Effect Of Thermo-oxidative Aging Research Articles

Effects of thermo-oxidative aging on progressive bending damages and electromechanical behaviors of carbon fiber/epoxy 3D woven composites

The effect of thermo-oxidative aging on mechanical properties is important to designing carbon fiber-reinforced composites serviced in long-term atmospheric environments. Here, we report the progressive bending damage behaviors of carbon fiber/epoxy 3D angle-interlock woven composites (3DAWCs) after thermo-oxidative aging. Three-point bending tests were conducted to characterize bending damage behaviors after different aging days. The electrical resistance change of 3DAWCs was also simultaneously measured with the two-probe method during three-point bending tests. Combining side image and digital image correlation (DIC) technology, we found that the bending strength and modulus deteriorated rapidly during thermo-oxidative aging. The strain distribution and progressive bending damage modes also changed significantly, i.e., a symmetrical strain distribution for the unaged specimens, while the existing interface cracks of the aged specimen changed this symmetry. The electrical resistance method (ERM) effectively identified the early-stage damages, and the first derivative of the rate of resistance change (FDC) revealed differences in the progressive damage modes of aged and unaged specimens.

Effect of thermo-oxidative aging on thermal elongation performance of XLPE insulation for high-voltage cables

The thermal elongation of cross-linked polyethylene (XLPE) insulation for high-voltage cables is an important factor for evaluating the high-temperature mechanical performance, which is an important parameter included in the testing standards of the power cable insulation. Previous studies have found that the thermal elongation of XLPE insulation for high-voltage cable depends on the cross-linking degree, but have not dealt with the effect of the thermo-oxidative aging during the thermal elongation test. In this paper, the thermal elongation experiments of the XLPE samples compounded with different kinds of antioxidants were carried out under both air and nitrogen atmospheres. The molecular structure changes of the XLPE samples after thermal elongation under air atmosphere were examined by gel content, FTIR spectra and X-ray diffraction. The oxidation induction periods were also measured to analyze the antioxidation performance of the phenolic antioxidants and study its contribution to the thermal elongation performance. The results showed that the XLPE samples underwent thermo-oxidative aging in the thermal elongation test under air atmosphere at 200 °C. It caused that the thermal elongation properties can not accurately reflect the cross-linking degree of the original XLPE samples, but has a strong correlation with the gel content of the aged samples. Antioxidants can inhibit the thermo-oxidative aging effect on the network structure, leading to a slower uptrend of elongation under the air atmosphere. This indicates that the thermal elongation performance of XLPE insulation is determined by the synergistic effect of the network structure and the antioxidation performance, and this can provide reference significance for optimizing the evaluation methods of high-voltage cable XLPE insulation performance.

Effect of thermo-oxidative aging on the Payne effect and hysteresis loss of carbon-black filled rubber vulcanizates

In the tire industry, the Payne effect and hysteresis loss of carbon-black (CB) filled rubber vulcanizates are the most concerning issues. CB filled rubber vulcanizates are susceptible to thermo-oxidative aging in the applications. In this paper, the effects of thermo-oxidative aging are investigated from experimental and theoretical aspects. The specimens are subjected to thermo-oxidative aging at 80, 100 and 120 °C for various periods of time ranging from 1 to 6 days and then the dynamic mechanical tests are conducted. The results show that both the storage modulus and the loss modulus increase with increasing aging time. The hysteresis loss of the material shows an increasing tendency with the increase of dynamic strain amplitude, aging time and aging temperature. The Kraus model is used to describe the Payne effect and a viscoelastic model consisting of dynamic strain amplitude and loss modulus is used to calculate the energy dissipation.

