CN113896867A - Method for synthesizing polylactic acid from lactic acid in one step and polylactic acid synthesized by method - Google Patents
Method for synthesizing polylactic acid from lactic acid in one step and polylactic acid synthesized by method Download PDFInfo
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Abstract
The invention relates to a method for synthesizing polylactic acid by lactic acid in one step, which comprises the steps of adding a product obtained after dehydration reaction and polycondensation reaction of lactic acid in a first-stage reaction kettle into a second-stage reaction kettle, uniformly coating the product on the inner wall of the second-stage reaction kettle, and stirring to keep the total retention time of the product in the second-stage reaction kettle to be 30-60 minutes to obtain the polylactic acid; the first-stage reaction kettle completely removes free water in the lactic acid in a stirring and vacuumizing mode; the product presents a linear molecular structure, and the secondary reaction kettle is a helical belt type reaction kettle with a scraper, a screw type reaction kettle with a scraper or an anchor type reaction kettle with a scraper. The weight average molecular weight of the polylactic acid prepared by the method is 6-12 ten thousand g/mol, the melting point is 165-175 ℃, the melting enthalpy is 42-51J/g, and the crystallinity is 45-55%. The polymerization method of the invention is simple, can ensure the crystallization performance of the polylactic acid while improving the molecular weight of the polylactic acid, and has less investment on reaction devices and easy industrialization.
Description
Technical Field
The invention belongs to the technical field of high polymer materials, and relates to a method for synthesizing polylactic acid by lactic acid in one step and the synthesized polylactic acid.
Background
With the increasing severity of the plastic pollution problem, people have attracted extensive attention to recycling plastics and developing plastic products from degradable materials. Among many degradable high molecular materials, polylactic acid (PLA) is a high molecular material obtained by polymerizing small molecular lactic acid obtained by microbial fermentation of biomass raw materials (corn, cassava, sugar beet, sugar cane), is a completely biodegradable green new material, has good biocompatibility and biodegradability, can be made into films, fibers, sheets and the like by adopting processes such as injection molding, extrusion, spinning and the like, and is widely applied to the fields of packaging, clothing, agriculture and the like.
At present, the synthesis method of polylactic acid mainly comprises a direct lactic acid polycondensation method, also called a 'one-step method', and a lactide ring-opening polymerization method, also called a 'two-step method'. The one-step method is to directly dehydrate and condense lactic acid under high temperature and high vacuum conditions to prepare polylactic acid, and has the advantages of simple production process, short flow, small equipment investment, low product cost and the like, but the prepared polylactic acid has lower molecular weight and is difficult to meet the requirements of actual use, so the development is slow.
The process of synthesizing polylactic acid by the lactic acid one-step method is a process of gradually dehydrating, but in the later stage of reaction, along with the increase of the solution viscosity, the formed water molecules can not be removed in time, so that the lactic acid, the polylactic acid and water can form a dynamic balance, and the molecular weight of the polylactic acid is inhibited from being further improved. For example, the research results of document 1 (research on the synthesis of polylactic acid by one-step method, chemical and biological engineering, 2005) show that the viscosity average molecular weight of polylactic acid prepared by direct polymerization by one-step method is only 3000, and the actual use value is not high. In order to solve the problem of low molecular weight of one-step polymerization, patent CN1563139A discloses that the intrinsic viscosity of polylactic acid is increased to 1.5dL/g by adding a chain extender into the one-step reaction system, and the weight average molecular weight of polylactic acid is increased to 8.9 kg/mol by using the chain extender and a molecular sieve together (CN 1446836A). Document 2 (one-step method for synthesizing degradable polylactic acidResearch, packaging science and engineering, 2008) also increased the molecular weight of polylactic acid made in one step from 5100 to 7600 by simply adding molecular sieves to the polymerization system to remove water. In document 3 (high molecular weight L-polylactic acid synthesized by melt polycondensation, plastic, 2017), polylactic acid with a weight average molecular weight of 16 kg/mol is prepared by a melt polycondensation method of lactic acid and a 5A molecular sieve as a dehydrating agent through process optimization. Although the use of the chain extender and the molecular sieve effectively improves the molecular weight of the obtained polylactic acid, the introduction of the chain extender destroys the regularity of the molecular chain, for example, as described in document 4 (the research on TDI chain-extended hydroxyl-terminated polylactic acid, the polyurethane industry, 2010), a chain-extended product with a viscosity-average molecular weight of 13.2 ten thousand is prepared, which is 6.3 times that of the hydroxyl-terminated polylactic acid before chain extension, but the crystallinity is reduced from 27.95% before chain extension to 6.94% after chain extension; as described in document 5(Preparation and catalysis of high-molecular-weight poly (L-lactic acid) by chain-extension reactions with phosphorous acid), a polylactic acid having a molecular weight of 12.6 ten thousand is obtained by a one-step process, and the molecular weight of the polylactic acid is increased by 103% compared with that before chain extension, but the glass transition temperature (T) is higher than that before chain extensiong) From 57.1 ℃ to 49.4 ℃, the crystallization temperature (T)c) From 125 ℃ down to 100 ℃, melting point (T)m) From 149 ℃ down to 135 ℃, crystallinity (X)c) From 37.8% down to 33.9%; and the added molecular sieve also has the problem of later recycling.
