Montmorillonite intercalated by ammonium of octaaminopropyl polyhedral oligomeric silsesquioxane and its nanocomposites with epoxy resin

The octaammonium chloride salt of octaaminopropyl polyhedral oligomeric silsesquioxane (OapPOSS) was synthesized via the hydrolytic condensation of γ-aminopropyltrimethoxysilane in the methanol solution catalyzed by concentrated hydrochloric acid and was further used as the intercalating agent to modify sodium montmorillonite (MMT). X-ray diffraction (XRD) data indicate that the MMT was successfully intercalated by the ammonium of OapPOSS, as evidenced by the fact that the basal spacing of MMT galleries was expanded from 1.3 to 1.7 nm. The intercalation method used here introduced only the octaammonium POSS salt in contrast to the introduction of all hydrolyzed products from γ-aminopropyltriethoxysilane (APTEOS). The POSS-modified MMT was exploited to prepare the epoxy-MMT nanocomposites. Using a two-step technique, the disorderly exfoliated epoxy-MMT nanocomposites were obtained. XRD studies showed that the formation of the nanocomposites in all the cases with the disappearance of the peaks corresponding to the basal spacing of MMT. Transmission electronic microscopy (TEM) was used to investigate the morphology of the nanocomposites and indicates that the nanocomposites are comprised of a random dispersion of intercalated/exfoliated aggregates throughout the matrix. Differential scanning calorimetry (DSC) indicates that the glass transition temperatures of the as-prepared epoxy-MMT nanocomposites remained invariant in comparison with that of the control epoxy when the POSS-MMT content is less than 10 wt%. However, the nanocomposite containing 15 wt% of POSS-MMT displayed a decreased T_g, which could be attributed to the incomplete curing reaction resulting from the POSS-MMT loading. Thermogravimetric analysis (TGA) shows that the incorporation of POSS-MMT into epoxy networks displayed an apparent improvement in the thermal stability, and the char residue increased with increasing the concentration of POSS-MMT.     

Dielectric studies of three epoxy resin systems during microwave cure

Dielectric properties of three curing epoxy resin systems at an industrial microwave frequency, 2.45 GHz, were measured over a temperature range lower than the cure temperature. Extent of cure, which is determined by DSC, is used to describe the progress of the polymerization. It has been found that, normally, the real and the imaginary part of the complex dielectric constant increased with temperature and decreased during microwave cure. The changes of the dielectric properties during the reaction are related to the decreasing number of the dipolar groups in the reactants and the increasing viscosity. The Davidson-Cole model can be used to describe the experimental data. The Zong model is applicable to polymeric materials at high microwave frequencies and can be used to calculate the parameters of the Davidson-Cole model. The epoxy resins exhibit one γ relaxation, which can be described by the Arrhenius rate law. The evolutions of the parameters in the models are discussed.     

Effect of polythiourethane hardener modification on the behaviour of epoxy resin

Polythiourethanes based on oligomeric polymercaptans were employed as curing agent of epoxy resin. The epoxy matrices, in the form of castings, were characterized for their mechanical properties such as tensile strength, elongation at break and unnotched Charpy impact strength as per ISO methods. Mechanical studies indicated that the incorporation of polythiourethane into epoxy resin improves the toughness and flexibility with reduction in tensile strength for samples cured at ambient conditions and influences the mechanical and thermal properties according to its percentage content for samples cured at 130°C. The high increase of impact strength was explained by the development of two-phase morphology during the cure process. The results of this study indicate that both the stoichiometry of the curing mixture and the initial thermal condition are of critical importance in governing the curing mechanism, structure of the network, morphology and the final properties of epoxy/polythiourethane compositions.     

