MX2012008562A - Dried nanocrystalline cellulose of controllable dispersibility and method therefor. - Google Patents

Abstract

Dried nanocrystalline cellulose (NCC), in particular films of NCC, of controlled water dispersibility and a method to control the dispersibility of dried NCC by controlling electrolyte solution ionic strength and ion valency is described. Neutral M-NCC suspensions containing monovalent counterions (e.g., M = Na+, K+, NH4+, Et4N+) produced by neutralization of acid-form NCC (H-NCC) with the appropriate hydroxide, are readily dispersible in water when fully dried; this is in contrast to H-NCC. The dispersion of dried M-NCC in aqueous media is effectively prevented by a combination of (1) increased electrolyte concentration and ionic strength, and (2) higher valency of the cation component of the dissolved salt. Additionally, pre-treatment of dried M-NCC films with an electrolyte solution having a polyvalent cation, for example a divalent or trivalent cation is sufficient to prevent the subsequent dispersion of the M-NCC film in pure water.

Description

NANOCRYSTALLINE CELLULOSE DRY DISPERSIBILITY CONTROLLABLE AND METHOD FOR THE SAME TECHNICAL FIELD This invention relates to dried forms of nanocrystalline cellulose (NCC) of controlled dispersibility in water; and a method for producing a water dispersible dry form of non-dispersible NCC or modified water dispersibility; in particular the invention relates to dried M-NCC films which are not water dispersible and which have advantages over corresponding H-NCC films, where M is a neutral cation.

PREVIOUS TECHNIQUE Suspensions of nanocrystalline cellulose produced by hydrolysis with sulfuric acid (ie, the H-NCC form) are not dispersible in water or other aqueous solvents once they have completely dried. When the H + proton counterion is exchanged for monovalent M + cationic counterions, the dry forms of M-NCC can be spontaneously redispersed in water to give suspensions with properties similar to those of the native suspensions after sound treatment [1].

As examples of M-NCC dispersible in water, suspensions Na-NCC, K-NCC, Cs-NCC, NH4-NCC, Et ^ N-NCC, (tetraethylammonium + -NCC) Bu3MeN-NCC (tributylmethylammonium + -NCC), Bu4N-NCC (tetrabutylammonium + -NCC), and Hex4N-NCC (tetrahexylammonium + -NCC) are produced by titrating suspensions of H-NCC with the appropriate hydroxide solutions at neutral pH. The resulting M-NCC suspensions can be dried by various methods, including freeze drying, spray drying and self-supporting film formation or coatings on substrates. These dry forms of NCC are dispersed in deionized water to give colloidal suspensions of NCC.

Although H-NCC films have the advantage of being non-dispersible in water not shared by the aforementioned M-NCC films, they do not exhibit other advantages associated with M-NCC films.

Industrially, aqueous suspensions of NCC will have to be dried in order to transport and store large amounts of NCC. Therefore, dry NCC must be completely redispersible in water for applications that require the use of aqueous suspensions that have full expression of the unique properties of NCC. Also, the drying process should not interfere with the intrinsic / inherent properties of the NCC particles themselves and / or those of the resulting aqueous NCC suspension. The sodium form of NCC, Na-NCC (obtained by stoichiometrically exchanging the protons of the original acid form H-NCC with sodium, for example, by neutralization with NaOH), is the form of choice for this purpose. It is completely redispersible in water, much more thermally stable than H-NCC (thermal decomposition starts at 300 X for Na-NCC as opposed to 180 X for H-NCC) and does not undergo autocatalyzed desulfation (loss of surface sulfate ester groups with negative charge resulting in electrostatic stability of aqueous NCC suspensions) or degradation of cellulose after drying and during prolonged storage of the dried material.

It seems likely that Na-NCC will be used extensively in the industry as the initial form of NCC from which products will be manufactured. However, its dispersibility in water may not be desirable in many applications, although thermal and chemical stability may be. As such, dry Na-NCC has some advantages but also some disadvantages in relation to dry H-NCC.

