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Based on a novel phenylacetylene capped polyimide (PI) with unique high-temperature resistance, its curing kinetics and thermal decomposition behavior were investigated. The curing mechanism and kinetics were studied by differential scanning calorimetry (DSC), and the activation energy (Ea) and pre-exponential factor (A) of the curing reaction were calculated based on the Kissinger equation, Ozawa equation, and Crane equation. According to the curve of conversion rate changing with temperature, the relationship between the dynamic reaction Ea and conversion rate (α) was calculated by the Friedman equation, Starink equation, and Ozawa–Flynn–Wall (O-F-W) equation, and the reaction Ea in different stages was compared with the results of molecular dynamics. Thermogravimetric analysis (TGA) and a scanning electron microscope (SEM) were used to analyze the thermal decomposition behavior of PI resins before and after curing. Temperatures at 5% and 20% mass loss (T5%, T20%), peak decomposition temperature (Tmax), residual carbon rate (RW), and integral process decomposition temperature (IPDT) were used to compare the thermal stability of PI resins and cured PI resins. The results display that the cured PI has excellent thermal stability. The Ea of the thermal decomposition reaction was calculated by the Coats–Redfern method, and the thermal decomposition behavior was analyzed. The thermal decomposition reaction of PI resins at different temperatures was simulated by molecular dynamics, the initial thermal decomposition reaction was studied, and the pyrolysis mechanism was analyzed more comprehensively and intuitively. [ABSTRACT FROM AUTHOR]

A new series of high-temperature resistant bisphthalonitrile resins containing trifluoromethyl groups were prepared based on 4,4'-(hexafluoroisopropylidene) bisphthalonitrile (BFPh), which was toughened by hexafluoroisopropylidene-containing poly (aryl ether nitrile) oligomer capped by phthalonitrile (FPEN-Ph) in the different content. In addition, glass fiber reinforced composites were prepared by hot pressing process. The structure of the oligomer was characterized by FTIR and 1HNMR. The curing behavior of the blends was studied by DSC. Thermal stability and mechanical properties were also studied. The results showed that the introduction of appropriate content of FPEN-Ph could improve the reactivity of the curing reaction. TGA and DMA results showed that the cured polymers and composites had excellent thermal properties. The residual mass of FPEN-Ph content of 10% at 800°C was 72.4%, and the 5% thermal degradation temperature (T5%) under inert atmosphere was 530°C. The flexural strength of glass fiber reinforced composites was about 592.7 MPa, and the shear strength was about 61.6 MPa, showing excellent mechanical properties. The high-tech thermosetting resin was toughened and enhanced at the same time without reducing heat resistance. [ABSTRACT FROM AUTHOR]

Four novel phthalonitrile-capped polyarylene ether nitrile oligomers containing trifluoromethyl groups (FPEN-Ph) with different molecular weight were designed and synthesized by adjusting the ratio of bisphenol AF (BPAF) and 2,6-dicholorobenzonitrile (DCBN). The molecular structure of FPEN-Ph oligomers were characterized and analyzed by FTIR, 1HNMR and Gel permeation chromatography. Their curing behaviors were studied by Differential scanning calorimetry and rheological tests, and curing kinetics were also discussed by gel method in detail. The glass fiber cloth reinforced FPEN-Ph composites (FPEN-Ph/GF) had flexural strengths of 415.9–497.5 MPa, shear strengths of 34.5–50.5 MPa, and glass transition temperatures (T gs) in the range of 211.3°C–416.6°C. The initial thermal decomposition temperatures (T 5%) of various FPEN-Ph cured products were higher than 500°C under nitrogen. Meanwhile, Fracture morphologies showed that the GF/FPEN-Ph composites had excellent interfacial adhesion between FPEN-Ph matrix and GF reinforcement. Herein, the FPEN-Ph resin could be a good candidate for high-performance polymeric composites and the advanced FPEN-Ph/GF composites can be used under high temperature environment. [ABSTRACT FROM AUTHOR]

The properties of a RTM bismaleimide resin with low viscosity and ultra-high temperature resistance were systematically investigated, including its curing kinetics and rheological properties, and the thermal and mechanical properties of its cured resins. The thermal curing kinetics was investigated by differential scanning calorimetry (DSC) method with multiple heating rates. DSC curves display a cure regime in the temperature range of 150∼300°C and the exothermic peaks shift from 194°C to 231°C with heating rate. The apparent activation energy of curing reaction is calculated as 78.2 kJ/mol. The rheological properties were studied in terms of the changes of the non-isothermal and isothermal viscosity tested using a rotary viscometer. The test results show that the RTM resin has a wide molding temperature window from 90°C to 200°C and long molding time at 110°C for 275 min with a flow viscosity less than 1000 mPas. Dual-Arrhenius model was established to predict the viscosity characteristics at different constant temperatures, showing a good agreement with the experimental data. Four curing cycles were designed to obtain cured networks with different microstructures, and the thermal and mechanical properties of the cured resins suffered from various curing cycles were characterized by dynamic mechanical analysis (DMA) and universal material testing machine. The results exhibit that the cured product has a ultra-high glass transition temperature of 373.5°C and larger flexural strength of 145.4 MPa after post-curing at 250°C for 10 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of different molecular structures on evaporation were studied using MD. • The weak interaction in the evaporation process was quantitatively analyzed. • The key factors affecting the evaporation effect were discussed. • The guidance for the development of modifiers in BMI was provided. Evaporation is a common issue when using N-Phenylmaleimide (N-PMI) as a modifier for bismaleimide resins, often leading to porosity in the cured material and a failure to achieve the desired modification effect. This study simulated the evaporation process of five different structural modifiers liquid using molecular dynamics with 4,4′-Bismaleimidodiphenylmethane (BMI) molecules and N-PMI and its derivatives as the focus. It also involved calculating molecular properties such as electrostatic potentials through wave function analysis to explain the simulation results. The relationship between molecular structure, other properties, and the evaporation phenomenon was investigated from both molecular dynamics and experimental perspectives. The study revealed that the unique properties of F atoms result in a higher energy requirement for evaporation. This work provides guidance for the design and development of subsequent molecular structures including but not limited to BMI modifiers. [ABSTRACT FROM AUTHOR]

