Yi Xiaosu

Effect of bound water on thermal behaviors of native starch amylose and amylopectin

Thermal behavior of dry native starch, amylose and amylopectin originating from different plants was investigated using Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC). The decomposition temperature increased as the molecular weight increased and a sudden increase was observed at a molecular weight of 50,000 that can be the critical value. DSC analyses verified that the amorphous phase in the specimens was swollen by bound water within a temperature range of 323–428 K. The change in swelling enthalpy divided by the peak temperature of swelling depended linearly on the volume fraction of bound water, regardless of the origin and the composition or purity of the specimens. Furthermore, bound water depressed the melting points of crystallites in the specimens, which agreed well with the prediction of Florys lattice theory.

Morphological Characteristics and the Modulus of Liquid Crystalline Polymer Fibers Dispersed in a Thermoplastic Matrix

Abstract The morphology of a polycarbonate (PC)-based blend containing a thermotropic liquid crystalline polymer (LCP) component has been characterized in terms of the layer structure, layer thickness, aspect ratio, and number of the shear-induced fibers developed during injection molding. This dispersed LCP phase was still embedded as fibers and deformed droplets in the PC matrix, and their tensile modulus was usually unknown due to the testing problems. Based on the morphological characteristics, a calculation procedure has been developed to estimate the modulus of these fibers and droplets by using a set of micromechanical models. It has been found that the average tensile modulus of these shear-induced LCP fibers and deformed droplets seems to be a material constant, independent of the injection molding condition, i.e., the shear flow condition. For the LCP Vectra A950 studied, the calculated tensile modulus was 24.0 GPa. This value was in fair agreement with that reported in literature. It was larger...

TTT Diagram Used to Control Phase Structure of 2/4 Functional Epoxy Blends for Advanced Composites

This article uses a 2/4 functional epoxy blend system (E-54/AG-80) cured with diaminodiphenyl sulphone(DDS) as a raw material and develops a methodological procedure to establish a cure kinetic model with isothermal and dynamic differential scanning calorimeter(DSC) method and a gelation model with round-disk compression mode dynamic mechanical analyzer(DMA), thus acquiring a series of experimental data. Characteristic temperatures such as initial glass transition temperature Tg0, gelation glass transition temperature gelTg, and infinite glass transition temperature Tg∞ are determined. The cure degree at gelation is turned out to be 0.45, while gelTg is found to be 70.2 °C. The data are then used to form time-temperature-transition(TTT) diagram of the system, which serves to be a tool for process optimization of epoxy-matrix composites. A new cure processing is therefore derived from the TTT diagram. The final phase structure obtained from a controllable method is identified through scanning electron microscope(SEM) photographs to be of ‘ex-situ’ phase morphology.