Thermo-oxidative Aging Resistance Research Articles

Effect of lignin on the structure-property behavior of metal-coordinated and chemically crosslinked ethylene-propylene-diene-monomer composites

The efficient development and utilization of green biomass-based macromolecule engineering materials are essential for the sustainable development of human civilization. In this study, lignin-based ethylene-propylene-diene-monomer (EPDM) composites with excellent mechanical performance were fabricated using a simple method. The effects of water-insoluble enzymatically hydrolyzed lignin (EL) and alkali lignin (KL) on the mechanical performance of the composites were investigated separately. The results showed that the tensile strength of EPDM reinforced with KL and EL increased to 24.5 MPa and 22.1 MPa, respectively, surpassing that of the carbon black (CB)-reinforced EPDM. After 72 h of thermo-oxidative aging, the retention rates of the tensile strength and elongation at break in the lignin-reinforced EPDM were much better than those formed with pure CB, indicating that lignin significantly improved the thermo-oxidative aging resistance of the composites. In summary, the Zn2+ coordination bonds formed between the interface of EPDM and lignin in lignin/CB/EPDM ternary composites effectively improved the mechanical performance and aging resistance of the composites. This study has significant implications for enhancing the utilization of lignin and green functional polymer materials.

Aging Resistance Evaluation of an Asphalt Mixture Modified with Zinc Oxide

The phenomenon of the oxidation and aging of asphalt binders affects the strength and durability of asphalt mixtures in pavements. Several studies are trying to improve the resistance to this phenomenon by modifying the properties of the binders with nano-particles. One material that shows promise in this field is zinc oxide (ZnO), especially in improving ultraviolet (UV) aging resistance. Few studies have evaluated the effect of these nano-particles on the thermo-oxidative resistance of asphalt binders, and, on hot-mix asphalt (HMA), studies are even more scarce and limited. Therefore, in the present study, the resistance to thermo-oxidative aging of an HMA manufactured with an asphalt binder modified with ZnO was evaluated. An asphalt cement (AC 60–70) was initially modified with 0, 1, 3, 5, 7.5, and 10% ZnO (percentage by weight of asphalt binder; ZnO/AC in wt%), and then exposed to aging in Rolling Thin-Film Oven tests (RTFOT) and a Pressure Aging Vessel (PAV). Penetration, viscosity, and softening point tests were performed on these binders, and aging indices were calculated and evaluated. Samples of HMAs were then manufactured using these binders and designed by the Marshall method, determining the optimum asphalt binder content (OAC) and the optimum ZnO/AC ratio. Control (unmodified) and modified HMA were subjected to short-term oven aging (STOA) and long-term oven aging (LTOA) procedures. Marshall, Indirect Tensile Strength (ITS), and resilient modulus (RM) tests were performed on these mixtures. LTOA/STOA results of the parameters measured in these tests were used as aging indices. In this study, ZnO was shown to increase the thermo-oxidative aging resistance of the asphalt binder and HMA. It also contributed to an increase in the resistance under monotonic loading in the Marshall and ITS tests, and under repeated loading in RM test. Likewise, it contributed to a slightly increasing resistance to moisture damage. The best performance is achieved using ZnO/AC = 5 wt%.

Research on Durability and Long-Term Moisture Stability Improvement of Asphalt Mixture Based on Buton Rock Asphalt

Buton rock asphalt (BRA) has been used in asphalt pavement for its contribution to high-temperature stability. However, how BRA affects the durability of a corresponding asphalt mixture requires systemic discussion. This study investigated how BRA affected durability in terms of the fatigue resistance, thermo-oxidative aging resistance, and long-term moisture stability of asphalt mixture. Furthermore, improvement of the long-term moisture stability of asphalt mixture containing BRA modified asphalt (BRAM) was also included. An AC-20C asphalt mixture based on BRA asphalt, neat asphalt, and SBS-modified asphalt were prepared and their high-temperature, low-temperature, and moisture performance were examined. A semi-circular bending cyclic loading test was used to characterize fatigue performance. Thermo-oxidative aging tests in both the short-term and long-term were used to indicate the aging performance. Freeze–thaw cyclic splitting tests were carried out to investigate BRAM’s long-term moisture stability. Finally, the optimization and enhancement of BRAM’s long-term moisture stability was discussed in terms of ceramic, basalt, and polyester fiber, as well as hydrated lime. Results showed that BRA can enhance the high-temperature, low-temperature, and moisture performance of BRAM. The cracking fatigue resistance and thermo-oxidative aging resistance of BRAM were also improved by BRA. The long-term moisture stability of BRAM was lower than that of the asphalt mixture based on SBS and neat asphalt. It was found that the long-term moisture durability of BRAM can be optimally enhanced by replacing mineral filler with 50% hydrated lime by equal volume and using 0.2wt% ceramic fiber as an additive in BRAM.

