Research On Polymorphs Of D-sorbitol

D-sorbitol with several polymorphs is a natural hexahydric alcohol and widelyused in many fields. Polymorphs can be used in different ways because of theirdifferences in physicochemical properties, such as solubility, melting point andstability. Hence, investigation on polymorphism is important for the use and processof D-sorbitol and for the study of crystallization theory. Based on the research before,this dissertation focused on the polymorphism of D-sorbitol and the specific researchcontents are as follows:Basic thermodynamic data, such as solubility, are the necessary basic data todevelop new crystallization process and technology, and it is also an importantmethod to study the thermodynamic stability of polymorphs. The solubilities ofdifferent polymorphs of D-sorbitol in different solvents at various temperatures weremeasured by dynamic method, and were correlated with Apelblat empirical equation.It’s found that the solubilities of different forms of D-sorbitol increase with thetemperature increasing. The solubilities of gamma form are the lowest while thesolubilities of F form are the highest. And it preliminariely verified that gamma is themost stable form while F is the most unstable one.Preparation of different polymorphs is a prerequisite to study the polymorphismof materials and their properties. Solution crystallization methods for different formsD-sorbitol were studied. The products were analyzed and characterized by usingmodern analytical instruments and equipments, such as PXRD, DSC and Raman. Anda new polymoph named F form was discovered. The effect of temperature,supersaturation and seeding on the polymorphs of D-sorbitol product wasinverstigated. The preparation process of F form was optimized.Understanding of the transformation among different polymorphs and itsmechanism is the basis of controlling the polymorphs of materials. Polymorphictransformations of D-sorbitol polymorphs as well as its influencing factors wereinvestigated by solid-state analytical techniques and on-line technologies, such asRaman, FBRM and so on. It was shown that in several solvents, the resulted crystalform is different at different temperatures. F form would transform to alpha form atlower temperature. Other metastable forms will transform into gamma at higher tempperature because gamma is the most stable one. And it was speculated that thetransformation processes of D-sorbitol in dfferent solvents are monotropy andsolvent-mediated (SMT). Transformation of the solvates during desolvation processby thermal treatment at high temperature is solid-state transformation (SST).No similar reports to above research have been published in literatures up todate.