环氧树脂增韧方法研究进展

环氧树脂由于其自身结构和性质的原因,表现出脆性大、易断裂、韧性差等缺点,为了改善环氧树脂的力学性能,一般先进行增韧改性处理然后再应用。对环氧树脂的增韧处理方法进行了详细的介绍,其中包括:弹性体橡胶增韧环氧树脂,热塑性树脂增韧环氧树脂,纳米粒子增韧环氧树脂,生物质增韧环氧树脂,核壳聚合物增韧环氧树脂等。     

环氧树脂增韧改性研究进展

环氧树脂是一种综合性能优良的热固性树脂,但其韧性不足。从增韧机理出发,对增韧环氧树脂的主要方法进行了探讨,包括橡胶弹性体、无机刚性粒子、核壳粒子、热致液晶聚合物(TLCP)、互穿聚合物网络(IPN)、热塑性树脂增韧环氧树脂。在比较的基础上,对环氧树脂的增韧进行展望,指出其今后发展的方向。     

环氧树脂增韧改性方法研究进展

概述了环氧树脂的特性和环氧树脂增韧改性的主要途径,分别介绍了热塑性树脂增韧改性环氧树脂、核-壳结构增韧改性、膨胀性单体增韧改性、刚性粒子增韧改性、无机纳米粒子增韧改性、液晶聚合物增韧改性、液体橡胶增韧改性等方法.重点对液体橡胶增韧改性进行了讨论,同时分析了目前环氧树脂增韧改性技术存在的问题及发展趋势.     

不同纳米核壳粒子增韧环氧树脂体系的性能及机理研究

纳米核壳粒子通常为玻璃化转变温度较高的热塑性聚合物包裹橡胶内核结构,其优点在于在树脂固化前后结构不发生明显变化,不会因为固化过程中橡胶相分离不完全影响树脂性能。但是纳米粒子的均匀分散一直是环氧添加剂使用过程中的难题。采用三种不同组成、不同粒径的核壳粒子增韧环氧树脂,采用DDS固化的双酚F树脂基体,制备了一系列耐热性优良的环氧树脂体系。研究通过预制母液分散二步法分散纳米颗粒,解决纳米粒子的均匀分散问题,得到均一增韧体系。增韧后的三种体系均对树脂韧性有很大的提升作用。经力学性能、热力学性能、流变学性能和微观结构性能等测试和分析,优选出最佳的纳米多尺度核壳粒子增韧环氧体系,并阐明了其增韧机理。     

改进环氧树脂韧性的研究

本文介绍了:1)加入橡胶改性剂;2)改变交联网络化学结构;3)与热塑性树脂形成半IPN;4)控制分子交联状态的不均匀性等四种增韧环氧树脂的途径。其中对橡胶增韧环氧树脂的关健进行了较详细的讨论。本文还对新型的耐热热塑性树脂改性环氧树脂体系进行了介绍,将这类体系的改性效果与橡胶增韧体系作了比较,并就保持改性体系的模量及耐热性问题作了讨论。     

环氧树脂增韧改性研究进展

回顾了环氧树脂韧改性的一些常用方法,详细介绍了以橡胶弹性体,热塑性树脂及则性粒子增韧环氧树脂的一些重要研究情况。并且对环氧树脂增韧性性的进行了比较系统的总结,例举了一些已被人们承认的增韧机理。 还介绍了环氧树脂改性的最新方法,液晶聚合物改性,大分子固化剂增韧的一些研究情况。     

用含弹性体链段的共聚物增韧环氧树脂

1前言 环氧树脂具有高刚性、高耐热性等优点,但脆性较大。为了提高热固性树脂的韧性,人们研究开发了许多增韧材料。具有代表性的有液体橡胶CTBN和高Tg的热塑性塑料等。这些改性剂都是在环氧固化之前加入体系中。环氧树脂冲击性能的改性效果与相分离后改性剂的分散状态直接相关．上述的改性剂多半能溶解于环氧树脂中,环氧树脂的固化伴随着熵值降低,改性剂产生相分离而形数微米大小的相畴（domain）。对这种体系而言,为了得到性能平衡的环氧树脂,必须特别注意工艺控制。当前,电子行业和航空工业对环氧树脂性能提出了更高的要求,同时希望对环氧树脂的性能更易调节,这就需要研发新型的改性材料。     

