Thermokinetic effect of the aging of epoxy matrix prepregs for high performance composites

The reactivity and processability of prepregs for high performance composites have been investigated as a function of time and storing conditions. The study has been focused on the stability of epoxy matrix carbon fiber prepregs, affected by exposure to controlled environmental conditions before their use in composite manufacturing. Effects of the aging on glass transition temperature, reactivity and processability have been investigated by calorimetry. Dynamic, isothermal and cure simulating tests have been performed to this aim. Results on toughened TGDDMDDS epoxy matrix prepregs are reported. A theoretical kinetic model proposed for the unaged system has been adapted for aged prepregs, by properly evaluating the variations of kinetic parameters with the aging time.     

Viscoelastic and mechanical characterization of graphene decorated with graphene quantum dots reinforced epoxy composites

The article explores viscoelastic and mechanical property analysis of graphene decorated with graphene quantum dots (GDGQD) reinforced epoxy composite. Tensile, nanoindentation, and nano-dynamic mechanical analysis (DMA) tests were conducted on the composite with 0 to 1 wt% filler variation (an interval of 0.25 wt% maintained). The hardness and elastic modulus for two different loading conditions under a frequency range of 10 to 250 Hz were performed. The viscoelastic properties described through loss tangent and storage modulus graphically and the various factors such as modulus and depth of penetration were influenced by force frequency and mobility of the molecular chain. The results revealed the role of GDGQDs as filler material for enhancing the nanomechanical and tensile properties of the epoxy matrix. The differences in the properties can be ascribed to the filler interfacial bonding with the polymer matrix at the molecular level. The macro-level properties like tensile properties following the same trend as that of the micro-level properties like nano-indentation and nano-DMA results. Further, with the GDGQD aspect ratio, and assuming three-dimensionally filled randomly orientation of filler, the Halpin-Tsai model was satisfied with the experimental tensile modulus values.     

Processing and characterization of high content multilayer graphene/epoxy composites with high electrical conductivity

A new processing method was developed to fabricate nanocomposites with a high concentration of multilayer graphene (MLG) in a highly oriented morphology. MLG was first dispersed in a water‐based solution with the aid of polyethylenimine. A thin MLG film (paper) having highly in‐plane aligned platelets was produced by using a vacuum‐assisted self‐assembly (VASA) technique. After heat treatment, the MLG paper was immersed in an epoxy/acetone bath at room temperature under vacuum to produce an epoxy impregnated composite. After removal of the acetone, nanocomposites consisting of multiple layers of the MLG paper with up to 27 wt% MLG were fabricated and thermally cured. Scanning electron microscopy (SEM) examination showed that the MLG was well dispersed and aligned, and the MLG paper was fully impregnated with epoxy resin. At 30°C, dynamic mechanical analysis (DMA) results showed that the storage modulus of the resulting nanocomposites with 27.2 wt% MLG reached 10.2 GPa, a 300% increase compared to the neat epoxy. The resulting composites also exhibited electrical conductivity as high as 35 Siemens per centimeter (S/cm). This research demonstrates that the VASA processing technique is capable of fabricating well aligned, high content MLG nanostructured polymer composites with high electrical conductivity. POLYM. COMPOS., 37:2897–2906, 2016. © 2015 Society of Plastics Engineers     