BRIEF DESCRIPTION OF THE INVENTION This invention seeks to provide a dry form of nanocrystalline cellulose (M-NCC), particularly (but not limited to) a solid film, in which the dispersibility in water is controlled, and in particular to provide such a film which is non-dispersible in water. but that retains the advantages of a corresponding water dispersible film from which it can be derived.

Another object of this invention is to provide a method for controlling the dispersibility in water of a water dispersible dry form of M-NCC such as a solid film, and it is a particular object to provide said method in which a water dispersible film is converted to a film that is non-dispersible in water but retains the advantages of a corresponding water dispersible film from which it can be derived.

In one aspect of the invention, a nanocrystalline cellulose (M-NCC) is provided in a dry form in which monovalent M + cations of a water-dispersible dry form of M-NCC are at least partially replaced by polyvalent cations and mixtures of the same, with which the dispersibility in water is at least reduced.

In another aspect of the invention, there is provided a method for controlling the water dispersibility of a M-NCC dispersible in water in a dry form in which M is a monovalent cation M + comprising: pretreating the dry form with a solution of electrolytes containing polyvalent cations and mixtures thereof, to at least partially replace the monovalent cations by said polyvalent cations.

By adjusting the content of the monovalent cations replacing them with the polyvalent cations, the dispersibility in water of the dry form can be controlled, more especially by a change of dispersible in water at different levels of dispersibility or non-dispersibility culminating in a complete non-dispersibility .

In this way, the advantages associated with, for example, Na-NCC films dispersible in water can be retained in a film which is non-dispersible in water; and the advantages associated with H-NCC films that are also non-dispersible in water, are avoided.

DETAILED DESCRIPTION OF THE INVENTION In this specification, "dry form" with reference to NCC refers to a physical form of NCC produced by means of handling a suspension of the NCC in a liquid vehicle such that the NCC passes from the suspension to a dry solid form. in which the liquid vehicle of the suspension has been removed or essentially removed. Said dry solid forms include self-supporting films, sheets, pellets, threads or filaments, powders, flakes or lamellae or a coating on a support. Handling includes, for example, forming a film of the suspension and drying the formed film by evaporation, for example, drying in air at a temperature at which the formed film remains viable and retains its film form, typically the temperature will be below a temperature at which the shape of molded film is altered by the boiling of the liquid vehicle, and, therefore, will typically be a temperature below 100 ° C for an aqueous suspension and may conveniently be room temperature. , or drying the suspension by freeze drying or spray drying to remove the liquid vehicle and leave a dry form of the NCC. A formed film can be a self-supporting film, or it can be a coating on a support, for example, a paper, metal, or plastic object; the object may be flat or plain such as a sheet or it may be an article configured with surfaces or flat or non-planar faces. The invention is further described and illustrated by reference to the particular embodiment in which the dry form is a film and more especially a self-supporting film, but the teachings apply equally to other dry forms such as those mentioned above.

An M-NCC film such as Na-NCC can be converted to a polyvalent ion form, for example, Ca-NCC, according to the invention by brief treatment with a relatively dilute CaC solution.

It is much easier, and less costly, on an industrial scale to spray a diluted CaCl2 solution onto a dry NCC film than to use an acid solution such as HCI or H2SO4 to spray the film (or alternatively use an exchange resin). H + form cations to convert the dispersed Na-NCC suspension to H-NCC before drying). It is also less harmful to the environment.

The exchange of Na + by Ca2 + is rapid, often occurring in less than 1 minute when a delegated film is immersed in CaC ^ solution.

It is possible that only the outer layers of a film of Thicker Na-NCCs need to be exchanged for a polyvalent ion form such as Ca-NCC to prevent dispersion.

The polyvalent ion form such as Ca-NCC film thus produced retains the optical properties and thermal and physicochemical stability of the Na-NCC film.

A non-dispersible plastic film can possibly be produced from Na-NCC films plasticized in this way.

