19 June 2020 - Fluid Mechanics, Energy, Processes Ph.D. title
Understanding of the ageing phenomena occurring in electrotechnical papers in power transformers and research of industrial solutions. Supervision Gérard MORTHA, Professor, Grenoble INP-Pagora / LGP2 ♦♦ Nathalie MARLIN, Associate Professor HDR, Grenoble INP-Pagora / LGP2 ♦♦ Lucie BOIRON, Research Engineer, Ahlstrom-Munksjö Abstract
Power transformers are expensive devices and the degradation of the cellulosic insulation paper contributes to limiting the transformer life expectancy. This work studies the kinetic degradation of two electrotechnical papers during accelerated ageing trials in mineral oil: one standard paper and one Thermally Upgraded paper (TU) containing an additive.
The degradation of the standard paper, measured via the cellulose viscometric degree of polymerisation (DPv), follows a first order kinetic model and the calculated activation energy is close to activation energy reported for the acid hydrolysis of cellulose in the literature. The TU paper behaves differently since the additive slows the paper degradation, and none of the tested kinetics models succeed to model experimental data. A deeper study of the additive reaction mechanism confirms and completes the hypotheses presented in the literature.
Moreover, some mechanical characterizations of aged papers highlight a correlation between the cellulose DPv and the double fold resistance of the paper. Thereafter, it has been discussed if the presence of lignin in paper presents a protective effect on cellulose and it has been shown that it leads to the production of methanol (used as a marker of paper degradation to monitor power transformers).
Finally, a new protective solution on the paper surface, gave encouraging results, particularly in terms of paper mechanical strength properties preservation. Other members of the jury
Anne-Laurence DUPONT, CNRS Research Director, MNHN CRC, Paris ♦♦ Thierry PAILLAT, Professor, Université de Poitiers ♦♦ Nathalie BARNEL, Research Engineer, EDF ♦♦ Olivier LESAINT, CNRS Research Director, G2ELab, Grenoble
Manon LE GARS
5 March 2020 - Materials, Mechanical, Civil Engineering, Electrochemistry Ph.D. title
Surface modifications of cellulose nanocrystals for biobased food packaging applications. Supervision
Julien BRAS, Associate Professor HDR, Grenoble INP-Pagora / LGP2 ♦♦ Naceur BELGACEM, Professor, Grenoble INP-Pagora / LGP2 ♦♦ Philippe ROGER, Professor, Université Paris-Saclay ♦♦ Hanène SALMI-MANI, Associate Professor, Université Paris-Saclay Abstract
The purpose of this project is to develop new surface chemical modifications of cellulose nanocrystals (CNCs), in order to enhance their compatibility with biobased poly(lactic acid) (PLA) polymer, and to combine their respective outstanding intrinsic properties. Biobased PLA-based multi-phase materials, including the designed nanostructures, are produced. Furthermore, the final materials are expected to be used in food packaging sector, and the improvement of the barrier properties of the PLA, especially towards oxygen and water vapour, is a key point in the characterization of the materials. In this project, different routes are proposed for the grafting of various compounds – polymers or single molecules – on the surface of the CNCs. Their grafting efficiency has been confirmed and carefully characterized. The modified CNCs are then introduced in PLA-based materials via two different strategies. Indeed, they are either used as nanofillers in a PLA matrix with inclusion rates comprised between 2 and 10 wt%, or as an inner layer of PLA-based multi-layered materials. In both cases, final PLA-based materials including various designed cellulosic nanomaterials exhibit enhanced and highly encouraging properties in terms of homogeneity, transparency, and barrier towards oxygen and water vapour, in accordance with required properties for food packaging materials. Other members of the jury
Bénédicte LEPOITTEVIN, Associate Professor, ENSICAEN ♦♦ Jose-Maria LAGARON, Professor, CSIC, Espagne ♦♦ Hélène ANGELLIER-COUSSY, Associate Professor, Université de Montpellier ♦♦ Evelyne MAURET, Professor, Grenoble INP-Pagora / LGP2 ♦♦ Sandra DOMENEK, Associate Professor, AgroParisTech
Esakkiammal Sudha ESAKKIMUTHU
30 January 2020 - Materials, Mechanical, Civil Engineering, Electrochemistry Ph.D. title
Study of new chemical derivatization techniques for lignin size exclusion chromatography characterization. Supervision Gérard MORTHA, Professor, Grenoble INP-Pagora / LGP2 ♦♦ Nathalie MARLIN, Associate Professor HDR, Grenoble INP-Pagora / LGP2 Abstract
Lignin is the second most abundant biopolymer on earth after cellulose and it consists of highly-branched, three dimensional aromatic structures with variety of functional groups.