Dynamic mechanical properties of some epoxy matrix composites

Dynamic mechanical properties of some epoxy matrix composites have been studied, comparing experimental data with theoretical models. The matrix in all composite samples was Shell Epon 828, a diglycidyl ether of bisphenol A, cured with meta-phenylenediamine. Fibrous composite samples were made with glass and graphite fibers. Particulate composite samples were made with glass microspheres, atomized aluminum, powdered silica, alumina, asbestos, mica, carbon black, and graphite. The dynamic elastic modulus and damping of these samples were measured at temperatures between 85° and 345°K by a free-free flexural resonance technique. The dynamic modulus of parallel fiber composites follows the linear rule of mixtures for low fiber volume fractions; deviations from linearity at higher volume fractions appear to be due to defects caused by the sample fabrication technique. Dynamic moduli of the particulate composites conform, within experimental error, to the static modulus theory of Wu up to filler volume fractions of 0.35 to 0.40. Deviations from Wu's theory at higher volume fractions may be due to agglomeration of filler particles. The damping of particulate composites with quasi-spherical filler particles appears to follow the rule of mixtures. In particulate composites with needle- and flake-type fillers, and in fibrous composites, the fillers are more highly stressed; with more of the strain energy in the low-damping fillers, overall damping is reduced. Damping greater than that attributable to the matrix and filler may be due to slippage at the interface between them. In addition to supporting Wu's theory of the elastic modulus of a particulate composite, this study demonstrates the utility of the nondestructive free-free flexural resonance techniques for obtaining a large body of reliable data in a short time from relatively few small samples. This greatly facilitates the experimental testing of theoretical models and the evaluation of fillers, matrix materials, and fabrication techniques.     

Finite element modeling of curing of epoxy matrix composites

A two‐dimensional finite element model is developed to simulate and analyze the mechanisms pertaining to resin flow, heat transfer, and consolidation of laminated composites during autoclave processing. The model, which incorporates some of the best features of models already in existence, is based on Darcy's law, the convection–diffusion heat equation, and appropriate constitutive relations. By using a weighted residual method, a two‐dimensional finite element formulation for the model is presented and a finite element code is developed. Numerical examples, including a comparison of the present numerical results with one‐dimensional and two‐dimensional analytical solutions, are given to indicate the accuracy the finite element formulation. Moreover, using the finite element code, the one‐dimensional cure process of a laminate made of 228 and 380 plies of AS4/3501‐6 unidirectional tape is simulated and numerical results are compared with available experimental results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2310–2319, 2007     

环氧基体树脂的制备与性能表征

以MTHPA(甲基四氢苯酐)为固化剂,XY-748(C_(12-14)烷基缩水甘油醚)为稀释剂,DMP-30[2,4,6-三(二甲氨基甲基)苯酚]为促进剂,CTBN(端羧基丁腈橡胶)为增韧剂,再辅以扩链剂D-248改性混合环氧树脂F-47/E-51,制得了无溶剂新型环氧基体树脂;并对基体树脂的变温拉伸剪切强度、凝胶化时间、固含量、吸水性、介电性能、体积电阻率、接触角与表面能等进行了测试。研究结果表明:此新型环氧基体树脂具有优异的力学性、介电以及疏水性能。     

Understanding the decomposition and fire performance processes in phosphorus and nanomodified high performance epoxy resins and composites

This paper investigates the decomposition mechanism and fire performance of high performance epoxy amine resins and laminate systems, using thermogravimetry (TGA), energy dispersive spectroscopy (EDS), cone calorimetry and Fourier transform infra-red spectroscopy (FTIR). Two different, commercially-important epoxy resins, tetraglycidyl methylene dianiline (TGDDM) and diglycidyl ether of bisphenol A (DGEBA) have been cured separately with diethyl toluene diamine (DETDA) and bis(4-aminophenoxy)phenyl phosphonate (BAPP) and their relative combustion performance has been examined and discussed in terms of their decomposition profile. This paper highlights the close relationship between char yields (TGA and cone calorimetry) and thermal decomposition with the peak heat release rate, highlighting the role of the condensed phase in minimizing combustion. The lower decomposition temperatures and higher char yields of the tetra-functional epoxy (TGDDM) are therefore seen to provide superior fire performance compared to the bi-functional (DGEBA) epoxy. FTIR shows that the decomposition occurs through initial cleavage of P-O-C bonds in preference to other covalent bonds, which allows dehydration and subsequent charring and/or chain scission. TGA demonstrated that the laminated systems did not show a significant difference to the neat resin systems, with respect to initial decomposition of the network and the thermal stability of the char layer. Nanoclay addition was also found to have little effect upon degradation and fire performance.     

