Preparation, thermal properties and flame retardancy of phosphorus- and silicon-containing epoxy resins

Phosphorus- and silicon-containing epoxy resins were prepared from (2,5-dihydroxyphenyl)diphenyl phosphine oxide (Gly-HPO), diglycidyloxy methylphenyl silane (DGMPS) and 1,4-bis(glycidyloxydimethyl silyl)-benzene (BGDMSB) as epoxy monomers and diaminodiphenylmethane (DDM), bis(3-aminophenyl)methyl phosphine oxide (BAMPO) and bis(4-aminophenoxy)dimethyl silane (APDS) as curing agents. Epoxy resins with different phosphorus and silicon content were obtained. Their thermal, dynamic mechanical and flame retardant properties were evaluated. The high LOI values confirmed that epoxy resins containing hetero-atoms are effective flame retardants, but a synergistic efficiency of phosphorus and silicon on flame retardation was not observed.     

Network structure and glass transition of epoxy resins cured with active ester

The effect of network structure on the glass transition temperature (T _g) was examined by differential scanning calorimetry, thermomechanical analysis and dynamic thermomechanometry for epoxy resins cured with mixtures of curing agents consisting of an active ester, 1,3,5-triacetoxybenzene (TAB), and a polyfunctional phenol, 1,3,5-trihydroxybenzene (THB). Free hydroxyl groups are formed from THB after curing, whereas acetyl groups are left from TAB. TheT _g value of cured epoxy resins decreased with increasing TAB content in the curing agent, which is attributed to the looser network structure induced by the steric hindrance of acetyl groups from TAB in the curing reaction and also to the weaker intermolecular interaction and the internal plasticization of acetyl groups from TAB.     

Kinetics and thermal properties of epoxy resins based on bisphenol fluorene structure

The fluorene-containing epoxy, diglycidyl ether of 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) was synthesized by a two-step reaction procedure. In order to investigate the relationship between fluorene structure and material properties, DGEBF and a commonly used diglycidyl ether of bisphenol A (DGEBA) were cured with 4,4-diaminodiphenyl methane (DDM) and 4,4-(9-fluorenylidene)-dianiline (FDA). The curing kinetics, thermal properties and decomposition kinetics of these four systems (DGEBA/DDM, DGEBF/DDM, DGEBA/FDA, and DGEBF/FDA) were studied in detail. The curing reactivity of fluorene epoxy resins was lower, but the thermal stability was higher than bisphenol A resins. The onset decomposition temperature of cured epoxy resins was not significantly affected by fluorene structure, but the char yield and T_g value were increased with that of fluorene content. Our results indicated that the addition of fluorene structure to epoxy resin is an effective method to improve the thermal properties of resins, but excess fluorene ring in the chain backbone can depress the curing efficiency of the resin.     

Modification of epoxy resin using reactive liquid (ATBN) rubber

Epoxy resins are widely utilised as high performance thermosetting resins for many industrial applications but unfortunately some are characterised by a relatively low toughness. In this respect, many efforts have been made to improve the toughness of cured epoxy resins by the introduction of rigid particles, reactive rubbers, interpenetrating polymer networks and engineering thermoplastics within the matrix.In the present work liquid amine-terminated butadiene acrylonitrile (ATBN) copolymers containing 16% acrylonitrile is added at different contents to improve the toughness of diglycidyl ether of bisphenol A epoxy resin using polyaminoimidazoline as a curing agent. The chemical reactions suspected to take place during the modification of the epoxy resin were monitored and evidenced using a Fourier transform infrared. The glass transition temperature (T_g) was measured using a differential scanning calorimeter. The mechanical behaviour of the modified epoxy resin was evaluated in terms of Izod impact strength (IS), critical stress intensity factor, and tensile properties at different modifier contents. A scanning electron microscope (SEM) was used to elucidate the mechanisms of deformation and toughening in addition to other morphological features. Finally, the adhesive properties of the modified epoxy resin were measured in terms of tensile shear strength (TSS).When modifying epoxy resin with liquid rubber (ATBN), all reactivity characteristics (gel time and temperature, cure time and exotherm peak) decreased. The infrared analysis evidenced the occurrence of a chemical reaction between the two components. Addition of ATBN led to a decrease in either the glass transition temperature and stress at break accompanied with an increase in elongation at break and the appearance of some yielding. As expected, the tensile modulus decreased slightly from 1.85 to about 1.34 GPa with increasing ATBN content; whereas a 3-fold increase in Izod IS was obtained by just adding 12.5 phr ATBN compared to the unfilled resin. It is obvious that upon addition of ATBN, the Izod IS increased drastically from 0.85 to 2.86 kJ/m² and from 4.19 to 14.26 kJ/m² for notched and unnotched specimens respectively while K_IC varies from 0.91 to 1.49 MPa m^1/2 (1.5-fold increase). Concerning the adhesive properties, the TSS increased from 9.14 to 15.96 MPa just by adding 5 phr ATBN. Finally SEM analysis results suggest rubber particles cavitation and localised plastic shear yielding induced by the presence of the dispersed rubber particles within the epoxy matrix as the prevailing toughening mechanism.     