Investigation on the thermo-oxidative aging resistance of nitrile-butadiene rubber/polyamide elastomer blend and the swelling behaviors in fuels predicted via Hansen solubility parameter method

Temperature-induced degradation of nitrile butadiene rubber (NBR) can negatively affect its mechanical properties. Further improvement in the aging resistance of the elastomer is required in view of the stringent application requirements. Polyamide elastomers (PAE) were used as reinforcing agents of NBR to prepare NBR/PAE blend by physical blending. Interaction between NBR and PAE was investigated using FTIR, DMA, SEM and swelling test. After aging at 110 and 130 °C for 7 days, NBR/PAE blend exhibited the minimum change of tensile strength. The reason why NBR/PAE blend could maintain excellent tensile strength retention during thermo-oxidative aging was investigated. Finally, the swelling behavior of rubbers in biodiesel and IRM 903 was measured and validated in combination with the Hansen solubility parameter (HSP) method. FTIR and swelling mass changes were also used to explain the reduction of the mechanical properties of NBR/PAE blend in biodiesel. This work presents useful guidelines for the development of thermo-oxidative aging resistance rubber products.

Rheological and Thermo-Oxidative Aging Properties of Asphalt Modified with a Combination of Sasobit and Linear Low-Density Polyethylene

Research of different asphalt modifiers has been necessary for the attempt to construct durable roads with higher standards. Fischer Tropsch-paraffin wax (Sasobit) has recently attracted considerable attention over polymer modification due to its capacity to lower the energy requirements for asphaltic mix construction. In this study, Sasobit was used to recover the performance as well as the workability of 3 wt% linear low-density polyethylene (LLDPE) modified asphalt. A base asphalt binder with a penetration grade of 50/70 was blended with 3 wt% LLDPE and 3 wt% Sasobit separately and then combined with different Sasobit dosages (1–3 wt%). The performance of modified asphalt binders was evaluated using conventional, rheological, and thermal tests. As a result, it was found that loading Sasobit (1–3 wt%) into LLDPE-asphalt mixture steadily decreased the penetration and ductility at 25 °C from 25 to 12 dmm and 31 to 18 cm, respectively, and softening point increased by 20% indicating improved high-temperature performance. The binder workability and mix temperature were improved since the addition of Sasobit reduced the LLDPE-asphalt viscosity from 0.292 to 0.189 Pa.s (22% less). Sasobit improved the thermo-oxidative aging resistance of the binder by showing less weight variation (less than 0.001%) after the Rolling Thin-Film Oven Test (RTFOT) and high ductility retention (65%). Thermogravimetry (TG) and kinetics analysis results indicated that Sasobit-LLDPE delayed the initial and maximum decomposition temperature by 11 °C and hence increased the thermal stability of modified binders. Thus, the proposed binders are a suitable solution for asphalt pavement construction in regions that encounter high-temperature changes.

Construction of Biomass Tea Polyphenol-Functionalized Halloysite Nanotubes Enabling Green and Sustained-Release Antioxidants for Highly Antiaging Elastomers

The strategy of using sustainable biomass resources instead of traditional petrochemical products has been established as an environmentally friendly way to achieve the “green rubber” industry. Meanwhile, rubber antioxidants possessing high efficiency, long-lasting protection, migration resistance, and green multifunctional properties have attracted intensive investigation for rubber protection. Herein, a naturally extracted substance of tea polyphenol (TP)-functionalized halloysite nanotubes (HNTs), which generates the slow release of free-radical capturing activity and excellent interfacial interaction in the natural rubber matrix, is fabricated by vacuum-pumping and surface-decorating methods (denoted as HNTs-s-TP). Interestingly, the nontoxic and natural antioxidant HNTs-s-TP exhibited remarkable thermo-oxidative aging resistance and stability in a natural rubber (NR) matrix compared to that of TP directly pumped into the tubes due to the further modification of the chemical anchor TP on the outer surface of HNTs. In addition, we have systematically investigated the mechanism for highly efficient and sustainable antioxidation in the rubber matrix via the natural antioxidant HNTs-s-TP derived from the constructed galloyl structure. We envision that this new natural antioxidant fabrication technology will provide significant insights into the innovation for the construction of green and eco-friendly functionalized rubber additives.

