Adhesive composition including deacetylated chitosan

Abstract

The present invention relates to an adhesive composition comprising at least one deacetylated chitosan, an acid and an additional compound.

Claims

1. An adhesive composition comprising: (a) from 3 to 10% by weight of at least one deacetylated chitosan having a deacetylation degree greater than or equal to 75%; (b) from 0.5 to 5% by weight of at least one organic or inorganic acid; (c1) from 0.001 to 8% by weight of a polyanionic compound, (c2) from 0.001 to 2% by weight of a polyol of formula C.sub.nH.sub.2n+2O.sub.n, wherein n represents an integer between 2 and 10; and (d) an additional amount of an aqueous support.

2. The composition according to claim 1, comprising from 4 to 6% of said at least one deacetylated chitosan, or from 1 to 3% of said at least one organic or inorganic acid, or from 0.01 to 5% of said compound (c1), or from 0.5 to 1.5% of said compound (c2), or total or partial combinations thereof.

3. The composition according to claim 1, wherein the chitosan has a molar mass ranging from 10,000 to 500,000 g/mol.

4. The composition according to claim 1, wherein the acid is sulfuric acid in an aqueous solution or an organic acid selected from carboxylic acids in an aqueous solution.

5. The composition according to claim 4, wherein the carboxylic acid is acetic acid.

6. The composition according to claim 1, wherein the compound (c1) is selected from hydroxycarboxylic acids, polycarboxylic acids, hydroxypolycarboxylic acids, polysaccharides, salts or mixtures thereof.

7. The composition according to claim 1, wherein the compound (c1) is selected from citric acid salts or succinic acid salts.

8. The composition according to claim 1, wherein the compound (c1) is trisodium citrate dehydrate, or the compound (c2) is glycerol or mannitol.

9. The composition according to claim 1, for which the ratio (a)/(b) ranges from 3/1 to 10/3, or the ratio (a)/(c1) ranges from 1/2 to 200/1, or the ratio (a)/(c2) ranges from 2/1 to 12/1.

10. The composition according to claim 1, wherein the support (d) is water.

11. The composition according to claim 1, comprising: (a) from 3 to 10% by weight of at least one deacetylated chitosan having a deacetylation degree greater than or equal to 75%; (b) from 0.5 to 5% by weight of at least one organic or inorganic acid; (c1) from 0.001 to 8% by weight of a polyanionic compound; (c2) from 0.001 to 2% by weight of a polyol of formula C.sub.nH.sub.2n+2O.sub.n wherein n represents an integer between 2 and 10, (d) an additional amount of an aqueous support, and (e) from 0.1 to 20% by weight of a polysaccharide filler.

12. An adhesive composition comprising: (a) from 3 to 10% by weight of at least one de-acetylated chitosan having a deacetylation degree greater than or equal to 75%; (b) from 0.5 to 5% by weight of at least one organic or inorganic acid; (c) at least one compound selected from: (c1) from 0.001 to 8% by weight of a polyanionic compound, (c2) from 0.001 to 2% by weight of a polyol of formula C.sub.nH.sub.2n+2O.sub.n, wherein n represents an integer between 2 and 20; and (d) an additional amount of an aqueous support; and (e) a polysaccharide filler comprising a starch from cereals.

13. The composition according to claim 12, comprising from 0.1 to 20% by weight of polysaccharide filler (e).

14. The composition according to claim 12, for which the ratio (a)/(e) ranges from 1/10 to 1/1.

15. An adhesive composition comprising: (a) from 3 to 10% by weight of at least one deacetylated chitosan having a deacetylation degree greater than or equal to 75%; (b) from 0.5 to 5% by weight of at least one organic or inorganic acid; (c) at least one compound selected from: (c1) from 0.001 to 8% by weight of a polyanionic compound, (c2) from 0.001 to 2% by weight of a polyol of formula C.sub.nH.sub.2n+2O.sub.n, wherein n represents an integer between 2 and 20; and (d) an additional amount of an aqueous support, said adhesive composition having a shear strength ranging from 7 to 100 MPa.