基质沥青种类对高韧性环氧沥青混合料性能影响分析

采用5种不同种类的70#基质沥青,在相同条件下制备高韧性环氧沥青及其混合料,考察基质沥青种类对高韧性环氧沥青混合料路用性能的影响。结果表明,5种高韧性环氧沥青混合料的马歇尔稳定度均达到50 kN以上,劈裂抗拉强度均大于2.8 MPa, 70℃动稳定度均达到30 000次/mm以上,-10℃低温抗拉应变均在5 000με以上,残留稳定度和冻融劈裂强度比均在90%以上,600με微应变四点弯曲疲劳寿命均大于100万次。高韧性环氧沥青混合料具有出色的路用性能,其性能更多地由树脂的性能决定,而基质沥青的性能影响较小。高韧性环氧沥青对基质沥青的种类具有较强的普适性,工程应用局限性较小。     

Pseudoreinforcement effect of multiwalled carbon nanotubes in epoxy matrix composites

The carbon nanotube possesses outstanding physical properties. Theoretically, adding carbon nanotubes into a polymer matrix can remarkably improve the mechanical properties of the polymer matrix. In the present work, a series of composites was prepared by incorporating multiwalled carbon nanotubes (MWNTs) into an epoxy resin. The influences of MWNT content and curing temperature on the flexural properties of the epoxy resin were investigated. The results showed that a very low MWNT content should be used to ensure homogeneous dispersion of MWNTs in the epoxy matrix. A higher MWNT content may lead to deteriorated mechanical properties of the composites because of the aggregation of MWNTs. A decline in the flexural properties of the neat epoxy resin with increasing curing temperature was found. However, under the same curing conditions, improvement in flexural properties was observed for the composite with the low MWNT content and a mild curing temperature. The improvement was far beyond the predictions of the traditional short‐fiber composite theory. In fact, this improvement should be attributed to the retarding effect of MWNTs on the curing reaction of epoxy matrix. Therefore, the improvement in the flexural properties was only a pseudoreinforcement effect, not a nano‐reinforcement effect of the MWNTs on the epoxy resin. Perhaps, it is better for MWNTs to be used as functional fillers, such as electrical or thermal conductive fillers, than as reinforcements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3664–3672, 2006     

Ultrasonic characterization of conductive epoxy resin/polyaniline composites

This study presents the ultrasonic characterization of conductive epoxy resin (ER)/polyaniline (PANI) composites. The prepared PANI is mixed with ER matrix at weight percentages of 5%, 10%, and 15% for preparing the ER/PANI composites. The effects of PANI amount on the mechanical properties of ER/PANI composites are investigated by ultrasonic pulse‐echo‐overlap method. Also, electrical conductivity, ultrasonic wave velocity and ultrasonic micro‐hardness values of ER/PANI composites are correlated. Experimental results show that there is an excellent correlation between ultrasonic micro‐hardness and ultrasonic shear wave velocity. Also, the results of ultrasonic velocities and elastic constants values illustrate that the appropriate combination ratio is 95 : 5 for ER and PANI in ER/PANI composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42748.     

环氧树脂/ABS复合材料的制备及性能表征

以环氧树脂为基体,苯乙烯-丙烯腈-丁二烯（ABS）树脂为增韧剂,制备了环氧树脂/ABS复合材料,讨论了增韧剂对复合材料的热性能和机械性能的影响。结果表明,ABS的添加可提高复合材料的断裂韧性。扫描电镜结果显示,基体的剪切屈服和橡胶颗粒的微孔洞是ABS增韧环氧树脂的主要增韧机理。     

The nonlinear viscoelastic characterization of graphite/epoxy composites

Fiber reinforced plastics offer many structural advantages for a variety of designs. Before these material systems can achieve more widespread usage, however, some of the unanswered questions regarding the long-term behavior and durability of these materials must be answered. Nonlinear compliance data is presented for T300/934 and T300/5208 graphite/epoxy composites. Several nonlinear viscoelastic techniques are compared for modeling the response. Comments for applying nonlinear models to orthotropic materials are given. A procedure for predicting long term laminate response from short term unidirectional data is reviewed.     

