Long-term Thermo-oxidative Aging Research Articles

Experimental Study on the Cracking Resistance of Asphalt Mixture with Different Degrees of Aging

The cracking resistance of asphalt mixture is a non-negligible issue. However, the cracking resistance evolution law, motivated by two factors (thermos-oxidative aging degree and test temperature), is not yet well understood. The aim of this investigation is to gain more insight into the effect of thermos-oxidative aging and test temperature on the cracking resistance of asphalt mixture. Asphalt mixture (AC-13) and stone mastic asphalt mixture (SMA-13) were selected and exposed to different thermo-oxidative aging degrees (unaging (UA); short-term thermo-oxidative aging (STOA); long-term thermo-oxidative aging for 2/5/8 days (LTOA2d/LTOA5d/LTOA8d)). A direct tension test at different test temperatures (10 °C, 20 °C, 30 °C, 40 °C) was adopted to obtain their stress–strain curves and evaluation indexes (tensile strength, ultimate strain, pre-peak strain energy density, and post-peak strain energy density). The comprehensive index-cracking resistance index (CRI) was established by the entropy weight method combined with the technique to order preference by similarity to ideal solution (TOPSIS) method and the corresponding aging coefficient was determined. The results showed that STOA can increase the aging coefficient of asphalt mixture, thereby boosting the cracking resistance. Additionally, the effect can be weakened by elevations in the test temperature. Meanwhile, LTOA can decrease the aging coefficient and thereby weaken the cracking resistance. This effect becomes more prominent with elevations in the test temperature. SMA-13 possesses a superior cracking resistance to AC-13, with a gap in CRI value of 3–69%, regardless of the aging degree and test temperature. A good relationship exists between the aging coefficient and the two factors (aging degree and test temperature).

Real-Time Pyrolysis Dynamics of Thermally Aged Tire Microplastics by TGA-FTIR-GC/MS

Tire wear particles (TWPs), as a type of thermosetting microplastic (MP), accumulate in aquatic environments due to their wide application in road traffic globally. The increase in temperature because of friction heat may cause aging of tire materials, inducing water evaporation, additive volatilization, polymer decomposition, and may pose serious potential risks to aquatic and terrestrial ecosystems. However, research on real-time pyrolysis dynamics of thermally aged tire MPs is very limited. In this study, a thermogravimetric analyzer coupled with Fourier transform infrared spectrometry and gas chromatography-mass spectrometry (TG-FTIR-GC/MS) was used to investigate pyrolysis behaviors and products of thermally aged tire MPs. FTIR analysis indicated that the main pyrolysis gases included carbon dioxide, carbon monoxide, aliphatic compounds, aromatic compounds and carbonyl compounds. The GC/MS analysis further determined the main pyrolytic products, including methylbenzene, styrene, m-xylene and D-limonene. These data combined with TG analysis revealed that the main pyrolytic products of TWPs were released at 400–600 °C. Moreover, the results showed that the number of aliphatic/aromatic compounds released increased in short-term thermo-oxidative aging but decreased in long-term thermo-oxidative aging. Moreover, the aged TWPs presented higher released amounts of styrene and methylbenzene but lower amounts of D-limonene compared to the original TWPs. These results can provide new insights into the evaluation method of TWP aging and a better understanding on TWP fate in aquatic and terrestrial environments.

Aging behavior of polyphosphoric acid/styrene-butadiene-styrene-modified bio-mixed asphalt based on high-temperature rheological properties and microscopic mechanism

This study investigates the performance of polyphosphoric acid/styrene–butadienestyrene (PPA/SBS)-modified bio-mixed asphalt after thermo-oxidative and ultraviolet (UV) aging, based on its high-temperature rheological properties and microscopic characteristics. The temperature sweep test results revealed that long-term thermo-oxidative aging significantly increased the dynamic shear moduli of the composite-modified asphalts, where the maximum increment in composite-modified asphalts reached to 425 %. However, the dynamic shear modulus of the composite-modified asphalt decreased owing to the degradation of aromatic aldehydes to fatty aldehydes after ultraviolet aging, leading to softer composite-modified asphalts. In addition, the multiple-stress creep recovery (MSCR) test revealed that the maximum increment in the recovery rate of composite modified asphalt reached to 37.4 %. Moreover, the increasing rate of Jnr was significantly lower than that of the control asphalt after long-term aging, particularly at a stress level of 3.2 kPa. Finally, the microstructures of each asphalt sample before and after aging were observed using atomic force microscopy. The surface morphology of the composite modified asphalt after aging was relatively smoother, indicating that the molecular homogeneity of the aging residue of the composite-modified asphalt sample was better than that of the control asphalt sample.