Effects of a novel chitosan based macromolecule antioxidant COS-GMMP on the thermo-oxidative aging of styrene-butadiene rubber/silica composites

A chitosan based macromolecule antioxidant (COS-GMMP) was prepared by using chitosan (COS), 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylphenyl) methyl-4-methylp-henyl acrylate (antioxidant GM) and 3-mercaptopropionic acid (MPA) via Michael addition reaction and acylation reaction. The chemical structure of COS-GMMP was confirmed by 1H NMR, 13C NMR, FTIR and elemental analysis. The anti-aging behavior of styrene-butadiene rubber (SBR)/silica with COS-GMMP, as well as the low molecule antioxidant GM, was systematically investigated by the accelerated thermal aging tests, oxidation induction time (OIT), thermo-gravimetric analysis (TGA) and hot water extraction experiments. The results revealed that COS-GMMP significantly improved the thermo-oxidative aging resistance, thermal-oxidative stability and solvent extraction resistance of SBR/silica composites more effectively than the antioxidant GM. The preeminent antioxidative ability of COS-GMMP for SBR/silica composites was attributed to not only the synergistic antioxidative effect among hindered phenol, amide and thioether groups, but also its high molecular weight.

Effects of a novel hindered phenol samarium complex on the thermo-oxidative aging of styrene-butadiene rubber/silica composites

A novel rare-earth complex containing hindered phenol groups (DTSm) was prepared through coordination reaction between 3,5-di-tert-butyl-4-hydroxybenzoic acid and samarium chloride hexahydrate (SmCl3·6H2O). The chemical structure of DTSm was confirmed by FTIR, XPS, ICP-OES and elemental analysis. The results of the accelerated thermo-oxidative aging tests, FTIR-ATR, TGA, methanol extraction experiments, whiteness and yellowness index revealed that DTSm significantly improved the long-term thermo-oxidative aging resistance of styrene-butadiene rubber/silica composites without discoloration, and the DTSm exhibited excellent volatility resistance and solvent extraction resistance. The outstanding antioxidative ability of DTSm for SBR/silica composites was attributed to the synergistic antioxidative effect between hindered phenols and samarium ions due to its excellent thermal stability and volatility resistance. This research is fruitful for the preparation of long-term highly aging-resistant rubber composites.

Performance evaluation of surface-organic grafting on the palygorskite nanofiber for the modification of asphalt

This paper aims to promote the application of nano-mineral materials in asphalt and improve the compatibility of modifiers with asphalt to produce high-performance and economical modified asphalt. In this paper, palygorskite (Pal) was organic grafted by γ-aminopropyltriethoxysilane (ATPES) to obtain an organomodified palygorskite (A-Pal). Then A-Pal was adopted to modify asphalt by melt blending with different contents. The microstructure and elemental distribution of the modified asphalt were characterized to confirm the interface state of different components. The rheology, water stability and aging resistance of Pal and A-Pal in the asphalt were evaluated. The organic group was successfully grafted on the surface of Pal, and A-Pal had good compatibility with asphalt. Adding A-Pal could enhance the water stability, high-temperature stability and anti-rutting capacity of asphalt binder. The thermo-oxidative aging resistance of asphalt increased after TFOT and PAV aging under the shielding effect of A-Pal fibers. Considering high- and low-temperature performances, water stability, anti-aging performances and economic benefits, the optimal amount of A-Pal in asphalt was recommended from 4 to 6%. A-Pal has been proved to be an excellent and environmental-friendly asphalt modifier for the nanofiber effect.

