Effects of Mechanical Activation Methods on Thermo-oxidation Behaviors of Pyrite

To explore the effects of mechanical activation methods(ball mill, planetary mill and rod mill) on the oxidation and the spontaneous combustion of pyrite, the kinetic curves of non-activated pyrite and mechanically activated pyrite were created by simultaneous thermal analysis. The structural characteristics and changes of mechanically activated pyrite were investigated by X-ray diffraction and SEM, and the relationship between the mean diameter and the grinding time was obtained by using a laser particle size analyzer. The kinetic model of pyrite and the kinetic parameters were deduced using Bagchi method. The relationship between the kinetic parameters indicates that, pyrite activated by ball milling shows the best thermal stability at the same diameter. By comparing and analyzing the X-ray diffraction patterns, results show that different mechanical activation ways played different roles in structural changes of pyrite.

Effect of thermo-oxidation on the dynamical and physical properties of ethylene-propylene-diene monomer elastomer

Understanding the underlying processes associated with the thermo-oxidative performance of the ethylenepropylene-diene monomer(EPDM)is essential for assessing and improving its waterproofing performance in underground infrastructures.To explore the fundamentals of EPDM degradation behavior during thermal oxidation,this paper investigates the effects of hydrocarbon free chain,carbon crosslink,chain scission,hydroxyl,and ether crosslinks,on its kinetics and mechanical properties through molecular dynamics(MD)simulations.Several EPDM thermo-oxidative models were built and verified by comparing the simulation results of oxygen diffusivity,glass transition temperature,and mechanical properties with reported experimental ones.Then the radius of gyration,free volume,density,transport,glass transition,and uniaxial compression performance were investigated via MD simulations.The results show that crosslinking in the thermal oxidation process has a significant influence on the free volume,glass transition temperature,and mechanical properties of the system;the hydroxyl and chain scission mainly interfere with the transport properties;all of these affect the structural conformation.

Thermal and Thermo-oxidative Degradation of Flame Retardant High Impact Polystyrene with Triphenyl Phosphate and Novolac Epoxy Resin

Thermal and thermo-oxidative decomposition and decomposition kinetics of flame retardant high impact polystyrene （HIPS） with triphenyl phosphate （TPP） and novolac type epoxy resin （NE） were characterized using thermo-gravimetric experiment. And the flammability was determined by limited oxygen indices （LOI）. The LOI results show that TPP and NE had a good synthetic effect on the flame retardancy of HIPS. Compared with pure HIPS, the LOI values of HIPS/NE and HIPS/TPP only increased by about 5%, and the LOI value of HIPS/TPP/NE reached 42.3%, nearly 23% above that of HIPS. All materials showed one main decomposition step, as radical HIPS scission predominated during anaerobic decomposition. TPP increased the activity energy effectively while NE affected the thermal-oxidative degradation more with the help of the char formation. With both TPP and NE, the materials could have a comparable good result of both thermal and thermal-oxidative degradation, which could contribute to their effect on the flame retardancy.

The Accelerated Thermo-Oxidative Aging Characteristics of Wood Fiber/Polycaprolactone Composite:Effect of Temperature,Humidity and Time

This study investigated the characteristics of wood fiber/polycaprolactone composite after an artificial accelerated thermo-oxidative aging treatment.The effect of time,temperature and humidity during the treatment on their mechanical,chemical and morphology properties were evaluated.The composite was prepared from melted wood fibers and modified polycaprolactone by a molding process.A temperature and humidity controllable test chamber was used for the thermo-oxidative aging of the composite.The thermo-oxidative aging caused surface of the composite to be much more rougher and even a few cracks and holes appeared on it.According to the spectra of Fourier Transform Infrared(FTIR)and Gel Permeation Chromatography(GPC),C=O in the molecular chain of polycaprolactone was hydrolyzed and C–O was broken after the aging treatment,which resulted in a reduction in average molecular weight of the composite.Moreover,results showed that the mechanical strength decreased a lot with the increase in time,temperature and humidity,and the effect of temperature and humidity was more significant compared with that of time.Controlling the temperature and humidity during thermo-oxidative aging treatment could accelerate the aging of composite,which provided a quick and effective method for evaluating the aging resistance of the composite.

