Studies on the curing behavior,thermal, and mechanical properties of epoxy resin-co-amine-functionalized lead phthalocyanine

A high performance copolymer was prepared by using epoxy (EP) resin as matrix and 3,10,17,24-tetra-aminoethoxy lead phthalocyanine (APbPc) as additive with dicyandiamide as curing agent. Fourier-transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TGA) were used to study the curing behavior, curing kinetics, dynamic mechanical properties, impact and tensile strength, and thermal stability of EP/APbPc blends. The experimental results show that APbPc, as a synergistic curing agent, can effectively reduce the curing temperature of epoxy resin. The curing kinetics of the copolymer was investigated by non-isothermal DSC to determine kinetic data and measurement of the activation energy. DMA, impact, and tensile strength tests proved that phthalocyanine can significantly improve the toughness and stiffness of epoxy resin. Highest values were seen on the 20 wt% loading of APbPc in the copolymers, energy storage modulus, and impact strength increased respectively 388.46 MPa and 3.6 kJ/m², T_g decreased 19.46°C. TGA curves indicated that the cured copolymers also exhibit excellent thermal properties.     

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.     

Toughening epoxy resin with blocked isocyanate containing soft chain

A series of imidazole (MI) blocked 2,4‐toluene diisocyanate (TDI) with polyethylene glycol (PEG‐400) as soft segment (PEG‐MI‐b‐TDI) were synthesized for toughening and curing the bisphenol A type epoxy resin (E‐44). Fourier transform infrared (FTIR) spectrum indicates that the NCO groups of the isocyanate molecule are blocked with MI. For curing epoxy systems, elimination of epoxy group and the formation of urethane bonds were studied by FTIR spectroscopy. The results of mechanical property were shown that the tensile shear and impact strengths of neat MI and MI‐b‐TDI cured E‐44 are lower than those of PEG‐MI‐b‐TDI cured E‐44. Based on the scanning electron microscope studies, microstructure evolutions of the E‐44 cured by different curing agents were imaged. The mechanical, thermal, and dynamic mechanical properties were measured by universal testing machine, differential scanning calorimeter and dynamic mechanical analyzer (DMA). The toughness of E‐44 cured by PEG‐MI‐b‐TDI was effectively improved without sacrificing the tensile shear strength. Based on the DMA studies, the long soft chain of PEG brought in a noticeable lowering in the glass transition temperature (T_g). The glass transition temperature is near 165°C for the neat MI cured E‐44, which is higher than the T_gs of the other curing agents cured epoxy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41345.     

Preparation and properties of UV-autocurable BTDA-based epoxy-multiacrylate resins. Effects of the degree of polymerization and the epoxy type

A series of UV-autocurable epoxy-multiacrylate resins was synthesized, and the effects of degree of polymerization (DP) and epoxy type on their properties were investigated. These autocurable multiacrylate resins possess good pot life and are cured rapidly when exposed to ultraviolet (UV) without the addition of photoinitiator or photosensitizer. The curing rate of the autocurable resins was probably dependent on the number of abstractable hydrogen in epoxy resins. Stress-strain, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were used to characterize the properties of cured multiacrylate resins. Increased crosslinking density of cured films improved tensile properties. Increasing the molar ratio of epoxy resin in the multiacrylate resins was found to decrease the effective acrylate concentration of resins and to depress crosslinking density of cured resins, which also resulted in an increased elongation at break but a decreased Young's modulus and breaking strength. Furthermore, the different structures of epoxy resins were used to give wide range properties of cured epoxy-multiacrylate resins with a glass transition temperature (T_g range from 74 to 102°C. The film properties of the multiacrylate resins coated on steel plates were also investigated.     

