Structure and properties of epoxy resins modified with acrylic particles

The morphology and material properties of dicyandiamide (DICY)‐cured epoxy resins modified with acrylic particles consisting of a PBA (polybutyl acrylate) core and a PMMA (polymethyl methacrylate) shell and epoxy resins modified with acrylic rubber (PBA) particles alone were studied. It was found that the epoxy system modified with core/shell acrylic particles showed higher fracture toughness, indicating that the modification had a larger effect on improving the material properties of the epoxy resin. A characteristic shown by the core/shell acrylic particles is that they swell along with the epoxy resin under exposure to heat and gel before the latter cures. In this process, the epoxy resin penetrates the surface of the shell layer and a bond is formed between the epoxy matrix and the core/shell acrylic particles. This suggests that the epoxy matrix around the core/shell acrylic particles has the effect of increasing the level of energy absorption due to plastic deformation of the matrix. This is thought to explain why the epoxy resin modified with core/shell acrylic particles showed higher fracture toughness. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2955–2962, 1999     

Toughened cycloaliphatic epoxy resin for demanding thermal applications and surface coatings

An epoxy resin based on nonglycidyl ether and varying content of carboxyl‐terminated (poly)butadiene acrylonitrile copolymer was cured using an aromatic amine hardener. The ultimate aim of the study was to modify the brittle epoxy matrix by the liquid rubber to improve toughness characteristics. Fourier transform infrared spectroscopic analysis of the modified was performed to understand the structural transformations taking place during the uncured and cured stage of the modified systems. The decreasing trend in exothermal heat of reaction with increasing rubber content in the epoxy resin can be explained by the fact that the increase of carboxyl‐terminated butadiene acrylonitrile copolymer (CTBN) modifier might induce a high reactivity of the end groups with the epoxide ring and resulting shorter curing times and, hence, the faster curing process than the unmodified resin. Tensile strength, impact strength, and elongation‐at‐break behaviors of neat as well as modified networks have been studied to observe the effect of rubber modification. Blends sample exhibits better properties as compared to pure epoxy resin in terms of increase in impact strength and elongation‐at‐break of the casting and gloss, scratch hardness, adhesion, and flexibility of the film. The improvement in these properties indicate that the rubber‐modified resin would be more durable than the epoxy based on di glycidyl ether of bis‐phenol‐A and other epoxies. The films of coating based on epoxy with 15 wt % CTBN offered the maximum resistance toward different concentrations of acids, alkalies, and solvents as compared to the cured films of other blend samples. The thermal stability of the cycloaliphatic‐based epoxy resin was increased with the addition of 15 wt % CTBN in epoxy matrix. Cycloaliphatic‐based epoxy network modified with CTBN displayed two phase separated morphology with dispersed rubber globules in the matrix resin, i.e., they revealed the presence of two phase morphological features. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dispersed acrylate rubber-modified epoxy resins for electronic encapsulation

A process was developed to incorporate stable dispersed acrylate rubber particles in an epoxy resin matrix which greatly reduces the stress of cured epoxy resins for electronic encapsulation application. The effect of the alkyl group of the acrylate monomer on the phase separation of resultant elastomers from epoxy resin was investigated. The dispersed acrylate rubbers effectively reduce the stress of cured epoxy resins by reducing the flexural modulus, while the glass transition temperature (T_g) was hardly depressed. Electronic devices encapsulated with the dispersed acrylate rubber-modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and resulted in an extended device use life.     

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.     

The influence of clay and elastomer concentration on the morphology and fracture energy of preformed acrylic rubber dispersed clay filled epoxy nanocomposites

The influence of toughener and clay concentration on the morphology and mechanical properties of three-phase, rubber-modified epoxy nanocomposites was studied. Nanocomposite samples were prepared by adding octadecyl ammonium ion exchanged clay to a dispersion of pre-formed acrylic rubber particles in liquid epoxy, so as to minimize alteration to the rubber morphology in the final cured specimen. The state of clay platelet exfoliation and rubber dispersion in the cured nanocomposites was studied using transmission electron microscopy. The amounts of clay platelet separation and dispersion of clay aggregates in the epoxy matrix were found to be sensitive to clay and toughener concentration, and clay platelets preferentially adsorb to the rubber particles. Tensile modulus and strength increase and ductility decreases with increasing organoclay content, while rubber has the opposite effects on the properties of epoxy resin. When both additives are present in epoxy resin, a favorable combination is produced: ductility is enhanced without compromising modulus and strength. Modulus and strength are improved by nano and micro dispersion of nanoclay in the epoxy matrix, whereas elongation and toughness are improved by clay adsorption to the rubber particle surface, which promotes cavitation. The glass transition temperature of epoxy resin remains relatively unchanged with clay addition.     

