Influence of cyanate content on the morphology and properties of epoxy resins with phenolphthalein poly(ether ketone)

Phenolphthalein poly(ether ketone) (PEK‐C) was blended with the diglycidyl ether of bisphenol A epoxy resin and bisphenol A dicyanate ester. The effect of cyanate content on cure behaviors, thermal and mechanical properties of PEK‐C/epoxy/cyanate mixtures was investigated. As results, the increase of cyanate content slightly hindered the cure reaction of the mixtures. Fourier transform infrared results indicated that the curing reaction of the cured mixtures was complete. When the cyanate ester content increased, the flexural properties and T_g values were enhanced, and the initial thermal decomposition temperature was reduced. A significant improvement in fracture toughness was obtained when the cyanate group in the mixtures was excessive. The fracture toughness can be well explained by SEM observations. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fracture toughness improvement of epoxy resins with short carbon fibers

This study examined the thermal stability and fracture toughness of diglycidylether of bisphenol-A (DGEBA)/short carbon fiber (SCF) composites using several techniques. The thermal stability of the DGEBA/SCF composites was similar to that of neat epoxy resin. The fracture toughness of the composites was significantly improved relative to the neat resin. The SEM micrographs indicated that a relatively rough surface with shear deformation and tortuous cracks was formed, thereby preventing deformation and crack propagation and inducing higher fracture toughness in the DGEBA/SCF composites.     

Morphologies and mechanical properties of polyethersulfone modified epoxy blends through multifunctional epoxy composition

Thermoplastic polyethersulfone (PES) modified multifunctional tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) and triglycidyl para‐aminophenol (TGAP) epoxy prepolymers cured with 4,4′‐diaminodiphenylsulfone (44DDS) were prepared using a continuous reactor method and their reaction‐induced phase separated morphologies and mechanical properties were measured and correlated with chemical compositions. ¹H nuclear magnetic resonance (¹H NMR) and near‐infrared spectroscopy (NIR) were used to quantify the chemical network formation. Atomic force microscopy (AFM) with nanomechanical mapping was employed to resolve the nanoscale phase‐separated morphologies. The extent of phase separation in cured networks and resultant domain sizes were determined to be controllable depending upon the multifunctional epoxy compositions. The results obtained from mechanical studies further indicated that tensile modulus was not largely affected by multifunctional epoxy compositions while fracture toughness increased with increase of TGAP content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44775.     

Mechanical and morphological properties of epoxy resins modified by poly(phthalazinone ether sulfone ketone)

A series of blends have been prepared by adding a novel thermoplastic poly(phthalazinone ether sulfone ketone) (PPESK) in varying proportions to diglycidyl ether of bisphenol A epoxy resin (DGEBA) cured with p‐diaminodiphenylsulfone (DDS). All the blends showed two‐phase structures characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Addition of the PPESK resulted in great enhancement of glass transition temperatures (T_g) both in the epoxy‐rich phase and in the PPESK‐rich phase by reason of the special structure of PPESK. There was moderate increase in the fracture toughness as estimated by impact strength. Fracture mechanisms such as crack deflection and branches, ductile microcracks, ductile tearing of the thermoplastic, and local plastic deformation of the matrix were responsible for the increase in the fracture toughness of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of mixing temperatures on the morphology and toughness of epoxy/polyamide blends

A new mixing process was explored to increase further the fracture toughness and to investigate the toughening mechanisms of epoxy/nylon blend. In this process, without mechanical mixing, the mixtures of epoxy and premade nylon 6 powder were heated without the curing agent to specific temperatures, referred to as the “mixing temperature.” For epoxy/nylon blends, at sufficiently high temperatures, a semi‐interpenetrating network‐like structure can be developed at the interphase via the reaction between the amine end group and the epoxide group. The depth of interphase and the extent of reaction depends on the mixing temperature. The strong dependency of the fracture energy on mixing temperature reveals the positive effect of the newly developed structure at the interphase. The increase of fracture toughness is possibly due to the enhanced crack fingering bifurcation/deflection mechanism resulting from the lamellae developed in the interphase and the enhanced plastic deformation of epoxy as a result of preyielding of the interphase. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1055–1063, 1999     

Polyether and polyester polyol based glycidyl-terminated polyurethane modified epoxy resins: Mechanical properties and morphology

A glycidyl-terminated polyurethane prepolymer was synthesized and used to enhance the properties of epoxy resins. Some properties of glycidyl-terminated PU/epoxy with polyether based (PPG) and polyester based (PBA) glycidyl-terminated PU were investigated in this research. The polyether based glycidyl-terminated PU(PPG) modified epoxy resin proved to be superior to conventional epoxy resins in improved impact strength and fracture energy, but not tensile strength, tensile modulus, flexural strength and flexural modulus. On the other hand, the polyester based glycidyl-terminated PU(PBA) modified epoxy resin had increased mechanical properties while showing slight variation of impact strength and fracture energy. Different mechanisms for this behaviour are advanced in this paper.     