Effect of thermo-oxidative ageing on the rheological properties of bituminous binders and mixes: Experimental study and multi-scale modeling

The multiscale modeling of the complex modulus and phase angle of aged hot and warm mix asphalt (HMA and WMA) and bituminous mortar AC02 is investigated in this study. Four thermo-oxidative ageing durations (0, 3, 6 and 9 days) are considered to investigate the long-term thermo-oxidative ageing based on a RILEM ageing procedure. The binders of the aged mixes are extracted and characterized. Moreover, RTFOT and PAV tests are carried out on fresh bitumen to simulate the long-term thermo-oxidative ageing of HMA and WMA. Rheological tests are performed at different temperatures and frequencies to determine the stiffness moduli of binders and mixes that are subsequently curve-fitted with the modified 2S2P1D model. The results show that the stiffness moduli of binders and mixes increase with the long-term thermo-oxidative ageing duration. This increase is more pronounced for WMA and their binders than HMA, this is probably due to the higher water content (5.5%) used for this type of mixture. Moreover, the increase of the stiffness modulus is shown to be related to parameters such as asphaltene content, carbonyl and sulfoxide indices. Finally, a multi-scale model which combines the Mori–Tanaka scheme at mastic and mortar scales and the self-consistent scheme at the mixture scale with possible grain–grain contact between the coarse aggregates, is implemented. It is able to account the evolution of the master curves of the stiffness moduli |E∗| and the phase angles δ of the mixes based on bitumens’ and aggregates’ properties. The reliability of this multi-scale model is assessed through a comparison with experimental data, over a wide range of frequencies and temperatures.

Study of the damage behavior of T800 carbon fiber/epoxy resin composites after low-velocity impact under thermo-oxidative aging

Here, the effect of thermo-oxidative aging on domestic T800 carbon fiber/epoxy resin composites was studied using mass loss rate curves, interface morphology, infrared spectroscopy, and dynamic mechanical property analysis. The composites were subjected to thermo-oxidative aging tests after low-velocity impact. Then, the effect of environmental factors on the damage area of the composites and the compression performance after impact were investigated. The results showed that the composites underwent physical and chemical aging at 185°C. Due to the short aging time, the mass loss rate slowly increased. After aging, thermo-oxidative aging caused the matrix to crack, and the sample cracks that formed after impact expanded, and the damage area also slightly increased. The residual compressive strength of the material fluctuated due to the competing reinforcing and destructive effects of the composite during thermo-oxidative aging; however, aging had little effect on the impact damage morphology and compression failure mode. Upon extending the aging time, thermo-oxidative aging caused the tanδ peak to gradually shift to a higher temperature, and the glass transition temperature ( Tg) increased.

The eff ect of thermo-oxidative aging on the structure and properties of polysulfone and prediction of its service life

The eff ect of thermal oxidative aging on the structure and properties of polysulfones PSF-190 (Institute of Plastics JSC, Russia) and Udel P1700 (Solvay Specialty Polymers, Belgium) has been studied. The shelf life of the selected grades of polysulfones has been predicted. The diff erence in the course of the low-temperature thermo-oxidative aging process for PSF-190 and Udel P1700 is shown. It was found that the main changes in such characteristics as density, tensile yield stress, elongation at break occur during the fi rst 250 hours of thermo-oxidative aging. The value of the specifi c volume electrical resistance of polysulfones does not change under the infl uence of temperature and time under conditions of low-temperature thermo-oxidative aging.

Effects of thermo-oxidative aging on 3-D deformation field and mechanical behaviors of 3-D angle-interlock woven composites

The effect of thermo-oxidative aging on mechanical properties is a key factor in designing composites structures. This paper aims to explore the effects of thermo-oxidative aging on the mechanical behavior, surface deformation and damage evolution of 3-D angle-interlock woven composites (3DAWC) under compression. A bilinear stress-strain curve with high failure strength and compressive modulus were obtained for the unaged sample. The transition region of the stress-strain curve disappeared for the aged sample due to epoxy resin degradation and cracks. The transition strain decreases as the interface damage starts earlier after thermo-oxidative aging. The surface strain, off-plane displacement and Poisson's ratio distribution show structural correlation during compression. Both the surface average strain and the average Poisson's ratio decrease with aging time. A finite element model has been established to explore the mechanical degradation mechanisms.

