COMPOUND OR FILM CONTAINING THERMOPLASTIC STARCH AND A THERMOPLASTIC POLYMER

Abstract

The invention relates to a method for producing a compound or a film containing thermoplastic starch, an alpha-hydroxycarboxylic acid ROHCOOH, in which R is CH.sub.2 or CH.sub.3CH.sub.2, in an amount of from 0.1 to 5, preferably 0.1 to 3, particularly preferably 0.1 to 1 wt. % in relation to the thermoplastic starch, and a thermoplastic polymer, in which method the compound or the film is exposed during or after its extrusion to an additional heating step to 100-140° C. A thermoplastic starch usable for the production of the compound, a compound produced by the method, and a transparent film produced from such a compound are also described.

Claims

1.-13. (canceled)

14. A method for producing a compound or film comprising: mixing a thermoplastic starch, an alpha-hydroxycarboxylic acid ROHCOOH, wherein R is CH.sub.2 or CH.sub.3CH.sub.2 in an amount of 0.1 to 5% by weight in relation to the thermoplastic starch, and a thermoplastic polymer to obtain a mixture; extruding the mixture to form a compound or a film; and heating the compound or film to 100-140° C. during or after extrusion.

15. The method of claim 14, wherein the alpha-hydroxycarboxylic acid is lactic acid.

16. The method of claim 14, wherein the compound or film contains the alpha-hydroxycarboxylic acid in an amount of 0.1 to 1% by weight in relation to the thermoplastic starch.

17. The method of claim 14, wherein the heating is after extrusion and lasts at least 15 minutes for a compound or at least 2 minutes for a film.

18. The method of claim 14, wherein the thermoplastic polymer is a polyolefin, polyamide, polyurethane, polyester, or mixture thereof.

19. The method of claim 14, wherein, the thermoplastic starch is obtained by: mixing a starch, a polyol, and an epoxidised plant oil to form a mixture, wherein the polyol is in an amount of 10 to 25% by weight of the mixture and the epoxidised plant oil is in an amount of 0.1 to 6% by weight of the mixture; and extruding the mixture.

20. The method of claim 19, wherein the polyol is polyethylene glycol, a monosaccharide, or a sugar alcohol.

21. The method of claim 20, wherein the polyol comprises glycerol, sorbitol, erythritol, xylitol, and/or or mannitol.

22. The method of claim 19, wherein the epoxidised plant oil comprises soybean oil, linseed oil, sunflower oil, and/or rapeseed oil.

23. The method of claim 19, wherein the amount of epoxidised plant oil is 2.5 to 3.5% by weight of the mixture.

24. The method of claim 19, wherein the polyol comprises sorbitol or erythritol in an amount of 10 to 15% by weight of the mixture.

25. The method of claim 19, wherein the mixture comprises epoxidised plant oil to polyol ratio of 1:4 to 1:6.

26. The method of claim 19, wherein the mixture further comprises an acid in an amount of 0.1 to 1% by weight of the mixture.

27. The method of claim 26, wherein the acid comprises citric acid, malic acid, acetic acid, and/or tartaric acid.

28. The method of claim 26, wherein the mixture comprises the acid in an amount of 0.1 to 0.5% by weight of the mixture.

29. The method of claim 19, wherein the mixture is extruded at a temperature of 100-175° C.

30. The method of claim 29, wherein the mixture is extruded in a twin-screw extruder with a separate vacuum zone in which degassing takes place by applying negative pressure.

31. The method of claim 14, wherein extruding the mixture comprises using blown or flat film extrusion to produce a transparent film.

32. A method comprising: obtaining a compound produced by the method of claim 14; and using the compound to produce a transparent film.

33. The method of claim 32, wherein the transparent film is produced by blown or flat film extrusion of the compound.

Description

DESCRIPTION OF THE FIGURES

[0056] The present invention will now be explained in more detail with the aid of the following examples and figures. Unless otherwise stated, percentages and ratios are always by mass.

