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New lignocellulosic materials

The Ph.D. project of Edwige Privas, within the Industrial Chair in Bioplastics, concerns the use of lignin in materials or material additives.


Lignin, with more than 50 million tons per year, is the second main biopolymer on the Earth after cellulose. Lignin plays a role of“glue” in the vegetal fibers that are a kind of natural composite.

Lignin is an amorphous polymer with phenol groups. Lignin has antifungal properties; its resistance to water as well as its availability are very attractive properties, considering it is the largest source of aromatic compounds on Earth. Thus, lignin is a good candidate as a sustainable material.

Currently lignin is used as an additive in concrete and starts to be used as a glue in wood or cork panels. Using lignin in composites with vegetal fibers is in research stage.

This work is focused on the preparation of new sustainable materials based on lignin and containing a large bio-content.

 

The aim is to study blends and methods allowing the preparation of various composites:
    • composites : lignin + vegetal fibers
    •  lignin + fillers


    We shall have to find a balance between fiber content and mechanical properties of the final composite. Furthermore, increasing lignin content would allow the incorporation of fillers, bringing additional properties to these composites as fire-retarding or mechanical resistance. Mixing behavior, compatibility and adhesion will be considered.

      This first year was dedicated to the preparation of the composite with mixing fibers and lignin. Composites were prepared by compression moulding (see picture n°1).

Hemp
A) Hemp

B) Hay
flax
C) Flax
Picture n°1: Compression molding composite with various natural fibers.

     Mechanical properties were obtained by applying standard AITIM 1994 for wood panels. Three point bending test (scheme n°1) is carried out in order to calculate modulus of elasticity and modulus of rupture.

 Three point bending test
Scheme n°1: Three point bending test.

     Scanning electron microscopy is used to qualify adhesion between lignin and natural fibers. We can observe total, partial or non covering of the surface of fibers by lignin (see picture n°2).

Scanning electron microscopy of jute/lignin
Picture n°2: Scanning electron microscopy of jute/lignin composite


Influence of botanical origin of fibers

      Botanical origin, maturity, extraction process of fibers involve some structural and dimensional variation of fibers (diameter, length, chemical composition…). Such variation can influence mechanical and thermal behaviour of fibers themselves and then of the final composite.

      Composite prepared with fibers with high cellulose content gives good mechanical results. That’s why flax fibers, with 64 – 85 % cellulose, are the most used fibers in polymer matrix as reinforcement.

     The influence of botanical origin is studied by producing composite based on nine different fibers (hemp, flax, sisal…).
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