16. The composition according to claim 15, comprising from 4 to 6% of said at least one deacetylated chitosan, or from 1 to 3% of said at least one organic or inorganic acid, or from 0.01 to 5% of said compound (c1), or from 0.5 to 1.5% of said compound (c2), or total or partial combinations thereof.

17. The composition according to claim 15, wherein the chitosan has a molar mass ranging from 10,000 to 500,000 g/mol.

18. The composition according to claim 15, wherein the acid is sulfuric acid in an aqueous solution or an organic acid selected from carboxylic acids in an aqueous solution.

19. The composition according to claim 18, wherein the carboxylic acid is acetic acid.

20. The composition according to claim 15, wherein the compound (c1) is selected from hydroxycarboxylic acids, polycarboxylic acids, hydroxypolycarboxylic acids, polysaccharides, salts or mixtures thereof.

21. The composition according to claim 15, wherein the compound (c1) is selected from citric acid salts or succinic acid salts.

22. The composition according to claim 15, wherein the compound (c1) is trisodium citrate dehydrate, or the compound (c2) is glycerol or mannitol.

23. The composition according to claim 15, for which the ratio (a)/(b) ranges from 3/1 to 10/3, or the ratio (a)/(c1) ranges from 1/2 to 200/1, or the ratio (a)/(c2) ranges from 2/1 to 12/1.

24. The composition according to claim 15, wherein the support (d) is water.

Description

(1) FIG. 1 shows a test specimen with which it is possible to determine the shear strength of an adhesive composition according to the invention.

(2) The different objects of the invention and their embodiments will be better understood upon reading the examples which follow. These examples are given as an indication, without any limitation.

EXAMPLES

(3) For each of the following examples, the aluminum alloy test specimens were made in the following way.

(4) Each aluminum alloy test specimen consisted of four aluminum alloy 2014 elements with a length equal to 150 mm, with a width equal to 20 mm and with thicknesses e.sub.1 and e.sub.2 equal to 2 mm, two outer elements 2, and two inner elements 1. First, each aluminum alloy element has been soaked in trichloroethylene for 30 mins in order to remove the oils, each element having then been cleaned with a detergent and dried at room temperature. Next, each element has undergone a surface treatment by soaking in a 1 M soda solution for 1 hour. Next, each element was thoroughly washed with a mild detergent and kept for 12 hours in a 2% acetic acid aqueous solution. Next, each element was again washed and dried at room temperature.

(5) The adhesive composition was applied to the surface of each inner aluminum alloy element 1 with thickness e.sub.1 in order to form a layer with an initial thickness e.sub.c of 1 mm, the obtained final layer being thinner after drying, in order to form a test specimen according to FIG. 1. Each aluminum alloy element 2, of thickness e.sub.2 was attached to the other elements 1 and kept for 48 hours at a temperature of 40 C. The overlapping length is equal to L.

(6) Each test specimen was then subject to measurement of the tensile strength. For this, a tensile measurement method based on the ASTM D3528 standard was used. The apparatus used is a machine marketed by Zwick Roell under reference UTS Test System type BZC associated with the software package Text-expert VII 02 marketed by TestXpert Machine. The test specimens are subject to an imposed displacement according to a rate of 0.005 mm/s until breaking and the tensile strength F is thus measured for each test specimen.

(7) From the tensile strength, the shear strength of each exemplified adhesive composition was calculated expressed in MPa and resulting from the following mathematical formula, drawn from the Volkersen theory (Volkersen, Luftfahrtforschung, 15, 1938, pp. 41-47):

(8) $\left(0\right)=\frac{G_c{}_0}{\sinh \left({}_{i}L\right)e_c{}_i{E}_1}\left(\frac{E_1{e}_1}{E_2{e}_2}+\cosh \left({}_{i}L\right)\right)$
wherein: .sub.0=F/S, S being the section of the elements 1, F corresponding to the tensile strength of the test specimen, e.sub.1 and e.sub.2 corresponding to the thicknesses of the elements 1 and 2, e.sub.c corresponding to the thickness of the adhesive composition, E.sub.1 and E.sub.2 corresponding to the Young moduli of elements 1 and 2, L corresponding to the overlapping length of the elements 1 and 2,

(9) ${}_i=\sqrt{\frac{G_c}{e_c}\left(\frac{1}{e_1{E}_1}+\frac{1}{e_2{E}_2}\right)},$
wherein: G.sub.c=E.sub.c/(2(1+)) and corresponding to the shear modulus of the adhesive composition. For calculating it, it is assumed that the Poisson coefficient is equal to 0.3 and Young's modulus E.sub.c was measured to be 2 GPa.

