POLYSACCHARIDE SUSPENSION, METHOD FOR ITS PREPARATION, AND USE THEREOF

Abstract

The present invention relates to a novel stable colloidal polysaccharide suspension containing ?(1.fwdarw.3)-glucan, a cost-effective method for its preparation, and possible uses of these polysaccharide suspensions.

Claims

1. A phase-stable, colloidal polysaccharide suspension characterized in that the polysaccharide consists at least partly of ?(1.fwdarw.3)-glucan, that the ?(1.fwdarw.3)-glucan was never dried during its preparation, that the suspension was prepared from a press cake having a polysaccharide content between 4 and 80% by weight, preferably between 15 and 45% by weight, and that the polysaccharide concentration of the suspension is between 0.01 and 50% by weight, preferably between 1.0 and 20% by weight.

2. A suspension as claimed in claim 1, characterized in that the ?(1.fwdarw.3)-glucan content of the polysaccharide is between 1 and 100% by weight, more preferably between 80 and 100% by weight.

3. A polysaccharide suspension as claimed in claim 1, wherein at least 90% of the ?(1.fwdarw.3)-glucan consist of hexose units and at least 50% of the hexose units are linked via ?(1.fwdarw.3)-glycosidic bonds.

4. A polysaccharide suspension as claimed in claim 1, containing apart from the polysaccharide material 1 to 200% by weight, related to the polysaccharide quantity, in incorporated additives selected from the group comprising pigments, titanium oxides, especially substoichiometric titanium dioxide, barium sulfate, ion exchangers, polyethylene, polypropylene, polyester, latex, activated carbon, polymeric superabsorbents, and flame retardants.

5. A method for preparing a polysaccharide suspension, characterized in that a. the base material used is a press cake of an initially moist polysaccharide material consisting at least partly of ?(1.fwdarw.3)-glucan, b. the press cake has a solids content between 4 and 80% by weight (related to the entire press cake), preferably between 15 and 45% by weight, c. the desired polysaccharide concentration is adjusted to between 0.01 and 50% by weight (related to the entire suspension), preferably to between 1.0 and 20% by weight, d. subsequently comminution with a dispersing unit is carried out.

6. A method as claimed in claim 5, wherein after step d. an additional treatment with a dispersing unit, preferably with a high pressure homogenizer, is carried out.

7. A method as claimed in claim 5, wherein the degree of polymerization of the ?(1-.fwdarw.3)-glucan used, expressed as weight average DP.sub.w, is between 200 and 2,000, preferably between 400 and 1,000.

8. A use of the polysaccharide suspension as claimed in claim 1 for the production of polysaccharide layers.

9. A use of the polysaccharide suspension as claimed in claim 1 as a binder for other materials, wherein the adhesive effect is achieved by drying and the formation of hydrogen bonds.

10. The use of the polysaccharide suspension as claimed in claim 9, wherein the other material is a nonwoven material.

11. The use of the polysaccharide suspension as claimed in claim 9, wherein the other material is present in a quantity of 200 to 1000% by weight, related to the polysaccharide quantity.

12. A use of the polysaccharide suspension as claimed in claim 1 for the preparation of dried polysaccharide powder.

13. A dry polysaccharide powder as claimed in claim 12, prepared by spray drying.

14. A use of the polysaccharide suspension as claimed in claim 1 as a viscosity modifier.

Description

EXAMPLES

[0050] General information: percentages are always to be understood as % by weight unless indicated otherwise.

Example 1

[0051] A press cake of water-containing, initially moist ?(1.fwdarw.3)-glucan (dry matter content=17.6% by weight) is suspended in deionized water and, using an Ultraturrax? (UT), type IKA T50 basic, 6,000 rpm, is comminuted for 4 minutes. In this experiment, the suspension to be comminuted contained 3.05% by weight of ?(1.fwdarw.3)-Glucan (atro). The suspension prepared in this way was divided into two subquantities, and one subquantity was additionally pumped in circulation via a high pressure homogenizer (HDH), type GEA Niro Soavi NS 1001L-2K, operating pressure 1,000 bar, for 2 passes. Then, the two glucan suspensions were characterized based on viscosity and water retention capacity.