Recently resistance welding (RW) technique have emerged as a viable alternative method for the joining of fiber reinforced polymer (FRP) composites. It is more cost‐efficient as opposed to the conventional adhesive, mechanical and other joining methods. The objective of this paper is to provide a deeper insight into the recent development of the resistance welding technique for FRP composites. The main focus is set on the parameters that govern the welding process and the principal phenomena that affect the joints of the thermoplastic composite. The evaluation methods, the comprehensive failure modes, welding interface behavior and microscopic evaluation of interface are also looked at in detail. And this technology has been further extended to the connection of thermoset composites. In addition, several alternative fresh implants that involve micro-nano carbon materials and offer possibilities for future applications are systematically compared. Continuous resistance welding (CRW) is briefly introduced as one of the most promising methods in the end. [ABSTRACT FROM AUTHOR]

A series of high-temperature resistant structural adhesives were prepared based on the copolymerization of 4,4′-bismaleimidediphenylmethane (BDM) and 2,2′-diallylbisphenol A (DABPA) together with a novel maleimide-capped polyetherimide containing cardo side groups (mPEI-C) as toughening agent. The chemical structure of the adhesives and their cured networks was characterized by Fourier transform infrared (FTIR) spectrometer. Their curing behavior and kinetics were analyzed using differential scanning calorimetry (DSC). The thermal properties, mechanical properties, bonding strength and moisture absorption behavior of the cured products were investigated by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMA), etc. The modified resin system with mPEI-C exhibit similar curing behavior, and the apparent activation energy (E a) and reaction order (n) are equal to around 85.14 kJ/mol and 0.91, respectively. With increasing mPEI-C contends, the thermal stability is improved, the char yield is increased from 26.5% to 37.1%, and the glass transition temperatures have a slight decrease. The maximum flexural strength, impact strength and bonding strength are increased by 28.4%, 93.1% and 44.6%, respectively. The results of hygrothermal aging experiments exhibit the addition of mPEI-C has no obvious influence on the hygroscopicity of the modified resins. [ABSTRACT FROM AUTHOR]

Graphical abstract A rational structure of superior corrosion-resistant magnetic graphene foams decorated by Fe 3 O 4 (MGF@Fe 3 O 4) composites with a prominently improved EMW absorption property have been successfully designed and fabricated via a facile one-step hydrothermal route. Such graphene foam-based composites with controllable composition and structure can be as a light-weight, strong absorption and wide absorption bandwidth EMW absorption materials. Highlights • Porous 3D magnetic graphene foam composites have been successfully fabricated. • The products and acid-treated MGF@Fe 3 O 4 show enhanced EMW absorption properties. • The RL min value -64.4 dB was achieved and EAB is 6.0 GHz with a thickness of 2.4 mm. • The composites show superior corrosion-resistant. Abstract Superior corrosion-resistant magnetic graphene foams decorated by Fe 3 O 4 (MGF@Fe 3 O 4) have been constructed through in-situ simultaneous deposition of ferrous ion (Fe2+) induced graphene oxide (GO). Their chemical composition, micro structure and properties were investigated in detail by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and vector network analyzer. These 3D porous MGF@Fe 3 O 4 exhibit much better electromagnetic wave (EMW) absorption properties and corrosion resistance than 2D hybrid materials of magnetic metal particles and graphene sheets. The tunable EMW absorption performance can be easily implemented by tailoring their micro structure. Their minimum reflection loss (RL min) value reaches −64.4 dB at 10.8 GHz and maximum effective absorption bandwidth (EAB) is up to 6.0 GHz from 12 GHz to 18 GHz with a matching thickness of 2.4 mm. After treatment in hydrochloric acid for 70 days, the acid-treated MGF@Fe 3 O 4 still keeps excellent EMW absorption performance with their decrease of saturation magnetization lower than 16%. [ABSTRACT FROM AUTHOR]

Abstract Alkynyl-functionalized benzoxazine (A-BZ) resin containing phthalide side group with excellent heat resistance has been successfully synthesized with phenolphthalein, meta -aminophenylacetylene and formaldehyde solution as starting materials. Its chemical structure was characterized and analyzed by Fourier transform infrared (FT-IR) spectroscopy and hydrogen nuclear magnetic resonance (1 H -NMR) spectroscopy. A-BZ can easily dissolve in the common organic solvents including ethanol, acetone et al. The gelation time under different temperature of A-BZ resin was measured by dynamic mechanical analysis (DMA) according to the intersection time of the isothermal curves of the storage modulus and loss modulus. The gelation activation energy was determined by Arrhenius formula (E a = 48.51 kJ/mol). The optimal curing procedure was established by combing non-isothermal differential scanning calorimetry (DSC) and isothermal DMA. The curing mechanism was analyzed in in-situ FT-IR method by monitoring the change of characteristic peaks under different temperature. The reaction temperatures of ring-opening reaction of benzoxazine (170 °C) and trimerization cyclization of alkynyl groups (170–200 °C) were determined. The glass transition temperature (T g) of A-BZ cured product tested by DMA equals to 382 °C, which is much larger than those of counterparts (251–259 °C). [ABSTRACT FROM AUTHOR]

New aryl-ether-imide/phthalide-containing bismaleimide oligomers (MPEIBMI) with different molecular weight were designed and synthesized by adjusting the addition amount of diamine compound derived from o -cresolphthaleine, and dianhydride 4,4′-(4,4′-isopropylidene diphenoxy)-bis(phthalicanhydride) (mole ratio: 1.25/1.5/2.0). The chemical structures of the oligomers and their intermediate compounds were confirmed by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance ( 1 H and 13 C NMR) spectroscopy and elementary analysis. X-ray diffraction (XRD) results showed a blunt diffraction peak, suggesting an amorphous structure. The oligomers exhibited good solubility in a variety of common organic solvents. The heat flow curves of the oligomers measured by differential scanning calorimeter (DSC) displayed a broad curing exothermic peak. The thermal stability and thermal mechanical properties of the cured resins were investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The results indicated that the introduction of phthalide cardo structure and imide rings into the polybismaleimide network could effectively improve the thermal properties. The glass transition temperature and initial thermal decomposition temperature were above 260 °C and 423 °C, respectively, and the residual weight percentages at 700 °C were all > 58%. The mechanical tests revealed that the cured MPEIBMI films had excellent tensile strength and good retention at the temperatures above 200 °C. [ABSTRACT FROM AUTHOR]