Therefore, it is very important to research a preparation method of polylactic acid which can simultaneously improve the molecular weight and avoid destroying the molecular chain regularity.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method for synthesizing polylactic acid by lactic acid in one step and the synthesized polylactic acid. The method takes lactic acid as a raw material, obtains a prepolymer with a certain molecular weight through dehydration reaction and polycondensation reaction in a first-stage reaction kettle, and then quickly and effectively removes water generated in the reaction under the high vacuum condition through the structural design of the reaction kettle in a second-stage reaction kettle by utilizing the principle of increasing the specific surface area of a reaction melt, so that the reaction moves to the positive direction. The method for preparing the polylactic acid has the characteristics of simple process, short flow and low cost, and the prepared polylactic acid can be applied to the field of general plastics or composite materials.
In order to achieve the purpose, the invention adopts the following scheme:
a method for synthesizing polylactic acid by lactic acid in one step, adding the product after dehydration reaction and polycondensation reaction of lactic acid in a first-stage reaction kettle into a second-stage reaction kettle, uniformly coating the product on the inner wall of the second-stage reaction kettle, and stirring to keep the total retention time of the product in the second-stage reaction kettle at 30-60 minutes to obtain the polylactic acid;
the first-stage reaction kettle completely removes free water in the lactic acid in a stirring and vacuumizing mode, (meanwhile, water molecules between molecules are removed to different degrees), so that the product is in a linear molecular structure, and the weight average molecular weight is 3-5 ten thousand g/mol;
the secondary reaction kettle is a spiral belt type reaction kettle with a scraper, a screw type reaction kettle with a scraper or an anchor type reaction kettle with a scraper; the distance between the scraper and the inner side wall of the secondary reaction kettle is 2-10 mm, and the uniform coating means that the scraper in the secondary reaction kettle uniformly coats the product on the inner wall of the secondary reaction kettle. The product which is squeezed into the inner side wall of the secondary reaction kettle is uniformly coated on the kettle wall of the secondary reaction kettle, the specific surface area of the melt is increased, water molecules generated in the reaction are rapidly removed, and the polylactic acid with high molecular weight and regular molecular chains is obtained.
The structure schematic diagram of the device comprising the first-stage reaction kettle and the second-stage reaction kettle is shown in figure 1. As can be seen from the figure, the device of the invention comprises a first-stage reaction kettle 3 and a second-stage reaction kettle 7 which are communicated in sequence, a stirring mechanism is arranged in the first-stage reaction kettle to stir the melt, dehydration reaction and polycondensation reaction are carried out under the action of a condensing system I1 and a vacuum system I2, the product after the polycondensation reaction is sent to the second-stage reaction kettle by a melt pump 5 through a kettle bottom valve 4 of the first-stage reaction kettle, the second-stage reaction kettle comprises a stirring mechanism and a scraper 6, the scraper is used for uniformly coating the melt sent by the melt pump on the inner side wall of the second-stage reaction kettle, the position and the number of the scraper are determined by the whole inner side wall of the scraper which can be coated below a material inlet, the stirring mechanism is used for the stirring process during the scraper coating, the melt is fully reacted under the action of a condensing system II 9 and a vacuum system II 10 of the second-stage reaction kettle, a material outlet valve 8 is arranged at the bottom of the second-stage reaction kettle, discharging after the retention time is reached to obtain the polylactic acid.
As a preferred technical scheme:
in the method for synthesizing polylactic acid from lactic acid in one step, the step of adding the secondary reaction kettle is that the product is pumped into the kettle along the inner side wall of the secondary reaction kettle by a melt pump, and the height of the product at the feed inlet of the secondary reaction kettle is higher than the stirring height of the scraper in the secondary reaction kettle (generally, the highest position to which the scraper can stir).
In order to further increase the molecular weight, the product obtained by the reaction in the second-stage reaction kettle can be added into the third-stage reaction kettle, wherein the addition of the third-stage reaction kettle means that the product is uniformly coated on the inner wall of the third-stage reaction kettle while being added into the third-stage reaction kettle, and the product is stirred to keep the total residence time of the product in the third-stage reaction kettle within 30-60 minutes, so that the polylactic acid is obtained; the third-stage reaction kettle is the same as the second-stage reaction kettle, and the manner of adding the third-stage reaction kettle is the same as that of adding the second-stage reaction kettle.
In the method for synthesizing polylactic acid from lactic acid in one step, the primary reaction kettle is a helical belt type, screw type or anchor type reaction vessel with stirring function.
