Toughening of cyanate ester resin by carboxyl terminated nitrile rubber

The carboxyl terminated butadiene‐acrylonitrile (CTBN) rubber was used to improve the toughness of the cyanate ester (CE) resin. The toughness of the modified blends depended on the CTBN content. The addition of 10 phr (g/100gCE) CTBN in CE resin led to a 200% increase in the impact strength with a loss of storage modulus. The transmission electron microscopy result showed the existence of rubber particles, inferring that phase separation had occured after curing. The thermogravimetric analysis curve of CTBN indicated the presence of cavities which also can be observed on the fractured surface in the scanning electron microscopy pictures using high magnification. Thus, phase‐separation and cavities toughening mechanisms function together to improve the toughness. Copyright © 2004 John Wiley & Sons, Ltd.     

CTBN-TOUGHENED EPOXY RESINS——EFFECT OF CURING MECHANISM ON NETWORK STRUCTURE OF THE RUBBER PHASE

Epoxy resins toughened with carboxyl-terminated butadieneacrylonitrile copolymers (CTBN) are two-phase thermosets. The network of the in situ formed rubber particles depends upon the curing mechanism of the resin. When a primary polyamine such as triethylene tetramine was used as curing agent, the network of the rubber phase was quite incomplete, whereas a perfect rubber network was formed with 2-ethyl-4-methyl imidazole as the curing agent.     

双酚A在环氧树脂和端羧丁腈增韧的环氧树脂中作用的研究

本文分别以六氢吡啶、三乙醇胺、70~#酸酐和三氟化硼单乙胺络合物为固化剂,研究了用双酚A改性的环氧树脂和端羧丁腈(简称CTBN)增韧的环氧树脂体系的热、机械性能、微观形貌和交联密度。研究结果表明只有在碱性催化型固化剂六氢吡啶或三乙醇胺下,双酚A的加入才会有突出的增韧效果。结果指出固化物冲击韧性的提高与网络交联密度有关,断裂韧性的提高是析出橡胶相体积分数增大和基体交联密度减小的协同作用所致。     

Influence of carboxyl‐terminated (butadiene‐co‐acrylonitrile) loading on the mechanical and thermal properties of cured epoxy blends

A mixture of epoxy with liquid nitrile rubber, carboxyl‐terminated (butadiene‐co‐acrylonitrile) (CTBN) was cured under various temperatures. The cured resin was a two‐phase system, where spherical rubber domains were dispersed in the matrix of epoxy. The morphology development during cure was investigated by scanning electron microscope (SEM). There was slight reduction in the glass transition temperature of the epoxy matrix (T_g) on the addition of CTBN. It was observed that, for a particular CTBN content, T_g was found to be unaffected by the cure temperature. Bimodal distribution of particles was noted by SEM analysis. The increase in the size of rubber domains with CTBN content is due probably to the coalescence of the rubber particles. The mechanical properties of the cured resin were thoroughly investigated. Although there was a slight reduction in tensile strength and young's modulus, appreciable improvements in impact strength, fracture energy, and fracture toughness were observed. Addition of nitrile rubber above 20 parts per hundred parts of resin (phr) made the epoxy network more flexible. The volume fraction of dispersed rubbery phase and interfacial area were increased with the addition of more CTBN. A two‐phase morphology was further established by dynamic mechanical analysis (DMA). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2531–2544, 2004     

A positron annihilation study on the microstructure of cyanate ester resin toughened by carboxyl‐terminated butadiene‐acrylonitrile rubber system

The toughness of cyanate ester (CE) resin matrix improves significantly with the addition of carboxyl‐terminated butadiene‐acrylonitrile rubber (CTBN). The curing behavior of the system was studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The results show that carboxyl groups on the CTBN chain have a slight activation effect on the CE curing reaction at the beginning of the curing process. Phase separation was found to be the main toughening mechanism for CE/CTBN composites. The existence of macro‐size pores induced by the decomposition of a small amount of the low weight molecular part of CTBN might be another toughening mechanism. It is confirmed that positron annihilation lifetime spectroscopy (PALS) is still valid in such a system where macropores filled with gas molecules exist. When a high weight percentage of CTBN (>8%) was added to CE, free‐positron annihilation was found to be the dominant annihilation process in the macropores. For CTBN weight percentage higher than 8%, the contribution of ortho‐positronium (o‐Ps) annihilation in the macropores to τ₃ and I₃ was found to be insignificant. It is effective to use PALS as a probe of free‐volume properties in such systems by determining the changes in the τ₃ and I₃ of the composite. The compatibility and interfacial adhesion of the composites can be estimated from the changes in the free‐volume properties of the composites. Copyright © 2008 John Wiley & Sons, Ltd.     

