Effect Of Thermo-oxidative Aging Research Articles

Effect of Thermal-Oxidative Aging on the Mechanical Properties of Carbon Fiber Reinforced <i>Bis</i>-Maleimide Composites

Bis-maleimide (BMI) resins are widely applied in carbon fiber reinforced polymer composites in aerospace fields, for their excellent thermal and mechanical properties. The effects of thermo-oxidative aging on mechanical properties of carbon fiber reinforced BMI composites were investigated by SEM with the combination of flexural strength test and inter-laminar shear strength (ILSS) test. The results indicated that the thermal-oxidative aging had some effects on mechanical properties of carbon fiber/BMI composites; however the testing temperature or service temperature had much more effects than aging time. With aging time increased, the flexural strength at 150 oC and the ILSS at 25 oC slightly increased, while the ILSS at 150 oC decreased gradually. Both test results of mechanical properties and fracture models of damaged flexural specimens by SEM indicated that the matrix resin in the composites showed some viscoelastic behaviors that resulted in the remarkable dependence of mechanical properties of the composites on temperature. Therefore, the carbon fiber reinforced BMI composites had lower flexural strength and ILSS at 150 oC than that at 25 oC.

Effect of organo-montmorillonite on aging properties of asphalt

Effects of organo-montmorillonite (OMMT) on thermo-oxidative and ultraviolet (UV) aging properties of asphalt were investigated. The results show that the viscosity aging index (VAI) and softening point increment (Δ S) of OMMT modified asphalt decrease significantly due to introduction of OMMT, and the ductility retention rate of the modified asphalt is also evidently higher than that of the pristine asphalt after thin-film oven test (TFOT) and pressure aging vessel (PAV) aging. In the meantime, both VAI and Δ S of the modified asphalt are obviously lower than that of the pristine asphalt after UV aging. Furthermore, compared with the pristine asphalt, the results of dynamic shear rheometer (DSR) testing exhibit smaller changes in rut factor ( G*/sin δ) after TFOT and lower fatigue factor ( G*sin δ) after PAV for the modified asphalt, which suggests that the effect of thermo-oxidative aging on dynamic rheological behaviors of the modified asphalt is restrained due to introduction of OMMT.

The Effect of Prolonged Thermo-oxidative Ageing on the Mechanical Properties of Dynamically Vulcanized Poly(Vinyl Chloride)/Nitrile Butadiene Rubber Thermoplastic Elastomers

ABSTRACT Plasticized poly(vinyl chloride)/nitrile butadiene rubber (PVC/NBR) thermoplastic elastomers (TPEs) were dynamically vulcanized in the melt stage with the incorporation of a semi-efficient vulcanizing system using a Brabender Plasticorder at 150°C and 50 rpm rotor speed. Curative concentration was progressively increased from 0 to 1 part per hundred (phr) NBR in order to study the effect of dynamic curing on the plasticized blend. The mechanical properties investigated include tensile strength, elongation at break (%EB), modulus at 100% elongation (M100), tear strength, and hardness. The effect of thermo-oxidative ageing (TOA) on the mechanical properties was investigated by exposing the PVC/NBR TPEs in an air oven at 100°C for 3, 7, 14, and 21 days. It was found that tensile and tear strength passed through a maximum value, whereas, hardness and M100 increased steadily with the sulfur content and ageing time. On the contrary, the elongation at break reduced gradually with ageing time until it reaches a minimum value. The increase in crosslink density as well as the steady reduction in swelling index with increasing concentration of curatives provided an excellent evidence for the significant increase in crosslink density with ageing time. The changes in physical and mechanical properties of the TPEs is believed to be closely related to some microstructural changes taking place as a result of the formation of new crosslinks due to prolonged thermo-oxidative environment.

Partial Replacement of Silica by Rice Husk Powder in Polystyrene–Styrene Butadiene Rubber Blends

The effects of partial replacement of silica by rice husk powder on the processing, mechanical properties, effect of thermo-oxidative aging, water absorption and morphology of polystyrene (PS)–styrene butadiene rubber (SBR) blend were investigated. The composites were prepared in a Brabender Plasticorder PLE 331 with rotor speed of 50 rpm at 170 C for 10 min. Rice husk powder was hybridized with silica in order to achieve superior mechanical performance. Hybrid composites of silica and rice husk powder show that, with an increase in weight ratio of silica in the hybrid filler composites of PS–SBR, the tensile strength, Young’s modulus and impact strength increased up to a certain level and there was no significant difference in elongation at break. Effect of thermo-oxidative aging and water absorption also reduced with the increase in silica weight ratio. From SEM analysis it shows that increase in the silica loading in the hybrid filler causes smaller agglomerate sizes and better distribution in the composite. This also led to improve the properties of the composite apart from the reinforcement comfort by silica.