The method for synthesizing the polylactic acid by lactic acid in one step has the advantages that the temperature of the dehydration reaction in the first-stage reaction kettle is 80-150 ℃, and the pressure is 3 multiplied by 104～10×104Pa。
The method for synthesizing the polylactic acid by lactic acid in one step has the polycondensation reaction temperature in the first-stage reaction kettle of 150-180 ℃ and the pressure of 1 multiplied by 103～5×103Pa, the time is 6-12 hours.
In the method for synthesizing polylactic acid by lactic acid in one step, the catalyst for the polycondensation reaction is tin powder, stannous octoate, stannous chloride, p-toluenesulfonic acid or a composite catalyst; the addition amount of the catalyst is 0.5-2 per mill of the mass of the lactic acid, and the composite catalyst is a mixture of p-toluenesulfonic acid and stannous chloride.
The method for synthesizing the polylactic acid by lactic acid in one step has the advantages that the reaction temperature in the secondary reaction kettle is 150-180 ℃, and the pressure is 100-500 Pa.
According to the method for synthesizing the polylactic acid by lactic acid in one step, the reaction temperature in the three-stage reaction kettle is 150-180 ℃, and the pressure is below 300 Pa.
The invention also provides polylactic acid prepared by adopting the method for synthesizing the polylactic acid by lactic acid in one step, wherein the weight average molecular weight of the polylactic acid is 6-12 ten thousand g/mol, the melting point is 165-175 ℃, the melting enthalpy is 42-51J/g, and the crystallinity is 45-55%.
The principle of the invention is as follows:
both theory and experiment results show that the rapid and timely removal of water molecules in the reaction process is the key for improving the molecular weight of the polylactic acid. Therefore, the invention provides a method for increasing the molecular weight of polylactic acid by increasing the specific surface area of a melt at the later stage of polymerization, accelerating the removal of water molecules and optimizing the polymerization reaction mode and reaction process through device design on the premise of not changing the linear molecular structure of the polylactic acid and not adding external components (such as molecular sieves and other dehydrating agents). The secondary reaction kettle is a spiral belt type reaction kettle with a scraper, a screw type reaction kettle with a scraper or an anchor type reaction kettle with a scraper, a product obtained after dehydration and polycondensation reaction of lactic acid in the primary reaction kettle is quantitatively pumped into the kettle along the inner side wall of the secondary reaction kettle through a melt pump, and the product pumped into the inner side wall of the secondary reaction kettle is stirred by the spiral belt type reaction kettle with the scraper, the screw type reaction kettle with the scraper or the anchor type reaction kettle with the scraper, so that the melt is uniformly coated on the inner wall of the reaction kettle to form a thin layer of the melt, the specific surface area of the melt is increased, and the generated water molecules are rapidly removed under the conditions of high temperature and high vacuum, so that the reaction moves towards the polymerization direction.
Advantageous effects
(1) According to the invention, the second-stage reaction kettle is connected in series behind the first-stage reaction kettle, and the polymerization melt of the first-stage reaction kettle is uniformly coated on the kettle wall through the stirring device with the scraper in the kettle, so that the specific surface area of the melt is increased, water molecules generated in the reaction process are rapidly removed, the reaction is moved to the positive direction, the molecular weight of polylactic acid is improved, and the crystallization performance of the polylactic acid is ensured;
(2) the polymerization method provided by the invention is simple, the investment of the reaction device is low, the industrialization is easy to realize, and the performance of the prepared polylactic acid can meet the application of conventional plastic products.
Drawings
FIG. 1 is a schematic diagram of a device structure containing a first-stage reaction kettle and a second-stage reaction kettle, wherein 1-a condensation system I, 2-a vacuum system I, 3-the first-stage reaction kettle, 4-a kettle bottom valve, 5-a melt pump, 6-a scraper, 7-the second-stage reaction kettle, 8-a discharge valve, 9-the condensation system II and 10-a vacuum system II.
Detailed Description
The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1
A device for synthesizing polylactic acid by lactic acid in one step comprises a helical ribbon type reaction kettle, a secondary reaction kettle and a tertiary reaction kettle which are sequentially communicated and have a stirring effect; wherein, second grade reation kettle is the same with tertiary reation kettle, is the spiral shell belt reation kettle of taking the scraper blade, and the interval between scraper blade and second grade reation kettle's the inside wall is 2 mm. When the first-stage reaction kettle is communicated with the second-stage reaction kettle, the height of a feed inlet on the second-stage reaction kettle is higher than the stirring height (the height difference is 10cm) of the scraper in the second-stage reaction kettle.