Fracture toughness of a hybrid rubber modified epoxy. II. Effect of loading rate

Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1–1000 mm/min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1–10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10–1000), the fracture toughness of hybrid system decreased gradually to the level lower than that of ATBN-modified epoxy. Fractography of the damage zones showed the toughening mechanisms of ATBN-modified system was less affected by increasing the loading rate compared to that of hybrid system. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Relationship between gelation and morphology of rubber-modified epoxy resins

The addition of both a solid and a liquid rubber to an epoxy resin has been shown to strongly increase the toughness of the material. Moreover, it is well known that toughening depends on the morphology of the system, which, in turn, depends on the cure conditions. In the present work the morphologies of epoxy resins modified with mixtures of solid and liquid rubbers have been studied through transmission electron microscopy. An investigation of the influence of the elastomers and of the gel time on the morphology of the hardened material was carried out. Gel times were evaluated, through rheological measurements, at different cure temperatures.     

Studies on isotactic poly(phenyl glycidyl ether)‐modified epoxy resins. II. Toughening of epoxy resins

A semicrystalline polymer, isotactic poly(phenyl glycidyl ether) (i‐PPGE) was used as a modifier for epoxy resin; 1,8‐Diamino‐p‐methane (MNDA) and 4,4′‐Diamino diphenyl sulfone (DDS) were used as curing agents. In the MNDA‐cured resins, the dispersed phase were spherical particles with diameters in the range of 0.5–1.0 μm when the resin was blended with 5 phr i‐PPGE. In the DDS‐cured resins, the particle size distribution of the dispersed phase was much wider. The difference was traced back to the reactivity of the curing agent and the different regimes used for curing. Through dynamic mechanical analysis, it was found that in the MNDA‐cured systems, i‐PPGE had a lower crystallinity than in the DDS‐cured system. In spite of the remarkable difference in the morphology and microstructure of the modified resins cured with these two curing agents, the toughening effects of i‐PPGE were similar for these resins. The critical stress intensity factor (K_IC) was increased by 54% and 53%, respectively, for the resins cured by DDS and by MNDA, blending with 5 phr of the toughner. i‐PPGE was comparable with the classical toughners carboxyl‐terminated butadiene‐acrylonitrile copolymers in effectiveness of toughening the epoxy resin. An advantage of i‐PPGE was that the modulus and the glass‐transition temperature of the resin were less affected. However, this modifier caused the flexural strength to decrease somewhat. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1223–1232, 2002; DOI 10.1002/app.10445     

Fracture behavior of epoxy polymers modified with core-shell rubber particles

Physical and thermomechanical properties of BDMA-catalyzed DGEBA/Dicy epoxy toughened with core-shell particles were studied. Relationships between these properties and the level of toughening are reported. The blends have been made in well-defined processing conditions. In fact, the resulting properties depend on the state of dispersion of the particles in the prepolymer matrix before crosslinking and on the cure schedule. The considered core-shell particles were of two types: i) poly(butadiene-co-styrene) core/carboxy-functionalized poly(methyl methacrylate-co-styrene) shell. Such core-shell particles have been dispersed in the epoxy matrix at different volume fractions (from 9.5 to 24%); ii) poly(butyl acrylate) core/carboxy functionalized poly(methyl methacrylate-co-styrene) shell. These particles have been dispersed at a volume fraction of 24%. Static mechanical tests were performed in tension and compression modes on these core-shell polyepoxy blends. A slight decrease of Young's modulus and an increase of the ability to plastic deformation were noticed as the volume fraction of the core-shell particles increased. Using linear fracture mechanics (LEFM), an improvement of the fracture properties (K_IC) was measured. Fatigue crack-growth studied for blends demonstrates that the Paris's law can be used to describe the behavior of the materials. Increasing the volume fraction of core-shell particles leads to an improvement of the resistance to fatigue crack-propagation. The same trend is noted on the impact behavior studied by means of high-speed tests performed in a large range of temperatures. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2419–2431, 1997     

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     

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。     

Core-shell particles designed for toughening the epoxy resins. II. Core-shell-particle-toughened epoxy resins

The diglycidyl ether of bisphenol A–m-phenylene diamine (DGEBA–MPDA) epoxy resin was toughened with various sizes and amounts of reactive core-shell particles (CSP) with butyl acrylate (BA) as a core and methyl methacrylate (MMA) copolymerized with various concentration of glycidyl methacrylate (GMA) as a shell. Ethylene glycol dimethacrylate (EGDMA) was used to crosslink either core or shell. Among the variables of incorporated CSP indicated above, the optimal design was to obtain the maximum plastic flow of epoxy matrix surrounding the cavitated CSP during the fracture test. It could be achieved by maximizing the content of GMA in a shell-crosslinked CSP, the particle size, and the content of CSP in the epoxy resin without causing the large-scale coagulations. The incorporation of reactive CSP could also accelerate the curing reaction of epoxy resins. Besides, it was able to increase the glass transition temperature of epoxy resins if the particle size ≤0.25 μm and the dispersion was globally uniform. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2313–2322, 1998     

Studies of the properties of a thermosetting epoxy modified with block copolymers

