Isocyanate-terminated Polyethers Toughened Epoxy Resin:Chemical Modification,Thermal Properties,and Mechanical Strength

The toughening of the diglycidyl ether of bisphenol A epoxy resin with isocyanate-terminated polyethers(ITPE)was investigated.The progress of the reaction and the structural changes during modification process were studied using FTIR spectroscopy.The studies support the proposition that TDI(tolylene diisocyanate)acts as a coupling agent between the epoxy and polyethers,forming a urethane linkage with the former and the latter,respectively.Me THPA-cured ER/ITPs blends were characterized using dynamic mechanical analysis(DMA)and thermogravimetric analysis(TGA).It is indicated the glass transition temperature(T g )of systems was lower than the T g of pure epoxy resin and overfull ITPE separated from the modified epoxy resin and formed another phase at an ITPE-content of more than 10wt%.The thermal stability was decreased by the introduction of ITPE.The impact strength and the flexural strength of the cured modified-epoxy increased with increasing the ITPE content and a maximum plateau value of about 24.03 kJ/m2 and 130.56 MPa was measured in 10wt%ITPE.From scanning electron microscopy(SEM)studies of the fractrue surfaces of ER/ITPE systems,the nature of the micromechanisms responsible for the increases in toughness of the systems was identified.     

Damping properties of flexible epoxy resin

Amino-terminated polyethers and amino-terminated polyurethane were used as curing agent to cure the epoxy resin together and get a series of cured products. The damping properties of the composites were studied by DMA test at different measurement frequencies. Damping mechanical tests show that the flexible epoxy resin has higher loss factor than common epoxy. The highest loss factor reaches 1.57. Also the height and position of loss factor peak of the flexible epoxy resin varies by changing the content of amino-terminated polyethers. Results shows that the flexible epoxy resin can be used as damping polymer materials at room temperature or in common frequency range.     

Curing Kinetics and Properties of Epoxy Resin with 1,4-bis(2,4-diaminophenoxy)benzene

A multifunctional amine, 1,4-bis(2,4-diaminophenoxy)benzene(14 BDAPOB), was prepared and used as a novel hardener for novolac epoxy resin(ER). The structure of 14 BDAPOB was characterized with Fourier transform infrared(FT-IR) spectroscopy and differential scanning calorimetry(DSC). The curing kinetics of the novolac epoxy resin/1,4-bis(2,4-diaminophenoxy)benzene(ER/14 BDAPOB) system was studied by means of non-isothermal DSC experiments at five heating rates and determined by the Kissinger, Ozawa and Crane methods. The results showed that the activation energy Ea of the ER/14 BDAPOB(74.56 kJ/mol) system was higher than that of the epoxy resin/LCA-30(ER/LCA-30, 68.85 kJ/mol), where LCA-30 is a commercial modified diamine. The reaction order, frequency factor and the reaction rate constant at peak temperature of the two systems were calculated. The initial decomposition temperatures(Tonset) were 398.8 ℃(ER/14 BDAPOB)and 334.3 ℃(ER/LCA-30). The tensile shear strengths were 21.63 MPa(ER/14 BDAPOB) and 21.28 MPa(ER/LCA-30). The results showed that the two cured systems exhibited good thermal and mechanical properties.     

Preparation and properties of Nano-SiO2/TDE-85/BMI/BADCy composites

A new type of the nanometer particles and epoxy/bismaleimide-triazine nanocomposites were prepared using a nanometer silica (nano-SiO2), a 4,5-epoxycyclohexane 1,2-dicarboxylic acid dilycidyl (TDE-85) epoxy resin, a 4,4’-bismaleimidodiphenymethane (BMI) and a bisphenol a dicyanate (BADCy). The properties of nano-SiO2/TDE-85/BMI/BADCy composites, such as mechanical and thermal properties, were systemically investigated in detail by mechanical measurement, scanning electron microscope (SEM), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The experimental results showed that the addition of the appropriate amount of nano-SiO2 could improve the impact strength and the flexural strength of the nano-SiO2/TDE-85/BMI/BADCy composites. Simultaneously, the thermal stability of the blends was found to be higher than that of the TDE-85/BMI/BADCy copolymers.     

