The boron trifluoride monoethyl amine complex cured epoxy resins

The curing exotherm pattern is affected by the equivalent ratio of curing agent, boron trifluoride monoethylamine complex (BF₃ · MEA), to epoxy resin. The diglycidyl ether of 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) cures more slowly than the diglycidyl ether of bisphenol A (Epon 828). The glass transition temperatures (T_g's) of BF₃ · MEA cured Epon 828 are increased with inceasing concentration of curing agent (0.0450–0.1350 eq.) cured DGEBF. The activation energies for the thermal decomposition for BF₃ · MEA (0.0450–0.1350 eq.) cured DGEBF. The activation energies for the thermal decomposition for BF₃ · MEA (0.0450 eq./epoxy eq.) cured Epon 828 and DGEBF are almost equivalent 43 and 44 kcal/mol, respectively. DGEBF when added to DGEBA improves the T_g and char yield with the BF₃ · MEA curing system. The T_g of both resin systems can be increased by longer post cure, whereas the char yield does not appear to change significantly. No ester group formation is found for the BF₃ · MEA-cured DGEBF, although this has been previously reported for the DGEBA system. The BF₃ · MEA cure at 120°C is better than at 140°C because of vaporization and degradation of the curing agent at the higher temperature. The rapid gelation of the epoxy resin may be another reason for the lower degree of cure at high temperature.     

有机胺类固化环氧树脂热变形温度的实验研究

研究了脂肪族胺类固化环氧树脂热变形温度(HDT)。利用正交试验研究了固化工艺、固化剂、填料及环氧树脂4种因素对HDT的影响。结果表明,固化工艺是影响HDT的最显著因素,80℃固化3 h后HDT较常温7 d固化可提高约40℃,且平均挠度变化率最小。本文研究了在高温固化工艺下,不同结构固化剂对无填料体系胶粘剂HDT的影响。结果表明,在不同的固化工艺下,使用不同结构脂肪胺类固化剂的HDT不同,过分提高固化温度反而会降低固化体系的耐热性能。     

Thermal modification of amine cured epoxy resins - thermal and mechanical studies

Mechanical test data are reported on lap joints and tensile test specimens which have been subjected to a defined post cure cycle. The mechanical properties exhibited an apparently systematic variation with temperature. Inspection of the resins indicated that chemical modification does not appear to occur to a significant extent below 433K. The change in the strength of the joints tensile test samples are discussed in terms of the relative importance of physical and chemical changes on the mechanical properties. It is evident that in the presence of oxygen considerable chemical modification can occur and this is observed both in terms of a change in colour of the resin and the appearance of voids.     

Flame retardant epoxy resins from bisphenol-A epoxy cured with hyperbranched polyphosphate ester

A novel hyperbranched polyphosphate ester (HPE) was synthesized via the polycondensation of bisphenol-A and phosphoryl trichloride. The formed HPE was characterized by FTIR, ¹H NMR and ³¹P NMR to confirm its structure. Then, a series flame retardant epoxy resins from bisphenol-A epoxy cured with HPE and bisphenol-A were prepared. The combustion behavior of the flame retardant epoxy resins was studied using limiting oxygen index (LOI) and cone calorimeter test. The LOI value increased from 23 to 32 when HPE, instead of bisphenol-A, was used as a curing agent. The cone calorimeter test data revealed that the cured bisphenol-A epoxy resin with HPE as a curing agent possessed improved flame retardancy. The photo graphs and scanning electron microscopy (SEM) of char residues confirmed the cone calorimeter results.     