Rice husk powder–filled polystyrene/styrene butadiene rubber blends

AbstractNatural fibers are rich in cellulose and they are a cheap, easily renewable source of fibers with the potential for polymer reinforcement. The presence of large amounts of hydroxyl groups makes natural fibers less attractive for reinforcement of polymeric materials. Composites made from polystyrene (PS)/styrene butadiene rubber (SBR) blend and treated rice husk powder (RHP) were prepared. The RHP was treated by esterification and acetylation. A similar series of composites was also prepared using maleic anhydride–polypropylene (MA–PP) as a coupling agent. The processing behavior, mechanical properties, effect of thermooxidative ageing, and surface morphology of untreated and chemically modified RHP were studied. There was a decrease in tensile strength (except MA–PP composites), elongation at break, and Young's modulus in chemically treated RHP composites. The postreaction process during thermooxidative ageing enhanced the tensile strength and Young's modulus of the esterified and MA–PP composites. Acetylation treatment was effective in reducing the percentage of water absorption in RHP/PS–SBR composites. In general chemically treated RHP/PS–SBR composites and MA–PP showed a better matrix phase and filler distribution. However, the degree of filler–matrix interaction was mainly responsible for the improvement of mechanical properties in the composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3320–3332, 2004

A Comparative Study on Processing, Mechanical Properties, Thermo-oxidative Aging, Water Absorption, and Morphology of Rice Husk Powder and Silica Fillers in Polystyrene/Styrene Butadiene Rubber Blends

Rice husk powder (RHP) and silica-filled polystyrene (PS)/styrene butadiene rubber (SBR) composites were prepared by using the laboratory size internal mixer (Brabender Plasti-corder). The torque development, morphology, and mechanical properties such as tensile strength, elongation at break, Young modulus, and impact strength were studied. Water absorption and the effect of thermo-oxidative aging on tensile properties of composites were also examined. Filler loading and filler type influence the processibility of the composites in which RHP offers better processing advantage over silica. Tensile strength reduces with increasing filler loading for both RHP and silica composites. However, at 15 wt% the fillers act as reinforced materials to the composites. Young modulus also increases with increasing filler loading, whereas elongation at break shows no significant changes. Aging test results show that the tensile strength and elongation at break decrease and Young modulus increases with aging for RHP composites. However, for silica composites, there were no significant changes in Young modulus and elongation at break except reduction of tensile strength. The water uptake in RHP composites is higher than silica composites. Scanning electron microscopy on fracture surface shows poor filler matrix adhesion with the increasing of filler loading in the composite. This explains the reduction of tensile strength before and after aging with increasing filler loading.

Thermo-oxidative aging and fatigue behavior of dynamically vulcanized PVC/ENR thermoplastic elastomers

Dynamically vulcanized poly(vinyl chloride)/epoxidized natural rubber (PVC/ENR) thermoplastic elastomers (TPEs) were prepared following a semi-efficient vulcanization system (semi-EV) with the incorporation of di-ethylhexyl phthalate (DOP) as a plasticizer. The PVC/ENR TPEs were melt mixed at 150°C and 50 rpm using a Brabender Plasticorder. The effect of dynamic curing on the fatigue behavior of the PVC/ENR TPEs was investigated. The properties investigated include fatigue life, stress - strain behavior, strain energy, morphology, and the effect of hysteresis. The unaged samples showed that as the sulfur concentration increases the fatigue life increases which could be related to the increase in cross-link density as indicated from the swelling index data. The increase in cross-link density increases the resistance of these materials against external dynamic stress. Hysteresis study revealed that samples with higher sulfur concentration are less sensitive towards changes in strain energy. As a result they exhibited lower heat build-up and consequently higher fatigue life. The effect of thermo-oxidative aging (TOA) on the fatigue behavior was investigated by exposing the PVC/ENR TPEs in an air oven at 80°C for 168 hours. It was found that all the properties studied decreased after thermo-oxidative aging process. This suggests that some micro-structural changes such as the formation of new cross-links due to post curing has taken place. This accounts for the reduced fatigue life and resilience while hysteresis, modulus, and hardness increased.

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.

The effects of thermooxidative aging on the fatigue behavior of a structural adhesive

The kinetics of autoxidation of FM-73U, a rubber-modified epoxy adhesive, were investigated by Fourier transform infrared analysis. Absorbance spectra for thin samples aged in hot, moist, oxygen-rich environments were used to assess a plausible reaction mechanism; rate constants, Arrhenius plots, and oxidation rates were determined. Concurrently, crack growth rates were measured on specimens which had been exposed to similar environments for periods of up to 8 months. Paris parameters measured in these tests were correlated with the results of the oxidation studies. These correlations were used to predict the crack growth rate of the adhesive after 10 years of aging in ambient conditions. Although the prediction indicates that the adhesive becomes more brittle with age, the changes are not severe.