Alexander J. Mackinnon

Dielectric, mechanical and rheological studies of phase separation and cure of a thermoplastic modified epoxy resin : incorporation of reactively terminated polysulfones

Abstract Application of dielectric, mechanical and rheological measurements to the characterization of cure and phase separation in a thermoplastic modified epoxy resin is reported. These data indicate that the dielectric technique is not only useful for monitoring changes in network dynamics during the process of cure, but can also provide valuable information on the phase separation of the occluded phase. The paper discusses the modelling of the dielectric data, and considers the importance of understanding the relationship between morphology and mechanical properties.

Investigation of thermoplastic-modified thermosets: positron annihilation and related studies of an amine-cured epoxy resin

Abstract Real-time dielectric relaxation and rheological measurements are reported during the course of cure for three thermoplastic-modified thermoset resin blends. Two thermoset resin systems were used, one containing only a difunctional epoxy and the other containing a mixture of tri- and difunctional epoxies. The latter mixture was used to react two reactively terminated polysulfone thermoplastics with slightly different molecular weights. Positron annihilation measurements are reported on one of the thermoplastic-thermoset resin systems as a function of the thermoplastic composition, and indicate that changes in composition lead to variations in the free-volume content. Mechanical properties are presented for all three systems. These data indicate that the phase structure has a significant effect on mechanical performance, but the most dominant effect results from change in the thermoset matrix material.

Glass transitions and enthalpy relaxation in coals

Differential scanning calorimetry was used to investigate the glass-to-rubber transition at 383 K of Illinois No. 6 coal dried at 383 K and thermally treated to 523 K. The intensity of the transition is 0.2 Jg−1 K−1, similar in magnitude to that for polypyrrole and polystyrene. The temperatures of the glass transitions in the coal and the polymers are also very similar. It is concluded that the glass transition of the coal represents a significant change in structure. Annealing experiments were conducted on the coal at temperatures just below the glass transition. Enthalpy relaxation occurred after thermal treatment to 553 K.

Properties of second order transitions in Argonne Premium coals

Differential scanning calorimetry (DSC) has been used to investigate the thermal transitions occurring for a series of eight Argonne Premium coals. Each of the coals was subjected to different heating/cooling profiles in order to determine the effect of cooling at varying rates on the second order process and to determine the effect of temperature of exposure on the second order process. The variable cooling rate scans showed that the position of the transition increased with decreasing cooling rate of the previous scan. The sequential heating scans demonstrated that the rank of coal had a direct influence on the resistance of the second order process to exposure to heat. Low rank coals showed a greater degree of resistance and this was assumed to be related to the density of non-covalent bonds within the structure.

Temperature dependent low frequency dielectric and conductivity measurements of Argonne Premium coals

Abstract A study has been made of the dielectric properties of a series of Argonne Premium coals as a function of frequency and temperature. Measurements were made in the low frequency range, 0.01–10 5 Hz, over the temperature range 300–450 K. Two distinct processes were observed over the frequency range. At low frequency, real and imaginary components of the permittivity showed an increase with decreasing frequency, particularly at low frequency and high temperature. This type of behaviour is consistent with a Maxwell-Wagner-Sillars process. At higher frequency, a dipolar relaxation was observed for four of the coals and this was shown to be an activated process. The real conductivity of each coal measured at 0.01 Hz was shown to increase with temperature with the majority of coals showing a distinct break at 370–380 K.

Low-frequency dielectric measurements on Argonne Premium coals

Letter on the use of dielectric spectroscopy in the investigation and characterization of polymers.