Guide for Authors

The effects of epoxidized natural rubber (ENR) on the curing behaviors and adhesive strengths of an epoxy (diglycidyl ether of bisphenol-A) and dicyandiamide/2-methyl imidazole system are studied with differential thermal calorimetry (DSC), scanning electron microscopy (SEM), and Instron tensile testing instrument. From DSC analyses of specimens prepared with unsealed aluminum pans, it is obtained that the reaction exotherm, the time to maximal curing rate, the glass transition temperature, the rate constant, and the reaction order of the epoxy system change with respect to the content of ENR added because of the reaction of ENR with the epoxy system. The results obtained from SEM micrographs indicate that the particle size of the rubber phase increases with increasing the curing temperature and the ENR content. The volume fraction of the separated rubber phase also follows the similar trend except at the high curing temperature which implying that the dissolution of epoxy resin in the ENR phase also depends on the curing temperature and the amount of ENR present. The lap shear strengths of specimens prepared with etched aluminum substrates increase with increasing the curing temperature because of a better cure at a higher temperature, but decrease with increasing the ENR content resulting from an adverse effect of ENR on the mechanical properties of the cured resins.     

Thermodynamic analysis of the reaction-induced phase separation in model systems based on blends of a rubber in diepoxide / monoamine precursors

The reaction-induced phase separation in blends based on a carboxyl-terminated poly(butadiene-co-acrylonitrile) rubber (CTBN), dissolved in diglycidyl ether of bisphenol A (DGEBA) - benzylamine (BA) monomers, was studied. The polymerization kinetics was followed by size exclusion chromatography, for both the neat DGEBA-BA system and for blends containing 10 wt% CTBN. No effect of CTBN addition on the polymerization rate was observed within experimental error. The kinetics could be fitted with a model based on the presence of non-catalytic and OH-catalyzed reactions and assuming equal reactivity of primary and secondary amine hydrogens. Cloud-point conversions were determined at 60, 70 and 80 °C. The Flory-Huggins model provided a reasonable fitting of experimental data using an interaction parameter depending exclusively on temperature, and taking polydispersities of both linear polymers into account. Linear epoxy/amine systems may be used to test the reliability of thermodynamic theories in more complex situations (e.g., modifiers with a broad distribution of molar masses or mixtures of several modifiers).     

Characterization of Rubber Epoxy Blends by Thermal Analysis

Differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA) of the blends ofepoxy cresol novolac (ECN) resin toughened with liquid carboxy terminated butadiene-co-acrylonitrile (CTBN) rubber have been carried out. Exothermal heat of reaction (ΔH) due to crosslinking of the resin in presence of diaminodiphenyl methane(DDM, as amine hardener) showed a decreasing trend with increasing rubber concentration. Enhancements of thermal stability as well as lower percentage mass loss of the epoxy-rubber blends with increasing rubber concentration have been observed in TG. Dynamic mechanical properties reflected a monotonic decrease in the storage modulus (E′) with increasing rubber content in the blends. The loss modulus (E″) and the loss tangent(tanδ) values, however, showed an increasing trend with rise of the temperature up to a maximum (peak) followed by a gradual fall in both cases. Addition of 10 mass% of CTBN resulted maximum E″ and tanδ. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhancement of the crystallization and thermal stability of polyhydroxybutyrate by polymeric additives

The crystallization and thermal degradation of polyhydroxybutyrate (PHB) blended with a small amount of carboxyl-terminated butadiene acrylonitrile rubber (CTBN) and biocompatible polyvinylpyrrolidone (PVP) are analyzed by differential scanning calorimetry (DSC), dynamic thermogravimetric analysis (TG), gel permeation chromatography (GPC), polarized optical microscope (POM), and wide angle X-ray diffraction (WAXD). From results of DSC, TG, and GPC, it is shown that the presence of PVP or CTBN could affect the crystallization rate, crystallinity, melting temperature, and thermal stability of PHB. The changes of crystal sizes by the added CTBN and PVP are also confirmed by the POM and WAXD analyses. The addition of the 1 wt% PVP or CTBN into PHB can significantly increase the crystallization rate and thermal degradation temperature, and affect the degradation kinetics of PHB due to the steric hindrance effects of the added PVP and CTBN on retarding the degradation reaction. The best improvement of the thermal stability is obtained from the PVP-modified PHB. The method of using CTBN or PVP to improve the thermal stability of PHB is of great processing advantages in industry because it is functional with low purity PHB, henceforth, saves the cost of the purification process.     