改性酚醛胺环氧树脂体系耐蒸馏水的研究

通过宏观试验和AFM微观分析证明,改性酚醛胺固化环氧树脂体系的耐蒸馏水性能,优于低分子聚酰胺固化的环氧树脂体系。     

Use of inverse gas chromatography to quantify interactions in amine cured epoxy resins

Flory–Huggins interaction parameters, λ, were determined for a series of probes in an amine cured epoxy resin matrix (433–493 K) and its precursors (324–363 K) by inverse gas chromatography (IGC). Hildebrand–Scatchard theory was combined with Flory–Huggins theory in order to estimate infinte dilution solubility parameters (δ₂) for the matrix and its precursors at 298 K. It was shown that the value of the solubility parameter for the cured resin matrix lies between those of its precursors. Compared to the majority of published work, an unusual aspect of this application of IGC is that solubility parameters have been determined when the stationery phases are (i) small molecules and (ii) a highly crosslinked polymer. Moreover, all possible attempts have been made to ensure equilibrium conditions between probe and stationary phase, and compensation for asymmetry of peak profile has been applied in determining δ₂. The solubility parameters estimated by IGC are in good agreement with those calculated by other methods.     

Thermoplastic‐modified epoxy resins cured with different functionalities amine mixtures: Morphology,thermal behavior,and mechanical properties

Epoxy matrices inherent brittleness and poor crack resistance make necessary some form of toughening. In this work, to improve their fracture toughness and ductility epoxy matrices were modified by changing its architecture and by the addition of a third component. The matrices architecture were modified by stoichiometrically reacting a bifunctional epoxy resin with different functionalities amine mixtures, one of which being a monoamine that plays the role of chain extender. In the modification by the addition of a third component, poly(methyl methacrylate) (PMMA) was selected as modifier. PMMA is initially miscible with epoxy/amine systems but can phase separate during curing. The kinetics and miscibility of these systems were studied previously. At constant curing conditions, materials from completely opaque (phase separated) to transparent (miscible) can be obtained with the increase in monoamine content. In this work, the effects of the modifier content and of the monoamine : diamine ratio in stoichiometric epoxy/amine mixtures on the resultant morphologies as well as on their thermal and mechanical properties was studied.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of trifluoromethyl groups containing epoxy resins cured with amine for low Dk materials

The study synthesized a trifluoromethyl (CF₃) groups with a modified epoxy resin, diglycidyl ether of bisphenol F (DGEBF), using environmental friendly methods. The epoxy resin was cured with 4,4′‐diaminodiphenyl‐methane (DDM). For comparison, this study also investigated curing of commercially available diglycidyl ether of bisphenol A (DGEBA) with the same curing agent by varying the ratios of DGEBF. The structure and physical properties of the epoxy resins were characterized to investigate the effect of injecting fluorinated groups into epoxy resin structures. Regarding the thermal behaviors of the specimens, the glass transition temperatures (T_g) of 50–160°C and the thermal decomposition temperatures of 200–350 °C at 5% weight loss (T_d5%) in nitrogen decreased as amount of DGEBF increased. The different ratios of cured epoxy resins showed reduced dielectric constants (D_k) (2.03–3.80 at 1 MHz) that were lower than those of pure DGEBA epoxy resins. Reduced dielectric constant is related to high electrronegativity and large free volume of fluorine atoms. In the presence of hydrophobic CF₃ groups, the epoxy resins exhibited low moisture absorption and higher contact angles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Are cured epoxy resins inhomogeneous?

The alternating mechanism of network formation in the curing of epoxy resins from bisphenol A diglycidyl ether (BADGE) and amine curing agents does not offer any special opportunity for the formation of inhomogeneities caused by partial segregation or inhomogeneous crosslinking. Etched fracture surfaces of resins cured with 4,4′-diaminodiphenylmethane, hexamethylenediamine and hexahydrophthalic anhydride at various initial ratios of BADGE, studied by electron microscopy, reveal globular structures 20–40 nm in size. However, similar structures are observed with etched surfaces of amorphous polystyrene and poly(methyl methacrylate). The small-angle X-ray scattering curves for cured epoxy resins do not differ in principle from those of common amorphous polymers; swelling in a solvent of a lower electron density does not lead to an increase in scattering within the particle size range 10–10² nm. It is pointed out that the physical structure of simple cured epoxy resins does not essentially differ from that of common amorphous polymers. With more complicated systems, a more pronounced inhomogeneity might be caused by thermodynamic incompatibility or by non-alternating mechanisms of the curing reaction.     

