Degradation Of Rubber Research Articles

Oxygen diffusion effects in thermo-oxidative degradation of typical tire rubber

Thermo-oxidative degradation of tire rubber has been demonstrated as a green method for upcycling waste tire rubber. However, the complicated tire compositions present challenges to achieving the homogeneity and efficiency of the reclaimed products, which restricts their widespread industrial adoption. To address this challenge, natural rubber(NR)and natural rubber/butadiene rubber(NR/BR)were innovatively designed to simulate complex tire compositions and investigate the influence of oxygen diffusion on thermo-oxidative degradation at 150–240 °C. The evolution of chemical structural changes and mechanical properties during degradation was traced by FTIR, UV–vis, and nanoindentation test. A basic reactive-diffusion model based on Fickian oxygen diffusion was used to simulate the diffusion profiles. It was found that recrosslinking decreases the oxygen permeability coefficient during NR/BR degradation as the temperature increases, making it difficult for oxygen to diffuse into the inner layer, and therefore tire rubber degrades unevenly. Lower temperatures and prolonged treatment times were recommended to enhance degradation. These findings provide substantial guidance for optimizing the recycling process of tire rubber and its sustainable utilization.

Liquid carboxylated nitrile butadiene rubber via metathetic degradation with acrylic acid as chain transfer agent

Liquid carboxylated nitrile butadiene rubber (LXNBR) shows promising application in various fields. Facing the challenges in its preparation via radical emulsion copolymerization, such as gelation, molecular weight and carboxyl group content, novel approach has been developed for the controlled preparation of LXNBR via the metathetic degradation of nitrile butadiene rubber (NBR) with acrylic acid (AA) as chain transfer agent (CTA). Based on the molecular weight and carboxyl group content of the resultant products, the reaction pathway was proposed. Such understanding is expected to prepare LXNBR with designed Mn and carboxyl group content for various applications, by facile adjusting the reaction condition, mainly the feeding mode of AA, NBR concentration and reaction time.

Assessment of aging degradation in rubber using quasi-static components of ultrasonic longitudinal waves

Abstract Aging degradation is the main form of failure of rubber in service, leading to a decline in its physical and mechanical properties. This paper presents an efficient method for assessing the aging degradation of rubber using the quasi-static component (QSC) of ultrasonic longitudinal waves induced by acoustic radiation. The experiments quantitatively observe the response of the QSC pulse to different levels of ageing degradation. A pulse-echo ultrasonic transducer is employed to simultaneously capture the primary longitudinal wave (PLW) and QSC echoes, enabling the determination of the acoustic nonlinearity parameter of QSC with a single transducer excitation. The results suggest that, in comparison to traditional linear ultrasonic techniques based on attenuation coefficient and wave velocity measurements, the relative acoustic nonlinear parameter of QSC proves to be more sensitive to aging degradation in rubber. Particularly, the amplitude of the QSC pulse undergoes a significant change with increasing aging degradation, even when the PLW tone burst is completely attenuated. These findings confirm the effectiveness of QSC as a method for evaluating aging degradation in highly attenuative materials.

Study on the synergistic regeneration effect of tall oil and crumb rubber on aged SBS modified asphalt

The thermo-oxidative aging of Styrene-Butadiene-Styrene (SBS) modified asphalt (SMA) includes the aging of base asphalt and the degradation of SBS modifiers. With the aim of restoring the performance of base asphalt and making up for the loss of performance advantage caused by the degradation of SBS modifier, tall oil and crumb rubber (CR) were applied to synergistically regenerate aged SBS modified asphalt (ASMA). The effect of the particle size and content of CR, as well as the degree of microwave-activated CR on the properties and storage stability of the reclaimed ASMA were discussed in details. The regeneration mechanism of ASMA by CR was studied from the surface properties, morphology and thermal behavior, respectively. The results show that tall oil can restore the low-temperature properties of ASMA significantly, but it seriously detrimental to the high-temperature properties. CR play the role of secondary modification on the reclaimed ASMA, which can improve the high-temperature properties of the reclaimed ASMA at the cost of low-temperature properties and storage stability, and the modification effect is related to the particle size and content of CR. Microwave activation of CR can improve the storage stability of the reclaimed ASMA with CR, which is because that microwave activation modification disrupts the cross-linking structure of the CR and improves the surface properties, which are conducive to the diffusion migration of molecular chains and multiphase material exchange between the CR and the reclaimed ASMA. Thus, the interaction between the multiphases can be enhanced in the reclaimed ASMA with CR. This work provides an effective regeneration method for aged SBS modified asphalt, and also achieves the reuse of non-renewable resources.

