CN109721976B - Polylactic acid composition and preparation method thereof, and biaxially stretched polylactic acid film and preparation method thereof - Google Patents
Polylactic acid composition and preparation method thereof, and biaxially stretched polylactic acid film and preparation method thereof Download PDFInfo
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- CN109721976B CN109721976B CN201711054383.0A CN201711054383A CN109721976B CN 109721976 B CN109721976 B CN 109721976B CN 201711054383 A CN201711054383 A CN 201711054383A CN 109721976 B CN109721976 B CN 109721976B
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Abstract
The invention relates to the field of polylactic acid films, in particular to a polylactic acid composition and a preparation method thereof, and a bidirectional stretching polylactic acid film and a preparation method thereof. The composition contains polylactic acid and polylactic acid copolyester, wherein the polylactic acid copolyester is linear copolyester containing an aliphatic-aromatic copolymer chain segment, a polylactic acid chain segment and a chain extender structure provided by a chain extender; the aliphatic-aromatic copolymerized chain segment consists of an aromatic polyester structure and an aliphatic polyester structure; the aromatic polyester structure is a polyester structure formed by copolymerizing a component a and a component b, and the aliphatic polyester structure is a polyester structure formed by copolymerizing a component c and a component b. The biaxially oriented polylactic acid film provided by the invention has higher flexibility under the condition of ensuring higher mechanical property, thereby not only ensuring the strength, but also reducing the noise.
Description
Technical Field
The invention relates to the field of polylactic acid films, in particular to a polylactic acid composition and a preparation method thereof, and a bidirectional stretching polylactic acid film and a preparation method thereof.
Background
The biaxial stretching technology can be used for processing materials such as polyolefin, nylon, polylactic acid, polyethylene terephthalate, polystyrene and the like, and the obtained biaxial stretching film has smooth surface, high transparency and good mechanical strength and is widely applied to packaging films. However, the types of the biaxially oriented films are still few at present, so that more varieties of the biaxially oriented films need to be developed, the performances of the biaxially oriented films need to be researched, and the application types and the application range of the biaxially oriented films are widened.
Polylactic acid biaxially oriented films are a promising biaxially oriented film. However, a significant disadvantage of biaxially oriented films of polylactic acid is the high noise which can be annoying to the consumer in many packaging applications.
Disclosure of Invention
The invention aims to overcome the defect of over-noise of the existing polylactic acid biaxially oriented film, and provides a biaxially oriented polylactic acid film with higher flexibility under the condition of ensuring higher mechanical property, a preparation method thereof, a polylactic acid composition and a preparation method thereof.
In order to achieve the above objects, an aspect of the present invention provides a polylactic acid composition comprising polylactic acid and a polylactic acid copolyester which is a linear copolyester containing an aliphatic-aromatic copolymer segment, a polylactic acid segment, and a chain extender structure provided by a chain extender;
wherein the aliphatic-aromatic copolymerized chain segment consists of an aromatic polyester structure and an aliphatic polyester structure; the aromatic polyester structure is a polyester structure formed by copolymerizing a component a and a component b, and the aliphatic polyester structure is a polyester structure formed by copolymerizing a component c and a component b;
wherein the component a is C8-C20The aromatic dibasic acid of (1), the above C8-C20Acid anhydride of aromatic dibasic acid of (2) and said C8-C20Esters of aromatic dibasic acids of (2)One or more of; the component b is C2-C10And/or C3-C10The alicyclic diol of (a); the component C is C2-C20Aliphatic dibasic acid of (1), C5-C10One or more of the alicyclic dibasic acids of (a) and their anhydrides;
wherein, based on the weight of the polylactic acid copolyester, the content of the aliphatic-aromatic copolymerized chain segment is 9-90 wt%, the content of the polylactic acid chain segment is 9-90 wt%, and the content of the chain extender structure is 0.1-5 wt%.
In a second aspect, the present invention provides a method for preparing a polylactic acid composition, the method comprising:
(1) in the presence of a titanium catalyst, carrying out esterification reaction on the component a, the component b and the component c;
(2) prepolymerizing the esterification reaction mixture obtained in step (1) under vacuum;
(3) carrying out polycondensation reaction on the prepolymerization reaction mixture obtained in the step (2) in the presence of a rare earth metal catalyst to obtain a product of an aliphatic-aromatic copolymer;
(4) carrying out copolymerization reaction on the product of the aliphatic-aromatic copolymer obtained in the step (3) and lactide monomer;
(5) carrying out chain extension reaction on the copolymerization reaction product obtained in the step (4) and a chain extender to obtain polylactic acid copolyester;
(6) blending and extruding polylactic acid and the polylactic acid copolyester obtained in the step (5);
wherein the component a is C8-C20The aromatic dibasic acid of (1), the above C8-C20Acid anhydride of aromatic dibasic acid of (2) and said C8-C20One or more of esters of aromatic dibasic acids of (a); the component b is C2-C10And/or C3-C10The alicyclic diol of (a); the component C is C2-C20Aliphatic dibasic acid of (1), C5-C10One or more of the alicyclic dibasic acids of (a) and their anhydrides;
the method enables the obtained polylactic acid copolyester to be linear copolyester containing aliphatic-aromatic copolymerized chain segments, polylactic acid chain segments and chain extender structures provided by chain extenders, and in the polylactic acid copolyester, the content of the aliphatic-aromatic copolymerized chain segments is 9-90 wt%, the content of the polylactic acid chain segments is 9-90 wt%, and the content of the chain extender structures is 0.1-5 wt%.
The third aspect of the present invention provides a polylactic acid composition obtained by the above-mentioned production method.
The fourth aspect of the invention provides a preparation method of a biaxially oriented polylactic acid film, which comprises the following steps:
(1) carrying out melt tape casting on the polylactic acid composition to obtain a polylactic acid cast sheet;
(2) and (3) biaxially stretching the polylactic acid cast sheet to form a film.
The fifth aspect of the present invention provides a biaxially oriented polylactic acid film obtained by the above method.
The biaxially oriented polylactic acid film provided by the invention has higher flexibility under the condition of ensuring higher mechanical property, thereby not only ensuring the strength, but also reducing the noise.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a polylactic acid composition, which contains polylactic acid and polylactic acid copolyester, wherein the polylactic acid copolyester is linear copolyester containing aliphatic-aromatic copolymerized chain segments, polylactic acid chain segments and a chain extender structure provided by a chain extender;
wherein the aliphatic-aromatic copolymerized chain segment consists of an aromatic polyester structure and an aliphatic polyester structure; the aromatic polyester structure is a polyester structure formed by copolymerizing a component a and a component b, and the aliphatic polyester structure is a polyester structure formed by copolymerizing a component c and a component b;
wherein the component a is C8-C20The aromatic dibasic acid of (1), the above C8-C20Acid anhydride of aromatic dibasic acid of (2) and said C8-C20One or more of esters of aromatic dibasic acids of (a); the component b is C2-C10Aliphatic diol (i.e. C)2-C20Aliphatic linear diols) and/or C3-C10The alicyclic diol of (a); the component C is C2-C20Aliphatic dibasic acid (i.e. C)2-C20Aliphatic linear dibasic acid) of (2), C5-C10One or more of the alicyclic dibasic acids of (a) and their anhydrides;
wherein, based on the weight of the polylactic acid copolyester, the content of the aliphatic-aromatic copolymerized chain segment is 9-90 wt%, the content of the polylactic acid chain segment is 9-90 wt%, and the content of the chain extender structure is 0.1-5 wt%.
