Epoxy Blends Research Articles

Rheology of SiO2/(acrylic polymer/epoxy) suspensions. II. Nonlinear stress relaxation

Large deformation, nonlinear stress relaxation modulus G(t, γ) was examined for the SiO2 suspensions in a blend of acrylic polymer (AP) and epoxy (EP) with various SiO2 volume fractions (ϕ) at various temperatures (T). The AP/EP contained 70 vol.% of EP. At ϕ ≤ 30 vol.%, the SiO2/(AP/EP) suspensions behaved as a viscoelastic liquid, and the time-strain separability, G(t, γ) = G(t)h(γ), was applicable at long time. The h(γ) of the suspensions was more strongly dependent on γ than that of the matrix (AP/EP). At ϕ = 35 vol.% and T = 100°C, and ϕ ≥ 40 vol.%, the time-strain separability was not applicable. The suspensions exhibited a critical gel behavior at ϕ = 35 vol.% and T = 100°C characterized with a power law relationship between G(t) and t; G(t) ∝ t − n . The relaxation exponent n was estimated to be about 0.45, which was in good agreement with the result of linear dynamic viscoelasticity reported previously. G(t, γ) also could be approximately expressed by the relation $G(t,\gamma) \propto t^{-n^{\prime}}$ at ϕ = 40 vol.%. The exponent n ′ increased with increasing γ. This nonlinear stress relaxation behavior is attributable to strain-induced disruption of the network structure formed by the SiO2 particles therein.

Self-organized thermosets involving epoxy and poly(ɛ-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(ɛ-caprolactone) amphiphilic triblock copolymer

In this work, we investigated the self-assembly behavior of poly(ɛ-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(ɛ-caprolactone) (PCL-b-PEEE-b-PCL) triblock copolymer in epoxy thermosets. The PCL-b-PEEE-b-PCL triblock copolymer was synthesized via the ring-opening polymerization of ɛ-caprolactone with a hydroxyl-terminated poly(ethylene-co-ethylethylene) as the macromolecular initiator. The hydroxyl-terminated poly(ethylene-co-ethylethylene) was prepared with the hydrogenation reaction of a hydroxyl-terminated polybutadiene. The triblock copolymer was incorporated into the precursors of epoxy to obtain the nanostructured thermosets. It was found that the self-organized nanophases were formed in the mixture before curing reaction and the nanostructures can be further fixed via curing reaction. The self-assembly behavior of the triblock copolymer in epoxy thermosets was investigated by means of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and dynamic mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) shows that the formation of the self-organized nanophase in the thermosets caused that a part of poly(ɛ-caprolactone) subchains were demixed from epoxy matrix with the occurrence of curing reaction; the fractions of demixed PCL blocks were estimated according to the Tg-composition relation of the model binary blends of epoxy and PCL.

Gelation behavior of thermoplastic-modified epoxy systems during polymerization-induced phase separation

The rheological behavior and gelation characteristics of epoxy blends are of critical importance to property study and industrial application. In this work, we studied the rheological behavior and structural transition of different thermoplastics, including polyetherimide, polymethylmethacrylate, and polyethersulfone (PES), modified epoxy systems by using rheometry instrument, differential scanning calorimetry, time-resolved light scattering, and scanning electronic microscopes. At the same molecular weight level of thermoplastics, different epoxy blends show profound diversities on the rheological and gelation behavior due to the large differences in phase separation and curing process. For early phase-separation systems of PES-modified epoxy blends, two gel points are identified, which correspond to physical gelation and chemical gelation, respectively. With the variation of the PES molecular weight and curing rate, dramatic changes in gel time and critical exponent were observed. As the molecular weight of thermoplastics is increased, the gelation time becomes shorter and the gel strength gets lower, while the faster curing rate would increase the physical gel strength significantly.

