ACETYLATION OF NATURAL FIBRES TO OBTAIN THE FIBROUS STRUCTURE

Abstract

The invention relates to a method for the acetylation of lignocellulose-containing fibrous materials and to acetylated lignocellulose-containing fibrous materials obtained according to said method, and to the use thereof.

Claims

1. A method for the acetylation of lignocellulosic fibrous materials which comprises the steps of: (i) treating the lignocellulosic fibrous material with acetic anhydride in the absence of a catalyst under a pressure of no greater than 0.5 bar above standard pressure (101325 Pa) and a temperature of ≤200° C.; (ii) separating the acetylated lignocellulosic fibrous material from excess acetic anhydride, and (iii) distillatively separating the acetic acid generated during acetylation.

2. The method according to claim 1, wherein the lignocellulosic fibrous material is a natural fiber selected from the group consisting of hemp fibers, flax fibers, jute fibers, rapeseed fibers, miscanthus fibers and palm fibers.

3. The method according to claim 1, wherein the lignocellulosic fibrous material is pre-dried prior to the step of treating the lignocellulosic fibrous material by applying a vacuum or by heating.

4. The method according to claim 1, wherein the step of pre-drying of the lignocellulosic fibrous material ensues at a temperature of approximately 80° C. to 95° C. and a pressure of approximately 50 mbar to 100 mbar for a time period of approximately 4 hours to 12 hours.

5. The method according to claim 1, wherein the step of treating the lignocellulosic fibrous material with acetic anhydride occurs at a temperature of approximately 90° C. to 140° C. and a pressure of approximately ±150 mbar below/above the standard pressure for a time period of approximately 1 hour to 8 hours, wherein the weight ratio of acetic anhydride to lignocellulosic fibrous material is approximately 35:1 to 5:1, and wherein the weight ratio is calculated based on the mass of the lignocellulosic fibrous material.

6. The method according to at least claim 1, wherein the acetic anhydride is in a gaseous form.

7. The method according to claim 1, wherein the step of distillatively separating the acetic acid is conducted under a vacuum at approximately 50 mbar to 60 mbar.

8. The method according to claim 1, further comprising the steps of: (iv) eliminating any acetic anhydride and acetic acid residues adhered to the acetylated lignocellulosic fibrous material by treating the acetylated lignocellulosic fibrous material filtered out under reduced pressure of approximately 50 mbar to 60 mbar; and (v) washing the fibrous material obtained in step (iv) with water.

9. The method according to claim 1, wherein the step of distillatively separating the acetic acid occurs simultaneously with the step of treating the lignocellulosic fibrous material.

10. The method according to claim 1, the step of distillatively separating the acetic acid occurs after the step of separating the acetylated lignocellulosic fibrous material from the excess acetic anhydride.

11. An acetylated lignocellulosic fibrous material produced pursuant to the method according to claim 1.

12. The acetylated lignocellulosic fibrous material according to claim 11, wherein the acetylated lignocellulosic fibrous material has an acetyl value in the range of 22% to 45% and a degree of substitution (DS) in the range of 0.3 to 1.5.

13. The acetylated lignocellulosic fibrous material according to claim 11, wherein the acetylated lignocellulosic fibrous material is configured to be used as a component of composite materials, for use in horticulture, furniture construction, household goods and vehicle construction.

14. The acetylated lignocellulosic fibrous material according to claim 11 wherein the acetylated lignocellulosic fibrous material is configured to be used as a component of building materials, insulating materials, batting and blow-in insulation materials, insulating mats, nonwovens, or as an absorbent for oil.