The thermal decomposition behaviors and kinetics of diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured by a novel phthalide-containing aromatic diamine (BAPP), were studied by thermal gravimetric analysis (TGA) technique in comparison with these of epoxy systems cured by 4,4′-diaminodiphenylsulfone (DDS) and equimolar mixture of DDS/BAPP, respectively. The initial decomposition temperature ( T initial ) and integral procedure decomposition temperature (IPDT) were used to evaluate the thermal stability of cured epoxy resins. T initial values are reduced with increasing BAPP content, while IPDT results show the cured DGEBA/BAPP system has the highest inherent thermal stability. The microstructure morphology of charred products, derived from the thermal decomposition of the cured epoxy networks, were characterized by scanning electron microscope (SEM). The decomposition kinetics was investigated by isoconversional approach and the activation energy ( E a ) calculated by Starink equation exhibits different dependence on conversion ( α ) for three epoxy systems. Truncated Sestak-Berggren model was used to describe the thermal decomposition mechanism, and the result shows a good agreement between the experimental data and the theoretical model. [ABSTRACT FROM AUTHOR]

3,3-Bis[4-(4-aminophenoxy)phenyl]phthalide (PPDA) and 4,4′-bimaleimidodiphenyl-methane (BDM) were prepared via a Michael-type addition using molar ratio 1:2(PM2), 1:3(PM3) and 1:4(PM4) in acetone as solvent and acetic acid as a catalyst. The chemical structures of prepolymers were characterized by hydrogen-1 nuclear magnetic resonance (1H NMR) spectroscopy and Fourier transform infrared spectroscopy. These prepolymers exhibit good solubility in common organic solvents. The thermal properties of the prepolymers were investigated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Composites composed of carbon cloth and the phthalide-containing Michael addition-type prepolymers (0.5% triphenylphosphine) were also prepared. The DMA results demonstrated that the resulting composites have excellent thermal stability. Besides, N,N-4,4′-bismaleimidodiphenylmethylene (BDM) and O,O′-diallyl bisphenol A (DABPA) resin blends were modified by PM2. We investigated the effects of mole concentration of prepolymers on the curing process, mechanical properties, fracture toughness, and heat resistance of the modified resins. The investigations of the mechanical properties showed a complicated trend with an increase in prepolymer contents. When the proportion of PM2 is 0.05, the impact strength of modified resins was increased by 121.3%. In addition, the moisture resistance of cured resins was improved with the increase in prepolymer contents. [ABSTRACT FROM AUTHOR]

A novel phthalide-containing aromatic amine (PBMI-DDE) was synthesized by Michael addition of 3,3-bis[4-(4-maleimidophenoxy)phenyl]phthalide (PBMI) and 4,4′-diaminodiphenylether (DDE), its chemical structure was confirmed by nuclear magnetic resonance (NMR) spectrometer and Fourier transform infrared (FTIR) spectrometer. A serial of phthalide-containing epoxy resins were prepared with the PBMI-DDE/DDE blends in different molar ratios as curing agents. The cure behavior, thermal and mechanical properties, and shape memory performance of the cured resins were carefully characterized using differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), dynamic mechanical analyses (DMA), universal material testing machine and notched Izod impact test, respectively. DMA and TGA thermograms show the glassy storage modulus and the initial decomposition temperature increase while the rubbery storage modulus and the glass transition temperature are reduced as PBMI-DDE content increases. The investigations of mechanical properties exhibit a complicated trend with increasing PBMI-DDE content, and the epoxy resin with an equal molar ratio of PBMI-DDE/DDE has a maximum mechanical strength. The fracture morphology investigated by scanning electron microscope (SEM) indicates the existence of hole defects in the cured products with higher PBMI-DDE content. The shape memory performance of these fully cured epoxy networks is improved with PBMI-DDE content, and the shape fixity ratio ( R f ) and shape recovery ratio ( R r ) of the pure PBMI-DDE cured epoxy resins are both lager than 95% with a deformation strain above 12%. [ABSTRACT FROM AUTHOR]

Benzoxazine resins are widely employed in a variety of applications due to their exceptional heat resistance and treatment properties. However, traditional benzoxazine resins still confront hurdles in today's engineering applications, such as their inability to provide long-term service in high-temperature settings and their inadequate toughness. In this study, four alkyne-functionalized benzoxazines with phthalide side groups and cyano groups of varying molecular weights were produced. Fourier transform infrared spectroscopy (FT-IR) and hydrogen nuclear magnetic resonance spectroscopy (1H-NMR) were used to characterize the resin structure, and differential scanning calorimetry (DSC) was used to investigate the thermal curing kinetics at different warming rates. The apparent activation energy was 116.9 kJ/mol. In-situ FT-IR was used to investigate the cure mechanism. Dynamic mechanical analysis (DMA) was used to evaluate the gelation time of BOZ series resins at various temperatures, and the curing process was designed by combining the results with DSC. The Tg of the composites made using BOZ-1N21 as the matrix was 336 °C, which was much higher than the Tg of the BP-a resin made with aniline, phenolphthalein, and formaldehyde (Tg = 251 °C). As a result, the resin system is expected to be employed in applications requiring high-temperature resistance and toughness. [ABSTRACT FROM AUTHOR]

In this study, an analytical analysis and a finite element method (FEM) study of the overall strength and interfacial stress distribution of single lap joints with an embedded inclusion in the adhesive layer were performed. The stress analysis model for the single lap adhesive joints including inclusion layers was firstly established, and the effects of the thickness and stiffness of the inclusions on their mechanical strength were discussed in detail. The results show that the bond strength of the adhesive joints is highly dependent on the geometric parameters and properties of the inclusions, and increases with the inclusion thickness and stiffness. When the stiffness of inclusions is lower than that of the adhesive layers, their introduction degrades the bond strength of the single lap adhesive joints. The interface stress distribution and failure mechanism caused by the inclusion layers are intuitively analyzed by FEM, which is in good agreement with the analytical analysis. [ABSTRACT FROM AUTHOR]