Study of curing behaviour and thermal properties of elastomer-modified bismaleimide resin

Bismaleimide resin (Compimide 353) was modified with the liquid elastomer carboxyl-terminated acrylonitrile butadiene (CTBN). The prereaction synthesis and curing of the CTBN-bismaleimide resin is discussed. The structure of the modified resin was identified by IR and NMR spectroscopy. The basic curing mechanism is also discussed. DSC and TG were used to study the curing behaviour and kinetic parameters, viz. the order of reaction, energy of activation and preexponential factor. Adhesive properties such as lap shear strength and peel strength at room temperature and elevated temperature were evaluated and are discussed.     

用反射吸收红外光谱法对改性环氧胶粘剂界面的研究

<正> 液体端羧基丁腈(CTBN)是环氧树脂的一种优良增韧剂。McGarry等发现其增韧效果与橡胶在环氧体系固化时分相出来的粒子的直径和橡胶粒子与树脂的相互作用有关。余云照等发现CTBN改性环氧胶粘剂因固化剂不同其胶接强度有很大差异,并提出只有当羧基在环氧凝胶前几乎全部与环氧反应才能显示出它的增韧作用。我们认为这里胶接界面问题不可忽略。红外反射吸收光谱法是新近发展起来的一种特殊红外技术,它以较高的灵敏度测出金属表面的吸附物或0.05μ以下的薄膜的结构并能得到它们对金属表面取向的资料。所以用反射吸收红外光谱来研究胶粘剂与被粘金属的界面相互作用将能反映胶接强度诸问题的本质。     

Phase separation behavior of epoxy resin modified with crosslinked rubber

Low molecular weight liquid rubber (ATBN = amine terminated butadiene acrylonitrile copolymer or CTBN = carboxyl terminated butadiene acrylonitrile copolymer)–DGEBA (diglycidyl ether of bisphenol A) blends indicated upper critical solution temperature (UCST) behavior. The phase separation behavior of the neat and crosslinked rubber (ATBN, CTBN)–epoxy blends was analyzed by a laser light scattering experiment. Lauryl peroxide (LPO) was employed to crosslink the rubber during the initial annealing stage. The onset point of the phase separation in the crosslinked ATBN–epoxy system occurred later than in the case of the neat ATBN–epoxy system. However, the onset point of the phase separation process started earlier in the case of the crosslinked CTBN–epoxy system. The domain correlation length of the crosslinked rubber-added system was smaller than that of the neat rubber-added system.     

Interface and properties of epoxy resin modified by elastomeric nano-particles

Epoxy resin has been widely used as structuralmaterials and adhesives in electronics, aerospace in-dustries and etc. for its impressive overall properties.However, epoxy network is brittle and notch sensitive,which restricts its application scope. As a re…     

STUDY ON THE EPOXY RESIN TOUGHENED BY HYDROXY-TERMINATED BUTADIENE-ACRYLONITRILE COPOLYMER

Toughened epoxy resin with excellent properties was obtained by adding organic acid anhydride curing agent and hydroxy-terminated butadiene-acrylonitrile copolymer (HTBN), which is cheaper than CTBN. The anhydride reacts with both epoxy groups on epoxy resin and hydroxyl groups on HTBN. As a result the soft long chains of HTBN and the rigid chain of epoxy resin form one network, giving the resin toughness. Two-phase structure of the toughened resin was observed by SEM and TEM.     

Thermal and morphological characteristics of solution blended epoxy/NBR compound

Systematic study about the effect of acrylonitrile–butadiene rubber (NBR) concentration on the fracture toughness and thermal behavior of epoxy resin is conducted in this study. NBR is solved in an aromatic hydrocarbon solvent and is added to epoxy resin. We used diethylene-teriamin as the curing agent for epoxy resin. Tensile test results, performed followed by molding procedure, show that the toughness is improved owing to the increase of rubber content. Scanning electron microscopy (SEM) and atomic force microscopy besides thermogravimetric analysis (TG) are used to investigate the epoxy/rubber interface and chemical decomposition of the resultant mixture. The thermal behavior of cured epoxy resin was analyzed via TG instrument at different heating rates. Thermogravimetry curves showed that the thermal decomposition of epoxy system was occurred in only one stage regardless of the rubber content. The apparent activation energies of the rubber/epoxy systems containing 0, 5, and 10 phr of rubber were determined by Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman methods. The results prove that the thermal stability of epoxy resin was decreased with enhancing the rubber content. However, the trend of changing activation energy versus conversions is totally different followed by adding the elastomer to the system compared to neat epoxy resin. Moreover, the results obtained via our proposed facile solution blending method are compared to those of resins modified with nano-powdered elastomer.     