Effect of Residual Maleic Anhydride in PP-g-MAH on the Thermo-Oxidative Aging Properties of RGF-PP

The mechanical, morphological and thermo-oxidative aging properties of the glass fiber reinforced polypropylene (RGF-PP) were studied based on four different maleic anhydride grafted polypropylene (PP-g-MAH) compatibilizers with different content of residual maleic anhydride (MAH). It was shown that PP-g-MAH compatibilizer could significantly improve the mechanical properties of RGF-PP, while from thermal and morphological analysis results, the content of residual MAH had negative influence on long term thermo- oxidative aging properties of RGF-PP with adding PP-g-MAH compatibilizer;the lower the residual content of MAH is, the better the thermo stability of the PP-g-MAH is, and also the better the thermo-oxidative aging properties was obtained.

High-temperature Thermo-oxidative Aging of Vulcanized Natural Rubber Nanocomposites:Evolution of Microstructure and Mechanical Properties

The aging of natural rubber(NR)at high temperatures will seriously affect its service lifetime in many key applications.In the present work,the changes in microstructure and mechanical properties of semi-efficient vulcanized NR/carbon black(CB)vulcanizates during thermooxidative aging at high temperatures(150-200℃)and a moderate temperature(95℃)were compared.At high temperatures,a two-stage aging behavior,which was characteristic of a first rapid decline and then a continuous rise in the crosslinking density(ve),was identified and was found to be closely related to the depletion behavior of antioxidants.The surface cracking behavior observed in the second stage of high-temperature aging was discussed in terms of the grafting reaction of macromolecular radicals on CB particles and thermal expansion.In contrast,the aging of NR at moderate temperatures was much mild,which featured a continuous increase in ve and an oxidation mechanism dominated by peroxy radicals attacking double bonds.In general,the mechanical properties of NR vulcanizates during high-temperature aging depended on the competition effects of structural evolution in the crosslinked network and oxidation-induced chain scission.

Thermo-oxidative ageing behavior of cerium oxide/silicone rubber

Cerium oxide/silicon rubber was prepared via mechanical blending.Mechanical and frictional properties,as well as thermal stability after thermo-oxidative ageing were investigated in this rubber composite.3D surface profilometry,scanning electron microscopy(SEM)and thermogravimetry analysis(TGA)were used to study the friction surface characteristics,friction mechanism and thermal stability,respectively.Additionally,swelling experiments were carried out to investigate the variation of crosslinking density.After thermo-oxidative ageing,the tear strength of cerium oxide/silicon rubber decreases.However,in the early ageing stage,improvements in tensile strength,elongation at break,and frictional performance are caused by crosslinking density increments.Moreover,the addition of cerium oxide remarkably improves the re-cross linking degree during ageing process,which in turn decreases the number of holes on the friction surface and endows the silicon rubber with better mechanical and frictional properties,as well as thermo-oxidative ageing resistance.

Detection of the Destruction Mechanism of Perfluorinated Elastomer(FFKM)Network under Thermo-oxidative Aging Conditions

The changes of crosslinking network of perfluorinated elastomer(FFKM)cured by TAIC and DBPH under thermo-oxidative aging conditions were investigated.Two competitive processes including post-curing and network destruction occur simultaneously,which directly affect the storage modulus and crosslinking density.With the increase of aging temperature,the network destruction becomes dominant.FTIR and XPS characterizations further reveal that the network destruction happens preferentially on the crosslink points of TAIC structure,and the post-curing is mainly caused by the decomposition of residual curing agent DBPH.Unlike the easier breaking of TAIC structure in the crosslinking network,both the backbone and the pendent groups of FFKM itself are much more stable.To further figure out the destruction mechanism,TGAFTIR-GC-MS test was also conducted and a schematic degradation process of TAIC structure was proposed.It is found that the destruction of TAIC crosslinking points happens first on the unstable exocyclic C―N bonds and the intermediate ring radicals could eventually decompose into volatile hydrogen isocyanate(HCNO)under extreme condition.

