Degradation Of Rubber Research Articles

Natural rubber composites with antioxidant‐loaded activated calcium silicate for improved thermo‐oxidative aging resistance

AbstractGreen and low‐cost methods are required as alternatives to conventional approaches for impeding the thermo‐oxidative degradation of natural rubber (NR). Herein, to improve the dispersibility of N‐1,3‐dimethylbutyl‐N′‐phenyl‐p‐phenylenediamine (antioxidant 4020) and simplify the loading procedure, antioxidant 4020 was precipitated from acetone using activated calcium silicate (ACS), a byproduct of alumina extraction from fly ash, as a carrier. In the obtained antioxidant 4020‐loaded ACS (ACS‐4020) particles, which had a loading of 7.8%, the antioxidant was physisorbed on the surface of ACS with a uniform distribution. In composites with NR, ACS‐4020 was uniformly dispersed in the NR matrix via chemisorption. ACS‐4020/NR exhibited a faster vulcanization speed, better static mechanical properties, and greater thermal stability than the composite in which antioxidant 4020 was directly integrated (ACS/4020/NR). Changes in the tensile strength, elongation at break, hardness, and thermo‐oxidative aging degree of the composites at different aging times and temperatures showed that ACS‐4020/NR had enhanced resistance to thermo‐oxidative aging. Furthermore, the nitrogen‐containing compounds in ACS‐4020/NR were more stable and performed better against thermo‐oxidative aging. These findings can act as guidelines for the preparation of NR composites with superior thermo‐oxidative aging resistance.

Converting polyisoprene rubbers into bio-jet fuels via a cascade hydropyrolysis and vapor-phase hydrogenation process

Producing alternative drop-in bio-jet fuels from biomass provides a promising approach to achieve carbon neutrality. To upcycle biomass-based polyisoprene rubbers into jet-fuel range C10 cycloalkane, we proposed a cascade hydropyrolysis and vapor-phase hydrogenation process in a flow-through two-stage pressurized fixed-bed reactor. The hydropyrolysis temperature in the first stage is of vital importance for the formation of primary limonene intermediate in the non-catalytic degradation of polyisoprene rubbers, and a reaction temperature of 460 °C maximized limonene yield to 588.6 mg/g for natural rubber and 546.2 mg/g for Eucommia rubber. Over a Pt/C catalyst loaded in the second stage, the limonene intermediate produced from the first-stage reactor can be completely hydrogenated, giving a 642.7 mg/g yield of jet-fuel range C10 cycloalkane with 83.6% selectivity. The depolymerization mechanism of polyisoprene rubbers was thoroughly studied, and a competitive reaction between limonene hydrogenation and limonene dehydrogenation was observed. This is the first report on producing C10 cycloalkane from natural rubbers via a cascade hydropyrolysis and hydrogenation process, providing a promising strategy to upcycle polyisoprene rubbers into bio-jet fuels.

Molecular Weight and Functional Group Analysis of Low Molecular Weight of Liquid Cyclic Natural Rubber

The research about molecular weight and functional group analysis of low molecular weight liquid cyclic natural rubber has been done. The aim of this research is to achievement the quality of low molecular weight of liquid cyclic natural rubber. This research has been made in several steps such as preparation of the sample of rubber, the process of molecular degradation of cyclic rubber, and characterization of LCNR by using FTIR, GPC and viscosity test. Degradation is done with the help of the phenylhydrazine reagent with oxygen gas atmosphere with a flow rate of 2 LMin-1 for 24 hours. Molecular weight analysis by GPC had result the LCNR sample had a Mw is 60,556, a Mn is 6,661, and a PDI is 11,08613. The intrinsic viscosity can be used by relating it to the molecular weight by the Mark Houwink – Sakurada (MHS) equation and get the result 63.533 for LCNR molecular weight. The C-H stretching and bending region are two of the most difficult regions to interpret in infrared spectra. The ranges between 3300 to 2750 cm-1 is the C-H stretching region, is the more practical of the two regions. The frequency with which C-H bonds are obstructed is largely determined by the type of hybridization attributed to the bond. The stronger the vibrational force constant, the higher the vibration frequency.