Vulcanization and antioxidation effects of accelerator modified antioxidant in styrene-butadiene rubber: Experimental and computational studies

In this work, a new kind of accelerator modified antioxidant denoted as BTC was synthesized successfully through a thiol-ene click reaction between accelerator 2-mercaptobenzothiazole (MBT) and antioxidant N-(4-anilino phenyl) maleic imide (MC). Then, the effects of BTC on the vulcanization and antioxidation of styrene-butadiene rubber (SBR) were comprehensively studied via experimental and computational methods. It was discovered that BTC not only reduced the negative effect of MC on the vulcanization of SBR composite but also accelerated the vulcanization reaction. Besides, the aromatic amino and thioether groups in BTC played a crucial role in improving the thermo-oxidative aging resistance of SBR composites. Moreover, as against MBT or MC, BTC with a high molecular weight, amorphous state, and low solubility parameter exhibited lower migration and better dispersion in the SBR matrix. Therefore, in contrast to MBT/SBR or MBT/MC/SBR composite, BTC/SBR composite manifested an optimal overall performance, i.e., high vulcanization efficiency, outstanding mechanical properties, and good thermo-oxidative stabilization. These results indicated that BTC could be used as a prospected multifunctional additive to fabricate the high-performance SBR composites. Furthermore, molecular simulation as a useful tool can offer valuable theoretical guidance for the molecule design of high-efficiency antioxidants.

Thermoplastic Elastomeric Composites Filled with Lignocellulose Bioadditives, Part 2: Flammability, Thermo-Oxidative Aging Resistance, Mechanical and Barrier Properties.

The work covers the characteristics of the functional properties of composites bordering thermoplastics and elastomers. The research is a continuation of considerations on blends in the form of a mixture of natural rubber (NR) with an ethylene–vinyl acetate copolymer (EVA) and the addition of a lignocellulose biofiller (wheat straw). After describing the processing and rheology as well as examining the thermal properties and morphology of composites (Part 1), the second part focuses on the characteristics of their performance. The effect of both different ratios of mixed polymers and the amount of filler on tensile strength and elongation at break, resistance to thermo-oxidative aging, hardness, tear resistance, barrier and damping properties, as well as flammability were investigated. The increased EVA content has shown a positive effect on tensile strength, elongation at break, resistance to thermo-oxidative aging, hardness, relative damping, tear strength, barrier and burning delay. On the other hand, a larger amount of natural rubber provides high flexibility and promotes the creation of a reinforcing structure by the filler used. Moreover, a significant impact of the addition of cereal straw on the barrier, damping, strength and flammability properties of composites was also noted. The great advantage of the prepared compositions in relation to commercial plastics is their environmental friendliness, primarily by replacing some petroleum derivatives of plastics with natural rubber and straw fibers.

Lignin-Reinforced Nitrile Rubber/Poly(vinyl chloride) Composites via Metal Coordination Interactions

In this work, half the mass of carbon black (CB) was replaced by lignin for preparation of high-performance nitrile rubber/poly(vinyl chloride) composites via constructing interfacial Zn2+-based coordination bonds. It was demonstrated that lignin played a significant role as a natural ligand to form the Zn2+-based coordination interactions in the interphase between lignin and a rubber matrix. The tensile strength and Young’s modulus of the composites were significantly enhanced by the Zn2+-based coordination bonds owing to the dynamic fracture of coordination bonds. The thermo-oxidative aging resistance of the composites was improved by lignin and could be conveniently regulated by the content of ZnCl2 and sulfur. The high-temperature oil resistance of the composites also benefited from the partial substitution of CB by lignin and incorporation of the metal coordination bonds. This work opens a facile method for the potential application of green lignin in rubber–plastic composites through a conventional ...

A novel rare-earth complex containing hindered phenol and thioether groups for styrene-butadiene rubber/silica composites with improved antioxidative properties

A novel rare-earth complex containing hindered phenol and thioether groups (Sm-GMMP) was prepared by using 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylphenyl) methyl-4-methylp-henyl acrylate (GM), 3-mercaptopropionic acid (MPA) and samarium chloride hexahydrate (SmCl3·6H2O) via Michael addition reaction of sulfydryl with acrylate and coordination reaction. The chemical structure of Sm-GMMP was confirmed by 1H-NMR, FT-IR, XPS and elemental analysis. It was revealed by the results of the accelerated thermal aging tests, FTIR-ATR, TGA, whiteness and yellowness index that Sm-GMMP significantly improved the thermo-oxidative aging resistance and thermal-oxidative stability of styrene-butadiene rubber/silica composites without discoloration. The outstanding antioxidative ability of Sm-GMMP for SBR/silica composites was attributed to not only the synergistic antioxidative effect between hindered phenol and thioether groups, but also the deactivation role of samarium ions to oxygen free radicals and its excellent thermal stability.