The polyvalent cations are in particular neutral ions, for example metal cations and can be, for example, divalent cations M2 +, trivalent cations M3 +, tetravalent cations M4 + or a mixture of two or more thereof. Other "multivalent" ions that can act as a polyvalent cation may include polyelectrolytes (polymer chains having ionic charges distributed over their entire length, each charge may be monovalent or higher, eg, divalent, etc., but the numerous charges may allowing the polymer chain to act as a bridging agent) such as starches and polyamines or cationic proteins (e.g., bovine serum albumin) having a pKa sufficiently high (ie, above that of the acid sulfate ester groups) and carboxylic acid groups attached to the NCC particles) to enable them to be cationic in the presence of the anionic NCC particles. The proteins that have a pl or pKa high enough to be cationic while the NCC remains anionic are of particular interest. The NCC pKa is between 3 and 4; proteins that have a pKa or pl above 3, such as bovine serum albumin are, therefore, of special interest.

Typical polyvalent cations are Ca2 +, Cu2 +, Fe2 +, Mg2 \ Zn2 +, Ni2 +, Mn2 +, Al3 +, Fe3 +, Sn4 +, Pb4 + and Ti4 +. Preferred divalent cations are Ca + and Cu2 +; and a preferred trivalent cation is Al3 +; mixtures of polyvalent cations are within the scope of the invention.

Dispersibility of dry NCC in aqueous electrolyte solutions When placed in aqueous solutions of electrolytes that are composed of a monovalent cation and anion, the Na-NCC films retain their structure at ionic strengths of solution (/ = l? C, .z, 2, where c, is the concentration molar of ionic species / ', zi is the charge number of that ionic species, and the sum is taken over all the ionic species n in the solution) > 10 mM, regardless of the pH of the solution (for example, in HCl, NaOH, or NaCl). At sufficiently high ionic strengths (~ 2 M), the films do not swell much and are not dispersible, although the iridescence always changes at longer wavelengths.

At a given molar concentration, it is found that electrolytes containing a divalent or trivalent cation or anion (eg, Na2S04, CaCl2, CuS04, AI (N03) 3) are more effective in preventing dispersion or swelling of dry M-NCC than those with only monovalent ions such as NaCl or KCI, due to their higher ionic strength and, where applicable, the bridging action of a polyvalent cation as described further ahead.

At a given ionic strength, electrolytes containing a divalent or trivalent cation (eg, CaCl2, CuS04, AI (03ta), according to the invention, are more effective in preventing dispersion than electrolytes with monovalent cations (e.g. , NaCl, KCI) In contrast, the valence of the anion does not affect the dispersion of the Na-NCC film, only the polyvalent cations contribute to the bridging mechanism described below. Table 2 and Figure 1.

There seem to be two different mechanisms of prevention of dry NCC film dispersion in electrolyte solutions: (a) For all dissolved ionic species, regardless of valence, the effects of electrolyte-induced gelling of the polyelectrolyte NCC caused by the Donnan equilibrium [2] prevent the dispersion of Na-NCC (or other M-) films. NCC dispersible in water) or other forms of dry NCC. It is known that the added NaCl causes gelling in suspensions of aqueous biphasic NCC [3], the minimum ionic strength necessary to cause gelation decreases with increasing NCC concentration. Because solid forms of NCC such as films have a very high effective NCC concentration, much lower electrolyte concentrations can prevent their dispersion. The counterions associated with the sulfate ester groups on the NCC surface create an ionic imbalance between the inside of the film structure and the surrounding aqueous media, causing the aqueous solution (water, dissolved cations and anions) to penetrate the film structure. . Once inside the film, the electrolyte solution produces two competing effects, swelling (caused by water that breaks NCC layers) and gelation (caused by electrolyte ions that protect electrostatic repulsion between adjacent anionic NCC particles). ). The higher the ionic strength of the solution surrounding the film, the greater will be the tendency of the dissolved ions to cause gelation of the NCC film, reducing swelling and preventing film dispersion. (b) In addition to this equilibrium gelling effect of Donnan, divalent and trivalent cations are also capable of forming "bridges" between two or three ester sulfate groups (monovalent) in separate NCC particles, and, therefore, are more effective in preventing the dispersion of NCC films dry and other forms. Also, divalent and trivalent cations are more likely to remain within the solid NCC film structure if it is then placed in pure water.