Evaluation of effects of short and long-term thermo-oxidative aging on chemo-rheological and mechanical properties of asphalt concretes

The effects of short and long-term thermo-oxidative aging on stripping resistance, rut depth, stiffness modulus, fracture and fatigue resistances of asphalt concretes have been assessed. A modified RILEM thermo-oxidative aging procedure on loose asphalt mixtures has been used to evaluate the gradual evolution of these properties with the aging duration. Two short-term aging durations (4 and 8 hours at 135C) and three long-term thermo-oxidative aging durations (3, 6 and 9 days at 85C) and a reference mixture (0 day aging) have been considered to this end. The impact of long-term thermo-oxidative aging on the chemo-rheological properties of recovered asphalt binders have been investigated. At the binder scale, the results show an increase in the Fraass temperature, the softening point, the shear modulus , the aging index (AI= + ) and a decrease in the penetration grade with the aging duration. Some correlations between the viscoelastic transition parameters (, and ) of the recovered asphalt binders and the aging index have been established. At the mixture scale, the results show that the stiffness modulus () increases with the aging duration, while the index of fracture resistance (IFR), the stripping resistance (), the rut depth (P) and the fatigue deformation () decrease with the aging duration. Finally, some correlations between the aging index and the rheological and the mechanical properties of binders and concretes (, , P, IFR, ) have been proposed.

Investigation on microstructure and aging resistance of bitumen modified by zinc oxide/expanded vermiculite composite synthesized with different methods

By synthesizing zinc oxide/expanded vermiculite (ZnO/EVMT) with a modified hydrolytic precipitation method, the composite could remarkably strengthen the resistance of bitumen to thermo-oxidative and ultraviolet (UV) aging. Nonetheless, the microstructure of the composite synthesized using different methods and their effects on microstructure and aging resistance of bitumen have been insufficiently researched. Thus, a modified sol–gel (SG) method and the hydrolytic precipitation (HP) method were used to produce ZnO/EVMT composite (remarked as SG-ZnO/EVMT and HP-ZnO/EVMT respectively) in this study. Then, the effects of two synthesis methods on the microstructure of ZnO/EVMT composite and its corresponding modified bitumen were characterized with a series of experiments, including X-ray diffractometer (XRD), field emission scanning microscopy (FESEM), Fourier transform infrared spectrometer (FTIR) and ultraviolet–visible spectrometer (UV–Vis) tests. Finally, the resistance of the two ZnO/EVMT composite modified bitumen to short-term aging, long-term UV aging and long-term thermo-oxidative aging was evaluated with softening point increment and viscosity aging index. Results indicated that the two methods are feasible to synthesize ZnO/EVMT composite, and ZnO particles in HP-ZnO/EVMT have higher crystallinity and purity with the HP method. Furthermore, HP-ZnO/EVMT has a more homogeneous distribution of ZnO particles, higher UV absorption capacity and better bituminous compatibility than SG-ZnO/EVMT. With the addition of the SG-ZnO/EVMT or HP-ZnO/EVMT into bitumen, intercalated phase structures are formed in the corresponding modified bitumen. Additionally, the ZnO particle composition completely separated with EVMT composition in the SG-ZnO/EVMT modified bitumen, but HP-ZnO/EVMT composite in its corresponding modified bitumen still maintained the original characteristics. Based on the above, bitumen modified by HP-ZnO/EVMT has stronger aging resistance than that of SG-ZnO/EVMT regardless of the aging conditions. Therefore, the HP method is recommended to synthesize ZnO/EVMT composite for bitumen modification.

Study on the Aging Resistance of Polyurethane Precursor Modified Bitumen and its Mechanism

As an environmentally friendly alternative for the production of high-performance modified asphalt by chemical reactions, a liquid-state polyurethane-precursor-based reactive modifier (PRM) was developed and employed in the asphalt modification. In contrast to the traditional solid bitumen modifier, for example, rubber and thermoplastic elastomers, the PRM as a liquid modifier has more significant advantages in reducing energy consumption and improving asphalt performance, which has attracted widespread attention. However, the aging resistance and its mechanism are not clear. In view of this, the aging performance of two PRM-modified bitumen (PRM-70 and PRM-90), under the short-term thermo-oxidative aging, long-term thermo-oxidative aging, and ultraviolet (UV) aging conditions, was investigated through chemical and mechanical methods. The results show that the PRM-90 is more susceptible to the thermos-oxidative aging and UV aging. The use of low-penetration-grade bitumen and ensuring an adequate reaction are beneficial to enhance the aging resistance of PRM-modified bitumen. The impact of aging on high-temperature performance of PRM-modified bitumen is great, followed by the low-temperature performance and the anti-fatigue performance. The mechanic-relevant rheological aging index (RAI) and fracture energy index (FEI) are recommended to evaluate aging properties for PRM-modified bitumen. This study not only provides support for further research on the relationship between the aging properties and mechanical performance of PRM-modified bitumen, but also provides a reference for conducting mechanism analysis.