According to the present invention, the polylactic acid is not particularly limited, and may be various polylactic acids commonly used in the art, but in order to be more compatible with the polylactic acid copolyester obtained in the present invention, the polylactic acid preferably has a weight average molecular weight of 8 to 20 ten thousand, and may be, for example, 4042D of natureworks corporation, revolute 210 of haizheng corporation, or the like.
According to the invention, the ratio of the polylactic acid and the polylactic acid copolyester can be changed in a wide range, and preferably, the weight ratio of the polylactic acid to the polylactic acid copolyester is 100: 10-100, preferably 100: 15-60, more preferably 100: 25-50.
According to the invention, the polylactic acid copolyester is prepared by firstly forming an aliphatic-aromatic copolymer composed of an aromatic polyester structure and an aliphatic polyester structure, wherein the tail end of the aliphatic-aromatic copolymer is basically hydroxyl and can be regarded as a macroinitiator, then introducing a lactide monomer, combining polylactic acid chain segments at two ends of the aliphatic-aromatic copolymer to obtain polylactic acid- (aliphatic-aromatic copolymer chain segments) -polylactic acid, wherein the tail end of the polylactic acid- (aliphatic-aromatic copolymer chain segments) -polylactic acid is basically hydroxyl, and then adding a chain extender to increase the molecular weight of the polylactic acid- (aliphatic-aromatic copolymer chain segments) -polylactic acid, so that the polylactic acid copolyester is formed.
According to the present invention, although it is sufficient to control the content of the aliphatic-aromatic copolymerized segment to 9 to 90% by weight, the content of the polylactic acid segment to 9 to 90% by weight, and the content of the chain extender structure to 0.1 to 5% by weight, in order to obtain a polylactic acid copolyester having more excellent properties, it is preferable that the content of the aliphatic-aromatic copolymerized segment is 12 to 78.5% by weight, the content of the polylactic acid segment is 22 to 80% by weight, and the content of the chain extender structure is 0.5 to 2% by weight, based on the weight of the polylactic acid copolyester. More preferably, based on the weight of the polylactic acid copolyester, the content of the aliphatic-aromatic copolymerized chain segment is 25-60 wt%, the content of the polylactic acid chain segment is 40-70 wt%, and the content of the chain extender structure is 0.5-1.5 wt%.
Wherein the structural unit of the aliphatic-aromatic copolymerized segment has a structure represented by formula (1):
wherein Ar is a group having a benzene ring, a naphthalene ring or an anthracene ring; m is preferably an integer from 1 to 20; n is preferably an integer from 1 to 16; t is preferably an integer from 1 to 20; x may be an integer of 1 to 100, preferably an integer of 15 to 60; y may be an integer of 1 to 100, preferably an integer of 15 to 60.
Preferably, Ar is an aryl group as follows:
wherein R is1、R2、R3、R4、R5And R6Each independently is hydrogen, C1-C4 alkyl, F,Cl、-NO2-CN OR-OR7Wherein R is7Is C1-C4 alkyl.
Most preferably, Ar is
Wherein R is1And R2As described above.
According to the present invention, in order to obtain better transparency and flexibility, it is preferable that the aliphatic-aromatic copolymerized segment has a weight-average molecular weight of 3,000-40,000g/mol and a molecular weight distribution coefficient of 1.2 to 2.5. More preferably, the aliphatic-aromatic copolymer segment has a weight average molecular weight of 6,000-35,000g/mol and a molecular weight distribution coefficient of 1.4 to 2.2.
According to the present invention, in order to obtain a polylactic acid copolyester more excellent in flexibility and degradation property, it is preferable that the component a is one or more of isophthalic acid, terephthalic acid, phthalic acid, 2, 6-naphthalenedicarboxylic acid, 1, 5-naphthalenedicarboxylic acid, 2, 7-naphthalenedicarboxylic acid, 4 '-biphenyldicarboxylic acid and 3, 4' -biphenyldicarboxylic acid, more preferably one or more of terephthalic acid, isophthalic acid and phthalic acid, and still more preferably terephthalic acid.
Preferably, the component b is one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, cyclohexanediol, and norbornanedimethanol, more preferably one or more of butanediol, hexanediol, and cyclohexanediol, and still more preferably butanediol.
Preferably, the component c is one or more of succinic acid, succinic anhydride, adipic acid, adipic anhydride, azelaic acid, sebacic acid, dodecanedioic acid, 1, 4-cyclohexanedicarboxylic acid, 1,2,4, 5-cyclohexanetetracarboxylic dianhydride and norbornanedioic acid, more preferably one or more of succinic acid, adipic acid and 1, 4-cyclohexanedicarboxylic acid, and still more preferably adipic acid.
According to the present invention, preferably, the molar ratio of the component a, the component b and the component c is 1: 2-5: 0.8 to 3, preferably 1: 2-4.5: 0.8-2.5, more preferably 1: 2-4.4: 1-1.5. Wherein, the copolymerization of the component a and the component b is that the aromatic dibasic acid and the dihydric alcohol are dehydrated and condensed to form a corresponding ester structure, and the copolymerization of the component c and the component b is that the aliphatic dibasic acid and the dihydric alcohol are dehydrated and condensed to form a corresponding ester structure. Thus, the above molar ratio can essentially represent the ratio of aromatic polyester structures to aliphatic polyester structures, although component b is usually used in larger amounts to facilitate the formation of hydroxyl termini for subsequent reactions.
