Tak Jin Moon

Curing reaction of biphenyl epoxy resin with different phenolic functional hardeners

The investigation of cure kinetics and relationships between glass transition temperature and conversion of biphenyl epoxy resin (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl) with different phenolic hardeners was performed by differential scanning calorimeter using an isothermal approach over the temperature range 120–150°C. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of formulations using xylok and dicyclopentadiene type phenolic resins (DCPDP) as hardeners proceeds through a first-order kinetic mechanism, whereas the curing reaction of formulations using phenol novolac as a hardener goes through an autocatalytic kinetic mechanism. The differences of curing reaction with the change of hardener in biphenyl epoxy resin systems were explained with the relationships between Tg and reaction conversion using the DiBenedetto equation. A detailed cure mechanism in biphenyl-type epoxy resin with the different hardeners has been suggested.

Cure Kinetics of Biphenyl Epoxy-Phenol Novolac Resin System Using Triphenylphosphine as Catalyst

The effects of the concentration of triphenylphosphine as a catalyst on the cure reaction of the biphenyl epoxy/phenol novolac resin system were studied. The kinetic study was carried out by means of the analysis of isothermal experiments using a differential scanning calorimeter. All kinetic parameters including the reaction or- ders, activation energy and kinetic rate constants were evaluated. To describe the cure reaction with the catalyst concentration, the normalized kinetic model was developed. The suggested kinetic model with a diffusion term was successfully able to describe and predict the cure reaction of epoxy resin compositions as functions of the catalyst content and temperature.

Kinetic study of the effect of catalysts on the curing of biphenyl epoxy resin

The investigation of cure kinetics of biphenyl epoxy (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl)dicyclopentadiene type phenolic resin system with different kinds of catalysts was performed by a differential scanning calorimeter using an isothermal approach. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of the formulations using triphenylphosphine (TPP), 1-benzyl-2-methylimidazole (1B2MI), and tris(4-methoxyphenyl)phosphine (TPAP) as a catalyst proceeds through an nth-order kinetic mechanism, whereas thatof the formulations using diazabicycloundecene (DBU) and tetraphenyl phosphonium tetraphenyl borate (TPP–TPB) proceeds by an autocatalytic kinetic mechanism. To describe the cure reaction in the latter stage, we have used semiempirical relationship proposed by Chern and Poehlein. By combining an nth-order kinetic model or an auto-catalytic model with a diffusion factor, it is possible to predict the cure kinetics of each catalytic system over the whole range of conversion.

Dispersion characteristics of the complex permeability-permittivity of Ni-Zn ferrite-epoxy composites

The effects of volume fraction and particle size of ferrite on the electric and magnetic properties of epoxy composites containing Ni-Zn ferrite were investigated. The composites were prepared by the cement mixed method and shaped as coaxial, toroidal and disc types. The complex permeability and permittivity were measured using an impedance-gain phase analyser (HP4194A) and a network analyser (HP8753C) in the frequency range 1 MHz–5 GHz.The complex permeability of the composites was found to increase as the ferrite content increased, and was characteristic of the frequency dispersion. A model to describe the frequency dispersion characteristics of the composite, which was a function of the ferrite content, is proposed here. The complex permittivity of the composite was found to be dependent mainly on the volume fraction of the ferrite and was relatively independent of frequency and particle size of the ferrite.

Frequency dispersion characteristics of the complex permittivity of the epoxy-carbon black composites

The effects of frequency, volume fraction of carbon black, and porosity on the complex permittivity of the epoxy-carbon black composites were investigated and the frequency dispersion behavior model for the complex permittivity was proposed. In the epoxy-carbon black composites, the frequency dispersion behaviors of the complex permittivity changed from relaxation spectrum to resonance spectrum with increasing the amount of carbon black. The complex permittivity of the composites increased with decreasing the porosity. Comparing the complex permittivity of the composites filled with 2 vol % of carbon black with the values obtained from three types of previously reported model equations, the relaxation behavior coincided with the Havriliak-Negami model. The damping and asymmetrical factor values were increased with increasing porosity in the composites. The empirical equation proposed here was useful in describing the complex permittivity of the composites of >3 vol % carbon black with resonance type. The damping factor (γ) decreased as the filler content increased, but the asymmetrical factor (κ) increased reversely.

Frequency dispersion model of the complex permeability of the epoxy-ferrite composite

The factors that influence the complex permeability of the epoxy—ferrite composite were investigated, and the frequency dispersion behavior model for the complex permeability was proposed. The complex permeability of the composite was measured by an impedance/gain phase analyzer and a network analyzer in the frequency range from 1 MHz to 5 GHz. The permeability of the composite was increased with increasing particle size. The frequency dispersion behavior was found to be dependent on the porosity of the composite at a given particle size and ferrite content. The relaxation curve of the complex permeability became broader and flatter as the porosity increased. The equation proposed in this article coincided with the frequency dispersion behavior of the complex permeability of the composite fairly well. It was also found that the variation of σ and ν had a close relationship with the shape variation of the frequency dispersion curve, and that σ and ν were the parameters related to the porosity, particle size, and particle size distribution.

Composition dependence of rheological properties of polymer blends

Abstract A semi-empirical rheological equation of state was developed to described temperature, shear rate and composition dependence of the steady-state shear viscosity of poly( l -lactic acid)(PLA)/poly(e-caprolactone)(PCL) systems. The composition dependent rheological equation of state proposed here has a very simple algebraic form with a few adjustable parameters. Its simplicity is a great advantage for practical application and it appears to be suitable for describing the rheological behaviour of PLA/PCL blends.

Poly(methyl methacrylate) toughened by core–shell impact modifier: Applicability of rheological equation of state

A simple rheological equation of state was developed to describe the steady-state shear viscosity of poly(methyl methacrylate) (PMMA) toughened by core–shell impact modifier. The suggested equation was successfully able to describe and predict viscosity of toughened PMMA as a function of shear rate (γ˙) and temperature.