Comparison of thermal curing behavior of liquid and solid urea–formaldehyde resins with different formaldehyde/urea mole ratios

This study was undertaken to compare thermal cure kinetics of urea–formaldehyde (UF) resins, in both liquid and solid forms as a function of formaldehyde/urea (F/U) mole ratio, using multi-heating rate methods of differential scanning calorimetry. The requirement of peak temperature (T _p), heat of reaction (ΔH) and activation energy (E) for the cure of four F/U mole ratio UF resins (1.6, 1.4, 1.2 and 1.0) was investigated. Both types of UF resins showed a single T _p, which ranged from 75 to 118 °C for liquid resins, and from 240 to 275 °C for solid resins. As the F/U mole ratio decreased, T _p values increased for both liquid and solid resins. ΔH values of solid resins were much greater than those of liquid resins, indicating a greater energy requirement for the cure of solid resins. The ΔH value of liquid UF resins increased with decreasing in F/U mole ratio whereas it was opposite for solid resins, with much variation. The activation energy (E _a) values calculated by Kissinger method were greater for solid UF resins than for liquid resins. The activation energy (E _α ) values calculated by isoconversional method which showed that UF resins in liquid or solid state at F/U mole ratio of 1.6 followed a multi-step reaction in their cure kinetics. These results demonstrated that thermal curing behavior of solid UF resin differed greatly from that of liquid resins, because of a greater branched network structure in the former.     

Benzoxazine modified diglycidyl ether of bisphenol-a/silicon/siliconized epoxy hybrid polymer matrices: Mechanical,thermal, electrical and morphological properties

Benzoxazines modified epoxy hybrid polymer matrices were developed using benzoxazines (CB_DDM and BMPB_DDM) and epoxy resins (DGEBA, SE and EP-HTPDMS) to make them suitable for high performance applications. The benzoxazine-epoxy hybrid polymer matrices were prepared via in-situ polymerization and were investigated for their thermal, thermo-mechanical, mechanical, electrical and morphological properties. Two types of skeletal modified benzoxazines namely 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane benzoxazine (CB_DDM) and bis(4-maleimidophenyl) benzoxazine (BMPB_DDM) were synthesized by reacting paraformaldehyde and 4,4′-diaminodiphenylmethane with 1,1-bis (3-methyl-4-hydroxyphenyl)cyclohexane and N-(4-hydroxyphenyl)maleimide respectively. Epoxy resins viz., diglycidyl ether of bisphenol-A (DGEBA), silicon incorporated epoxy (SE) and siliconized epoxy resin (EP-HTPDMS) were modified with 5, 10 and 15 wt% of benzoxazines using 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. The chemical reaction of benzoxazines with the epoxy resin was carried out thermally and the resulting product was analyzed by FT-IR spectra. The glass transition temperature, curing behavior, thermal stability, char yield and flame resistance of the hybrid polymers were analysed by means of DSC, TGA and DMA. Mechanical properties were studied as per ASTM standards. The benzoxazines modified epoxy resin systems exhibited lower values of dielectric constant and dielectric loss with an enhanced values of of arc resistance, glass transition temperatures, degradation temperatures, thermal stability, char yield, storage modulus, tensile strength, flexural strength and impact strength.     

Preparation and shape memory behavior of novel heat-resistance epoxy networks containing phthalide cardo structure

Heat-resistance epoxy shape memory (SM) materials were prepared based on diglycidylether of bisphenol A (DGEBA) epoxy resin with the mixture of 4,4′-diaminodiphenylether (DDM) and phthalide-containing aromatic amine (PBMI-DDM), which was synthesized by Michael addition of 3,3-bis[4-(4-maleimido phenoxy)phenyl] -phthalide (PBMI) and DDM, in different molar ratios as curing agents. The chemical structure of PBMI-DDM was confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra. The dynamical mechanical behavior and high-temperature tensile properties, and the influence of PBMI-DDM content and number of cycles on SM performance were investigated in detail. With increasing PBMI-DDM content, the glass transition temperatures (T_g) decreased, damping loss factors increased, and shape recovery ratio (R_r) and shape fixity ratio (R_f) were improved significantly. R_r and R_f of the pure PBMI-DDM cured epoxy resins are both lager than 90% with a deformation strain above 15%. The T_g and activation energies (△E) of α-relaxation for the epoxy system with unstable SM performance are constantly increased with SM cycles due to the adjustment and rearrangement of network chains.     

