Dan Rosu

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.

FTIR and color change of the modified wood as a result of artificial light irradiation

The effect of UV-visible light irradiation on the changes in color and chemical composition of the surfaces of Abies alba L. (fir, a softwood), non-modified and chemically modified, was studied. Chemical modification of the wood was performed by reaction with succinic anhydride in xylene at different concentration values. The wood samples were irradiated in air using a rotative device equipped with a middle pressure mercury lamp. Analysis of the color changes in wood surfaces during photo-degradation was carried out by measuring CIELAB parameters. Fourier transform infrared spectroscopy was used to study chemical changes caused by light irradiation. Irradiation modified physical and chemical characteristics of wood surfaces and resulted in rapid color changes, degradation of lignin and increased content of chromophoric groups on the wood surfaces. Color changes (DeltaE(ab)) correlate well with degradation of lignin.

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.

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.

Synthesis and characterization of some epoxy resins bearing azomethine groups

Abstract New epoxy resins bearing azomethine groups were synthesized by the reaction between the diglycidyl ether of bisphenol-A (DGEBA) and some aromatic azomethines, in the presence of n-butylamine as catalyst. The azomethines were obtained through the condensation reaction of aromatic diamines with 2-hydroxybenzaldehyde. The epoxides synthesized at 100 °C were characterized by i.r., u.v. and 1H-NMR spectral techniques, as well as by DSC and TG thermoanalytical methods. Some other properties of the resins are presented, such as epoxy equivalent, melting points and nitrogen content. The epoxy resins containing azomethine groups show an apparent higher thermal stability than that of crude DGEBA epoxy resin, and some of them show a pronounced tendency towards crystallization.

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.

Studies on Diels–Alder thermoresponsive networks based on ether–urethane bismaleimide functionalized poly(vinyl alcohol)

Thermoreversible networks obtained by the Diels–Alder cycloaddition reaction of poly(vinyl furfural) with urethane bismaleimides containing polyether chain were synthesized. The formation of the networks was confirmed by attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy (ATR–FTIR). The materials thermal properties were investigated using differential scanning calorimetry (DSC) and a coupling of dynamic thermogravimetry with Fourier transform infrared spectroscopy and mass spectrometry (TG–FTIR–MS) for pyrolysis behaviour under nitrogen atmosphere. A thermal decomposition mechanism of the networks and poly(vinyl furfural) was discussed via evolved gas analysis. The thermoreversibility of the networks was demonstrated by the presence of the endothermic peak characteristic to the retrodienic process on the DSC heating curves and also the appearance of the exothermic peak, due to the dienic process, on the DSC cooling curve. The dynamic contact angle and free surface energy values of the networks were determined. Measures of the heterogeneity and roughness of the surfaces suggested that the surfaces of the networks’ films are more homogenous than the initial poly(vinyl furfural) surface. Dynamic water vapour sorption studies were conducted.

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.