Bi-axially stretched article and silage film

Abstract

The present invention relates to biaxially stretched article obtained by stretching a thermoplastic composition in a machine direction and a transverse direction at elevated temperature, said thermoplastic composition comprising: a polyolefin phase containing at least one polyolefin, a starch phase containing thermoplastic starch, at least one compatibilizer selected from the group consisting of ethylene vinyl alcohol copolymers, block saponified polyvinyl acetate and random terpolymers of ethylene, butylacrylate and maleic anhydride, wherein the total of the at least one polyolefin, the thermoplastic starch and the at least one compatibilizer is more than 80 wt % of the weight of the thermoplastic composition and wherein the article has a layered morphology with alternating layers of starch phase and polyolefin phase, said layers of starch phase and polyolefin phase extending in machine direction and transverse direction.

Claims

1. A biaxially stretched article obtained by stretching a thermoplastic composition in a machine direction and a transverse direction at elevated temperature, said thermoplastic composition comprising: a polyolefin phase containing a polyolefin, a starch phase containing thermoplastic starch, compatibiliser selected from the group consisting of ethylene vinyl alcohol copolymers, block saponified polyvinyl acetate and random terpolymers of ethylene, butylacrylate and maleic anhydride, wherein the total of the polyolefin, the thermoplastic starch and the compatibiliser is more than 80 wt % of the weight of the thermoplastic composition; and wherein the article has a layered morphology with alternating layers of starch phase and polyolefin phase, said layers of starch phase and polyolefin phase extending in machine direction and transverse direction; wherein the thermoplastic composition comprises from 10-70 wt % of the polyolefin from 10-70 wt % of the thermoplastic starch from 5-40 wt % of the compatibiliser the weight percentages being based on the weight of the thermoplastic composition; and wherein the thermoplastic starch comprises borax at a concentration of 0.5 wt % to 8 wt %.

2. The article according to claim 1, wherein the thermoplastic composition comprises the polyolefin and the thermoplastic starch at a weight ratio of 20:80-55:45.

3. The article according to claim 1, wherein the amount of the compatibiliser is 5-15 wt % based on the thermoplastic composition.

4. The article according to claim 1, wherein the thermoplastic starch comprises glycerol and plasticiser components and the weight ratio between the glycerol and the plasticiser components is 0.3-1.0.

5. The article according to claim 1, wherein the thermoplastic composition comprises a further compatibiliser different from the compatibiliser.

6. The article according to claim 5, wherein the further compatibiliser is selected from the group consisting of ethylene acrylic acid copolymers, ethylene vinyl acetate copolymers, polyolefins having at least 1 wt % maleic anhydride grafted thereon, random, partially hydrolised and saponified polyvinylacetate and random terpolymers of ethylene, vinylacetate and maleic anhydride.

7. The article according to claim 1, wherein the thermoplastic composition comprises at least 90 wt % of the polyolefin, the thermoplastic starch and the compatibiliser.

8. The article according to claim 1, having a stretch ratio in transverse direction of at least 1.5, the stretch ratio in transverse direction being defined as: ${\mathrm{SR}}_{\mathrm{td}}=\frac{W_1}{W_0}$ and a stretch ratio in machine direction of at least 2, the stretch ratio in machine direction being defined as: ${\mathrm{SR}}_{\mathrm{md}}=\frac{T_0}{T_1{\mathrm{SR}}_{\mathrm{td}}}$ wherein SR.sub.md=Stretch ratio in machine direction SR.sub.td=Stretch ratio in transverse direction W.sub.0=Width of the thermoplastic composition before stretching in transverse direction [mm] W.sub.1=Width of the biaxially stretched article [mm] T.sub.0=Thickness of the thermoplastic composition before stretching in machine and transverse direction [mm] T.sub.1=Thickness of the biaxially stretched article [mm].

9. The article according to claim 1, wherein the article is a film having a thickness of from 2-250 m, a modulus of at least 50 MPa as measured according to ASTM 882, and an elongation at break of at least 200% as measured according to ISO 527-3.

10. A multilayer film comprising the film according to claim 9, wherein said film is provided with a further synthetic film of a synthetic polymer extending in machine direction and transverse direction.