Poly[(n‐butyl acrylate)‐block‐poly(methyl methacrylate)‐co‐(glycidyl methacrylate)] (BMG) diblock copolymers incorporating an epoxy‐reactive functionality in one block have been synthesized and used as modifiers for the model epoxy resin E‐51 cured with 4,4′‐diaminodiphenyl methane (DDM). The properties and morphologies of the modified epoxy thermosets were investigated by dynamic mechanical analysis (DMA), impact testing and scanning electron microscopy (SEM). The results reveal that addition of the block copolymers leaves the glass transition temperatures of the blends relatively unchanged, with small decreases in the storage moduli at room temperature. The toughening effect is dependent on the chemical structures of the block copolymers and an increase in the impact strength by a factor of two was obtained by the addition of ‘relatively symmetrical’ block copolymers. Moreover, the impact test results are consistent with the morphologies of the fracture surfaces as evidenced by SEM. Copyright © 2005 Society of Chemical Industry     

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。     

Structure and toughness of polyethersulfone (PESU)‐modified anhydride‐cured tetrafunctional epoxy resin: Effect of PESU molecular mass

A tetrafunctional, anhydride hardened epoxy resin (EP) was modified with polyethersulfones (PESU) of different molecular mass (MM) without using additional solvent in 10 wt %. The morphology, thermal, and fracture mechanical properties of the EP/PESU systems were determined. PESU was present as dispersed phase in the EP matrix. The final morphology of EP/PESU depended on MM of PESU. PESU of low and medium MM formed submicron scale spherical droplets, whereas PESU of high MM was present in micron scale inclusions of complex (sea‐island) structure. With increasing MM of PESU, the fracture mechanical properties, and especially the fracture energy, were increased. This was traced to differences in the morphology (dispersion of PESU) of the EP/PESU systems triggering different failure mechanisms. The onset of thermal degradation was slightly reduced, whereas the char yield enhanced by PESU modification compared with the reference EP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Toughening of epoxy resins by modified m-phenylene diamine having soft ether chain

A new soften curing agent for toughening epoxy resins was synthesized by m-phenylene diamine modified with epoxypropyl butyl ether. The curing processes of epoxy resin/modified m-phenylene diamine were traced by differential scanning calorimetry (DSC), then kinetic parameters, ΔE and n, were deduced. Fourier transform infrared (FTIR) analysis showed that the longer the reaction time was, the smaller the absorption peaks of epoxy group were. The results of the mechanical properties demonstrated that the impact property of the epoxy resin cured by modified m-phenylene diamine at the moderate temperature was better than that of cured by unmodified one because of the introduction of soft ether chain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of the structure of curing agents modified by epoxidized oleic esters on the toughness of cured epoxy resins

The aim of this study was to determine the effect of the ester carbon chain length of curing agents modified by epoxidized oleic esters on the toughness of cured epoxy resins. An amine‐terminated prepolymer (i.e., curing agent G) was synthesized from a bisphenol A type liquid epoxy resin and triethylene tetramine. The toughening curing agents (G1 and G2) were prepared by reactions of epoxidized oleic methyl ester and epoxidized oleic capryl ester, respectively, with curing agent G. Fourier transform infrared spectrometry was used to characterize the chemical structure of the curing agents. The effects of the carbon chain length of the oleic ester group in the curing agents on the toughness and other performances of the curing epoxy resins were investigated by analysis of the Izod impact strength, tensile strength, elongation at break, thermal properties, and morphology of the fracture surfaces of the samples. The results denote that the toughness of the cured epoxy resins increased with the introduction of oleic esters into the curing agents without a loss of mechanical properties and that the toughness and thermal stability of the materials increased with increasing ester carbon chain length. The toughness enhancement was attributed to the flexibility of the end carbon chains and ester carbon chains of the oleic esters in the toughening curing agents. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Polyetherimide-modified epoxy networks: Influence of cure conditions on morphology and mechanical properties

The morphologies and mechanical properties of thermoplastic-modified epoxy networks generated through the reaction-induced phase separation procedure were studied as a function of isothermal cure conditions. The selected model system was diglycidyl ether of bisphenol A cured with 4,4′-methylenebis [3-chloro,2,6-diethylaniline] in the presence of a nonfunctionalized polyetherimide. Appropriate precuring and postcuring schedules were selected. The precure temperature had a strong effect on final morphologies because it affected the viscosity of the system at the cloud point and the extent of the separation process. The morphologies generated are discussed in connection with phase separation mechanisms. The ratio of the height of the loss peaks corresponding to each phase was an appropriate parameter to qualitatively predict the shape of morphology and to determine if the system was phase-inverted or not. The fracture toughness, K_Ic was significantly improved only when bicontinuous or inverted structures were generated, resulting from the plastic drawing of the thermoplastic-rich phase. Before phase inversion, K_Ic was hardly higher than that of the neat matrix due to poor interfacial adhesion. Nevertheless, the thermoplastic-rich particles constitute obstacles to the propagation of the crack and contribute to the toughening of the material, measured through impact resistance measurements. The observation of fracture surfaces revealed the occurrence of microcracking and crack-pinning. Strain recovery experiments showed that particle-induced shear yielding of the matrix was present as well. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2433–2445, 1997