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Structure of the vulcanized rubber containing mono, di-and poly-sulfidic crosslinks as well as carbon-carbon bonds
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Devulcanization of natural rubber (NR) compound was carried out by means of benzoyl peroxide as a devulcanizing agent by two different techniques namely (a) chemical process and (b) mechano-chemical process. Furthermore, the effects of time and concentration of devulcanizing agent on the devulcanization process were investigated. The extent of devu...
Citations
... Additionally, a decrease in carbon content to 48.19% by weight was observed, compared to previous results. The utilization of benzoyl peroxide as the devulcanizing agent and o-xylene as the solvent for devulcanization process at a temperature of 80℃ for 2 hours, resulted in a 10.5% devulcanization [25]. However, in the process mentioned in this paper, employing sulphur-free toluene as the solvent, achieved a significantly higher devulcanization of 38.09% in just 1.5 hours, highlighting the efficiency and effectiveness of the approach. ...
Chemical devulcanization of waste rubber from the automotive industry was carried using benzoyl peroxide as devulcanizing agent and, o-xylene and toluene, as solvents. The effect of time on the process of devulcanizing was investigated. The extent of sulphur removal from the reclaimed rubber was studied by using EDAX technique. Thus, this devulcanized rubber can be blended with virgin rubber and on revulcanizing the mixture, it becomes possible to reuse waste rubber and give it a new life.
... Regarding the mechanical properties of recycled rubber compounds, the literature indicates a wide variety of industrial rubber waste streams that can be effectively devulcanized and reused to replace a certain amount of virgin rubber while retaining useful mechanical properties. Rooj et al. [13] used benzoyl peroxide as a devulcanizing agent via a mechano-chemical process for natural rubber. At 20% replacement, tensile strength increased by around 30% with a 20% reduction in strain at break. ...
The amount of rubber scraps derived from rubber goods production consists of about 20–30% of the processed material, so it is necessary to enhance this material by developing new recycling techniques as well as a new market for recycled rubber products. In the present research, nitrile-butadiene rubber (NBR) scraps are reprocessed via a calendering process acting with a mechanical devulcanization. Compounds were prepared with 20%, 80%, and 100% recycled rubber content and characterized. The experimental results highlighted that the compound prepared with 20% recycled rubber content via calendering and compression molding processes shows comparable mechanical properties to that of virgin NBR. The tensile properties are the most penalized by the increasing content of recycled material (100% recycled shows − 25% and − 50% stress and strain at break, respectively). Other properties remain comparable to the standard material up to 80% recycled material: 60 ± 5 Shore A, compression elastic modulus 8 MPa, compression set 20%. FTIR analysis revealed no changes in chemical structure from the recycling process. The results demonstrate that simple mechanical devulcanization can effectively reprocess industrial rubber waste while largely maintaining useful properties. This provides a potential pathway to enhance sustainability in rubber production through the valorization of process scraps.
Graphical Abstract
... They evaluated the success of the process using IR, CNMR, TG, GPC and TPD-MS analysis. Rooj et al. 11 devulcanized NR rubber in presence of benzoyl peroxide as a chemical devulcanizing agent and monitored the process by measuring crosslink density, tensile properties and IR and SEM analysis. They showed that chemomechanical devulcanization is more efficient than separate chemical and mechanical methods. ...
To prepare a reliable method for predicting the properties of devulcanized rubbers a nitrile rubber (NBR) compound was prepared and masticated before vulcanization for 0, 30 and 60 min under mechanical stress to prepare NBRs with different molecular weights. The masticated samples were vulcanized at different accelerator contents to prepare damples with different crosslink densities. The physical/mechanical/thermal properties (i.e. crosslink density, tensile strength, modulus, modulus at 100 and 300% elongation, elongation at break, hardness, curing behavior and molecular weight) of the samples were experimentally evaluated. In the next step, the prepared samples were assumed as devulcanized NBRs that underwent chains scission (masticated samples) or crosslinks breakage (vulcanized at different accelerator contents). On this basis, hypothetical devulcanization routes were considered between each sample that underwent chains scission or crosslinks breakage. Based on the results, numerical relationships between the number of chains scission or crosslinks breakage and decrease in the properties were obtained. Finally, the numerical reationships were used to calculate the properties of the samples that underwent both of chains scission and crosslinks breakage. It was found that the calculated contents of hardness, modulus at 100% and molecular weight (MZ) using the prepared method were very close to the evaluated ones.
... Different recycling methods for rubber are described in the literature [7,8], namely, mechanical [9][10][11][12], ultrasonic [13][14][15], chemical [16,17], microwave [18][19][20], cryogenic [21][22][23], microbial [24][25][26], thermo-mechanical-chemical [27][28][29], etc. Most of the recycling processes are mainly based on the random scission of the polymer network and crosslinks [4], whereas the selective breakdown of the crosslinks is required to improve the recycled rubber quality. ...
