M. G. Lu

Curing Reaction and Phase Change in a Liquid Crystalline Monomer

An epoxy monomer was cured in liquid crystalline phase with three different amines to form (LCT). The thermal transitions of the LCT were studied by differential scanning calorimetry (DSC), wide angle X-ray diffraction. (WAXD) and polarized optical microscopy (POM). Different curing features are observed depending on the curing agent and reaction condition, which is related to the formation and development of LC phase during cure. An isoconversional analysis is used to characterize the cure process.

Dynamic DSC Characterization of Epoxy Resin by Means of the Avrami Equation

A phenomenological approach was used to characterize the cure processes of epoxy resins (a diglycidyl ether of bisphenol A and its modifier CTBN) from dynamic experiments by DSC. Various kinetic parameters were obtained by using a modified Avrami expression. The resulting overall activation energies for the two systems agreed very well with the published data in the whole cure temperature range. In contrast with the isothermal results and the general dynamic models, a change in the exponent and the non-linear temperature dependence of the rate constant were also observed.

Kinetics and thermal characterization of epoxy-amine systems

The curing behavior of epoxy resins was analyzed based on a simple kinetic model. We simulated the curing kinetics and found that it fits the experimental data well for both diglycidylether of bisphenol A–4,4′-methylene dianiline and diglycidylether of bisphenol A–carboxyl-terminated butadiene acrylonitrile–4,4′-methylene dianiline systems. The kinetic results showed the curing of epoxy resins involves different reactive process and reaction stages, and the value of activation energy is dependent on the degree of conversion. By analyzing the effect of vitrification, at low curing temperature, we found the curing reaction at the later stage was practically diffusion-controlled for unmodified resin, and the rubber component did not markedly decrease Tg at the early stage of reaction as would be expected.

Thermal degradation of LC epoxy thermosets

A novel liquid crystalline (LC) epoxy monomer was cured with different types of hardeners. The thermal-degradation properties of cured thermosets were evaluated by thermogravimetric (TG) analysis. Several widely used kinetic models were reviewed and used to fit the TG data. The experimental results showed that the methods from one constant heating rate are insensitive to the magnitude of reaction order n. The Kissinger and Osawa methods from multiple processes would give more confident kinetic parameters in these observed systems.

Reaction mechanism of an unsaturated polyester system containing thickeners

The thickening process and curing reaction of unsaturated polyester resins were characterized by viscosity measurement and differential scanning calorimetry when a thickener was involved. Various kinetic parameters were determined by means of dynamic and isothermal experimental data and rheological process. The different values of activation energy reflected the different reaction mechanisms occurred in the curing course. Under isothermal conditions, polymerization reaction is one-order and diffusion-controlled reaction becomes significant when high concentration of thickener was applied.

Bulk properties of epoxy resin modified by epoxy–aminosilane copolymers

A linear epoxy-aminopropyltriethoxysilane addition polymer was used as a new epoxy modifier. In this paper, the thermal and mechanical properties have been determined by differential scanning calorimetry (DSC) and mechanical testing. The experimental results show that this copolymer modifier can effectively improve the toughness of resins without sacrificing their thermal resistance, stiffness and strength. As a comparison, the properties of epoxy resin blended with aminopropyltriethoxysilane (γ-APS) have been carried out simultaneously.

The macrokinetic model of thermosetting polymers by phase-change theory

Abstract The general rate law frequently used to describe the cure process of thermosetting polymers (thermosets) can be deduced by analysing the Avrami theory. Every parameter in it can be given reasonably. From the macrokinetic model, it is also possible to describe the non-isothermal cure process of thermosets. A comparative example shows that the theoretical prediction is in good agreement with the experimental data.