Biodegradation of Natural Rubber by Fungi and Bacteria

Environmental pollution is currently one of the major problems that are threatening biodiversity, ecosystems, and human health around the world. Natural rubber, which is one of the most significant polymers due to its variety of uses, has now become a serious environmental concern. Rubber waste management poses one of the greatest problems because it is extremely resilient and persists in the environment despite several mitigation efforts. Biodegradation is an eco-friendly alternative to conventional disposal methods and has gained tremendous interest in recent years. Several studies on rubber biodegradation utilizing fungi and bacteria have been reported. However, except for a few studies on technical applications, the majority of research on these microbes has focused on the fundamentals of rubber biodegradation. The challenge with biodegradation as a potential solution for rubber waste management is that we have limited mechanistic insight into rubber biodegradation, and the complicated composition of rubber products inhibits cell growth and activity of microbes. Thus it becomes important to fully comprehend the mechanism of rubber biodegradation and continue the search for new microbial strains so that the acquired knowledge can be utilized to develop a biodegradation process suitable for scale-up. In this short review, rubber degradation using fungi and bacteria is highlighted.

Beyond Substituted p-Phenylenediamine Antioxidants: Prevalence of Their Quinone Derivatives in PM2.5.

Substituted para-phenylenediamine (PPD) antioxidants have been extensively used to retard oxidative degradation of tire rubber and were found to pervade multiple environmental compartments. However, there is a paucity of research on the environmental occurrences of their transformation products. In this study, we revealed the co-occurrence of six PPD-derived quinones (PPD-Qs) along with eight PPDs in fine particulate matter (PM2.5) from two Chinese megacities, in which N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine quinone (77PD-Q) was identified and quantified for the first time. Prevalent occurrences of these emerging PPD-Qs were found in Taiyuan (5.59–8480 pg/m3) and Guangzhou (3.61–4490 pg/m3). Significantly higher levels of PPDs/PPD-Qs were observed at a roadside site, implying the possible contribution of vehicle emissions. Correlation analysis implied potential consistencies in the fate of these PPD-Qs and suggested that most of them were originated from the transformation of their parent PPDs. For different subpopulation groups under different exposure scenarios, the estimated daily intakes of PPD-Qs (0.16–1.25 ng kgbw–1 day–1) were comparable to those of their parent PPDs (0.19–1.41 ng kgbw–1 day–1), suggesting an important but overlooked exposure caused by novel PPD-Qs. Given the prolonged exposure of these antioxidants and their quinone derivatives to traffic-relevant occupations, further investigations on their toxicological and epidemiological effects are necessary.

Development of Chemical Kinetics Models from Atomistic Reactive Molecular Dynamics Simulations: Application to Iso-octane Combustion and Rubber Ablative Degradation.

Modeling the complex chemical phenomena resulting from multiple active species and long-chain polymers is limited by uncertainties in the reaction rate parameters, which increase rapidly with the number of active species and/or reaction pathways. Reactive molecular dynamics simulations have the potential to help obtain in-depth information on the chemical reactions that occur between the polymer (e.g., ablative material) and the multiple active species in an aggressive environment. In this work, we demonstrate that molecular dynamics (MD) simulations using the ReaxFF interatomic potential can be used to obtain the reaction kinetics of complex reaction pathways at high temperatures. We report two recently developed tools, namely, MolfrACT and KinACT, designed to extract chemical kinetic pathways by postprocessing reactive MD simulation data. The pathway extraction is based on a new algorithm, Consistent Reaction Stoichiometry via an Iterative Scheme (CReSIS), for the automated extraction of reactions and kinetics from MD trajectories. As a validation of the methodology, we first report the kinetic analysis and mechanisms for the high-temperature combustion of iso-octane. The observed reaction pathways are consistent with experimental models. In addition, we compare the activation energies of select iso-octane combustion pathways with experimental data and show that nanosecond timescale molecular dynamics simulations are sufficient to obtain realistic estimates of activation energies for different fuel consumption reaction pathways at high temperatures. The framework developed here can potentially be combined with time-series forecasting and machine learning methods to further reduce the computational complexity of transient molecular dynamics simulations, yet yielding realistic chemical kinetics information. Subsequently, the CReSIS scheme applied to ethylene-propylene-diene-monomer (EPDM) rubber ablative reveals that H2O, C2H4, and HCHO are the major products during the initial stages of the polymer degradation in high-temperature oxidative environments. While prior work involving ReaxFF simulations is restricted to overall rates of formation of any species, we extract kinetic information for individual reaction pathways. In this paper, we present several reaction pathways observed during the EPDM rubber degradation into the dominant products and report the pathway-specific reaction rates. Arrhenius analysis reveals that the dominant reaction pathway activation energies for the formation of water, ethylene, and formaldehyde are 34.42, 27.26, and 6.37 kcal/mol, respectively. In contrast, the activation energies for the overall formation (across all reaction pathways) of these products are in the 40-50 kcal/mol range.