Synthesis of a novel lignin-based epoxy resin curing agent and study of cure kinetics,thermal, and mechanical properties

In this contribution, first of all, the methoxy groups of organic solvent lignin (OSL) was converted to phenolic hydroxyl groups through demethylation reaction for the purpose of fabricating demethylated organic solvent lignin (DOSL). In addition, the resulting DOSL was utilized as a renewable material to synthesize a novel esterified lignin (EDOSL) by reacting with isobutyryl chloride for curing of epoxy resin. Finally, commercial liquid diglycidyl ether of bisphenol A was cured by EDOSL in the presence of 4-dimethylaminopyridine (DMAP) used as a catalyst based on dual-curing mechanism. Dual curing is a processing methodology based upon the alliance of two diverse and compatible polymerization reactions occurring sequentially or simultaneously. According to the FTIR spectra and ¹H-NMR analyses, the demethylation of OSL, esterification of DOSL, and the curing reaction of epoxy resin with EDOSL were successfully conducted. The value of the phenolic hydrogen in the DOSL was approximately 4.89 mmol/g, which increased by 12.64% after demethylation. The thermal and mechanical performances of these cured epoxy samples were measured by DSC, DMA, TGA, and tensile testing. The epoxy system cured by 10%wt esterified lignin with 1%wt DMAP possessed the tensile strength of 71.54 ± 7.50 MPa and the initial degradation temperature (T_5%) of 370°C, which can compete fairly with commercial aromatic curing agents or other lignin-based agents studied currently for the curing of epoxy systems.     

聚氨酯改性环氧树脂性能研究

采用2,4-甲苯二异氰酸酯、聚乙二醇为主要原料合成端异氰酸酯基聚氨酯预聚体,将预聚体和环氧树脂、活性稀释剂混合。用D-230进行固化,得到PU／EP增韧固化物。研究了聚氨酯不同含量对环氧树脂力学性能的影响,并用FT—IR进行了表征。用DMA研究了PU／EP固化物的阻尼性能。结果表明,加入聚氨酯预聚体明显改善了EP的阻尼性能;随着DMA测试频率的增大,tan δ-T谱向高温移动。     

Curing studies on the epoxides of carbono- and thiocarbonohydrazones

The curing behavior of a new class of N? N bonded epoxy resins has been analyzed using the simultaneous DTA-TG, dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA) techniques. The resin systems, viz, diglycidyl ether of furfuraldehydecarbonohydrazone (DGFCH), diglycidyl ether of furfuraldehydethiocarbonohydrazone (DGFTCH), and tetraglycidyl ether of vanillinthiocarbonohydrazone (TGVTCH) with the curative, diaminodiphenylmethane (DDM), taken in stoichiometric amounts have been examined. The curing exotherm could be resolved from the decomposition exotherm qualitatively using DTA-TG analysis. The DMA has been carried out in both the dynamic and isothermal mode to follow the curing process of the systems DGFCH/DDM and TGVTCH/DDM. The storage modulus (G′), loss modulus (G″), complex viscosity (η) and creep factor (tan δ) were measured simultaneously. The crossover point of G′ and G″, taken as the gelation point in isothermal runs, was determined to obtain time to gelation at that temperature. The isothermal runs at different temperatures have been used to calculate activation energy of the curing process up to gelation. For the difunctional resin DGFTCH, the activation energy value was found to be 18.7 kcal/mol. The thermomechanical analysis (TMA) has been used to find the glass transition (T_g0, and melt transition (T_m) temperatures. The cured tetrafunctional TGVTCH/DDM system as expected, has higher T_g than those of the two difunctional resin systems. © 1994 John Wiley & Sons, Inc.     

Biphenyl liquid crystal epoxy containing flexible chain: Synthesis and thermal properties