11. The article according to claim 1, wherein the article is a silage film.

12. A silage film consisting of an article according claim 1.

13. A method for producing an article according claim 1, comprising; providing a thermoplastic composition comprising polyolefin, thermoplastic starch and compatibiliser comprising at least one of ethylene vinyl alcohol copolymers, block saponified polyvinyl acetate and random terpolymers of ethylene, butylacrylate and maleic anhydride, wherein the total of the polyolefin, the thermoplastic starch and the compatibiliser is more than 80 wt % of the weight of the thermoplastic composition, and feeding said thermoplastic composition to an extruder, extruding the thermoplastic composition through an extrusion die and stretching the thermoplastic composition upon exiting the extrusion die at elevated temperature, that is above the melting points of both the thermoplastic starch and the polyolefin, in machine direction and transverse direction, or feeding a polyolefin or a mixture of two or more polyolefins, starch, processing aid for making thermoplastic starch and compatibiliser comprising at least one of ethylene vinyl alcohol copolymers, block saponified polyvinyl acetate and random terpolymers of ethylene, butylacrylate and maleic anhydride to an extruder, extruding these components under such conditions that a thermoplastic composition comprising polyolefin, thermoplastic starch and compatibiliser, wherein the total of the polyolefin, the thermoplastic starch and the compatibiliser is more than 80 wt % of the weight of the thermoplastic composition, is formed in the extruder and stretching the thermoplastic composition upon exiting the extruder via an extrusion die at elevated temperature, that is above the melting points of both the thermoplastic starch and the polyolefin, in machine direction and transverse direction.

14. The article according to claim 1, wherein the thermoplastic composition is free from thermoplastic polyester.

15. The article according to claim 1, wherein the article has an oxygen permeability of at most 50 (cm.sup.3.Math.mm)/(m.sup.2.Math.day) as measured according to ASTM D-3985 at 23 C., 0% relative humidity, and 100% oxygen.

16. The article according to claim 15, wherein the article has an oxygen permeability of at most 25 (cm.sup.3.Math.mm)/(m.sup.2.Math.day).

17. A biaxially stretched article obtained by stretching a thermoplastic composition in a machine direction and a transverse direction at elevated temperature, said thermoplastic composition comprising: a polyolefin phase containing a polyolefin, a starch phase containing thermoplastic starch, compatibiliser selected from the group consisting of ethylene vinyl alcohol copolymers, block saponified polyvinyl acetate and random terpolymers of ethylene, butylacrylate and maleic anhydride, wherein the total of the polyolefin, the thermoplastic starch and the compatibiliser is more than 80 wt % of the weight of the thermoplastic composition and wherein the article has a layered morphology with alternating layers of starch phase and polyolefin phase, said layers of starch phase and polyolefin phase extending in machine direction and transverse direction; and wherein the thermoplastic starch comprises borax.

18. The article according to claim 17, wherein the thermoplastic starch comprises the borax at a concentration of 1 wt % to 4 wt %, based on the weight of the thermoplastic starch.

19. The article according to claim 18, wherein the thermoplastic starch comprises the borax at a concentration of 2 wt % to 3 wt %, based on the weight of the thermoplastic starch.

20. The article according to claim 17, wherein the thermoplastic composition comprises less than 20 wt % of thermoplastic polyester based on the total of the thermoplastic composition and wherein the thermoplastic starch comprises the borax at a concentration of at a concentration of 0.5 wt % to 8 wt %.

Description

(1) The present invention will now be further explained by the following non limiting Figures and Examples.

(2) FIG. 1 shows a model of the layered morphology of the article according to the present invention.

(3) FIG. 2 schematically shows a method for producing the article according to the present invention.

(4) FIG. 1 is a schematic representation of a biaxially stretched article 1 according to the present invention. The machine direction is indicated as MD, the transverse direction is indicated as TD and the thickness direction is indicated as Z. From FIG. 1 it is clear that the layers 2,3 extend in machine direction and transverse direction. The layers indicated with reference numeral 2 represent the polyolefin phase whereas the layers indicated with reference numeral 3 represent the starch phase. As can be clearly seen layers 2 and layers 3 alternate, i.e. the polyolefin phase layers 2 are stacked with the starch phase layers 3 in an alternating manner. The number of layers 2,3 predominantly depends on stretch ratios, thickness of the article and the thermoplastic composition. Article 1, not to scale, shows five layers 2,3 but the skilled person will understand that article 1 according to the present invention is not limited to such number of layers. In FIG. 1 the outer layers (i.e. the layers on the top and on the bottom of the stack) are shown to be layers of polyolefin. However, the present inventors have established that such outer layers may also be of thermoplastic starch.