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.

A thermodynamically consistent chemo-mechanically coupled large deformation model for polymer oxidation

In this paper, a thermodynamically consistent continuum level model is developed for high temperature oxidation in polymers, that incorporates the coupling between diffusion, chemical reaction and large deformation of polymers. The kinetics of the oxidative reactions have been incorporated in the continuum model in a consistent way. The specific constitutive forms for all the physical-chemical processes are derived based on the thermodynamic inequality conditions. Deformation due to the oxidative shrinkage has been incorporated in the kinematics as an irreversible effect. Subsequently, the model is implemented in a finite element framework to analyze numerically the coupled diffusion-reaction and mechanical behavior of polymers undergoing oxidation. Several numerical simulations are performed to understand the effect of various ambient conditions and the general stress-coupled effect on the oxidative response. The model is shown to be capable of predicting the heterogeneous oxidation profile for the diffusion-limited, reaction-limited cases within a polymer material. The model has been used to track the growth of oxide layer in the case of a long-term thermo-oxidative aging process.

Influence of Reinforcement Structures and Hybrid Types on Inter-Laminar Shear Performance of Carbon-Glass Hybrid Fibers/Bismaleimide Composites under Long-Term Thermo-Oxidative Aging

The effects of reinforcement structures and hybrid types on the inter-laminar shear strength (ILSS) of carbon-glass hybrid fibers/bismaleimide composites under thermo-oxidative aging conditions were investigated. The process resulted in progressive deterioration of the matrix and fiber/matrix interfaces, in the form of chain scissions, weight loss, and fiber/matrix debonding, which significantly led to the decrease of the ILSS of composites. Moreover, the three-dimensional orthogonal woven hybrid composites (3D composites) showed higher ILSS retention rate than those of the laminated orthogonal hybrid composites (laminated composites). No delamination occurred in the aged 3D composites like in the aged laminated composites. This was because the Z-binder yarns in the 3D composites resisted the inter-laminar shear load, although the resin was damaged and the adhesive force between fiber bundles and resin decreased seriously after thermo-oxidative aging. Meanwhile, the ILSS retention rate of the laminated composites with the carbon fiber as intermediate layers was higher than that of the laminated composites with the glass fiber as the intermediate layers. This was because the carbon fiber/bismaleimide interface bonding performance was stronger than that of the glass fiber/bismaleimide at the same thermo-oxidative aging condition.

Investigation on Thermo-Oxidative Aging Properties of Asphalt Binder with Hindered Phenolic Antioxidant

Abstract The modified asphalt binders with hindered phenolic antioxidant (Irganox 1010) were prepared by melt blending, and the effects of Irganox 1010 on physical and rheological properties of base asphalt were investigated by means of conventional physical properties tests and dynamic shear rheometer (DSR) tests. The short-term and long-term thermo-oxidative aging properties of asphalts with Irganox 1010 were studied by thin-film oven test (TFOT) and pressure aging vessel (PAV) test. The influence of Irganox 1010 on the chemical structure and compositions of asphalt before and after the aging test were evaluated using Fourier transform infrared spectroscopy (FTIR) analysis and thin-layer chromatography with flame ionization detection (TLC-FID) analysis, respectively. The results show that the penetration and ductility are increased, whereas the viscosity and softening point are decreased, with the addition of Irganox 1010, and Irganox 1010 also decreases the complex modulus and increases the phase angle of asphalt binder. The antioxidant-treated binders exhibit excellent resistance to thermo-oxidative aging. Furthermore, Irganox 1010 inhibits the carbonyl (at 1,700 cm−1) index and sulfoxide (at 1,035 cm−1) index increment by oxidation of phenolic hydroxyl and degradation of ester group, and changes of chemical compositions of asphalt show that Irganox 1010 peptizes the asphaltenes and exhibits effective inhibition of gelatinization of asphalt binder during the process of thermal oxidation aging.

