Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
1999-05-07
2001-05-15
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S731000, C106S805000, C426S658000, C514S781000
Reexamination Certificate
active
06231657
ABSTRACT:
The present invention relates to compositions comprising essentially amorphous cellulose nanofibrils, carboxycellulose as additive, and optionally co-additives, as well as to a process for their preparation.
The invention relates to the suspensions obtained from such compositions.
Cellulose microfibrils and nanofibrils are well-known compounds which are used as additives for modifying the texture of media into which they are introduced. In the case of fluid media, they modify their viscosity or even their rheological profile.
However, there is a problem with cellulose microfibrils and nanofibrils, which is that they are obtained in the form of an aqueous suspension whose solids content is relatively low, from about 1 to about 5% by weight approximately. The development of these products in such a form is thus not economically viable, either in terms of storage or transportation, for example. It has thus been considered, naturally, to present them in a dry form. Unfortunately, when the cellulose microfibril or nanofibril suspensions are dried, very strong hydrogen bonds are created between the fibrils which make it necessary to use very high-shear means to redisperse these fibrils, when it is possible to resuspend them.
Attempts have been made to propose solutions to the problem of drying cellulose microfibrils. Thus, additives have been introduced during the preparation of microfibril suspensions, and more particularly at the time of the homogenization.
For example, U.S. Pat. No. 4,481,076 proposes drying the cellulose microfibrils obtained from wood pulp in the presence of additive. The contents which are most favourable for good redispersion after drying, and thus for a good viscosity level of the suspension, are from about 50 to about 100% by weight relative to the dry microfibrils. As may be observed, the amounts of additives introduced are very large. Moreover, these methods are not entirely satisfactory, even though it is possible, in principle, to redisperse these dried microfibrils, since the means used for the redispersion are still very high-shear.
International patent application WO 95/02966 describes the supplementation of microcrystalline cellulose with xanthan gum or carboxymethylcellulose, with contents of less than 33% by weight relative to the weight of microcrystalline cellulose. However, extremely high-shear conditions are used to suspend the dried cellulose, since they are carried out under the standard conditions for stirring formulations intended for applications in the food sector. The dried microfibrils can thus not be considered as easily redispersible.
The teaching provided by the prior art regarding the redispersion of microcrystalline cellulose microfibrils, and in particular those obtained from wood pulp, cannot be transposed to cellulose nanofibrils, obtained from cells with primary walls.
Firstly, the cellulose microfibrils obtained from wood are derived from secondary walls. This means that they have a greater than 70% degree of crystallinity. During the step of homogenization of the microfibrils obtained from wood, rather than observing a disentangling of the fibres, as is the case during the step of homogenization of the cellulose nanofibrils obtained from primary walls, these fibrils are found to break. Consequently, the cellulose microfibrils obtained from secondary walls do not have the characteristics of amorphous fibrils, but, rather, have the characteristics of microcrystalline microfibrils.
Moreover, the morphologies of the microfibrils and nanofibrils are different. In point of fact, the microcrystalline microfibrils, for example obtained from cellulose with secondary walls, such as wood pulp, are conventionally in the form of aggregates from a few tens of nanometers to a few micrometers, consisting of elementary fibrils, which cannot be disentangled during the homogenization step. As regards the cellulose nanofibrils obtained from cells with primary walls, they have a diameter of not more than a few nanometers and have the appearance of filaments.
It is relatively well established that the difficulty in redispersing cellulose microfibrils or nanofibrils is associated with the existence of numerous hydrogen bonds between the fibrils, which are created during drying. Now, the number of hydrogen bonds per weight unit of cellulose is directly associated with the morphology of the said microfibrils or nanofibrils, and, more specifically, proportional to their specific surface; the greater the specific surface, the larger the number of hydrogen bonds per weight unit of cellulose. Given the particular morphology of the cellulose nanofibrils obtained from cells with primary walls, the specific surface of these nanofibrils is much higher than that of the microfibrils. A person skilled in the art would thus logically expect to encounter greater difficulties in redispersing cellulose nanofibrils.
Thus, given the state of the art presented above, it could be envisaged that larger amounts of additive than those used for the microfibrils would be necessary in order to obtain good redispersion of the dried nanofibrils.
However, the present invention has shown, against all expectations, that relatively low amounts of additive are sufficient to allow good redispersion of the dried nanofibrils, and without it being necessary to use extremely high-shear conditions. In addition, it has been found, surprisingly, that amounts of the order of those recommended in the prior art have considerable drawbacks as regards conserving the Theological properties of the nanofibrils.
This arises from the difference in behaviour between the crystalline microfibrils, for example the cellulose microfibrils obtained from secondary walls, and the nanofibrils obtained from cells with primary walls.
The reason for this is that the non-supplemented microcrystalline microfibrils are not dispersible in aqueous medium; they separate out by settling as soon as the stirring is stopped, even when very high-shear stirring means are used. Furthermore, they do not give shear-thinning Theological properties.
On the other hand, the nanofibrils obtained from primary walls are of a nature which is dispersible in aqueous medium. In addition, they give a quite specific Theological profile, of shear-thinning type, to the medium into which they are introduced.
Now, in general, drying adversely affects not only the capacity for redispersion of the dried nanofibrils and their viscosity, but also their rheological profile. Thus, large amounts of additives of the type usually used to redisperse microcrystalline microfibrils, such as those obtained from wood, i.e. as much additive as microfibrils, do not give good results as regards the shear-thinning Theological profile of the cellulose nanofibrils obtained from primary walls: the profile becomes more Newtonian, i.e. less shear-thinning.
As may be observed, the consequences of drying essentially amorphous cellulose nanofibrils in terms of the redispersion of these fibrils and their Theological properties (viscosity at low and high shear, rheological profile) cannot be solved in a satisfactory manner based on the knowledge obtained from the supplementation of microcrystalline microfibrils, for example of microfibrils obtained from cells with secondary walls.
The present invention thus provides a simple and effective solution to these problems.
These aims and others are achieved by the present invention, a first subject of which is a composition comprising essentially amorphous cellulose nanofibrils, carboxycellulose with a degree of substitution of less than or equal to 0.95 as additive, and optionally at least one co-additive, the content of additive and of optional co-additive being less than or equal to 30% by weight relative to the weight of nanofibrils and of additive and optional co-additive.
Another subject of the present invention consists of a process for preparing a composition, in which cellulose nanofibrils are prepared from cellulosic pulp by carrying out at least one extraction, optionally followed by at least one step of bleaching t
Benchimol Joël
Cantiani Robert
Guerin Gilles
Senechal Alain
Vincent Isabelle
Brunsman David
Rhodia Chimie
Seugnet Jean-Louis
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