The method for synthesizing the polylactic acid from the lactic acid in one step is carried out by adopting the device, and comprises the following steps:
(1) preparing raw materials:
lactic acid: l-lactic acid with the mass content of 90% (the rest is water);
catalyst: stannous chloride;
(2) the lactic acid was used as a raw material, and the air in the first-stage reaction vessel was replaced with nitrogen gas to conduct dehydration reaction of L-lactic acid in the first-stage reaction vessel (temperature 100 ℃ C., pressure 5X 10)4Pa for 5 hours), and then continuously adding the catalyst into the first-stage reaction kettle to perform polycondensation reaction (the temperature is 150 ℃, and the pressure is 2 multiplied by 103Pa, for 8 hours);
wherein the addition amount of the catalyst is 1 per mill of the mass of the L-lactic acid, and free water in the lactic acid is completely removed in a first-stage reaction kettle by stirring (the stirring speed of the dehydration reaction and the polycondensation reaction is consistent and is 40r/min) and vacuumizing;
the product obtained in the step (1) presents a linear molecular structure, and the weight average molecular weight is 3.9 ten thousand g/mol;
(3) pumping one product obtained after the reaction in the step (2) into a kettle along the inner side wall of a secondary reaction kettle by a melt pump, uniformly coating the product on the inner wall of the secondary reaction kettle by a scraper blade, and stirring to keep the total retention time of the product in the secondary reaction kettle to be 30 minutes; the reaction temperature in the secondary reaction kettle is 160 ℃, and the pressure is 300 Pa.
(4) Pumping the product reacted in the step (3) into a kettle along the inner side wall of the third-stage reaction kettle by a melt pump, uniformly coating the product on the inner wall of the third-stage reaction kettle by a scraper blade, and stirring to keep the total residence time of the product in the third-stage reaction kettle to be 30 minutes to obtain polylactic acid; the reaction temperature in the third-stage reaction kettle is 160 ℃, and the pressure is 200 Pa.
The obtained polylactic acid had a weight average molecular weight of 11.3 ten thousand g/mol, a melting point of 175 ℃, a melting enthalpy of 49J/g, and a crystallinity of 52.7% as measured by permeation gel chromatography (GPC) using chloroform as a solvent.
Example 2
A device for synthesizing polylactic acid by lactic acid in one step comprises a helical ribbon type reaction kettle, a secondary reaction kettle and a tertiary reaction kettle which are sequentially communicated and have a stirring effect; wherein the second-stage reaction kettle and the third-stage reaction kettle are the same and are both helical-ribbon reaction kettles with scrapers; and the distance between the scraper and the inner side wall of the secondary reaction kettle is 5 mm. When the first-stage reaction kettle is communicated with the second-stage reaction kettle, the height of a feed inlet on the second-stage reaction kettle is higher than the stirring height (the height difference is 10cm) of the scraper in the second-stage reaction kettle.
The method for synthesizing the polylactic acid from the lactic acid in one step is carried out by adopting the device, and comprises the following steps:
(1) preparing raw materials:
lactic acid: l-lactic acid with the mass content of 90% (the rest is water);
catalyst: p-toluenesulfonic acid;
(2) the lactic acid was used as a raw material, and the air in the first-stage reaction vessel was replaced with nitrogen gas to conduct dehydration reaction of L-lactic acid in the first-stage reaction vessel (temperature 130 ℃ C., pressure 10X 10)4Pa for 5 hours), and then continuously adding the catalyst into the first-stage reaction kettle to perform polycondensation reaction (the temperature is 170 ℃, and the pressure is 4 multiplied by 103Pa for 12 hours);
wherein the addition amount of the catalyst is 2 per mill of the mass of the L-lactic acid, and free water in the lactic acid is completely removed in a first-stage reaction kettle by stirring (the stirring speed of the dehydration reaction and the polycondensation reaction is consistent and is 60r/min) and vacuumizing;
the product obtained in the step (1) presents a linear molecular structure, and the weight average molecular weight is 4.8 ten thousand g/mol;
(3) pumping one product obtained after the reaction in the step (2) into a kettle along the inner side wall of a secondary reaction kettle by a melt pump, uniformly coating the product on the inner wall of the secondary reaction kettle by a scraper blade, and stirring to keep the total retention time of the product in the secondary reaction kettle to be 30 minutes; the reaction temperature in the secondary reaction kettle is 180 ℃ and the pressure is 100 Pa.
(4) Pumping the product reacted in the step (3) into a kettle along the inner side wall of the third-stage reaction kettle by a melt pump, uniformly coating the product on the inner wall of the third-stage reaction kettle by a scraper blade, and stirring to keep the total residence time of the product in the third-stage reaction kettle to be 30 minutes to obtain polylactic acid; the reaction temperature in the third-stage reaction kettle is 180 ℃, and the pressure is 300 Pa.
The obtained polylactic acid had a weight average molecular weight of 11.5 ten thousand g/mol, a melting point of 175 ℃, a melting enthalpy of 50J/g, and a crystallinity of 53.8% as measured by permeation gel chromatography (GPC) using chloroform as a solvent.
Example 3
A device for synthesizing polylactic acid by lactic acid in one step comprises a helical ribbon type reaction kettle, a secondary reaction kettle and a tertiary reaction kettle which are sequentially communicated and have a stirring effect; wherein the second-stage reaction kettle and the third-stage reaction kettle are the same and are both helical-ribbon reaction kettles with scrapers; and the distance between the scraper and the inner side wall of the secondary reaction kettle is 10 mm. When the first-stage reaction kettle is communicated with the second-stage reaction kettle, the height of a feed inlet on the second-stage reaction kettle is higher than the stirring height (the height difference is 10cm) of the scraper in the second-stage reaction kettle.
