigated. The response surface methodology (RSM) involving Box-Behnken Design (BBD) was utilized for the optimization of different factors, i.e., reaction temperature, reaction time, and the content of devulcanization aids. Samples were prepared in a Brabender mixer at a temperature of 100°C, and a rotor speed of 80 RPM for 15 min, and the devulcanization percentage of the samples was determined using swelling test, Mooney viscosity, and Horikx’s theory. The results demonstrated that when 5 phr devulcanization agents were used, the devulcanization percentages for samples containing DSO and TMTD were 73 and 80%, respectively. In addition, the effect of reaction temperature, reaction time, and the content of devulcanization agents on the crosslink scission was also investigated. It was found that by increasing these three parameters, the crosslink density decreased while the devulcanization percentage increased. All in all, the results indicated that the performance of TMTD as devulcanization agent was better than that of DSO. We believe that our presented research study will open new avenues for effective recycling of waste rubbers.

Low-Temperature Mechano-Chemical Rubber Reclamation Using Terpinene as a Swelling Agent to Enhance Bond-Breaking Selectivity.

Common swelling agents used in the mechano-chemical rubber devulcanization process usually require high temperatures to achieve satisfactory swelling effects, which results in severe production of pollutants and reduces the selectivity of bond scissions. This work presents an environmentally friendly swelling agent, terpinene, which can swell the rubber crosslink structures at low temperatures. Both a rubber swelling experiment and a rubber reclaiming experiment with a mechano-chemical devulcanization method are conducted to explore the swelling effects of terpinene. After soaking in terpinene at 60 °C for 90 min, the length elongation of the rubber sample reaches 1.55, which is much higher than that in naphthenic oil and is comparable to that in toluene. When adding 3 phr of terpinene for every 100 phr of waste rubber during the reclaiming process, the bond scissions exhibit high selectivity. After revulcanization, the reclaimed rubbers have a tensile strength of 17 MPa and a breaking elongation of 400%. Consequently, the application of terpinene as the swelling agent in the LTMD method can greatly improve the properties of reclaimed rubbers, thereby enhancing the dual value for the economy and environment.

Mechanochemical devulcanization of waste tire rubber in high pressure water jet pulverization

The resource reclamation of waste tire rubber (WTR) is regarded as the most suitable strategy for these solid wastes. Water jet pulverization (WJPul) is a sustainable reclamation technique for WTR, since both size reduction and rubber devulcanization can be achieved. Aiming at understanding the mechanisms related with pulverization and devulcanization of WTR, this work detailed the interactions between WTR and high pressure water jet (HPWJ). The results show that WJPul can be defined as a mechanochemical process for WTR. The compressive shear failure of rubber mainly induces rubber devulcanization and results in fine ground tire rubber (GTR) particles, HPWJ erosion mainly intensifies rubber depolymerization and results in coarse GTR particles. Chemical reactions can be detected between the devulcanized GTR from WJPul and asphalts, thus resulting in better modification performances of GTR from WJPul in asphalt. The results can help better understand the WJPul mechanisms and provide guidelines for WJPul application.

Effectiveness of original additives in waste rubbers for revulcanization after reclamation with a low-temperature mechanochemical devulcanization method

The low-temperature mechanochemical devulcanization (LTMD) method can maintain the effectiveness of the original additives in waste rubbers after rubber reclamation. To confirm this discovery, the LTMD method and the traditional high-temperature atmospheric devulcanization (HTAD) method are used to reclaim waste rubber powders. The reclaimed rubbers are mixed with different amounts of additional additives and then revulcanized alone or revulcanized after blending with all-terrain vehicle (ATV) tread rubbers. The properties of the reclaimed rubbers and the revulcanized rubbers are characterized, and the results reveal that the original sulfur agent is inactive in both the LTMD and HTAD processes and that the original curing assistants maintain high effectiveness after the LTMD process but not after the HTAD process. The tensile strength of the revulcanized LTMD-reclaimed rubbers with no additional curing assistants reaches 97% of that of the revulcanized LTMD-reclaimed rubbers with full additional curing assistants, and 30% higher than that of the revulcanized HTAD-reclaimed rubbers with full additional curing assistants. When blended with 40% reclaimed rubber from ATV tread rubber, the tensile strength of the vulcanized LTMD blends with only the sulfur agent reaches 89% of the pristine ATV tread rubber while that of the vulcanized HTAD blends with full additives only reaches 76% of the pristine ATV tread rubber. The LTMD method not only achieves high-value recycling of waste rubbers but also avoids the failure of the original curing assistants in waste rubbers, thereby saving large amounts of materials and showing great application prospects.