The curing reaction of diglycidyl ether of bisphenol A (DGEBA) with a novel aromatic diamine containing phthalide structure (BAPP) was studied by differential scanning calorimetery (DSC). The optimal formulation of DGEBA/BAPP system was obtained in terms of the curing behavior and glass transition temperature determined by dynamic DSC. The n th-order reaction model and autocatalytic model were used to analyze the curing kinetics and mechanism based on the isothermal DSC technique. The results indicated that the Kamal autocatalytic model had a great agreement with the experimental data from the start of curing reaction to the initiation of diffusion control stage. Diffusion-controlled effect was also taken into account and then the extended Kamal model could describe precisely the curing reaction of BAPP/DGEBA in the entire conversion range. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1. An innovative ultra-fast resistance welding was proposed for the fusion bonding PP. • 2. The ultra-fast resistance welding was finished within 1 s to protect the PP from excessive heat damage. • 3. The best welding process was obtained when SS wire with a diameter of 0.6 mm as an implant. In this paper, an innovative ultra-rapid resistance welding process was proposed for the bonding of polypropylene (PP) plates to alleviate the dilemma of edge effect. The ultra-rapid resistance welding of PP plates was conducted under different heating time (t h) and diameter (d s) of stainless-steel (SS) wire in this research, the SS wire of d s = 0.6 mm and t h = 1 s was separately selected as the most suitable heat transfer implant and welding time. The edge effect was proved by the interface morphology at different positions of the joint and the thermal simulation results of COMSOL. [ABSTRACT FROM AUTHOR]

The use of novel aromatic diamine containing phthalide structure (BAPP) as curing agent of diglycidylether of bisphenol A (DGEBA) epoxy resin has been studied. BAPP can react with epoxy monomers by an epoxy-amine condensation mechanism, which renders phthalide cardo incorporate into the network structure of the thermoset. The curing behavior and kinetics have been investigated by differential scanning calorimetry (DSC) and the kinetic analysis of non-isothermal cure shows that autocatalytic model is suitable to describe the cure mechanism. The thermal–mechanical properties have been determined with dynamic mechanical analysis (DMA) and the activation energies for relaxation were calculated according to the Arrhenius law. Thermogravimetric analysis exhibits a lower initial decomposition temperature, decreased rate of decomposition and higher char yield compared with DGEBA cured with commercially available 4,4′-diaminodiphenylsulfone (DDS). [ABSTRACT FROM AUTHOR]

• A cross-scale component of CNT-CCFs prepared by the flame method was firstly used as an enhancer for epoxy adhesive. • The CNT-CCFs can strengthen the bonding joint by alleviating the stress on the interface. • The CCFs and CNTs achieved the purpose of synergistically strengthening the joint by reducing the pores at the interface. The cross-scale combination of carbon nanomaterials and macro-materials is a key application in the advanced manufacturing technology of composite materials. In this work, a cross-scale component of carbon nanotube combined with chopped carbon fibers (CNT-CCFs) prepared by the flame method was firstly used as an enhancer for adhesive. The effects of component on the mechanical and fracture properties of thermoset composite bonded joint were investigated. The composites reinforced with CNT-CCFs exhibit higher strength than the composites reinforced solely with CCFs, with over 30.8% improvement for the combined CNTs and CCFs toughened adhesive joints. [ABSTRACT FROM AUTHOR]

Highlights: [•] The cure temperature of BMIP is reduced in the presence of epoxy group. [•] The Michael addition of BMIP and DDS is of higher reactivity than BMIP homopolymerization. [•] The blends contain three different cure regimes in the temperature range of 150–350°C. [•] The T gs of the cured resins are decreased with the DGEBA content. [•] The cured resins containing higher DGEBA content possess lower thermal stability. [ABSTRACT FROM AUTHOR]

Abstract: A novel bismaleimide containing phthalide cardo structure (BMIP) was mixed with 2,2′-diallyl bisphenol A (DABPA), and the cure behavior of the mixture was studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The FTIR results demonstrated the cure reaction below 200°C progressed preferentially via alternating copolymerization of maleimide and allyl groups. The DSC thermogram of the prepolymer showed three different cure regimes in the temperature range of 100–350°C and the 2nd exothermic peak was predominant. The kinetic parameters of the 2nd curing process were evaluated using various kinetic models: Kissinger and Ozawa–Flynn–Wall, and the apparent activation energies obtained from two methods were consistent with each other. Thermal properties of the cured network were characterized by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Experimental results exhibited that the onset decomposition temperature (T 5%) was ∼431°C and char yield at 600°C was ∼39.1%. In addition, the glass-transition temperature (T g) reached 274°C based on the tan δ peak temperature. [Copyright &y& Elsevier]

The joining of metals and polymer-matrix composites (PMCs) is a highly pressing and challenging task in the manufacturing industries. To achieve the reliable hybrid joint, a solid-state joining technique of top-thermic friction stir lap welding (TT-FSLW) was proposed and performed in the joining of 7075 aluminum alloy and SGF/PEEK materials. Through the TT-FSLW with low rotational speed, the excessive overflow of polymer material in conventional FSLW was suppressed, so the satisfactory joint with smooth surface was formed. Thanks to the low heating and cooling rates and the reduced interfacial stress, common FSLW defects of void and crack were eliminated in the TT-FSLW joint. Characterized by the widened effective interfacial joining area and the enhanced interfacial joining with micro and macro mechanical interlockings, the maximum shear strength of joint was enhanced to 59.9 MPa under TT-FSLW, which was increased by 52.4% compared to that under the conventional FSLW. The TT-FSLW technique has been preliminarily proved to be superior to other conventional welding methods in joining metals and PMCs. [Display omitted] • The innovative top-thermic friction stir lap welding (TT-FSLW) technique is proposed. • Sound metal to polymer-matrix composites (PMCs) joint with satisfactory surface and no defects was obtained by TT-FSLW. • The TT-FSLW joint is competitive to the other conventional welding methods in joining metals and PMCs. [ABSTRACT FROM AUTHOR]

Heat-resistance epoxy shape memory (SM) materials were prepared based on diglycidylether of bisphenol A (DGEBA) epoxy resin with the mixture of 4,4′-diaminodiphenylether (DDM) and phthalide-containing aromatic amine (PBMI-DDM), which was synthesized by Michael addition of 3,3-bis[4-(4-maleimido phenoxy)phenyl] -phthalide (PBMI) and DDM, in different molar ratios as curing agents. The chemical structure of PBMI-DDM was confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra. The dynamical mechanical behavior and high-temperature tensile properties, and the influence of PBMI-DDM content and number of cycles on SM performance were investigated in detail. With increasing PBMI-DDM content, the glass transition temperatures (T g) decreased, damping loss factors increased, and shape recovery ratio (R r) and shape fixity ratio (R f) were improved significantly. R r and R f of the pure PBMI-DDM cured epoxy resins are both lager than 90% with a deformation strain above 15%. The T g and activation energies (△E) of α -relaxation for the epoxy system with unstable SM performance are constantly increased with SM cycles due to the adjustment and rearrangement of network chains. • Synthesis of a novel phthalide-containing aromatic amine and epoxy SMPs. • Their crosslinked density reduces with the content of phthalide groups. • Their optimal deformability can be achieved by adjusting phthalide content. • Their tensile ultimate elongation at deformation temperature is better. • Their shape memory performance is improved with increasing phthalide groups. [ABSTRACT FROM AUTHOR]