环氧树脂增韧改性研究现状

概述了近年来橡胶弹性体、刚性粒子、热塑性树脂、液晶聚合物及核-壳结构聚合物增韧环氧树脂的研究现状,并展望了环氧树脂增韧改性研究的发展前景。     

环氧树脂的改性研究进展

介绍了环氧树脂的特性和环氧树脂改性的主要趋势-提高环氧树脂的韧性,分别论述了橡胶类弹性体增韧环氧树脂、热塑性塑料增韧环氧树脂、热致液晶聚合物增韧环氧树脂、柔性链段固化剂增韧环氧树脂、无机纳米材料改性环氧树脂以及互穿网络(IPN)结构的环氧树脂体系等环氧树脂增韧改性的方法.同时,对聚氨酯的特性、用聚氨酯改性环氧树脂的六种方法以及互穿聚合物网络技术,进行了较为详细的介绍,并分析了改性环氧树脂目前存在的技术问题.     

环氧树脂增韧改性研究进展

本文综述了环氧树脂增韧改性研究进展。结合对环氧树脂的橡胶弹性体增韧改性、刚性纳米粒子增韧改性和热塑性树脂增韧改性等改性方法的研究现状,讨论了环氧树脂改性方法的优缺点并针对环氧树脂增韧改性研究提出建议。     

The Fracture Behavior of CTBN Modified Epoxy

Rubber toughened epoxy resins are widely used as adhesives, as a matrix for glass and carbon fiber composites for rocket cases and sporting goods, and as a potting agent in the electronics industry. A common rubber added is CTBN, a carboxyl terminated copolymer of butadiene and acrylonitrile.

In this study we have measured toughness (K_1C and G_1C) using the E399 ASTM standard for a compact tension (CT) specimen, with special attention to the variability of the measured K_1C and G_1C with the method of starter crack formation and the time delay between starter crack formation and toughness measurement. We also investigated the toughness of the toughened epoxy after initiation, for a growing crack, by using the short rod (SR) method and when possible in a CT specimen by using a simple marking technique.

The CT toughness of unmodified epoxy measured using a liquid nitrogen initiator crack technique is the same as that of earlier work, but we found that the K_IC and G_1C toughness increases when there is a delay between initiator crack formation and toughness measurement. Moreover, an initiator crack produced at room temperature gave higher toughness values. For the rubber toughened samples, we obtained low toughness for a liquid nitrogen initiated crack and a higher toughness measured either in a CT or SR test after the crack grew. The low values differ from earlier works, but is the same as that previously obtained at lower temperatures and for 5% and 20% rubber modified epoxy. Moreover, we found no K_1C and G_1C dependence with rubber content or rate (0.002-0.2 in/min crosshead speed). The higher toughness of the growing crack was the same as that for the 15% material of previous work. Presumably the apparent toughness of these systems is very dependent on the method of producing the initiator crack, and we possibly produced a sharper crack. This sharper crack shows no dependence on rubber content or rate.

Our results suggest that the advantage of adding rubber to epoxy is not in the load that the material will normally be able to sustain. A crack in bulk epoxy may not be sharp and even if it is, will spontaneously blunt with time. There is, however, a greater tendency for a blunter crack to be produced in the rubberized epoxy and for an initiated crack to grow stably. Moreover, a stable, slowly-growing crack will increase the toughness of the modified epoxy.     

Effects of rubber‐rich domains and the rubber‐plasticized matrix on the fracture behavior of liquid rubber‐modified araldite‐F epoxies

The fracture behavior of a bisphenol A diglycidylether (DGEBA) epoxy, Araldite F, modified using carboxyl‐terminated copolymer of butadiene and acrylonitrile (CTBN) rubber up to 30 wt%, is studied at various crosshead rates. Fracture toughness, K_IC, measured using compact tension (CT) specimens, is significantly improved by adding rubber to the pure epoxy. Dynamic mechanical analysis (DMA) was applied to analyze dissolution behavior of the epoxy resin and rubber, and their effects on the fracture toughness and toughening mechanisms of the modified epoxies were investigated. Scanning electron microscopy (SEM) observation and DMA results show that epoxy resides in rubber‐rich domains and the structure of the rubber‐rich domains changes with variation of the rubber content. Existence of an optimum rubber content for toughening the epoxy resin is ascribed to coherent contributions from the epoxy‐residing dispersed rubber phase and the rubber‐dissolved epoxy continuous phase. No rubber cavitation in the fracture process is found, the absence of which is explained as a result of dissolution of the epoxy resin into the rubber phase domains, which has a negative effect on the improvement of fracture toughness of the materials. Plastic deformation banding at the front of precrack tip, formed as a result of stable crack propagation, is identified as the major toughening process.     