The method for synthesizing the polylactic acid from the lactic acid in one step is carried out by adopting the device, and comprises the following steps:
(1) preparing raw materials:
lactic acid: l-lactic acid with the mass content of 90% (the rest is water);
catalyst: tin powder;
(2) the lactic acid was used as a raw material, and the air in the first-stage reaction vessel was replaced with nitrogen gas to conduct dehydration reaction of L-lactic acid in the first-stage reaction vessel (temperature 80 ℃ C., pressure 3X 10)4Pa for 3 hours), and then continuously adding the catalyst into the first-stage reaction kettle to perform polycondensation reaction (the temperature is 180 ℃, and the pressure is 1 multiplied by 103Pa, time 10 hours);
wherein the addition amount of the catalyst is 2 per mill of the mass of the L-lactic acid, and free water in the lactic acid is completely removed in a first-stage reaction kettle by stirring (the stirring speed of the dehydration reaction and the polycondensation reaction is consistent and is 30r/min) and vacuumizing;
the product obtained in the step (1) presents a linear molecular structure, and the weight average molecular weight is 4.7 ten thousand g/mol;
(3) pumping one product obtained after the reaction in the step (2) into a kettle along the inner side wall of a secondary reaction kettle by a melt pump, uniformly coating the product on the inner wall of the secondary reaction kettle by a scraper blade, and stirring to keep the total retention time of the product in the secondary reaction kettle to be 60 minutes; the reaction temperature in the secondary reaction kettle is 180 ℃ and the pressure is 500 Pa.
(4) Pumping the product reacted in the step (3) into a kettle along the inner side wall of the third-stage reaction kettle by a melt pump, uniformly coating the product on the inner wall of the third-stage reaction kettle by a scraper blade, and stirring to keep the total residence time of the product in the third-stage reaction kettle to be 60 minutes to obtain polylactic acid; the reaction temperature in the third-stage reaction kettle is 180 ℃, and the pressure is 300 Pa.
The obtained polylactic acid had a weight average molecular weight of 11.8 ten thousand g/mol, a melting point of 175 ℃, a melting enthalpy of 50J/g, and a crystallinity of 53.8% as measured by permeation gel chromatography (GPC) using chloroform as a solvent.
Example 4
A device for synthesizing polylactic acid by lactic acid in one step comprises a helical ribbon type reaction kettle and a secondary reaction kettle which are sequentially communicated and have a stirring effect; wherein the secondary reaction kettle is a helical ribbon type reaction kettle with a scraper; and the distance between the scraper and the inner side wall of the secondary reaction kettle is 2 mm. When the first-stage reaction kettle is communicated with the second-stage reaction kettle, the height of a feed inlet on the second-stage reaction kettle is higher than the stirring height (the height difference is 5cm) of the scraper in the second-stage reaction kettle.
The method for synthesizing the polylactic acid from the lactic acid in one step is carried out by adopting the device, and comprises the following steps:
(1) preparing raw materials:
lactic acid: 90% by mass of L-lactic acid (the balance being water);
catalyst: stannous chloride;
(2) the lactic acid was used as a raw material, and the air in the reaction vessel was replaced with nitrogen gas to conduct dehydration reaction of L-lactic acid in a primary reaction vessel (temperature 100 ℃ C., pressure 5X 10)4Pa for 4 hours), and then continuously adding the catalyst into the first-stage reaction kettle to carry out polycondensation reaction (the temperature is 150 ℃, and the pressure is 2 multiplied by 103Pa, for 8 hours);
wherein the addition amount of the catalyst is 1 per mill of the mass of the L-lactic acid, and free water in the lactic acid is completely removed in a first-stage reaction kettle by stirring (the stirring speed of the dehydration reaction and the polycondensation reaction is consistent and is 50r/min) and vacuumizing;
the product obtained in the step (2) presents a linear molecular structure, and the weight average molecular weight is 3.6 ten thousand g/mol;
(3) pumping one product obtained after the reaction in the step (2) into a kettle along the inner side wall of a secondary reaction kettle by a melt pump, uniformly coating the product on the inner wall of the secondary reaction kettle by a scraper blade, and stirring to keep the total retention time of the product in the secondary reaction kettle within 30 minutes to obtain polylactic acid; the reaction temperature in the secondary reaction kettle is 160 ℃, and the pressure is 300 Pa.
The obtained polylactic acid has a weight average molecular weight of 6.7 ten thousand g/mol, a melting point of 168 deg.C, a melting enthalpy of 47J/g, and a crystallinity of 50.5% as determined by permeation gel chromatography (GPC) using chloroform as a solvent.