A cure kinetics, diffusion controlled and temperature dependent, identification of the Araldite LY556 epoxy

The curing of the LY556 epoxy system, a DGEBA-type epoxy resin with an anhydride hardener HY917 and a l-methyl imidazole DY 070 accelerator, mass ratio 100:90:2, was investigated by isothermal and nonisothermal differential scanning calorimetry (DSC). Dynamic measurements were used to evaluate the total, ultimate, heat of the epoxy resin thermosetting reaction and enable experimental conversion determination for isothermal curing. Aiming further finite element modelling of the curing, this article especially focuses on a complete, temperature dependent, cure kinetics parameters identification strategy with the Kamal and Sourour phenomenological model expanded by a diffusion factor. A special attention was given for diffusion description which allows the identification of a fixed order of reaction for the LY556 epoxy resin. Based on isothermal conversion data analysis, the methodology for cure kinetics parameters identification is presented. This led to a temperature dependent identification of all cure kinetics parameters of the LY556 epoxy blend, including diffusion control description and corresponding temperature dependency. Cure kinetics identification quality and importance of diffusion control phenomenon for the curing of the epoxy are then highlighted by computed conversion results that fit almost well the data in the range of temperature used for identification.

Curing behavior and adhesion properties of epoxy resin blended with polyhydric alcohol-liquefied Cryptomeria japonica wood

Cryptomeria japonica (Japanese cedar) wood was liquefied using polyethylene glycol (PEG-400 and PEG-600)/glycerol as the solvent with H2SO4 as a catalyst. The blended epoxy resins were prepared by mixing the liquefied wood with epoxy resin of various weight ratios and used for wood gluing. The results showed that blended epoxy resins could cure under room temperature with an exothermic reaction. DSC thermoanalysis showed that increasing the blending amount of liquefied wood would shift the peak of curing reaction to a higher temperature but with less heat released. Blended epoxy resins had a good dry bonding strength for wood when cured at room temperature. However, curing with heat treatment could improve the wet bonding strength of blended epoxy resins, especially for those prepared with PEG-400-liquefied wood.

Thermal Properties, Fracture Toughness and Water Absorption of Epoxy-Palm Oil Blends

Epoxidized palm oil (EPO) was blended with cycloaliphatic epoxide, epoxy novolac and diglycidyl ethers of bisphenol-A. The fracture toughness and thermal properties of epoxy/EPO blends were characterized using single-edge notched bending tests and differential scanning calorimetry. Increased EPO loading improved the fracture toughness (K IC ) of the epoxy blends. The epoxy blends with higher EPO loading exhibited higher degree of conversion. The glass transition temperature (T g ) of the epoxy blends shifted to higher temperature as the increasing of DSC heating rate. Water absorption caused T g reduction of epoxy blends but it was determined that the water molecules absorbed were totally reversible.

Studies of Silicon-Containing Bismaleimide Resins – Preparation and Characteristics of Reactive Blends of Silicon-Containing Bismaleimide and Epoxy

Abstract Three kinds of silicon-containing bismaleimide (4,4′-Bismaleimido phenoxy silane) monomers were synthesized and added through blending to general epoxy system for the study of their applications as reactive flame retardants. The thermal analysis of the BMI monomers in bisphenol type epoxy system had been discussed. An increase in the BMI contents decreased the storage modulus and glass-transition temperature and slightly reduced the mechanical strength of the epoxy blends. Although the initial pyrolysis temperatures of all the blending systems gradually decreased as the silicon-content increased, all the silicon-containing epoxy systems still had good thermal stability and the flame retardancy was promoted significantly by increasing contents of BMI. The LOI values of all the blend types were increased to about 30 as the BMI concentration reached 20%.

Morphology and Fracture Toughness of Nanostructured Epoxy Resin Containing Amino-Terminated Poly(propylene oxide)

Amino-terminated poly(propylene oxide) (ATPPO) was incorporated into epoxy resin to toughen thermosets. It was found that nanostructured thermosets were obtained; the nanostructures were characterized by means of atomic force microscopy and small-angle X-ray scattering. The formation of the nanostructures is interpreted on the basis of the occurrence of the reaction of terminal groups of ATPPO with diglycidyl ether of bisphenol A; this reaction is suggested to result in the formation of star-shaped block copolymers composed of poly(propylene oxide) (PPO) and epoxy blocks. Due to the presence of the star-shaped block copolymer produced in situ, the phase separation of PPO induced by the reaction was confined to the nanometer scale. The glass-transition behavior and fracture toughness of the nanostructured thermosets were investigated by means of differential scanning calorimetry, dynamic mechanical thermal analysis, and the measurement of critical stress intensity factors. The epoxy thermosets were significantly toughened by the inclusion of a small amount of ATPPO. The thermal and mechanical properties of the nanostructured thermosets are compared to the binary blends of epoxy resin containing hydroxyl-terminated poly(propylene oxide) (HTPPO) with identical molecular weight. With the identical composition, the nanostructured thermosets displayed higher fracture toughness than that of their binary blends. The difference in morphology and properties is interpreted in terms of the formation of the nanostructures.

