Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,...
Patent
1998-07-09
2000-09-12
Weisberger, Richard
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
428358, 428359, 428400, 428393, 428105, 428107, 428113, 162 24, 162 26, 162 70, 162 72, 81161, 8120, C08B 320, C08B 306
Patent
active
061175455
DESCRIPTION:
BRIEF SUMMARY
The invention relates to cellulose microfibrils which are useful in particular as reinforcing fillers or structuring agents for composite materials.
The invention relates more particularly to surface-modified cellulose microfibrils, to a method for manufacturing them and to their use as reinforcing fillers or structuring agents for composite materials.
It is known to use fibres such as glass, plastic or carbon fibres as reinforcing fillers or structuring agents in composite materials. It has also been proposed to use cellulose fibres of various origins as reinforcing fillers. Thus, European patent No. 0,200,409 describes the use of cellulose fibres of bacterial origin as reinforcers for thermosetting materials. International patent application WO 93/10172 describes the use of cellulose microfibrils of natural origin as reinforcing fillers for thermosetting resins. Mention may also be made of the article by P. Gatenholm et al., published in J. Appl. Pol. Sc. - vol. 45, 1667-1677 (1992) under the title "Biodegradable Natural Composites", which describes the use of natural, and thus biodegradable, fibres, such as cellulose fibres, as reinforcing fillers for composite materials based on biodegradable polymers such as polyhydroxybutyrate or polyhydroxyvalerate.
However, one of the problems encountered in the use of such fillers lies in the difficulty in ensuring good dispersion of the filler in the composite material. The phenomenon of agglomeration of the filler is observed in particular with the cellulose fibres used as fillers for matrices made of thermoplastic resin. Poor dispersion of the filler in the matrix of a composite material seriously affects its mechanical properties. In order to improve the dispersion of the fibres, it has been proposed to chemically modify or to hydrolyse the cellulose fibres. However, in order to obtain a material with properties that are improved by reinforcing fillers, it is necessary to add a large amount of fibres. The use of microfibrils makes it possible to improve the properties of material reinforced with a low level of filler, if the microfibrils are appropriately dispersed in the material. Such a dispersion is often difficult to obtain.
To overcome these drawbacks, the invention proposes surface-modified cellulose microfibrils, and a method for manufacturing these microfibrils. The products of the invention retain the intrinsic properties of cellulose since the microfibrils still consist of an arrangement of unmodified cellulose chains. However, they have a surface containing chemical species whose nature is determined on the basis of the matrix to be reinforced, in order to make the cellulose microfibrils chemically compatible with the matrix in which they will be dispersed.
To this end, the invention proposes surface-modified cellulose microfibrils having an L/D ratio of greater than 20, preferably greater than 100, and an average diameter of between 1 nm and 50 nm (L being the length of the microfibril and D its average diameter). These microfibrils are characterized in that at least 25%, on a number basis, of the hydroxyl functions present at their surface are esterified with at least one organic compound comprising at least one function which can react with the hydroxyl groups of cellulose. This organic compound will be referred to in the rest of the text as the esterifying organic compound. Advantageously, the percentage of esterification is at least 50%.
The organic residues originating from the esterifying organic compounds bound to the surface of the microfibrils ensure compatibility of the cellulose microfibril with the medium in which it is dispersed.
Thus, in the preferred embodiment of the invention, when the esterifying organic compound residue is an acetic radical, the surface-modified microfibrils are compatible in particular with cellulose acetate and will advantageously be able to be used as reinforcing fillers for composite materials based on cellulose acetate, as will be described below.
The cellulose microfibrils can be of any origin, for example
Cavaille Jean-Yves
Chanzy Henri
Fleury Etienne
Sassi Jean-Fran.cedilla.ois
Rhodia Chimie
Seugnet Jean-Louis
Weisberger Richard
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