Modification of epoxy resin by isocyanate‐terminated polybutadiene

Hydroxy‐terminated polybutadiene was functionalized with isocyanate groups and employed in preparation of a block copolymer of polybutadiene and bisphenol A diglycidyl ether (DGEBA)‐based epoxy resin. The block copolymer was characterized by Fourier transform infrared (FTIR) spectroscopy and size‐exclusion chromatography (SEC). Cured blends of epoxy resin and hydroxy‐terminated polybutadiene (HTPB) or a corresponding block copolymer were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMTA), and scanning electron microscopy (SEM). All modified epoxy resin networks presented improved impact resistance with the addition of the rubber component at a proportion up to 10 wt % when compared to the neat cured resin. The modification with HTPB resulted in milky cured materials with phase‐separated morphology. Epoxy resin blends with the block copolymer resulted in cured transparent and flexible materials with outstanding impact resistance and lower glass transition temperatures. No phase separation was discernible in blends with the block copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 838–849, 2002     

Aminosiloxane-modified epoxy resins as microelectronic encapsulants

Amine-terminated poly(dimethylsiloxanes) (ATPDMS) were used to improve the toughness of a cresol-formaldehyde novolac epoxy resin cured with a phenolic novolac resin for electronic encapsulation application. The effect of molecular weight of amine-terminated polysiloxanes on the phase separation of the resultant elastomers from epoxy matrix were investigated. Mechanical and dynamic viscoelastic properties of siloxane-modified epoxy networks were also studied. The dispersed silicone rubbers effectively improve the toughness of cured epoxy resins by reducing the coefficient of thermal expansion and flexural modulus, while the glass transition temperature was hardly depressed. Electronic devices encapsulated with the dispersed silicone rubber-modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and have resulted in an extended device use life.     

Mechanical and damping properties of epoxy/liquid rubber intercalating organic montmorillonite integration nanocomposites

Two different kinds of micro‐nanoconstrained damping structure units (M‐NCDSUs) were prepared by carboxyl‐terminated butadiene acrylonitrile copolymer and epoxy‐terminated butadiene acrylonitrile copolymer liquid rubbers intercalating organic montmorillonite, respectively. The prepared M‐NCDSUs were then blended with epoxy resin to obtain damping structure integration nanocomposites. The X‐ray diffraction and transmission electron microscope measurements applied for the obtained samples confirmed the good formation of M‐NCDSUs in the epoxy network. The tensile strength decreased slightly with the addition of M‐NCDSUs, whereas the damping properties measured by dynamic mechanical analysis showed a remarkable increase. Besides, the cured epoxy resin exhibited a two‐phase morphology where the spherical rubber phase dispersed uniformly in the epoxy matrix. The nanocomposites containing M‐NCDSUs showed superior comprehensive properties compared with that without the functional units. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39797.     

Adhesive strength and mechanisms of epoxy resins toughened with pre-formed thermoplastic polymer particles

The aim of this study was to characterize the adhesive properties of epoxy resins toughened with pre-formed polyamide-12 particles in comparison to the conventional approach using core–shell rubber particles. Dicyandiamide-cured diglycidyl ether of bisphenol-A was used as the base epoxy resin. The T-peel adhesive strength of the toughened resin containing 20 phr polyamide-12 particles was about 3-times higher than that of the unmodified resin. In the case of rubber toughening, the improvement in adhesive strength tended to reach a plateau, even after improvement in the resin toughness itself. Besides, the polyamide particle toughening utilizes the bulk resin toughness for the peel adhesive strength, even in a thin adhesive layer between the substrates. The polyamide particles embedded in epoxy resin matrix were fractured after bridging cracks and stretching in the peel process. The crack-bridging mechanism by the pre-formed thermoplastic polymer particles was operative behind the crack-tip and would, therefore, experience a relatively small constraint by the presence of rigid metal substrates in comparison to conventional rubber toughening. The requirements for the polymer particles to work as a modifier using the bridging mechanism would be good adhesion to the epoxy matrix, high toughness and a relatively lower modulus of elasticity than that of matrix resin.     