Epoxidized natural rubber/epoxy blends: Phase morphology and thermomechanical properties

Epoxidized natural rubbers (ENRs) were prepared. ENRs with different concentrations of up to 20 wt % were used as modifiers for epoxy resin. The epoxy monomer was cured with nadic methyl anhydride as a hardener in the presence of N,N‐dimethyl benzyl amine as an accelerator. The addition of ENR to an anhydride hardener/epoxy monomer mixture gave rise to the formation of a phase‐separated structure consisting of rubber domains dispersed in the epoxy‐rich phase. The particle size increased with increasing ENR content. The phase separation was investigated by scanning electron microscopy and dynamic mechanical analysis. The viscoelastic behavior of the liquid‐rubber‐modified epoxy resin was also evaluated with dynamic mechanical analysis. The storage moduli, loss moduli, and tan δ values were determined for the blends of the epoxy resin with ENR. The effect of the addition of rubber on the glass‐transition temperature of the epoxy matrix was followed. The thermal stability of the ENR‐modified epoxy resin was studied with thermogravimetric analysis. Parameters such as the onset of degradation, maximum degradation temperature, and final degradation were not affected by the addition of ENR. The mechanical properties of the liquid‐natural‐rubber‐modified epoxy resin were measured in terms of the fracture toughness and impact strength. The maximum impact strength and fracture toughness were observed with 10 wt % ENR modified epoxy blends. Various toughening mechanisms responsible for the enhancement in toughness of the diglycidyl ether of the bisphenol A/ENR blends were investigated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39906.     

Synergic Effect of Acrylate Liquid Rubber and Bisphenol A on Toughness of Epoxy Resins

The synergic effect of acrylate liquid rubber with pendant epoxy group and bisphenol A on the toughness of epoxy resins was presented in this paper. The addition of bisphenol A enhances the impact strength and elongation at break of epoxy resin and actually increases the ductibility of epoxy resin matrix. Much higher toughness efficiency can be achieved for the ALR modified epoxy resins by the incorporation of bisphenol A at the same time. The synergic promotion effect of acrylate liquid rubber and bisphenol A on the toughness efficiency of epoxy resins is attributed to the two-phase morphology and high ductibility of matrix, and the resultant large stress white zones and high shear yielding during the fracture process.     

Mechanical Strength Behavior of Hybrid Composites Tailored by Glass/Kevlar Fibre-Reinforced in Nano-Silica and Micro-Rubber Blended Epoxy

Silicon - The present work aims to investigate the mechanical properties and fracture toughness of woven fabric Glass/Kevlar based hybrid composite tailored using modified epoxy with micro rubber...     

The influence of cure conditions on the morphology and phase distribution in a rubber-modified epoxy resin using scanning electron microscopy and atomic force microscopy

In this paper, we consider the effect of cure conditions on the morphology and distribution of the rubber in a phase separated rubber-modified epoxy resin, which in effect is a two phase composite. Novel aspects of this study were measuring the elastic modulus of the dispersed rubber phase particles by atomic force microscopy (AFM) and verifying the presence of nano-dispersed rubber.The purpose of introducing dispersed rubber particles into the primary phase in these systems is to enhance their toughness. It is known that both the rubber particle size and volume fraction affect the degree to which the epoxy is toughened. It is not known, however, how the specific mechanical properties of the rubber phase itself affect the toughness.The objectives of this study were to: (1) use scanning electron microscopy (SEM) and atomic force microscopy (AFM) to determine the morphology and phase distribution of the rubber particles and (2) to measure the mechanical properties of the rubber particles using AFM. Ultimately, we would like to develop a clear understanding of how the changes in morphology and mechanical properties measured at the micro and nano-scales affect both the elastic modulus and fracture toughness of rubber-modified epoxy polymers.The epoxy system consisted of a diglycidyl ether of bisphenol-A, Epon 828, cured with piperidine and incorporating a liquid carboxyl-terminated acrlonitrile-butadiene rubber (CTBN). The carboxyl groups of the rubber are capable of reacting with the epoxy. The cure conditions considered were based on a statistically designed full factorial curing matrix, with the variables selected being cure temperature, initiator (piperidine) concentration, and rubber acrylonitrile concentration.Each of these primary variables was found to affect the phase distribution that resulted during cure. A statistical analysis of the effect of these variables on the phase morphology showed that the acrylonitrile content (%) of the rubber affected both the rubber particle size and volume fraction. The cure temperature strongly influenced the rubber particle volume fraction and modulus. Volume fractions of the rubber phase of up to 24% were obtained even though the amount of rubber added was only 12.5%. The rubber particle modulus varied from 6.20 to 7.16 MPa. Both the volume fraction and modulus of the rubber particles were found to influence the macroscopic mechanical properties of the composite. While larger volume fractions favor improved toughness, we note that that the toughness is greatest when the particle modulus values do not exceed ∼6.2 MPa. Thus, increased volume fraction by itself may not always result in increased toughness. The particles also must be sufficiently ‘soft’ in order to improve toughness. In the system of interest here, the processing conditions are a key factor in achieving the most appropriate material properties. By inference, this is likely to be the case as well in other rubber-modified thermosets.     