These mechanisms can be exploited separately and highlighted as two different ways of obtaining changed barrier properties and dispersibility of dry NCC films.

Effect of pretreatment with an electrolyte solution on the dispersibility in water of dry NCC If a film of Na-NCC dispersible in water (for example) is soaked in a solution of electrolytes containing a divalent or trivalent cation which is of sufficient concentration / ionic strength, and then placed in pure water, it will no longer disperse. As described above, divalent or trivalent cations form bridges or entanglements between two sulfate ester groups on the NCC particle surfaces, effectively causing ion exchange with the original sodium counterions and forming cationic bonds between NCC particles. . Figure 2 illustrates the dispersibility of Na-NCC films previously treated in this manner. The pretreatment with diluted Ca2 + solutions (50 mM) prevents the dispersion of the treated film in pure water, while the previous treatment with solutions of very high ionic strength (4.3 M) of monovalent cations such as Na + no. This type of exchange of counterions has been described in the literature and used to interlace and prevent the dispersion of alginate films [4,5].

A minimum pre-treatment time is necessary, depending on the concentration of electrolytes: the exchange of counterions the fast, occurring in about one minute for a film of Na-NCC that has a thickness of 90 μ ?? placed in 50 mM CaCl2 (see Figure 3); it can be very brief (<10 s) in concentrated electrolyte solutions (see Table 3). The exchange is also reversible if the movie is not dried For example, if the newly formed Ca-NCC film is immediately exposed to concentrated NaCl solution (or to another concentrated electrolyte), a film of Na-NCC (water dispersible) will re-form. The higher the concentration or ionic strength of the electrolyte solution with which the Na-NCC film is treated, the less swelling occurs when the film is placed in pure water (see Figure 4). The results are summarized in Table 4 for various electrolytes that have ions of different valences.

Effect of the counterions on the dispersibility of dry M-NCC The nature of the M-NCC counterion also affects the dispersibility of the dry product in aqueous electrolyte solutions. Two series of cations were examined: monovalent alkali cations (Na +, K +, Cs +) and monovalent organic ammonium counterions (NH4 +, EI4N +, Bu3MeN +, Bu4N +, and Hex N +). The resistance of dry NCC films to dispersion in water has been examined and appears to be slightly improved as the hydration number of the alkali counterions decreases (in the order Na +> K +> Cs + [6]) [1 ] In the case of monovalent organic counterions, the effects of hydrophobicity and steric repulsion must compete: the longer hydrocarbon chains are more hydrophobic and repel water better, but they also experience greater steric repulsion, which will tend to prevent close proximity of water. M-NCC particles, weakening the nter-NCC hydrogen bond network and thus facilitating the penetration of water into the structure of the film. It was found that the dispersibility properties in electrolyte solutions of dried M-NCC films with organic counterions are minimally affected compared to M-NCC films with alkali counterions (data not shown). further, the high counter hydrophobicity slightly reduces the effectiveness of pretreatment with electrolyte solution (eg, 50 mM CaCl2) in preventing the dispersion of NCC film in pure water compared to less hydrophobic counterions, as shown in Table 5 For example, after a 1 min pre-treatment in 50 mM CaC solution, a complete ion exchange was obtained on a Na-NCC film, while the ion exchange was only 78% complete on a Hex4N film. -NCC (the data is not shown). However, it is reasonable to assume that another 60 s in the CaCl2 solution would result in a complete exchange. Although the nature of the counterions examined here does not significantly affect the dispersibility of the dry product in aqueous solutions, other M + organic counterions can reduce the dispersibility to a greater degree.