The joining of titanium (Ti) alloy and composite parts with weight reduction and cost saving is being developed to improve aircraft performance. The high-efficiency resistance welding technology was explored for joining Ti alloy plate and glass fabric reinforced polyetherimide (GF/PEI) laminate in this work and a carbon nanotube (CNT) reinforced laminae was embedded into the interface of the welding region to enhance the strength of the hybrid joints of Ti -GF/PEI. The CNTs were in-situ grown on the surface of the Ti alloy plate, and their structures and morphologies were characterized by Raman spectrum, scanning electron microscope (SEM) and transmission electron microscope (TEM). The single lap shear strength (LSS) of the hybrid joints was evaluated with tensile tests. The LSS values first increased and then decreased with welding time (t w) due to the combined effects of the improving molten state of PEI resin and its local thermal degradation induced by excessive heat accumulation. The optimum LSS of the hybrid joint with CNT reinforced lamina is increased by 146% to 17.28 MPa in comparison with that of the hybrid joint without CNTs. The failure modes shift from interlayer debonding of the Ti alloy plate and the implant to the cohesive fracture of the implant and the delamination of the GF/PEI laminate with increasing t w. The ultrasonic C-scan images also show an increase of the number of internal defects of GF/PEI laminates with t w. Unlabelled Image • Carbon nanotubes (CNTs) was deposited on the surface of titanium (Ti) alloy by flame method. • The CNTs act as connectors of the implant and Ti alloy and nano reinforcement for enhancing resistance-welding hybrid joint of thermoplastic composites and Ti alloy. • Strengthening mechanism of CNTs on the welded joints was proposed. [ABSTRACT FROM AUTHOR]

Multi-walled carbon nanotubes (MWCNTs) in the form of "forests" were synthesized directly on the surface of stainless steel (SS) mesh from ethanol flame volume. The growth dependence of the MWCNT forests on the porosity of SS mesh substrate and the morphologies and growth mechanism of the MWCNT forests were investigated in detail by a combination of turbulent flow simulation, scanning electron microscopy (SEM), transmission electron microscope (TEM), and Raman and X-ray diffraction (XRD) spectroscopy. The growth height of the MWCNT forests exhibited a strong dependence on the flame gas flow rate controlled by the porosity of SS mesh substrate, and the maximum averaged height of the MWCNT forests reached 34 μm. Most MWCNTs grew perpendicularly on the surface of SS wires, and some branch, welded, and spiral structures were observed by SEM and TEM. The MWCNT-decorated mesh was used as a novel heating element to weld glass-fabric-reinforced polyetherimide (GF/PEI) thermoplastics. We found that the maximum tensile lap-shear strength (LSS) of the welded joints could reach 39.21 MPa, an increase of 41% in comparison with that of conventional SS mesh-based joints. [ABSTRACT FROM AUTHOR]

A novel glycidylamine epoxy resin containing phthalide cardo structure (TGMP) was designed and synthesized based on o -cresolphthalein using a three-step procedure. Its curing systems were prepared using methyl-nadilic anhydride (MNA) and 2-ethyl-4-methylimidazole (EMI-24) as the curing agent and accelerating agent, respectively. The chemical structures of synthetic intermediate, epoxy resin and its curing systems were characterized by Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance (NMR) spectra. The curing behavior and kinetics were investigated by differential scanning calorimetry (DSC) and the activation energies were calculated according to the Kissinger equation and Flynn-Wall-Ozawa (FWO) equation. The TGMP/MNA/EMI-24 system is of more reactivity more that of pure TGMP. The Friedman method was used to describe the progress of the curing reaction of the TGMP/MNA/EMI-24 system, finding it follows the autocatalytic reaction model and n th-order reaction mechanism is predominant. The thermal-mechanical properties of the TGMP/MNA/EMI-24 composites were studied by dynamic mechanical analysis (DMA). The tan δ curves show double peaks and the maximum glass transition temperature is up to 345 °C. • Synthesis of a multifunctional phthalide-containing glycidylamine epoxy resin (TGMP). • The homopolymerization activation energy of the pure TGMP resin equals to 114.23 kJ/mol. • The curing activation energy of TGMP/MNA/EMI-24 system equals to 57.64 kJ/mol. • The TGMP/MNA/EMI-24 curing reaction follows the autocatalytic mechanism. • T g of TGMP/MNA/EMI-24 cured product is above 345 °C. [ABSTRACT FROM AUTHOR]

Thermal behavior and fire reaction properties of aerial glass fiber (GF)/bismaleimide (BMI) composites were tested using thermogravimetric analysis (TGA), thermogravimetric coupled with Fourier transform infrared spectroscopy (TG-FTIR), cone calorimeter, limiting oxygen index, and smoke density chamber. The results showed that the pyrolysis process was one stage in a nitrogen atmosphere with the prominent volatile components of CO2, H2O, CH4, NOx, and SO2. The release of heat and smoke increased with the increase in heat flux, while the time required to reach hazardous conditions decreased. The limiting oxygen index decreased monotonically from 47.8% to 39.0% with increasing experimental temperature. The maximum specific optical density within 20 min in the non-flaming mode was greater than that in the flaming mode. According to the four kinds of fire hazard assessment indicators, the greater the heat flux, the higher the fire hazard, for the contribution of more decomposed components. The calculations of two indices confirmed that the smoke release in the early stage of fire was more negative under flaming mode. This work can provide a comprehensive understanding of the thermal and fire characteristics of GF/BMI composites used for aircraft. [ABSTRACT FROM AUTHOR]