Metathetic degradation of waste natural rubbers for potential reutilization

Waste rubbers have caused a severe environmental pollution now. Their reutilization is an urgent eco-economic demand for the sustainable society by converting the wastes into feedstock for the chemical industry. In the present work, the metathetic degradation of waste rubbers (waste natural rubber gloves as model) was comprehensively investigated with different chain transfer agents (CTAs). The waste natural rubber gloves could be degraded with three CTAs with different polarities (styrene, methyl acrylate (MA) and acrylic acid (AA)), catalyzing with the HG2 catalyst in chloroform. Four kinds of main reactions were proposed in the olefin cross-metathesis (OCM) degradation, based on the product analysis. It was also found that the degradation was favored by a consistent low concentration of the CTA, inhibiting the by-reactions and subsequently improving the degradation yield. Therefore, an easy and effective strategy for the high-performance OCM degradation of waste rubbers was proposed by dropping the CTA.

Multiscale enhancement mechanism of low-temperature performance for degraded recycled waste rubber asphalt binders: MD simulation and microscopic investigation

Desulfurization and degradation are important processes to facilitate the storage of waste rubber asphalt and improve its utilization. However, this process is extremely complex and the mechanisms underlying the resulting performance enhancement remain unclear. This study aims to investigate the multiscale mechanism of rubber degradation and its impact on the low-temperature performance of degraded rubber modified asphalt (DRMA) binder through differential scanning calorimetry (DSC), bending beam rheometer (BBR), fluorescence microscopy (FM) and Fourier transform infrared spectroscopy (FTIR) tests and molecular dynamics (MD) simulations. The results showed that as the degradation of rubber powder deepens, lightweight components decomposed from the rubber are more easily dissolved into the virgin asphalt, thus improving its dispersion. In addition, the small molecular structure after rubber degradation penetrates and fills the aggregation space between asphalt molecules, effectively increasing the molecular activity of asphalt, thus enhancing the low-temperature performance of asphalt.

Thermal degradation and thermo-oxidative aging behavior of vinylidene fluoride-containing fluoroether rubber

Vinylidene fluoride-containing fluoroether rubber has better low temperature performance, expansion resistance and heat resistance. After curing by peroxide, it can be applied to a variety of fuel mixtures and is expected to be widely used in aerospace as a sealing material or other fields. In this work, the thermal degradation and thermo-oxidative aging behavior of Vinylidene fluoride-containing fluoroether rubber cured by 2,5-dimethyl-2,5-di-(tert‑butylperoxy) hexane/Triallyl isocyanurate (DBPH/TAIC) were investigated. For comparison, raw rubber without any crosslinking has been taken. The results indicated that the thermal degradation of vinylidene fluoride-containing fluoride rubber started with the degradation of TAIC in addition to the removal of HF on the backbone and the breakage of the side chain of ether monomers. During thermo-oxidative aging, the main chain formed C = C structure under the mechanism of dehydrofluorination. Meanwhile, the molecular chain broke under the action of thermal oxygen and was accompanied by the formation of carbonyl groups. The destruction of the polymer cross-linked structure occured at the TAIC cross-linking point and mainly occurred in the early stage of aging. However, the crosslinking was not completely disrupted, as the crosslinking density increased with aging time. The destruction and recombination of the crosslinked structure occurred simultaneously during the whole aging process and were dominated by recombination. Over-crosslinking after aging reduced the tensile properties of composites. This work contributes to a better comprehending of the stability of fluoroether rubber seals in a thermal-oxygen environment.

