BIODEGRADABLE CONTAINER AND PLATE MATERIAL AND METHOD FOR THE MANUFACTURE THEREOF

Abstract

The invention pertains to a biodegradable container or plate material comprising a layer of cellulose-based material provided with a composite surface layer comprising cellulose-based material and a polyester derived from an aliphatic polyalcohol with 2-15 carbon atoms and an aliphatic polycarboxylic acid with 3 to 15 carbon atoms, wherein the polycarboxylic acid comprises at least 50 wt. % of tricarboxylic acid. The biodegradable container or plate material according to the invention shows one or more, in particular a combination of, the following properties: light weight, high (wet) strength, a desirable degree of flexibility, good (temporary) resistance against water, oil, and fat, and attractive visual and tactile characteristics.

Claims

2. The biodegradable container or plate material according to claim 1, wherein the cellulose-based material contains at least 50 wt. % of a cellulose material.

3. The biodegradable container or plate material according to claim 1, which comprises one or more additives to improve one or more of hydrophobicity, dry strength, and wet strength, and/or one or more fillers or binders.

4. The biodegradable container or plate material according to claim 1, wherein the aliphatic polyalcohol is selected from the group consisting of trialcohols selected from the group consisting of glycerol, sorbitol, xylitol, and mannitol, and dialcohols selected from the group consisting of 1,2-propanediol, 1,3-propanediol, and 1,2-ethanediol.

5. The biodegradable container or plate material according to wherein the polyalcohol consists at least 50 mole % of glycerol, xylitol, sorbitol, or mannitol.

6. The biodegradable container or plate material according to claim 1, wherein the polycarboxylic acid comprises at least 70 wt. % of tricarboxylic acid, calculated on the total amount of polycarboxylic acid.

7. The biodegradable container or plate material according to claim 1, wherein the tricarboxylic acid is selected from the group consisting of citric acid, isocitric acid, aconitic acid (both cis and trans), and 3-carboxy-cis,cis-muconic acid.

8. The biodegradable container or plate material according to claim 1, wherein the aliphatic polycarboxylic acid comprises dicarboxylic acids selected from the group consisting of itaconic acid, malic acid, succinic acid, glutaric acid, adipic acid and sebacic acid.

9. The biodegradable container or plate material according to claim 1, wherein, calculated on the total of polyester-containing composite surface layer and polyester-free cellulose-based material, in a cross-section of the biodegradable container or plate material, 1-90% of the cross-section is polyester-containing composite surface layer and 99-10% of the cross-section is polyester-free cellulose-based material.

10. The biodegradable container or plate material according to claim 1, wherein the amount of polyester resin present in the biodegradable container or plate material is in the range of 0.5-90 wt. %.

11. The biodegradable container or plate material according to claim 1, which is a plant pot, or a packaging material.

12. A method for manufacturing a biodegradable container or plate material according to claim 1, which comprises a step of contacting the surface of a cellulose-based material with a liquid medium comprising polyester or polycarboxylic acid and polyalcohol precursors thereof until the cellulose-based material is partially but not completely impregnated with the liquid medium, the polyester being derived from an aliphatic polyalcohol with 2-15 carbon atoms and an aliphatic polycarboxylic acid with 3 to 15 carbon atoms, wherein the polycarboxylic acid comprises at least 50 wt. % of tricarboxylic acid, and a curing step.

13. The method according to claim 12, wherein the step of contacting the surface of a cellulose-based material with a liquid medium is carried out through dipping, spraying, flowing, rolling, brushing or cascading.

14. The method according to claim 12, wherein the curing step is carried out at a product temperature of 80-250° C.

15. The method according to claim 12, wherein a drying step is carried out before the curing step.

16. The biodegradable container or plate material according to claim 1, wherein the cellulose-based material contains at least 70 wt. % of cellulose material.

17. The biodegradable container or plate material according to claim 1, wherein the aliphatic polyalcohol is selected from the group consisting of glycerol, sorbitol, xylitol, and mannitol.

18. The biodegradable container or plate material according to claim 1, wherein at least 70 mole % of the aliphatic polyalcohol is glycerol.

19. The biodegradable container or plate material according to claim 1, wherein the polycarboxylic acid comprises at least 90 wt. % of tricarboxylic acid, calculated on the total amount of polycarboxylic acid.

20. The biodegradable container or plate material according to claim 1, wherein he tricarboxylic acid is selected from the group consisting of itaconic acid, succinic acid and citric acid,

Description

EXAMPLE 1

Preparation of Solution of Polyol and Polycarboxylic Acid Polyester Precursor

[0069] 12 kg of tap water was heated to 90° C. in a 50 l container. 25 kg of citric acid monohydrate (purity >99%) was added under stirring. A solution was obtained with a temperature of 38° C. 12.5 kg of 99% pure glycerol was added to this solution. The solution was allowed to cool to room temperature and further diluted with tap water until a water concentration of 50% was obtained. 0.5 wt % of boric acid was added as catalyst.