According to the invention, the chain extender is as described above, one molecule of chain extender can bond two molecules of macromolecules, so that the chain extender can achieve the effect of chain extension, and the structure provided by the chain extender plays a role of a connection point in the polylactic acid copolyester. Preferably, the chain extender is one or more of polyisocyanate, bisoxazoline and epoxidized soybean oil, preferably 1, 4-cyclohexane-diisocyanate, 1, 3-cyclohexane-diisocyanate, 1, 2-cyclohexane-diisocyanate, 1-methyl-2, 4-diisocyanato-cyclohexane, 1-methyl-2, 6-diisocyanato-cyclohexane, tetramethylene-diisocyanate, octamethylene-diisocyanate, decamethylene-diisocyanate, dodecamethylene-diisocyanate, H6-2, 4-diisocyanatotoluene, 4 '-diisocyanatodiphenylmethane, 2' -diisocyanatodiphenylmethane, m-xylylene-diisocyanate, p-xylylene-diisocyanate, 2, 4-diisocyanatotoluene, 2, 6-diisocyanatotoluene, isopropenyldimethyltolylene-diisocyanate, α, α, α ', α' -tetramethyl-m-xylylene-diisocyanate, α, α, α ', α' -tetramethyl-p-xylylene-diisocyanate, 1, 6-hexamethylene-diisocyanate, trimethylhexane-diisocyanate, mixtures thereof, and mixtures thereof, Tetramethylhexane diisocyanate, nonane triisocyanate, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate), 4 '-diisocyanato-dicyclohexylmethane and the monomethyl-and dimethyl-substituted derivatives thereof, 2' - (1, 4) diisocyanato, 2 '-diisocyanato-dicyclohexylmethane and the monomethyl-and dimethyl-substituted derivatives thereof, 2' - (1, 4) diisocyanatoOne or more of (E) -phenylene) bisoxazoline, 2' - (1, 3-phenylene) bisoxazoline and epoxidized soybean oil
According to the present invention, the polylactic acid copolyester of the present invention can be considered as a linear copolyester containing an aliphatic-aromatic copolymerized segment, a polylactic acid segment and a chain extender structure provided by a chain extender, particularly a linear copolyester composed of an aliphatic-aromatic copolymerized segment, a polylactic acid segment and a chain extender structure provided by a chain extender, wherein, preferably, the weight average molecular weight of the polylactic acid copolyester is 100,000-1,000,000g/mol, preferably 110,000-500,000g/mol, more preferably 120,000-200,000g/mol, still more preferably 130,000-170,000 g/mol; the molecular weight distribution index is from 1.2 to 3, preferably from 1.5 to 2.8.
In a second aspect, the present invention provides a method for preparing a polylactic acid composition, the method comprising:
(1) in the presence of a titanium catalyst, carrying out esterification reaction on the component a, the component b and the component c;
(2) prepolymerizing the esterification reaction mixture obtained in step (1) under vacuum;
(3) carrying out polycondensation reaction on the prepolymerization reaction mixture obtained in the step (2) in the presence of a rare earth metal catalyst to obtain a product of an aliphatic-aromatic copolymer;
(4) carrying out copolymerization reaction on the product of the aliphatic-aromatic copolymer obtained in the step (3) and lactide monomer;
(5) carrying out chain extension reaction on the copolymerization reaction product obtained in the step (4) and a chain extender to obtain polylactic acid copolyester;
(6) blending and extruding polylactic acid and the polylactic acid copolyester obtained in the step (5);
wherein the component a is C8-C20The aromatic dibasic acid of (1), the above C8-C20Acid anhydride of aromatic dibasic acid of (2) and said C8-C20One or more of esters of aromatic dibasic acids of (a); the component b is C2-C10And/or C3-C10The alicyclic diol of (a); the component C is C2-C20Aliphatic dibasic acid of (1), C5-C10One or more of the alicyclic dibasic acids of (a) and their anhydrides;
the method enables the obtained polylactic acid copolyester to be linear copolyester containing aliphatic-aromatic copolymerized chain segments, polylactic acid chain segments and chain extender structures provided by chain extenders, and in the polylactic acid copolyester, the content of the aliphatic-aromatic copolymerized chain segments is 9-90 wt%, the content of the polylactic acid chain segments is 9-90 wt%, and the content of the chain extender structures is 0.1-5 wt%.
According to the present invention, as described above, the method preferably allows the obtained polylactic acid copolyester to have a content of the aliphatic-aromatic copolymer segment of 12 to 78.5 wt%, a content of the polylactic acid segment of 22 to 80 wt%, and a content of the chain extender structure of 0.5 to 2 wt%. More preferably, in the obtained polylactic acid copolyester, the content of the aliphatic-aromatic copolymerized chain segment is 25-60 wt%, the content of the polylactic acid chain segment is 40-70 wt%, and the content of the chain extender structure is 0.5-1.5 wt%.
According to the present invention, the component a, the component b and the component c are as described above, and the present invention is not described herein again.
According to the present invention, the steps (1) to (3) will produce an aliphatic-aromatic copolymer product containing a large amount of the aliphatic-aromatic copolymer and a small amount of a titanium-based catalyst and a rare earth metal catalyst, and those skilled in the art will understand that the aliphatic-aromatic copolymer product is composed of the aliphatic-aromatic copolymer and the catalyst. Preferably, the titanium-based catalyst is contained in the product in an amount of preferably 0.04 to 0.08% by weight, preferably 0.04 to 0.073% by weight, and more preferably 0.05 to 0.073% by weight. Preferably, the rare earth metal catalyst is contained in an amount of 0.022 to 0.1 wt%, preferably 0.025 to 0.095 wt%, more preferably 0.028 to 0.055 wt%.
Wherein the esterification reaction in step (1) is carried out for the purpose of sufficiently esterifying between the component a and the component b, and the component c and the component b, and preferably, the titanium-based catalyst is used in an amount of 0.01 to 0.04mol%, preferably 0.016 to 0.029mol%, based on the total molar amount of the component a, the component b and the component c, in step (1). The titanium catalyst in the dosage range has enough quantity to meet the requirement of the esterification reaction, promotes the copolymerization of the aliphatic-aromatic copolymer and the lactide monomer, and does not introduce excessive metal element content into the copolymerization of the aliphatic-aromatic copolymer and the lactide monomer and subsequent polylactic acid copolyester product chain-extended by the chain extender.
According to the invention, the purpose of step (2) is to pre-polymerize the esterification reaction product obtained in step (1) to obtain a low molecular weight pre-polymerized product, thereby facilitating the subsequent polycondensation in step (3).
According to the present invention, it is preferable that the rare earth metal catalyst is used in an amount of 0.005 to 0.03mol%, preferably 0.008 to 0.015mol%, based on the total molar amount of the component a, the component b and the component c, in the step (3). The dosage range is enough to meet the requirement of the polycondensation reaction in the step (3), promote the copolymerization of the aliphatic-aromatic copolymer and the lactide monomer, and avoid introducing excessive metal element content into the copolymerization of the aliphatic-aromatic copolymer and the lactide monomer and the subsequent polylactic acid copolyester product chain-extended by the chain extender.
According to the present invention, it is preferable that the molar ratio of the amount of the titanium-based catalyst used in the step (1) to the amount of the rare earth metal catalyst used in the polycondensation reaction in the step (3) is 1: 0.4 to 1, more preferably 1: 05-1.
According to the present invention, the titanium-based catalyst is preferably one or more of tetrabutyl titanate titanium isopropoxide, titanium dioxide and titanium tetrachloride, more preferably one or more of tetrabutyl titanate, titanium dioxide and titanium isopropoxide. The titanium catalyst can be a commercial product or can be prepared by a conventional method, and the preparation method of the titanium catalyst is not described herein again.