Characterization of the phase structure of an amine cured rubber modified epoxy

The phase structure of an amine cured, rubber-modified epoxy was characterized. The sharpness of the interface between the matrix and the dispersed phase, the volume fraction of the dispersed phase, the distribution of particle sizes, and the concentration of epoxy in the dispersed phase were determined. Scanning transmission electron microscopy coupled with energy dispersive X-ray analysis revealed that the interface width is less than 500 Å. Variation in the fraction of mobile hydrogens with temperature determined by nuclear magnetic resonance indicated that a small fraction of segments participated in mixing at the interface. Differential scanning calorimetry and nuclear magnetic resonance showed that the volume fraction of the dispersed phase equalled that predicted by assuming all of the rubber plus the epoxy monomer units bonded directly to the rubber precipitates. The distribution of particles greater than 0.1 μm in diameter was measured, and the average diameter of these particles was found to be 0.8 μm. This distribution accounted for approximately 50% of the dispersed phase. The epoxy concentration in the dispersed phase was determined using ¹³C nuclear magnetic resonance spectroscopy. This concentration was found to be less than that predicted if all the epoxy monomer units attached to the rubber molecules were present in the dispersed phase.     

航空用改性酚醛胺环氧防腐涂料的研制

以改性酚醛胺固化的环氧树脂制成的防腐底漆,具有更好的耐水性和耐湿热性能。介绍其涂料配方及制备,并与俄罗斯航空通用防腐底漆进行了比较。     

Morphology and toughness characterization of epoxy resins modified with amine and carboxyl terminated rubbers

The morphology (dispersed phase composition, size distribution, and particle/matrix interface shapes) of epoxy resins modified with 5–15 parts by weight (pbw) of carboxyl (CTBN) and amine (ATBN) terminated butadiene acrylonitrile rubber have been characterized. The characterization techniques were transmission electron microscopy coupled with energy dispersive X-ray analysis, differential scanning calorimetry and proton and ¹³C nuclear magnetic resonance. ATBN modified epoxies have a diffuse-appearing interface between the dispersed rubber phase and the epoxy matrix, in contrast to the sharp boundaries of CTBN particle interfaces. Interface mixing of epoxy and rubber, hypothesized initially to explain the interface diffuseness in ATBN modified epoxy, was not found in either CTBN or ATBN modified epoxy. The difference in interface appearance is attributed to ATBN particles having highly irregular shapes compared to the nearly spherical CTBN particles. Bimodal particle size distributions are observed with both modifiers. Both rubber modifiers also produce essentially identical toughness values which do not increase with rubber content in the range 5–15 pbw despite a commensurate increase in the population of large particles.     

多元醇与环氧树脂共混改性的研究

采用自制的聚酯多元醇对环氧树脂进行共混改性,对改性环氧树脂固化物的拉伸强度、断裂伸长率、冲击强度、剪切强度等进行了考察,同时探讨了多元醇分子量变化及加入量不同对性能的影响。结果表明,改性后的体系韧性得到了明显的提高,如冲击强度从13.2kJ/m2提高到26.3kJ/m2。室温剪切强度从24.2MPa提高到43.75MPa。     

UV-curable epoxy varnishes modified with polyvinyl resins

Epoxy varnishes based on 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate (EEC) and polyvinyl components, i.e., two polyvinyl butyral resins (PVB) and one polyvinyl butyral-stat-acetal resin (PVBA) were prepared and cured using a commercial cationic iodonium photoinitiator and medium-pressure mercury lamp. An influence of a type and content of polyvinyl resin (5, 10, and 20 wt.%) on thermal, optical, mechanical, and barrier features of varnish coatings was investigated. Coats containing the highest amount of PVB resins exhibited higher epoxy group conversion, higher gloss, and smoother surface in comparison with EEC/PVBA samples. Moreover, cured coats and films with PVB reached markedly higher barrier features, i.e., limited distilled water absorption and low water vapor transmission rate. An influence of reactivity and UV transmittance value of the photocurable varnishes on coat wrinkling process was presented and discussed.     