Rubber reclamation with high bond-breaking selectivity using a low-temperature mechano-chemical devulcanization method

Based on the low-temperature mechano-chemical devulcanization (LTMD) method, we propose low-temperature rubber reclaiming equipment (LTRE) and a devulcanizing agent for rubber reclamation. Reclaiming experiments performed with the LTMD method and the traditional high-temperature atmospheric devulcanization (HTAD) method are conducted, and the performances of the reclaimed rubbers obtained by the two methods are characterized. The results indicate that the mechanical shear force provided by the LTRE in the LTMD method can selectively break crosslink bonds, while the bond breaking in the HTAD method is nonselective. The selective bond breaking greatly improves the physical and mechanical properties of the reclaimed rubber. The developed devulcanizing agent in the LTMD method is able to couple with the free radicals generated by crosslink scissions and thus prevent recrosslinking, which increases the stability of the reclaimed rubber. The application properties of revulcanized rubbers obtained by the LTMD method are also better than those obtained by the HTAD method. Additionally, the LTMD method is a cleaner technique which does not produce waste gases or liquids as the HTAD method does. Therefore, the LTMD method based on the developed LTRE and devulcanizing agent is a superior alternative for high-quality reclaimed rubber and environmentally friendly production.

Feasibility of oxidized soybean oil for rubber devulcanization

This study investigates the feasibility of using oxidized soybean oil (Ox-SO) for mechano-chemical devulcanization of sulfur-cured natural rubber. A 22 full factorial design of experiment was used to determine the effect of devulcanization time (20, 40 min) and amount of Ox-SO (6, 10 phr) in the crosslink density and sol-gel content of devulcanized VR (DVR). After conductive heating and stirring of soybean oil for 60 h, a peroxide value of 316.3 meq O2 kg−1 oil was achieved which corresponds to approximately 2500 ppm of lipid hydroperoxides. Decreasing the devulcanization time (from 40 to 20 min) and amount of Ox-SO (from 10 to 6 phr) decreased the crosslink density by 71.1% and increased the sol content by 228.2%. The optimum conditions are 20 min of devulcanization time and 6 phr of Ox-SO where the crosslink density of VR is reduced to 6.2×10−5 mol cm−3 and the sol content is 10.2% (control VR crosslink density: 2.1×10−4 mol cm−3, sol content: 3.1% ). In summary, Ox-SO was found to be a feasible agent for rubber devulcanization. DVR blends with virgin rubber are required to assess Ox-SO’s commercial readiness.

A review on devulcanization of waste tire rubber

Rubber has become an indispensable material for the technological development of civilization, including simple balloon and complex rocket propellant. Rubber Industry worldwide is using on an average 50% of raw materials. These materials were mostly petroleum-based, except natural rubber (NR), steel cord and bead wire. Using of these petroleum-based raw materials not only depletes natural resources, but also produces more extreme environmental hazards. The waste tire rubber problem is of great magnitude and has far reaching environmental and economic implications. There are some ways for recycling of rubber, such as reclaiming technology, surface treatment, grinding and pulverization technology, devulcanization technology. Methods of devulcanizing rubber (or elastomers) have been researched almost since the time of the discovery of the rubber/sulfur vulcanization process. By devulcanization process the cross-links in the structure of rubber are broken and devulcanized rubber can be revulcanized into a raw material for rubber industry, which is a highly valued form of waste rubber. This study provides a review of the recent advances in understanding of methods of recycling rubber and claims that the capacity of thermomechanical and mechanochemical devulcanization methods of recycling waste tire rubber can be improved in future studies.

Tailoring the properties of ground tire rubber/high-density polyethylene blends by combining surface devulcanization and in-situ grafting technology

A modified method of dynamic vulcanization was proposed to prepare ground tire rubber/high-density polyethylene (GTR/HDPE) blends. The procedure combined the surface devulcanization of GTR (d-GTR) with tetraethylenepentamine and in-situ grafting of HDPE with the grafting monomers of styrene and glycidyl methacrylate. The mechanisms of the mechano-chemical devulcanization of GTR, and the grafting and cross-linking reactions between d-GTR and HDPE were revealed. The influence of initiator and grafting monomers on the mechanical properties, crystallization behavior and rheological behavior of the blends were investigated in detail. Furthermore, the dynamic mechanical properties and morphology of d-GTR/HDPE blend and unmodified GTR/HDPE blend were compared. Results indicated that the compatibility and mechanical properties of d-GTR/HDPE blend were obviously improved by the modified method and they could be tailored by adjusting initiator/grafting monomers ratio. Moreover, the d-GTR/HDPE blends possessed a stable processing and reprocessing ability.

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

ABSTRACTDevulcanization 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.