Synthesis,Characterization, Curing and Shape Memory Properties of Epoxy‐Polyether System

Epoxy resins were cured by an amine telechelic poly(tetramethylene oxide) (PTMO). The telechelic amine was synthesized from hydroxy telechelic PTMO and was characterized. The kinetics of curing of epoxy monomer by the polyether amine was studied in detail by differential scanning calorimetry (DSC) and rheology to optimize the cure conditions. The cured epoxy system exhibited shape memory properties where PTMO served as the switching segment. Molar ratios of the epoxy monomer and the amine were varied to get polymers with different compositions. The developed polymers were analyzed by DSC, X‐ray diffraction, and Dynamic Mechanical Thermal (DMTA) analyses. Shape memory property was evaluated by bending tests. As the concentration of epoxy resin increased, the transition temperature (T_trans) increased. The tensile strength and % elongation also increased with epoxy resin‐content. The extent of shape recovery increased with PTMO‐content with a minor penalty in recovery time. The polymer with the maximum PTMO‐content exhibited 99% shape recovery with a recovering time of 12 s.     

Synthesis and effect of hyperbranched (3-hydroxyphenyl) phosphate as a curing agent on the thermal and combustion behaviours of novolac epoxy resin

A novel type of hyperbranched (3-hydroxyphenyl) phosphate (HHPP) with high functionality as a curing agent of epoxy resins was synthesized and characterized by FTIR, ¹H NMR and vapor phase osmometry (VPO). The cured epoxy resin with HHPP possessed improved glass transition temperature. The thermostability and flame retardancy of O-cresol novolac epoxy resin cured with different contents of HHPP were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI) and cone calorimetry. The obtained results show that the samples containing a higher percentage of HHPP exhibit relatively lower thermostability at lower temperature while higher thermostability at elevated temperature and more char was formed compared with those containing a lower percentage of HHPP. The LOI value increased from 22.0 to 30.0 when HHPP, instead of 1,3-dihydroxybenzene, was used as a curing agent. The 25 wt% addition of HHPP in the curing agent complex effectively decreased the heat release rate and improved the char yield to the content nearly similar as those of the epoxy resin cured with pure HHPP.     

Synthesis and thermal properties of epoxy resins from ester-carboxylic acid derivative of alcoholysis lignin

Alcoholysis lignin (AL) was dissolved in ethylene glycol and the obtained mixture was reacted with succinic anhydride to form a mixture of ester-carboxylic acid derivatives (AL-polyacid, ALPA). Ethylene glycol-polyacid (EGPA) was also prepared from ethylene glycol. The obtained mixture of ester carboxylic acid derivatives was treated with ethylene glycol diglycidyl ether in the presence of catalytic amount of dimethylbenzylamine to form ester-epoxy resins. The curing reaction was analyzed by Ozawa's method using differential scanning calorimetry. The activation energy of curing reaction in the initial step was found to be ca. 84 kJ mol⁻¹. The molar ratios of epoxy groups to carboxylic acid groups ([EPOXY]/[AA] ratios) were varied from 0.8 to 1.3. The contents of ALPA in the mixture of ALPA and EGPA were also varied from 0 to 100%. Thermal properties of epoxy resins were studied by DSC and thermogravimetry. Glass transition temperatures of epoxy resins showed a maximum value of −11.5 °C when [EPOXY]/[AA] ratio was 1.1. T_g increased with increasing ALPA contents suggesting that lignin acts as a hard segment in epoxy resin networks. Thermal degradation temperatures of epoxy resins slightly decreased with increasing ALPA contents.     

Preparation and Properties of Epoxy Resins Containing Quinazolone Rings

Epoxy resins containing quinazolone rings were synthesized and characterized. Epoxy resins were made by reacting bisquinazolone phenol or bisquinazoline with epichlorohydrin or the diglycidyl ether of Bisphenol A. These resins were analyzed by DSC, GPC, IR, and NMR. The electrical and mechanical properties of the cured resins were evaluated. They have glass transition temperature above 200°C and excellent thermal stability, and T_g increases in the order of o-, m-, p-substituted phenol groups.     