Volatile organic compounds emission in the rubber products manufacturing processes

Volatile organic compounds (VOCs) emission from rubber products manufacture processes, mixing, shaping and vulcanization were investigated in four rubber products factories in China. The source emission air was passively sampled by pre-vacuumized stainless steel canister and analyzed by gas chromatography-mass spectrometry-flame ionization detection (GC/MS-FID). The species profile of 107 VOCs in the emission processes were obtained. We calculated the photochemical ozone formation potential (OFP) and carcinogenic risk (CR) of the VOCs for each manufacture process. The results showed that mixing process mainly released dichloromethane (14.53%), carbon disulfide (CS2) (6.88%), styrene (5.72%), 4-methyl-2-pentanone (5.22%) and naphthalene (3.69%) for solvents used and raw rubber degradation in the process. The C6–C8 alkanes, especially heptane and isomers of heptane (44.71%), were dominated in shaping process. The major species released from vulcanization process were carbon disulfide (29.72%), naphthalene (8.17%), acetone (7.73%) and dichloromethane (4.26%). VOCs emitted from vulcanization process had the highest OFP, which contributed by naphthalene, m/p-xylene, o-xylene and carbon disulfide. VOCs emission from mixing process had the highest CR, and 1,2-dibromoethane, 1,2-dichlorethane and 1,3-butadiene were the main contributors to CR. We also estimated the total VOCs emissions into the atmosphere from tires manufacturing in China, which were 7.58 × 105 t in 2018 and contributed about 9% of total industry processes VOCs emissions.

Streptomyces sp. AC04842: Genomic Insights and Functional Expression of Its Latex Clearing Protein Genes (lcp1 and lcp2) When Cultivated With Natural and Vulcanized Rubber as the Sole Carbon Source.

Rubber-degrading Actinobacteria have been discovered and investigated since 1985. Only recently, through the advancement of genomic sequencing and molecular techniques, genes and pathways involved in rubber degradation are being revealed; however, the complete degradation pathway remains unknown. Streptomyces sp. AC04842 (JCM 34241) was discovered by screening at a Culture Collection Centre in Sarawak for Actinomycetes forming a clear zone on natural rubber latex agar. Streptomyces is a dominant and well-studied soil bacterium playing an important role in soil ecology including carbon recycling and biodegradation. Streptomyces sp. AC04842 draft genome revealed the presence of 2 putative latex clearing protein (lcp) genes on its chromosome and is closely related to Streptomyces cellulosae. Under the Streptomyces genus, there are a total of 64 putative lcp genes deposited in the GenBank and UniProt database. Only 1 lcp gene from Streptomyces sp. K30 has been characterized. Unlike Streptomyces sp. K30 which contained 1 lcp gene on its chromosome, Streptomyces sp. AC04842 contained 2 lcp genes on its chromosome. Streptomyces sp. AC04842 lcp1 and lcp2 amino acid sequences showed 46.13 and 69.11%, respectively, similarity to lcp sequences of Streptomyces sp. K30. Most rubber degrading strains were known to harbor only 1 lcp gene, and only recently, 2–3 lcp homologs have been reported. Several studies have shown that lcp-homolog expression increased in the presence of rubber. To study the expression of lcp1 and lcp2 genes for Streptomyces sp. AC04842, the strain was incubated in different types of rubber as the sole carbon source. In general, the lcp1 gene was highly expressed, while the lcp2 gene expression was upregulated in the presence of vulcanized rubber. Mixtures of natural and vulcanized rubber did not further increase the expression of both lcp genes compared with the presence of a specific rubber type. In this study, we paved the way to the exploration of lcp homologs and their function in degrading different types of rubber.