Comparative example 1
A method for synthesizing polylactic acid from lactic acid in one step comprises the following steps: adding 90% L-lactic acid into first-stage reaction kettle, replacing air in the reaction kettle with nitrogen gas, and reacting at 100 deg.C and 5 × 104Removing free water under Pa to obtain dehydrated lactic acid (4 hr), adding stannous chloride as catalyst with L-lactic acid mass of 1 ‰, slowly raising temperature of the first-stage reaction kettle to 150 deg.C, and gradually reducing vacuum degree to 2 × 103Pa, and carrying out polycondensation reaction for 10 hours to obtain the polylactic resin.
The weight average molecular weight of the polylactic acid resin was measured by GPC using chloroform as a solvent, and the polylactic acid resin had a melting point of 158 ℃ by DSC, a melting enthalpy of 48J/g and a crystallinity of 51.6% by DSC.
Comparative example 2
A method for synthesizing polylactic acid from lactic acid in one step comprises the following steps: adding 90% L-lactic acid into first-stage reaction kettle, replacing air in the reaction kettle with nitrogen gas, and reacting at 100 deg.C and 5 × 104Removing free water under Pa to obtain dehydrated lactic acid (4 hr), adding stannous chloride as catalyst with L-lactic acid mass of 1 ‰, slowly raising temperature of the first-stage reaction kettle to 150 deg.C, and gradually reducing vacuum degree to 2 × 103Pa, performing polycondensation reaction for 5 hours, adding a chain extender (toluene diisocyanate TDI), and continuing the reaction for 5 hours to obtain the polylactic resin.
The weight average molecular weight of the polylactic acid resin was 10.3 ten thousand g/mol by GPC using chloroform as a solvent, the melting point was 155 ℃ by DSC, the melting enthalpy was 25J/g, and the crystallinity was 26.9%. It can be seen that the addition of the chain extender to the polycondensation reaction, although the molecular weight can be increased, the melting point, enthalpy and the like of the final product are lowered.
Example 5
A device for synthesizing polylactic acid by lactic acid in one step comprises a helical ribbon type reaction kettle and a secondary reaction kettle which are sequentially communicated and have a stirring effect; wherein the secondary reaction kettle is a helical ribbon type reaction kettle with a scraper; and the distance between the scraper and the inner side wall of the secondary reaction kettle is 5 mm. When the first-stage reaction kettle is communicated with the second-stage reaction kettle, the height of a feed inlet on the second-stage reaction kettle is higher than the stirring height (the height difference is 5cm) of the scraper in the second-stage reaction kettle.
The method for synthesizing the polylactic acid from the lactic acid in one step is carried out by adopting the device, and comprises the following steps:
(1) preparing raw materials:
lactic acid: 90% by mass of L-lactic acid (the balance being water);
catalyst: the mass ratio is 1: 1, a mixture of p-toluenesulfonic acid and stannous chloride;
(2) the lactic acid was used as a raw material, and the air in the reaction vessel was replaced with nitrogen gas to conduct dehydration reaction of L-lactic acid in the first-stage reaction vessel (temperature 1)At 50 deg.C and a pressure of 9X 104Pa for 5 hours), and then continuously adding the catalyst into the first-stage reaction kettle to perform polycondensation reaction (the temperature is 170 ℃, and the pressure is 2 multiplied by 103Pa for 12 hours);
wherein the addition amount of the catalyst is 1 per mill of the mass of the L-lactic acid, and free water in the lactic acid is completely removed in a first-stage reaction kettle by stirring (the stirring speed of the dehydration reaction and the polycondensation reaction is consistent and is 30r/min) and vacuumizing;
the product obtained in the step (2) presents a linear molecular structure, and the weight average molecular weight is 4.8 ten thousand g/mol;
(3) pumping one product obtained after the reaction in the step (2) into a kettle along the inner side wall of a secondary reaction kettle by a melt pump, uniformly coating the product on the inner wall of the secondary reaction kettle by a scraper blade, and stirring to keep the total retention time of the product in the secondary reaction kettle within 30 minutes to obtain polylactic acid; the reaction temperature in the secondary reaction kettle is 180 ℃ and the pressure is 500 Pa.
The obtained polylactic acid has a weight average molecular weight of 8.4 ten thousand g/mol, a melting point of 170 ℃, a melting enthalpy of 44J/g, and a crystallinity of 47.3% as determined by permeation gel chromatography (GPC) using chloroform as a solvent.
Example 6
A device for synthesizing polylactic acid by lactic acid in one step comprises a helical ribbon type reaction kettle and a secondary reaction kettle which are sequentially communicated and have a stirring effect; wherein the secondary reaction kettle is a helical ribbon type reaction kettle with a scraper; and the distance between the scraper and the inner side wall of the secondary reaction kettle is 10 mm. When the first-stage reaction kettle is communicated with the second-stage reaction kettle, the height of a feed inlet on the second-stage reaction kettle is higher than the stirring height (the height difference is 5cm) of the scraper in the second-stage reaction kettle.