Influence of aliphatic amine epoxy hardener on the adhesive properties of blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with epoxy resin

AbstractThe adhesive properties have been investigated in blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with diglycidyl ether of bisphenol A and three different aliphatic amine epoxy hardener. The adhesives properties are evaluated in steel alloy substrate using single‐lap shear test. The copolymers are initially miscible in the stoichiometric blends of epoxy resin and hardener at room temperature. Phase separation is noted in the course of the polymerization reaction. Different morphologies are obtained according to the amine epoxy hardener. The most effective adhesive for steel–steel joints in single‐lap shear test is the blends using 1‐(2‐aminoethyl)piperazine (AEP) as hardener. This system shows the biggest lap shear strength. However, the modified adhesives show a reduction in the mechanical resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Thermal properties of anhydride-cured bio-based epoxy blends

Epoxidized palm oil (EPO) (0–12 wt%) was added into petrochemical-based epoxy blends (diglycidyl ether of bisphenol-A (DGEBA)/cycloaliphatic epoxide resin/epoxy novolac resin) to develop a thermal curable bio-based epoxy system. The thermal behaviors of the EPO, epoxy blends (EB), and bio-based epoxy blends (EB/EPO) were characterized using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMT) and thermo-mechanical analysis (TM). The glass transition temperature (T g) and storage modulus (E′) of the EB/EPO system was reduced with the increasing of the EPO loading. This is attributed to the plasticizing effect of the EPO. It was found that epoxy blends with higher loading of EPO possessed higher coefficient of thermal expansion (CTE) and tanδ value. This is due to the increase of the free volume and chain flexibility in the three-dimensional network of the epoxy blends. The internal thermal stresses of the EB/EPO were decreased as the increasing loading of EPO, owing to the reduction of crosslink density, modulus of elasticity, and T g in the epoxy blends.

Epoxy and hyperbranched polymer blends: Morphology and free volume

AbstractIn this work, the phase separation of an epoxy‐functionalized hyperbranched polymer (HBP) in a blend with a conventional epoxy resin is examined. Morphology development with the advancement of curing reaction was investigated by hot‐stage polarized optical microscope, where it was found that HBP is miscible in epoxy resin solvent at 120°C and undergoes phase separation during the curing reaction, leading to a two‐phase microstructure which maintains a dispersed morphology up to 20 wt % HBP. The degree of phase separation and morphology were also investigated using differential scanning calorimetry, and the resultant microstructure was confirmed by atomic force microscopy. The epoxy/HBP blends were characterized by positron annihilation lifetime spectroscopy for their free volume characteristics where behavior typical of miscible blends was seen, likely due to chemical bonding between the two phases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

N‐pyrrolidine functionalized C60‐fullerenes/epoxy nanocomposites

AbstractA series of functionalized C60‐fullerene/epoxy nanocomposites were prepared, and their respective ultimate tensile strengths were determined. The functionalization route of the fullerenes was performed using the Prato reaction, with modified amino acids, resulting in the formation of N‐pyrrolidine rings across the [6,6] junctions. Characterization of the functionalized fullerenes was done using Laser Desorption Ionization Time‐of‐Flight (LDI‐TOF) mass spectrometry. The mechanical properties of the nanocomposites were affected by the type of modified amino acid, the degree of functional group attachment, and the consequent degree of dispersion into the epoxy matrix. A specially blended diglycidyl ether of bisphenol A (DGEBA) epoxy, having a low viscosity and high strain‐to‐failure was prepared by adding 1,4‐butanediol diglycidyl ether to DGEBA. The lower viscosity blended epoxy allowed for easier mixing of the fullerenes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Thermophysical properties of CTBN and HTPB liquid rubber modified epoxy blends