High performance HTLNR/epoxy blend—Phase morphology and thermo-mechanical properties

An attempt was made to toughen diglycidyl ether of bisphenol A (DGEBA) type epoxy resin with liquid natural rubber possessing hydroxyl functionality (HTLNR). Epon 250 epoxy monomer is cured using nadic methyl anhydride as hardener in presence of N, N dimethyl benzyl amine as accelerator. HTLNR of different concentrations up to 20 wt % is used as modifier for epoxy resin. The addition HTLNR to an anhydride hardener/epoxy monomer mixture has given rise to the formation of phase-separated structure, consisting of small spherical liquid natural rubber particles bonded to the surrounding epoxy matrix. The particle size increased with increase in rubber content. The viscoelastic properties of the blends were analyzed using dynamic mechanical thermal analysis. The T_g corresponding to epoxy rich phase was evident from the dynamic mechanical spectrum, while the T_g of the rubber phase was overlapped by the β relaxation of epoxy phase. Glass transition of the epoxy phase decreased linearly as a function of the amount of rubber. The mechanical properties such as impact and fracture toughness were also carefully examined. The impact and fracture toughness increase with HTLNR content. A threefold increase in impact strength was observed with 15 wt % HTLNR/epoxy blend. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Correlation between stress-whitening and fracture toughness in rubber-modified epoxies

Fracture toughness of rubber modified epoxy systems was evaluated in relation to stresswhitening. The epoxy systems consisted of diglycidyl ethers of bisphenol A (DGEBA)-based epoxy resin, 4,4′ diaminodiphenyl sulphone (DDS) as curing agent, and carboxylterminated butadiene-acrylonitrile (CTBN) rubber. It was found that a peak value of fracture toughness occurs at a small amount of rubber content (∼ 4 phr) and closely corresponds to that of stress-whitening size. Other properties such as flexural strength and flexural modulus were also found to display maxima at a similar amount of rubber content. © 1996 John Wiley & Sons, Inc.     

聚丙烯酸酯液体橡胶增韧环氧树脂体系研究

采用溶液聚合法合成了以丙烯酸丁酯、丙烯酸乙酯、丙烯酸缩水甘油酯为主链的液体橡胶,将其用于增韧改性环氧树脂/间苯二甲胺(EP 828/mXDA)体系,研究了聚丙烯酸酯液体橡胶用量对共混体系的微观形态、力学性能和玻璃化温度的影响。电镜观察显示液体橡胶改性EP828/mXDA的共混物呈海岛结构,连续相为环氧树脂,分散相为液体橡胶。随着丙烯酸酯液体橡胶用量增加,海岛相区的粒径和数量均呈增长趋势。当丙烯酸酯液体橡胶质量分数为15%时,共混物中海岛相区的尺寸为1μm左右,共混体系的冲击强度增加151.8%,玻璃化温度下降11.3℃。以丙烯酸液体橡胶改性EP828/mXDA环氧树脂体系,可以较大程度提高其韧性,同时其耐热性基本保持不变。     

Rubber-modified epoxy resins containing high functionality acrylic elastomers

The effect of the functionality of n-butylacrylate/acrylic acid copolymers upon the impact resistance of epoxy resins modified with these rubbery copolymers as a second phase was investigated using a high speed tensile test and scanning electron microscopy. It was found that an optimum functionality of copolymer existed for maximum impact resistance. This optimum value was the result of the competition between the amount of rubber–matrix reaction, an increases in which tended to increase toughness, and solubility of the rubber in the epoxy matrix, which eventually decreased toughness.