Interfacial control and mechanical properties of carbon black‐reinforced carboxyl‐terminated butadiene acrylonitrile rubber/epoxy polymer composites

Carbon black (CB) particles were employed as a reinforcing filler in carboxyl‐terminated butadiene acrylonitrile rubber (CTBN)/epoxy resin (diglycidyl ether of bisphenol‐A (DGEBA))/aromatic diamine (diamino diphenyl methane (DDM)) network polymer blends. The strength, modulus, and ability to absorb impact energy of the resulting composites were evaluated. The aim of this work was to determine the effects of interfacial interactions between components, and processing conditions (especially temperature) on mechanical properties. The application of high temperatures during the kneading process resulted in strong interfacial interactions between the CB particles and the CTBN. The formation of strong bonds at the CB/CTBN interfaces during kneading was the key factor in obtaining high strength and high impact energy absorbance. The composites also exhibited good adhesive strength during both shear and peel stress tests.     

Fatigue crack propagation and related failure in modified,andhydride-cured epoxy resins

The fatigue crack propagation (FCP) of neat and modified, anhydridecured epoxy resin (EP) was studied in tensile-tensile mode at ambient temperature. As modifiers, liquid carboxyl-terminated acrylonitrile-butadiene (CTBN) and silicon rubber (SI) dispersions were used. The latter modifier in a defined particle size distribution was produced by a special latex technology, whereas the former developed in situ in the EP by phase separation during curing. The dispersion-type morphologies of the EPs were characterized by using polished sections and viewing them in a scanning electron microscope (SEM). The resulting frequency distribution curves were compared with those analyzed from fatigue fracture surfaces. Probable failure mechanisms were also studied by SEM-fractography.Both modifiers improved the resistance to FCP by shifting the curves to higher stress intensity factor ranges (K) in relation to the reference curve determined for the neat EP-matrix. The failure mechanisms, summarized also schematically, differed basically for the various modifiers. According to this, rubber-induced cavitation and shear yielding of the matrix seemed to be dominant for CTBN, which did not affect the principal crack plane. In contrast to this, crack bifurcation, branching and, hence, a forced deviation in the fatigue crack path induced by debonded SI-particles in the EP-matrix were concluded for the SI modifier. The common use of both modifiers yielded a positive synergistic effect due to the superposition of the above failure mechanisms.Dedicated to the 60th birthday of Prof. H. H. Kausch     

An Epoxy-Siloxane Composite with Enhanced Deformation Heat Resistance and Improved Deformation and Strength Characteristics

The curing of an epoxy-triphenol resin (ETP) using an amine curing agent in the presence of a polyorganosyloxane modifier is studied. It is shown that mixing of ETP with a modifier favors the formation of a completely compatible system, which, however, undergoes phase separation upon the curing. It has been established that curing of the epoxy-siloxane composite results in a denser mesh-structure buildup, while the cured samples exhibit higher deformation and strength characteristics and deformation heat resistance.     

耐高温改性环氧树脂粘接剂的制备及改性机理研究

采用新型固化体系和端羧基丁腈橡作为环氧树脂的改性剂，制备了一种具有耐高温、高强度、韧性好等特点的环氧树脂粘接材料。同 时对改性机理及增韧机理进行了初步探讨。     

橡胶增韧环氧树脂机理的研究

本文研究了固化剂种类、环氧基体平均网链长度和分散相与基体间键合情况对体系韧性等的影响.结果说明,基体平均网链长度是一个更为重要的影响因素.分散相与基体间的化学键合也是重要的.文中对橡胶增韧环氧树脂的机理提出了见解.在交联密度较低的材料中,在橡胶颗粒附近叠加的应力场诱发下发生纵深度较大的断裂过程.分散相与基体间的化学键合增大该应力场强度有利于加大断裂过程区.