Interface is an important microstructure for advanced polymer-matrix composite. The composite interface is the bridge and the link for stress transferring between the fiber and the matrix resin. In this work, oxygen plasma treatment was used for modification of aramid fiber surface. The effects of plasma treatment power on interlaminar shear strength of composite were evaluated by short-beam shear test. The morphologies of both the aramid fiber surface and its composite interface fracture were observed by SEM. The chemical structure and surface chemical composition of the plasma-treated and separated fibers were analyzed by Fourier transform infrared (FTIR) and XPS, respectively. The results showed that the interlaminar shear strength of composite was enhanced by 33% with plasma treatment power of 200 W. The FTIR and XPS results indicated that the active functional groups were introduced onto the aramid fiber surface by plasma treatment forming chemical bonds with the poly(phthalazinone ether sulfone ketone) resin. The SEM results proved that the aramid fiber surface was roughened by plasma treatment enhancing the mechanical bond with the poly(phthalazinone ether sulfone ketone) resin. The composite rupture occurred from the composite interface to the fiber or the matrix resin. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

[Display omitted] • A validated PBO/EP single fiber pull-out test method is proposed. • The IFSS was found to have an inverse relationship with the test temperature. • The accuracy of single fiber pull-out was verified by COMSOL simulation results. In the micromechanical test of fiber-reinforced composites, single fiber pull-out test is the most widely used test method. However, for high performance fibers/matrix, different test equipment and sensor accuracy can affect the single fiber pull-out test results very much. In this study, an innovative single fiber pull-out test method is proposed for testing the interfacial shear strength (IFSS) of high performance fibers/resins at different temperatures. Single fiber pull-out test was carried out on PBO fiber/epoxy resin (EP) composites at room temperature and elevated temperature. The IFSS was found to have an inverse relationship with the test temperature. The IFSS value of PBO/EP decreased from 25.25 MPa at room temperature to 6.25 MPa as the temperature approached the glass transition temperature. COMSOL simulations showed that fiber pull-out with angular tilt exhibited better interfacial strength, demonstrating the validity of the method. The results of this paper provide ideas to study the effect of temperature on the mechanics of fiber-reinforced resin matrix composites and expand the way to design stiffer, stronger and more robust composites. [ABSTRACT FROM AUTHOR]

The approach for joining carbon fiber reinforced epoxy (CF/Epoxy) composites proposed in this study is based on the use of a plasticizing chip (PC), one side with rich resin and the other side with bare fiber, prepared by 1, 2, 3 or 4 pieces of glass fiber reinforced polyetherimide (GF/PEI) prepregs and a piece of glass fiber cloth (GFC), added as a last ply in the stacking sequence of CF/Epoxy composites. During curing, the epoxy partially penetrates in the side with a bare fiber of PC, leading to micro-mechanical interlocking as the main connection mechanism between the PC and the CF/Epoxy composites. To verify the effects of PC on the thermal and mechanical properties of CF/Epoxy composites, TGA, DMA, DCB, bending, interlaminar shear and drop-weight tests were carried out. The results showed that PC can effectively alleviate the impact of thermal degradation without weakening the properties of CF/Epoxy composites. [ABSTRACT FROM AUTHOR]

The molecular structure of curing agents significantly influences the properties of epoxy resins. In this article, the effect of the molecular structure of curing agents on the thermomechanical (TM) properties of an epoxy resin was investigated by a molecular dynamics method. First, the influence of the sizes of 3D systems on the performance of cured systems was preliminarily analyzed. From the results, four kinds of fully atomistic models were constructed and simulated. The effects of curing agents' molecular chain lengths, polar groups, side-chain groups on the TM properties of epoxy resin systems were analyzed from various perspectives. The results showed that the longer the molecular chain and the smaller the group polarity, the inferior the TM properties of the cured system, and vice versa; further, the side-chain group significantly weakened the movement ability of the chain, which has a primary effect on cured system TM properties. Molecular structures of curing agents have little effect on thermal expansion coefficient and thermal conductivity of epoxy curing systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • A double-layer structure film of PI and PEEK was successfuly prepared. • The surface of PI film was treated with atmospheric plasma to improve the interface adhesion. • Materials Studio (MS) software was used to investigate the active groups' grafting mechanism. Due to the increase of service temperature, the bond strength of polyimide composite film will decrease significantly, the continuity of the lapped structure is broken. Therefore, this study proposed a double-layer structure consisting of a polyimide (PI) substrate and Polyetheretherketone (PEEK) coating. The PI/PEEK interface adhesion was improved by using atmospheric plasma treatment. The surface wettability, surface chemical structure, surface element analysis, surface morphology and surface roughness of PI films were studied, respectively. The Materials Studio (MS) was used to model the active groups' grafting mechanism after plasma treatment. The results shown that the surface free energy increased obviously from 27.65 mJ/m2 to 66.93 mJ/m2. Reactive groups containing oxygen, such as C = O, C–O, were generated on the surface of PI film due to etching and addition reactions during the plasma process. The mechanical properties of PI films had little change after plasma treatment. The inorganic particles on the surface of the PI film were exposed by plasma etching, which would increase the adhesion between the PI film and the PEEK coating. MS simulated the sequence, relative energy change, and energy barrier of the three functional groups, revealing that the reactivity sequence of the three groups was: –OH > –COOH > –CO–. [ABSTRACT FROM AUTHOR]

The surface of stainless steel (SS) mesh was modified by in-situ growing carbon nanotubes (CNTs) from ethanol flame. Then the interfacial bond strength of SSM and polyetherimide (PEI) was improved by the CNTs-modified SSM, a heating element (HE) for the resistance welding of carbon fiber reinforced epoxy (CF/Epoxy) laminates. The effects of CNTs growth time (tg) on the wettability of PEI solution to SS mesh, interfacial microstructure, and mechanical properties of the welded joint were investigated. The results indicated that the addition of CNTs increased the wettability of PEI solution to SS mesh due to the capillary action of high porosity CNTs coating. The microstructure of the welded joints changed with tg. The maximum single lap shear strength (SLSS) value of the welded joint reached 24.7 MPa when tg = 10 min. The strengthening mechanism of CNTs and the failure modes of the welded joints were systematically analyzed. [ABSTRACT FROM AUTHOR]

Two novel n ≈ 1 oligomeric bismaleimide monomers containing phthalide cardo and cyano groups (PCBMI and MCBMI) were designed and synthesized. The chemical structures of the monomers were confirmed from proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. Both BMIs exhibit good solubility in common organic solvents, enabling easy solution processing. Thermal curing behaviors of the monomers were investigated by differential scanning calorimetry, displaying broad exothermic peaks and large thermal processing windows. Furthermore, PCBMI/carbon fiber composites were prepared, with their thermal stability and mechanical properties investigated. Thermogravimetric analysis and test of interlaminar shear strength indicated that the thermal polymerization of cyano groups improved the heat resistance of BMI resins and enhanced the interfacial adhesion at higher temperature. [ABSTRACT FROM AUTHOR]