(5) By means of electron microscopy the present inventors have established that the layer thickness (i.e. the thickness in Z direction) of the starch phase may be from 0.1-50 m, and the thickness of the polyolefin layers may be from 0.1-50 m. Preferably the layers are at most 20 m, more preferably at most 10 m.

(6) FIG. 2 schematically shows the stretching in machine and transverse direction for producing the article according to the present invention. Volume element 4 having a certain width in transverse direction, a certain length in machine direction (MD) and thickness in thickness direction is bi-axially stretched, meaning it is stretched in machine direction and transverse direction. As a consequence of the stretching in machine direction and transverse direction the thickness in thickness direction Z will decrease. Article 1 of the present invention is not a foam and consequently the density of volume element 4 remains substantially unchanged upon the stretching in machine and transverse direction. In the embodiment where the article of the present invention is manufactured by means of film blowing the stretch ratio in machine direction is equal to the ratio of take up speed of the blown film and the speed of the extrudate leaving the extrusion die. Such has been defined as ratio for draw down in U.S. Pat. No. 5,082,616 for example.

EXAMPLES

Experiment Set 1

(7) Blends of polyethylene granules and thermoplastic starch granules were compounded on a co-rotating twin screw extruder to produce a strand. Pieces of the strand were observed by a light microscopy to examine their homogeneity and morphology.

(8) Smooth appearance/low roughness of the surface of the strand and high homogeneity in the observed microstructure indicate that a blown film made from the same composition has a high gloss and low haze and is highly transparent. Rough surface and low homogeneity indicate that a blown film made from the same composition has a disturbed appearance.

(9) Materials

(10) The LDPE was LD2404, commercially available from SABIC having an MFI of about 4 g/10 min as measured according to ISO 1133 at 190 C. and 2.16 kg and having a density of about 924 kg/m.sup.3. The polyester was Ecoflex F blend C1200, commercially available from BASF, having an MFI at 190 C. and 2.16 kg of between 2.4 and 4.5 g/10 min. Three types of compatibilisers were used: Lotader 3410 (supplier: Arkema) which is a random terpolymer of ethylene, butylacrylate and maleic anhydride; Yparex 9603 (supplier: Yparex) which is polyethylene having at least 1 wt % maleic anhydride grafted thereon and Orevac 9305 (Arkema) which is a random terpolymer of ethylene, vinylacetate and maleic anhydride. TPS with borax comprises 2.4 wt % of borax and 28.6 wt % of glycerol with respect to the weight of the TPS. TPS without borax comprises no borax and 29.3 wt % of glycerol with respect to the weight of the TPS.

(11) The thermoplastic starch (TPS) composition was prepared by feeding the starch, glycerol, borax and regular processing agents to a first zone of a twin screw co-rotating extruder. The temperature profile of the extruder was 40-80-110-130-130-110 C. at a screw speed of 123 rpm. The thermoplastic starch was formed in the extruder. To avoid degradation and/or yellowing of the starch the temperature of the last zone of the extruder including the extrusion die was reduced to about 110 C. The starch was used as such, i.e. it was not dried or otherwise treated before feeding to the extruder.

(12) The polyethylene/thermoplastic starch (TPS) compounds forming the basis of the article according to the present invention were prepared by feeding the dry blend of polyethylene and the thermoplastic starch granules as prepared above and the compatibilizer and other additives to a first zone of a twin screw co-rotating extruder. The temperature profile of the extruder was 120-150-160-160-160-140-110 C. at a screw speed of 110 rpm and a torque of 63-73 Nm.

(13) Strand of each compound has been collected and the roughness and homogeneity has been determined.

(14) In Table 1 the composition of the polyethylene/thermoplastic starch (expressed in wt %) is listed.