Mechanical characterization of new glass fiber reinforced epoxy composites

Glass fiber reinforced plastic (GFRP) composites were made using CTPEGA [carboxyl terminated poly(ethylene glycol) adipate] modified epoxy as a matrix and characterized for their flexural properties, impact strength and interlaminar shear stress (ILSS). The volume fraction of glass was about 0.45 for all the composites. The concentration of CTPEGA in the matrix was varied gradually from 0 to 40 phr (parts per hundred parts of resin), to investigate the effect of CTPEGA concentration on the mechanical properties of the composites. It was found that the flexural strength and ILSS gradually decreases with increase in CTPEGA concentration. However, the impact strength of the composites increases up to 20 phr of CTPEGA concentration and decreases thereafter. Scanning electron microscope (SEM) analysis of the fracture surface indicates massive plastic deformation in modified epoxy based composites. Polym. Compos. 25:165–171, 2004. © 2004 Society of Plastics Engineers.     

高性能环氧树脂胶粘剂的研制

以MTHPA(甲基四氢苯酐)为固化剂,以活性稀释剂(CE-793)为稀释剂,分别以CTBN(端羧基丁腈橡胶)和聚硫橡胶为增韧剂,再辅以扩链剂(D-248)改性混合环氧树脂(JP-80/E-51),制得了两种高性能环氧树脂胶粘剂,分别命名为K胶和B胶;并对胶粘剂的变温拉伸剪切强度、凝胶化时间、吸水性、介电性能进行了测试。研究结果表明:以CTBN为增韧剂的胶粘剂综合性能更好。     

Preparation of high performance adhesives matrix based on epoxy resin modified by bis-hydroxy terminated polyphenylene oxide

A bis-hydroxy terminated polyphenylene oxide (MPPO) modification was tried for the purpose of simultaneously enhancing the processability and heat resistance of epoxy resin. The thermal stability, chemorheology, morphology and mechanical properties of epoxy-polyphenylene oxide blends were investigated, respectively. The structure of MPPO was characterized by nuclear magnetic resonance and fourier transform infrared spectroscopy which indicated that MPPO was successfully synthesized. Epoxy-polyphenylene oxide blends exhibited a wide range of processing temperature mainly owing to the existence of bis-hydroxy in MPPO. Mechanical properties results revealed that the impact strength, tensile strength and elongation at break of MPPO/EP systems were performed satisfactorily. Scanning electron microscopy studies revealed the two-phase morphology and modification mechanism of the epoxy-polyphenylene oxide. Dynamic mechanical analysis and thermal gravimetric analyzer results showed that the introduction of MPPO leading to an enhancement to the thermal stability of epoxy matrix. Therefore, epoxy-polyphenylene oxide blends meet the requirements for the prepreg and high performance adhesives matrix.     

Viscoelastic behavior of epoxy/carbon fiber/Zno nano‐rods hybrid composites

The insufficient viscoelastic resistance of fiber reinforced plastics can be retrofitted by the addition of more rigid nano fillers to the polymer matrix. In this study, carbon fibers plies were grafted with zinc oxide (ZnO) nano‐rods and the hybridized reinforcement was utilized in laminated composites. Flexural creep tests were carried out using dynamic mechanical analysis (DMA) and the time/temperature superposition principle was employed for accelerated testing. To verify the applicability of TTPS, prolonged stress relaxation tests were also carried out in flexural mode. Data from the DMA flexural creep tests revealed that the whiskerization of carbon fibers with ZnO nano rods reduced the creep compliance by 23% at elevated temperatures and prolonged durations. Also, the relaxation data confirmed the applicability of TTPS to these hybrid composites. The stress relaxation modulus improved by 65% in comparison to composites based on neat carbon fibers. POLYM. COMPOS., 36:1967–1972, 2015. © 2014 Society of Plastics Engineer     