[0052] The water retention capacity (WRC) of the glucan particles was determined as follows: an exactly defined quantity of suspension was introduced into special centrifuge tubes (with a drain for the water). Then, centrifuging was carried out for 15 min at 3,000 rpm, and the moist glucan was weighed immediately thereafter. The moist glucan was dried over night at 105? C., and then the dry weight was determined. The WRC was calculated according to the following formula:

WRC[%]=(m.sub.f?m.sub.t)/m.sub.t*100 [0053] (m.sub.f=moist mass, m.sub.t=dry mass)

[0054] The determined dry contents (TS) and WRC are compiled in Table 1.

TABLE-US-00001 TABLE 1 Dry contents and WRC of the glucan suspensions Suspension after UT Suspension after UT + HDH TS [%] WRC [%] TS [%] WRC [%] 3.05 1203 3.01 1538

[0055] The viscosities of the two suspensions exhibit shear-diluting behavior and do not differ in their curves (FIG. 1). The viscosities were determined using a Malvern Kinexus rheometer with a cone plate measuring system (CP4/40 S0687 SS) in a shear rate range from 10-200 s.sup.?1.

[0056] For comparison purposes, experiments with dried glucans were conducted. The glucans used were linear glucans with different degrees of polymerization (DP.sub.w 1,000 and DP.sub.w 500) and a branched glucan. In each of the three cases, the gels formed were not uniform, and there was phase separation. The suspensions were adjusted to a solids content of 2-3%, pre-comminuted by treatment in the Ultraturrax? (UT, IKA T50 basic, 6,000 rpm) for 4 min, and then treated with the high pressure homogenizer for 2 passes at an operating pressure of 1,000 bar. Following that, dry content and WRC were determined (Table 2). The WRC is far below the values of the gels produced from initially moist glucan. Also, these suspensions exhibit no increase in viscosity.

TABLE-US-00002 TABLE 2 Dry contents and WRC of the gels from dried glucan Linear glucan DPw 1,000 Linear glucan DPw 500 Branched glucan TS [%] WRC [%] TS [%] WRC [%] TS [%] WRC [%] 2.23 247 2.20 164 2.77 203

[0057] The suspensions treated in this way were swollen over night in order to make the surface more accessible. On the following day, the samples were treated again with the HDH for 4 passes at 1,000 bar. It was demonstrated that the dried glucans used are unsuitable for preparing suspensions: even after 6 passes on the HDH, there still was phase separation, and particles were visually recognizable (FIG. 2).

Example 2

[0058] By preparing a bigger quantity of glucan gel (4% by weight) in a pilot-plant-based experiment with a colloid mill (IKA Colloid Mill MK2000/10), it was to be demonstrated that even large quantities of polysaccharide can be processed into a homogeneous suspension without the use of high pressure homogenizers.

[0059] From 3.69 kg of never-dried, initially moist ?(1.fwdarw.3)-glucan (TS=16.25%) and 11.3 kg of water, a glucan gel having a solids content of 3.9% was prepared by grinding in the colloid mill (IKA Colloid Mill MK2000/10). After 15 minutes of grinding with a gap of 0.1 mm at maximum output, the glucan gel was ready. Subsequently, it was characterized as follows:

[0060] Viscosity: the glucan gel was measured on the Malvern Kinexus rheometer with a cone plate measuring system (CP4/40 S0687 SS) in a shear rate range from 10-200 s.sup.?1. The suspension according to the invention exhibited shear-diluting behavior (FIG. 3).