Nanofragmentation of Expanded Polystyrene Under Simulated Environmental Weathering (Thermooxidative Degradation and Hydrodynamic Turbulence)

Fragmentation of macroplastics into microplastics in the marine environment is probably one of the processes that have generated most drive for developing the microplastics research field. Thus, it is surprising that the level of scientific knowledge on the combinative effect of oxidative degradation and mechanical stressors on fragmentation is relatively limited. Furthermore, it has been hypothesized that plastic fragmentation continues into the nanoplastic size domains, but environmentally realistic studies are lacking. Here the effects of thermooxidative aging and hydrodynamic conditions relevant for the shoreline environment on the fragmentation of expanded polystyrene (EPS) were tested in laboratory simulations. The pre-degraded EPS was cut into pieces and subjected to mechanical, hydrodynamic simulations during four-day stirring experiments. Subsamples were filtered and subsequently analyzed with light microscopy with automated image analysis particle size distribution determinations, polymer identification with Raman spectroscopy, Scanning Electron Microscopy (SEM) with automated image analysis particle size distribution. The nanoplastic size fraction was measured using nanoparticle tracking analysis. In addition, the degree of polymer oxidation was spectroscopically characterized with Fourier transform infrared (FTIR) spectroscopy. The results illustrate that fragmentation of the mesoplastic objects is observed already after 2 days, but that is more distinct after 4 days, with higher abundances for the smaller size fractions, which imply more release of smaller sizes or fragmentation in several steps. For the nanoplastic fraction, day four shows a higher abundance of released or fragmented particles than day two. The conclusions are that nanofragmentation is an important and understudied process and that standardized test protocols for both thermooxidative degradation and mechanical treatments mimicking realistic environmental conditions are needed. Further testing of the most common macro- and mesoplastic materials to assess the rates and fluxes of fragmenting particles to micro- and nanoplastic fractions should be conducted.

Thermo-Oxidative Behavior of Carbon Black Composites for Self-Regulating Heaters

The composite materials for self-regulating heaters are conductive composites based on a polymer matrix and a dispersed conductive filler consisting in either carbon black or another carbon material, such as graphite or nanotubes. Similar materials are suitable for sensors and current limitations. As these materials used in heating applications work usually at elevated temperatures in presence of air, the ageing processes would be an important limiting factor of their lifetime. Therefore, thermal oxidation processes and crystallinity changes during the service of these products are of major interest in durability studies. The potential interference of carbon-based materials with the oxidation and ageing of polymer matrix shall be known in order to correctly estimate the durability of such materials. The effect of radiation exposure is studied taking into account the potential use of such materials in radiation environments. In this work, the activation energies of some initial, unaged and aged products at elevated temperatures are compared in order to characterize the effect of thermo-oxidative ageing and hence to evaluate their durability. The effect of some antioxidants is also discussed. The crystallinity, calculated from DSC was used for evaluation of the physical changes induced within the aged materials, following the procedures described in previous work. FTIR-ATR technique was used for characterization of chemical changes induced by ageing.

Influence of thermo-oxidative aging on flame retardancy, thermal stability, and mechanical properties of long glass fiber–reinforced polypropylene composites filled with organic montmorillonite and intumescent flame retardant

In this work, the effect of thermo-oxidative aging on organic montmorillonite/intumescent flame retardant/long glass fiber–reinforced polypropylene composites was investigated for different exposure times at 140°C. Limiting oxygen index, Underwriters Laboratories-94 tests, cone calorimeter test, and thermogravimetric analysis were used to evaluate the flammability and thermal stability. The results of limiting oxygen index values, Underwriters Laboratories 94 test, and cone calorimeter test show that aging performs negative effect on the flame retardancy of organic montmorillonite/intumescent flame retardant/long glass fiber–reinforced polypropylene composites. Thermal oxidation aging markedly changes the decomposition process of organic montmorillonite/intumescent flame retardant/long glass fiber–reinforced polypropylene composites. The scanning electronic microscopy images of the external surface of composites indicate that many ground particles and micro-scale cracks are scattered in the surfaces of the composites after aging. The sharp micro-scale cracks and crazing formed on the surface promote the heat and oxygen to penetrate into the bulk of polypropylene matrix. According to the mechanical test results, the thermal oxidation aging reduces the tensile, flexural, and notched impact strengths of organic montmorillonite/intumescent flame retardant/long glass fiber–reinforced polypropylene composites.