AbstractThermal conductivity and diffusivity of carboxyl‐terminated copolymer of polybutadiene and acrylonitrile (CTBN) and hydroxyl‐terminated polybutadiene (HTPB) liquid rubber‐ modified epoxy blends were investigated. A good agreement was observed between the calculated values of the specific heat estimated from thermal conductivity, diffusivity, and density measurements and the DSC results. Measurements of the thermal conductivity values of HTPB/Epoxy blends were in good agreement with three simple theoretical models, which have been used thereafter for the estimation of the unknown value of the thermal conductivity of CTBN (kCTBN = 0.24 Wm−1K−1). The morphology of the rubber‐modified epoxy blends has been quantified and indicate a tendency towards co‐continuous phase upon the inclusion of higher weight percentage of rubber (≥30 wt %). Moreover, we notice a significant enhancement of the thermal conductivity during this morphological shift. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Rheology of SiO2/(acrylic polymer/epoxy) suspensions. I. Linear viscoelasticity

Linear viscoelastic properties of SiO2/(AP/EP) suspension with various SiO2 volume fractions (ϕ) in a blend of acrylic polymer (AP) and epoxy (EP) were investigated at various temperatures (T). The AP/EP contained 70 vol.% of EP. The SiO2 particles were treated with epoxy silane coupling agent. The effects of the SiO2 particles are more pronounced in the terminal zone: a transition from viscoelastic liquid (ϕ ≤ 30 vol.%) to viscoelastic solid (ϕ ≥ 40 vol.%) was observed which can be interpreted as a critical gelation occurring at a critical particle content and critical gel temperature. The SiO2/(AP/EP) systems exhibited a critical gel behavior at ϕ ≅ 35 vol.% and T ≅ 100°C characterized with a power–law relationship between the storage and loss moduli (G ′ and G ″) and frequency (ω); G ′ = G ″/tan(nπ/2) ∝ ω n . The critical gel exponent (n) was estimated to be about 0.45. The gelation occurred with increasing T.

Thermal and mechanical properties of a dendritic hydroxyl‐functional hyperbranched polymer and tetrafunctional epoxy resin blends

AbstractBlends of a tetrafunctional epoxy resin, tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM), and a hydroxyl‐functionalized hyperbranched polymer (HBP), aliphatic hyperbranched polyester Boltorn H40, were prepared using 3,3′‐diaminodiphenyl sulfone (DDS) as curing agent. The phase behavior and morphology of the DDS‐cured epoxy/HBP blends with HBP content up to 30 phr were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The phase behavior and morphology of the DDS‐cured epoxy/HBP blends were observed to be dependent on the blend composition. Blends with HBP content from 10 to 30 phr, show a particulate morphology where discrete HBP‐rich particles are dispersed in the continuous cured epoxy‐rich matrix. The cured blends with 15 and 20 phr exhibit a bimodal particle size distribution whereas the cured blend with 30 phr HBP demonstrates a monomodal particle size distribution. Mechanical measurements show that at a concentration range of 0–30 phr addition, the HBP is able to almost double the fracture toughness of the unmodified TGDDM epoxy resin. FTIR displays the formation of hydrogen bonding between the epoxy network and the HBP modifier. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 417–424, 2010

Compatibility and biodegradability studies of linseed oil epoxy and PVC blends

Abstract With the aim to utilize linseed oil epoxy – a product from sustainable resource for the processing of hard polymers, blends of linseed oil epoxy (LOE) with polyvinylchloride (PVC) were prepared for the first time by solution blending of the requisite amounts of the two components in the weight ratios LOE/PVC- 85/15, 65/35, 55/45, 45/55, 35/65, and 15/85 through solution method by mixing in tetrahydrofuran (THF). The miscibility of the two components in solution phase was investigated by relative viscosity, reduced viscosity and density measurements. The blend with 85 wt% of LOE yielded stiff and flexible films with maximum stress of 33 MPa and 216% elongation at break. Biodegradability of these blends has been studied by soil burial test, enzymatic degradation, and hydrolytic degradation in phosphate buffer. The blend LOE/PVC 85/15 showed the highest biodegradation of 68 wt% in 6 months in the soil burial test. The degradability was found to increase with the increase in LOE content in the blend compositions. The potential applications for such sustainable resource based blend films include packaging materials and biodegradable plastic sheets which can be formed into products such as bio-bags.