High-performance magnetic graphene aerogels nanocomposites with low density and enhanced microwave absorption properties have been developed firstly by a two-step strategy combining hydrothermal reaction and in situ pyrolysis. TEM images indicate that ultra-fine Ni nanocrystals with a relatively uniform size of 8 nm are anchored to the graphene nanosheets. Meanwhile, the resulting magnetic graphene aerogels possess superparamagnetism. The GA@Ni hybrids of paraffin mixed with an ultra-low filling content (<5 wt%) show superior capability of microwave absorption (MA) for practical application owing to their excellent impedance matching and synergistic effect. The minimum reflection loss (RL min) reaches −52.3 dB at 11.9 GHz and the maximum effective absorption bandwidth (EAB) exceeding −10 dB is up to 6.5 GHz with an absorber layer thickness of 2.6 mm. Furthermore, the nanocomposites of epoxy resin mixed with 4.25 wt% GA@Ni exhibit an ultrawide EAB of 6.7 GHz with a thinner thickness of 2.52 mm. Interestingly, the electromagnetic parameters can be rationally regulated by adjusting the calcination temperature and filler contents to carry out highly efficient microwave absorption. Results indicate that magnetic graphene aerogels nanocomposites can be as superior microwave absorption materials and the two-step strategy will open an avenue for the fabrication of synergistic microwave absorbers. Image 1 [ABSTRACT FROM AUTHOR]

An oligomeric bismaleimide (BMI) containing both phthalide cardo and cyano group (PCBMI) was mixed with O,O'‐diallyl bisphenol A (DABPA). The thermal properties of PCBMI/DABPA in different proportions (1:0.87, 1:1, and 1:1.2) and their composites were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). In addition, the mechanical properties of the prepared composites were also investigated. The results exhibited excellent thermal stability, heat resistance, and mechanical properties. We further investigated the effects of thermal ageing at 200°C and 250°C in air for up to 1000 h on inter laminar shear strength (ILSS) of the carbon fiber–bismaleimide composites (T700/DPC87). Scanning electron microscopy (SEM) and scanning acoustic microscope (SAM) were employed to characterize interfacial property changes, and Fourier transform infrared (FTIR) was employed to characterize chemical changes due to ageing. The results indicated PCBMI/DABPA resin had an excellent interface bonding capacity and aging resistance. It can, therefore, be widely used in aeronautics and space industries. POLYM. COMPOS., 40:E1283–E1293, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Pure zinc foil was selected as an interlayer to improve the strength of the AZ31B Mg/7075-T6 Al dissimilar alloys friction stir lap welding joint. Compared with the conventional lap joint, the joint with the zinc interlayer has a higher effective sheet thickness, a larger effective lap width and a wider stir zone. The dispersed Mg-Zn intermetallic compounds are achieved instead of the continuous Mg-Al intermetallic compounds, improving the tensile shear load. The maximum fracture load of the joint with the zinc interlayer reaches 6.6 K N at the rotating velocity of 1000 rpm. [ABSTRACT FROM AUTHOR]

[Display omitted] • The temperature distribution of the welding interface are simulated by COMSOL. • The thermocouples are integrated into PEI film to monitor interface temperature. • The fusion evolution of interface is studied to evaluate the effects of amplitude. This work focuses on the effects of ultrasonic welding amplitudes on carbon fiber reinforced polyetherimide (CF/PEI) composite joint properties. The interface temperature measurement, single-lap shear tests and fracture morphology observation were used to evaluated on welding specimens with different welding amplitude. The accuracy of the temperature measurements was verified by the temperature field simulation of COMSOL. The analysis of mechanical strength and fracture morphology of joints were performed by tensile testing machine and SEM. The results indicated that PEI resin of the joint interface fully melted and the joints with good quality were formed under the appropriate welding amplitude. However, the excessive welding amplitude resulted in the extreme melting of PEI resin of the joint interface, which deteriorated the mechanical properties of joints. [ABSTRACT FROM AUTHOR]

ABSTRACT: A novel allyl compound containing liquid crystalline structure, i.e., 4,4’‐bis(4‐allyloxy benzoic acid) phenyl ester (BAOBE), was synthesized. The chemical structure of BAOBE was characterized by Fourier transform infrared (FTIR) spectroscopy and 1H NMR spectra, and the liquid crystalline properties were confirmed by polarized optical microscopy (POM). Besides, a series of modified bismaleimide (BMI) resins were prepared based on N,N′‐4,4′‐bismaleimidodiphenylmethylene (BDM), BAOBE, and O,O’‐diallyl bisphenol A (DABPA). The results of thermogravimetric analysis (TGA) indicate that the modified resins have excellent thermal stability with the highest temperatures for 5% weight loss above 438°C. The results of dynamic mechanical analysis (DMA) suggest that the glass transition temperature (Tg) of the modified resins are above 280°C. Besides, the introduction of BAOBE leads to a significant improvement in the flexural and impact properties of the modified BMI resins. Compared with the resin with only DABPA as a modifier, the highest flexural and impact strength can reach 156.2 MPa and 15.6 kJ/m2, increased by 19.2% and 90.2%, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • An innovative ultrasonic implant welding was proposed for the fusion bonding PP. • The copper mesh was used for implant for ultrasonic implant welding. • The welding heat was provided by rubbing between the metal implant and horns. In this paper, an innovative ultrasonic implant welding technology was proposed for the welding of polypropylene (PP) plates. Welding heat required for the interface was provided by rubbing between the metal implant and the horns to avoid damage of the base material. Ultrasonic implant welding of PP plates was conducted under different welding time (t w) in this research, while copper (Cu) mesh was selected as heat transfer implant. The micro morphology and mechanical property of joint were investigated by SEM and tensile test, which shown a strong correlation with t w. The mechanical property of joints increased from 2.8 to 7.6 MPa as t w increased from 3 to 10 s and the maximum joint strength reaches about 80% of the base materials. The evolution of heat distribution with t w was simulated using COMSOL. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) Buckypapers can be infused with resin and easily incorporated into conventional fiber reinforced composites. In this paper, we propose to use Buckypaper (BP) as a new measuring method to determine the glass transition temperature of polymeric composites. The CNT-only BP was fabricated by spray-vacuum filtration method with monodispersion of multi-wall carbon nanotubes, and then co-cured with polymeric composites. After manufacturing, the glass transition temperature of polymeric composites could be obtained from the relationship between resistance and temperature of BP during the dynamic heating process. Experimental results show that the glass transition temperature of composite samples A and B monitored by BP sensors were 127 °C and 180 °C, while such temperatures obtained from a dynamical mechanical analyzer (DMA) were 128 °C and 184 °C respectively. This paper not only reveals the ability of BP as a sensor for monitoring the glass transition temperature of composite but also provides a new way to understand the glass transition phenomenon of composite. [ABSTRACT FROM AUTHOR]