Effects of thermo-oxidative aging on structure and low temperature impact performance of rotationally molded products

In this work, the effects of thermo-oxidative aging on the microstructure and impact properties of polyethylene during the rotational molding process were studied. FTIR and Raman analysis showed that the degradation of polyethylene was responsible for the low-temperature impact strength (LT-IS) and the brittle fracture behavior of samples those subjected to prolonged heating time during rotational molding process. The DSC and polarizing microscope analysis showed that the degradation process was delayed by the addition of antioxidants. Through use and optimization of antioxidants, the thermo-oxidative aging of polyethylene can be modulated, a broader processing window can be achieved, and the products may exhibit better mechanical properties with a wider heating time range.

The effect of thermo-oxidative ageing on crystallization, dynamic and static mechanical properties of long glass fibre-reinforced polyamide 10T composites.

The performances and microstructure of long glass fibre-reinforced polyamide 10T (PA10T/LGF) composites that experienced different ageing temperatures (160 and 200°C) with increasing ageing time are characterized by differential scanning calorimetry (DSC), mechanical analysis, thermogravimetric analysis (TGA) and scanning electron microscopy to probe the correlation between properties of the composites and thermo-oxidative ageing. The DSC results show that PA10T/LGF composites occur on degradation, the fracture of molecular chains and the destruction of crystallization structure, which leads to the crystallization and melting peaks of PA10T/LGF composites to shift to high temperature. On the basis of dynamic mechanical analysis data, the reduction of the interfacial bonding between the glass fibre and PA10T matrix and the motion of molecular chain segments result in the thermo-oxidative ageing of composites. According to the calculation of activation energy (E), thermo-oxidative temperature and ageing time can bring about the decline of the E value, proving the deterioration in performance of PA10T/LGF composites. In view of TGA, the increase in the thermo-oxidative temperature and ageing time promotes the degradation of PA10T/LGF composites. The tensile, flexural and notched impact strengths of PA10T/LGF composites decline with prolonging the ageing temperature and time. The surface of materials produces some microcracks and the cross-section surface of PA10T/LGF composites becomes rougher.

A new constitutive equation for solid propellant with the effects of aging and viscoelastic Poisson’s ratio

A new constitutive equation for solid propellant with the effects of aging and viscoelastic Poisson’s ratio is proposed. Effects of thermo-oxidative aging and viscoelastic Poisson’s ratio are considered in this comprehensive constitutive equation with two sets of reduced time system coping with the time and temperature dependence. In order to simulate the single and combined effects of aging and viscoelastic Poisson’s ratio, constitutive equation is rewritten into an incremental form and implemented in the user subroutine UMAT at the platform of finite element code ABAQUS. Detailed procedure for acquiring the parameters in constitutive equation is introduced and conducted for the subsequent applied analysis. Two typical loading cases during the service life of solid rocket motor and four sets of combined constitutive models are simulated. Von Mises strain and stress distribution and their changes versus time are utilized as the main analysis index. The results show that the effects of aging and viscoelastic Poisson’s ratio or their combinations will improve or decrease the level and change the distribution of Von Mises strain and stress in varying degrees.

Formulation and aging resistance of modified bio-asphalt containing high percentage of waste cooking oil residues

Waste cooking oil residues (WCOR) based bio-asphalt is a potential substitute for petroleum asphalt. This study aims to prepare a bio-asphalt with high percentage of WCOR derived from esterification reaction for biodiesel. According to the uniform design results, the optimum mass ratios of materials were determined as WCOR of 33.3%, resin (RE-1) of 30.3%, hard asphalt particles (HAP) of 31.8%, low density polyethylene particles (LDPE) of 4.6% and linear SBS (L-SBS) of 4%. Based on the orthogonal design results, the WCOR based bio-asphalt would have the best performance when stirred for 40 min and sheared for 50 min (4000 rpm) under the condition of 170 °C with the optimum mass ratios. Rotational viscosity (RV) test results indicated that the viscosity of optimal bio-asphalt (OBA) was between PEN 70 base asphalt (PEN 70) and SBS modified asphalt (SBS-MA). Dynamic shear rheometer (DSR) test and bending beam rheometer (BBR) test results proved that OBA exhibited excellent high-temperature performance similar with SBS-MA, and it had superior low-temperature performance to SBS-MA and PEN 70. Furthermore, the effect of thermo-oxidative aging on the properties of OBA was studied. DSR test results revealed that the complex modulus and phase angle of thin film oven (TFO)-aged OBA both increased with the elevated aging level, indicating an increase in viscosity during aging process. Fourier transform infrared spectroscopy (FTIR) test results showed that there was no obvious variation on the functional groups of OBA after 15 h TFOT aging process. It was confirmed that less aging susceptibility of OBA was found compared with PEN 70, which demonstrated that OBA had a better aging resistance performance.

