Carboxyl‐terminated butadiene acrylonitrile rubber/epoxy polymer alloys as damping adhesives and energy absorbable resins

Carboxyl‐terminated butadiene acrylonitrile (CTBN) liquid rubber/epoxy (diglycidyl ether of bisphenol‐A: DGEBA) / diamino diphenyl methane (DDM) resins, in which CTBN was 60 wt % as the major component, were formulated to evaluate the damping and adhesive properties. In cases where acrylonitrile (AN) was 10～18 mol % as copolymerization ratio in CTBN, the blend resins showed micro‐phase separated morphologies with rubber‐rich continuous phases and epoxy‐rich dispersed phases. The composite loss factors (η) for steel laminates, which consisted of two steel plates with a resin layer in between, depended highly on the environmental temperature and the resonant frequencies. On the other hand, in the case where AN was 26 mol % in CTBN, the cured resin did not show clear micro‐phase separation, which means the components achieve good compatibility in nano‐scale. This polymer alloy had a broad glass‐transition temperature range, which resulted in the high loss factor (η > 0.1) for the steel laminates and excellent energy absorbability as the bulk resin in a broad temperature range. Also the resin indicated high adhesive strengths to aluminum substrates under both shear and peel stress modes. The high adhesive strengths of the CTBN/epoxy polymer alloy originated in the high strength and the high strain energy to failure of the bulk resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Cryogenic microcracking of rubber toughened composites

This study investigated the influence of carboxyl‐terminated butadiene acrylonitrile (CTBN) liquid rubbers on the microcracking response of polymeric composite materials to cryogenic cycling. Matrices of carbon fiber/epoxy prepregs were modified with different concentrations of two CTBN liquid rubbers. The glass transition temperature and the interlaminar shear strength of the laminate systems were depressed as a result of the presence of CTBN in the epoxy phase. An increase in total rubber concentration with the continuous phase was found to decrease and in some cases eliminate microcracking in laminates exposed to cryogenic cycling.     

CTBN增韧环氧树脂微孔发泡研究

研究了液体端羧基丁腈橡胶(CTBN)增韧高分子量环氧树脂(EP,牌号CYD–014U)的超临界二氧化碳(SC–CO_2)微孔发泡及其泡孔结构,通过差示扫描量热(DSC)、动态热力学分析(DMA)和扫描电子显微镜(SEM)分别研究了不同含量CTBN共混体系的热性能、动态模量、断面形貌和不同发泡条件下的泡孔结构。研究发现,当CTBN含量从0%增加到30%时,EP/CTBN体系的玻璃化转变温度持续下降,其DSC测试结果从98.44℃下降至81.89℃。SEM观察断面和气体传质发现,CTBN含量增加基体塑化,出现两相结构,体系气体吸附量增加,解吸附速率加快。CTBN含量为10%~15%时,经60℃/12 MPa/72 h气体饱和以及110℃发泡10~15 s,泡孔尺寸为1~2μm,泡孔密度为5.60×10~(10)~6.28×10~(10)个/cm~3;随着发泡时间增加,泡孔经历成核、生长、聚并三个阶段,泡孔尺寸增加,泡孔密度先增后降。     

Relationships between structure and mechanical properties of rubber-modified epoxy networks cure with dicyanodiamide hardener

Epoxy network systems based on DGEBA and dicyanodiamide (DDA) and modified with a low molecular weight rubber (CTBN) were prepared and characterized. The kinetics of the adduct formation is followed using GPC analysis. The phase separation of the rubber phase is evidenced with DSC and SEM for all samples up to 20% CTBN. The GPC analysis of the soluble fraction demonstrates a chemical modification of the network. The mechanical properties and specially the impact strength behavior are enhanced with CTBN, but exhibit a maximum for 15% CTBN. In connection with SEM of fracture surfaces, these results are discussed and both modification of the rubber morphology and decrease in crosslinking density are taken into account.     

Phase separation behavior of the epoxy-CTBN mixture during the curing process

To improve the impact resistance of cured epoxy resin, a carboxyl-terminated butadiene-acrylonitrile rubber (CTBN) was added. The phase separation behavior during the curing reaction was analyzed by a light scattering experiment. The measurement of transmitted light intensity showed the onset and ending of the phase separation. The change of the scattered light intensity at different angles showed the process of the phase separation, such as the formation and growth of the dispersed domain. The morphology of the blend was also observed by scanning electron micrography (SEM) and was compared with the domains measured by the light scattering method. The impact strength and dynamic mechanical properties of epoxy resin of different rubber concentrations and cured at different temperature were compared, and the effect of the domain size on these properties was analyzed.     

