This issue addresses several kinds of non-reactive and reactive processes in the aim to predict the microstructure of polymers and its link with processing conditions and in particular the study of melting and sintering of powders, crystallization of molten polymers and gelation of reactive thermosets mixtures.

 

We first are involved in the crystallization of confined polymers and the occurrence of Rigid Amorphous phase being showed to be detrimental for the barrier properties of semi-crystalline polymers.

                                                                                            

                                                                                            SEM observations of PLA spherulites and schematization of Rigid Amorphous Phase.

 

In link with the use of new aromatic polymers for composites materials with thermoplastic matrices (for example PEKK), we are also interested in the mechanisms and kinetics of crystallization from the melt, since those later are linked to the mechanical properties of polymers.  

                                                                                    

Differential scanning calorimetry thermograms of neat poly(ether ketone ketone) crystallized from the melt at 200°C with understanding of crystallization mechanism (a) and Time-temperature-transformation diagram of the relative crystallinity of poly(ether ketone ketone) crystallized from the melt.

In the specific case of high pressure or laser sintering (an additive manufacturing process where parts are build layer by layer) of polymer particles, the densification and air trapping triggers the final mechanical performances. The issue of particle sintering and macromolecular diffusion at interfaces is for example studied by rheology. Researches are carried out to predict the thermal behaviour, basing on C-NEM modeling.

                                                                                                      

                                      Sintering of 20 µm particles (left) and C-NEM simulation of temperature profile in a PEEK particle after laser exposure (5 W at 0,5 m s^-1).

 

Very recently, we also tried to enlarge our investigations on the polymeric blends with taking into account the phenomena of interfacial tension, and miscibility which requires the implementation of new numerical methods.

 

                                                                                                       

                                                                                                                                Sintering of PVDF/PMMA blend.

 

In the case of reactive processes for manufacturing thermosets, we also implement modeling approaches to address the challenge of the coupling between rheology, thermal behavior and kinetics of polymerization.

                                                                                                            

                                                                                        SPH (Smoothed Particle Hydrodynamics) simulation of reactive rotomoulding.

 

Last, flow instabilities are known to appear in many polymer-processing operations. These instabilities can be the result of inertial or capillary forces and are influenced by the viscoelastic properties of the polymeric fluids. The animated image shows the time-evolution of the stretching of an aqueous of 1000 ppm high molecular weight polymer, PEO (polyethylene oxide). The final drop diameter is approximately 300 micrometers.    

                                                                                                                                      

                                                                                                                   Viscoelastic instabilities of PEO solutions