Cold crystallization and multiple melting behavior of poly(l-lactide) in homogeneous and in multiphasic epoxy blends

Cold crystallization and melting of poly(l-lactide) (PLLA) blended with an uncured or with an amino-cured epoxy resin (diglycidyl ether of bisphenol-A [DGEBA]) were investigated. It was found that the uncured PLLA/DGEBA blends were miscible, as they exhibited a single composition-dependent glass transition temperature (T g). Melting point depression measurements indicated the existence of some type of interaction between the blend components, which was confirmed by Fourier transform infrared spectroscopy. Depending on the crystallization conditions and on the blend composition, a mixture of α and α′ crystals have been detected in PLLA and in uncured DGEBA/PLLA blends when crystallized from the glassy state. At high DGEBA contents, preferably imperfect α crystals are formed. On the contrary, at low DGEBA contents, the α′ form predominates and an exotherm associated to the α′–α transformation appears on the differential scanning calorimetry (DSC) scan before the main melting peak. Upon curing, the system transforms from a homogeneous mixture with a single refractive index into an opaque multiphasic one, as revealed by the existence of two T gs in the DSC scans. These cross-linked immiscible blends displayed a single crystallization exotherm which scarcely changed with composition, and PLLA cold crystallized mainly into the α′ form from an almost pure PLLA phase; subsequently, the α′ crystals transform into the α form just before melting during the DSC scan.

Predicting the thermomechanical properties of an epoxy resin blend as a function of temperature and strain rate

Group Interaction Modelling is used to predict the properties of a popular aerospace epoxy resin matrix. The thermomechanical and engineering properties of a blend of multifunctional epoxy resins cured with a typical amine hardener are predicted. The properties are predicted as a function of temperature, strain rate and blend ratio and compare very well to experimental values. The properties are rationalised in terms of the chemical and physical nature of the highly crosslinked 3D network nature of the cured polymer.

Effect of polypyrrole–montmorillonite nanocomposites powder addition on corrosion performance of epoxy coatings on Al 5000

The synthesis of hybrid polypyrrole–montmorillonite (Ppy–MMT) nanocomposites and their effects on the improvement of the protection efficiency of the epoxy coatings on aluminum corrosion were studied. In order to understand the effect of MMT and Ppy on the corrosion inhibition performance of the epoxy coatings in 3.5% NaCl solution, the epoxy (E), epoxy blend with MMT (EM) and polypyrrole (EP) coatings were investigated by electrochemical impedance spectroscopy (EIS). It was shown that EM and EP systems could not provide a good corrosion protection for long-time applications. The results showed that the incorporation of Ppy–MMT nanocomposites inside the epoxy notably increases the resistance of the coating in comparison to the other coatings for long-time period. These phenomena can be attributed to specific morphology of the nanocomposite. The structure and morphology of nanocomposites were studied by FT-IR and XRD techniques, as well as, scanning electron microscopy (SEM).

TTT Diagram Used to Control Phase Structure of 2/4 Functional Epoxy Blends for Advanced Composites

This article uses a 2/4 functional epoxy blend system (E-54/AG-80) cured with diaminodiphenyl sulphone(DDS) as a raw material and develops a methodological procedure to establish a cure kinetic model with isothermal and dynamic differential scanning calorimeter(DSC) method and a gelation model with round-disk compression mode dynamic mechanical analyzer(DMA), thus acquiring a series of experimental data. Characteristic temperatures such as initial glass transition temperature Tg0, gelation glass transition temperature gelTg, and infinite glass transition temperature Tg∞ are determined. The cure degree at gelation is turned out to be 0.45, while gelTg is found to be 70.2 °C. The data are then used to form time-temperature-transition(TTT) diagram of the system, which serves to be a tool for process optimization of epoxy-matrix composites. A new cure processing is therefore derived from the TTT diagram. The final phase structure obtained from a controllable method is identified through scanning electron microscope(SEM) photographs to be of ‘ex-situ’ phase morphology.