According to the present invention, preferably, the rare earth metal catalyst is one or more of lanthanum acetylacetonate, lanthanum chloride, neodymium isopropoxide, 2, 6-dibutyl-4-methylphenoxy-neodymium and lanthanum stearate, more preferably one or more of lanthanum acetylacetonate, neodymium isopropoxide and lanthanum stearate. The rare earth metal catalyst may be a commercially available product or may be prepared by a conventional method, for example, a method described in "organic Chemistry 1970,9,2505, j.chem.soc.chem.Commun.1983, 1499", and a detailed process of the preparation method thereof will not be described herein.
According to the present invention, preferably, the esterification reaction conditions include: the reaction temperature is 150 ℃ and 230 ℃, and the reaction time is 2-7 h. More preferably, the esterification reaction in step (1) comprises: firstly, carrying out a first esterification reaction on the component a and the component b, and then carrying out a second esterification reaction on the material after the first esterification reaction and the component c. Wherein the conditions of the first esterification reaction comprise: the reaction temperature is 150 ℃ and 230 ℃, and the reaction time is 1-3 h. The conditions of the second esterification reaction include: the reaction temperature is 180 ℃ and 220 ℃, and the reaction time is 1-4 h. More preferably, the conditions of the first esterification reaction include: the reaction temperature is 180 ℃ and 200 ℃, and the reaction time is 2-3 h. The conditions of the second esterification reaction include: the reaction temperature is 200 ℃ and 220 ℃, and the reaction time is 2-4 h.
According to the present invention, preferably, in step (2), the prepolymerization conditions include: the absolute pressure is below 500Pa, the reaction temperature is 200-250 ℃, and the reaction time is 1-6 h. More preferably, the prepolymerization conditions include: the absolute pressure is below 400Pa, the reaction temperature is 200-240 ℃, and the reaction time is 1-3 h.
Preferably, in step (3), the conditions of the polycondensation reaction include: under the absolute pressure of below 400Pa, the reaction temperature of 220 ℃ and 250 ℃, and the reaction time of 1-5 h. More preferably, the conditions of the polycondensation reaction include: the absolute pressure is below 400Pa, the reaction temperature is 220-240 ℃, and the reaction time is 1-2 h.
According to the present invention, the reactions of the above steps (1) to (3) are preferably carried out under an inert atmosphere, which may be provided by one or more of nitrogen, helium, neon, argon, and the like.
According to the present invention, the product of the aliphatic-aromatic copolymer of the present invention can be obtained by vacuum devolatilizing and drying the product obtained through the above steps (1) to (3) to remove unreacted monomers and the like, and therefore, most of the catalyst added during the reaction of the steps (1) to (3), i.e., the titanium-based catalyst and the rare earth metal catalyst, remains in the product of the aliphatic-aromatic copolymer of the present invention, and almost all of the product of the aliphatic-aromatic copolymer is the aliphatic-aromatic copolymer except the titanium-based catalyst and the rare earth metal catalyst. As described above, it is understood by those skilled in the art that the product of the aliphatic-aromatic copolymer of the present invention is composed of a titanium-based catalyst and a rare earth metal catalyst as well as the aliphatic-aromatic copolymer.
According to the present invention, the product of the aliphatic-aromatic copolymer obtained in the above steps (1) to (3) is subjected to copolymerization reaction with lactide monomer in step (4), thereby obtaining the aliphatic-aromatic-polylactic acid copolyester.
Wherein, because the product of the aliphatic-aromatic copolymer is provided with a small amount of titanium catalyst and rare earth metal catalyst, the copolymerization reaction in the step (4) is actually carried out in the presence of the titanium catalyst and the rare earth metal catalyst, and preferably, the product of the aliphatic-aromatic copolymer and the lactide monomer are used in the following amounts: the content of the titanium catalyst is 0.017-0.08 wt%, preferably 0.02-0.073 wt% based on the total weight of the lactide monomer; the content of the rare earth metal catalyst is 0.0033 to 0.1 wt%, preferably 0.01 to 0.095 wt%.
In addition, the product of the aliphatic-aromatic copolymer and the lactide monomer are used in the above ranges to achieve the object of the present invention. More preferably, the aliphatic-aromatic copolymer product is used in an amount of 15 to 110 parts by weight, more preferably 17 to 100 parts by weight, and still more preferably 35 to 100 parts by weight, based on 100 parts by weight of the lactide monomer.
According to the present invention, preferably, in the step (4), the copolymerization reaction conditions include: the reaction temperature is 150 ℃ and 190 ℃, and the reaction time is 2-5 h. More preferably, the copolymerization reaction conditions include: the reaction temperature is 170-185 ℃, and the reaction time is 2.5-5 h.
Wherein, preferably, the copolymerization reaction is carried out under a nitrogen atmosphere, and the copolymerization reaction is started after nitrogen is firstly introduced into the reaction system for 1-5 hours.
According to the present invention, in the step (5), the copolymerization reaction product obtained in the step (4) is subjected to a chain extension reaction with a chain extender, wherein the chain extender is selected as described above, and in a preferred embodiment of the present invention, the chain extender is used in an amount of 0.1 to 5 parts by weight, preferably 0.5 to 1.5 parts by weight, based on 100 parts by weight of the total weight of the lactide monomer and the aliphatic-aromatic copolymer.
Preferably, in step (5), the conditions of the chain extension reaction include: the reaction temperature is 150 ℃ and 190 ℃, and the reaction time is 20-100 min. More preferably, the conditions of the chain extension reaction include: the reaction temperature is 170-185 ℃, and the reaction time is 25-60 min.
According to the present invention, preferably, after the chain extension reaction is finished, a diluting solvent is added for dilution, and then methanol is added for precipitation, so as to obtain a precipitate of the polylactic acid copolyester product. The diluting solvent may be one or more of chloroform, dichloromethane, tetrahydrofuran and N, N-dimethylformamide, and preferably one or more of chloroform, dichloromethane and tetrahydrofuran.
In the invention, no catalyst is additionally added in the copolymerization reaction of the aliphatic-aromatic copolymer product and the lactide monomer in the step (4), so that the obtained polylactic acid copolyester product contains a very small amount of metal elements. For example, the content of the metal element in the polylactic acid copolyester product is 0.02 wt% or less, preferably 0.002 to 0.015 wt%, and more preferably 0.004 to 0.008 wt%.
According to the invention, in step (6), the polylactic acid is as described above, preferably the weight ratio of the polylactic acid to the polylactic acid copolyester is 100: 10-100, preferably 100: 15-60, more preferably 100: 25-50.
According to the present invention, the blending extrusion may be carried out in a manner and under conditions conventional in the art, for example, in a twin-screw extruder, and the temperature for extrusion pelletization may be, for example, 100 ℃ or 200 ℃. Thus, the polylactic acid composition of the present invention can be obtained.
The third aspect of the present invention provides a polylactic acid composition obtained by the above-mentioned production method.
The polylactic acid composition is as described above, and the method obtains a blended extruded product of polylactic acid and polylactic acid copolyester.
