Influence Of Thermo-oxidative Ageing Research Articles

Effect of Aging and Modification on the Interfacial Interaction in Asphalt Mastics

In the temperature range –10–30°С the influence of thermo-oxidative aging, frequency and deformation on the interfacial interaction according to the parameters K–B–G* and К–В–δ in asphalt mastics and modified mastics based on bitumen grade BND 60/90 has been investigated. The filler was introduced into bitumen in the ratio of 1/1 by weight. Active powder of discretely devulcanized rubber (APDDR) as a modifier was introduced in the ratio bitumen/APDDR = 87.5/12.5 by weight. It is shown that the modification of APDDR provides a greater thickness of adsorbed layer on the surface of filler particles under various conditions of external influences compared to mastic, and this thickness depends on the sequence of introduction of filler and APDDR.

Influence of the curing system on the physical-mechanical, dynamic properties, and aging resistance of ethylene–propylene–diene monomer formulations for applications at high temperatures

The effects of three curing systems on rheometric, morphological, physical-mechanical, thermal, and dynamic properties of ethylene–propylene–diene monomer (EPDM) composites was investigated. The influence of thermo-oxidative aging on crosslink density and physical-mechanical properties was studied. Based on a standard composition for application at high temperatures, EPDM formulations with semi-efficient vulcanization systems (ES), efficient vulcanization systems (ED), and peroxide curing systems (EP) were prepared. Experimental results indicated that EPDM compounds cured with efficient vulcanization systems exhibit the highest scorch time with an intermediate maximum torque value at 150°C. The filler dispersion in the elastomeric matrix was greater than 94%; however, the ED formulation showed a more pronounced decrease, with the increase in deformation indicating a greater filler–filler interaction. In comparison with those cured with peroxide and semi-efficient systems, EPDM formulations cured with an efficient system presented better thermal resistance and the crosslink density was sufficient to maintain the mechanical integrity, leading to an intermediate hardness value, tensile strength, modulus, and greater elongation at breaking. In summary, the results indicated that the efficient curing system was the most appropriate to be used in the envelope’s manufacture, due to the better performance of the mechanical properties associated with the better resistance to thermal aging.

Influence of thermo-oxidative aging on mechanical performance of three-dimensional orthogonal carbon/glass fiber/bismaleimide composites

Influence of thermo-oxidative aging on mechanical performance of three-dimensional orthogonal carbon/glass fiber/bismaleimide composites

Ageing behaviour of a polyethylene blend: influence of chemical defects and morphology on charge transport

The properties of novel cable insulation systems will rely critically upon the morphology of the material. Here, a blend of high and low density polyethylene was processed in order to generate three sets of samples with different morphologies. The influence of thermo-oxidative ageing at 120 °C was then considered. The resulting chemical changes included the introduction of unsaturation and oxygen-containing groups and was determined by antioxidant consumption and oxygen permeability. Such chemical defects were found to be concentrated in the fraction of each system that was molten at 120 °C and, consequently, served to inhibit recrystallisation following ageing. The resulting spatial distribution of charge trapping sites was therefore strongly dependent on morphology. The electrical conductivity of each system varied non-monotonically with ageing: short times reduced the conductivity; a rapid increase in conductivity over five orders of magnitude occurred beyond a critical ageing threshold. Despite the pronounced structural differences between the morphologically distinct sets of samples, all exhibited comparable conductivity values beyond this threshold, implying that while charge transport is strongly influence by chemical factors, crystallinity is relatively unimportant. This experimental finding appears at odds with theoretical studies of the electronic states in crystalline and amorphous polyethylene.

Payne effect of thermo-oxidatively aged isoprene rubber vulcanizates

While many works focus on aging mechanisms and mechanical performances of aged vulcanizates, rare is performed to investigate the influences of aging induced network variation on the Payne effect and energy dissipation. Herein the influence of thermo-oxidative aging on Payne effect of isoprene rubber (IR) gum vulcanized with conventional vulcanization (CV) and efficient vulcanization (EV) systems at similar crosslinking densities was investigated, in order to disclose the roles of the crosslink types and therefore the thermo-oxidative degradation on the Payne effect. The results indicate that the crosslink structure and thus the Payne effect are highly susceptible to the thermo-oxidative aging. The aging induced degradation is more severe in CV than that in EV systems, which greatly improves the dissipation of accompanying the Payne effect. This work is helpful for understanding the contribution of network structure to the Payne effect for design rubber materials with optimized aging and dynamic properties.