A biphenyl type liquid crystal epoxy (LCE) monomer 4,4′-di(2,3-epoxyhexyloxy)biphenyl (LCBP4) containing flexible chain was synthesized and the curing behavior was investigated using 4,4′-diaminodiphenylmethane (DDM) as the curing agent. The effect of curing condition on the formation of the liquid crystalline phase was examined. The cured samples show good mechanical properties and thermal stabilities. Moreover, the relationship between thermal conductivity and structure of liquid crystalline domain was also discussed. The samples show high thermal conductivity up to 0.28–0.31 W/(m*K), which is 1.5 times as high as that of conventional epoxy systems. In addition, thermal conductive filler, Al₂O₃, was introduced into LCBP4/DDM to obtain higher thermal conductive composites. When the content of Al₂O₃ was 80 wt%, the thermal conductivity of the composite reached to 1.86 W/(m*K), while that of diglycidyl ether of bisphenol A (Bis-A) epoxy resin/DDM/Al₂O₃ was 1.15 W/(m*K). Compared with Bis-A epoxy resin, the formation of liquid crystal domains in the cured LCE resin enhanced the thermal conductivity synergistically with the presence of Al₂O₃. Furthermore, the introduction of Al₂O₃ also slightly increased the thermal stabilities of the cured LCE.     

Effects of curing program on mechanical behavior and water absorption of DGEBA/TETa epoxy network

Water uptake in organic coatings remains an interesting challenge for fundamental and applied researches because chemical, physical, and mechanical properties are concerned. The polymer network, which is affected by the curing program, is a key factor for water absorption. In this work, an epoxy network based on diglycidyl ether of bisphenol A and a hardener triethylentetramine was cured at different temperatures: below T_g (protocol 1) and above T_g (protocol 2). DMA, Differential Scanning Calorimetry (DSC), and FT‐IR measurements showed that both protocols allow to obtain totally cured networks. However, DSC and DMA results revealed that both cured networks present different levels of homogeneity, depending on the different curing conditions, which affect the free volume and the activation volume associated with visco‐elastic properties. The mechanical properties of free films and water sorption behaviors were investigated as function of cured conditions. It was found that protocol 1‐cured networks present higher mechanical properties and was less affected by water ingress than protocol 2‐cured systems, leading to better barrier properties. These results highlight the influence of the curing program onto the heterogeneous distribution of the epoxy network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Properties and processing characteristics of dielectric-filled epoxy resins

A family of casting composites, epoxy resins with mineral fillers, having a range of electrical properties, are being developed. In such composites, the dielectric constant is controlled primarily by varying the filler material in composition and proportions. The present work reports on the mechanical properties of composites made with two types of filler, an alumina powder (XA3500 from ALCOA) and a BaTiO₃/TiO₂ ceramic powder (ATD-50 from Ampex). Dependence of mechanical properties on curing agents was also determined. Filler contents from 0 to 40 percent volume were used. Epoxy systems contained single epoxy resin with both amine and anhydride hardeners. Processing of the anhydride-cured systems was easier than that of the amine-based systems because of their lower viscosity and longer gel time of the former. However, the anhydride-cured systems required higher processing temperatures. Curing kinetics and molecular bonding were investigated using a combination of differential scanning calorimetry, dynamic mechanical thermal analysis, and scanning electron microscopy. Activation energies of 11.2 kcal/mole and 12.1 kcal/mole were obtained for the curing of the amine-based and the anhydride-based composites respectively, and a small difference in the glass transition temperature was also observed. These effects can be attributed to the difference in the structure of the curing agents. The epoxy resin cured with NMA is less ductile compared with those cured with MTHPA or MHHPA due to slight chemical modification on the ring structures. This dependence of ductility on curing agent was observed in specimens with different filler contents. Although the presence of the filler materials was found to enhance the mechanical properties of the epoxy, the fracture mode in these materials is still brittle.     

Reaction kinetics,thermal properties of tetramethyl biphenyl epoxy resin cured with aromatic diamine

Epoxy resins, 4, 4′‐diglycidyl (3, 3′, 5, 5′‐tetramethylbiphenyl) epoxy resin (TMBP) containing rigid rod structure as a class of high performance polymers has been researched. The investigation of cure kinetics of TMBP and diglycidyl ether of bisphenol‐A epoxy resin (DGEBA) cured with p‐phenylenediamine (PDA) was performed by differential scanning calorimeter using an isoconversional method with dynamic conditions. The effect of the molar ratios of TMBP to PDA on the cure reaction kinetics was studied. The results showed that the curing of epoxy resins contains different stages. The activation energy was dependent of the degree of conversion. At the early of curing stages, the activation energy showed the activation energy took as maximum value. The effects of rigid rod groups and molar ratios of TMBP to PDA for the thermal properties were investigated by the DSC, DMA and TGA. The cured 2/1 TMBP/PDA system with rigid rod groups and high crosslink density had shown highest T_g and thermal degradation temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

