Molecular Aspects of Flow Effects on Crystallization in iPP

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Technical Description: Semicrystalline polymers comprise over two-thirds of the annual production of all synthetic polymers and are in the midst of a renaissance, as recently developed metallocene catalysts give access to new combinations of final properties through control of macromolecular structure. The present research uses novel instrumentation and model polymers to discover the molecular basis of self-assembly of the semicrystalline nanostructure, particularly under the influence of flow. During the next three years the axial propagation velocity of threadlike precursors will be measured as a function of the molecular characteristics of the polymer, temperature and stress. Polymers of well-defined length and distribution will be used to specify the chain dynamics in the melt. Birefringence and synchrotron x-ray measurements will track the formation of oriented precursors and the growth of crystallites from them. Toward the goal of enabling rational design of the molecular structure of polyolefins, experimental observations will guide advances in theory and modeling. Specifically, collaborative research with Han Meijer and Gerrit Peters will apply experimental results to incorporate molecular descriptors into the recoverable strain model for flow-induced crystallization. Intellectual Merit: The fundamental basis of the profound effects of processing on crystallization kinetics and morphology is the interplay of the conformational dynamics of the molten chains, the kinetics and anisotropy of nucleation from a distorted melt, and their effects on the subsequent kinetics and morphology of crystallization. This research adopts a comprehensive experimental approach to reveal the connection between molecular attributes, flow behavior and crystallization. To extend academic experiments to technological design tools, new knowledge of the role of molecular structure is translated into advances in predictive modeling. In terms of basic science, this program elucidates the fundamental mechanism by which processing affects polymer structure development. In terms of industrial practice, fundamental knowledge of the processes involved is used to develop predictive models that bridge from molecules to macroscopic properties that have the potential to revolutionize macromolecular and process design of semicrystalline polymers. Broader Impacts: Technology transfer activities include ongoing collaboration with Procter and Gamble on the development of new bimodal resins for non-woven fabrics. The educational experience of the doctoral researcher engaged in the project is enriched by close interaction with industrial and international scientists. In addition, DMR support fosters ongoing outreach activities: Kornfield contributes to the Sally Ride Science Festival that targets middle-school girls and participates in the Caltech Engineering preview providing information on graduate studies to underrepresented undergraduates.