(15) TABLE-US-00001 TABLE 1 TPS TPS LD Poly- Lotader Yparex Orevac with without dispersion 2404 ester 3410 9603 9305 borax borax roughness quality comp. 56 0 0 0 9 0 36 rough 0 ex. A example 1 56 0 9 0 0 0 36 smooth 0 comp. 22 33 9 0 0 36 0 very ex. B rough example 2 56 0 9 0 0 36 0 smooth ++ example 3 47 0 9 9 0 36 0 smooth +++ Dispersion quality +++ very fine ++ fine + reasonably fine 0 many drops bad

(16) Comparing comp ex A and ex 1, it can be understood that use of a random terpolymer of ethylene, butylacrylate and maleic anhydride results in a smooth surface compared to the use of a random terpolymer of ethylene, vinylacetate and maleic anhydride.

(17) Comparing comp ex B and ex 2, it can be understood that the addition of polyester results in a rough surface and a bad dispersion quality.

(18) Comparing ex 1 and ex 2, it can be understood that the addition of borax has an advantage that it improves dispersion quality.

(19) Comparing ex 2 and ex 3, it can be understood that the addition of polyethylene having at least 1 wt % maleic anhydride grafted thereon further improves the dispersion quality.

Experiment Set 2

(20) Polyethylene and thermoplastic starch were compounded on a co-rotating twin screw extruder and the obtained compound was used as the middle layer in three layer blown films. The outer layers of that three layer blown film consist of polyethylene or a dry blend of polyethylene and the random terpolymer of ethylene, bytylarcylate and maleic anhydride (Lotader 3410).

(21) Materials

(22) LDPE: LD2404 commercially available from SABIC having an MFI of about 4 g/10 min as measured according to ISO 1133 at 190 C. and 2.16 kg and having a density of about 924 kg/m.sup.3 and LD2008 commercially available from SABIC having an MFI at 190 C. and 2.16 kg of about 8 g/10 min as measured according to ISO 1133 at 190 C. and 2.16 kg and having a density of about 920 kg/m.sup.3. Type of compatibiliser used: Lotader 3410 (supplier: Arkema) which is a random terpolymer of ethylene, butylacrylate and maleic anhydride

(23) The polyethylene/thermoplastic starch composition forming the basis of the article according to the present invention was prepared by feeding the starch, glycerol, borax and the polyethylene components and the compatibilizer and other additives to a first zone of a twin screw co-rotating extruder. The temperature profile of the extruder was 30-60-110-160-160-110 C. at a screw speed of 80 rpm and a torque of 60-110 Nm. The thermoplastic starch was formed in the first zones of the extruder before the polyolefin started to melt. To avoid degradation and/or yellowing of the starch the temperature of the last zone of the extruder including the extrusion die was reduced to about 110 C. The starch was used as such, i.e. it was not dried or otherwise treated before feeding to the extruder.

(24) On a three layer blown film machine the polyethylene/thermoplastic starch material as described above was used for the inner layer while polyethylene or a dry blend of polyethylene and the random terpolymer Lotader 3410 was used for the outer layer. The temperature of the extruders (feeding the separate materials) was 125-140-135-130130 C. at a screw speed of 50 rpm, line speed of 9 m/min and throughput rate of about 20 kg/hr.

(25) The blow up rate (BUR) of all the three layer materials was 3.

(26) In Table 2 the composition, the quality and the oxygen permeability coefficient and the water vapour coefficient of the three layer blown films are listed.

(27) The composition of the inner layers in these three layer films are summarized in Table 3.

(28) TABLE-US-00002 TABLE 2 three layer film oxygen water [cc .Math. mm]/ [g .Math. mm]/ [m.sup.2 .Math. day] [m.sup.2 .Math. day] Gloss film average average 45 Haze inner outer ratio thickness [23 C. [38 C. ASTN ASTM layer layer inner/outer quality (m) 0% RH] 100% RH] D2456 D1003 LD2404 LD2404 70/30 Transparent 56 219 0.7 53 12.2 layer 1 LD2008 70/30 Transparent 75 34.6 1.5 layer 2 LD2008 70/30 Transparent 53 53.7 1.5 52.4 17.3 layer 2 LD2008 80/20 Transparent 57 46 1.6 44.4 16.7 layer 2 LD2008/ 70/30 Transparent 49 56.8 1.7 53.2 15.0 Lotader 3410 (90/10) layer 3 LD2008/ 60/40 very 14.4 68.3 Lotader disturbed 3410 (90/10)