Investigation of interfacial degradation mechanism and debonding behavior for degraded rubber asphalt-aggregate molecular system using a molecular dynamics method

This study aims to investigate the debonding damage behaviors in rubber asphalt-aggregate interfaces under different rubber degradation degrees from a molecular-scale perspective. The pull-off test was simulated using molecular dynamics (MD) to determine the damage patterns at the asphalt-aggregate interface. The digital image processing (DIP) technique was employed to quantify the percentages of cohesive debonding, and the radial distribution function (RDF) and mean square displacement (MSD) was performed to explain the adhesion and cohesion damage mechanisms. In addition, the pull-out test results were compared with the simulated values to verify the reliability of the asphalt-aggregate molecular model. The findings of this study reveal that the presence of rubber powder molecules enhances the cohesion among asphalt molecules and mitigates damage to the cohesion at the asphalt-aggregate molecular interface. As rubber degradation progresses, the damage mode undergoes a gradual transition from adhesive damage to cohesive damage at the asphalt-aggregate interface. At lower temperatures, there is an increase in the internal aggregation of asphalt molecules, and the debonding rate of asphalt molecules at the mineral-aggregate interface rises from 7.67% to 35.67% following complete rubber degradation. Conversely, at higher temperatures, the asphalt-aggregate molecular system is primarily governed by the bonding of “double bond” and “single bond” groups, with cohesive damage dominating the asphalt matrix. The pull-out test results showed similar trends with the simulated values, indicating that the asphalt-aggregate molecular model in this study was relatively reasonable. The present study provides some guidance on the damage behavior of degraded rubberized asphalt-aggregate interface.

Study of sequential abiotic and biotic degradation of styrene butadiene rubber

Styrene butadiene rubber is one of the main constituents of tire tread. During tire life, the tread material undergoes different stresses that impact its structure and chemical composition. Wear particles are then released into the environment as weathered material. To understand their fate, it is important to start with a better characterization of abiotic and biotic degradation of the elastomer material. A multi-disciplinary approach was implemented to study the photo- and thermo- degradation of non-vulcanized SBR films containing 15 w% styrene as well as their potential biodegradation by Rhodoccocus ruber and Gordonia polyisoprenivorans bacterial strains. Each ageing process leads to crosslinking reactions, much surface oxidation of the films and the production of hundreds of short chain compounds. These degradation products present a high level of unsaturation and oxidation and can be released into water to become potential substrates for microorganisms. Both strains were able to degrade from 0.2 to 1.2 % (% ThOD) of the aged SBR film after 30-day incubation while no biodegradation was observed on the pristine material. A 25–75 % decrease in the signal intensity of water extractable compounds was observed, suggesting that biomass production was linked to the consumption of low-molecular-weight degradation products. These results evidence the positive impact of abiotic degradation on the biodegradation process of styrene butadiene rubber.

A New Life For Nitrile-Butadiene Rubber: Co-Harnessing Metathesis And Condensation For Reincorporation Into Bio-Based Materials.

Efficient plastic recycling processes are crucial for the production of value-added products or intermediates. Here, we present a multicatalytic route that allows the degradation of nitrile-butadiene rubber, cross-metathesis of the formed oligomers, and polymerization of the resulting dicarboxylic acids with bio-based diols, providing direct access to unsaturated polyesters. This one-pot approach combines the use of commercially available catalysts that are active and selective under mild conditions to synthesize renewable copolymers without the need to isolate intermediates.

Recent Developments in Synthesis, Properties, Applications and Recycling of Bio-Based Elastomers.