Mechanochemical devulcanization of natural rubber vulcanizate by dual function disulfide chemicals

Devulcanized natural rubber (DeVulcNR) was produced from NR vulcanizate in an open roll mixing mill by using bis(3-triethoxysilyl propyl) tetrasulfide (TESPT), a novel devulcanizing agent. The versatility of the proposed devulcanizing agent TESPT is that it acts as a devulcanizing agent during devulcanization and as a coupling agent during dispersion of silica filler in devulcanize rubber compound. The extent of devulcanization was monitored through the measurements of sol content, gel content, crosslink density, molecular weight between crosslinks, Mooney viscosity of devulcanized rubber and degree of devulcanization as a function of devulcanization time and the concentration of TESPT. The study of extent of devulcanization by monitoring the above mentioned parameters clearly indicate that the optimum concentration of TESPT is 6 mL. Therefore, for further study DeVulcNR is prepared using 6 mL TESPT and designated as DeVulcNR-6 to optimize the devulcanization time. Determination of the fraction of immobilized polymer chains of DeVulcNR-6 by differential scanning calorimetry (DSC) study indicates that with sol content the fraction of immobilized polymer chains decreases due to increasing molecular weight between crosslinks. To get an idea about the application of DeVulcNR in product formulation revulcanization characteristics in the presence of silica filler were studied. The optimum cure time decreases whereas cure rate increases with devulcanization time. The mechanical properties e.g., modulus at 50% and 100% elongation, tensile strength and elongation at break increases with devulcanization time upto 40 min. To see the reinforcement of silica filler, the mechanical properties of ReVulcNR-6 with silica is compared to that of the ReVulcNR-6 without silica. The mechanical property and thermal behavior data clearly indicates that the optimum time for devulcanization is 40 min. Scanning electron microscopy (SEM) studies further show the coherency and homogeneity of DeVulcNR-6 in the revulcanizate when devulcanization is carried out by optimum TESPT concentration 6 mL and devulcanization time 40 min.

Styrene butadiene-based blends containing waste rubber powder: Physico-mechanical effects of mechanochemical devulcanization and gamma irradiation

Waste rubber (WR) powder was introduced in a two-roll mill in the presence of various ratios of curatives to develop sheets of devulcanized waste rubber (DWR). The selected product was investigated by FTIR, TGA and SEM. In a roll mill and hot press, styrene butadiene rubber (SBR) gum was differentially replaced by DWR feed ratios, and thereafter irradiated with gamma rays. The mechanical parameters of the developed blend were examined. Oil resistance and thermogravemetric behavior were discussed. Remarked improvement in the mechanical, thermal and physical parameters of SBR was generally determined by the incorporation of DWR and gamma irradiation.

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

AbstractThe 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

Mechanochemical preparation of devulcanized ground fluoroelastomers for the enhancement of the thermal stability of nitrile–butadiene rubber vulcanizates

AbstractMechanochemically devulcanized ground fluoroelastomer (FKM) was used as a low‐cost functional additive for the enhancement of the thermal stability of nitrile–butadiene rubber (NBR) vulcanizates. Without the use of any chemicals, the stress‐induced mechanochemical devulcanization of ground FKM was achieved through solid‐state mechanochemical milling at ambient temperature. The sol fraction of the ground FKM was increased from its original 1.4 to 19.8% after milling; this confirmed the realization of the mechanochemical devulcanization of FKM. Moreover, the oxygen‐containing polar groups on the surface of the mechanochemically milled FKM benefitted its interfacial adhesion with the polar NBR matrix. The curing characteristics and mechanical properties of the devulcanized, FKM‐filled NBR vulcanizates were investigated and compared with those of the untreated FKM‐filled NBR vulcanizates. The results show that the mechanical properties of the devulcanized FKM‐filled NBR vulcanizates were much better than those of the untreated FKM‐filled NBR vulcanizates. The presence of the reclaimed FKM significantly increased the onset degradation temperature of the NBR vulcanizates as a result of the improved polymer–filler interaction, uniform dispersion, and high thermal stability of the reclaimed FKM. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thiosalicylic acid as a devulcanizing agent for mechano-chemical devulcanization

A mechano-chemical devulcanization process for vulcanized natural rubber (NV) was investigated. Thiosali- cylic acid was used as a test devulcanizing agent in comparison to diphenyl disulfide as the reference. The optimum condition for devulcanization of NR vulcanizates (NVs) was found to be grinding of the NV and subsequent mixing with a selected devulcanizing agent at 140 o C for 30 min. The degree of devulcanization was indicated by using sol-gel fractions of the devulcanized rubber (DVR). Revulcanized rubber was made by using virgin natural rubber (NR) con- taining DVR at different ratios. The tensile strength of the DVR/NV composite, after revulcanization, decreased by 5-10%, while the elongation at brake was improved by 5-10% at a DVR content of 5-15%. Devulcanization of indus- trial truck tires, as a typical sample of industrial products, was also demonstrated for the practical application of this technique.

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%.

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

AbstractComposites 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