Degradation and service-life prediction of silicone rubber in a highly alkaline environment simulating concrete

This research investigates the aging resistance of a silicone product exposed to highly alkaline conditions. A silicone membrane was immersed in a pH 13.5 solution and aged up to 30 days at four temperatures between 40 °C and 70 °C. The effects of alkaline aging on morphology, mechanical properties, thermal properties and surface chemistry of the alkaline-exposed silicone membranes were scrutinized by various techniques. On alkaline solution aging, both surface and bulk morphology and chemical structure were found to evolve as the silicone membrane experienced toughness deterioration. After failure criteria were established based on practical considerations, the service life of the silicone product was estimated using the Dakin-Arrhenius model, which provided for a cross-linking activation energy of 60 kJ/mol. The calculated service life of over one year for silicone membranes revealed alkaline immersion provides significant aging acceleration, although prediction of silicone performance in contact with concrete in field situations requires further investigation.

Poly-cis-isoprene Degradation by Nocardia sp. BSTN01 Isolated from Industrial Waste.

The natural and synthetic rubber (NR and SR) products are made up of poly-cis-isoprene which are estimated as one of the major solid-wastes and need to be cleared through bacterial bioremediation. The present research reports isolation and characterization of a gram-positive, non-spore forming, filamentous actinomycete Nocardia sp. BSTN01 from the waste of a rubber processing industry. We found NR- and SR-dependent growth of BSTN01 over a period of time. BSTN01 has been found to degrade NR by 55.3% and SR by 45.9% in 6weeks. We have found an increase in the total protein of BSTN01 cells up to 623.6 and 573.9µg/ml for NR and SR, respectively, after 6weeks of growth in rubber-supplemented MSM medium. Scanning electron microscopy revealed adhesive growth of BSTN01 on the surface of NR and SR. Formation of aldehyde groups due to the degradation was indicated by Schiff's test and confirmed by FTIR-ATR analysis. The genome sequence of BSTN01 revealed the gene responsible for rubber degradation. The presence of lcp gene and structural analysis of the latex clearing protein further confirmed the reliability. Studies on quantification of rubber degradation capability by the isolated strain prove it to be an efficient degrader of NR and SR. This study revealed the genome sequence and structural analysis of the proteins responsible for degradation of rubber. A new fast-growing Nocardia strain can degrade both NR and SR with higher efficiency and have future potential for rubber solid-waste management either alone or in consortia.

Effect of oxygen on the radiation of silicone rubber determined by gaseous chromatograph and DFT calculation

The radiation effects of silicone rubber under different atmospheres are of great significance to evaluate the aging behavior of materials, and to assess their practical application life. The radiation-induced cross-linking and degradation of polydimethylsiloxane rubber were confirmed firstly by 1H NMR and high-temperature GPC, respectively. By using the established gas collecting system and gaseous chromatography method, we systematically investigated the gaseous products of irradiated silicone rubber at different oxygen concentrations. With the increase of oxygen concentration, the yield of CH4 decreases sharply, while the yield of hydrogen changes slightly. It can be further demonstrated that the reduction of CH4 concentration in the irradiated silicone rubber system is mainly due to the inhibition of CH4 formation, instead of the CH4 degradation, indicating that oxygen directly influences the conversion process of methyl radicals. Similarly, by monitoring the oxygen consumption, it is proved that oxygen is directly involved in the degradation process of silicone rubber, and oxygen scavenged the methyl radicals, which supressed the conversion process of methyl radicals to CH4. Finally, the radiation-induced crosslinking and degradation mechanism of raw silicone rubber was deduced by combining the gaseous products analysis and DFT calculation. It is demonstrated that the release of CH4 can be used to assess the radiation effect of silicone rubber. This work provides a novel method to understand deeply the radiation-induced crosslinking and degradation mechanism of silicone rubber under different atmospheres.