[0061] Microscopy: the glucan gel was filled between two microscope slides, whereby a thin layer was formed. This layer was subjected to microscopic examination. A strip of adhesive tape (Scotch tape, matt, approx. 0.3 mm) was adhered to the rim of each lower slide in order to achieve uniform layer thickness. The photos were taken on the ZEISS Discovery V12 stereomicroscope with 50-fold magnification and bottom illumination (FIG. 4). Agglomerates can be recognized that are formed from the very small particles in the suspension. However, these agglomerates can not be felt when rubbed between the fingers and will disintegrate again under the slightest shear.

[0062] Glass tube method: 10 g of glucan gel were weighed into glass tubes (length=approx. 9.7 cm, ? 2.5 cm) provided with closure caps, shaken, placed upside down, and photographed after 10 seconds. The glass tube was positioned in front of a black background and illuminated from the above using a table lamp (distance to underlying surface about 22 cm).

[0063] The photos were taken using a Canon EOS450D digital camera. Again, no particles are visible (FIG. 5). A uniform, dense film is formed along the glass wall.

[0064] The film-forming properties of these suspensions were tested on different surfaces.

[0065] The suspension according to the invention of Example 2 was applied onto polyester (PES) sheets or glass by doctoring and spraying, respectively. Both coating methods produced continuous, uniform films that adhere readily to the substrates. FIG. 6 shows the transparency of such films on PES sheets: the right-hand side of the picture is covered with the coated PES sheet; the left-hand side is not covered.

[0066] SEM photos (Hitachi S-4000 SEM scanning electron microscope) were taken of the air-dried films; here, we see the structure of the dense layer which simultaneously exhibits a large inner surface (FIG. 7).

[0067] In addition, SEM photos were taken of the freeze-dried glucan gel (FIG. 8). Here, we can notice the 3-dimensional spongy network that is formed in the glucan gel and imparts to the inventive suspension its unique properties.

Example 3

[0068] Glucan gels having different solids concentrations were produced in a manner similar to Example 2. As the solids content increases, the viscosities of the suspensions increase (FIG. 9), while the water retention capacity (WRC) decreases. While suspensions having a solids content of 3 and 4% can still be processed with an HDH, suspensions having a solids content of 5% can only be comminuted with a device with lower shear such as an Ultraturrax IKA T50 basic (IKA), as the HDH is unable to pump such highly viscous suspensions. Table 3 shows that, as the solids content increases, the viscosity increases, but the WRC decreases at the same time.

TABLE-US-00003 TABLE 3 Comparison of viscosities and WRC of the various glucan gels after comminution. Treatment after HDH after IKA after UT TS [%] 3 4 5 WRC [%] 1538 1504 506 Viscosity [50.sup.s?1] 0.2009 0.8555 1.731

Example 4

[0069] In the following example, the 3% glucan gel from Example 3 was dried in a laboratory spray dryer (B?chi Mini Spray Dryer 8-290, see FIG. 10). The particle size distribution was determined by means of laser diffraction (measuring apparatus from Helos) in iso-propanol. Parameters: supply air temperature 180? C. and exhaust air temperature 62? C.; nozzle size 1.4 mm. The particle size distribution was as follows:

x.sub.10=0.79 ?m; x.sub.50=2.2 ?m; x.sub.90=5.29 ?m; x.sub.99=8.27 ?m.

Example 5

[0070] 1.887 kg of never-dried, initially moist ?(1.fwdarw.3)-glucan (TS=39.74%) and 5.613 kg of water were used to prepare a suspension with 10% of glucan by using an IKA mill (IKA MK2000/10 colloid mill). After 20 minutes of grinding with a gap of 0.1 mm and at maximum output, the glucan suspension was ready. A stable suspension was formed which in terms of its viscosity is comparable with the 4% glucan suspension from Example 2 (FIG. 12).

[0071] Furthermore, microscopic photos (FIG. 13) were taken of the gel from Example 5 under the conditions described in Example 2. Again, small particles can be noticed which, however, also in this case cannot be felt between the fingers.