Buckypapers are free-standing porous mats of entangled CNT ropes cohesively bounded by van der waals interactions, and can be used to monitor the manufacturing process of glass fiber reinforced composite. In this paper, the buckypaper (BP) was fabricated with monodispersion of multi-wall carbon nanotubes via spray-vacuum filtration, and its morphology and pore size distribution were characterized by scanning electron microscope and nitrogen adsorption/desorption. The resistance of the BP sensor was obtained using a four-point probe method, and the resistance changes could be related to phase changes of the resin matrix,. Experimental results show that the BP sensor embedded in the glass/epoxy composite laminates has indicated a relative resistance change from −2.9% to 226.5% during the manufacturing process. In addition, the temperature sensitivity of a pristine BP sensor and a BP sensor embedded in composite were also characterized. The results demonstrate that the effect of resin phase changes on the resistance changes of a BP sensor is greater than that of the temperature during composite manufacturing. [ABSTRACT FROM AUTHOR]

A novel composite heating element constructed by carbon nanotube film and stainless steel meshes was used to resistance welding of carbon fiber reinforced polyetherimide (CF/PEI) laminates. The microstructure and mechanical property of the resistance welding joints under different t w were respectively investigated by scanning electron microscopy (SEM) and tensile test. The failure interface and failure model matched the mechanical properties were analyzed in detail, and the characteristic area shown a strong correlation with morphological changes of CNT film. [ABSTRACT FROM AUTHOR]

Novel bismaleimide resins based on 9,9-bis[4-(4-maleimidophenoxy)phenyl]fluorene (PFBMI), 2,2′-diallyl bisphenol A (DABPA), and 4,4′-dimaleimido diphenylmethane (BDM) were prepared in this article. The thermal properties of PFBMI/DABPA in different proportions (1:0.87, 1:1, and 1:1.2) were carefully characterized using differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The results showed that resins had good thermal stabilities especially the one at 1:0.87. Its 10% weight loss reached 433.4°C, and the residual weight percentage (RW%) was more than 50%. In addition, PFBMI was blended into BDM/DABPA in a different ratio, and the curing characteristic, thermomechanical behavior, thermal stability, mechanical properties, and moisture absorption behavior of these blends were investigated. The results revealed that the introduction of PFBMI into BDM/DABPA did not decrease the thermal stability of the modified resins but increased the RW% at 600°C. Moreover, the impact strength of the modified resins can be significantly enhanced; when the ratio is 0.08:1, it increased by 35%. The water absorption rate also decreased with the increase in the concentration of PFBMI. PFBMI monomers play an important role on the toughness reinforcement of the BDM/DABPA resin. [ABSTRACT FROM AUTHOR]

After exposure to the atmospheric-pressure air plasma at different discharge powers, the adhesion characteristics of Twaron aramid fibers were investigated. For the 12 s-300 W plasma treatment, the interlaminar shear strength of Twaron fiber reinforced thermoplastic poly(phthalazinone ether sulfone ketone) was increased from 46.0 to 61.7 MPa by 34.1%, and the diffusion of water molecule into the resulting composites was proved to be effectively prevented. These results showed that surface adhesive properties of the plasma-treated aramid fibers were improved. At the power level of 300 W, X-ray photoelectron spectroscopy analysis revealed the increases in concentrations of oxygen and nitrogen polar groups on the fiber surface, and atomic force microscopy observations led to the conclusion that the fiber surface morphology was changed and the surface roughness was greatly increased. These new polar and irregular surface structures accounted for the better adhesion between the fiber and the matrix, while due to the reasonability of this discharge power level applied to the surface modification, the measured fiber tensile strength only decreased by 2.0%. POLYM. COMPOS., 37:620-626, 2016. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The effects of electron irradiation in simulated space environment on thermal and mechanical properties of high performance carbon fiber/bismaleimide composites were investigated. The dynamic mechanical properties of the composites exposed to different fluences of electron irradiation were evaluated by Dynamic mechanical analysis (DMA). Thermogravimetric analysis was applied to investigate the changes in thermal stability of the resin matrix after exposure to electron irradiation. The changes in mechanical properties of the composites were evaluated by flexural strength and interlaminar shear strength (ILSS). The results indicated that electron irradiation in high vacuum had an impact on thermal and mechanical properties of CF/BMI composites, which depends on irradiation fluence. At lower irradiation fluences less than 5 × 10 15 cm −2 , the dynamic storage modulus, cross-linking degree, thermal stability and mechanical properties that were determined by a competing effect between chain scission and cross-linking process, decreased firstly and then increased. While at higher fluences beyond 5 × 10 15 cm −2 , the chain scission process was dominant and thus led to the degradation in thermal and mechanical properties of the composites. [ABSTRACT FROM AUTHOR]

Two novel bismaleimide (BMI) monomers containing fluorene cardo group and aryl ether linkage, that is, 9,9-bis[4-(4-maleimidophenoxy)phenyl] fluorene (PF-BMI) and 9,9-bis[4-(4-maleimidophenoxy)-3-methylphenyl] fluorene (MPF-BMI) based on 9,9-bis(4-hydroxyphenyl)fluorene and its derivative were designed and synthesized. The chemical structures of the monomers were confirmed from1H NMR,13C NMR spectroscopy, and Fourier transform infrared spectroscopy. Both monomers obtained are readily soluble in common organic solvents, such as acetone, dichloromethane, and chloroform, enabling an easy solution processing. The thermal curing behavior of the monomers and their non-isothermal thermal curing processes were investigated using differential scanning calorimetry, displaying that both monomers have lower melt points and broad thermal processing windows. The corresponding kinetic data, for example, activation energy (Ea), pre-exponential factor (A), and the order of the reaction (n), were obtained by the Kissinger and Ozawa method. The BMI resins based on these new monomers have good thermal stability seen from the thermogravimetric analysis results. [ABSTRACT FROM PUBLISHER]