[0057] FIG. 1 shows the improvement in transparency of a film of glycerol-TPS/PBAT 1:1, which is—from left to right—untreated, untreated but with the addition of lactic acid, and with the addition of lactic acid and after the heating step provided in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0058] In the following tests, maize starch was introduced into an extruder as the starting raw material by means of solid dosing. Stearic acid is used (1% by weight) to improve the processability (reduction in torque). The mixture is processed in a twin-screw extruder using a temperature profile in the range 100-130° C. and at a speed of 250 rpm and granulated at the die plate by means of a hot die. The resulting material is water-soluble and can be incorporated as finely distributed TPS (disperse phase) into polyester melts for example (continuous phase) via a separate extrusion step. The thermoplastic starch is compounded together with polybutylene adipate terephthalate (PBAT) as polyester in a ratio of 1:1 in a twin-screw extruder.

[0059] Suppliers:

[0060] Sorbitol, glycerol, stearic acid—Brenntag, AT

[0061] DL-lactic acid—Sigma Aldrich

[0062] PBAT—BASF

[0063] ESBO—Hobum, AT

[0064] Citric acid—Jungbunzlauer, AT

[0065] Machine Types:

[0066] Extrusion (TPS and compound): Theysson TSK 30, 28D, 7 zones

[0067] Blown film line: OCS BFT400V3

[0068] The opacity of the pure carrier polymer, such as pure polyester (as a continuous compound phase), is used as the threshold value for the increase in transparency provided in accordance with the invention. To explain this, the following table 1 shows the opacity comparison of a film consisting of pure polybutylene adipate terephthalate (PBAT, Ecoflex) with a film consisting of a mixture of PBAT and glycerol-plasticised TPS (mixture 1:1) and with a film consisting of a mixture of PBAT and glycerol-plasticised TPS with addition of lactic acid (mixture 1:1):

TABLE-US-00001 TABLE 1 Comparison of opacity on film materials without thermal treatment PBAT film (thickness 65 PBAT/glycerol-TPS μm) PBAT/glycerol-TPS 1:1 1:1 film, TPS 5% with Comparison Reference film (40 μm) lactic add (50 μm) Absorption 0.30 1.02 0.36 (wavelength 550 nm) Conversion with 4.60 25.38 7.20 reference to film thickness*) OPACITY *) the correlation between absorption and layer thickness via the extinction coefficient according to Lambert-Peer was verified in the following test: [00001]$A=\log 10\frac{I0}{I}=\mathrm{.Math.}.Math.|.Math.c$(where ε = extinction coefficient, | = layer thickness, c = concentration −> the opacity-causing factor in this case is the starch - since the starch content was kept constant in the tests, the factor c is neglected or not considered separately).

TABLE-US-00002 TABLE 2 Influence of film thickness on ε .Math. c Sample thickness PBAT/glycero- TPS 1:1 film with lactic acid Absorption = Comparison (mm) = | A ε .Math. c 0.050 0.360 7.2 0.100 0.720 7.2 0.150 1.080 7.2 0.200 1.420 7.1

[0069] Table 3 below shows the various results after the thermal treatment provided in accordance with the invention, in this case of the films, at 130° C. for a duration of 15 minutes:

TABLE-US-00003 TABLE 3 Comparison after thermal treatment of films at 130° C. for 15 minutes PBAT film PBAT/glycerol- PBAT/glycerol-TPS (thickness TPS 1:1 film, TPS with 65 μm) 1:1 film 5% lactic acid Comparison Reference (40 μm) (50 μm) Absorption 550 0.16  0.46 0.12 (wavelength nm) Conversion with 2.42 11.38 2.46 reference to film thickness*) OPACITY

[0070] Table 4 shows the properties of film materials (before and after thermal treatment) based on compounds consisting of PBAT and various thermoplastic starches, the difference being the plasticiser used for TPS production.