The method for synthesizing the polylactic acid from the lactic acid in one step is carried out by adopting the device, and comprises the following steps:
(1) preparing raw materials:
lactic acid: 90% by mass of L-lactic acid (the balance being water);
catalyst: stannous octoate;
(2) is derived from the above-mentioned lactic acidThe air in the reaction kettle is replaced by nitrogen, and the dehydration reaction of the L-lactic acid is carried out in a first-stage reaction kettle (the temperature is 80 ℃, and the pressure is 3 multiplied by 10)4Pa for 3 hours), and then continuously adding the catalyst into the first-stage reaction kettle to perform polycondensation reaction (the temperature is 150 ℃, and the pressure is 1 multiplied by 103Pa for 6 hours);
wherein the addition amount of the catalyst is 2 per mill of the mass of the L-lactic acid, and free water in the lactic acid is completely removed in a first-stage reaction kettle by stirring (the stirring speed of the dehydration reaction and the polycondensation reaction is consistent and is 60r/min) and vacuumizing;
the product obtained in the step (2) has a linear molecular structure, and the weight average molecular weight is 3.2 ten thousand g/mol;
(3) pumping one product obtained after the reaction in the step (2) into a kettle along the inner side wall of a secondary reaction kettle by a melt pump, uniformly coating the product on the inner wall of the secondary reaction kettle by a scraper blade, and stirring to keep the total retention time of the product in the secondary reaction kettle within 30 minutes to obtain polylactic acid; the reaction temperature in the secondary reaction kettle is 160 ℃, and the pressure is 100 Pa.
The obtained polylactic acid has a weight average molecular weight of 6.2 ten thousand g/mol, a melting point of 165 ℃, a melting enthalpy of 51J/g, and a crystallinity of 54.8% as determined by permeation gel chromatography (GPC) using chloroform as a solvent.
Example 7
A device for synthesizing polylactic acid by lactic acid in one step comprises a helical ribbon type reaction kettle and a secondary reaction kettle which are sequentially communicated and have a stirring effect; wherein the secondary reaction kettle is a helical ribbon type reaction kettle with a scraper; and the distance between the scraper and the inner side wall of the secondary reaction kettle is 8 mm. When the first-stage reaction kettle is communicated with the second-stage reaction kettle, the height of a feed inlet on the second-stage reaction kettle is higher than the stirring height (the height difference is 5cm) of the scraper in the second-stage reaction kettle.
The method for synthesizing the polylactic acid from the lactic acid in one step is carried out by adopting the device, and comprises the following steps:
(1) preparing raw materials:
lactic acid: 90% by mass of L-lactic acid (the balance being water);
catalyst: the mass ratio is 1: 2, a mixture of p-toluenesulfonic acid and stannous chloride;
(2) the lactic acid was used as a raw material, and the air in the reaction vessel was replaced with nitrogen gas to conduct dehydration reaction of L-lactic acid in a primary reaction vessel (temperature 130 ℃ C., pressure 4X 10)4Pa for 4 hours), and then continuously adding the catalyst into the first-stage reaction kettle to perform polycondensation reaction (the temperature is 165 ℃ and the pressure is 1 multiplied by 103Pa, time 10 hours);
wherein the addition amount of the catalyst is 0.5 per mill of the mass of the L-lactic acid, and free water in the lactic acid is completely removed in a first-stage reaction kettle by stirring (the stirring speed of the dehydration reaction and the polycondensation reaction is consistent and is 40r/min) and vacuumizing;
the product obtained in the step (2) presents a linear molecular structure, and the weight average molecular weight is 4.7 ten thousand g/mol;
(3) pumping one product obtained after the reaction in the step (2) into a kettle along the inner side wall of a secondary reaction kettle by a melt pump, uniformly coating the product on the inner wall of the secondary reaction kettle by a scraper blade, and stirring to keep the total retention time of the product in the secondary reaction kettle to be 60 minutes to obtain polylactic acid; the reaction temperature in the secondary reaction kettle is 180 ℃ and the pressure is 200 Pa.
The obtained polylactic acid has a weight average molecular weight of 9.6 ten thousand g/mol, a melting point of 172 ℃, a melting enthalpy of 49J/g and a crystallinity of 52.7% as determined by permeation gel chromatography (GPC) using chloroform as a solvent.
Example 8
A device for synthesizing polylactic acid by lactic acid in one step comprises a helical ribbon type reaction kettle and a secondary reaction kettle which are sequentially communicated and have a stirring effect; wherein the secondary reaction kettle is a helical ribbon type reaction kettle with a scraper; and the distance between the scraper and the inner side wall of the secondary reaction kettle is 6 mm. When the first-stage reaction kettle is communicated with the second-stage reaction kettle, the height of a feed inlet on the second-stage reaction kettle is higher than the stirring height (the height difference is 5cm) of the scraper in the second-stage reaction kettle.
