Grégory Martin

Grafting of polyethylene onto graphite oxide sheets: a comparison of two routes

Polyethylenes and azide-terminated polyethylenes can be converted to macroradicals and nitrenes, respectively followed by addition reactions onto the unsaturated system of graphite oxide sheets. For the first time, the addition of these macroradicals to graphite oxide sheets was compared by performing grafting reactions at 190 °C in 1,2,4-trichlorobenzene as a solvent and at 100 °C followed by a solvothermal reduction at 150 °C in a solvent mixture of 1,4-dioxane and 1,2-dichlorobenzene. Dispersion of PE coated graphite oxide in a DMF–heptane mixture was utilised to follow the introduction of polyethylene onto the GO sheet surface while the thermogravimetric analysis indicated the extent of this grafting. The grafting ratio was found to be in the 1.5 wt% range and despite this low grafting content, the amount of grafted PE was high enough to dramatically improve the affinity of GO with the heptane phase in the DMF–heptane (50/50 v/v) mixture. Polyethylene functionalised GO was imaged by scanning electron microscopy showing a significant difference in morphology between the two grafting paths. It was found that a higher level of grafting was obtained using a radical grafting reaction in the presence of benzoyl peroxide rather than the thermal cleavage of PE-N3 onto GO while a similar grafting content was obtained with the thermal cleavage of PE-N3 onto GO grafted trimethoxy(7-octen-1-yl)silane.

Structuring of non-Brownian ferrite particles in molten polypropylene: Viscoelastic analysis

This paper focuses on the relation between the structure and the rheological properties of non-Brownian ferrite particles suspended in a molten polypropylene matrix with and without the addition of a dispersant agent. The studied filler levels were 2, 15, and 20 vol. %. Under low deformation, the measurement of the complex shear modulus over time showed that the material structure was not stable. Such evolution was, on the one hand, more visible at concentrations near the percolation threshold ( ϕc≈0.25) and on the other hand, less visible when adding a dispersant agent. Oscillatory time sweep experiments were performed after a preshearing. It was shown that the kinetics of the evolution strongly depends on the applied deformation. Such evolution has also been highlighted by optical microscopy, in which an agglomeration phenomenon was clearly observed after few hours, again less visible for formulations with a dispersant agent. Under high deformations, no structure evolution was noticeable. Our results st...

Morphology Development in Thermoplastic Vulcanizates (TPV)

The mechanisms of fragmentation and dispersion in molten polypropylene (PP) of several pre-crosslinked and plasticized ethylene-propylene-diene terpolymer (EPDM) networks were studied. The results highlight the importance of the gel fraction of the pre-crosslinked EPDMs on the quality of the dispersion of such networks. As a result, pre-crosslinked EPDM having a gel fraction below gEPDM=0.7 can be finely and homogeneously fragmented and dispersed in presence of PP. Nevertheless, contrarily to some theoretical model expectations, a partial fragmentation of the chemical networks was always observed even at very high crosslink density (gEPDM>0.7). It can be then admitted a collisioncoalescenceseparation type erosion mechanism of the EPDM domains. Finally, these results brought significant information on TPV morphology stabilization and their related mechanical properties.