EXAMPLE 2

Preparation of Solution of Polyester Prepolymer

[0070] 1.0 kg of >99% pure glycerol and 2.0 kg of citric acid (purity >99%) were put in a stirred and heated reactor. Also 9 g of boric acid (0.5 m/m, >99% purity) was added. The mixture was heated up in about 15 minutes until 135° C. and kept at that temperature for 15 minutes followed by dilution with tap water to a water content of 50% and further cooling down.

EXAMPLE 3

Partial Impregnation of Cellulose-Based Plant Pot Based on Recycled Paper

[0071] Moulded cylindrical plant pots made of cellulose fibre pulp regenerated from predominantly unprinted recycled book paper, containing 0.5% of alkylsuccinic anhydride were used as starting material. The pots were 9 cm in height, 11 cm in diameter at the top and 7 cm in diameter at the bottom. The average weight was 14.2 gram.

[0072] Pots as described above were dipped at room temperature for 6 seconds in the solution of polyester prepolymer described in Example 2. The wet pots were dried at room temperature for 4 hours and cured for 20 min in a ventilation oven with an internal temperature of 190° C. Final product temperature was 180° C. After curing the pots weighed on average 16.7 gram, with a polyester content of 15 wt. %. A cross-section of the wall of the pot showed the existence of a resin-free layer between two resin-containing layers.

[0073] The following table shows the dry strength, the strength after immersion in water for five minutes at room temperature, and the strength after immersion in sunflower oil for 10 seconds at room temperature, for starting pots and for pots provided with the polyester resin. For each measurement four pots were used. Strength was determined using the universal testing machine (UTM) (Testrometic, M350-20CT) with a plate compression test and measuring the peak force when the pot was placed upside down (bottom to the top plate and top to the bottom compression plate).

TABLE-US-00001 After 5 minutes in After 10 seconds in Dry water oil peak force peak force peak force Sample (N) (N) (N) Impregnated 1090 777 1044 Starting material 789 170 548

[0074] From the table it can be seen that impregnated pots have a higher strength than the starting material.

[0075] Further, the strength of the impregnated pot after immersion for 5 minutes in water at room temperature decreased with about 30% as compared to the strength of the impregnated pot before impregnation, resulting in the retention of acceptable strength. In contrast, upon immersion for 5 minutes in water at room temperature, unimpregnated pots collapsed, showing no acceptable strength retention.

[0076] The strength of the impregnated pot after immersion for 10 seconds in sunflower oil at room temperature remained unchanged. In contrast, upon immersion for 10 seconds in sunflower oil at room temperature, unimpregnated pots showed a decrease in strength of 30% as compared to the pot before immersion.

[0077] The impregnated pots were more rigid than the unimpregnated pots but still showed some flexibility (top edges of the pot can be moved towards each other 2-3 cm before the pots are gets damaged).

[0078] The application of the impregnation resulted in an considerably improved mechanical (wet) strength for water and oil. Furthermore, the colour of the pot changed from off while to an attractive light brown.

EXAMPLE 4

Partial Impregnation of Cellulose-Based Plant Pot Based on Virgin Paper

[0079] As starting materials pots were prepared with the same size, shape, and weight as those used in Example 3. The pots were based on virgin cellulose fibre, modified with 0.5 wt. % alkylsuccinic anhydride. The pots were 9 cm in height, 11 cm in diameter at the top and 7 cm in diameter at the bottom. They weighed on average 14.5 gram.

[0080] The pots were dipped at room temperature for 6 seconds in the solution of polyol and polyacid described in Example 1. The wet pots were dried at room temperature for 4 hours and cured for 20 min in an ventilation oven with an internal temperature of 190° C., with a final product temperature of 180° C. After curing the pots weighed on average 17.7 grams, corresponding to a polyester content of 18 wt. %. A cross-section of the wall of the pots showed the existence of a resin-free layer between two resin-containing layers. The pot was much more rigid than the unimpregnated pot but still showed some flexibility (top edges of the pot can be moved towards each other 2-3 cm before the pot gets damaged). Furthermore, it had an attractive brown coloured outer surface and very good tactile properties. The latter is probably due to the fact that the tactile properties of the virgin paper pot are better than those of the pot based on recycled paper.

[0081] The strength of the impregnated pots was about 80% higher (average 1332 N) than the strength of the pot before impregnation (average 734 N), and about 20% higher to that of the impregnated pot described in Example 3. The latter may be due to the pot having a slightly higher resin content and the fibers of the virgin cellulose being longer than those of the recycled paper used in Example 3.

[0082] After immersion in water or oil under the conditions described in the previous example, the impregnated pots retained most of their strength, while unimpregnated pots did not.

EXAMPLE 5

Impregnation of Virgin Cellulose-Based Plant Pot—Comparative

[0083] A comparative pot was prepared by impregnating a plant pot of virgin cellulose fibre with the solution of Example 1 under such conditions that it was completely impregnated with resin. The wet pot was dried at room temperature for 4 hours and cured for 20 min in an ventilation oven with an internal temperature of 190 ° C. (final product temperature id 180° C.). After curing the container weighed 41 grams gram, with a polyester content of ˜65 wt. %.