Synthesis and characterization of a functional polyhedral oligomeric silsesquioxane and its flame retardancy in epoxy resin

A functional polyhedral oligomeric silsesquioxane (NPOSS) with two epoxy ring groups was synthesized via the reaction between trisilanolisobutyl-POSS and triglycidyl isocyanurate, and then a halogen-free epoxy composite containing silicon/nitrogen was prepared. The results of microscale combustion calorimeter indicate that the presence of NPOSS (10% weight ratio) in epoxy resin (EP) can decrease its peak heat release rate by about 30%. The thermal oxidation and degradation behaviors of EP and EP/NPOSS composites were characterized by DSC, TG, FTIR-TG and dynamic FTIR. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to explore the char residues of composites. The thermal degradation and flame retardant mechanism has been evaluated. NPOSS can retard the movement and scission of polymeric chains of EP and form a stable charred layer in the condensed phase to prevent the underlying materials from further combustion.     

Morphology and thermal properties of inorganic-organic hybrids involving epoxy resin and polyhedral oligomeric silsesquioxanes

The organic-inorganic hybrids involving epoxy resin and polyhedral oligomeric silsesquioxanes (POSS) were prepared via in situ polymerization of diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenylmethane (DDM) in the presence of the two structurally similar POSS monomers. The organic groups on silsesquioxane cage are aminophenyl and nitrophenyl groups, respectively. The curing reactions were started from the initially homogeneous mixture of DGEBA, DDM and the POSS cages. The inorganic-organic hybrids containing up to 20 wt% of POSS were obtained. The morphologies of the resulting hybrids were quite dependent on the types of R groups in the POSS monomers. The phase separation induced by polymerization occurred in the hybrids containing octanitrophenyl POSS (OnpPOSS) and the spherical particles of POSS-rich phase (<0.5 μm in diameter) were uniformly dispersed the continuous epoxy matrix as shown by scanning electronic microscopy. In marked contrast to the OnpPOSS-containing hybrids, the octaaminophenyl POSS (OapPOSS)-containing nanocomposites exhibited a homogeneous morphology. Differential scanning calorimetry and dynamic mechanical analysis showed that the glass transition temperatures (T_g) of the POSS-containing hybrids were lower than that of the control epoxy. The moduli of glass states for the hybrids are significantly higher than that of the control epoxy. For the OapPOSS epoxy nanocomposites the storage moduli of the rubbery plateau were higher than that of the control epoxy when the contents of POSS are less than 20 wt%, indicating the nanoreinforcement effect of POSS cages. Thermogravimetric analysis indicates that the thermal stability of the polymer matrix was not much sacrificed by introducing a small amount of POSS, whereas the properties of oxidation resistance of the materials were significantly enhanced. The OapPOSS epoxy nanocomposites displayed more pronounced improvement than the OnpPOSS hybrids, which could be ascribed to the nanoscaled dispersion of POSS cages and the formation of tether structure of POSS cages with epoxy matrix.     

Thermo mechanical behaviour of unsaturated polyester toughened epoxy–clay hybrid nanocomposites

The intercrosslinked networks of unsaturated polyester (UP) toughened epoxy–clay hybrid nanocomposites have been developed. Epoxy resin (DGEBA) was toughened with 5, 10 and 15% (by wt) of unsaturated polyester using benzoyl peroxide as radical initiator and 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. The chemical reaction of unsaturated polyester with the epoxy resin was carried out thermally in presence of benzoyl peroxide-radical initiator and the resulting product was analyzed by FT-IR spectra. Epoxy and unsaturated polyester toughened epoxy systems were further modified with 1, 3 and 5% (by wt) of organophilic montmorillonite (MMT) clay. Clay filled hybrid UP-epoxy matrices, developed in the form of castings were characterized for their thermal and mechanical properties. Thermal behaviour of the matrices was characterized by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Mechanical properties were studied as per ASTM standards. Data resulted from mechanical and thermal studies indicated that the introduction of unsaturated polyester into epoxy resin improved the thermal stability and impact strength to an appreciable extent. The impact strength of 3% clay filled epoxy system was increased by 19.2% compared to that of unmodified epoxy resin system. However, the introduction of both UP and organophilic MMT clay into epoxy resin enhanced the values of mechanical properties and thermal stability according to their percentage content. The impact strength of 3% clay filled 10% UP toughened epoxy system was increased by 26.3% compared to that of unmodified epoxy system. The intercalated nanocomposites exhibited higher dynamic modulus (from 3,072 to 3,820 MPa) than unmodified epoxy resin. From the X-ray diffraction (XRD) analysis, it was observed that the presence of d ₀₀₁ reflections of the organophilic MMT clay in the cured product indicated the development of intercalated clay structure which in turn confirmed the formation of intercalated nanocomposites. The homogeneous morphologies of the UP toughened epoxy and UP toughened epoxy–clay hybrid systems were ascertained from scanning electron microscope (SEM).     

