Caroline FRANCOLLE DE ALMEIDA: New heat exchanger materials for the food industry

Summary :
In this thesis, carbonaceous materials were studied in their raw, impregnated, chemically grafted or coated state to replace stainless steel in heat exchangers and reduce fouling while improving energy efficiency. Different materials have been used: (i) graphite and graphite- based composites; (ii) glassy carbon with controlled surface energy and roughness to become bases of Slippery Liquid-Infused Porous Surface (SLIPS), and treated to become superhydrophobic. In addition, polymer-based coatings and surfaces with a 3D-printed texture were also prepared. Once these surfaces were characterized (composition, structure, surface properties, thermal conductivity), they were tested in terms of anti-fouling and fouling-release properties in a pasteurization pilot at l’institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement in Villeneuve d'Ascq, France. Among all these materials, graphite and graphite- polytetrafluoroethylene composite as well as Polyvinylidene fluoride and PTFE-based coatings showed good fouling-release properties. Glassy carbon became superhydrophilic after reactive ion etching, could be converted into SLIPS by introducing canola oil, and became superhydrophobic by grafting perfluorosilane chains onto it. The results of fouling tests showed that the more hydrophobic the surface, the greater the fouling mass, but that good fouling-release properties can be expected if their superhydrophobic character, or oil trapping for SLIPS, can be maintained over time. On the other hand, the fouling-release properties depend strongly on the product used and the process conditions as well as on surface properties such as roughness and surface energy.

Composition of the jury :
> Rapporteurs :
- Anouk GALTAYRIES, Maître de Conférences, Ecole Nationale Supérieure de Chimie de Paris, Institut de Recherche de Chimie de Paris (IRCP)
- Michel HAVET, Professeur, Ecole Nationale Vétérinaire, Agroalimentaire et de l’Alimentation Nantes Atlantique (ONIRIS), Génie des Procédés - Environnement- Agroalimentaire (GEPEA)
> Examiners :
- Maude JIMENEZ, Professeur, Université de LIlle, Unité Matériaux et Transformations (UMT)
- Nicolas BATISSE, Maître de Conférences, Université Clermont Auvergne, Institut de Chimie de Clermont Auvergne (ICCF)
- Vanessa FIERRO, DR CNRS, Institut Jean Lamour (Co-Directeur de thèse),
- Alain CELZARD, Professeur, Université de Lorraine, Institut Jean Lamour (Directeur de thèse).