(29) TABLE-US-00003 TABLE 3 inner layer components (wt %) Layer 1 Layer 2 Layer 3 LDPE1 (LD2404) 35.5 LDPE2 (LD2008) 35.5 13.5 Starch 29.4 29.4 52.3 Glycerol 19.8 19.8 23.4 Borax 1.1 1.1 2.0 Lotader 3410 11.8 11.8 4.5 Others 2.4 2.4 4.3

(30) It can be seen that three layer films were obtained with a good oxygen barrier property and a good water barrier property according to the invention.

(31) If the weight ratio of polyethylene over the thermoplastic starch becomes too low, e.g. less than 20:80, then the morphology of the polyethylene/thermoplastic starch blown film is not co-continuous anymore resulting into significant lower oxygen and water barrier properties.

Experiment Set 3

(32) Polyethylene and thermoplastic starch were compounded on a co-rotating twin screw extruder and the obtained compound was used as the middle layer in three layer blown films.

(33) Materials

(34) LDPE:

(35) Nexcoat 5, commercially available from SABIC having an MFI of about 5 g/10 min as measured according to ISO 1133 at 190 C. and 2.16 kg and having a density of about 919 kg/m.sup.3

(36) LD2404, commercially available from SABIC having an MFI of about 4 g/10 min as measured according to ISO 1133 at 190 C. and 2.16 kg and having a density of about 924 kg/m.sup.3

(37) LD2008, commercially available from SABIC having an MFI of about 8 g/10 min as measured according to ISO 1133 at 190 C. and 2.16 kg and having a density of about 920 kg/m.sup.3

(38) LD2015, commercially available from SABIC having an MFI of about 15 g/10 min as measured according to ISO 1133 at 190 C. and 2.16 kg and having a density of about 920 kg/m.sup.3

(39) Compatibiliser:

(40) Lotader 3410 (supplier: Arkema) which is a random terpolymer of ethylene, butylacrylate and maleic anhydride

(41) Granules for Inner Layer of Three Layer Blown Film

(42) Powder mixtures of starch, borax (if any) and regular processing agents were dry blended and dosed in the throat of an extruder. Pellet mixtures of LDPE and Lotader 3410 were also dosed in the throat of the extruder. Glycerol was heated up to 50 C. and gravimetrically fed to the extruder just after the throat of the extruder. The compositions are shown in Table A.

(43) The temperature profile of the extruder was 40-80-135-160-160-160-11095 C. at a screw speed of 225 rpm. The thermoplastic starch was formed in the first zones of the extruder before the LDPE started to melt. Strands from the die were cut into granules with underwater cutter equipment (LPU).

(44) Blown Film

(45) Three layer blown films were made by an extruder using the obtained granules for the inner layer and LDPE or dry blend of LDPE and Lotader 3410 for the outer layers. The weight ratio between the inner layer and the outer layers was 70:30.

(46) The temperature profile of the extruders was 125-140-135-130130 C. at a screw speed of 50 rpm, line speed of 9 m/min and throughput rate of about 20 kg/hr. The blow up rate (BUR) of all the three layer materials was 3.

Experiments 3-1

(47) The effects of the TPS content and Lotader 3410 content were investigated. The outer layers of the three layer blown film were made of Nexcoat 5.

(48) TABLE-US-00004 TABLE 3-1 components of inner layer (wt %) 1.1 1.2 1.3 1.4 1.5 Nexcoat 5 43.62 34.71 20.92 48.16 25.64 Starch 29.78 36.05 44.19 29.78 44.19 Glycerol 12.90 15.79 19.89 12.90 19.89 Borax 1.11 1.35 1.65 1.11 1.65 Lotader 3410 10.14 9.15 9.73 5.60 5.01 Others 2.45 2.95 3.62 2.45 3.62 total 100 100 100 100 100 glycerol/starch ratio 0.43 0.44 0.45 0.43 0.45 TPS in total (wt %) 43.79 53.19 65.73 43.79 65.73 (starch + glycerol + borax) ratio PE:TPS 50:50 39:61 24:76 52:48 28:72 Borax in TPS (wt %) 2.5 2.5 2.5 2.5 2.5 Properties of film oxygen [cc .Math. mm]/ 104 42 15 48 1.44 [m.sup.2 .Math. day] average [23 C., 0% RH] water [g .Math. mm]/ 1.2 1.4 1.6 1.2 2.5 [m.sup.2 .Math. day] average [38 C., 100% RH]