The influence of thermo-oxidative aging on the electromagnetic absorbing properties of 3D quasi-isotropic braided carbon/glass bismaleimide composite

The hybrid carbon/glass fibers reinforced polymer matrix composites (CF/GF-PMCs) used as structural materials of weapon systems often suffer high-temperature condition, leading performance degradation of them. The electromagnetic (EM) absorbing properties are essential for the survival of the weapon systems. However, the influence of thermo-oxidative aging on laws and mechanisms of EM absorbing properties of CF/GF-PMCs has not been reported. In this paper, the 3D quasi-isotropic braided CF/GF bismaleimide composites were newly designed, and its EM absorbing properties were investigated under thermo-oxidative aging. The results indicate that the aged composite has better EM absorbing properties than the unaged one. This is because of thermo-oxidative aging results in an uneven surface and numerous cracks and voids in the aged composite. The uneven surface of the aged sample could diffuse the incident EM wave. And the cracks and voids on the surface and interior of the aged sample could provide channels for the EM wave to enter into the aged samples.

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.

Influence of Thermo-Oxidative Ageing on the Thermal and Dynamical Mechanical Properties of Long Glass Fibre-Reinforced Poly(Butylene Terephthalate) Composites Filled with DOPO.

In this work, the long glass fibre-reinforced poly(butylene terephthalate) (PBT) composites filled with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were prepared by melt blending, and the influence of thermo-oxidative ageing on the static and dynamic mechanical properties, thermal behaviours and morphology of composites with different ageing time at 120 °C were investigated and analysed. The results showed that the mechanical properties decreased in the primary stage of ageing, while embrittlement occurs in the later period, and the crystallinity of PBT decreases first, and then recovers to some extent. The scanning electron microscopy (SEM) photos of the samples indicated that the obvious crack appeared on the sample surface and a deeper, broader crack occurred with a longer ageing time. The results of energy dispersive X-ray analysis (EDAX) proved the DOPO filler diffused to the sample surface by measuring the content of phosphorus. Thermal gravimetric analysis (TGA) curves showed that the thermal stabilities of composites increased with longer ageing time, as did the values of the limited oxygen index (LOI). Meanwhile, the results of dynamic mechanical analysis (DMA) indicated that the glass transition temperature shifted to a higher temperature after ageing due to the effect of crosslinking, and both the crosslinking and degradation of PBT molecular chains act as the main factors in the whole process of thermo-oxidative ageing.

Thermooxidative aging of rubber composites based on NR and NBR with incorporated strontium ferrite

Rubber magnetic composites were prepared by incorporation of strontium ferrite in concentration scale ranging from 0 phr to 100 phr into rubber matrices based on natural rubber (NR) and acrylonitrile-butadiene rubber (NBR). The composite systems were exposed to the conditions of thermooxidative aging at 70°C for 7, 14, and 28 days. The influence of aging period on the behavior of prepared materials was considered based on investigation of their cross-link density, physical–mechanical, and magnetic characteristics. The results revealed that the influence of thermooxidative aging on composite characteristics is dependent on the type of rubber matrix. The thermooxidative aging was found to have negative effect on the cross-link density and tensile properties of composites based on NR, which were deteriorated in dependence of aging time. The possible influence of magnetic filler content on aging mechanism was observed during last period of aging after which the decrease in cross-link density and tensile characteristics was more pronounced with increasing content of strontium ferrite. By contrast, the cross-link density, modulus, and hardness of composites based on NBR were found to be positively influenced by aging as their values showed increasing trend with extension of aging period.