The fourth aspect of the invention provides a preparation method of a biaxially oriented polylactic acid film, which comprises the following steps:
(1) carrying out melt tape casting on the polylactic acid composition to obtain a polylactic acid cast sheet;
(2) and (3) biaxially stretching the polylactic acid cast sheet to form a film.
According to the present invention, the melt-casting cast sheet may be carried out in a casting machine, and preferably, the temperature of the melting is 180-200 ℃. The melt-cast sheet is preferably such that the thickness of the polylactic acid cast sheet is 200-500. mu.m.
According to the invention, preferably, the bidirectional stretching is synchronous stretching, and the synchronous stretching comprises preheating the polylactic acid cast sheet and then simultaneously performing MD and TD stretching; the conditions for the simultaneous stretching include: the stretching temperature is 60-90 ℃, the MD stretching ratio is 2-6 times, and the TD stretching ratio is 2-6 times.
The fifth aspect of the present invention provides a biaxially oriented polylactic acid film obtained by the above method.
The thickness of the biaxially stretched polylactic acid film is preferably 15 to 30 μm.
The biaxially oriented polylactic acid film has high mechanical strength and good flexibility. The biaxially stretched polylactic acid film may have a tensile strength of, for example, 27MPa or more, preferably 30MPa or more, more preferably 35MPa or more, and preferably 35 to 50 MPa; the TD tensile strength may be, for example, 35MPa or more, preferably 40MPa or more, more preferably 40 to 55 MPa; the MD elongation at break may be, for example, 70% or more, preferably 100% or more, more preferably 150% or more, preferably 160-250%; the TD elongation at break may be, for example, 50% or more, preferably 80% or more, more preferably 90% or more, and still more preferably 95 to 200%; the light transmittance may be, for example, 85% or more, preferably 88 to 95%; the haze may be, for example, 15% or less, preferably 5 to 12%.
The present invention will be described in detail below by way of examples.
In the following examples:
the weight average molecular weight and molecular weight distribution index were determined by Gel Permeation Chromatography (GPC) using Tetrahydrofuran (THF) as solvent, on a Waters-208 (with Waters 2410RI detector, 1.5mL/min flow rate, 30 ℃) instrument, molecular weight calibrated with monodisperse linear polystyrene standards;
the tensile strength and the tensile strength at break were measured according to the method described in GB/T1040.2-2006;
the light transmittance and haze were measured according to the methods described in GB/T2410-.
Catalyst preparation example 1
Lanthanum chloride (9.37 mmol) was dissolved in 50mL of water, and the solution was added to an aqueous solution containing 56.2mmol of acetylacetone, stirred at room temperature, and adjusted to neutral by adding an aqueous solution of 2N KOH. The reaction mixture was stirred, filtered and dried under vacuum at 60 ℃ to give 4g of lanthanum acetylacetonate.
Catalyst preparation example 2
Lanthanum chloride (9.37 mmol) was dissolved in 50mL of water, and the solution was added to an aqueous solution containing 20mmol of sodium stearate, stirred at room temperature, and adjusted to neutral by the addition of 2N HCl in water. The reaction mixture was stirred, filtered and dried under vacuum at 60 ℃ to give 11g of lanthanum stearate.
Preparation example 1
2.2mol of terephthalic acid, 5mol of butanediol and 1.6mmol of tetrabutyl titanate (purchased from Beijing chemical reagent company, chemical purity) are added into a reactor, stirred and heated to reflux under the protection of nitrogen, the reaction temperature is controlled at 180 ℃, and distilled water is collected until the water is almost collected (about reaction for 2 h). Adding 2.5mol succinic acid into the system, continuously stirring and heating to reflux, controlling the reaction temperature at 200 ℃, and collecting distilled water until the water is almost completely collected (about reaction for 2 h). Then, the system was prepolymerized at a temperature of 230 ℃ and an absolute pressure of 400Pa for about 1 hour. Finally, 0.85mmol of lanthanum acetylacetonate was added to the system, and polycondensation was carried out for about 1 hour under conditions of a temperature of 230 ℃ and an absolute pressure of 200Pa or less, and drying was carried out by vacuum devolatilization to obtain 750g of a white aliphatic-aromatic copolyester P1 having a weight-average molecular weight of 10,000g/mol and a molecular weight distribution index of 2.2, and in the copolyester P1, the content of tetrabutyl titanate was 0.060% by weight and the content of lanthanum acetylacetonate was 0.041% by weight.
Preparation example 2
2.2mol of terephthalic acid, 5mol of butanediol and 1.6mmol of tetrabutyl titanate are added into a reactor, stirred and heated to reflux under the protection of nitrogen, the reaction temperature is controlled at 200 ℃, and distilled water is collected until the water is almost collected (about reaction for 2 h). Adding 2.5mol succinic acid into the system, continuously stirring and heating to reflux, controlling the reaction temperature at 220 ℃, and collecting distilled water until the water is almost completely collected (about reaction for 2 h). Then, the system was prepolymerized at 240 ℃ and an absolute pressure of 400Pa for about 1 hour. Finally, 0.85mmol of lanthanum stearate was added to the system and polycondensation was carried out for about 1.5h at a temperature of 240 ℃ and an absolute pressure of 200Pa or less, and a purification process by vacuum devolatilization drying yielded 700g of a white aliphatic-aromatic copolyester P2 having a weight average molecular weight of 31,000g/mol and a molecular weight distribution index of 1.67, and in the copolyester P2, the tetrabutyl titanate content was 0.041% by weight and the lanthanum stearate content was 0.025% by weight.
Example 1
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
50g of L-lactide monomer (LLA) and 50g of aliphatic-aromatic copolyester P1 are respectively added into a reactor, after uniform mixing, high-purity nitrogen is used for purging for 5 hours, a reaction bottle is placed at 170 ℃ in the nitrogen atmosphere for reaction for 5 hours, 0.5g of 1, 6-hexamethylene diisocyanate is added, after reaction for 30 minutes, cooling is carried out, chloroform is used for dissolving the mixture, and precipitation is carried out in anhydrous methanol, so that the obtained precipitate is polylactic acid copolyester A192 g, and the weight average molecular weight, the molecular weight distribution index and the structure content of the precipitate are shown in Table 1.
200g of polylactic acid (natural works company brand 4042D) and 200g of polylactic acid copolyester A1 are added into a double-screw extruder for extrusion, wherein the temperature of each section from a feed inlet to an extrusion outlet is 100 ℃, 170 ℃ and 160 ℃. Drying the granulated material, and casting: the temperature of the melt casting is 190 ℃, and the temperature of the discharge port is 180 ℃; a cast polylactic acid sheet having a thickness of about 450 μm was obtained.