TABLE-US-00004 TABLE 4 Material properties of film materials based on TPS and the polyester Ecoflex from BASF, DE (compounded 1:1), wherein different plasticisers in comparable proportions (13% by weight of each of the substances listed in the table in combination with 4% by weight solid sorbitol) were used in the production of the TPS-the ″treatment″ described refers to heating the produced films at 130° C. for a period of 15 minutes. Opacity before Opacity after Plasticiser treatment treatment Glycerol 25.38 11.38 Xylitol 27.08 10.43 Sorbitol 21.17 16.72

[0071] Table 5 shows film materials containing 30% TPS (glycerol-plasticised and plasticised with water only). It can be seen that the transparency effect also occurs when plasticisation occurs with water only (an additional plasticiser is not absolutely necessary to achieve the effect).

TABLE-US-00005 TABLE 5 Films produced on the basis of water-plasticised and glycerol- plasticised TPS in comparison (30% TPS in the mixture), treatment 130° C., 15 minutes Opacity before Opacity after Plasticiser treatment treatment Glycerol 18.93 10.76 Water  8.09  3.30

[0072] It can be seen that the opacity can be reduced by thermal treatment and, depending on the plasticiser used, approaches the opacity or transparency achievable on the reference film (pure PBAT, opacity untreated=4.6; opacity treated=2.42).

[0073] In the following examples concerning the production of a preferably used TPS, native starch (native maize starch, Maisita 21000) was mixed with a plasticiser (10-25% by weight), acid (0.1-1% by weight) and, of course only in the preferred examples, an epoxidised plant oil (0.1-6% by weight) in a one-step extrusion process, broken down and plasticised. For this purpose, the TPS was produced in a twin-screw extruder with vacuum degassing; all additives are added directly to the extrusion process via appropriate metering units. Processing takes place in a temperature range between 100 and 160° C. (a strong brown colouring may be seen above 160° C.).

[0074] The plasticiser may be presented in both solid and liquid form, and it is also possible to split the addition (i.e. addition partly in solid and partly in liquid form). The oil component is added untreated in liquid/pumpable form. The oil component is added untreated in liquid/pumpable form. The extrudates produced are suitable for further processing into compounds according to the invention (for example in combination with polyesters). Only on the basis of the compounds as well as the addition of an alpha-hydroxycarboxylic acid ROHCOOH, wherein R denotes CH.sub.2 or CH.sub.3CH.sub.2 (preferably lactic acid), in an amount of 0 to 10, preferably 0 to 7.0, particularly preferably 0 to 4.5% by weight in relation to the thermoplastic starch, and the heating step to 100-160° C., preferably to 120-140° C., for at least 15 minutes, preferably at least 30 minutes, particularly preferably at least 60 minutes (compound) or to 100-160° C., preferably to 110-150° C., for at least 2 minutes, preferably at least 5 minutes, particularly preferably at least 60 minutes (film) either during or after production of the compound or after production of a blown film from the compound is it possible to produce transparent end products such as transparent film materials.

[0075] The use of plasticisers other than glycerol without the addition of epoxidised plant oil leads to a deterioration of the mechanical properties. The exclusive substitution of glycerol by plasticisers such as sorbitol, isosorbide or xylitol in a TPS is therefore not appropriate and, in the case of film materials based on TPS and polymer, has been shown to lead to losses in terms of the achievable mechanical material properties. Of course, according to the invention, a TPS produced using glycerol and without the addition of epoxidised plant oil can also be used; in fact any TPS can be used as long as the addition according to the invention of an alpha-hydroxycarboxylic acid ROHCOOH, wherein R denotes CH.sub.2 or CH.sub.3CH.sub.2 (preferably lactic acid), is provided in an amount of 0 to 10, preferably 0 to 7.0, particularly preferably 0 to 4.5% by weight in relation to the thermoplastic starch, and either during or after production of the compound or after production of a blown film from the compound, said heating step is maintained at 100-160° C., preferably at 120-140° C., for at least 15 minutes, preferably at least 30 minutes, particularly preferably at least 60 minutes (compound), or at 100-160° C., preferably at 110-150° C., for at least 2 minutes, preferably at least 5 minutes, particularly preferably at least 60 minutes (film).