Multifunctionality in Epoxy Resins

Abstract

Epoxy resin will continue to be in the forefront of many thermoset applications due to its versatile properties. However, with advancement in manufacturing, changing societal outlook for the chemical industries and emerging technologies that disrupt conventional approaches to thermoset fabrication, there is a need for a multifunctional epoxy resin that is able to adapt to newer and robust requirements. Epoxy resins that behave both like a thermoplastic and a thermoset resin with better properties are now the norm in research and development. In this paper, we viewed multifunctionality in epoxy resins in terms of other desirable properties such as its toughness and flexibility, rapid curing potential, self-healing ability, reprocessability and recyclability, high temperature stability and conductivity, which other authors failed to recognize. These aspects, when considered in the synthesis and formulation of epoxy resins will be a radical advance for thermosetting polymers, with a lot of applications. Therefore, we present an overview of the recent finding as to pave the way for varied approaches towards multifunctional epoxy resins.     

Effect of vinyltriethoxysilane addition on the pyrolytic conversion of tetraethoxysilane based silica gel

The effect of vinyltriethoxysilane (VTES) addition on the pyrolytic conversion of tetraethoxysilane (TEOS) based silica gel had been studied. Thermogravimetric analysis coupled with mass spectroscopy was carried out to study the thermal decomposition behavior of precursor gels. The ceramic yield of precursor gels was decreased with the increase of the VTES content. ²⁹Si magic angle spinning nuclear magnetic resonance indicated that the incorporation of VTES into TEOS not only changed the composition and structure of precursor gels, but also increased carbon-enriched SiO _x C_4?x units of silicon oxycarbide ceramics during the pyrolysis conversion. The carbon content of SiOC ceramic was almost unchanged between 1,000 and 1,500 °C. However, the O/Si ratio of the silicon oxycarbide ceramic was reduced and the free carbon content was increased with the increasing molar ratios of VTES/TEOS. Moreover, the carbothermal reduction reaction led to the free carbon content decreased with the increase of the sintering temperature.     

Micro phase separated epoxy/poly(ε-caprolactone)-block-poly(dimethyl siloxane)-block-poly(ε-caprolactone)/4,4′-diaminodiphenylsulfone systems: Morphology,viscoelasticity, thermo-mechanical properties and surface hydrophobicity

Epoxy resin/4,4′-diaminodiphenylsulfone (DDS) system was modified by the incorporation of poly(ε-caprolactone)-block-poly(dimethyl siloxane)-block-poly(ε-caprolactone) (PCL–PDMS–PCL) triblock copolymer (TBCP). Morphology, viscoelasticity, thermo-mechanical and surface properties of these blends were investigated. All the blends were opaque after curing. PCL blocks of the TBCP were miscible with epoxy resin while the PDMS fraction was immiscible. However in the cured state, both PCL and PDMS blocks were phase separated from epoxy/DDS matrix. The blends exhibited matrix-droplet morphology in which TBCP phase dispersed as spherical domains in epoxy matrix. Addition of TBCP had profound impact on the cure reaction kinetics. Storage modulus and glass transition temperature (T_g) decreased while impact strength significantly increased. Incorporation of 15 phr of TBCP resulted in 80% improvement in impact strength. Further, thermal stability was unaffected while surface hydrophobicity of the blends increased.     

Mechanical and Thermal Properties and Morphology of Epoxy Resins Modified by a Silicon Compound

A silicon compound (GAPSO) was synthesized to modify the diglycidyl ether of bisphenol-A (DGEBA). The chemical structure of GAPSO was confirmed using FT-IR, ²⁹Si NMR and GPC. The mechanical and thermal properties and morphologies of the cured epoxy resins were investigated by impact testing, tensile testing, differential scanning calorimetry and environmental scanning electron microscopy. The impact strength and tensile strength were both increased by introducing GAPSO, meanwhile the glass transition temperature (T_g ) was not decreased and the morphologies of the fracture surfaces show that the compatibility of GAPSO with epoxy resin was very good and the toughening follows the pinning and crack tip bifurcation mechanism. The high functional groups in GAPSO can react during the curing process, and chemically participate in the crosslinking network. GAPSO is thus expected to improve the toughness of epoxy resin, meanwhile maintain the glass transition temperature.     

Characterization of alkyd based thermosetting resins

The rate of cure of different oxidative drying oil modified alkyd resins are investigated by DSC, when the cure is made under UV light or not. We determine, from the Kissinger equation, the apparent activation energy at different stages of the curing process. This activation energy depends on the curing conditions (temperature, illumination or not). These variations lead to the determination of a time constant, characteristic of the curing kinetics. Two particular values of the apparent activation energy are also defined. The first one called ΔE _o is a characteristic of the varnish at the liquid state, the second one called ΔE _inf characterizes the stability of the structural state of the final film.     