Simultaneous reduction and functionalization of graphene oxide via antioxidant for highly aging resistant and thermal conductive elastomer composites

Preparation of elastomer/graphene composites with high aging resistance and thermal conductivity is of great significance for constructing many advanced materials, such as solar cells and light emitting diodes. Herein, an efficient one-step approach was developed to simultaneously reduce and functionalize GO via N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine (antioxidant 4020). It was found that oxygen-containing groups in GO were effectively removed and sp2 carbon network was restored after reduction. In addition, antioxidant molecules (∼10 wt%) were chemically immobilized on the surface of reduced GO (G-4020). The immobilized antioxidant not only showed much better antimigratory efficiency than free antioxidant in styrene-butadiene rubber (SBR), but also prevented the restacking of G-4020. Consequently, apart from the enhanced mechanical strength, SBR/G-4020 composites exhibited exceptionally high long-term thermo-oxidative aging resistance compared with SBR/r-GO/4020 composites (SBR with hydrazine hydrate reduced GO and 4020). Moreover, the thermal conductivity of SBR/G-4020 composites was superior to that of SBR/r-GO/4020 composites due to the reduced interfacial thermal resistance. Potentially, one-step reaction and high-efficiency make the approach of using antioxidants a promising strategy for the eco-friendly reduction and functionalization of GO, which may offer a new path to construct high-performance elastomer/graphene composites.

Accelerated thermo-oxidative aging for carbon fiber reinforced polycyanate under high pressure atmosphere

The aim of this study is to accelerate thermo-oxidative aging in carbon fiber reinforced plastics (CFRP) submitted to high temperature atmospheric pressure. In this study, long-term thermo-oxidative aging test was conducted to examine the effect of high pressure atmospheric environment on the weight and mechanical properties of CFRP to accelerate the rate of thermo-oxidative degradation. The effect of thermo-oxidative environment under high atmospheric pressure on the change in weight, strength, and shrinkage behavior of a CFRP with polycyanate (FSD-M-08178) was investigated. The aging test was conducted at 180 °C up to 8,000 h under atmospheric pressure and the test result was used as a reference data. Other aging tests were also conducted under elevated pressure conditions (0.3 and 0.5 MPa) at the same exposure temperature up to 2,000 h and the test results were treated as the accelerated aging test data. Unidirectional laminates [0]8 and [90]8 for tensile specimens and angle ply laminates [±45]2S for off-axis tensile specimens were aged in oven, and then mechanical tests were carried out on them. The results indicated that elevated pressure would cause faster and larger weight gain in earlier aging period. The outcomes of these experiments were changes in weight, strength, and local shrinkage deformation were changed quickly under elevated atmospheric pressure environment. Same micro damage onset and extension irrespective of pressure during thermo-oxidative aging and subsequent loading test were observed. The test results indicate that the change in weight, strength, and local shrinkage deformation could be accelerated by elevated pressure without change in thermo-oxidative degradation mechanism. Therefore, the elevated pressure testing would be a better method to accelerate thermo-oxidative degradation. On the other hand, the change in strength under elevated pressure conditions is faster than local shrinkage deformation. Equivalent acceleration rate of degradation could not be obtained.

Effect of long-term thermo-oxidative aging on weight and fracture toughness of polycyanate neat resin

This study focuses on the effect of long-term thermo-oxidative aging on weight and fracture toughness (KIC) of polycyanate ester (PCy) neat resin (FSD-M-08178). Thermo-oxidative aging was conducted at 180 °C up to 8000 h under atmospheric pressure in order to investigate susceptibility to thermo-oxidative environment in the PCy. Weight and KIC changes were investigated with chemical structure changes due to thermo-oxidative degradation. The chemical structure changes were analyzed by means of Fourier transformed infrared spectroscopy with attenuated total reflection system. To investigate degree of degradation, carbonyl index (CI) was analyzed with triazine ring peak which is characteristic peak of the cured polycyanate resin. Single-edge-notch bending test was conducted for each aged (non-aged, 100, 197, 500, 1000, 2000, 4000, and 8000 h) condition to investigate KIC change and evaluated with CI. The result indicated that the weight increased first 500 h. Then, the weight decreased. The result also indicated that the KIC sharply dropped first 100 h. After 100 h, the KIC was almost same up to 8000 h. The result suggested the KIC depend on the CI which was chemical structure changes of the specimen surface due to thermo-oxidation degradation.