[0076] Only when an alpha-hydroxycarboxylic acid ROHCOOH, wherein R is CH.sub.2 or CH.sub.3CH.sub.2 (preferably lactic acid), is added in the specified amount and the above heating step is provided can blown films with a surprising transparency be produced.

[0077] The table below shows the influence of the alpha-hydroxycarboxylic acid concentration, in this case the lactic acid concentration, on the opacity of the films described:

TABLE-US-00006 TABLE 6 Changes in opacity with increasing lactic acid content-after thermal treatment of the films at 130° C. for 15 minutes PBAT/glycerol- PBAT/glycerol- PBAT/glycerol- PBAT PBAT/ TPS 1:1 film, TPS 1:1 film, TPS 1:1 film, film glycerol- TPS with 1% TPS with 3% TPS with 5% (thickness TPS 1:1 lactic acid lactic acid lactic acid 65 μm) film (50 μm), (50 μm), (50 μm), Reference (40 μm) acc. to inv. acc. to inv. acc. to inv. Absorption 0.157 0.455 0.232 0.166 0.123 (wavelength 550 nm) Conversion 2.420 11.375 4.640 3.320 2.460 with reference to film thickness*) OPACITY

[0078] In accordance with the present invention, it has surprisingly been found that the thermal treatment of a compound containing an alpha-hydroxycarboxylic acid (as compared to an untreated compound) also causes a reduction in the opacity or increase in the transparency of a film produced from the compound:

TABLE-US-00007 TABLE 7 Transparency values of films before the production of which only the compounds were thermally treated (130° C. for a duration of one hour) PBAT/sorbitol-TPS 1:1 PBAT/sorbitol-TPS 1:1 film, film TPS with 5% lactic TPS treated with 5% lactic add, (36 μm)-compound add, (43 μm)-compound Comparison untreated treated Absorption 0.552 0.427 (wavelength 550 nm) Conversion 15.333 9.930 with reference to film thickness*) OPACITY

[0079] In a preferred embodiment of the present invention, the addition of epoxidised plant oils (for example epoxidised linseed oil (ELO), epoxidised sunflower oil, epoxidised rapeseed oil or epoxidised soybean oil (ESBO) and mixtures thereof) during the production of the TPS, even when using, for example, sorbitol, results in the incorporation/mixing of the plasticiser into the TPS.

TABLE-US-00008 TABLE 8 Film based on TPS modified with 3% ESBO, 0.1% citric acid and 3% lactic acid in the compound 1:1 with PBAT-the thermal treatment was performed at 130° C. for a duration of 15 minutes (film thickness 75 μm) Film untreated Film treated OPACITY 5.61 2.97

[0080] The activation of the epoxide functionality in the epoxidised plant oils is promoted by the addition of acids. Carboxylic acids (which ideally may be produced on a sustainable basis) such as citric acid, tartaric acid, acetic acid, itaconic acid, malic acid or lactic acid can be used for this activation.

[0081] Methods of Analysis:

[0082] Film Thickness Determination by Means of Conventional Micrometer

[0083] Apart from the increased transparency (or reduced opacity), the superior material properties of films produced from TPS or compounds produced in accordance with the invention are also evident in an extensibility: >300% with a tensile strength of >10 MPa. A TPS content of 50% by weight and above can be used in the method according to the invention (a TPS content of 50% by weight was used for the above tests).

[0084] Determination of Opacity:

[0085] Direct insertion of the films into the beam path of the spectrometer and measurement in the visible range (wavelength 300-900 nm). Evaluation of the measurement result based on the absorption measured at a wavelength of 550 nm with reference to the film thickness.

[0086] The improved transparency or reduced opacity is reflected in a reduction of the parameter ε.Math.c to a value of <10 (see optical comparison in the figures) at a TPS content of 50% in the film (with a minimum content of 35% pure starch).