Effect of non-rubber components on the crosslinking structure and thermo-oxidative degradation of natural rubber

Non-rubber components (NRCs) in natural rubber (NR), including proteins, phospholipids, fatty acids, etc., determine to a large extent the structure and properties of NR. In this study, the effects of NRCs on the network structure and thermo-oxidative aging behavior of unvulcanized and vulcanized NR were investigated. NRCs were found to form physically crosslinked networks in the unvulcanized NR and acted as a natural antioxidant to scavenge free radicals, which contributed to improved thermo-oxidative stability of the unvulcanized NR. Swell analysis, chemical probe analysis (DPPH), and XPS results showed that the NRCs accelerated the vulcanization reaction and increased the crosslink density, and promoted the formation of more mono- and disulfide bonds during vulcanization. When aged at high temperatures, more monosulfide bonds were formed in the vulcanized rubber with high contents of NRCs by cleaving and rearranging the poly- and disulfide bonds. NRCs were also found to increase the activation energy of thermal degradation and led to the better mechanical stability of vulcanized NR against thermal oxidation.

Evaluating impacts of desulfurization and depolymerization on thermodynamics properties of crumb rubber modified asphalt through molecular dynamics simulation

In this study, the thermodynamics properties of crumb rubber modified asphalt (CRMA) were evaluated using molecular dynamics (MD) simulations. CRMA models with different crumb rubber degradation (desulfurization and depolymerization) degrees were constructed and verified through the thermodynamics parameters. Then the effects of desulfurization and depolymerization behaviors as well as temperature field on thermodynamics properties were investigated. For the CRMA, its compatibility, interfacial properties, diffusion behaviors and volumetric properties were analyzed by a series of methods, involving solubility parameter, binding energy, mean square displacement and fractional free volume. The results showed that both the crumb rubber desulfurization and depolymerization could promote the compatibility between crumb rubber and asphalt, with crumb rubber desulfurization contributing more to the improvement of compatibility. In addition, it was discovered that desulfurization and slight depolymerization of crumb rubber increased the interfacial performance between CR and asphalt, while the excessive depolymerization for crumb rubber showed the opposite effects. Furthermore, increasing the temperature could reduce the binding energy when the temperature was over 373 k. Moreover, the diffusion behaviors of CRMA were more sensitive to the crumb rubber degradation degree at high temperatures. The diffusion coefficients of CRMA at high temperatures showed a more obvious increase with the degradation of crumb rubber than those at low temperatures. Finally, the FFV was not suitable for evaluating the effects of crumb rubber degradation on the volumetric properties of CRMA that both the temperature increasing and probe radius decreasing improved the FFV of CRMA, while it did not show an obvious trend with the variation of crumb rubber degradation degree.

Waste tire rubber as heavy metal ion adsorbent

The objective of this work was to develop waste tire rubber (WTR) as a heavy metal ion (Cu(II)) adsorbent. Effects of heat and acid treatment on efficiency of Cu(II) removal were examined from h-WTR, a-WTR, h/a-WTR and a/h-WTR with 40 mesh size. Results from UV-Vis spectrometer revealed that, at 0.5g/50ml adsorbent dosage, h-WTR had higher %removal of Cu(II) than other treated-WTRs. This may result from the highest surface area (51.61 m2/g) and pore volume (0.24 cm3/g) of h-WTR. The pores were possibly formed by the departure of small compounds generated from the rubber degradation. On the other hand, acid treated adsorbent present low efficiency, positive charges of the residual acid occupied on adsorbent surfaces played an important role on the Cu(II) adsorption capacity of a-WTR, h/a-WTR. SEM image presented the number of pores on surface of h-WTR. Results from h-WTR with different size revealed that the smaller size of WTR provided the higher %removal of Cu(II). This was possibly due to the higher efficiency of surface activation. Increasing an amount of adsorbent dosage from 0.5 to 5g/50ml slightly enhanced the %removal. In this study, WTR with > 90% Cu(II) removal was achieved when heat treatment was applied on 40 mesh WTR and 0.5g/50ml adsorbent dosage.