This research work was to establish lignin derivatization methods for lignin analysis, to quantify functional groups and to determine lignin molar mass distribution (MMD) by size exclusion chromatography. Five technical lignin samples are considered: Protobind 1000, Organosolv, Pine Kraft, Eucalyptus Kraft and Indulin. They are derivatized through classical acetylation method and new methods such as fluorobenzylation and fluorobenzoylation. The number of hydroxyl present in the lignin samples are quantified through GC and NMR (1H, 13C, 19F and 31P) techniques. The molar mass distribution of derivatized lignin samples are calculated using different SEC columns with different solvents (DMAc and THF). Conventional and universal calibration methods are used for MMD calculations.
With this approach, new derivatization methods significantly enhance lignin solubility in THF and improve chromatographic results. Universal calibration leads to about three times higher molar mass values than by conventional calibration. Other members of the jury
Nicolas BROSSE, Professor, Université de Lorraine ♦♦ Christophe GEANTET, CNRS Research Director, Université Lyon 1 ♦♦ Sami HALILA, CNRS Researcher, Université Grenoble Alpes ♦♦ Marie-Christine BROCHIER-SALON, Research Engineer, Grenoble INP ♦♦ Dominique LACHENAL, Emeritus Professor, Grenoble INP
8 january 2020 - Fluid Mechanics, Energy, Processes Ph.D. title
Development of fibrous cellulosic materials for the production of bio-based 3D printed objects by extrusion. Supervision Didier CHAUSSY, Professor, Grenoble INP-Pagora / LGP2 ♦♦ Aurore DENNEULIN, Associate Professor, Grenoble INP-Pagora / LGP2 ♦♦ Davide BENEVENTI, CNRS Research Director, Grenoble INP-Pagora / LGP2 ♦♦ Sabine ROLLAND DU ROSCOAT, Associate Professor, Université Grenoble Alpes / 3SR Abstract
First, this project has evaluated the compatibility of aqueous and high solid content formulations with AM by extrusion. Formulations composed of micrometric organics fillers (cellulose fibers or powder) and cellulose derivatives (carboxymethyl cellulose) were investigated and results in a selection of homogeneous pastes with strong potential for AM by extrusion and limited deformation of the printed part upon air drying.
The second stage of this project focused on adjustment and optimization of AM by extrusion equipment and the related settings to guarantee an optimum shape accuracy of 3D printed parts compared to the 3D numerical model. A printing setting guideline and design limitations adapted to the developed paste were suggested. To characterize the printing parts, different innovative methods such as the temporal monitoring by X-ray tomography of a printed part upon drying were implemented.
The results of this project lead to the AM by extrusion of complex part 100% cellulose based with mechanical properties close to thermoplastic materials commonly used with fused filament fabrication process. Other members of the jury
Roberta BONGIOVANNI, Professor, Politecnico di Torino, Italy ♦♦ Pierre DUMONT, Professor, INSA Lyon ♦♦ Gilberto DE FREITAS SIQUEIRA, Researcher, Empa, Switzerland ♦♦ Laurent ORGÉAS, CNRS Research Director, Université Grenoble Alpes / 3SR