Effect of thermo-oxidative aging on compressive behavior of carbon fiber polymer matrix composites

The effects of reinforcement architecture on the compressive behaviors of carbon fiber polymer matrix composites (CF-PMCs) under thermo-oxidative aging conditions were investigated. Samples of three-dimensional and four-directional braided carbon fiber/epoxy composites (BC) and laminated plain woven carbon fiber/epoxy composites (LC) were subjected to isothermal aging at 80℃, 100℃, 120℃ and 140℃ in air circulating ovens for various durations up to 1200 h. The process resulted in progressive deterioration of the matrix reins and fiber/matrix interfaces, in the form of chain scissions, weight loss and fiber/matrix debonding, which significantly led to the decrease of the compressive strength. In addition, the compressive strength retention rates of BC were higher than those of LC at the same aging conditions due to the differences of their reinforcement architecture. On the one hand, LC lost more weight than BC because the percentage of exposure of fiber ends to air in the LC samples was five times more than that in the BC samples. Moreover, the BC samples could resist the compressive load as an integral structure and did not show delamination damage as in the case of LC samples, although the resin was damaged and the adhesive force between fiber bundles and resin decreased after thermo-oxidative aging. Therefore, adopting the three-dimensional and four-directional braided preform as the reinforcement of CF-PMCs is an effective way to improve their compressive strength under thermo-oxidative aging conditions.

Influence of thermo-oxidative aging on vibration damping characteristics of conventional and graphene-based carbon fiber fabric composites

The effect of thermo-oxidative aging on the vibration damping characteristics of the conventional fabric composites reinforced by three-dimensional (3D) and four-directional (4Dir) braided preform and laminated plain woven fabric and the 3D-4Dir braided graphene-based carbon fiber composites was investigated. Specimens were isothermally aged at 140 °C for various periods of time up to 1,200 h. The results indicated that the thermo-oxidative aging resulted in deterioration of the matrix and interface performance, in the form of chain scissions, weight loss, microcracks and interfacial debonding, which should be responsible for the decrease of nature frequency and the increase of damping coefficient of the composites. After aging for 1,200 h, the first nature frequency and first damping coefficient retention rates of 3D-4Dir braided graphene-coated carbon fiber/epoxy composite were 5.5% and 6.4% higher than those of laminated composite, respectively. One of the reasons was the integrated structure of 3D-4Dir braided composite exposed lower fiber end area to air than that of laminated composite, leading to less interface oxidation. Another reason was that the graphene reinforced gradient interphase provided an effective shield against interface oxidation and restricted the movement of the different phase of the materials at the composites interface. This synergetic reinforcing effect of 3D-4Dir braided structure and graphene reinforced hierarchical interface provides an easy and effective way to design and improve the thermo-oxidative stability of carbon fiber reinforced polymer composites. POLYM. COMPOS., 37:2871–2883, 2016. © 2015 Society of Plastics Engineers

The Effect of Thermooxidative Aging on the Durability of Glass Fiber-Reinforced Epoxy