Putting the obtained polylactic acid casting sheet into a stretching clamp of a biaxial stretching device, and adopting synchronous stretching to prepare a film, wherein the method comprises the following steps: preheating a polylactic acid casting sheet, and simultaneously performing MD stretching and TD stretching; the conditions include: preheating temperature is 80 ℃, stretching temperature is 80 ℃, MD stretching magnification is 4 times, and TD stretching magnification is 4 times; finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 2
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
Respectively adding 50g of L-lactide monomer (LLA) and 100g of aliphatic-aromatic copolyester P1 into a reactor, uniformly mixing, purging with high-purity nitrogen for 5h, placing a reaction bottle at 180 ℃ in a nitrogen atmosphere for reacting for 3.5h, adding 1.5g of 2, 4-toluene diisocyanate, reacting for 40min, cooling, dissolving the mixture with chloroform, and precipitating in anhydrous methanol to obtain a precipitate, namely polylactic acid copolyester A2135 g, wherein the weight average molecular weight, the molecular weight distribution index and the structural content of the precipitate are shown in Table 1.
200g of polylactic acid (natural works company brand 4042D) and 300g of polylactic acid copolyester A2 are added into a double-screw extruder for extrusion, wherein the temperature of each section from a feed inlet to an extrusion outlet is 100 ℃, 170 ℃ and 160 ℃. Drying the granulated material, and casting: the temperature of the melt casting is 190 ℃, and the temperature of the discharge port is 180 ℃; a cast polylactic acid sheet having a thickness of about 450 μm was obtained.
Putting the obtained polylactic acid casting sheet into a stretching clamp of a biaxial stretching device, and adopting synchronous stretching to prepare a film, wherein the method comprises the following steps: preheating a polylactic acid casting sheet, and simultaneously performing MD stretching and TD stretching; the conditions include: preheating temperature is 80 ℃, stretching temperature is 80 ℃, MD stretching magnification is 4 times, and TD stretching magnification is 4 times; finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 3
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
According to the method of example 1, except that the polylactic acid copolyester is different, in the preparation thereof, the aliphatic-aromatic copolyester P2 is used instead of the aliphatic-aromatic copolyester P1; the polylactic acid copolyester A3 is obtained, and the weight average molecular weight, the molecular weight distribution index and the structure content are shown in Table 1.
Finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 4
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
According to the method of example 1, except that the polylactic acid copolyester was different, 1, 6-hexamethylene diisocyanate was used in an amount of 0.2g in the preparation thereof to obtain polylactic acid copolyester A4, whose weight average molecular weight, molecular weight distribution index and structural content are shown in Table 1.
Finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 5
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
According to the method described in example 1, except that the polylactic acid copolyester was different, 1, 6-hexamethylene diisocyanate was used in an amount of 4g in the preparation thereof, to obtain polylactic acid copolyester A5 having a weight average molecular weight, a molecular weight distribution index, and a structural content as shown in Table 1.
Finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Because the content of the chain extender is higher and the material contains gel with higher content, in GPC measurement, macromolecules and gel components are filtered, and the molecular weight of the measured material cannot be obviously increased. Also, the performance of the film is rather degraded due to more gel.
Example 6
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
The process of example 1 was followed except that the polylactic acid copolyester was prepared in such an amount that the L-lactide monomer was used in an amount of 15g and the aliphatic-aromatic copolyester P1 was used in an amount of 85 g; the polylactic acid copolyester A6 is obtained, and the weight average molecular weight, the molecular weight distribution index and the structure content are shown in Table 1.
Finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 7
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
According to the method of example 1, except that the polylactic acid copolyester was prepared, the amount of L-lactide monomer was 80g and the amount of aliphatic-aromatic copolyester P1 was 20 g; the polylactic acid copolyester A7 is obtained, and the weight average molecular weight, the molecular weight distribution index and the structure content are shown in Table 1.
Finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 8
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
According to the method described in example 1, except that the amount of polylactic acid copolyester A1 was 50g, a biaxially oriented polylactic acid film having a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 9
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
According to the method described in example 1, except that the amount of polylactic acid copolyester A1 was 100g, a biaxially oriented polylactic acid film having a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 10
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
According to the method described in example 1, except that the amount of polylactic acid copolyester A1 was 20g, a biaxially oriented polylactic acid film having a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Example 11
This example is intended to illustrate the polylactic acid composition and the method of preparing the same, and the biaxially oriented polylactic acid film and the method of preparing the same according to the present invention.
According to the method described in example 1, except that the amount of polylactic acid copolyester A1 was 400g, a biaxially oriented polylactic acid film having a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Comparative example 1
According to the method of example 1, except that the polylactic acid copolyester was different, 1, 6-hexamethylene diisocyanate was not used in the preparation thereof, to obtain polylactic acid copolyester D1, the weight average molecular weight, the molecular weight distribution index and the structural content of which are shown in Table 1.
Casting and biaxial stretching cannot be performed because the molecular weight is too low.
Comparative example 2
According to the method of example 1, except that the polylactic acid copolyester was different, 1, 6-hexamethylene diisocyanate was used in an amount of 10g in the preparation thereof, to obtain polylactic acid copolyester D2 having a weight average molecular weight, a molecular weight distribution index, and a structural content as shown in Table 1.
Finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Because the content of the chain extender is higher and the material contains gel with higher content, in GPC measurement, macromolecules and gel components are filtered, and the molecular weight of the measured material cannot be obviously increased. Also, the performance of the film is rather degraded due to more gel.
Comparative example 3
The process of example 1 was followed except that the polylactic acid copolyester was prepared in such an amount that the L-lactide monomer was used in an amount of 5g and the aliphatic-aromatic copolyester P1 was used in an amount of 95 g; the obtained polylactic acid copolyester D3 has the weight average molecular weight, molecular weight distribution index and structure content shown in Table 1.
Finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Comparative example 4
According to the method of example 1, except that the polylactic acid copolyester was prepared, the amount of L-lactide monomer was 95g and the amount of aliphatic-aromatic copolyester P1 was 5 g; the obtained polylactic acid copolyester D4 has the weight average molecular weight, molecular weight distribution index and structure content shown in Table 1.
Finally, a biaxially oriented polylactic acid film with a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
Comparative example 5
According to the method described in example 1, except that the polylactic acid copolyester was not used, a biaxially oriented polylactic acid film having a thickness of 25 μm was obtained, and the properties thereof are shown in Table 2.
TABLE 1
TABLE 2
Note: the noise is divided into class A, class B, class C and class D, wherein the noise of class D is very small, and the noise of class A is very large, wherein the noise size is class A > class B > class C > class D.