Example 1

Evaluation of the Shear Strength of Adhesive Compositions According to the Invention

(10) 3 test specimens were made by using a composition according to the invention respectively comprising 6% of deacetylated chitosan having a deacetylation degree greater than or equal to 75%, 2% of acetic acid and a variable content of trisodium citrate dihydrate equal to 0.08, 0.14 and 0.5%. The control test specimen was made by using a composition comprising 6% of deacetylated chitosan with a deacetylation degree greater than or equal to 75% and 2% of acetic acid.

(11) The shear strength values are shown in Table I.

(12) TABLE-US-00001 TABLE I Adhesive composition Shear strength (MPa) Control 16.5 6% chitosan 28.4 2% acetic acid 0.08% citrate 6% chitosan 29.8 2% acetic acid 0.14% citrate 6% chitosan 24.5 2% acetic acid 0.5% citrate

(13) The results show that the compositions according to the invention exhibit an enhanced shear strength.

Example 2

Evaluation of the Shear Strength of Adhesive Compositions According to the Invention

(14) 3 test specimens were made by using a composition according to the invention respectively comprising 6% of deacetylated chitosan having a deacetylation degree greater than or equal to 75%, 2% of acetic acid and a variable glycerol content equal to 0.5, 1 and 1.5%. The control test specimen was made by using a composition comprising 6% of deacetylated chitosan having a deacetylation degree greater than or equal to 75% and 2% of acetic acid.

(15) The shear strength values are shown in Table II.

(16) TABLE-US-00002 TABLE II Adhesive composition Shear strength (MPa) Control 16.5 6% chitosan 25 2% acetic acid 0.5% glycerol 6% chitosan 26.2 2% acetic acid 1% glycerol 6% chitosan 24.7 2% acetic acid 1.5% glycerol

(17) The results show that the compositions according to the invention exhibit enhanced shear strength.

Example 3

Evaluation of the Shear Strength of Adhesive Compositions According to the Invention

(18) 5 test specimens were made by using a composition according to the invention respectively comprising 5% of deacetylated chitosan with a deacetylation degree greater than or equal to 75%, 1% of acetic acid, a variable glycerol content equal to 0.5, 1 and 1.5% and a variable content of trisodium citrate dihydrate equal to 0.11, 0.14 and 0.17%. The control test specimen was made by using a composition comprising 5% of deacetylated chitosan with a deacetylation degree greater than or equal to 75% and 1% of acetic acid.

(19) The shear strength values are shown in Table III.

(20) TABLE-US-00003 TABLEAU III Adhesive composition Shear strength (MPa) Control 22.2 5% chitosan 31.8 1% acetic acid 0.5% glycerol 0.14% citrate 5% chitosan 33.9 1% acetic acid 1% glycerol 0.14% citrate 5% chitosan 28.4 1% acetic acid 1.5% glycerol 0.14% citrate 5% chitosan 33 1% acetic acid 1% glycerol 0.11% citrate 5% chitosan 34.7 1% acetic acid 1% glycerol 0.17% citrate

(21) The results show that the compositions according to the invention exhibit enhanced shear strength.

Example 4

Comparison of the Shear Strength Between an Adhesive Composition According to the Invention and a Synthetic Structural Adhesive

(22) 2 test specimens were made: the first test specimen by using a composition according to the invention comprising 6% of deacetylated chitosan having a degree of deacetylation greater than or equal to 75%, 2% of acetic acid and 1% glycerol, the second one by using a structural adhesive based on epoxide marketed under the name of Epoxy adhesive E-504 by EPOTECHNY. The aluminum alloy elements forming the second test specimen were attached to the other ones and kept for 40 hours at temperature of 40 C.

(23) The shear strength values are shown in Table IV.