Synthesis and properties of novel epoxidized soybean oilmodified phenolic resin/montmorillonite nanocomposites

The novel epoxidized soybean oil-modified-phenolic resin/clay nanocomposites（ESO-M-PR/ CN） was prepared. The coupling agent-benzyldimethylphenylammonium chloride [C6H5CH2N^＋（CH3）2C6H5Cl^- , B2MP] was adopted to modify the interface between the organic and inorganic phases. The effect of the nanocomposite structure on its physical and chemical properties was discussed. During the synthesizing process of ESO-M-PR/CN, the phenol hydroxyl was etherified by ESO or ESO epoxy resin prepolymer to provide long ESO epoxy segments. Long ESO epoxy resin chain segments enhanced the crosslink density of ESO-M- PR/CN. The thermal and mechanical properties exhibit a significant improvement. The temperature at which a weight loss of 5% occurs increases from 287.1 ℃ to 402.3 ℃. The flexural strength increases by 25%, while the flexural modulus increases by 39%. Moreover, the properties of resin were enhanced by the effect of the inorganic nanoparticles, while the size of the nanomontmorillonites in the phenolic resin was characterized with a scanning electron microscope. The particle size of inorganic montmorillonites in the modified system is less than 100 nm.     

Study on T700/cyanate/PS/epoxy composites with ex-situ toughening technique

Composites were prepared with polysulfone through ex-situ toughening technique. The dynamic parameters of cyanate/epoxy resin were studied by differential scanning calorimetric（DSC） analysis and dynamic mechanical analysis（DMA）. Microstructual toughening mechanism was studied through scanning electron microscopy（SEM）. The particle microstructure in interlaminar region of composites toughened through ex-situ toughening technique revealed that a reaction induced phase decomposition and phase inversion happened in the interlaminar region. The thermosetting particles were surrounded by the PS phase, which could signifi cantly improve the delamination resistance of composites. The compression after impact（CAI） can be signifi cantly improved from 180 MPa to 260 MPa by using ex-situ toughening while the mechanical properties are not affected.     

Curing of Epoxy Resin Induced by Femtosecond Laser Pulse

The possibility of curing of epoxy resin induced by femtosecond laser beam was explored through choosing different initators.Absorption spectroscopy, infrared spectroscopy（IR）,stereomicroscopy and scanning electron microscopy（SEM0 were applied to analyze the structure of epoxy resin systems after irradiation with a femtosecond laser beam.The experimental results show that the epoxy resin systems containing diaryliodonium salts can be cared by irradiation of femtosecond laser pulse,while the systems containing benzoing can not be cured.It is found that diaryliodonium salts decompose under the irradiation of femtosecond lase pulse through multi（two）-photon absorption,initiating the ring-opening polymerization of epoxy resin.And the appearance of cured area has a sheet structure consisting of many tiny lamellar structures.     

Mechanical behavior and failure mechanism of 2.5D (shallow bend-joint,deep straight-joint) and 3D orthogonal UHWMPE fiber/epoxy composites by vacuum-assistant-resin-infused

Ultra-high molecular weight polyethylene(UHMWPE) fiber/epoxy composites were fabricated by a vacuum assisted resin infused(VARI) processing technology. The curing condition of composites was at a cure temperature of 80 ℃ for 3h in a drying oven. The characteristics of 2.5D(shallow bend-joint and deep straight-joint) structure and 3D orthogonal structure were compared. The failure behavior, flexural strength, and microstructures of both composites were investigated. It was found that the flexural property was closely related to undulation angle θ. The flexural strength of 3D orthogonal structure composite was superior to the other two structures composites with the same weave parameters and resin.     

Structural characteristics and properties of PU-modified TDE-85/MeTHPA epoxy resin

Diglycidyl-4,5-epoxycyclohexane-1,2-dicarboxylate (TDE-85)/methyl tetrahydro-phthalic anhydride (MeTHPA) epoxy resin was modified by polyurethane(PU), and its structural characteristics and properties were studied by infrared spectrum analysis (IR), scanning electronic microscopy (SEM), mechanics testing and thermogravimetric analysis (TG). The results indicate that epoxy polymeric network I and polyurethane polymeric network II are formed in the PU-modified TDE-85/MeTHPA epoxy resin. Meanwhile the PU-modified TDE-85/MeTHPA resins have heterogeneous structure. The miscibility between epoxy (EP) and polyurethane (PU) as well as the phase size are dominantly determined by the mass fraction of polyurethane prepolymer (PUP) in the EP/PU blends. With the increase of PUP mass fraction, the tensile strength, impact strength and thermal stability of the PU-modified TDE-85/MeTHPA epoxy resin all firstly exhibit increasing tendency, and decrease after successively reaching their maxima. When the number-average molecular mass of PPG is 1 000 and the mass fraction of PUP is 15%, the tensile strength, impact strength and thermal stability of materials obtained, compared with TDE-85/MeTHPA epoxy resin, are improved obviously.     