Characterization in the Toughening Process of CTBN Modified Epoxy Resins Induced by Electron Beam Radiation

Epoxy resins are widely utilized as high performance thermosetting resins for many industrial applications but characterized by a relatively low toughness. Electron beam (EB) curing of polymer resins has a number of advantages over conventional thermal curing, such as shorter curing time, low energy consumption, low cure temperature, dimensional stability, reduced manufacturing cost. In the present work liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymers containing 8% acrylonitrile is added at different contents to improve the toughness of diglycidyl ether of bisphenol A (DGEBA) epoxy resins using triarylsulfonium hexafluoroanimonate as a photointiator. The EB irradiation was conducted 5 kGy to 250 kGy in nitrogen. The physics properties of CTBN modified epoxy resins were examined by determine gel content, DMA (dynamic mechanical analysis), UTM (Instron model 4443), SEM (scanning electron microscopy).     

The influence of silicon-containing acrylate as active diluent on the properties of UV-cured epoxydiacrylate films

A new silicon-containing acrylate, which can be a good active diluent for UV-curable epoxydiacrylate systems, was prepared by reacting N-cyclohexyl-γ-aminopropylmethyldimethoxysilane (CAMS) with trimethylolpropane triacrylate (TMPTA) by Michael-type addition reaction. The reactivity of -NH groups of CAMS with the acrylic groups of TMPTA was characterized by FTIR. The contents of the new active diluent in the UV-cured polymeric films were varied between 5% and 15% by weight. Mechanical, physical, and thermal characterizations of the UV-cured films were investigated: An increase in silicon-containing acrylate content caused a dramatic change of the surface properties of the films, and a decrease in mechanical properties besides the relative elongation. Thermogravimetric analysis of silicon-containing acrylate revealed that incorporating silicon into the structure resulted in a high char yield at 700 °C. Water absorption values of UV-cured films were also affected by the amount of silicon-containing acrylate.     

Influence of cellulose nanofibers on the curing behavior of epoxy/amine systems

Epoxy composites were prepared using diglycidyl ether bisphenol F and water-dilutable diglycidyl ether bisphenol A with curing agents, polyoxypropylenediamine and diethylmethylbenzenediamine, in water or dimethylformamide as a solvent. The influence of cellulose nanofibers and solvents on curing kinetics of epoxy composites was investigated. Curing kinetic parameters were calculated using the model-fitting methods and the isoconversional method. Among these, the Sestak–Berggren equation best fit the experimental data. Results indicated that dimethylformamide decreased the reaction rate, whereas water revealed the opposite pattern. Cellulose nanofibers catalyzed the reaction between bisphenol F resins and the aromatic curing agent.     

Acid–base Properties of Ion-exchange Resins. Dissociation and Swelling of Resin Copolymers of Methacrylic Acid,Methyl Methacrylate,Divinylbenzene, and Ethylvinylbenzene

The dissociation, capacity, swelling, and water content of crosslinked methacrylic acid—methyl methacrylate resins have been measured. Resins were prepared with different degrees of crosslinking for the same carboxylate content, and vice versa. The ionic strength of the external solution was also varied, and the behavior of commercial resins compared with that of the laboratory resins. Potentiometric titration curves were obtained, and curves were also obtained by back-titration of the salt form of the resins with acid. The capacities showed that almost all carboxyl groups are accessible in resins containing 2.5% or 4.0% divinylbenzene, but not in those containing 8% or 12%. For these highly crosslinked resins the back-titration curves differed from the forward curves. Apparent dissociation constants pK′_a = pH + n log [(1 ? α)/α] decreased with increased ionic strength, increased with increased crosslinking, and showed no trend with carboxylate content. Swelling is decreased by increased salt concentration, particularly for lightly crosslinked resins. Maximum swelling is achieved at about 80% dissociation. The reciprocal of the swollen volume is proportional to the per cent of divinylbenzene. Commercial resins showed much lower swelling than laboratory prepared resins ostensibly having the same composition. The Gibbs-Donnan theory of resin dissociation was applied to calculate the intrinsic dissociation constant (pK′₀). Assuming a model of randomly kinked chains dissolved in the sorbed solution, good agreement with the expected value of 4.85 was found (calcd. pK′₀ = 4.81 = 0.14), except for the most highly crosslinked resins. For polyampholyte resins, agreement was found by using a model having a uniform potential distribution throughout the resin (pK′₀ = 4.9).