The effects of curing cycles on properties of the epoxy system 3221/RH glass fabric composites

In this work, the epoxy system 3221 and its glass fabric laminates were thermally cured under different curing temperatures. The curing degree of the resin was increased with elevated reaction temperature. Dynamic mechanical analysis was performed on the laminate coupons and glass transition temperature (T_g) and relative stiffness (E′) of composites were measured before and after soaked in distilled water at 70°C. A shift in glass transition temperature to higher values and the splitting of the tan δ curve were observed with extent of cure under dry conditions. T_g values shifted to lower temperatures after immersion. Under wet condition, the change in T_g1 was very small when the curing degree was up to 96%. The relative stiffness experienced a reduction both in initial modulus and the initial sharp drop temperature after immersion. It also suggested that the excessively high curing temperature (>130°C) had a negative effect on the retention of relative stiffness under wet condition. Both the interlaminar shear strength and dielectric properties of laminates were determined before and after immersion. The compared results demonstrated that the elevated curing temperature played a good influence on both of the properties before aged. However, for samples cured above 130°C, lower retention of interlaminar shear strength and poor dielectric properties were observed during immersion due to their higher moisture contents. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

A dynamic mechanical analysis method for predicting the curing behavior of phenol-formaldehyde resin adhesive

In this work, filter paper was proven to be suitable as the substrate for the preparation of dynamic mechanical analysis (DMA) testing specimens to predict the curing behavior of phenol-formaldehyde (PF) resin adhesives for its stability during the curing temperature span. With this method, the curing behavior of PF resin was monitored by DMA in tensile-torsion mode. With the strain curves, the onset of curing temperature of PF resin could be determined clearly. The curing degree of PF resin could be calculated by the integral area in strain curves. The method to combine storage modulus (G′), tan δ, and strain curves together could explain the curing behavior of PF resin more comprehensively than the commonly used method using only G′ and tan δ curves. The DMA test results of PF resin with different viscosity and with accelerator implied the reliability of this novelty method.     

A Study of the Interphase Region in Carbon Fibre/Epoxy Composites using Dynamic Mechanical Thermal Analysis

We have examined the effect of fibre addition on the glass transition temperature (T _g ) of two epoxy resin systems (an amine cured and an anhydride cured epoxy system) using dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). The presence of fibres changes the glass transition temperature (T _g ) of an anhydride cured epoxy resin but does not affect that of an amine cured epoxy. The data suggest that two counteracting mechanisms are responsible for these changes: firstly, the presence of fibres causes a restriction of the molecular motion in the resin system, and secondly, the presence of carboxyi and keto-enol groups on the fibre surface inhibit curing of the resin close to the fibre, i.e. in the interphase region. The former increases the T _g and is a long range effect whereas the latter decreases the T _g and is a localised phenomenon. Changes in the dynamic properties of the interphase region are only detected when the samples are loaded in the longitudinal direction and not in the transverse direction where bulk matrix properties dominate. Sizing the fibres before their incorporation into the epoxy resin eliminates the variation in interfacial properties arising from differences in fibre surface chemistry.     

