Leader : Sbirrazzuoli Nicolas
Soutiens financiers : 2 MESR PhD grants ; European project Marie Curie, Industry-Academia Partnerships and Pathways (IAPP), "BIOpolymers and BIOfuels from FURan based building blocks" (BIOFUR), FP7-PEOPLE-2012-IAPP, in collaboration with with Avantium Inc. and the University of Messina (Italy), from year 2013 to 2016.
We want to develop a new experimental and theoretical approach to better understand the relationship between nucleation, glass transition and crystallization (from the solid and from the liquid). The process of crystal formation determine the macroscopic properties of materials in general and of semi-crystalline polymers in particular. The first work on this subject have begun with the study of the kinetic aspects of crystallization and of the glass transition of widely used synthetic polymers (PET, PS, PTFE and PDMS) and of typical and atypical processes of gelation of gelatin (cover featured article of SoftMatter). These studies are being generalized to other semi-crystalline polymers, bio-based and bio-inspired polymers and composites. The starting point of this work lies in the fact that, despite numerous studies on the subject, all the phenomena occurring during the crystallization of thermoplastic polymers cannot be integrated in complex mathematical equations. We proposed a new method to calculate the parameters of the equation of Hoffman-Lauritzen (theory of crystallization of polymers) and activation energy at the glass transition (which is related to mechanisms). This method represents a unique way to extract the important parameters of crystallization from simple calorimetric measurements, unlike the conventional method based on time-consuming optical microscopy measurements. In addition, the coupling between DSC and ultrafast DSC (FlashDSC that can apply heating rates of 2.4 million K.min-1 and cooling rates of 240 000 K.min-1) can reach a temperature range 10 to 20 times higher than that reached by microscopy or by isothermal DSC measurements (calculation of the kinetic parameters over 150 ° C in the case of PTFE). This is a unique way to study the mechanisms of crystallization on cooling over a wide temperature range and to get a better understanding of the phenomena of nucleation and growth. To validate this new approach and improve the theoretical understanding of the dynamics of these phenomena in semi-crystalline polymers, polymers with very different crystallization kinetics were studied. In the case of nanocomposites, our studies highlight the role of nano-silica on the phenomena of nucleation, growth and diffusion. Determining the size of the volumes that rearrange cooperatively at the glass transition (VCRR) provided information on the molecular mobility and was connected to the temperature and the energy of the transition. These macroscopic parameters were interpreted in the light of experimental results obtained on the PDMS-nanosilica system by neutron diffraction (coll. Prof. J. Persello).
The objective of this work is to highlight and understand the role of nanofillers on nucleation phenomena preceding the crystal growth, and the mechanisms of the glass transition. Indeed, nanoscale silica introduced into polymers (after chemical changes) leads to a highly organized structure, which facilitates the formation of heterogeneous nucleation sites regularly distributed in the polymer matrix. The new methodology developed will be transposed to the study of a new semi-crystalline thermoplastic polymer fully biobased, the PEF (PolyEthylene Furanoate). PEF is a biobased analogue of PET. This polymer devoted to replace the PET is more compatible with food, its constituent unit (the Furan DiCarboxylic Acid) being naturally degraded by the body unlike phthalates in case of PET. The main application of PEF is now in the manufacture of food packaging bottles. It is obtained from derivatives of the processing of agricultural plant waste. It is therefore a "plastic" of 2nd generation not competing with food. Beyond the biobased aspects, it is important to note that the PEF has barrier properties of liquid (H2O) and gases (CO2, O2) higher than that of the PET. One objective of this project is to understand the mechanisms governing its crystallization and to make the link with the resulting thermomechanical properties (coll. G. Bossis). This study is being conducted under the European project IAPP (Marie Curie) " BIOFUR " in partnership with Avantium and the University of Messina.
Fluides & Matériaux Complexes, Magnétorhéologie - Nanomatériaux, Matériaux Éco-compatibles
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