Structural characteristics and properties of polyurethane modified TDE-85/MeTHPA epoxy resin with interpenetrating polymer networks

Diglycidyl-4,5-epoxycyclohexane-1,2-dicarboxylate（TDE-85）/methyl tetrahydrophthalic anhydride （MeTHPA） epoxy resin was modified with polyurethane（PU） and the interpenetrating polymer networks（IPNs） of PU-modified TDE-85/MeTHPA resin were prepared. The structural characteristics and properties of PU-modified TDE-85/MeTHPA resin were investigated by Fourier transform infrared（FTIR） spectrum,emission scanning electron microscopy（SEM） and thermogravimetry（TG）. The results indicate that epoxy polymer network （Ⅰ） and polyurethane polymer network （Ⅱ） of the modified resin can be obtained and the networks （Ⅰ） and （Ⅱ） interpenetrate and tangle highly each other at the phase interface. The micro morphology presents heterogeneous structure. The integrative properties of PU-modified TDE-85/MeTHPA epoxy resin are improved obviously. The PU-modified TDE-85/ MeTHPA resin’s tensile strength reaches 69.39 MPa,the impact strength reaches 23.56 kJ/m,the temperature for the system to lose 1% mass （t1%） is 300 ℃,and that for the system to lose 50% mass （t50%） is 378 ℃. Compared with those of TDE-85/MeTHPA resin,the tensile strength,impact strength,t1% and t50% of the PU-modified resin increases by 48%,115%,30 ℃,11 ℃,respectively. The PU-modified TDE-85/MeTHPA resin has the structure characteristics and properties of interpenetrating polymer networks.     

Melt synthesis and characterization of poly(L-lactic acid) chain linked by multifunctional epoxy compound

High molecular weight(Mw) poly(L-lactic acid)s(PLLAs) were synthesized using multifunctional epoxy compound(Joncryl-ADR4370) as chain extender. The products were characterized by gel permeation chromatography(GPC) and spectroscopy(¹HNMR and FTIR). The results indicated that the Mw of PLLA increased with the increasing of the ratio of epoxy compound and the extending of reaction time. The highest M _w of PLLA reached 360 000 g/mol when the ratio of epoxy compound was 1.5 wt%. However, the reactants turned to cross-linking when the ratio of epoxy compound was over 1.5 wt%. Differential scanning calorimetry(DSC) measurements demonstrated that the glass transition(T _g) and melting temperatures(T _m ) of products increased slightly as the increase of the molecular weight. Analysis of the hydrolytic degradation in vitro showed that the branched PLLA possessed the quicker degradability than that of the linear PLLA.     

Cold resistant properties of high modulus polyurethane

Six kinds of polyurethane (PU) elastomers were prepared based on different polyesters, polyethers and chain extenders. The structure, mechanical properties and cold resistant properties of PU were systematically investigated by FTIR, XRD, DMTA, universal testing machine and flex ductility machine. The results show that T _g of soft segment is the main factor of the cold resistant properties of polyurethane elastomer. Compared with the same relative molecular mass of the polyester and the polyether, the polyether flexibility is better, the glass transition temperature (T _g) is lower and the cold resistant properties is remarkable, for example the cold resistant properties of PU based on poly (tetramethylene glycol), 1, 4-BG and MDI achieves the fifth level. The physics performances of polyurethane elastomers, such as breakdown strength, Young’s modulus and the cold resistant properties, are all superior.     

Non-isothermal curing kinetics and thermal properties of benzoxazine-phenolic copolymers

Using novolac phenolic resin, aniline and formaldehyde as raw materials, benzoxazine-phenolic copolymers with different percentages of benzoxazine rings were prepared. FT-IR was adopted to characterize the molecular structure of the novolac-type phenolic resin and the benzoxazine-phenolic copolymer BP31. In order to understand the curing process of the copolymers, the curing behavior and curing kinetic characteristics were studied by differential scanning calorimetry (DSC), and the catalytical effect of phenolic hydroxyl on the curing behavior of copolymers was investigated. To investigate the thermal properties of this resin, the thermal degradation behaviors of the cured samples were studied by thermal gravimetric (TG) method, and glass-transition temperatures (T _g) of the cured copolymers were also evaluated by DSC. The dynamic Ozawa method was adopted to determine the kinetic parameters of the curing process as well. The activation energy is 78.8 kJ/mol and the reaction rate constant is in the range from 40.0 to 5.2 (K/min) ⁿ according to reaction temperatures. The Ozawa exponent decreases from 2.4 to 0.7 with the increase of reaction temperature, and curing mechanism is expounded briefly according to the results. TG result shows that the highest char yield of copolymers is 50.3%. The highest T _g of copolymers is 489 K, which is much higher than that of pure benzoxazine resin. Foundation item: Project (20050106) supported by the Key Science and Technology Item of Guangdong Province, China     