[0084] A cross-section of the wall of the pot showed no resin-free layer. The pot was completely made up of composite material. The pot has a nice brown color, a high strength, and a ceramic appearance. It had, however, little flexibility which may be disadvantageous in filling and emptying the pot. Additionally, it was quite brittle. Further, the relatively large weight makes it less attractive because of the higher material and transportation costs.

EXAMPLE 6

Partial Impregnation of Paper-Based Food Tray

[0085] A smooth small rectangular food tray (L*W at the top 21*14 cm, and at the bottom 17*10 cm and a height of 5.5 cm) made of dense thin walled thermoformed fiber derived from cellulose fibre regenerated from unprinted recycled paper, containing 0.6 wt. % alkylsuccinic anhydride, and weighing 20.1 grams was dipped at room temperature for 6 seconds in the solution described in Example 2. After dipping the wet tray was dried at room temperature for 4 hours and cured for 20 min in a ventilation oven with an internal temperature of 190° C. (final product temperature 180° C.). After curing the pot weighed 22.2 grams and the estimated polyester content was 10%. A cross-section of the wall of the tray showed the existence of a resin-free layer between two resin-containing layers

[0086] The tray was more rigid than the unimpregnated tray but still showed some flexibility. The top layer had an attractive glossy light brown appearance.

[0087] The oil resistance of the impregnated tray was tested at 50° C. in a ventilation oven for 2 hours. An amount of 10 drops of sunflower oil was put on the bottom of an impregnated tray and an unimpregnated tray, respectively. The impregnated tray showed good oil resistance as no oil permeated in or through the tray. The oil stayed completely on the surface of the tray and the colour of the tray remained unchanged. On the unimpregnated tray the oil permeated immediately into the paper and a dark “wet stain” appeared on the top and bottom of the tray where the oil had been applied.

EXAMPLE 7

Neutralized Acid

[0088] To 100 grams of a polyester solution as in example 2 was added 1.0 g of 2-amino-2-methyl-1-propanol, commercially available from Angus Chemie under the trade name of AMP. A similar small cylindrical plant pot as described in Example 3 was treated the same way as described in example 3 and similar material characteristics were obtained. In this case, the addition AMP to the solution stabilised the prepolymer solution. Upon curing the pot, the base evaporates, and the polyester cures further to its final degree of polymerisation.

EXAMPLE 8

Comparison With Polyesters Based on Diacid and Diol

[0089] Moulded cylindrical plant pots made of cellulose fibre pulp regenerated from predominantly unprinted recycled book paper, containing 0.5% of alkylsuccinic anhydride were used as starting material. The pots were 8.4 cm in height, 11 cm in diameter at the top and 7 cm in diameter at the bottom. The average weight was 13.7 gram.

[0090] Two dipping solutions were prepared, with the following respective compositions:

TABLE-US-00002 Solution A - dialcohol - diacid Comparative wt. % Glutaric acid 31.5 1,3-propanediol 18.4 Water 50.1

TABLE-US-00003 Solution B - trialcohol - triacid Invention wt. % Citric acid (anhydrous) 32.4 Glycerol 17.2 Water 50.5

[0091] Pots as described above were dipped at room temperature for 10 seconds in solution A or B. The solutions were at a temperature of 45° C. The wet pots were dried at room temperature for 1 hour and cured for 20 min in a ventilation oven with an internal temperature of 190° C.

[0092] The weight of the pots after dipping and drying was as given below. The values are the average of 6 measurements. The numbers in parentheses are the percentage increase compared to the weight of the dry starting pots.

TABLE-US-00004 Dipped with solution A Dipped with solution B Comparative Invention Dry pots 14 g (100%) 14 g (100%) After dipping an 1 hour drying in 30 g (219%) 18 g (129%) air After overnight storage 16 g (120%) 15 g (109%)

[0093] Water uptake was determined after submerging the pots for 10 minutes in water. The values are the average of 3 measurements. The numbers in parentheses are the percentage increase compared to the weight of the dry starting pots.

TABLE-US-00005 Dipped with solution A Dipped with solution B Comparative Invention Dry weight 16 g 15 g Weight after 10 minutes immersion 38 g (232%) 19 g (124%)

[0094] Compression strength was determined as described in Example 3, both for the wet and dry plant pots. For the dry pots the data are the average of 4 measurements. For the wet pots the data were the average of 2 measurements. The results were as follows:

TABLE-US-00006 After 10 minutes in Dry pots - peak force (N) water - peak force (N) Dipped with solution A 692 183 Comparative Dipped with solution B 825 320 Invention

[0095] From the above comparisons it can be seen that the pots impregnated with solution B according to the invention have a higher compression strength than pots impregnated with comparative solution A, both in the dry state and in the wet state. Additionally, the pots impregnated with solution B have a lower water uptake than the pots impregnated with solution A. It should be noted that the pots impregnated with solution B have a lower resin content than the pots impregnated with solution A, making the effects obtained with the polyester according to the invention even more surprising.