Interphase cure characterization in epoxy composites by fluorescence technique

Monitoring the reaction of an aromatic diamine cure agent with epoxy by fluorescence technique was used for cure characterization of the interphase in epoxy/glass and epoxy/carbon composites. The effect of the various surface treatments was first studied by the model interphase obtained by using a quartz plate for glass or a modified quartz plate for carbon surface. Aminosilane treated quartz cured faster and showed increased cure extent, while water aging and air oxidation showed almost no effect on the cure kinetics in comparison to the untreated quartz surface. For a model carbon surface, air oxidation showed a faster reaction only at the early stage of cure. The effects of the various surface treatments on glass or carbon fiber were also studied with the actual composites made by a thin coating of epoxy-diamine melt on glass or carbon fiber bundles. Epoxy/glass fiber composite showed a similar trend as the model interphase system. In the case of epoxy/carbon fiber composite, both air oxidation and water aging treatment showed a faster cure reaction at the early stage of cure. Furthermore, air oxidation treatment for the epoxy/carbon fiber composite showed somewhat increased cure extent. The reasons for these trends have been discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1769–1775, 1997     

Thermoforming of high performance thermoplastic composites

Matched-die forming of a 90° bend in a quasi-isotropic 16 ply laminate of ICI's APC-2, containing 61 volume % Hercules AS-4 continuous carbon fiber in poly(etheretherketone) (PEEK), is described. To uncouple and characterize elementary deformation phenomena, a series of simple tests are developed. Single ply bending of APC-2 tape up to 420°C has been performed to characterize elastic bending. Transverse flow, axial interply shear flow, and z direction elasticity have been characterized in an instrumented matched die mold. Interply shear flow is characterized using a simple shear test fixture. Transverse flow and interply slip are relatively easily induced. Precautions should be taken to avoid fiber buckling and to provide for laminate reconsolidation.     

Preparation and characterization of waterborne epoxy latexes and epoxy/(silica sol) composites

A series of waterborne epoxy latexes was synthesized, and epoxy/(silica sol) composite latexes were prepared. The effects of functional monomer methacrylic acid (MAA) and silica sol on the latex particle size, morphology, and stability were investigated. With increasing amounts of MAA, the conversion rate increased, the particle size reduced, and the viscosity of the epoxy latexes increased. The epoxy latexes had storage stability and could be stored at room temperature for more than 6 months with a solid content variation of less than 1%. For the (silica sol)‐modified waterborne epoxy latexes, the effects of preparation techniques and silica sol content on the latexes and latex films were investigated. When the silica sol content increased, the particle size of the composite latexes decreased. The morphology investigation showed that when the silica sol content increased, the uneven surface level of the latex films was increased. The increase of elemental silica on the surface was in accord with the improvement of the water resistance of the composite latex films. The heat resistance of these films was improved as well, and their overall performance was better than that of the epoxy latex films. J. VINYL ADDIT. TECHNOL., 20:57–64, 2014. © 2014 Society of Plastics Engineers     

Salicylic acid modified high performance epoxy matrices

This study focuses on the processing-structure-property relations for salicylic acid modified high performance epoxy matrix systems for carbon fiber composites. Differential scanning calorimetry and dynamic mechanical data have shown that as the concentration of salicylic acid increases, the degree of cure first increases, reaches a maximum, and then decreases steadily. Analysis of the results indicated that small amounts of salicyclic acid accelerates the amine-epoxide reactions resulting into crosslinked networks with increased degree of cure; increasing amounts, however, give rise to networks with reduced crosslinking by reducing the net available diaminodiphenyl sulfone (DDS) content in the system by a reaction of the DDS with salicylic acid. Overall, this study has demonstrated that salicyclic acid modification offers the potential for monitoring and controlling amine-epoxide reactions that may influence the application and usage of epoxy matrices in composite systems.