A new range of uses for NCC barrier films can be seen based on the results presented here. For example, a Na-NCC film in which areas or patterns of different colors have been produced, for example, thermally during the formation (USSN 12/591, 906) or by other means can be treated with a CaCl2 solution. more diluted (for example, 50 mM), which will not affect the final color and will prevent the dispersion of the film in water. NCC films resulting from the exchange of counterions of, for example, Na-NCC films with, for example, CaC solutions have the advantage of retaining the thermal and physical-chemical stability properties of the original films, dispersible in water while they are Not dispersible in water. It should be mentioned that the highly swollen NCC films are quite fragile and probably do not have the barrier properties; divalent or trivalent cation high ionic strength solutions are more likely to maintain the structural integrity and barrier properties of the films. The behavior of the film can be different if it is supported (i.e., as a coating) or plasticized.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram illustrating the dispersibility after 24 h in various electrolyte solutions of different concentration of solid Na-NCC films. A solid Na-NCC film A is placed in the electrolyte solution E and after 24 h, it can retain its structure without bloating B, swelling but remaining structurally intact C, or disintegrating and / or dispersing in the aqueous medium, D.

Figure 2 is a diagram illustrating the water dispersibility of Na-NCC films exposed for 1 min to electrolyte solutions of different concentrations.

Figure 3 is a graph illustrating the exchange of calcium ions with sodium ions when treating a film of Na-NCC with a thickness of ~ 90 μ? T? with a 50 mM CaCl2 solution for different times.

Figure 4 is a graph illustrating the increase in mass due to swelling of a Na-NCC film placed for 30 s in deionized water after a 30-s pretreatment in CaCl 2 (ac) solutions.

EXAMPLES TABLE 1 Dispersion of the Na-NCC film in electrolyte solutions that they contain monovalent cations Salt C (mM) Swelling after 5 Dispersion mine after 18 h NaCI 1 Strong, immediate 30 min KCI 1 Strong, immediate 30 min Na2S0 1 Strong, immediate 2 hc NaCI 15 Moderate, in 1 min N KCI 15 Moderate, in 1 min N Na2S0 15 Light N a Relative degree of swelling and time in which it becomes noticeable. b All-night samples, unaltered; time to the dispersion indicated in parentheses. 0 Unaltered films are separated within 20 min.

TABLE 2 Dispersion of the Na-NCC film in electrolyte solutions that contain di-vivalent cations AI (N03) 3 1 Light N CaCI2 10 Minimum0 N AI (N03) 3 10 Minimum "N a Relative degree of swelling after 5 min in solution. b The film becomes transparent and colorless (infrared iridescence [IR]) but does not visibly swell.

TABLE 3 Effect of previous treatment with CaCb solution on the dispersibility of a Na-NCC film in pure water [CaCl2] (M) Time in CaCl2 Swelling Dispersion in water ac. (s) in water < 1a S S 1 s S 5 s S 0. 10 10 s S 20 s N 30 Nb N < 1 to Nb N 1 Nb N 5 Nb N 1. 00 10 Nb N 20 Nb N 60 Nb N a The film was submerged as briefly as possible in the electrolyte solution. b The film swelled only as much as was represented by the increase in the chiral nematic passage; the degree of swelling decreased as the treatment time increased (for example, a film treated for 60 s in 1 M CaCl 2 showed red / gold iridescence, while the same film treated for 5 s in 1 M CaCl 2 was clear and colorless (in the IR region)).

TABLE 4 Changes in Na-NCC film structure over time when left unaltered in pure water after pretreatment for 1 min in the indicated electrolyte solutions Transparent (IR range).

TABLE 5 Dispersibility in pure water (after <18 h) of dry M-NCC containing neutral monovalent counterions, after pretreatment for 1 min in electrolyte solutions D = dispersion, S = moderate swelling, s = minimal swelling, ND = no dispersion or visible swelling. The times in parentheses indicate the time to dispersion.

References 1. Dong, X.M. and Gray, D.G. "Effect of counterions on ordered phase formation in suspensions of charged rodlike cellulose crystallites," Langmuir 13 (8): 2404-2409 (1997). 2. Towers, M. and Scallan, A.M. "Predicting the ion exchange of kraft pulps using Donnan theory," J. Pulp Pap. Sci. 22 (9): J332-J337 (1996). 3. Revol, J.-F., Godbout, L. and Gray, D.G. "Solid self-assembled films of cellulose with chiral nematic order and optically variable properties," J.