Preparation and characterization of low-melting glasses used as binder for protective coating of steel slab

The low-melting phosphate glass was prepared for production of glass binders for protective coating of steel slab. Effects of different O/P ratios on glass structures and properties were analyzed. Differential thermal analysis (DTA) and infrared spectroscopy (IR) techniques were applied for low-melting glass binder. It was found that the glass transition temperature(T _g) was about 300 °C and softening temperature(T _f) was about 480 °C. The choice of O/P ratio was very important to the glass transition and softening temperatures. When more P=O bonds existed in the glass networks, P-O-P bond angle was deformed with decreasing of the ratio of O/P. The coatings could adhere to the substrates instantaneously at 800 °C when the content of binder exceeded 3wt%. The optimal content of glass binder was 5wt%.     

Coordination properties and structural units distribution of Q^iT in calcium aluminosilicate melts from MD simulation

The distribution of AI(j) and the structural units distribution of Q^iT in calcium aluminosilicate melts were studied by means of molecular dynamics simulation. The results show that provided there exists lower-field strength cation relative to Al^3 , such as alkaline and alkaline earth metals, AI will be four-coordinated but not six-coordinated. Meanwhile, if there exist a large number of higher-field strength cations such as Si^4 and little lower-field strength cation, six-coordinated aluminum will be formed. The relation of structural units distribution of Q^iT with chemical composition shift was also extracted, showing that as Ca^2 exists, the distributions of Q^Si, QAl or QT have the similar changing trend with the variation of component. Because of high-temperature effect, the Al-tetrahedral units in melts are greatly active and unstable and there exist dynamic transforming equilibria of Al(3)←→AI(4) and Al(5)←→Al(4). The three-coordinated oxygen and charge-compensated bridging oxygen are proposed to explain phenomena of the negative charge redundancy of AIO4 and location of network modifier with charge-compensated function in aluminosilicate melts.     

Modification of LiCo1/3Ni1/3Mn1/3O2 cathode material by CeO2-coating

LiCo_1/3Ni_1/3Mn_1/3O₂ was coated by a layer of 1.0 wt% CeO₂ via sol-gel method. The bared and coated LiMn_1/3Co_1/3Ni_1/3O₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammogram (CV) and galvanotactic charge-discharge test. The results show that the coating layer has no effect on the crystal structure, only coating on the surface; the 1.0 wt% CeO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ exhibits better discharge capacity and cycling performance than the bared LiCo_1/3Ni_1/3Mn_1/3O₂. The discharge capacity of 1.0 wt% CeO₂-coated cathode is 182.5 mAh·g⁻¹ at a current density of 20 mA·g⁻¹, in contrast to 165.8 mAh·g⁻¹of the bared sample. The discharge capacity retention of 1.0 wt% CeO₂-coated sample after 12 cycles reaches 93.2%, in comparison with 86.6% of the bared sample. CV results show that the CeO₂ coating could suppress phase transitions and prevent the surface of cathode material from direct contact with the electrolyte, thus enhance the electrochemical performance of the coated material.     

端异氰酸酯基聚醚接枝环氧树脂的性能研究

合成了端异氰酸酯基聚醚（ITPs）改性双酚A型环氧树脂，通过红外光谱（IR）、动态热机械分析（DMA）研究了ITPs和EP之间的化学反应及改性环氧树脂酸酐固化体系的热性能，并测试了固化体系的力学性能。结果表明：ITPs作为枝链接枝到环氧树脂上：随着加入ITPs质量分率增加，其固化体系的冲击强度和弯曲强度上升，当ITPs含量为10％时，两者达到最大值：动态热机械分析（DMA）结果表明改性环氧树脂固化体系的玻璃化转变温度（Tg）随ITPs的含量增大而降低：当ITPs质量分率大于15%时，过量的ITPs与改性环氧树脂会形成相分离。