Physical properties and shrinkage of epoxy resins cured with lactams

In order to reduce the shrinkage of epoxy resin during the curing process, lactam is incorporated into epoxy in a copolymerization reaction. In this study, various amounts of lactams and BF₃-MEA were added to epoxy, and the volume shrinkage of polymerization was investigated. It was found that shrinkage decreases with the increase of the lactam content and with the lactam ring size as well. Infrared spectroscopic analysis, scanning electronic microscopic analysis, and mechanical tests were used to investigate the structure and properties of the copolymers. The results show that the incorporation of caprolactam leads to an increase in tensile strength and elongation, but the Izod impact strength is not improved.     

生物基胺固化的可降解、可重加工环氧树脂

对基于香草醛的可降解缩水甘油醚 (DEPVD)胺解得到生物基可降解胺(DAPVD)，再与樟脑酸缩水甘油酯(DGECA)固化得到环氧树脂。采用红外光谱(FTIR)对DAPVD的结构进行了表征，并制备了树脂样条及碳纤维复合材料，通过动态机械分析(DMA)、拉伸测试、应力松弛测试、降解实验、热重分析(TGA)等手段对环氧树脂的性能进行了表征，并使用拉曼光谱验证了碳纤维的回收效果。结果表明：固化剂中含有的螺环缩醛结构赋予了环氧树脂可降解的特性，而固化反应中原位形成的β羟基叔胺结构在加工温度下可以参与动态酯交换反应，赋予了环氧树脂自修复和可重加工的功能。此外，基于环氧树脂良好的降解性能，制得的碳纤维复合材料在经过0.1M H+酸性溶液中50℃/48h处理后，高价值的碳纤维可以完全回收。     

The supermolecular structures found in cured epoxy resins

The work arose from the need to explain the beneficial effect of post-curing at an elevated temperature on the strengths of lap-shear joints made with amine-cured epoxy resins. Supermolecular structures were imaged by several electromicroscopy techniques, usually at 100,000 X. Three, if not four, stages of supermolecular structure were made visible. (i) A phase-contrast image of 1.3 to 2.1 nm diameter which are probably stacked residues of bisphenol A. The d-spacing seen in the diffracting mode of the microscope probably arises from within this structure. (ii) A nodular structure of ca. 5 nm. (iii) Aggregates of nodules of ca. 17 nm rising to 40 n m on post-cure. These dimensions were obtained from cumulative distributions of sizes based on photodensitometer records from the electron-micrograph negatives. Aggregate dimensions vary with curing agent and state of cure although minor variations occur with specimen preparation.     

Influence of oxidation treatment of carbon powders on the cure kinetics of amine cured tetrafunctional epoxy resins

A tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) type tetrafunctional epoxy resin containing carbon powders was cured with the stoichiometric amount of a tetrafunctional curing agent, namely m-phenylenediamine (mPDA). Carbon powders were oxidised with air or nitric acid. The influence of carbon powders on curing of the resin was followed by dynamic mechanical analysis, Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Gelation and vitrification times were determined as a function of the variations of dynamic properties. The evolution of viscoelastic modulus during curing of the different mixtures showed that untreated carbon powder clearly accelerated the kinetics of curing whilst oxidation of carbon powders could remove their catalysing effect. These results were confirmed by monitoring the changes in conversion of epoxy and amine groups during cure using the FTIR technique. DSC experiments also showed the influence of carbon powder as a catalyst and the loss of the catalysing effect as a consequence of chemical treatment.     

纳米材料改性环氧树脂的研究进展

综述了国内外纳米材料改性环氧树脂(EP的研究现状。介绍了不同纳米材料对EP复合材料力学性能、热性能、电磁性能等的影响。重点介绍了碳纳米管和无机纳米粒子如蒙脱土、TiO2、SiO2、Al2O2等对EP的改性。探讨了纳米材料在改性EP时存在的问题,并对纳米材料改性EP的趋势作出展望。