Elastomer‐modified epoxy/amine systems in a resin transfer moulding process

The effect of the elastomer structure on toughening highly crosslinked epoxy systems in a resin transfer moulding process (RTM) was investigated. Two kinds of elastomers containing carboxyl functionalized groups were used: (1) a reactive liquid elastomer based on carboxyl‐terminated butadiene‐acrylonitrile copolymer (CTBN), (2) a preformed core‐shell rubber (CSR). The introduction of CTBN rubber caused the modification in the glass transition temperature due to the miscibility in the epoxy matrix, whereas CSR particles did not. During cure, these elastomers affected the morphological, rheological and dielectric behaviour of epoxy/amine systems. A blend of 5% CTBN and 5% CSR exhibited a bimodal distribution of rubber particle sizes (analyzed by transmission electron microscopy) whereas scanning electron microscopy showed the glass fibre‐matrix cohesion in fracture surfaces. A semi‐empirical model was used (developed by Castro‐Macosko for describing chemorheological behaviour of epoxy/amine systems for the RTM process). The increase in viscosity and the reduction in ion conductivity were the two key parameters to monitor the cure process. The presence of rubber affected the rheological behaviour involving initial viscosity and gel point. The investigation of temperatures, pressures and ionic conductivities in various glass fibre layers was conducted to control the front flow filling and the cure reaction. The introduction of rubber modified the inflexion area of the cured rubber–epoxy blends by changing the cure rate. Copyright © 2004 Society of Chemical Industry     

CTBN与ATBN改性环氧胶粘剂的研究

将端羧基丁腈橡胶(CTBN)接枝上环氧官能团进行改性,将改性后的CTBN添加到环氧胶粘剂的A组分中;将端氨基丁腈橡胶(ATBN)以不同的比例加入到环氧胶粘剂的固化剂即B组分中。考查胶粘剂的剪切、剥离强度和玻璃化转变温度以及2组分的配比对胶粘剂性能的影响。结果表明,将改性后的CTBN橡胶与ATBN配合使用比单独使用其中一种的综合性能更好,2者在A、B组分中分别占12质量份数左右时其增韧效果最显著。     

Mechanical and tribological properties of epoxy modified by liquid carboxyl terminated poly(butadiene-co-acrylonitrile) rubber

Diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin was modified using liquid carboxyl-terminated poly(butadiene-co-acrylonitrile) (CTBN) rubber. The liquid CTBN contents used ranged from 2.5 to 20 parts per hundred parts of resin (phr). Mechanical properties of the modified resins were evaluated and the microstructures of the fracture surfaces were examined using SEM technique. The changes in storage modulus and the glass transition temperature were also evaluated using dynamic mechanical analysis (DMA). The tribological tests were performed using a ball-on-disc tribometer. The worn surfaces and the ball counter-mates after tribological tests were investigated using optical microscope technique. The results revealed the influence of liquid CTBN content on mechanical and tribological properties, and also microstructure of the modified epoxy resins. Impact resistance increased whereas the storage modulus and the hardness decreased when the CTBN rubber was introduced to the epoxy network. The coefficient of friction of the CTBN-modified epoxy was lower than that of the neat epoxy. The CTBN content of lower than 10 phr was recommended for improving the wear resistance of epoxy resin. Changes in tribological properties of the CTBN-modified epoxy correspond well to those in mechanical changes, especially the toughness properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electron Beam Curing of the System Cycloaliphatic Diepoxide‐Epoxidized Natural Rubber‐Glycidyl Methacrylate in Presence of Cationic Initiators

Electron beam curing of the system cycloaliphatic diepoxide‐epoxidized natural rubber‐glycidyl methacrylate containing a cationic initiator was carried out. Storage modulus, glass transition temperature and pendulum hardness were measured as function of EB dose, photoinitiator concentration, content of epoxidized natural rubber, post cure temperature and post cure time. At electron beam doses larger than 100 kGy a highly cross‐linked polymer network is generated which shows a two phase morphology. Microscale elastomeric domains are incorporated into a continuous epoxy resin phase. Dynamical mechanical analysis and pendulum hardness measurement show that an increase of the ENR ratio leads to a more elastic polymer network. Post curing results in increased glass transition temperatures. This EB cured polymer system is believed to provide both toughness and favorable viscoelastic properties to be used as component of EB curable composites.     