Effects of Sodium Dodecyl Sulfate Filler Treatment and Thermo-Oxidative Ageing on the Properties of Poly(Vinyl Chloride)/Epoxidized Natural Rubber/Kenaf Core Powder Composites

An experimental study was conducted to investigate the influence of thermo-oxidative ageing on the tensile properties of PVC/ENR/KCP composites. Sodium dodecyl sulfate filler treatment was also carried out to evaluate the effect of filler treatment. The composites were prepared by melt compounding using Haake Polydrive internal mixer at 140 °C and 50 rpm. Compression-moulded samples were subjected to fracture surface morphology analysis and thermo-oxidative ageing for 3, 5 and 7 days. Thermo-oxidative ageing test indicates that after 3 days of exposure to heat, tensile strength increases, which is due to the further cross-linking reaction. With further exposure for 5 days and 7 days, the tensile strength is reduced probably due to the reduction in flexibility of the cross-link, which affect the stress distribution in the composites.

Influence of thermo-oxidative aging on the thermal conductivity of carbon fiber fabric reinforced epoxy composites

The present paper examined the thermo-oxidative aging (TOA) mechanism of the thermal conductivity of carbon fiber polymer composites (CF-PMCs) and the role of reinforced structure on the thermal conductivity of CF-PMCs under TOA conditions. The three dimensional and four directional braided carbon fiber/epoxy composites (BC), the laminated plain woven fabric/epoxy composites (LC), and the neat resins (NR) were investigated for up to 1200 h at 140 °C in air. The process resulted in progressive deterioration of the matrix rein and fiber/matrix interfaces, in the form of chain scissions, oxidization of carbon elements, weight loss, and cracks, which significantly led to the decrease of the thermal conductivity of the NR, LC, and BC. The ratio of fiber end area to the total surface area in a sample determined the rate of weight loss and the changes in thermal conductivity. The LC samples had 1.2 times higher ratio of fiber end area to the total surface area, and their loss in thermal conductivity and weight were significantly higher than that of BC samples at the same aging conditions. Besides, the thermal conductivity of CF-PMCs was highly negatively correlated with the weight loss under TOA 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

Influence of thermo-oxidative aging on the impact property of conventional and graphene-based carbon fabric composites

The effects of reinforced structure (three-dimensional braided preform and laminated plain woven fabric) and graphene nanoplatelet-reinforced hierarchical interface on the impact properties of carbon fabric composites after thermo-oxidative aging were investigated. The results indicated that the impact properties decreased with increasing aging time due to the degradation of the matrix and fiber–matrix interface. After exposure to 140℃ for 1200 h, the peak impact force and impact strength retention rates of 3D-braided graphene nanoplatelet-coated carbon fiber-reinforced composite were 13% and 8% higher than those of the laminated composite, respectively. One of the reasons was the graphene nanoplatelet-reinforced gradient interphase may provide an effective shield against interface oxidation, transfer the localized thermal stress, and restrict the movement of the different phase of the materials at the composites interface. Another reason was the integrated structure of the 3D-braided composite can make the fiber bear impact force together although the resin was damaged and the adhesive force between fiber bundles and resin decreased after thermo-oxidative aging. This synergetic reinforcing effect of 3D-braided structure and graphene nanoplatelet-reinforced hierarchical interface provides an easy and effective way to design and improve the thermo-oxidative stability of carbon fiber-reinforced composites.

Influence of mixed sulfur/peroxide curing system and thermo-oxidative ageing on the properties of rubber magnetic composites

The present work was focused on the study of preparation a evaluation of properties of rubber magnetic composites based ethylene propylene diene monomer rubber EPDM as elastomeric matrix and strontium ferrite as magnetic filler. The mixed peroxide and sulfur curing systems were applied for cross-linking of rubber compounds. The research was aimed at the evaluation of the type of curing system on curing process of rubber compounds. Then, the influence of the observed parameter on cross-link density and physical-mechanical properties of prepared composites was investigated. The influence of thermo-oxidative ageing on the properties of tested composite materials was also under consideration. The achieved results showed that tensile strength was not dependent on the type of curing system, while cross-link density and physical-mechanical properties were changed in dependence on mutual ratio of sulfur and peroxide in the applied curing systems. Ferrite seems to act as a reinforcing filler in composites cured mainly with peroxide system, in which co-agent contributes to the improvement of compatibility and adhesion on the phase interface filler-rubber. The thermo-oxidative stability of composites was also found to be influenced by the curing system composition.

