Glass Transition And Dispersal Stability Of Amorphous Macromolecule Polymer Powders

Amorphous powders as end or middle products are closely related to many industries such as food, drinking, nurture, medicine and so on. Both the processing properties and the guality of the amorphous products are directly affected by their dispersal state. It is a valuable research subject, not only academically but also practically, to study the caking mechanism of amorphous powders and find methods to keep them in the dispersal state. The main contents of the subject are how to measure the glass transition temperature (Tg) of amorphous powders and how to analyze the influence of the glass transition of amorphous powders. The purpose of this thesis is to study the characteristics of glass transition experimentally with several typical amorphous starch powders, and try to find the way and the method to prevent them from caking by changing Tg of the powders.An experimental scheme on the glass transition of amorphous powders is designed after analyzing and comparing various experimental techniques, experimental setups and their application conditions. The procedures and the principle of differential scanning calorimeters (DSC) are introduced in detail. An experimental apparatus of the thermodynamics dilatometer analysis (TDA) is designed and set up. The feasibility of the equipment to measure Tg of amorphous powder is verified with a lot of experimentl results.The Tgs of some typical starches such as corn, pachyrhizus, buckwheat and pea in different water content are obtained by TDA. It is found that the water has plastic effect on starch and the Tg of starch decreases with the increase of water content. Through this study a quantitative expression is established to relate Tg and water content, and it is testified with experimental results for the sticky rice starch with different water content. This will serve as a base for predicting Tgs starches with different water content and further for processing and storing them.The methods of Ubbelohde viscosimeter, TDA and DSC are used to measure molecular weight and Tgs of starch. It is found that Tg increases with the increase of molecular weight before reaching critical molecular weight. After this critical molecular weight the increase of Tg with molecular weight is slowed down. A quantitive expression is obtained to express the relationship between Tg and molecular weight. Based on this relationship, we can change the Tg of starch by changing its molecular weight to meet the pratical needs.The DSC technique is used to estimate the consistence character of starch with different additives. The glass transition behavious of starch blended with water and Xanthan gum are examined respectively. An expirical expression is obtained for the Tg of starch blendee with additives according to the blending model of polymers and verified with the experimental results. This expression can be used as a base to predict the Tg of starch blended with Xanthan gum.This study of this thesis makes a contribution not only to the knowledgment of the glass transition characteristies and their effective factors of amorphous powders, but also to basic information and useful data to prevent caking formation and to study further.