... Polymers 2023, 14, x FOR PEER REVIEW 2 of 18 Different recycling methods for rubber are described in the literature [7,8], namely, mechanical [9][10][11][12], ultrasonic [13][14][15], chemical [16,17], microwave [18][19][20], cryogenic [21][22][23], microbial [24][25][26], thermo-mechanical-chemical [27][28][29], etc. Most of the recycling processes are mainly based on the random scission of the polymer network and crosslinks [4], whereas the selective breakdown of the crosslinks is required to improve the recycled rubber quality. ...
... Polymers 2023,15, 2848 ...
The disposal of tires at the end of their lifespan results in societal and environmental issues. To tackle this, recycling and reuse are effective solutions. Among various recycling methods, devulcanization is considered to be a very sustainable option, as it involves the controlled breakdown of crosslinks while maintaining the polymer backbones. The objective of this study is to develop a sustainable devulcanization process for passenger car tire rubber using silanes. In this study, a thermo-mechanical-chemical devulcanization process was conducted to screen six potential devulcanization aids (DAs). Silanes were chosen as they are widely used in tire rubber as coupling agents for silica. The efficiency of the devulcanization was studied by the degree of network breakdown, miscibility of the devulcanized material, and mechanical properties of the de-and revulcanized material. Compared to the parent compound, a 55-60% network breakdown was achieved for the devulcanizate along with 50-55% of tensile strength recovery. In addition to superior devulcanization efficiency, this DA offers a sustainable alternative to the conventional ones, such as di-phenyl-di-sulphide, due to its compliance with safety regulations. The devulcanizate can be utilized in high-performance applications, such as tires and seals, while 100% devulcanizate can be employed in low-strength technical rubber products.
... These methods make use of different types of additives in both thermochemical and mechanical-chemical processes. 63,77,110,111 In view of sustainability, attention should be paid to utilize greener devulcanization and compatibilization methods by the aid of advanced reactive extrusion processes preserving mechanical properties of thermoplastics/GTR blends. 112 In this regard, assessment of Volatile Organic Compound (VOC) emissions has been taken into account most recently by the researchers. ...
... Other kinds of catalysts, inorganic, and sulfur-free organic compounds were developed in the past decades. Among them are propane thiol/piperidine, Grubbs catalysts, PPh 3 , trialkyl phosphites, lithium aluminum hydride, methyl iodide, 1,8-diazobicyclo [5.4.0]undec-7-ene (DBU), and benzoyl peroxide (BPO) [68,69]. ...
The interesting thermomechanical properties of rubber materials have favored their widespread application in many fields, with a consequent increase in the amount of worn synthetic and natural rubber discarded every year. However, the complex three-dimensional molecular structure of rubber complicates the recycling and degradation process, and the current rubber waste management measures (i.e., landfilling, incineration, rubber grinding) are found to be unsustainable or substantially inadequate. On the other hand, devulcanization technologies, thanks to the selective cleavage of crosslinks, represent a sustainable and feasible approach to obtain a material that can be reintroduced into the rubber value chain or reused in novel eco-sustainable thermoplastic or elastomeric blends. Hence, this review provides an overview of the current rubber waste management techniques and devulcanization technologies, highlighting the underlying devulcanization mechanisms, describing the pros and cons of each method, and presenting some literature examples. Since most of the research on devulcanization has been made on waste tires, this review mainly focuses on the most widely used rubber classes for this application, i.e., natural rubber (NR) and styrene-butadiene rubber (SBR) and the most common vulcanization technique, i.e., sulfur vulcanization. Considering the importance of the application of a circular economy approach, this work also reviews the applications of rubber devulcanizates, focusing on how devulcanized rubber can be compounded with different polymeric matrices to develop eco-sustainable polymer blends with suitable physical properties.
... The crosslink density (CLD) of the original samples and the residual crosslink density of the devulcanized samples were determined by swelling method applying (Rooj et al., 2011). Correction for filler is not applied for volume fraction (j) calculation in the case of chemical probe analysis as the carbon black of samples ooze out of the vulcanizate after probe treatment. ...