Thin-skinned organic matrix composites within aeronautical structures are subjected to thermooxidative aging during their service life, leading to reductions in their durability. In this paper, a durability evaluation of fiberglass epoxy prepreg is performed on the original composite thickness before and after 800 h isothermal aging at 82°C. The characterization of both aged and unaged composites comprised tensile tests, DMA, FTIR, weight loss measurements, SEM, and DSC. The tensile strength and modulus of the composites increased after being exposed to pronounced aging conditions, whereas a decrease was observed in the toughness. DMA results revealed that the glass transition temperature and rubbery state modulus increased as a result of the thermooxidative aging. FTIR spectroscopy demonstrated the formation of carbonyl compounds due to oxidation of the chemical structure of the resin. SEM observations indicated the existence of minor superficial cracking and poor fiber-matrix adhesion after aging. In addition, a minor mass change was observed from mass loss monitoring methods. The overall findings suggest that postcuring and physical aging enhanced the brittleness of the resin, leading to a significant decline in the useful structural life of the thin-skinned composite.

Effect of thermo-oxidative aging on three-dimensional and four-directional braided carbon fiber/epoxy composite

An experimental study was performed to investigate the effect of high temperature exposure on flexural properties of the three-dimensional and four-directional braided carbon fiber/epoxy composite and the corresponding neat resin. For this purpose, samples were exposed to 90℃, 120℃, 150℃, and 180℃ (below and above the glass transition temperature of the matrix resin) for various periods of time up to 13 days. The flexural properties combining with Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), weight loss, scanning electron microscope (SEM), and optical microscope analyses were performed on the unaged and aged samples. The results revealed that the thermo-oxidative behavior of the braided composite was significantly different from the neat resin. The flexural strength of the neat resin decreased dramatically due to the oxidation degradation of the sample surface when the aging temperature was equal to its glass transition temperature. The extensive degradations of both the matrix and the fiber/matrix interface, especially for the interface, were responsible for the significant decrease in flexural strength of the braided composite. The flexural strength retention rates of the braided composite were higher than that of the neat resin after exposure to 90℃, 120℃ and 150℃ because the integral structure of the braided composite can make the fiber bear flexural force together although the matrix resin and the fiber/matrix interface had a certain degree of damage after longtime thermo-oxidative aging.

The effect of thermo-oxidative aging on carbon fiber reinforced cyanate ester composites

In this work, the aging of two different carbon fiber reinforced cyanate ester polymer matrices (CFRP-A and CFRP-B) was investigated after their exposure to aggressive thermo-oxidative conditions. The materials’ degradation at 230℃ under 1 atm for 30 days in oxidative atmosphere was evaluated with regard to changes in mass (mass loss), glass transition temperature Tg, interlaminar shear strength, as well as physical characteristics that were examined under scanning electron microscopy. For both the systems, the aging study showed significant mass loss that reached ∼4% in the case of CFRP-B. The mass loss is accompanied with a considerable decrease in interlaminar shear strength and Tg properties. The study of the scanning electron microscopic images clearly shows the surface deterioration due to the oxidation process, accompanied with formation of matrix microcracking and development of matrix-fiber interfacial debonding. The contribution of the chains scission to the materials degradation was also detected by performing in situ aging through isothermal thermo-gravimetric analysis measurements at 230℃ under oxidative and inert atmosphere. However, the thermo-gravimetric analysis results showed minor chain scission proving thus, that the oxidation was the main degradation mechanism for both materials.

Effects of thermo‐oxidative aging on chain mobility, phase composition, and mechanical behavior of high‐density polyethylene

AbstractThe thermo‐oxidative degradation behavior of high‐density polyethylene (HDPE) was investigated during oven aging at 100°C. 1H low‐field solid‐state nuclear magnetic resonance (NMR) was used to characterize the behaviors of molecular chains and the changes in phase content of HDPE during aging. NMR free induction decays (FIDs) were fitted by three components corresponding to the crystalline phase, interphase, and amorphous phase, respectively. The prolongation of aging led to a progressive increase in the crystalline phase at the expense of the other two phases. A slight decrease in chain mobility of the crystalline phase and interphase was observed simultaneously. The results obtained from other traditional technical approaches are also discussed in the context of the molecular dynamics properties revealed by NMR. The reduction in molecular weight, in chain mobility and the increase in crystallinity during thermo‐oxidation were the main factors, which caused the loss of mechanical performance of HDPE. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers