Surface molecular degradation of 3D glass polymer composite under low earth orbit simulated space environment

Epoxy resin reinforced with 3D parabeam glass fibre was subjected to low earth orbit (LEO) simulation conditions comprising ultra high vacuum, temperature cycling (TC), and ultraviolet (UV) radiation and atomic oxygen (AO) bombardment. Inspection of the same composite using only a selection of these hazardous conditions provided comparison measures to identify the effect of each condition on the surface degradation of the resin composite. Each of the individually selected conditions showed a different degradation mechanism that is accelerated by the presence of other conditions. X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM) were used to provide surface information. The resin composite samples suffered surface oxidation that increased the oxygen content to 17.24% in comparison with the untreated sample (only 14.2%). The samples that were treated with AO showed higher C-O and CO functional groups on the surface in comparison with the rest of the samples (as indicated by XPS). Molecular information (from ToF-SIMS) showed that surface oxidation differs with different conditions and in comparison with the use of all conditions. All treated samples were shown to suffer significant chain scission and loss of volatiles as a result of the LEO conditions. The extent of the chain scission reaction for each condition can be indicated by the extent of the reduction of the relative concentration of the aliphatic hydrocarbon ions. The relative intensity of the C₄H₁₁N₄O₂⁺ ion showed that AO bombardment accelerated the oxidation of the surface. The AO effect is doubled when UV and TC are also present. SEM results indicated that sample surfaces were eroded and roughened upon exposure to LEO conditions. Presence of AO and UV in the LEO conditions introduced white deposits onto the surface, believed to be crosslinked formations.     

Impact resistance of hybrid glass fiber reinforced epoxy/nanoclay composite

The effect of nanoclay addition in Glass Fiber Reinforced Epoxy (GFRE) composites on impact response was studied. The epoxy nanocomposite matrix with 1.5 and 3.0 wt% loading of I.30E nanoclay was produced by high shear mixing. Hybrid GFRE nanoclay composite plates were manufactured by hand layup and hot pressing techniques using electrical grade-corrosion resistant (E-CR) glass fiber mats. The laminates were then subjected to low-velocity impact with energies between 10 and 50 J. Addition of nanoclay was found to improve peak load and stiffness of GFRE. Nanoclay loading of 1.5 wt% resulted in optimum properties, with 23% improvement in peak load and 11% increase in stiffness. A significant reduction in physical damage was also observed for hybrid nanocomposite samples as compared to GFRE. This was mainly attributed to transition in damage mechanism due to nanoclay addition. Clay agglomeration in samples with 3.0 wt% loading contributed towards limiting the improvement in impact resistance.     

Sliding Wear Behavior of Nanoclay Filled Polypropylene/Ultra High Molecular Weight Polyethylene/Carbon Short Fiber Nanocomposites

In the present investigation, authors made an attempt to study the sliding wear behavior of polypropylene/ultrahigh molecular weight polyethylene (PP/UHMWPE, 90/10) blends loaded with 30% carbon short fibers (CSF) as reinforcement and nanoclay as filler material. The nanocomposites have been prepared with varying amounts viz., 0, 1, 2 and 3 wt% of nanoclay. The composites were prepared by melt mixing at 60 rpm extruder speed and compression moulding at 180°C. From all the composites, 6 mm diameter and 25 mm length sliding wear specimens were prepared. Sliding wear loss, specific wear rate and coefficient of friction were investigated by using computerized pin-on–disc machine at normal applied loads of 20, 30 and 40 N; at a sliding velocity of 1.5 m/s and at two abrading distances viz., 200 and 300 m. The wear behavior data reveals that 3 wt% nanoclay filled composite exhibits higher wear resistance and lowest specific wear rate as compared to other nanocomposites. Also morphological study was carried out for wear out surfaces of all the composites using scanning electron microscopy (SEM).     

Glass Fiber Reinforced Polymer-Clay Nanocomposites: Processing,Structure and Hygrothermal Effects on Mechanical Properties

Polymer composites have been the mainstay of high-performance structural materials, but these materials are inherently sensitive to environmental factors such as temperature, exposure to liquids, gases, electrical fields and radiation, which significantly affects their useful life. Addition of layered silicate nanofillers in the polymer matrix has led to improvements in the elastic moduli, strength, heat resistance, decreased gas permeability and flammability. In the present work epoxy modified with Cloisite 30 B̈ nanoclay (at 1, 3 and 5 wt% of resin) and E-glass unidirectional fibers are used to prepare fiber reinforced nanocomposites using hand lay-up method. The nanocomposites have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results show that the interlayer spacing between the clay platelets increased significantly indicating that the polymer is able to intercalate between the clay layers. The mechanical properties are measured by carrying out tensile, hardness and flexural tests and values are compared with those found for fiber reinforced neat epoxy composites. The tests show that an addition of nano-clay up to 3 wt% increases tensile strength and micro-hardness and there is a decrease in values with further clay addition up to 5 wt%. The flexural strength increased significantly with clay loading and the highest value is observed for specimens with 5 wt% of clay. Further, durability studies on nanocomposites have been performed in water and NaOH baths under accelerated hygrothermal conditions. During the exposure it is observed that the degradation in NaOH environment is more severe than in water.     

Preparation and properties characterization of gallic acid epoxy resin/succinic anhydride bionanocomposites modified by green reduced graphene oxide

Graphene oxide was reduced into reducing-graphene oxide (r-GO) successfully using gallic acid (GA) as a green reducing agent. Biobased gallic acid epoxy resin (GAER) was synthesized from renewable GA, and the biobased GAER/r-GO nanocomposites and glass fiber-reinforced composites were prepared with succinic anhydride as a curing agent. The dynamic mechanical, thermal, and mechanical properties of the composites with varying r-GO contents were characterized. When the content of r-GO was 0.5 wt%, the glass transition temperature was 10.4°C higher than the pure resin system. The thermal and mechanical properties were increased with increasing r-GO content; when the r-GO content was 1.0 wt%, the initial degradation temperature was enhanced by approximately 6.8°C, the tensile and impact strengths were 34.5% and 49.1% higher, respectively, than the pure cured GAER. The impact strength of GAER was higher than that of the bisphenol A epoxy resin/SUA curing system, but the tensile strength was lower than it.     

Surface molecular degradation of selected high performance polymer composites under low earth orbit environmental conditions

Carbon fibre (CF), carbon nanotube (CNT), nano-clay (NanoC), and 3D-glass (3DG) reinforced polymer composites were selected to undergo treatment with an accelerated Low Earth Orbit (LEO) simulated space environment. Surface degradation mechanisms of the selected polymer composites with different types of reinforcements are discussed. The extent of the oxidation reaction at the surface as a result of LEO exposure was linked to the increase in the intensity of the oxygen-containing ions, as revealed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). X-ray photoelectron spectroscopy (XPS) indicated that an increasing duration of surface treatment correlates with increasing oxygen concentration and decreasing carbon concentration. The degraded CF composite showed the least amount of oxygen (15.6%) and nitrogen (2.5%) on the surface, likely indicating less surface degradation. Further, XPS high resolution region scans showed decreases in the overall carbon concentration accompanied increases in oxygen-containing carbon species C-O, CO and O-CO; functional groups which are attributed to the LEO treatment of the composite materials. All the sample surfaces were eroded upon exposure to LEO conditions with erosion mostly confined to encapsulating epoxy resin.     

X-ray diffraction and X-ray photoelectron spectroscopy studies of Ni-P deposited onto carbon fiber surfaces: impact properties of a carbon-fiber-reinforced matrix

In this work, the Ni-P coating on carbon fiber surfaces was carried out in order to improve the impact resistance of carbon fibers-reinforced epoxy matrix composites. The fiber surfaces and the fracture behaviors of composites were measured in terms of X-ray diffraction spectrometry (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), and falling weight impact testing. From the XRD and XPS measurements, it was observed that Ni-P coating of carbon fibers led to an increase in two phases, i.e., microcrystalline and amorphous, mainly due to the increase of NiP(2), Ni(3)P, and Ni metal. Energy adsorbed by composites through the various fracture mechanisms was seen to be the characteristic distinguishing between nontreated and treated fiber-reinforced composite systems. The Ni-P alloy technique to improve the impact resistance of the composites was shown to be the modification of fiber-epoxy resin interfaces.     

Interlaminar and ductile characteristics of carbon fibers-reinforced plastics produced by nanoscaled electroless nickel plating on carbon fiber surfaces

In this work, a new method based on nanoscaled Ni-P alloy coating on carbon fiber surfaces is proposed for the improvement of interfacial properties between fibers and epoxy matrix in a composite system. Fiber surfaces and the mechanical interfacial properties of composites were characterized by atomic absorption spectrophotometer (AAS), scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), interlaminar shear strength (ILSS), and impact strength. Experimental results showed that the O(1s)/C(1s) ratio or Ni and P amounts had been increased as the electroless nickel plating proceeded; the ILSS had also been slightly improved. The impact properties were significantly improved in the presence of Ni-P alloy on carbon fiber surfaces, increasing the ductility of the composites. This was probably due to the effect of substituted Ni-P alloy, leading to an increase of the resistance to the deformation and the crack initiation of the epoxy system.     

Investigation of degradation mechanisms in mechanical properties of polyimide films exposed to a low earth orbit environment

The degradation of the mechanical properties of polyimide films was evaluated by means of tensile tests after exposure to a low earth orbit (LEO) environment. Polyimide films irradiated with atomic oxygen (AO), ultraviolet (UV) light, and electron beam (EB) rays using ground simulation facilities were also evaluated similarly and compared. In these experiments tensile stress (7.0 MPa or less) was applied to the samples in order to assess its effects on mechanical properties. The mechanical properties of the flight samples decreased concomitantly with increased exposure duration. The fracture surfaces exhibited characteristic radiated patterns initiating from the exposed surfaces which showed a rough texture. In the AO-irradiated samples the mechanical properties degraded and the surface texture developed as the AO fluence increased; similar fracture surfaces appeared in the flight samples. In contrast, UV and EB irradiation had little impact on mechanical properties. Based on these results, the eroded surfaces by AO irradiation served as the starting points of the rupture, resulting in degradation of mechanical properties of polyimide films exposed to a LEO environment. The tensile stress states induced no difference in evaluations.     

Mechanical, thermal, and moisture absorption properties of nano-clay reinforced nano-cellulose biocomposites

In this research, fully environment-friendly, sustainable and biodegradable ‘green’ composites were fabricated. A novel material comprised of microfibrillated cellulose and laponite clay with different inorganic/organic ratios (m/m) was prepared. The composites were characterized by tensile, bending and water absorption tests as well as dynamic mechanical analysis. The morphologies of these nanocomposites were evaluated through scanning electron microscopy. Results showed considerable improvement of mechanical properties; specifically in elastic modulus, tensile strength and flexural modulus with the addition of nanoclay up to 7.5 wt% nano-clay. The modulus of elasticity increased significantly by about 26 % at 5 wt% nanocaly. The flexural modulus increased by about 90 % at 7.5 wt% nanoclay. However, with an increased load of clay in the nanocomposite, the mechanical properties decreased due to the agglomeration of excessive nanoclay. The storage modulus was significantly increased at high temperature with increasing the load of nanoclay.     

Structural and tribological properties of polytetrafluoroethylene composites in atomic oxygen environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of glass fiber (GF) and MoS₂ filled polytetrafluoroethylene (PTFE) composites were investigated in a ground‐based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 10¹⁵ cm^–2 s^–1. The structural changes were characterized by XPS and attenuated total‐reflection Fourier transform infrared spectroscopy, and the tribological changes were evaluated by friction and wear tests and SEM analysis of the worn surfaces. It was found that AO irradiation induced the degradation of PTFE molecular chains, and the primary erosion mechanism is collisionally induced rather than chemically induced. The addition of MoS₂ filler significantly increased the AO resistance of PTFE composites. Friction and wear tests indicated that GF and MoS₂ improved the tribological properties of materials before and after AO irradiation. Short GF and MoS₂ exhibited a good synergistic effect for improving the AO resistant and tribological properties of PTFE material. Copyright © 2012 John Wiley & Sons, Ltd.     

Environmental degradation of E‐glass/nanocomposite under the combined effect of UV radiation,moisture, and rain

This study seeks to investigate how the enhanced properties of the nanoclay E‐glass/epoxy composite can withstand the combined effects of ultraviolet radiation, moisture, and rain. The montmorillonite nanoclay's affinity to moisture compounded the moisture absorption ability of the nanoclay E‐glass/epoxy composites. The moisture in the polymer structure caused delamination, debonding of the fibers/matrix, microvoids, and fiber pullouts. The high clay content (2 wt %), therefore, recorded the highest rate of degradation of 15% in flexural stress for the first 20 days, compared to about 8 and 6% loss for the unmodified (0 wt %) and 1 wt % composites respectively. However, as the aging progressed beyond 20 days, the rate of degradation of the nanoclay E‐glass/epoxy composites laminates was steady at 10 and 18%, respectively, for the 1 and 2 wt %, while that of the unmodified polymer continued to degrade progressively. On the contrary, the viscoelastic properties of the nanoclay E‐glass/epoxy composites continued to deteriorate at a faster rate than the unmodified polymer composite. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1024–1029     

Effects of atomic oxygen irradiation on structural and tribological properties of polyimide/Al2O3 composites

To understand the effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polymer composites, polyimide/Al₂O₃ composites were irradiated with AO in a ground‐based simulation facility. The structural changes were characterized by X‐ray photoelectron spectroscopy and attenuated total‐reflection FTIR, whereas the tribological changes were evaluated by friction and wear tests as well as scanning electron microscopy analysis of the worn surfaces. It was found that AO irradiation induced the oxidation and degradation of polyimide molecular chains, which increased the O concentration and decreased the C concentration in the composite surfaces. The destruction action of AO changed the surface chemical structure and morphology of the samples. Friction and wear tests indicated that AO irradiation decreased the friction coefficient but increased the wear rate of both pure and Al₂O₃ filled polyimides. In terms of the tribological properties, appropriate content of Al₂O₃ might be favorable for the improvement of tribological properties in AO environment. Copyright © 2011 John Wiley & Sons, Ltd.     

The effect of the addition of talc on tribological properties of aramid fiber‐reinforced polyimide composites under high vacuum,ultraviolet or atomic oxygen environment

The aramid fibers‐reinforced polyimide composites filled with talc were fabricated by means of a hot press molding technique, and mechanical and tribological behaviors were comparatively investigated. Experimental results showed that the elastic modulus of the composites increased with an increase of the talc, but the impact intensity and loss factor decreased. Besides, the coefficient of friction decreased with the increase of the talc content. To contrast the effects of the ultrahigh vacuum (VC), ultraviolet (UV) or atomic oxygen (AO) on the composites, experiments without irradiation or after UV or AO irradiation were conducted. Scanning electron microscopy and X‐ray photoelectron spectroscopy (XPS) analysis showed that UV or AO irradiation can change the surface structure and chemical composition of the polymer because of the photooxidation and chemical erosion. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and properties of organo-fly ash/polyaniline with core/shell structure based on emulsion polymerization

Organo-fly ash(OFA) was prepared with pretreated fly ash(FA) and hexadecyltrimethyl ammonium bromide (HDTMAB),and the composites composed of OFA and polyaniline were obtained by emulsion polymerization at different OFA weight ratios(2.0 wt%,5.0 wt%,10.0 wt%,15.0 wt%and 20.0 wt%) in the presence of dodecylbenzenesulfonic acid as dopant and emulsifier.A polymerization procedure was supposed.The electrical conductivities of the composites were tested by the four-probe technique.The chemical structure and crystallinity of the composites were confirmed by FT-IR and X-ray diffraction,respectively.Morphologies of FA,OFA and the composites were observed by SEM.The element analysis was performed by energy dispersive spectrometry.The thermal stability of the composites was analyzed by TGA.The results showed that the electrical conductivity of the composites decreased with increasing the feed weight ratio of OFA,and the lowest value was 0.62 S/cm.HDTMAB and PAn were just adsorbed on the surface of FA and OFA,respectively according to the physical adsorption without destroying the crystalline structure of FA or OFA.The surface became smoother after organification of FA by using HDTMAB,and its content on FA surfaces was about 26.9 wt%.The core/shell structure of the composite was observed by SEM analysis.The composites showed a higher thermal stability than pure PAn by introduction of OFA into this polymerization system,the heat stability of PAn was increased by decreasing 31.8 wt%of weight loss after introducing 20 wt%of OFA.     

Improved mechanical properties of epoxy composites reinforced with surface‐treated UHMWPE fibers

The surface treatment of ultra‐high molecular weight polyethylene fiber using potassium permanganate and the mechanical properties of its epoxy composites were studied. After treatment, many changes were happened in the fiber surface: more O‐containing groups (―OH, ―C═O, and ―C―O groups), drastically decreased contact angles with water and ethylene glycol, slightly increased melting point and crystallinity, and formed cracks. Different contents (0.1–0.5 wt%) ultra‐high molecular weight polyethylene fibers/epoxy composites were prepared. The results indicated that the surface treatment decreased the tensile strength of epoxy composites, but increased the bending strength. When the fiber content was 0.3 wt%, the above properties reached the maximum. At the same fiber content, the interlaminar shear strength of the composites was increased by 26.6% up to the as‐received fiber composites. Dynamic mechanical analysis of the composites suggested the storage modulus and tanδ were decreased due to the surface treatment. Fractured surface analysis confirmed that the potassium permanganate treatment was effective in improving the interface interaction.     

Development and thermo‐mechanical behavior of nanocomposite epoxy adhesives

Two kinds of organo‐modified (OM) clays were dispersed in an epoxy resin for the preparation of nanocomposite adhesives at various filler amounts. XRD tests evidenced the formation of intercalated structures, increasing the intercalation degree with the clay hydrophilicity. The original transparency of the samples was retained up to a filler content of 3 wt%, and then decreased due to filler agglomeration. The glass transition temperature of nanocomposites filled with the more hydrophilic clay (30B) raised up to a filler content of 3 wt% and then decreased, probably because of the concurrent and contrasting effects of the physical chain blocking and reduction of the cross‐linking degree. Also elastic modulus, stress at break, and fracture toughness were sensibly improved by nanoclay addition up to filler loadings of 0.5–1 wt%. For higher concentrations the positive contribution of clay nanoplatelets was counterbalanced by the presence of agglomerated tactoids in the matrix. Mechanical tests on single‐lap composite (epoxy/glass) bonded joints evidenced an enhancement of the shear strength by about 25% for an optimal filler content of 1 wt%. Therefore, it was concluded that the addition of a proper amount of OM clay to epoxy adhesives could represent an effective way to improve the shear resistance of adhesively bonded composite structures. Copyright © 2011 John Wiley & Sons, Ltd.     

Nanoclay modified silica phenolic composites: mechanical properties and thermal response under simulated atmospheric re‐entry conditions

Ablative nanocomposites based on nanoclay‐dispersed addition curable propargylated phenolic novolac (ACPR) resin, reinforced with chopped silica fiber, were investigated for their thermal response behavior under simulated heat flux conditions corresponding to typical atmospheric re‐entry conditions. Organically modified nanoclay (Cloisite 30B) was incorporated to different extents (1–10%) in the ACPR resin matrix containing silica fiber to form the composite. The composites displayed optimum mechanical properties at around 3 wt% of nanoclay loading. The resultant composites were evaluated for their ablative characteristics as well as mechanical, thermal and thermo‐physical properties. The reinforcing effect of nanoclay was established and correlated to the composition. The mechanical properties of the composites and its pyrolysed product improved at moderate nanoclay incorporation. Plasma arc jet studies revealed that front wall temperature is lowered by 20°C and that at backwall by 10–13°C for the 3 wt% nanoclay‐incorporated composites due to impedance by nanoclay for the heat conduction. Nanoclay diminished the coefficient of thermal expansion by almost 50% and also reduced the flammability of the composites. The trend in mechanical properties was correlated to the microstructural morphology of the composites. The nanomodification conferred better strength to the pyrolysed composites. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of Mechanical Properties of Epoxy/Nanoclay/Multi-Walled Carbon Nanotube Nanocomposites using Taguchi Method

This paper reports the improvement of the mechanical properties of epoxy/nanoclay/multi-walled carbon nanotube (MWNT) nanocomposites prepared by the solution casting method for a range of pre-cure temperatures (room temperature, 50, and 70 °C), cure temperature (120, 130, and 140 °C), nanoclay content (0.5, 1.0, 1.5 wt%) and content of MWNT (0.2, 0.6, 1.0 wt%) for three levels. The influence of these parameters on the mechanical properties of epoxy/nanoclay/MWNT has been investigated using Taguchi's experimental design. The output measured responses are the tensile properties (tensile modulus, tensile strength and strain at break), impact strength and fracture toughness. From the Analysis of Mean (ANOM) and Analysis of Variance (ANOVA), MWNT content, pre-cure temperature and cure temperature had the most significant effects for the impact strength with contribution percentages of 38%, 28% and 23% respectively. However, for the fracture toughness and strain at break, the enhancements of properties come from the nanoclay content (59%), MWNT content (18%) and pre-cure temperature (23%). While the improvement in tensile strength was influenced by nanoclay and MWNT content, the cure temperature has a stronger effect on the tensile modulus. In this respect, Taguchi method points to the Taguchi method, in this way, points to the dominant parameters and gives the optimum parameter settings for each mechanical property. Confirmation experiments were performed with the optimum parameter settings and the mechanical properties were measured compared with the predicted results.     

热塑性淀粉/蒙脱石复合材料性能研究

用柠檬酸活化蒙脱石(CMMT),用尿素和甲酰胺塑化热塑性淀粉(UFTPS),制备了热塑性淀粉/蒙脱石(UFTPS/CMMT)复合材料.广角X-ray衍射(WAXD)、透射电子显微镜(TEM)表明,UFTPS和CMMT形成复合材料.CMMT质量分数2%~10%时,将复合材料在相对湿度50%(RH=50%)的环境下保存10 d,力学测试得出,复合材料的最大拉伸应力达到24.86 MPa,应变为134.50%,杨氏模量和断裂活化能分别由UFTPS的87.25MPa,1.87 N.m上升到复合材料625.25 MPa,2.45 N.m;可以看出,和纯UFTPS相比,复合材料强度明显提高;流变行为研究得出,通过改变加工温度和螺杆挤出机速度可以调整复合材料的流变行为;与传统的甘油体系相比,复合材料很好的抑制了材料长时间放置的结晶行为;并且该材料比纯UFTPS具有很好的耐水性能和热稳定性.