Few-layer boron nitride nanosheets: Preparation,characterization and application in epoxy resin

Large-scale exfoliated boron nitride nanosheets were achieved via a liquid exfoliation sonication method by using sodium fluoride and ammonium hydroxide as Lewis base compounds. The crystal structure, surface functional groups, morphology and thickness of the as-prepared samples were characterized by X-ray diffraction, fourier transform infrared spectroscopy, transmission electron microscopy and atomic force microscopy, respectively. The as-prepared samples were introduced into epoxy resin to fabricate the polymer-based composites. Experimental results showed that the layer thickness of the as-prepared nanosheets was in the range of 1 to 3 layers. Moreover, it could improve the tensile properties of the matrix. When the loading of the as-prepared nanoparticles was 0.4 wt%, the tensile strength and elongation at break of the composites reached to their maximum values 65.6 MPa and 25.9%, which were increased by 118% and 192% more than that of pure resin. In addition, the as-prepared boron nitride samples could improve the thermostability and promote the curing of the matrix.     

Effects of titanate coupling agent on the dielectric properties of NiZn ferrite powders–epoxy resin coatings

During ferrite powder–polymer resin slurry preparation, the ferrite particles tend to hold together, forming agglomerates, which lead to the formation of micro-structural defects in the ferrite powder–polymer coatings. These defects affect the quality of magnetic devices. In this study, the titanate coupling agent effects on the NiZn ferrites powder dispersion in an epoxy resin and solvent system and the electromagnetic properties of NiZn ferrite powders–epoxy resin composite coatings are investigated. It was observed that the dispersion of NiZn ferrite powders and the affinity of NiZn ferrites and epoxy resin can be substantially enhanced by coating a titanate coupling agent onto the ferrite powder surfaces. This coating promotes mixing homogeneity and increases the dielectric constants at low frequencies (below 100 Hz) due to the increase in phase boundary between the NiZn ferrite powders and epoxy resin.     

The thermal characteristics of epoxy resin: Design and predict by using molecular simulation method

Trial-and-error approaches for experimentally designing and optimizing the polymer matrix for advanced composites are time-consuming and expensive. The simulation for curing behavior and structure–property relationships of epoxy resins can provide a guideline for designing resin matrix which will possess desirable properties. So far there are few reports in which the accuracy of the molecular simulation for the different amine-epoxy systems are addressed. In this paper, an atomistic modeling technique was used to theoretically investigate the curing and thermal transition behavior of two epoxy resin matrices containing amine curing agent with different chemical structures i.e. diaminodiphenyl methane (DDM)/diglycidyl-4,5-epoxycyclohexane-1,2-dicarboxylate (TDE85) and diaminodiphenyl sulfone (DDS)/TDE85 to give help for designing high heat-resistant epoxy matrix. The simulated results successfully predicted that the reaction process was catalyzed in the early stage of the curing and the slight modification in the diamine structure resulted in significant change in the curing and glass transition behavior of epoxy resin. As the bridging group of diamine changed from methylene to sulphone, the reactivity of diamine toward epoxy declined and the glass transition temperature increased from about 190 °C to about 230 °C. This simulated method presented a good agreement with experimental data, and can be used to design and predict high performance resin matrix for advanced composites.     