Preparation and properties of TiO2‐filled poly(acrylonitrile‐butadiene‐styrene)/epoxy hybrid composites

Poly (acrylonitrile‐butadiene‐styrene) (ABS) was used to modify diglycidyl ether of bisphenol‐A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO₂ reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS‐cured epoxy/ABS/TiO₂ hybrid composites systems have two T_gs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO₂ particles. The addition of TiO₂ induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO₂ filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO₂ components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO₂ are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Curing of epoxy/novolac system modified with reactive liquid rubber and carbon filler

The curing behaviour of epoxy resins modified with reactive liquid rubber, using a novolac resin as a hardner was studied by means of differential scanning calorimetry in isothermal (100, 130 and 150 °C) and non-isothermal conditions (2, 5, 10 and 15 °C min^-1). The influence of carboxyl- (CTBN) and epoxy- (ETBN) terminated butadiene-acrylonitrile copolymers on the kinetic parameters and glass transition temperature (T_g) of cured epoxy systems was determined. The effect of grinded bituminous coal as an organic filler into epoxy network was also investigated. The carboxyl-end groups strongly enhanced the curing rate, in contrast to the epoxy-terminated rubber (ETBN) that had only a minor effect on the curing reactions. The presence of coal accelerated curing in its early stage. The T_g of completely cured epoxy was practically unaffected by the presence of carbon filler and reactive rubbers and was equal about 132 °C. The apparent curing activation energies were determined. A smaller activation energy was observed only for CTBN/epoxy/novolac system. The effect of reactive rubber and coal on the Charpy impact resistance of cured epoxy systems was also discussed.     

Structure and viscoelastic properties of epoxy resins prepared from o-cresol novolacs

The relation between the structure and viscoelastic properties of the epoxy resins prepared from o-cresol novolacs was studied. Our model epoxy resins were two kinds of epoxy compounds synthesized from three-nuclei and four-nuclei o-cresol novolacs. In addition to these models, a commercially available o-cresol novolac-type epoxy resin was also studied. Each of the three epoxy compounds was cured with one of three kinds of novolacs, which were starting materials of the above-mentioned epoxy resins. Characteristic properties of the cured resins, such as glass transition temperature (T_g), average molecular weight between crosslinking points (M¯_c), and front factor (?) were obtained. It was concluded that the number of functional groups contained in the curing system almost dominated the viscoelastic properties of the cured resins.     

Curing and Morphology of BPA Epoxy Resin/LC Epoxy Resin PEPEB Composites

Liquid crystalline epoxy resin (LC epoxy resin) – p-phenylene di{4-[2-(2,3-epoxypropyl)ethoxy]benzoate} (PEPEB) was synthesized. The mixture of PEPEB with bisphenol-A epoxy resin (BPAER) was cured with a curing agent 4,4-diamino-diphenylmethane (DDM). The curing process and thermal behavior of this system were investigated by differential scanning calorimeter (DSC) and torsional braid analysis (TBA). The morphological structure was measured by polarizing optical microscope (POM) and scanning electron microscope (SEM). The results show that the initial curing temperature Ticu (gel point) of this system is 68.1°C, curing peak temperature T _pcu is 102.5°C, and the disposal temperature T _fcu is 177.6°C. LC structure was fixed in the cured epoxy resin system. The curing kinetics was investigated by dynamic DSC. Results showed that the curing reaction activation energy of BEPEB/BPAER/DDM system is 22.413 kJ/mol. The impact strength is increased 2.3 times, and temperature of mechanical loss peak is increased to 23°C than the common bisphenol-A epoxy resin, when the weight ratio of BEPEB with BPAER is 6 100.     

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     

The effects of additives on curing properties,resin contents,and mechanical properties of graphite/epoxy composites

The effects of additives such as boron trifluride-monoethylene amine (BF₃MEA) and fumed silica in the TGDDM/DDS epoxy formulations on the curing properties, resin contents, and mechanical properties of their graphite/epoxy (Gr/Ep) composites were investigated. The addition of BF₃MEA increased the viscosity of resin as well as the resin contents of cured laminates because of its catalytic effect. Although the fumed silica was considered a thickening agent, it also acted like a co-catalyst with BF₃MEA. As the resin content of cured laminates was increased, the excess resin was likely to accumulate in the interlaminar region, which increased the interlaminar shear strength but decreased the flexure strength as well as the interlaminar fracture toughness value, G_IC.