Kinetic studies on polymerization of poly lactic acid using suitable catalyst

Abstract

Biodegradable polymer materials are of great interest because these are used in packaging, agriculture, medicine and other areas. Poly (lactic acid), PLA is one of the most promising biodegradable polymers (biopolymers) and has been the subject of abundant study over the last decade. This thesis embodies the subject matter resulting out of this study. The entire work is arranged in five chapters. A brief introduction, historical background and the applications of biodegradable polymers (plastics) are described first. The importance of lactic acid, monomer used in the synthesis of polylactide, is also discussed. A brief account of physical characteristics and advantages and disadvantages of PLA is presented. Ring-opening polymerization technique is more useful for the production of high molecular weight PLA than polycondensation, which yield low molecular weight of PLA. For an estimation of kinetic parameters, mathematical modeling of the ring-opening polymerization is also described. Both the methods for the synthesis of PLA from lactide are described and out of these the ring-opening polymerization method has been chosen for the present work because it gives higher molecular weight of PLA. Three major reaction mechanisms: cationic, anionic, and coordination-insertion are discussed. However, high molecular weight polyesters have only been obtained by using anionic or coordination-insertion ring-opening polymerization. Studies on the effects of different parameters: polymerization temperature, polymerization time, monomer/initiator ratio, nature of the initiator, amount of water or other impurities etc. which affect the polymerization of lactide are reviewed. Determination of kinetic rate constants by modeling and simulation and polymerization mechanism is also discussed. Relevant literature for the determination of intrinsic viscosity by using Ubbelohde viscometer (Mark-Houwink equation) is also reviewed.