Synthesis and properties of epoxy resin modified with epoxy-terminated liquid polybutadiene

Epoxy resin networks have been modified with block copolymer of polybutadiene and bisphenol A diglycidyl ether (DGEBA)-based epoxy resin. Block copolymers prepared from isocyanate-terminated polybutadiene (NCOPBER) resulted in cured transparent epoxy networks with no discernible phase-separated morphology, as indicated by scanning electron microscopy. Epoxy resin modified with block copolymer derived from carboxyl-terminated polybutadiene (CPBER) presented an opaque aspect with dispersed rubber particle diameters in the range of 0.5-3μm. This value is substantially smaller than that found in epoxy matrix modified with hydroxyl-terminated polybutadiene. The different morphological characteristics observed in these modified systems were attributed to the different times to achieve the gelation (gel time) and also to the different structures of the block copolymers. The visual homogeneity of the NCOPBER block copolymer-modified network cannot be attributed to the presence of dissolved rubber, since the glass transition temperature of the epoxy matrix (determined from dynamic mechanical analysis) has not been substantially influenced by the presence of this block copolymer. The epoxy resin modified with the different block copolymers presented an improved impact resistance. The best mechanical performance in terms of flexural and tensile properties was achieved with the block copolymer derived from carboxyl-terminated polybutadiene, whereas a more flexible material has been obtained with NCOPBER block copolymer-modified network.     

Toughening of epoxy resins by modification with aromatic polyesters

Aromatic polyesters, prepared by the reaction of phthalic or isophthalic acids and α,ω-alkanediols, were used to reduce the brittleness of bisphenol-A diglycidyl ether epoxy resin cured with methyl hexahydrophthalic anhydride. These polyesters were effective as modifiers for toughening of the epoxy resin system. The most suitable composition for modification of the epoxy resins was inclusion of 20 wt % of poly(ethylene phthalate) (MW 7200), which resulted in a 150% increase in the fracture toughness (K_IC) of the cured resin at no expense of its mechanical properties. The effectiveness of poly(alkylene phthalate)s as modifiers decreased with increasing the chain length of alkylene units. The toughening mechanism was discussed based on the morphological and dynamic mechanical behaviors of the modified epoxy resin system.     

高性能室温固化环氧结构胶的制备与研究

为了改善环氧固化物的韧性,又保持其热稳定性及提高其抗冲击性能,采用超细全硫化羧基丁腈橡胶粒子改性环氧树指技术,并辅以玻璃微珠,球型硅微粉,ACR丙烯酸酯橡胶微球等抗冲剂填充,制备出一款高性能室温固化环氧结构胶.实验中采用高速搅拌球磨法在环氧树脂中分散超细全硫化羧基丁腈橡胶粒子,辅以填充物,制备的环氧树脂结构胶剪切冲击强...     

Dynamic mechanical analysis of rubber toughened epoxy resins

Dynamic mechanical analysis (DMA) was used to characterize cured epoxy resin formulations from ?150°C to temperatures above their α transitions. The resins were aromatic amine and aliphatic amine cured and were modified with carboxylterminated acrylonitrile-butadiene (CTBN) rubbers to improve their toughness, A DuPont 981 dynamic mechanical analyzer was used to measure the modulus and mechanical loss factor (tan δ) of the samples. Changes in the α and β transitions in the scan of tan δ as a function of temperature were related to changes in the formulation. Relations were also sought between changes in the DMA data and fracture and impact toughness of the cured formulations obtained using an instrumented impact test. Impact tests were performed at ?196°C and at room temperature. Results indicate that fracture toughness and the dynamic mechanical properties are affected by the amount of rubber, the compatibility of the rubber and epoxy, and changes in the curing agent stoichiometry.     

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.     

橡胶增韧环氧树脂低温韧性的研究

以低分子量聚酰胺(PA300)为固化剂,以液体端羧基丁腈橡胶(CTBN)为增韧剂增韧改性双酚A型环氧树脂,考察了橡胶增韧剂、固化剂、稀释剂和无机填料对环氧树脂低温韧性的影响。通过对增韧体系应力应变特性和动态力学性能的研究表明,该体系具有优异的低温韧性。     

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.     