Long-term Thermo-oxidative Degradation Modeling of a Carbon Fiber Reinforced Polyimide Composite:Multistep Degradation Behaviors and Kinetics

This study aims to disclose the thermo-oxidative degradation behaviors and kinetics of a carbon fiber reinforced polyimide(CFRPI)composite for modeling of the Iong-term degradation process.The degradation behaviors were revealed through off-gas products analysis,and the overall kinetic interpretation was achieved from study of the mass-loss curves recorded under dynamic conditions.It was found that thermooxidative degradati on of the CFRPI composite was a multistep process,which in eluded four main reaction steps.Since most kinetic an alysis methods were derived from simple reactions described by a single kinetic triplet,they cannot be applied reliably to such a process.Therefore,we firstly separated the four overlapped reaction steps by peak fitting of derivative thermogravimetric curves using Fraser-Suzuki equation consider!ng the asymmetrical n ature of kin etic curves,and subsequently an a lyzed each in dividual reaction employing Friedma n method and experimental master-plots method.Four sets of kinetic triplets were determined to characterize the entire degradation process.The validity of four corresponding kinetic triplets was confirmed by perfect simulation of mass-loss curves recorded at both dynamic conditions used in kinetic analysis and entirely different isothermal conditions.Finally,modeling of Iong-term aging at 400°C of the CFRPI composite was successfully achieved based on these kinetic triplets.The predicted mass loss and flexural property correlated well with experimental results.This study can serve as a basis for rapid evaluation of the long-term durability of the CFRPI composite in various application environments.

Thermo-oxidative degradation of Nylon 1010 films:Colorimetric evaluation and its correlation with material properties

The thermo-oxidative aging behaviors of Nylon 1010 films were studied by various analytical methods,such as measuring the chromaticity,relative viscosity,carbonyl index,UV absorbance at 280 nm and elongation at break of the aged films.The thermo-oxidative aging plots of the results obtained via these various methods at different temperatures are subjected to the time-temperature superposition analysis,which are found to be well superposed.The b＊ values are used as X axis and the other results,i.e.,relative viscosity,carbonyl index,UV absorbance at 280 nm and elongation at break,are used as V axis,respectively.The relationship between the b values and the other results is obtained,from which we can derive the changes of physical and chemical properties at different b＊ values.Since the b＊ values can be quickly determined by using a portable spectrophotometer,the on-line evaluation of the thermo-oxidative aging of Nylon 1010 can be realized.

Accelerated Ageing Tests for Evaluations of a Durability Performance of Glass-fiber Reinforcement Polyester Composites

The paper presented accelerated ageing test results of a durability study on ortho-phthalic anhydride-type unsaturated polyester resin （191#） and its glass-fiber reinforcement polyester composites （GFRPC）. The samples were exposed in an artificial xenon arc lamp ageing cell or a thermo-oxidative ageing cell. Morphology and gloss of the specimens were investigated by using a microscope and a gloss-meter, respectively. The tensile strength, bending strength and inter-laminar shear strength （ILSS） of GFRPC were tested before and after exposure, and were considered to evaluate the durability performance of this material. The polyester resin was analyzed by fourier transform infrared （FT-IR） spectroscopy. The results showed that the glossiness of the specimens got worse and some cracks appeared on their surface during the course of ageing, the tensile strength and bending strengths of the specimens first increased and then decreased. The ILSS of the composites decreased after they were aged in the xenon arc lamp cell, but increased while they were aged in the thermo-oxidative cell. The changes of these trends become more obvious during ageing in the xenon arc lamp cell, so the main influencing factor leading to the failure of this material is UV irradiation.

Thermal degradation of epoxidized natural rubber in presence of neodymium stearate

The effect of neodymium stearate （NdSt） synthesized by saponification method on thermal degradation and thermo-oxidative degradation of expoxidized natural rubber with 25 mol.% epoxidation （ENR25） was investigated by thermogravimetric analysis （TGA）, and the structure of ENR25 vulcanized with NdSt after thermo-oxidative decomposition was characterized using Fourier transform infared spectroscopy-attenuated total-reflectance （FTIR-ATR）. The thermal degradation kinetic parameters of ENR25 with different loadings of NdSt were determined by Coats-Redfern method. The results showed that the thermal degradation of ENR25 in nitrogen was a one-step reaction regardless of NdSt content, whereas the thermo-oxidative degradation was a multiple-step reaction. The thermal and thermo-oxidative stability of the ENR25 vulcanizates with the addition of NdSt was higher than that of pure ENR25 vulcanizates. The ENR25 vulcanizates with the incorporation of 1 phr （per hundred parts of rubber） NdSt imparted the highest activa- tion energy （E） of thermal and thermo-oxidative degradation. This could be attributed to the many unoccupied orbits in rare earth Nd, which could capture the free radicals and make the epoxide groups stable in the process of thermal and thermo-oxidative degradation for ENR25.