In 2021, global plastics production was 390.7 Mt; in 2022, it was 400.3 Mt, showing an increase of 2.4%, and this rising tendency will increase yearly. Of this data, less than 2% correspond to bio-based plastics. Currently, polymers, including elastomers, are non-recyclable and come from non-renewable sources. Additionally, most elastomers are thermosets, making them complex to recycle and reuse. It takes hundreds to thousands of years to decompose or biodegrade, contributing to plastic waste accumulation, nano and microplastic formation, and environmental pollution. Due to this, the synthesis of elastomers from natural and renewable resources has attracted the attention of researchers and industries. In this review paper, new methods and strategies are proposed for the preparation of bio-based elastomers. The main goals are the advances and improvements in the synthesis, properties, and applications of bio-based elastomers from natural and industrial rubbers, polyurethanes, polyesters, and polyethers, and an approach to their circular economy and sustainability. Olefin metathesis is proposed as a novel and sustainable method for the synthesis of bio-based elastomers, which allows for the depolymerization or degradation of rubbers with the use of essential oils, terpenes, fatty acids, and fatty alcohols from natural resources such as chain transfer agents (CTA) or donors of the terminal groups in the main chain, which allow for control of the molecular weights and functional groups, obtaining new compounds, oligomers, and bio-based elastomers with an added value for the application of new polymers and materials. This tendency contributes to the development of bio-based elastomers that can reduce carbon emissions, avoid cross-contamination from fossil fuels, and obtain a greener material with biodegradable and/or compostable behavior.

Degradation during Mixing of Silica-Reinforced Natural Rubber Compounds.

The optimal mixing conditions for silica-filled NR compounds dictate the need to proceed at a high temperature, i.e., 150 °C, to achieve a sufficient degree of silanization. On the other hand, natural rubber is prone to degradation due to mechanical shear and thermal effects during mixing, particularly at long exposure times. The present work investigates NR rubber degradation during mixing in relation to prolonged silanization times. The Mooney viscosity and stress relaxation rates, bound rubber content, storage modulus (G'), and delta δ were investigated to indicate the changes in the elastic/viscous responses of NR molecules related to rubber degradation, molecular chain modifications, and premature crosslinking/interaction. In Gum NR (unfilled), an increase in the viscous response with increasing mixing times indicates a major chain scission that causes a decreased molecular weight and risen chain mobility. For silica-filled NR, an initial decrease in the Mooney viscosity with increasing silanization time is attributed to the chain scission first, but thereafter the effect of the degradation is counterbalanced by a sufficient silanization/coupling reaction which leads to leveling off of the viscous response. Finally, the higher viscous response due to degradation leads to the deterioration of the mechanical properties and rolling resistance performance of tire treads made from such silica-filled NR, particularly when the silanization time exceeds 495 s.

The value of different recycling technologies for waste rubber tires in the circular economy—A review

The issue of used rubber tires is becoming an ever-greater problem for the environment. Often these are disposed of in an illegal manner. Whether on forest paths, fields, or other unsuitable areas—illegal disposal of used tires is a punishable offense and a risk to people and the environment. Nevertheless, the number of cases increases from year to year. This is partly caused by the lack of suitable recycling options for waste tires. Reuse does take place but mainly in the form of downcycling, with the majority currently either being incinerated for energy recovery or, as shredded tires, used as substrate or filler material in roads and sporting grounds. Several reclamation technologies have been developed in the past, using for example mechanical, thermal energy and/or chemicals, aiming to provide a better solution to the waste tire problem, however, most processes cause some form of rubber degradation that limits reuse to low value applications. Only devulcanisation using a biotechnological approach with microorganisms and/or enzymes shows currently promise to reuse waste rubber for high value applications such as new tires. This review provides an overview of the technological development of different recycling options and their potential benefit to the circular economy.