According to the data, the polylactic acid copolyester and the polylactic acid are blended to prepare the soft low-noise biaxially-oriented polylactic acid film; the film has excellent transmittance, lower haze and good mechanical properties.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (48)
1. A polylactic acid composition for preparing a biaxially oriented polylactic acid film is characterized by comprising polylactic acid and polylactic acid copolyester, wherein the polylactic acid copolyester is linear copolyester containing an aliphatic-aromatic copolymer chain segment, a polylactic acid chain segment and a chain extender structure provided by a chain extender;
wherein the aliphatic-aromatic copolymerized chain segment consists of an aromatic polyester structure and an aliphatic polyester structure; the aromatic polyester structure is a polyester structure formed by copolymerizing a component a and a component b, and the aliphatic polyester structure is a polyester structure formed by copolymerizing a component c and a component b;
wherein the component a is terephthalic acid; the component b is butanediol; the component c is succinic acid;
wherein, based on the weight of the polylactic acid copolyester, the content of the aliphatic-aromatic copolymerized chain segment is 9-90 wt%, the content of the polylactic acid chain segment is 9-90 wt%, and the content of the chain extender structure is 0.1-5 wt%; the weight average molecular weight of the polylactic acid copolyester is 100,000-1,000,000 g/mol;
the polylactic acid chain segment is provided by an L-lactide monomer, and the chain extender is polyisocyanate.
2. The composition of claim 1, wherein the chain extender structure is present in an amount of 0.5 to 2 wt.%, based on the weight of the polylactic acid copolyester.
3. The composition of claim 1, wherein the chain extender structure is present in an amount of 0.5 to 1.5% by weight, based on the weight of the polylactic acid copolyester.
4. The composition of claim 1, wherein the molar ratio of component a, component b, and component c is 1: (2-5): (0.8-3).
5. The composition of claim 1, wherein the molar ratio of component a, component b, and component c is 1: (2-4.5): (0.8-2.5).
6. The composition as claimed in claim 1, wherein the aliphatic-aromatic copolymerized segment has a weight-average molecular weight of 3,000-40,000 g/mol; the molecular weight distribution coefficient is 1.2-2.5.
7. The composition as claimed in claim 1, wherein the aliphatic-aromatic copolymerized segment has a weight-average molecular weight of 6,000-35,000 g/mol; the molecular weight distribution coefficient is 1.4-2.2.
8. The composition of any one of claims 1-7, wherein the chain extender is 1, 4-cyclohexane-diisocyanate, 1, 3-cyclohexane-diisocyanate, 1, 2-cyclohexane-diisocyanate, 1-methyl-2, 4-diisocyanato-cyclohexane, 1-methyl-2, 6-diisocyanato-cyclohexane, tetramethylene-diisocyanate, octamethylene-diisocyanate, decamethylene-diisocyanate, dodecamethylene-diisocyanate, H6-2, 4-diisocyanatotoluene, 4 '-diisocyanatodiphenylmethane, 2' -diisocyanatodiphenylmethane, m-xylylene-diisocyanate, p-xylylene-diisocyanate, 2, 4-diisocyanatotoluene, 2, 6-diisocyanatotoluene, isopropenyldimethyltolylene-diisocyanate, α, α, α ', α' -tetramethyl-m-xylylene-diisocyanate, α, α, α ', α' -tetramethyl-p-xylylene-diisocyanate, 1, 6-hexamethylene-diisocyanate, trimethylhexane-diisocyanate, tetramethylhexane-diisocyanate, nonane-triisocyanate, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane, N-isocyanato-3, 3, 5-dimethylene-diisocyanate, N-isomer, N-isomer-N-O, 4,4' -diisocyanato-dicyclohexylmethane and its monomethyl-and dimethyl-substituted derivatives, 2,4' -diisocyanato-dicyclohexylmethane and its monomethyl-and dimethyl-substituted derivatives and 2,2' -diisocyanato-dicyclohexylmethane and its monomethyl-and dimethyl-substituted derivatives.
9. The composition as claimed in any one of claims 1 to 7, wherein the weight average molecular weight of the polylactic acid copolyester is 110,000-500,000 g/mol; the molecular weight distribution index is 1.2-3.
10. The composition as claimed in any one of claims 1 to 7, wherein the weight average molecular weight of the polylactic acid copolyester is 120,000-200,000 g/mol; the molecular weight distribution index is 1.5-2.8.
11. The composition as claimed in any one of claims 1 to 7, wherein the weight average molecular weight of the polylactic acid copolyester is 130,000-170,000 g/mol.
12. The composition according to any one of claims 1 to 7, wherein the weight ratio of polylactic acid to polylactic acid copolyester is 100: 10-100.
13. The composition according to any one of claims 1 to 7, wherein the weight ratio of polylactic acid to polylactic acid copolyester is 100: 15-60.
14. The composition according to any one of claims 1 to 7, wherein the weight ratio of polylactic acid to polylactic acid copolyester is 100: 25-50.
15. A method for preparing a polylactic acid composition for preparing a biaxially oriented polylactic acid film, the method comprising:
(1) in the presence of a titanium catalyst, carrying out esterification reaction on the component a, the component b and the component c;
(2) prepolymerizing the esterification reaction mixture obtained in step (1) under vacuum;
(3) carrying out polycondensation reaction on the prepolymerization reaction mixture obtained in the step (2) in the presence of a rare earth metal catalyst to obtain a product of an aliphatic-aromatic copolymer;
(4) carrying out copolymerization reaction on the product of the aliphatic-aromatic copolymer obtained in the step (3) and lactide monomer;
(5) carrying out chain extension reaction on the copolymerization reaction product obtained in the step (4) and a chain extender to obtain polylactic acid copolyester;
(6) blending and extruding polylactic acid and the polylactic acid copolyester obtained in the step (5);
wherein the component a is terephthalic acid; the component b is butanediol; the component c is succinic acid;
the method enables the obtained polylactic acid copolyester to be linear copolyester containing aliphatic-aromatic copolymerized chain segments, polylactic acid chain segments and chain extender structures provided by chain extenders, and in the polylactic acid copolyester, the content of the aliphatic-aromatic copolymerized chain segments is 9-90 wt%, the content of the polylactic acid chain segments is 9-90 wt%, and the content of the chain extender structures is 0.1-5 wt%; the weight average molecular weight of the polylactic acid copolyester is 100,000-1,000,000 g/mol; the chain extender is polyisocyanate.
16. The preparation method of claim 15, wherein the method is used for obtaining the polylactic acid copolyester, wherein the content of the chain extender structure is 0.5-2 wt%.
17. The preparation method of claim 15, wherein the method is used for obtaining the polylactic acid copolyester, wherein the content of the chain extender structure is 0.5-1.5 wt%.
18. The method of claim 15, wherein the molar ratio of component a, component b, and component c is 1: (2-5): (0.8-3).
19. The method of claim 15, wherein the molar ratio of component a, component b, and component c is 1: (2-4.5): (0.8-2.5).
20. The production method as claimed in claim 15, wherein the step (3) is carried out such that the weight average molecular weight of the resulting aliphatic-aromatic copolymer is 3,000-40,000 g/mol; the molecular weight distribution coefficient is 1.2-2.5.
21. The production method as claimed in claim 15, wherein the step (3) is carried out such that the weight average molecular weight of the resulting aliphatic-aromatic copolymer is 6,000-35,000 g/mol; the molecular weight distribution coefficient is 1.4-2.2.