(49) The increase in the TPS amount in the inner layer leads to improvement in the oxygen barrier property of the film, as can be understood by comparison of films with inner layers 1.1, 1.2 and 1.3 (compatibiliser about 10 wt %) and comparison of films with inner layers 1.4 and 1.5 (compatibiliser about 5 wt %).

(50) The decrease in the compatibiliser amount in the inner layer leads to improvement in the oxygen barrier property of the film, as can be understood by comparison of films with inner layers 1.1 and 1.4 (TPS 43.79 wt %) and comparison of films with layer 1.3 and 1.5 (TPS 65.73 wt %%).

Experiments 3-2

(51) The effects of the MFI of the LDPE in the inner layer of the film were investigated. The outer layers of the three layer blown film were made of 80 wt % of LD2008 and 20 wt % of Lotader 3410.

(52) TABLE-US-00005 TABLE 3-2 components (wt %) 2.1 2.2 2.3 2.4 2.5 LDPE Type Nexcoat 5 LD2015 LD2404 LD2008 LD2015 MFI (g/10 min) 5 15 4 8 15 LDPE 25.64 25.64 22.71 22.71 22.71 Starch 44.19 44.19 40.29 40.29 40.29 Glycerol 19.89 19.89 26.96 26.96 26.96 Borax 1.65 1.65 1.50 1.50 1.50 Lotader 3410 5.01 5.01 5.24 5.24 5.24 Others 3.62 3.62 3.30 3.30 3.30 total 100 100 100 100 100 glycerol/starch ratio 0.45 0.45 0.67 0.67 0.67 TPS in total 65.73 65.73 68.75 68.75 68.75 (starch + glycerol + borax) ratio PE:TPS 28:72 28:72 25:75 25:75 25:75 Borax in TPS (wt %) 2.5 2.5 2.2 2.2 2.2 oxygen [cc .Math. mm]/ 1.44 3.75 0.49 1.12 2.77 [m.sup.2 .Math. day] average [23 C., 0% RH] water [g .Math. mm]/ 2.5 2.3 3.0 2.1 1.8 [m.sup.2 .Math. day] average [38 C., 100% RH]

(53) The decrease in the MFI of the LDPE in the inner layer leads to improvement in the oxygen barrier property of the film, as can be understood by comparison of films with inner layers 2.3, 2.4 and 2.5 (glycerol/starch ratio 0.67).

(54) The increase in the glycerol/starch ratio leads to improvement in the oxygen barrier property of the film, as can be understood by comparison of films with inner layers 2.2 and 2.5.

Experiments 3-3

(55) The effects of the presence of borax in the inner layer of the film were investigated. The outer layers of the three layer blown film were made of LD2008.

(56) TABLE-US-00006 TABLE 3-3 components (wt %) 3.1 3.2 3.3 LD2008 25.37 22.71 22.71 Starch 46.51 41.68 40.97 Glycerol 19.89 26.96 26.96 Borax 0 0 1.53 Lotader 3410 5.28 5.24 5.24 Others 2.95 3.41 2.59 total 100 100 100 glycerol/starch ratio 0.43 0.65 0.66 TPS in total (wt %) 66.4 68.64 69.46 (starch + glycerol + borax) ratio PE:TPS 28:72 25:75 25:75 Borax in TPS (wt %) 0 0 2.2 oxygen [cc .Math. mm]/ 6.4 2.18 0.145 [m2 .Math. day] average [23 C., 0% RH] water [g .Math. mm]/ 1.9 1.7 1.9 [m2 .Math. day] average [38 C., 100% RH]

(57) The increase in the glycerol/starch ratio leads to improvement in the oxygen barrier property of the film, as can be understood by comparison of films with inner layers 3.1 and 3.2.

(58) The presence of borax in the inner film leads to improvement in the oxygen barrier property of the film, as can be understood by comparison of films with inner layers 3.2 and 3.3.