Laboratory short-term aging of crumb rubber modified asphalt: RTFOT temperature optimization and performance investigation

Improper disposal of substantial scrap tires can result in significant environmental issues, such as air pollution, water resources, and soil contamination. The scrap tires can be turned into valuable materials by preparing tire rubber powder into Crumb rubber modified asphalt (CRMA). This method can effectively reduce environmental pollution and achieve the concept of energy conservation, environmental protection, and low-carbon. However, during the production process of CRMA mixtures, the elevated construction temperature may induce more severe short-term aging of the mixtures. The standard laboratory short-term aging scheme of asphalt binders, the Rolling Thin Film Oven Test (RTFOT), cannot simulate the short-term aging of CRMA due to the increase in construction temperature. Besides, the determination methods and indices of RTFOT aging temperature are still unclear and inconsistent. In this study, three CRMA binders were treated by RTFOT with five temperatures, and the short-term oven aging (STOA) protocol was conducted on CRMA mixtures with three types of gradations. Firstly, the chemical and rheological performance of CRMA binders and mixtures were investigated by conducting Gel permeation chromatography (GPC), Fourier transformation infrared spectroscopy (FTIR), Dynamic shear rheology (DSR) tests, and Bending beam rheometer (BBR) test. Then, the equivalent aging temperatures were determined to optimize RTFOT temperatures by comparing the chemical indicators of binders and mixtures. Finally, the correlations of chemical and rheological indices were established, and the rheological properties of aged asphalt in mixtures were predicted. The analysis results indicate that suitable RTFOT temperature is not only related to the technical routes and viscosity of CRMA binders, but also relevant to the mixture gradations. Binders with higher viscosity need elevated RTFOT temperatures from 173 °C to 193 °C, especially simulating short-term aging of mixtures with higher air voids. The swelling and degradation of crumb rubber contribute to the enhancement of the anti-aging performance. The aging index (AI) can reflect the anti-aging performance of CRMA binders, and the variation of AI can validate the rationality of the optimized RTFOT temperatures.

Assembly strategies for rubber-degrading microbial consortia based on omics tools.

Numerous microorganisms, including bacteria and fungus, have been identified as capable of degrading rubber. Rubber biodegradation is still understudied due to its high stability and the lack of well-defined pathways and efficient enzymes involved in microorganism metabolism. However, rubber products manufacture and usage cause substantial environmental issues, and present physical-chemical methods involve dangerous chemical solvents, massive energy, and trash with health hazards. Eco-friendly solutions are required in this context, and biotechnological rubber treatment offers considerable promise. The structural and functional enzymes involved in poly (cis-1,4-isoprene) rubber and their cleavage mechanisms have been extensively studied. Similarly, novel bacterial strains capable of degrading polymers have been investigated. In contrast, relatively few studies have been conducted to establish natural rubber (NR) degrading bacterial consortia based on metagenomics, considering process optimization, cost effective approaches and larger scale experiments seeking practical and realistic applications. In light of the obstacles encountered during the constructing NR-degrading consortia, this study proposes the utilization of multi-omics tools to discern the underlying mechanisms and metabolites of rubber degradation, as well as associated enzymes and effective synthesized microbial consortia. In addition, the utilization of omics tool-based methods is suggested as a primary research direction for the development of synthesized microbial consortia in the future.

Characterization of Rubber Degradation in a Brake Wheel Cylinder under Cyclic Loading

Characterization of Rubber Degradation in a Brake Wheel Cylinder under Cyclic Loading

Degradation and stability studies of butadiene rubber: Correlation between experimental and computational values

Butadiene rubber (BR) is the second highest consuming synthetic elastomer after styrene butadiene rubber. It contains one double bond from each monomer unit in the polymeric backbone prone to oxidation and degradation process. The present study deals with oxidative stability study of BR with different type of antioxidants. Effect of concentrations of antioxidant is studied on degradation of BR by monitoring the stability through change in Mooney viscosity and color index. These exposed samples are characterized by FTIR and TGA to understand the polymer degradation behavior. The difference in Mooney viscosity vs antioxidant concentration of various experimental runs and their measured color levels are modeled successfully by data science models. A Random Forest model was used to model changes to Mooney Viscosity and a Support Vector Machine (SVM) classification model was used to model measured color levels as a function of experimental parameters such as antioxidant concentrations, temperature, and ageing time of samples. The model for Mooney Viscosity was further verified successfully by additional experiments which validated the model predictions.