Immobilization of rubber additive on graphene for high-performance rubber composites

It is still a challenge to achieve simultaneous improvements in aging resistance, mechanical strength, thermal conductivity and dielectric constant of rubber composites via incorporation of graphene obtained by conventional methods. Herein, an effective and green method was proposed to simultaneously reduce and functionalize graphene oxide (GO) with 2-mercaptobenzimidazole (antioxidant MB) via a one-pot method. GO was successfully reduced by MB which was also chemically grafted on the reduced GO (G-MB). G-MB sheets were uniformly dispersed in rubber with strong interfacial interaction, and graphene-graphene conductive paths were formed through intermolecular H-bonding between the grafted antioxidant molecules. Consequently, rubber composites with G-MB showed higher thermal conductivity, mechanical strength and dielectric constant than rubber composites with hydrazine hydrate reduced GO (rGO). Moreover, the thermo-oxidative aging resistance of rubber composites with G-MB was also superior to that of rubber composites with rGO because of the elimination of blooming effect of the grafted MB molecules. Thus, this work may open a new way for the eco-friendly functionalization and reduction of GO and may boost the development of high-performance, functional graphene-elastomer composites.

Improving Thermo-Oxidative Stability of Nitrile Rubber Composites by Functional Graphene Oxide.

Graphene oxide (GO), modified with anti-aging agent p-phenylenediamine (PPD), was added into nitrile rubber (NBR) in order to improve the thermo-oxidative stability of NBR. The modification of GO and the transformation of functional groups were characterized by Fourier transform infrared spectroscopy (FTIR), Raman, and X-ray diffraction (XRD). Mechanical performances of NBR composites before and after the thermo-oxidative aging were recorded. The results of dynamic mechanical analysis (DMA) show an increased storage modulus (G’) and a decreased value of area of tan δ peak after introducing modified GO into NBR. It indicates that filler particles show positive interaction with molecular chains. The thermo-oxidative stability of composites was investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). Then, the thermo-oxidative aging kinetic parameters were obtained by the Flynn–Wall–Ozawa (FWO) equation. The results of aging tests show that the thermo-oxidative stability of rubber matrix increases obviously after introducing GO–PPD. In addition, mechanical properties (tensile strength and elongation at break) of both before and after aged NBR/GO–PPD composites were superior to that of NBR. This work provides meaningful guidance for achieving multifunction thermo-oxidative aging resistance rubber composites.

Aging-Resistant Functionalized LDH⁻SAS/Nitrile-Butadiene Rubber Composites: Preparation and Study of Aging Kinetics/Anti-Aging Mechanism.

With the aim of improving the anti-aging properties of nitrile-butadiene rubber (NBR), a functional organic filler, namely LDH–SAS, prepared by intercalating 4-amino-benzenesulfonic acid monosodium salt (SAS) into layered double hydroxides (LDHs) through anion exchange, was added to nitrile-butadiene rubber (NBR), giving the NBR/LDH–SAS composites. Successful preparation of LDH–SAS was confirmed by XRD, TGA and FTIR. LDH–SAS was well dispersed in the NBR matrix, owing to its strong interaction with the nitrile group of NBR. The obtained NBR/LDH–SAS composites exhibited excellent thermo-oxidative aging resistance as shown by TGA-DSC. Further investigation by ATR-FTIR indicated that SAS can capture the radical groups, even during the aging process, which largely accounts for the improved aging resistance.