Influence of thermooxidative aging on the static and dynamic mechanical properties of long‐glass‐fiber‐reinforced polyamide 6 composites

ABSTRACTThe static and dynamic mechanical properties, thermal behaviors, and morphology of pure long‐glass‐fiber‐reinforced samples [polyamide 6 (PA6)/long glass fiber (LGF)] with different thermal exposure times at 160°C were studied by comparison with stabilized samples in this study. The aging mechanism of the PA6/LGF samples under heat and oxygen was studied with the methods of thermal Fourier transform infrared (FTIR), differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy (SEM), and so on. The results indicate that the static mechanical strength, melting temperature, and crystallization temperature decreased because of the decomposition of the macromolecular chain of PA6 resin and the debonding of the interface between the glass fibers and matrix. The glass‐transition temperature and crystallinity also increased and decreased, respectively, after aging. The macromolecular chain decomposition dominated in the subsequent aging process; this resulted in many sharp and brittle microcracks appearing on the surfaces of the aged samples, as shown by SEM and the FTIR spectra. The existence of stabilizers endowed the PA6/LGF composites with better retention of static and dynamic mechanical properties. The reason was that the metal ions of the copper salt antioxidant acted as an anti‐aging catalyst in the reinforced PA6 system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39594.

Influence of thermo-oxidative aging on chemical composition and physical properties of polymer modified bitumens

This paper presents some experimental results on property changes due to thermo-oxidative aging of bitumen modified by styrene–butadiene–styrene (SBS) and ethylene vinyl acetate (EVA) copolymer incorporated at various concentrations, i.e. 3, 5 and 7 wt.%. The chemical compositions, the properties and the morphology of the samples have been determined and characterized using SARA (saturates, aromatics, resins and asphaltenes) analysis, conventional test methods and optical microscopy, respectively. The study reveals that polymer modification globally improves the conventional properties of the base bitumen as evidenced by a decrease in penetrability, an increase in softening point and a reduction in temperature susceptibility inducing a rubbery elastic behavior to the base bitumen. This effect is dependent on both the type and the content of polymer used. Moreover, samples prepared with SBS show better improvement as compared with EVA modified bitumens. The morphological analysis shows that there is a clear difference between the SBS and EVA modified bitumens. For 3 wt.% SBS modified bitumens, the polymer phase is homogenously dispersed in a continuous bituminous matrix consisting of polymer particles swollen by the solvating phase of the bitumen. In the case of EVA modified bitumen with the same polymer content, much finer dispersion of EVA particles is observed. After thermo-oxidative aging, the results clearly indicate a hardening of samples, being more pronounced for the base bitumen and those modified with EVA. For all samples, aging reduces the content of aromatics and at the same time increases the contents of resins and asphaltenes, while changes in the content of saturates are almost negligible. These structural modifications may result from oxidation of the bitumen and some chemical interactions with the polymers.

Rheological and mechanical properties of dynamically cured poly(vinyl chloride)/nitrile butadiene rubber thermoplastic elastomers

AbstractPlasticized poly(vinyl chloride)/nitrile butadiene rubber (PVC/NBR) thermoplastic elastomers (TPEs) were dynamically cured in the melt stage with the incorporation of a semi‐efficient curing system using a Brabender Plasticorder at 150 °C and rotor speed of 50 rev min−1. Sulfur concentration was progressively increased from zero to 1 part per hundred NBR to study the effect of dynamic curing on mechanical and rheological behaviour of the TPEs. The compounds were characterized in respect of their rheological and mechanical properties. The effectiveness of dynamic curing was studied using Brabender plastograms, a moving disc rheometer and swelling index measurement. The mechanical properties investigated include tensile strength, elongation at break, modulus at 100% elongation, tear strength and hardness. The influence of thermooxidative ageing on the mechanical properties was investigated by incubating the PVC/NBR TPEs in an air oven at 80 °C for 168 h. The torque values obtained from both rheometers increased with increasing sulfur dosage, while the swelling index decreased. The significant increase in the degree of curing evidenced by the steady reduction in the swelling index provided excellent proof of the efficiency of the dynamic curing technique. Thermo‐oxidative ageing resulted in a pronounced enhancement in mechanical properties as a function of sulfur content. This observation seems to indicate that some microstructural changes, such as the formation of new crosslinks, occur in the thermo‐oxidatively aged TPEs. This trend was supported by further reduction in the swelling index of the aged TPEs.© 2003 Society of Chemical Industry