Post-doc position: 3D imaging and micromechanics of novel strengthened papers and paperboards

Project summary

Designing renewable and biodegradable materials for, e.g., food or health packaging is of major importance. Many research efforts are being developed purposely, in particular by looking for novel processing routes with ligno-cellulosic fibers extracted from the vegetal biomass to produce novel papers and paperboards with enhanced thermo-hygro-mechanical properties. In particular, this challenging objective require the improvement of fiber-fiber links to reinforce the mechanical properties of fibrous networks, by optimizing the density and/or the quality of nanoscale chemo-physical bonds (hydrogen, electrostatic…) between fibers.

Several strategies are known for that purpose. For example, fiber refining to produce “forests” of cellulose microfibrils around fibers that increase the connections between fibers during paper making operations is a well-known and efficient solution. However, it is energy consuming since it requires substantial effort to extract water from the fibrous network during paper pressing.

Here, we wish to explore another strategy, less energy consuming, by improving the morphology, and thus the mechanical properties of usual fiber bonds. This is the main objective of the “FibreFlex” project. Papers and paperboards will be manufactured using fibers the morphology of which will be optimised with chemo-mechanical pre-treatments. The role of the postdoc will consist in characterising

• (i) the 3D fibrous structures of the processed papers with a special focus on the density and the geometry of fiber-fiber bonds,
• (ii) the micromechanics of individual fiber-fiber bonds,
• (iii) the macroscopic hygro-mechanical properties of papers,
• and (iv) in proposing a micromechanical approach to model their macroscopic mechanical behaviour

For that purpose, various experimental/numerical analyses will be carried out:

• Mechanical tests with various mechanical loadings (uniaxial, plane strain tensile tests), controlled environment (temperature, relative humidity) and kinematical field measurements (SDIC),
• Micromechanical tests on fiber-fiber bonds 3D imaging using X-ray nano-tomography and dedicated image analysis to extract relevant descriptors of fiber and fiber-bonds.

A discrete element code will be improved and used to mimic the macroscopic mechanical properties from the knowledge of the fibrous microstructure and micromechanics.

The proposed offer is part of the Carnot Insitute Polynat (http://www.celluwiz.eu/) project FibreFlex which includes academic (CNRS - 3SR Lab and LGP2) and industrial partners (CTP).

The postdoc project will be located in the ComHet research group of the 3SR Lab, a Solids Mechanics research lab of the CNRS and the Univ. Grenoble Alpes, with strong interactions with the projects partners, LGP2 and CTP.

Duration: 12 months

Starting date: may 2022

Salary: from 2663.79 €/month, depending on the professional experience

PhD in mechanics of materials or materials science

Keywords : Bio-based materials, experimental mechanics, 2D/3D imaging for heterogeneous/fibrous materials, discrete simulation

Interested applicants should fill the application form and deposit their extended CV as well as their motivation letter on the CNRS recruitment site: https://emploi.cnrs.fr/Offres/CDD/UMR5521-LAUORG-004/Default.aspx

Dealine for application: March, 7, 2022

For further details, please contact Laurent.Orgeas@3sr-grenoble.fr