Functionalized graphene as an effective antioxidant in natural rubber

To improve the thermo-oxidative aging resistance of natural rubber, a kind of functionalized graphene (FGE) was prepared by grafting 2-tert-butyl-6-(3-tertbutyl-2-hydroxy-5-methylphenyl) methyl-4-methylp-henyl acrylate (GM) onto graphene oxide (GO) using (3-mercaptopropyl) trimethoxysilane as bridging agent. In comparison to GO, FGE appeared more curled surface and reached the higher water contact angle of 134°. By latex-mixing method, the uniformly dispersed FGE endowed NR vulcanizates with obviously improved thermal stability. Importantly, the NR/FGE nanocomposites exhibitd excellent thermo-oxidative aging resistance, which was attributed to not only the synergistic antioxidative effect of hindered phenol groups and thioether bonds, but also the barrier role of graphene sheets to oxygen. Our findings provide a new strategy to prepare functionalized graphene as effective antioxidant for rubber and other polymer materials.

Hindered phenol functionalized graphene oxide for natural rubber

Hindered phenol functionalized graphene oxide (HPFGO) was prepared by grafting 2,6-Di-tert-butyl-4-hydroxymethyl phenol (DBHMP) onto graphene oxide (GO) using isophorone diisocyanate as bridging agent. FT-IR, XPS, XRD and TGA results confirmed the chemical structure of HPFGO. By latex-mixing method, HPFGO was uniformly dispersed in natural rubber (NR) matrix and obviously enhanced the thermal stability. Importantly, HPFGO significantly improved the thermo-oxidative aging resistance of NR vulcanizate, which was attributed to not only the synergistic antioxidative effect between hindered phenol and urethane groups, but also the barrier role of HPFGO sheets to oxygen.

Thermo-oxidative aging resistance and mechanism of a macromolecular hindered phenol antioxidant for natural rubber

Macromolecular antioxidant due to its low physical loss, high thermal stability, and good compatibility has been considered to be a promising candidate to inhibit polymer aging. In this study, thermo-oxidative aging resistance and antioxidative mechanism of a macromolecular hindered phenol antioxidant, namely, polyhydroxylated polybutadiene containing thioether binding 2, 2′-thiobis (4-methyl-6-tert-butylphenol) (PHPBT-b-TPH) for natural rubber (NR) vulcanizate was studied in detail by oxidation induction time and accelerated thermal aging tests. The results showed that the antioxidative efficiency of PHPBT-b-TPH was very high. When the amount of PHPBT-b-TPH was only 1 phr, the NR vulcanizate could exhibit excellent thermo-oxidative aging resistance, obviously higher than that of NR vulcanizate with low-molecular-weight antioxidant TPH. After aged at 100°C for 168 h, the retentions of tensile strength and elongation at break of NR vulcanizate with PHPBT-b-TPH were 43.6% and 58.6%, respectively. However, those of NR vulcanizate with TPH were 35.6% and 54.5%. In addition, it was found that both thioether and urethane groups in PHPBT-b-TPH had antioxidative ability and had synergistic effect with hindered phenol. Through our findings, new strategy to design and synthesize the macromolecular antioxidant with multi-antioxidative groups for rubber materials and other polymer materials could be developed.

THE INFLUENCE OF POLYMER ON RHEOLOGICAL AND THERMO OXIDATIVE AGING PROPERTIES OF MODIFIED BITUMEN BINDERS

Polymer modified bitumen (PMB) has been used for many years to improve the performance of asphalt concretes against premature pavement defects. In this research, modified samples were prepared with 2%, 3%, 4%, 5% and 6% Linear Low Density Polyethylene (LLDPE) polymer by weight of bitumen binder. The influence of LLDPE polymer was evaluated through binder properties test which includes penetration, softening point, storage stability, temperature susceptibility, rutting, fatigue and thermal oxidative aging resistance from a dynamic shear rheometer (DSR) measurements at a temperature of 20 OC to 60 OC. Results show that LLDPE polymer has a significant effect on binder properties. Penetration decreases and softening point increases with increasing LLDPE content on the modified binder after aging, which implies LLDPE improves the thermo oxidative aging resistance of the binder. Furthermore, the storage stability test shows that at higher LLDPE concentrations phase separation may occur. DSR analysis shows that modified binders have lower temperature susceptibility and higher aging resistance with increased stiffness and elastic behavior compared with unmodified binders. In addition, modified binders show enhanced resistance against high temperature rutting and at low temperature fatigue performance. It was found that the optimum LLDPE content is 6%.