(24) TABLE-US-00004 TABLE IV Adhesive composition Shear strength (MPa) Composition according to the invention 39.4 6% chitosan 2% acetic acid 1% glycerol Epoxy adhesive E-504 39.1

(25) The results show that the adhesion properties of a composition according to the invention are equivalent to those of an adhesive based on epoxides and therefore the compositions according to the invention represent an alternative to structural adhesives of synthetic origin.

Example 5

Evaluation of the Adhesion Thickness of Adhesive Compositions According to the Invention

(26) The adhesion thickness was determined for the following adhesive compositions: a composition comprising 4% chitosan (Sigma Aldrich; molecular weight: 3.308.10.sup.5 g/mol) and 1% acetic acid, a composition containing 6% chitosan, 1% acetic acid, 1% glycerol and 0.14% citrate, a composition comprising 6% chitosan, 1% acetic acid, 1% glycerol, 0.14% citrate and 10% soluble wheat starch.

(27) The adhesive thickness measurements were conducted in a beaker of 50 ml, on wooden parts (27279 mm.sup.3) and on aluminum test specimens treated with soda as shown in FIG. 1 (dimensions of each element 1 and 2: 350202 mm.sup.3; dimension of each overlapping area between the elements 1 and 2: 1,000 mm.sup.2).

(28) The adhesive composition was applied in an identical way for each of the supports and the final thickness was measured by means of a sliding caliper.

(29) The values of the adhesive thickness are shown in Tables V, VI and VII below and are expressed in mm:

(30) TABLE-US-00005 TABLE V beaker Applied volume (ml) Adhesive composition 2.5 5 7.5 4% chitosan 0.085 0.155 0.29 1% acetic acid 6% chitosan 0.215 0.47 0.66 1% acetic acid 1% glycerol 0.14% citrate 6% chitosan 0.225 0.515 0.83 1% acetic acid 1% glycerol 0.14% citrate 10% starch

(31) TABLE-US-00006 TABLE V wooden parts Applied volume (ml) Adhesive composition 2.5 5 7.5 4% chitosan 0.07 0.1 0.315 1% acetic acid 6% chitosan 0.051 0.061 0.236 1% acetic acid 1% glycerol 0.14% citrate 6% chitosan 0.3 .08 0.9 1% acetic acid 1% glycerol 0.14% citrate 10% starch

(32) TABLE-US-00007 TABLE VII aluminum test specimens Applied volume (ml) Adhesive composition 2.5 5 7.5 4% chitosan 0.04 0.02 0.02 1% acetic acid 6% chitosan 0.035 0.02 0.045 1% acetic acid 1% glycerol 0.14% citrate 6% chitosan 0.6 0.51 0.2 1% acetic acid 1% glycerol 0.14% citrate 10% starch

(33) The above results show that the thickness of the adhesive composition according to the invention after application is improved as compared with a composition only comprising chitosan and acetic acid, and thus that the composition according to the invention has better properties relatively to withdrawal.

(34) It should be noted that by adding starch in the composition according to the invention as a polysaccharide filler, it is possible to significantly reduce withdrawal.

Example 6

Evaluation of the Influence of the Presence of Starch on the Shear Strength of an Adhesive Composition Based on Chitosan

(35) Shear strength measurements were conducted like in Examples 1, 2, 3 and 4.

(36) The following compositions were tested: a composition comprising 4% chitosan and 1% acetic acid, a composition comprising 4% chitosan, 1% acetic acid and 5% of soluble wheat starch, a composition comprising 4% chitosan, 1% acetic acid and 10% soluble wheat starch.

(37) The results are shown in the Table VIII below:

(38) TABLE-US-00008 TABLE VIII Adhesive composition Shear strength (MPa) 4% chitosan 20.1 1% acetic acid 4% chitosan 19.5 1% acetic acid 5% starch 4% chitosan 20.6 1% acetic acid 10% starch

(39) The results above show that the addition of starch in an adhesive composition based on chitosan does not have any significant influence on the adhesive properties of said composition.

(40) These results thus show that the introduction of starch, in an adhesive composition according to the invention, does not alter the adhesive properties of said composition.