Mechanical,thermal, and viscoelastic response of novel in situ CTBN/POSS/epoxy hybrid composite system

The present study focuses on the preparation of a novel hybrid epoxy nanocomposite with glycidyl polyhedral oligomeric silsesquioxane (POSS) as nanofiller, carboxyl terminated poly(acrylonitrile‐co‐butadiene) (CTBN) as modifying agent and diglycidyl ether of bisphenol A (DGEBA) as matrix polymer. The reaction between DGEBA, CTBN, and glycidyl POSS was carefully monitored and interpreted by using Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC). An exclusive mechanism of the reaction between the modifier, nanofiller, and the matrix is proposed herein, which attempts to explains the chemistry behind the formation of an intricate network between POSS, CTBN, and DGEBA. The mechanical properties, such as tensile strength, and fracture toughness, were also carefully examined. The fracture toughness increases for epoxy/CTBN, epoxy/POSS, and epoxy/CTBN/POSS hybrid systems with respect to neat epoxy, but for hybrid composites toughening capability of soft rubber particles is lost by the presence of POSS. Field emission scanning electron micrographs (FESEM) of fractured surfaces were examined to understand the toughening mechanism. The viscoelastic properties of epoxy/CTBN, epoxy/POSS, and epoxy/CTBN/POSS hybrid systems were analyzed using dynamic mechanical thermal analysis (DMTA). The storage modulus shows a complex behavior for the epoxy/POSS composites due to the existence of lower and higher crosslink density sites. However, the storage modulus of the epoxy phase decreases with the addition of soft CTBN phase. The T_g corresponding to epoxy‐rich phase was evident from the dynamic mechanical spectrum. For hybrid systems, the T_g is intermediate between the epoxy/rubber and epoxy/POSS systems. Finally, TGA (thermo gravimetric analysis) studies were employed to evaluate the thermal stability of prepared blends and composites. POLYM. COMPOS., 37:2109–2120, 2016. © 2015 Society of Plastics Engineers     

Effects of Rubber Addition to an Epoxy Resin and Its Fiber Glass‐Reinforced Composite

Epoxy resins are considered as one of the most important class of thermosetting polymers and find extensive use in various fields. However, these materials are characterized by a relatively low toughness. In this respect, many efforts have been made to improve the toughness of cured epoxy resins. In this work, samples of epoxy resin diglycidyl ether of bisphenol‐A and fiber glass‐reinforced composite of this polymer with and without liquid carboxyl‐terminated butadiene acrylonitrile (CTBN) copolymer were prepared to assess the effect of CTBN rubber on the properties of polymeric and composite laminate specimens. The addition of CTBN into the polymeric specimens led to a decrease in the glass transition temperature, fracture stress (from 70.39 to 56.34 MPa), and tensile elasticity modulus (from about 3.51 to 2.65 GPa), accompanied by an increase in elongation (from 2.47 to 5.64%). However, the degradation temperature of the polymeric system was not modified. Infrared analysis evidenced the occurrence of chemical reaction between the two components, and scanning electron microscopy results suggested rubber particles deformation as the prevailing toughening mechanism. The rubber addition in the composite specimens, promoted an increase simultaneous in fracture stress and in elongation at fracture. The elasticity tensile modulus has not changed. This probably results from the increased deformation capacity of the matrix, which prevents its premature cracking, and better adhesion between fibers and matrix observed in the CTBN‐modified composite laminates. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Mechanical and Dielectric Properties of NiZn Ferrite Powders-CTBN Modified Epoxy Resin Coatings

In this study, the effects of carboxyl terminated butadiene-acrylonitrile liquid rubber (CTBN) addition on the mechanical and dielectric properties of NiZn ferrite powders-CTBN modified epoxy resin coatings were investigated. It was observed that the occurrence of the small, dispersed spherical CTBN domains in the epoxy resin resulted from the phase separation between epoxy and CTBN could enhance the toughness and dielectric constant at low frequency due to the increase in the phase boundary between ferrite powders and epoxy resin for the samples modified with proper CTBN. The addition of ferrite powders can effectively improve the thermal stability of epoxy resin.     

