Constantin N. Cascaval

Cure kinetics of epoxy resins studied by non-isothermal DSC data

Abstract The curing kinetics of diglycidyl ether of bisphenol A (DGEBA) and diglycidyl ether of hydroquinone (DGEHQ) epoxy resins in presence of diglycidyl aniline as a reactive diluent and triethylenetetramine (TETA) as the curing agent was studied by non-isothermal differential scanning calorimetry (DSC) technique at different heating rates. The kinetic parameters of the curing process were determined by isoconversional method given by Malek for the kinetic analysis of the data obtained by the thermal treatment. A two-parameter (m, n) autocatalytic model (Sestak–Berggren equation) was found to be the most adequate selected to describe the cure kinetics of the studied epoxy resins. Reactive diluent decreases both the activation energy and the cure kinetic parameters. Non-isothermal DSC curves obtained using the experimental data show a good agreement with that theoretically calculated.

Cure kinetics of a liquid-crystalline epoxy resin studied by non-isothermal data

Abstract The curing kinetics of diglycidyl ether of 4,4′-bisphenol (DGEBP) epoxy mesogenic resin in the presence of sulphanilamide (SAA) was studied by non-isothermal differential scanning calorimetry (DSC) at different heating rates. At low heating rates (2–5 °C min −1 ), the curing reaction takes place by two processes evidenced by the presence of a double peak on the DSC thermograms. The first process is due to the reaction of primary amine with epoxy, while the second one corresponds to the formation of the crosslinked network with liquid crystalline (LC) properties by the attack of the secondary amine previously formed onto the epoxide groups unreacted in the first stage of the reaction. An activation energy ( E a =59 kJ mol −1 ) was evaluated for the second process and an autocatalytic kinetic model (Sestak–Berggren equation) was proposed to better describe the cure kinetics of the studied system. The theoretical DSC curves calculated using the kinetic parameters determined in non-isothermal conditions show good agreement with those experimentally determined.

Thermal degradation of semi-interpenetrating polymer networks based on polyurethane and epoxy maleate of bisphenol A

Abstract Two polyurethane–epoxy maleate of bisphenol A semi-interpenetrating polymer networks were synthesized and their thermal behavior studied. The data obtained by thermogravimetry showed that the decomposition of the tested samples is complex, occurs in three steps, and depends on the degree of crosslinking. The main decomposition takes place between 290 and 480 °C, with weight losses between 62 and 66%. The apparent thermal stability of the sample synthesized with a low content of epoxy maleate of bisphenol-A (11.11 wt%) is lower compared with polyurethane, while the sample with high content of epoxy maleate of bisphenol-A (27.3 wt%) shows a higher stability.

Liquid Crystalline Epoxy Thermoset Obtained from Biphenyl Mesogen

Abstract: A liquid crystalline epoxy polymer based on an epoxy monomer with biphenyl type mesogenic compound was synthesized and characterized using differential scanning calorimetry, optical microscopy, and X-ray diffraction. The monomer without liquid crystalline properties was transformed into a liquid crystalline state by a curing reaction with 2,7-diaminofluorene. A smectic-like structure developed in time, in the temperature range between 132 and 162°C.

Polyhydroxyacrylate–polyurethane semi-interpenetrating polymer networks

Abstract A series of semi-interpenetrating polymer networks based on a polyhydroxyacrylate of Bisphenol A and a polyurethane was synthesized by the simultaneous polymerization technique. The polyhydroxyacrylate resin was cross-linked in the presence of dicumyl peroxide at 130°C, including in its network structure the linear polyurethane. The synthesized semi-interpenetrating polymer networks were characterized by infrared spectroscopy, differential scanning calorimetry, density measurements, as well as by thermal and mechanical analyses. It was remarked by a high degree of miscibility within the studied systems, and an improvement of the mechanical properties of polyurethane by incorporation of polyhydroxyacrylate resin.