22. The production method according to any one of claims 15 to 21, wherein in the aliphatic-aromatic copolymer product in the step (3), the content of the titanium-based catalyst is 0.04 to 0.08 wt%, and the content of the rare earth metal catalyst is 0.022 to 0.1 wt%.
23. The production method according to any one of claims 15 to 21, wherein the titanium-based catalyst is used in an amount of 0.01 to 0.04mol% in step (1), based on the total molar amount of the component a, the component b and the component c.
24. The production method according to any one of claims 15 to 21, wherein the titanium-based catalyst is used in an amount of 0.016 to 0.029mol% in the step (1) based on the total molar amount of the component a, the component b and the component c.
25. The production method according to any one of claims 15 to 21, wherein the rare earth metal catalyst is used in an amount of 0.005 to 0.03mol% in step (3) based on the total molar amount of the component a, the component b and the component c.
26. The production method according to any one of claims 15 to 21, wherein the rare earth metal catalyst is used in an amount of 0.008 to 0.015mol% based on the total molar amount of the component a, the component b, and the component c in the step (3).
27. The production method according to any one of claims 15 to 21, wherein the molar ratio of the amount of the titanium-based catalyst used in step (1) to the amount of the rare earth metal catalyst used in the polycondensation reaction in step (3) is 1: 0.4-1.
28. The production method according to any one of claims 15 to 21, wherein the titanium-based catalyst is one or more of tetrabutyl titanate, titanium isopropoxide, titanium dioxide, and titanium tetrachloride; the rare earth metal catalyst is one or more of lanthanum acetylacetonate, lanthanum chloride, neodymium isopropoxide, 2, 6-dibutyl-4-methylphenoxy neodymium and lanthanum stearate.
29. The production method according to any one of claims 15 to 21, wherein the chain extender is 1, 4-cyclohexane-diisocyanate, 1, 3-cyclohexane-diisocyanate, 1, 2-cyclohexane-diisocyanate, 1-methyl-2, 4-diisocyanato-cyclohexane, 1-methyl-2, 6-diisocyanato-cyclohexane, tetramethylene-diisocyanate, octamethylene-diisocyanate, decamethylene-diisocyanate, dodecamethylene-diisocyanate, H6-2, 4-diisocyanatotoluene, 4' -diisocyanatodiphenylmethane, 2,2' -diisocyanatodiphenylmethane, m-xylylene-diisocyanate, p-xylylene-diisocyanate, 2, 4-diisocyanatotoluene, 2, 6-diisocyanatotoluene, isopropenyldimethyltolylene-diisocyanate, α, α, α ', α ' -tetramethyl-m-xylylene-diisocyanate, α, α ', α ' -tetramethyl-p-xylylene-diisocyanate, 1, 6-hexamethylene-diisocyanate, trimethylhexane-diisocyanate, tetramethylhexane-diisocyanate, nonane-triisocyanate, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane, 4,4' -diisocyanato-dicyclohexylmethane and its monomethyl-and dimethyl-substituted derivatives, 2,4' -diisocyanato-dicyclohexylmethane and its monomethyl-and dimethyl-substituted derivatives and 2,2' -diisocyanato-dicyclohexylmethane and its monomethyl-and dimethyl-substituted derivatives.
30. The production method according to any one of claims 15 to 21, wherein in step (1), the esterification reaction conditions include: the reaction temperature is 150 ℃ and 230 ℃, and the reaction time is 2-7 h.
31. The production method according to any one of claims 15 to 21, wherein in the step (2), the prepolymerization conditions include: the absolute pressure is below 500Pa, the reaction temperature is 200-250 ℃, and the reaction time is 1-6 h.
32. The production method according to any one of claims 15 to 21, wherein in step (3), the conditions of the polycondensation reaction include: the absolute pressure is below 400Pa, the reaction temperature is 220-250 ℃, and the reaction time is 1-5 h.
33. The production method according to any one of claims 15 to 21, wherein in step (4), the conditions of the copolymerization reaction include: the reaction temperature is 150 ℃ and 190 ℃, and the reaction time is 2-5 h.
34. The production method according to any one of claims 15 to 21, wherein in step (5), the conditions of the chain extension reaction include: the reaction temperature is 150 ℃ and 190 ℃, and the reaction time is 20-100 min.
35. The production method according to any one of claims 15 to 21, wherein, in the step (1), the esterification reaction comprises: firstly, carrying out a first esterification reaction on the component a and the component b, and then carrying out a second esterification reaction on the material after the first esterification reaction and the component c; wherein the conditions of the first esterification reaction comprise: the reaction temperature is 150-230 ℃, and the reaction time is 1-3 h; the conditions of the second esterification reaction include: the reaction temperature is 180 ℃ and 220 ℃, and the reaction time is 1-4 h.
36. The preparation method as claimed in any one of claims 15 to 21, wherein the method is such that the weight average molecular weight of the obtained polylactic acid copolyester is 150,000-500,000 g/mol; the molecular weight distribution index is 1.2-3.
37. The preparation method according to any one of claims 15 to 21, wherein the method is such that the molecular weight distribution index of the obtained polylactic acid copolyester is 1.5 to 2.8.
38. The method according to any one of claims 15 to 21, wherein the weight ratio of the polylactic acid to the polylactic acid copolyester is 100: 10-100.
39. The method according to any one of claims 15 to 21, wherein the weight ratio of the polylactic acid to the polylactic acid copolyester is 100: 15-60.
40. The method according to any one of claims 15 to 21, wherein the weight ratio of the polylactic acid to the polylactic acid copolyester is 100: 25-50.
41. A polylactic acid composition produced by the production method according to any one of claims 15 to 40.
42. A method for preparing a biaxially oriented polylactic acid film, which comprises the following steps:
(1) melt-casting a polylactic acid composition according to any one of claims 1 to 14 and 41 to obtain a cast polylactic acid sheet;
(2) and (3) biaxially stretching the polylactic acid cast sheet to form a film.
43. The method as claimed in claim 42, wherein the melting temperature is 180-200 ℃.
44. The method as claimed in claim 42, wherein the thickness of the cast polylactic acid sheet is 200-500 μm.
45. The method of any one of claims 42-44, wherein the biaxial stretching is simultaneous stretching comprising preheating a cast polylactic acid sheet followed by simultaneous MD and TD stretching; the conditions for the simultaneous stretching include: the stretching temperature is 60-90 ℃, the MD stretching ratio is 2-6 times, and the TD stretching ratio is 2-6 times.
46. A biaxially oriented polylactic acid film obtained by the method of any one of claims 42 to 44.
47. The biaxially stretched polylactic acid film according to claim 46, wherein the film has an MD tensile strength of 30MPa or more; TD tensile strength is more than 40 MPa; the MD elongation at break is more than 100%; the TD breaking elongation is more than 80%; the light transmittance is 88-95%; the haze is 5-12%.
48. The biaxially stretched polylactic acid film according to claim 46, wherein the film has an MD tensile strength of 35MPa or more; the MD elongation at break is more than 150%; the TD elongation at break is 90% or more.
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