Environmental Durability of Polymerization of Monomer Reactants-type Polyimide–Clay Nanocomposites

The environmental durability of PMR-15 nanocomposites prepared from an unmodified Na+-montmorillonite (PGV) and two organically modified PGV (PGVC10COOH, PGVC12) have been investigated using an accelerated hydrolytic aging test and a long-term thermo-oxidative aging study. PGV was modified with an amino acid (11-amino-undecanoic acid) and a primary amine (dodecylamine). The PGV/PMR-15 nanocomposite exhibited higher moisture gain than the neat resin, while PGVC10COOH, PGVC12/PMR-15 nanocomposites exhibited lower moisture gains. XRD data of the nanocomposites correlated well with the moisture gain data for the nanocomposites. PGVC10COOH and PGVC12/PMR-15 nanocomposites exhibited more than a 50% reduction in the flexural modulus drop off. These results suggest that nanocomposites provide a viable approach in decreasing the susceptibility of PMR-15 to hydrolytic degradation. No improvement in the thermal oxidative stability of the nanocomposites was achieved. This may be attributable to the relatively low thermal stability of the organic modifiers and/or the presence of impurities, which catalyzed the PMR-15 degradation.

Long-Term Thermo-Oxidative Aging in Composite Materials: Experimental Methods

The combination of this work, an earlier study [1] concerning the effects of thermo-oxidative aging on the thermal, fracture and compressive behavior of carbon-fiber reinforced epoxy composites, and a companion paper [2] discussing the failure mechanisms due to thermo-oxidative aging provide the first published comprehensive study of the effects of long-term thermo-oxidative aging on such a wide range of properties for the same materials systems. In this phase of the work, tensile tests (both unidirectional 0° and ±450 layups), edge delamination, and compression-after-impact (CAI) were examined for G30-500/R922-1 and G30-500/R6376 carbon/epoxy specimens aged in air at 177°C (350°F) up to 10,000 hours. Additionally, 10,000 hour data not included in the previous study are also included for comparison. The purpose of the present study is not to identify suitable candidate materials, but to evaluate the effect of test methods and failure modes in characterizing thermo-oxidative stability. The materials systems chosen were selected as model materials for the study of degradation phenomena and not for performance evaluation at 177°C which is clearly beyond the useful range of these materials. Nevertheless, unidirectional tensile properties were found to be relatively unaffected up to 5,000 hours of aging. By contrast ±45° tensile strengths and unidirectional compression strengths decreased between 10 and 35% after only 1,000 hours exposure. Mode I fracture toughness increased with aging due to increased fiber bridging and Mode II fracture toughness was, by contrast, relatively unaffected. Edge delamination fracture toughness was severely affected by thermo-oxidative aging decreasing to between 5 and 15% of the unaged value after 10,000 hours aging suggesting a strong effect of interfacial degradation. Because even small weight losses lead to correspondingly large reductions in certain mechanical properties, even small errors in the determination of weight loss lead to large errors in estimates of mechanical properties. Indeed, it is likely that weight loss, even with the presence of corresponding mechanical data is not a good indicator of property degradation. Weight loss is only useful as a negative indicator: it indicates an unacceptable material; it does not yield useful information as to useful lifetimes.

Long-term thermo-oxidative aging in composite materials: Failure mechanisms

This work, an earlier study (Tsotsis, T. K., J. Compos. Mater., 1995, 29(3) 410–422) and a companion paper (Tsotsis, T. K., J. Compos. Mater., in press) constitute a comprehensive analysis of the effects of thermo-oxidative aging (177 °C in air for up to 10 000 h) on the thermal, fracture and compressive behavior of two carbon-fiberreinforced epoxy composites: G30-500/R922-1 and G30-500/R6376. The two materials studied were not designed for long-term use at 177 °C but were chosen as model systems for establishing a meaningful aging test methodology. This paper focuses on the mechanisms controlling property degradation to determine the roles of matrix, fiber and interface on the aging behavior observed. Delamination-critical strain-energy release rates G Ic (mode I), G IIc (mode II) and G c (edge delamination) clearly showed the effects of matrix and, especially, interface degradation as a consequence of aging. Compressionafter-impact (CAI) strengths exhibited a sharp drop during initial aging because of such effects and then leveled off at longer aging time as extensive delamination induced other failure modes (e.g. transverse cracking and fiber breakage) to limit the damage zone growth. Examination of aged specimens by means of scanning electron microscopy revealed pronounced degradation regions close to composite surfaces or edges, indicating that the oxidative diffusion mechanism dominated the degradation process. Residual stresses arising from aging-induced differential resin shrinkage and interaction between plies of different orientations were found to have a strong effect on the degradation process for plies close to the surface and, especially, near free edges. Comparison between the toughened (R6376) and standard (R922-1) resins suggests that resin fracture toughness contributed to thermo-oxidative resistance by suppressing resin cracks which would create additional paths for oxygen diffusion. This study revealed the importance of matrix and interface degradation, matrix toughness, ply interaction, and edge effects in the thermo-oxidative aging of polymeric composites.