Mechanism behind Time Dependent Elasticity of Crumb Rubber-Nano-Asphalt Hybrids Using Discrete Relaxation Spectrum

Crumb rubber powder is a successfully used renewable material obtained from waste tire rubber, which has been incorporated into paving asphalt since the 1930s due to its good resistance to deformation and fatigue as well as its eco-friendly performance. In this study, carbon nanotubes and nano silica were incorporated into the terminal blend crumb rubber modified asphalt technology to remedy the issues of excessive desulfurization and degradation of ground tyre rubber with this technology. The mechanism behind the high temperature delayed elastic properties of the crumb rubber-nano-asphalt hybrids was experimentally investigated based on discrete relaxation spectrum. Development of the discrete relaxation spectra was accomplished by fitting on the 60°C storage modulus data tested by the dynamic shear rheometer using the generalized Maxwell model. Subsequently, the feasibility of characterizing delayed asphalt elasticity using main relaxation time was verified by test results from the 60°C creep and recovery test. Results indicated that the crumb rubber-nano-asphalt hybrids exhibited arrheodictic behavior and the asphalt elasticity was strengthened by two nano agents. Moreover, the elasticity reinforcement with carbon nanotubes was greater than with nano silica. Additionally, a good correlation was observed between the 60°C zero shear viscosity and main relaxation time, and greater 60°C zero shear viscosity was correlated to longer main relaxation times. Furthermore, longer main relaxation time of the asphalt was related to greater average recovery rate in the creep and recovery test. This research is expected to shed some light on the mechanism behind time-dependent elasticity of crumb rubber modified asphalt from the perspective of polymer physics.

Rubber aging life prediction based on interpolation and improved time-temperature superposition principle

With focus on quickly and accurately predicting and evaluating the aging performance degradation of rubber at room temperature, the pseudo-failure life at each different acceleration temperature is proposed to be calculated by interpolation method based on indoor high temperature accelerated aging data, and on the basis of the obtained pseudo-failure life. By introducing the time-temperature equivalence principle, a shift factor obeying to an Arrhenius law is derived, and master curves are built as well for the compression set as for the ultimate mechanical properties. The concept of the sum of squares of dispersion coefficient errors is proposed to evaluate the prediction accuracy. Meanwhile a quantitative calculation method that considers the effect of temperature on the performance degradation curve and the shift factor is innovatively proposes. The results show that the proposed optimization method based on the traditional time-temperature superposition principle can quickly process the aging life at room temperature, and the prediction results are distributed within the 3-fold dispersion line, which can well meet the engineering requirements. The reduction of the DSC value from 1.4164 to 1.0828 further demonstrates the effectiveness of the proposed method above. This method can provide some reference for other related polymer materials accelerated aging data processing and life prediction.

Quantitative determination for effective rubber content in aged modified asphalt binder

During the aging process, the desulfurization and degradation process of crumb rubber modified asphalt binders (CRMA) consistently occurs. In this paper, a toluene insoluble test, an electrochemical titration method, viscosity, FTIR and GPC were developed to determine the effective crumb rubber content of CRMA after exposure to various aging conditions. Centering on efficiency and accuracy, these five methods were compared with the Pearson coefficient method. The results show that when the degree of aging was severe, the desulfurization and degradation of rubber were aggravated, causing the CC bond in the rubber to break and an increase in the large molecular weight of the asphalt binder. The effective rubber content in the aged CRMA was 7.7–14.2% less than the unaged CRMA. At the same time, the correlation coefficients among the five methods were all above 0.90, but the electrochemical titration and FTIR had priority over the other methods.