2022). Stable free radical assisted mechanical devulcanization of rubber: Comparison with contemporary industrial devulcanization processes. Rubber Science, 35(1): 103-118. A comparative study of stable free radical, 4-Hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl free radical (4HT/ 4-hydroxy TEMPO) assisted mechanical devulcanization, with commercial mechano-chemical devulcanization processes based on US Patent 5770632 A and US Patent 6387966 B1 is presented in this paper. The similarity in the mode of action of the chemically dissimilar modifiers used in these patents to accomplish comparable results suggests that, if chemicals which are related in no way can bring about the same result through similar processes, it is the process of shearing and not the chemical per se that causes devulcanization. The present paper demonstrated that the efficiency of devulcanization could be substantially increased, if the recombination of free radicals generated by shear scission of crosslinks were blocked by a stable free radical. The stable free radical assisted devulcanization gave higher re-vulcanizate properties while devulcanization as per the patents gave results at par with mechanical devulcanization without using any devulcanizing agents. The characterization of devulcanized rubber (DVR) by estimation of residual cross link density, Horikx analysis, chemical probe analysis and re-vulcanizate properties suggested that, in the mechano-chemical devulcanization of natural rubber under the influence of shear; (i) devulcanization was effected by the cleavage of crosslinks under the influence of shearing force alone (ii) devulcanizing agents played no role in devulcanization and (iii) efficiency of devulcanization could be significantly improved if the recombination of broken crosslinks could be arrested as in the case of stable free radical assisted devulcanization.
... In a research work conducted by Masaki et al. [50], devulcanization of nitrile butadiene rubber (NBR) in nitrobenzene was performed at optimum conditions of 200 • C and 3 h. In another study, chemical and mechano-chemical methods were used by Rooj et al. [51] for devulcanizing natural rubber (NR) utilizing benzoyl peroxide as a devulcanization aid. As the outcomes revealed, sulfur crosslink happened selectively at the optimum temperature and optimum time of 80 • C and 6 h, respectively. ...
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.
... A similar mechanism for the reactive extrusion of this type of compound was proposed by Yoon [46]. On the other hand, Rooj [47] indicates that the effect of organic peroxide on natural rubber may lead to its devulcanization. Figure 9a shows the FTIR spectra recorded for PP and PP-P, which are very similar to each other. ...
Ground rubber from automobile tires is very difficult to recycle due to the cross-linking of the macromolecules and thus the lack of thermoplastic properties. The research consisted of assessing the processing possibility via the injection of highly filled PP/GTR compounds modified with 1.5 wt.% 2.5-dimethyl-2.5-di-(tert-butylperoxy)-hexane. GTR dosing ranged from 30 wt.% up to 90 wt.%. The evaluation of the processing properties of the obtained materials was carried out on the basis of the melt flow index test results and the signals recorded during processing by the injection molding by temperature and pressure sensors placed in the mold. The influence of the applied modifier on the changes in the mechanical properties of PP/GTR was determined with hardness, impact and static tensile tests. Moreover, thermal properties were obtained by the differential scanning calorimetry method. It has been found that it is possible to efficiently process compounds with high GTR content using injection molding. The presence of the filler allows to significantly reduce the cooling time in the injection mold and thus the time of the production cycle. It has been confirmed that 2.5-dimethyl-2.5-di-(tert-butylperoxy)-hexane modifies the rheological properties of PP and thus the PP/GTR composition. The lower viscosity of the matrix results in a more accurate bonding with the developed surface of the GTR grains, which results in better mechanical properties of the rubber-filled polypropylene.
... But TPE compatibility can be improved via different approaches: decreasing interfacial tension, morphology stabilization, size reduction of the dispersed phase and increasing the interfacial adhesion for better stress transfer. Several methods, such as partial regeneration 17,18 and coupling agent addition, 16,19,20 have been proposed to improve the compatibility between GTR and thermoplastics. Rubber crosslinked network breakdown through GTR regeneration can improve the rubber chain mobility (molecular freedom) and plasticity of recycled rubbers to promote molecular interactions and chains bonding through partially soluble fraction of regenerated rubber (RR). ...
This work investigates the properties of different types of regenerated recycled rubbers (RR 1 and RR 2 ) to produce thermoplastic elastomers (TPE) based on recycled high-density polyethylene (RHD) as the matrix. The higher regeneration degree of RR 2 (24%) compared to RR 1 (15%) was able to better restore the plasticity and processability of the ground tire rubber (GTR). So better entanglement between RR 2 free chains and the thermoplastic macromolecules was obtained inducing stronger interfacial interaction leading to higher elongation at break (159%) and impact strength (342 J/m) of the blends filled with 80 wt.% RR 2 . To further improve the adhesion and achieve rubber-like properties, ethylene vinyl acetate (EVA) was used as a compatibilizer. The microstructure analysis showed that uniform dispersion of the particles and ground tire rubber encapsulation by EVA increased the resistance to crack propagation and failure of the compatibilized blends. The swelling, mechanical and physical properties of the ternary blends (RHD/GTR/EVA) showed that EVA improved the interfacial interactions between GTR and RHD which was confirmed by enhanced elongation at break (203%) and impact strength (379 J/m) by the addition of 10 wt.% EVA.