Toughening of dicyandiamide-cured DGEBA-based epoxy resins by CTBN liquid rubber

Toughening of a diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin with liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymer has been investigated. For this purpose six blend samples were prepared by mixing DGEBA with different concentrations of CTBN from 0 to 25 phr with an increment of 5 phr. The samples were cured with dicyandiamide curing agent accelerated by Monuron. The reactions between oxirane groups of DGEBA and carboxyl groups of CTBN were followed by Fourier-transform infrared (FTIR) spectroscopy. Tensile, impact, fracture toughness and dynamic mechanical analysis of neat as well as the modified epoxies have been studied to observe the effect of CTBN modification. The tensile strength of the blend systems increased by 26 % when 5 phr CTBN was added, and it remained almost unchanged up to 15 phr of CTBN. The elongation-at-break and Izod notched impact strength increased significantly, whereas tensile modulus decreased gradually upon the addition of CTBN. The maximum toughness of the prepared samples was achieved at optimum concentration of 15 phr of CTBN, whereas the fracture toughness (K _IC) remained stable for all blend compositions of more than 10 phr of CTBN. The glass transition temperature (T _g) of the epoxy resin significantly increased (11.3 °C) upon the inclusion of 25 phr of CTBN. Fractured surfaces of tensile test samples have been studied by scanning electron microscopic analysis. This latter test showed a two-phase morphology where the rubber particles were distributed in the epoxy resin with a tendency towards co-continuous phase upon the inclusion of 25 phr of CTBN.     

Cure kinetics, morphology and miscibility of modified DGEBA-based epoxy resin - Effects of a liquid rubber inclusion

Kinetics of the curic reaction and morphology of a diglycidyl ether of bisphenol-A based epoxy resin (DGEBA), using an anhydride hardener (nadic methyl anhydride) at different weight contents of carboxyl-terminated copolymer of butadiene and acrylonitrile liquid rubber (CTBN) was investigated using a differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM). The aim of the work is to understand the effects of inclusion of the liquid rubber phase in the transition phenomena that occur during the curing reaction. The curic reaction at three different curic temperatures and at varying rubber contents in the range of 5-20 wt% has been studied. The reaction rate and conversions that occurred at the curic temperatures were analyzed. The increase in the rate with the curic temperature showed this as a thermally catalyzed reaction. The rate of the reaction was found to decrease in liquid rubber-modified epoxies due to the effect of dilution and viscosity increase as obtained from the gelation times. The experimental data showed an autocatalytic behavior of the reaction, which is explained by the model predicted by Kamal. This model includes two reaction constants k₁ and k₂ and two reaction orders m and n. The order of the overall reaction was found to be approximately 2. The activation energies Ea₁ and Ea₂ were estimated at all curic temperatures for neat and all modified epoxies. The results obtained from the DSC data were also applied to diffusion controlled kinetic models. A schematic model to represent the curic reaction and phase separation was introduced and the molecular mechanism of this curing reaction was discussed. During the curic reaction, phase separation of the liquid rubber from the epoxy matrix took place and the modified epoxies showed phase separated morphology. The dispersed phase showed a homogenous particle size distribution. The size of the phase separated domains increased with increasing concentration of the CTBN and decreased with rise in curing temperature. The glass transition temperature (T_g) of the modified epoxies decreased with increase in curic temperature as studied from dynamic mechanical thermal analysis. Addition of the liquid rubber lowered the T_g of the network. This became prominent in the modification of the matrix with 15 and 20 wt% of the elastomer. This is attributed to flexibilization of the matrix. The dissolved rubber plasticizes the epoxy network. The T_g of the neat rubber in the low-temperature region was shifted to higher temperature upon addition of the elastomer. A higher shift was noted for 15 and 20 phr inclusion. This was due to dissolved epoxy in the rubber-rich phase that increased the modulus of the rubbery phase. The inclusion of a large wt% of carboxyl-terminated butadiene-co-acrylonitrile (CTBN) decreased the cross-linking density of the thermoset matrix.     

Porous epoxy monolith prepared via chemically induced phase separation

Macroporous epoxy monolith was prepared via chemically induced phase separation using diglycidyl ether of bisphenol A (DGEBA) as a monomer, 4,4′-diaminodiphenylmethane (DDM) as a curing agent, and epoxy soybean oil (ESO) as a solvent. The morphology of the cured systems after removal of ESO was examined using scanning electron microscopy, and the composition of epoxy precursors/solvent for phase inversion was determined. The phase-separation mechanism was deduced from the optic microscopic images to be spinodal decomposition. The pore structure of the cured monolith was controlled by a competition between the rates of curing and phase separation. The ESO concentration, content of curing agent, and the curing temperature constituted the influencing factors on the porous morphology. The average pore size increased with increasing ESO concentration, increasing curing temperature, and decreasing the content of curing agent.     