铸造用自硬环氧树脂砂粘结性能的研究

采用聚酰胺作为环氧树脂固化剂,研究了树脂、固化剂另入量对型芯砂强度的影响,并测定了环 脂砂的硬化曲线,根据该曲线确定出其可和时间和可脱模时间。结果表明：自硬环氧树脂砂具有较高的强度,适宜的可使用时间及可脱模时间,能够满足铸造生产中造型和制芯的要求。     

纳米粒子对环氧树脂的增韧改性研究

介绍了近几年来研究的几种纳米粒子对环氧树脂韧性的影响情况。     

Synthesis and properties of waterborne epoxy acrylate nanocomposite coating modified by MAP-POSS

In this paper, waterborne epoxy acrylate (EA) coating modified with methylacryloylpropyl polyhedral oligomeric silsesquioxanes (MAP-POSS) was prepared. The cure kinetics of the coating was investigated by differential scanning calorimetry (DSC). The curing process, thermal and mechanical properties of the coating were investigated by FTIR, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). These results show that the non-isothermal curing process can be described by Kissinger method and a two-parameter autocatalytic Šesták–Berggren (S–B) model. The kinetic equations of curing reaction were obtained. The UV-curing property of MAP-POSS/EA nanocomposite coating is better than that of pure epoxy acrylate system. The glass transition temperature (T_g) increases with increasing MAP-POSS content. When MAP-POSS content is 12 wt%, the T_g reaches the maximum 54.3 °C which is 9.5 °C higher than that of pure epoxy acrylate.     

Development and characterization of phosphorus-containing siliconized epoxy resin coatings

The objective of the present work is the development and characterization of siliconized epoxy-phosphorus based bismaleimide coating systems using diglycidylether terminated poly (dimethylsiloxane) (DGTPDMS) and phosphorus-containing bismaleimide (PBMI) as chemical modifiers for epoxy resin. Phosphorus-containing diamine (DOPO-NH₂) was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 4,4′-diaminobenzophenone (DABP), which was utilized in the preparation of phosphorus-containing bismaleimide (PBMI) with maleic anhydride. Siliconized epoxy prepolymer was prepared using epoxy resin and functionally terminated polydimethylsiloxane. The purity and structural conformation of these materials were ascertained from FTIR and NMR spectral studies. The prepared siliconized epoxy prepolymer was blended with varying percentages of PBMI using diaminodiphenylsulfone (DDS) and diaminodiphenylmethane (DDM) as curing agents. The siliconized epoxy and bismaleimide modified epoxy and siliconized epoxy coating materials were characterized by dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), heat distortion temperature (HDT) and Limiting oxygen index (LOI).     

Flame retardancy and thermal degradation mechanism of epoxy resin composites based on a DOPO substituted organophosphorus oligomer

A series of flame-retardant epoxy resins (EP) with different content of poly(DOPO substituted dihydroxyl phenyl pentaerythritol diphosphonate) (PFR) were prepared. The PFR was synthesized via the polycondensation between 10-(2,5-dihydroxyl phenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-BQ) and pentaerythritol diphosphonate dichloride (SPDPC). The structure of PFR was confirmed by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance (¹H NMR). The flame retardancy and the thermal stability of the EP/PFR hybrids were investigated by limiting oxygen index (LOI) test and thermogravimetric analysis (TGA) in air. The results showed that the incorporation of PFR into EP can improve the thermal stability dramatically. The mechanical results demonstrated that PFR enhanced failure strain slightly accompanied by a decrease in tensile strength. The thermal oxidative degradation mechanisms of the EP/PFR hybrids were investigated by real time Fourier transform infrared spectra (RTFTIR) and direct pyrolysis/mass (DP-MS) analysis. X-ray photoelectron spectroscopy (XPS) was used to explore chemical components of the residual char of EP and EP/PFR hybrid. DP-MS analysis showed that the degradation process of EP/PFR hybrid was divided into two characteristic temperature regions, attributed to the decomposition of phosphate and aromatic structure.     