Swelling-degradation dynamic evolution behaviors of bio-modified rubberized asphalt under thermal conditions

The incorporation of bio-oil, derived from agricultural waste, as a partial substitute for asphalt, coupled with the modification of asphalt using crumb rubber from waste tires, synergistically enhances both sustainability and performance, resulting in bio-modified rubberized asphalt (BMR). Nevertheless, the properties of BMR are subject to fluctuations due to the interplay of crumb rubber swelling-degradation and asphalt aging, particularly under thermal conditions. This research delineates the temporal evolution of BMR's properties, with an emphasis on its rheological, chemical, and microscopic attributes. Three distinct phases were observed: initially, crumb rubber absorbed bio-oil, thereby swelling and augmenting high-temperature performance via the micro-skeletal effect. Subsequently, during the intermediate phase, rubber degradation manifested as macroscopic softening in the modified asphalt. Lastly, the aging of the asphalt resulted in hardening. The multi-stage properties of BMR are governed by the dynamic equilibrium between rubber swelling, degradation, and asphalt aging. These observations offer valuable insights for the quality control of BMR, thereby advancing waste reduction and recycling in downstream applications.

Preparation and Characterization of TiO2-Coated Hollow Glass Beads for Functionalization of Deproteinized Natural Rubber Latex via UVA-Activated Photocatalytic Degradation.

The photochemical degradation of natural rubber (NR) is a prevalent method used to modify its inherent properties. Natural rubber, predominantly derived from the Hevea Brasiliensis tree, exhibits an exceptionally high molecular weight (MW), often reaching a million daltons (Da). This high MW restricts its solubility in various solvents and its reactivity with polar compounds, thereby constraining its versatile applications. In our previous work, we employed TiO2 in its powdered form as a photocatalyst for the functionalization of NR latex. However, the post-process separation and reuse of this powder present substantial challenges. In this present study, we aimed to functionalize deproteinized NR (DPNR) latex. We systematically reduced its MW via photochemical degradation under UVA irradiation facilitated by H2O2. To enhance the efficiency of the degradation process, we introduced TiO2-coated hollow glass beads (TiO2-HGBs) as photocatalysts. This approach offers the advantage of easy collection and repeated reuse. The modified DPNR showed a reduction in its number-average MW from 9.48 × 105 to 0.28 × 105 Da and incorporated functional groups, including hydroxyl, carbonyl, and epoxide. Remarkably, the TiO2-HGBs maintained their performance over seven cycles of reuse. Due to their superior efficacy, TiO2-HGBs stand out as promising photocatalysts for the advanced functionalization of NR across various practical applications.

Performance evaluation and multiscale investigation of deodorant on mechanism of rubber modified asphalt

Asphalt fume emission caused by high-temperature is large during the production and construction of rubber modified asphalt, and the toxic and odor gas contained seriously pollutes the environment. This paper prepared rubber modified asphalt (RMA) and deodorant rubber modified asphalt (DRMA) and evaluated the impact of deodorants on the environmental and physical properties. Modern testing techniques, such as gel permeation chromatography, are used to explore the microscopic morphology of RMA, DRMA, and crumb rubber extracted from RMA and DRMA, so as to reveal the mechanism of deodorant in asphalt. Meanwhile, the effect of deodorant was monitored from macro scales by applying electrochemical sensing technology. The results show inhibiting the degradation of rubber in asphalt is the main mechanism of deodorant. Deodorant can not only promote the swelling of rubber in asphalt and improve the stability of sulfur elements, but also capture the odor particles in asphalt fume, reduce the concentration of polluting organic and H2S, realize the application of rubber modified asphalt environmentally-friendly, and promote the recycling of waste tires and the sustainability of pavements for pollution and carbon reduction.