POLYURETHANE-EPOXY MALEATE OF BISPHENOL A BLENDS

Blends of polyurethane with epoxy maleate of Bisphenol A were synthesized and their miscibility, the physico-mechanical properties, as well as the thermal behavior were studied. Differential scanning calorimetry (DSC) measurements showed a single composition-dependent glass transition temperature (Tg), and is evidence for a good miscibility of the studied systems. The variation of Tgs of the blends versus composition (Fox, Gordon-Taylor, and Schneider equations) showed the presence of some physical interactions between polyurethane and epoxy maleate polymers. Generally, the physico-mechanical properties of the blends are lower as than those of polyurethane. This suggests that epoxy maleate of Bisphenol A operates in a mixture with polyurethane only as a plasticizer. The thermal behavior of the studied blends showed no large differences to that of polyurethane.

Thermal degradation of some crosslinked acrylic copolymers functionalized as ion exchangers

Thermal degradation of some acrylic crosslinked copolymers based on divinyl benzene, ethyl acrylate and acrylonitrile as such, or functionalized with various amines was examined by thermogravimetry in the range of temperatures between 40 and 600°C. The original copolymers decompose in two stages, and the functionalized copolymers in three stages. In both cases the main decomposition is between 250 and 450°C. The decomposition of the crosslinked copolymers depends on the nature of copolymer, the amount of divinyl benzene used as the crosslinked agent and on the extent of conversion. The decomposition proper of the functionalized copolymers depends on the nature of both the copolymer and of the amine used in the aminolysis.

Synthesis and Characterization of Epoxy-Acrylic Polymer on the Basis of 2-Hydroxy-3-para-nonylphenoxy-propyl Acrylate

Abstract Poly(2-hydroxy-3-para-nonylphenoxy-propylacrylate) polymer was synthesized in solution and in bulk by radical polymerization of 2-hydroxy-3-para-nonylphenoxy-propylacrylate monomer. The polymer obtained in solution is soluble in various organic solvents. It was characterized by IR and 1H-NMR spectroscopy, cryoscopy, and viscometric behavior. The polymer synthesized in bulk is insoluble. It was characterized by IR spectroscopy and by solubility parameter. The number-average molecular weight of the soluble polymer is around 3100 and the intrinsic viscosity measured in cyclohexane at 25°C ± 0.05 is 2.8 × 10−2 dL/g. The polymer has a non-Newtonian Theological behavior of pronounced pseudoplastic type. The insoluble polymer has the solubility parameter 9.2 (cal/mL)1/2.

Synthesis and characterization of some Para-nonylphenol formaldehyde resins

Para-nonylphenol formaldehyde resins with molecular weights ranging within 490 and 1400 were synthesized in acidic catalysis. The resins were characterized by spectral methods (i.r. and 1H-NMR spectroscopy) and as rheological behavior. The i.r. spectra put in evidence the bands characteristic to —OH phenolic group, respective to —CH2 and —CH3 groups placed in the nonyl radical, and the bands for substituents in positions of the aromatic ring as follows: 1.2, 1.4 and 1.2.4, respectively. With the aid of 1H-NMR spectroscopy there have been calculated some structural parameters, such as: formaldehyde/para-nonylphenol molar ratio and the number of aromatic protons per phenolic units. The variation of the apparent shear viscosity vs the shear rate showed that para-nonylphenol formaldehyde resins have a non-Newtonian rhelogical behaviour of pseudoplastic type.

Rheological testing of p-tert-butylphenol epoxy-acrylic resin in the presence of reactive diluents

Abstract The rheological testing of synthesized para-tert-butylphenol epoxy–acrylic resin in the presence of reactive diluents based on epoxy–acrylic compounds of phenol, para-tert-butylphenol and para-nonylphenol was carried out with a “Rheotest 2” type viscometer. The synthesized resin, the tested reactive diluents, as well as the mixtures based on the resin and the reactive diluents, show non-Newtonian rheological behaviour of the pseudoplastic type. This behaviour can be explained by taking into consideration the possible interactions among the chains of the phenolic reactive diluents, and with the chain of the resin. These interactions can also be due to –OH phenolic groups. As a result, a false increase is registered in the molecular weight of the systems studied.