Dielectric properties of epoxy composites with modified multiwalled carbon nanotubes

We report here a high dielectric percolative polymer nanocomposite, fabricated by a combination of triethylene-tetramine (TETA) modified multiwalled carbon nanotube (named as TETA-MWNT) within epoxy resin matrix. In this composite system, with various TETA-MWNT volume fractions, the dielectric constant (K) is well fitted by the scaling law of the percolation theory with the percolation threshold f _c is 0.042 and the critical exponent p is 0.786. At 1,000 Hz of room temperature, the value of the dielectric constant is as high as 421 with the TETA-MWNT content of 4.14vol%, which is almost 60 times higher than that of epoxy resin. In contrast, a simple blend of pristine MWNT in epoxy composite shows evident lower dielectric constant and much higher loss with the same volume fraction.     

阻燃环氧树脂胶黏剂的研制

采用以KH-560硅烷偶联剂包覆三聚氰胺多聚磷酸酯（MPP）为阻燃剂,以环氧树脂E-44为基体,制备阻燃环氧树脂胶黏剂。通过对所制得胶黏剂进行剪切强度测试、热失重测试以及阻燃性能测试,研究了包覆阻燃剂对环氧树脂胶黏剂力学性能、热稳定性和阻燃性能的影响。结果表明,采用包覆处理MPP为阻燃剂制备的阻燃环氧树脂胶黏剂综合性能较好,其剪切强度为19．9MPa,氧指数为31．2。最佳配方为100份环氧树脂、30份阻燃剂、30份固化剂、温度为70℃。     

Changes in the dielectric relaxations of water in epoxy resin as a function of the extent of water ingress in carbon fibre composites

Dielectric relaxation measurements are reported over a frequency range from 10⁻¹ to 10⁹ Hz as a function of exposure time for an epoxy resin-carbon fibre composite, ageing at 60 °C in water. Investigation of the nature of the dipole relaxation of the water molecules, indicates the nature of their interaction with the polymer matrix. Analysis of the dielectric relaxation spectra allow identification of processes that can be attributed to ‘free’ and ‘bonded’ water, water in micro-cracking, located in carbon fibre disbonds and plasticizing the polymer matrix. Identification of the various types of location in which water exists was aided by use of the N_g factor from the Kirkwood-Frölich equation, which describes the constraints on free dipole ration nature imposed by the environment in which it is located. These data indicate the power of the dielectric technique for quantitative analysis of water ingress into epoxy composites.     

红外光谱法研究环氧类涂料对水汽的吸附

用红外光谱法研究了湿度对环氧类涂料表面吸附水汽的影响,并讨论了不同湿度对环氧类涂料和粘合剂之间的附着力的影响,为涂料的施工提供了快速质量监控的方法。     

高折射率含硫环氧树脂的合成与表征

通过2，2‘-二巯基二乙硫醚（MES）与环氧氯丙烷反应，合成了一种新型高折射率，低色散的2，2‘－二巯基二乙硫醚缩水甘油醚型光学环氧树脂（DGEMES），采用红外光谱和核磁共振谱图表征了该树脂的结构，并详细讨论了直接法和间接法合成DGEMES的各种反应条件对产率的影响，得出直接法制取DGEMES的最佳原料配比为：n(MES):n(环氧氯丙烷）：n(NaOH)=1:5:1.9，产率为981％，折射率为1．5450，间接法制取DGEMES中的最佳原料配比为：n(MES):n(环氧氯丙烷）:n(NaOH)=1:2.4:6，产率为99．32％，折射率为1．5661。