Pulp Pap. Sci. 24 (5): 146-149 (1998). 4. Nakamura, K., Nishimura, Y., Hatakeyama, T., Hatakeyama, H. "Thermal properties of water-insoluble alginate films containing di- and trivalent cations, "Thermochim, Acta 267: 343-353 (1995). 5. Nokhodchi, A, Tailor, A. "In situ cross-linking of sodium alginate with calcium and aluminum ions to sustain the reagent of theophylline from polymeric matrices," II Drug 59: 999-1004 (2004). 6. Davies, C. W. Ion Association; Butterworths 1962, p. 150

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - A nanocrystalline cellulose (M-NCC) in a dry form, in which monovalent M + cations of a water-dispersible dry form of M-NCC are at least partially replaced by polyvalent cations, whereby the dispersibility in water is at least reduced.

2 - . 2 - Nanocrystalline cellulose (M-NCC) according to claim 1, further characterized in that the dry form is a self-supporting film, sheet, powder, flakes or lamellae.

3. - The nanocrystalline cellulose (M-NCC) according to claim 1, further characterized in that the dry form is a self-supporting film.

4. - The nanocrystalline cellulose (M-NCC) according to claim 1, further characterized in that the dry form is a coating on a support.

5. - The nanocrystalline cellulose (M-NCC) according to any of claims 1 to 4, further characterized in that the monovalent M + cations are completely replaced by divalent M2 + cations.

6. - The nanocrystalline cellulose (M-NCC) according to any of claims 1 to 4, further characterized in that the monovalent M + cations are completely replaced by trivalent M3 + cations.

7. - The nanocrystalline cellulose (M-NCC) according to claim 5, further characterized in that the divalent cations M2 + are selected from Ca2 + and Cu2 +.

8. - The nanocrystalline cellulose (M-NCC) according to claim 6, further characterized in that the trivalent cations M3 + are Al3 +.

9. - The nanocrystalline cellulose (M-NCC) according to any of claims 1 to 3, further characterized in that the polyvalent cations comprise polymer chains having cationic charges distributed over their entire length; each ionic charge is monovalent or higher so that the polymer chain is polyvalent.

10. - The nanocrystalline cellulose (M-NCC) according to claim 3, further characterized in that the monovalent M + cations are completely replaced by polyvalent cations selected from the group consisting of divalent M2 + cations and trivalent M3 + cations.

1. The nanocrystalline cellulose (M-NCC) according to claim 4, further characterized in that the monovalent cations M + are completely replaced by polyvalent cations selected from the group consisting of divalent cations M2 + and trivalent cations M3 +.

12. - A method for controlling the dispersibility in water of a M-NCC dispersible in water in a dry form, in which M is a monovalent cation M + comprising: pretreating the dry form with an electrolyte solution containing polyvalent cations, for at least partially replace the monovalent cations by said polyvalent cations.

13. - The method according to claim 12, further characterized in that the pretreatment comprises submerging the dry form in the electrolyte solution.

14. - The method according to claim 12, further characterized in that the pretreatment comprises spraying the dry form with the electrolyte solution.

15. The method according to any of claims 12 to 14, further characterized in that the polyvalent cations are selected from the group consisting of divalent cations M2 +, trivalent cations M3 +, tetravalent cations M4 + and mixtures of two or more thereof.

16. - The method according to any of claims 12 to 15, further characterized in that the dry form is a self-supporting film, sheet, powder, flakes or lamellae or a coating on a support.

17. - The method according to any of claims 12 to 14, further characterized in that the dry form is a self-supporting film.

18. - The method of compliance with any of the claims 12 to 14, further characterized in that the dry form is a coating on a support.

19. - The method according to any of claims 12 to 18, further characterized in that the polyvalent cations are selected from the group consisting of Ca2 +, Cu2 + and Al3 +.

20. - The method according to any of claims 12 to 14, further characterized in that the polyvalent cations comprise polymer chains having cationic charges distributed over their entire length; each ionic charge is monovalent or higher so that the polymer chain is polyvalent.