环氧树脂/ABS复合材料的制备及性能表征

以环氧树脂为基体,苯乙烯-丙烯腈-丁二烯（ABS）树脂为增韧剂,制备了环氧树脂/ABS复合材料,讨论了增韧剂对复合材料的热性能和机械性能的影响。结果表明,ABS的添加可提高复合材料的断裂韧性。扫描电镜结果显示,基体的剪切屈服和橡胶颗粒的微孔洞是ABS增韧环氧树脂的主要增韧机理。     

Toughening of epoxy hybrid nanocomposites modified with silica nanoparticles and epoxidized natural rubber

Silica nanoparticles (SN) and epoxidized natural rubber (ENR) were used as binary component fillers in toughening diglycidyl ether of bisphenol A (DGEBA) cured cycloaliphatic polyamine. For a single component filler system, the addition of ENR resulted in significantly improved fracture toughness (K_IC) but reduction of glass transition temperature (T_g) and modulus of epoxy resins. On the other hand, the addition of SN resulted in a modest increase in toughness and T_g but significant improvement in modulus. Combining and balancing both fillers in hybrid ENR/SN/epoxy systems exhibited improvements in the Young’s modulus and T_g, and most importantly the K_IC, which can be explained by synergistic impact from the inherent characteristics associated with each filler. The highest K_IC was achieved with addition of small amounts of SN (5 wt.%) to the epoxy containing 5–7.5 wt.% ENR, where the K_IC was distinctly higher than with the epoxy containing ENR alone at the same total filler content. Evidence through scanning electron microscopy (SEM) and transmission optical microscopy (TOM) revealed that cavitation of rubber particles with matrix shear yielding and particle debonding with subsequent void growth of silica nanoparticles were the main toughening mechanisms for the toughness improvements for epoxy. The fracture toughness enhancement for hybrid nanocomposites involved an increase in damage zone size in epoxy matrix due to the presence of ENR and SN, which led to dissipating more energy near the crack-tip region.     

Synthesis of acid anhydride-modified flexible epoxy resins and enhancement of impact resistance in the epoxy composites

Epoxy resins are key materials used in various applications, including coatings, adhesives, and composites. Tougheners, such as nanoparticles, soft polymers, elastomeric polyurethanes, and core/shell particles, have been widely applied to compensate for the brittleness of the epoxy matrix and to enhance the impact resistance. Modifying epoxy resin by reacting it with a flexible component is one of the representative methods to overcome the weakness of cured epoxy polymers upon impact. For introducing flexible parts, we synthesized three types of epoxy-modified resins by reacting acid anhydride with glycidol, followed by reaction with bisphenol [F, S, or J] glycidyl ether to produce flexible modified epoxy resins. Mechanical tests, such as flexural strength and impact resistance tests, were performed by adding various amounts of the synthesized resin to the epoxy composites. The results of these tests suggest that the modified resins were effective in improving the toughness of the epoxy matrix.     

Mechanical properties and fracture behaviors of epoxy composites with phase‐separation formed liquid rubber and preformed powdered rubber nanoparticles: A comparative study

Epoxy composites filled with phase‐separation formed submicron liquid rubber (LR) and preformed nanoscale powdered rubber (PR) particles were prepared at different filler loading levels. The effect of filler loading and type on the rheological properties of liquid epoxy resin suspensions and the thermal and mechanical properties of the cured composites as well as the relative fracture behaviors are systematically investigated. Almost unchanged tensile yield strength of the cured epoxy/PR composites is observed in the tensile test compared with that of the neat epoxy; while the strength of the cured epoxy/LR composites shows a maximum value at ∼4.5 wt% and significantly decreases with increasing LR content. The glass transition temperature (T_g) of the cured PR/epoxy has shifted to the higher temperature in the dynamic mechanical thermal analysis compared with that of the cured pure epoxy and epoxy/LR composites. Furthermore, the presence of LR results in highly improved critical stress intensity factor (K_IC) of epoxy resin compared with the corresponding PR nanoparticles. In particular, the PR and LR particles at 9.2 wt% loading produce about 69 and 118% improvement in K_IC of the epoxy composites, respectively. The fracture surface and damage zone analysis demonstrate that these two types of rubber particles induce different degrees of local plastic deformation of matrix initiated by their debonding/cavitation, which was also quantified and correlated with the fracture toughness of the two epoxy/rubber systems. POLYM. COMPOS., 36:785–799, 2015. © 2014 Society of Plastics Engineers