Description

EXAMPLE 1: ACETYLATION OF HEMP LITTER WITHOUT DISTILLING OFF THE ACETIC ACID ALTHOUGH WITH SUBSEQUENT ACETIC ANHYDRIDE PURIFICATION

[0036] 85 g of hemp litter (10.5% moisture) is placed in a 1000 ml round bottom flask. 350 g of acetic anhydride (91%) is then added and the mixture refluxed with an oil bath. After 2 h reflux, the mixture is cooled and the litter filtered through a coarse sieve. The resulting acetic acid is distillatively separated (60 mbar, 80° C.) from the acetic anhydride filtrate and the acetic anhydride thereafter distillatively purified so it can be used it for a further acetylation. The hemp litter is freed from the filtrate in a vacuum to dryness and then washed with water to pH neutral. The hemp litter is subsequently oven-dried at 60° C. for two days. A yield of 83.9 g (<1% residual moisture) of the thusly produced acetylated hemp litter was obtained. The acetylated hemp litter exhibits an onset temperature in the TGA measurement of 327.6° C. It had an acetyl value of 27.5% (DS: 0.91). The product has no identifiable discoloration. The color index of the recovered acetic anhydride was 12, the color index of the recovered acetic acid was 19.

[0037] Moisture absorption: The moisture absorption was determined with the MA 37-1 infrared moisture analyzer from Sartorius.

[0038] The thermal stability was determined with a thermogravimetric analyzer (TGA) from the Netzsch company (TG209F1 Libra, 20K/min).

[0039] The acetylated hemp litter took on 2.2% moisture within 24 hours. Hemp litter which was not dried and acetylated as above took on approximately 7% moisture under the same conditions.

[0040] A further acetylated hemp litter product was produced along the same lines as the above description, whereby the reaction time was 8 h. Further acetylated hemp litter products were produced at reaction times of 1, 4 and 8 h, whereby the starting material was in each case dried to a residual moisture content of <1% before the reaction. The properties of the thusly produced hemp litter products are reproduced in Table 1 below. The results of the moisture absorption analyses are depicted in FIG. 1. The X in FIG. 1 denotes the non-acetylated hemp litter.

TABLE-US-00001 TABLE 1 Pre-dried Acetylation Acetyl value Identification hemp litter time [h] [%] DS mark no 8 30.75 1.06 .diamond-solid. yes 8 31.09 1.07 .square-solid. yes 4 29.97 1.02 .box-tangle-solidup. yes 1 26.12 0.86 X

EXAMPLE 2: ACETYLATION OF STRAW

[0041] 10 g of straw (12.21% moisture) is placed in a 1000 ml round bottom flask. 332 g of acetic anhydride (91%) is then added and the mixture refluxed with an oil bath. After 8 h reflux, the mixture is cooled and the straw filtered through a coarse sieve. The straw is freed from the filtrate in a vacuum to dryness and then washed with water to pH neutral. The straw is subsequently oven-dried overnight at 95° C. A yield of 9.93 g (<1% residual moisture) of the thusly produced acetylated straw was obtained. It had an acetyl value of 33.05% (DS: 1.16). The acetylated straw exhibits an onset temperature in the TGA measurement of 334.4° C.

[0042] Various samples of acetylated straw of different acetylation times/degrees were produced (see Table 2). The samples took on 2.5-4% moisture after 24 hours (see FIG. 2). The X in FIG. 2 denotes the non-acetylated straw.

Acetyl Value According to Acetylation Time:

[0043]

TABLE-US-00002 Pre-dried Acetylation Acetyl value Identification straw time [h] [%] DS mark no 8 33.05 1.16 .diamond-solid. yes 8 34.06 1.21 .square-solid. yes 4 32.34 1.13 .box-tangle-solidup. yes 1 27.81 0.93 X

EXAMPLE 3: ACETYLATION OF HEMP INSULATION MATERIALS

[0044] 30 g of hemp insulation material from the Thermo Nature company (10.2% moisture) is placed in a 250 ml round bottom flask. 1500 g of acetic anhydride (91%) is then added and the mixture refluxed with an oil bath. After 8 h reflux, the mixture is cooled overnight and then filtered through a coarse sieve. The hemp insulation material is freed from the filtrate in a vacuum to dryness and then washed with water to pH neutral. The hemp insulation material is subsequently oven-dried overnight at 60° C. A yield of 31.7 g (<1% residual moisture) of the thusly produced acetylated insulation material was obtained. It had an acetyl value of 20.6% (DS: 0.65). The acetylated insulation material exhibits an onset temperature in the TGA measurement of 316.2° C.