Gordonia sp. BSTG01 isolated from Hevea brasiliensis plantation efficiently degrades polyisoprene (rubber).

The online version contains supplementary material available at 10.1007/s13205-021-03063-5.

Fluorinated nitrile-butadiene rubber (F-NBR) via metathesis degradation: Closed system or open system?

Fluorinated nitrile-butadiene rubber (F-NBR) could be designed via the metathesis degradation of nitrile-butadiene rubber (NBR) with perfluoroalkylethyl acrylates as fluorination chain transfer agent (F-CTA). Ethylene was produced during the metathesis degradation. Different from the reported works in the open system in which the ethylene escaped, the reaction in a closed system is greener. Here, the metathesis degradation of NBR was investigated in a closed system for the first time, with 2,2,3,4,4,4-hexafluorobutyl acrylate (F6) or 1H,1H,2H,2H-perfluorooctyl acrylate (F13) as F-CTA, respectively. Compared with the reaction in the open system, the metathesis degradation in the closed system with F6 was suppressed due to the reaction equilibrium, while that with F13 was promoted owing to the ethenolysis reaction, which was caused by the ethylene produced during the metathesis degradation. With the proposed green and efficient approach, the fluorinated liquid nitrile-butadiene rubber (F-LNBR) could be designed for various applications.

Roles of Chitosan as Bio-Fillers in Radiation-Vulcanized Natural Rubber Latex and Hybrid Radiation and Peroxide-Vulcanized Natural Rubber Latex: Physical/Mechanical Properties under Thermal Aging and Biodegradability.

Although natural rubber was regarded as biodegradable, the degradation is a time-consuming process that could take weeks or months for any degradation or substantial weight loss to be observable, resulting in the need for novel processes/methods to accelerate the rubber degradation. As a result, this work investigated the potential utilization of chitosan (CS) as a biodegradation enhancer for radiation-vulcanized natural rubber latex (R-VNRL) and hybrid radiation and peroxide-vulcanized natural rubber latex (RP-VNRL) composites, with varying CS contents (0, 2, 4, or 6 phr). The R-VNRL samples were prepared using 15 kGy gamma irradiation, while the RP-VNRL samples were prepared using a combination of 0.1 phr tert-butyl hydroperoxide (t-BHPO) and 10 kGy gamma irradiation. The properties investigated were biodegradability in the soil and the morphological, chemical, mechanical, and physical properties, both before and after undergoing thermal aging. The results indicated that the biodegradability of both the R-VNRL and RP-VNRL composites was enhanced with the addition of CS, as evidenced by increases in the percentage weight loss (% weight loss) after being buried in soil for 8 weeks from 6.5 ± 0.1% and 6.4 ± 0.1% in a pristine R-VNRL and RP-VNRL samples, respectively, to 10.5 ± 0.1% and 10.2 ± 0.1% in 6-pph CS/R-VNRL and 6-pph CS/RP-VNRL composites, respectively, indicating the biodegradation enhancement of approximately 60%. In addition, the results revealed that the addition of CS could increase the value of tensile modulus by 119%, while decrease the values of tensile strength and elongation at break by 50% and 43%, respectively, in the specimens containing 6-phr CS. In terms of the color appearances, the samples were lighter and yellower after the addition of CS, as evidenced by the noticeably increased L* and b* values, based on the CIE L*a*b* color space system. Furthermore, the investigation into the effects of thermal aging showed that the overall tensile properties for both curing systems were reduced, while varying degrees of color change were observed, with the pristine R-VNRL and RP-VNRL samples having more pronounced degradation/changes for both properties. In conclusion, the overall results suggested that CS had great potential to be applied as a bio-filler in R-VNRL and RP-VNRL composites to effectively promote the biodegradability, environmental friendliness, and resistance to thermal degradation of the composites.