Performance improvement of rubber-modified polybenzoxazine

Polybenzoxazine as a noble phenolic resin was modified with amine-terminated butadiene acrylronitrile rubber (ATBN) and with carboxyl-terminated butadiene acrylronitrile rubber (CTBN) in order to improve its mechanical properties. The fracture toughness, flexural modulus, and flexural strength of rubber-modified polybenzoxazine were measured to investigate the effect of rubber modification. In fracture toughness, ATBN is more effective than CTBN. ATBN-modified polybenzoxazine showed better distribution of rubber particles in matrix phase than did CTBN-modified polybenzoxazine. The cure rates in these systems were monitored by differential scanning calorimetry to investigate the effect of cure rate on rubber size. The change of glass transition temperatures of rubber-modified polybenzoxazine was measured with a dynamic mechanical thermal analyzer to explain the variation of mechanical properties. In addition, the relationship between mechanical properties and the morphology of rubber-modified polybenzoxazines was also undertaken. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 1–10, 1998     

Micro‐mechanical deformation mechanisms in the fracture of hybrid‐particulate composites based on glass beads,rubber and epoxies

Two tougheners, glass beads and carboxyl terminated butadiene acrylonitrile copolymer (CTBN), are used to toughen and stiffen an epoxy thermoset. Rubber‐encapsulated glass beads are used and the hybrid particulate composites containing them are compared with those containing non‐encapsulated glass beads. Within a certain range of composition, the rubber encapsulation is found to change the interactions between glass beads and CTBN particles, resulting in an increase in fracture toughness. The toughening effect is explained by the fact that the cavities of CTBN particles are larger in encapsulation systems than in non‐encapsulation systems. As more CTBN particles are incorporated into glass bead filled epoxies, the cavitation/shear yielding mechanism of CTBN particles replaces the micro‐shear banding mechanism of glass beads as the major micro‐mechanical deformation. Rubber encapsulation seems to enable this transition of major micro‐mechanical deformation to occur at a lower volume fraction of CTBN.     

Analysis of polymer membrane formation through spinodal decomposition

A phenomenological model used in a previous work for spinodal decomposition of polymer-solvent systems is further analyzed. From the dimensionless form of the nonlinear Cahn-Hilliard equation, the dimensionless induction time is found to be a constant number for suddenly quenched systems. Computer simulation is carried out for prediction of early stage behavior with thermal history corresponding to a linear temperature drop followed by a constant temperature vs. time. In the areas of polymer membrane formation and phase separation studies, the universality of the constant dimensionless Induction time for suddenly quenched systems allows the determination of the minimum time needed for phase separation via spinodal decomposition. Also, simulation results for the double linear temperature history allows the convenient prediction of early stage spinodal decomposition behavior at every point of a membrane cross section undergoing thermal inversion phase separation.     

Phase Separation and Spatial Morphology in Sodium Silicate Glasses by AFM,Light Scattering and NMR

The morphological and structural properties of sodium silicate (Na₂O–SiO₂) glasses were analyzed using atomic force microscopy (AFM) and light scattering following thermal treatments. AFM observations indicated that the glass surface microstructure evolves during the phase separation mechanisms from continuous interpenetrating phases in the spinodal decomposition process to separated droplets embedded in a continuous matrix for the nucleation/growth one. Raman mapping gave evidence of a phase separation through the nucleation/growth process with formation of silica‐rich clusters characterized by higher polymerization degree as separate droplets. The variations in inhomogeneities versus temperature investigated by Brillouin are exponential for spinodal decomposition and linear in the case of nucleation/growth mechanism. Nuclear magnetic resonance spectroscopy was used to investigate the spatial distribution of the various Q_n species present in thermally treated glasses and allows determining fractal dimension between two and three.     

Phase Diagram for Liquid Crystalline Polymer/ Polycarbonate Blends

A novel mechanism to form binary polymer blends is through phase separation by spinodal decomposition in the unstable region of the phase diagram. The present work investigates the effects of thermally‐induced phase separation by spinodal decomposition on the morphology development of liquid crystalline polymer/polycarbonate blends. Moreover, a thermodynamic binary phase diagram is obtained using a twin‐screw extruder at various processing melt temperatures. Differential scanning calorimetry and scanning electron microscopy were used to study the miscibility of the blends and the resulting morphology. A thermodynamic binary phase diagram exhibiting a lower critical solution temperature was obtained. The droplet size distribution of the blend was also obtained and discussed in light of the Cahn‐Hilliard theory.