The method for synthesizing the polylactic acid from the lactic acid in one step is carried out by adopting the device, and comprises the following steps:
(1) preparing raw materials:
lactic acid: 90% by mass of L-lactic acid (the balance being water);
catalyst: the mass ratio is 2: 1, a mixture of p-toluenesulfonic acid and stannous chloride;
(2) the lactic acid was used as a raw material, and the air in the reaction vessel was replaced with nitrogen gas to conduct dehydration reaction of L-lactic acid in a primary reaction vessel (temperature 120 ℃ C., pressure 7X 10)4Pa for 3 hours), and then continuously adding the catalyst into the first-stage reaction kettle to perform polycondensation reaction (the temperature is 160 ℃, and the pressure is 4 multiplied by 10)3Pa for 12 hours);
wherein the addition amount of the catalyst is 1.5 per mill of the mass of the L-lactic acid, and free water in the lactic acid is completely removed in a first-stage reaction kettle by stirring (the stirring speed of the dehydration reaction and the polycondensation reaction is consistent and is 40r/min) and vacuumizing;
the product obtained in the step (2) presents a linear molecular structure, and the weight average molecular weight is 4.2 ten thousand g/mol;
(3) pumping one product obtained after the reaction in the step (2) into a kettle along the inner side wall of a secondary reaction kettle by a melt pump, uniformly coating the product on the inner wall of the secondary reaction kettle by a scraper blade, and stirring to keep the total retention time of the product in the secondary reaction kettle at 45 minutes to obtain polylactic acid; the reaction temperature in the second-stage reaction kettle is 175 ℃, and the pressure is 300 Pa.
The obtained polylactic acid has a weight average molecular weight of 7.4 ten thousand g/mol, a melting point of 166 ℃, a melting enthalpy of 46J/g, and a crystallinity of 49.5% as determined by permeation gel chromatography (GPC) using chloroform as a solvent.
Claims (10)
1. A method for synthesizing polylactic acid by lactic acid in one step is characterized in that: uniformly coating the product obtained after the dehydration reaction and the polycondensation reaction of lactic acid in the first-stage reaction kettle on the inner wall of the second-stage reaction kettle while adding the product into the second-stage reaction kettle, and stirring to keep the total residence time of the product in the second-stage reaction kettle within 30-60 minutes to obtain the polylactic acid;
completely removing free water in the lactic acid by the primary reaction kettle in a stirring and vacuumizing mode to enable the product to be in a linear molecular structure, wherein the weight average molecular weight is 3-5 ten thousand g/mol;
the secondary reaction kettle is a spiral belt type reaction kettle with a scraper, a screw type reaction kettle with a scraper or an anchor type reaction kettle with a scraper; the distance between the scraper and the inner side wall of the secondary reaction kettle is 2-10 mm, and the uniform coating means that the scraper in the secondary reaction kettle uniformly coats the product on the inner wall of the secondary reaction kettle.
2. The method for synthesizing polylactic acid from lactic acid in one step as claimed in claim 1, wherein the step of adding the secondary reaction kettle is that the product is pumped into the kettle along the inner side wall of the secondary reaction kettle by a melt pump, and the height of the feed inlet of the secondary reaction kettle is higher than the stirring height of the scraper in the secondary reaction kettle.
3. The method for synthesizing polylactic acid from lactic acid in one step according to claim 2, wherein the product obtained by the reaction in the second-stage reaction kettle is added into the third-stage reaction kettle, and the adding into the third-stage reaction kettle means that the product is uniformly coated on the inner wall of the third-stage reaction kettle while being added into the third-stage reaction kettle, and stirring is carried out to keep the total residence time of the product in the third-stage reaction kettle to be 30-60 minutes, so as to obtain the polylactic acid; the third-stage reaction kettle is the same as the second-stage reaction kettle, and the manner of adding the third-stage reaction kettle is the same as that of adding the second-stage reaction kettle.
4. The method for synthesizing polylactic acid from lactic acid in one step according to claim 1, wherein the primary reaction vessel is a helical ribbon type, screw type or anchor type reaction vessel with stirring function.
5. The method for synthesizing polylactic acid from lactic acid in one step according to claim 1, wherein one step isThe temperature of the dehydration reaction in the stage reaction kettle is 80-150 ℃, and the pressure is 3 multiplied by 104～10×104Pa。
6. The method for synthesizing polylactic acid from lactic acid in one step according to claim 1, wherein the polycondensation reaction temperature in the first-stage reaction kettle is 150-180 ℃ and the pressure is 1 x 103～5×103Pa, the time is 6-12 hours.
7. The method for synthesizing polylactic acid from lactic acid in one step according to claim 1, wherein the catalyst for polycondensation reaction is tin powder, stannous octoate, stannous chloride, p-toluenesulfonic acid or composite catalyst; the addition amount of the catalyst is 0.5-2 per mill of the mass of the lactic acid, and the composite catalyst is a mixture of p-toluenesulfonic acid and stannous chloride.
8. The method for synthesizing polylactic acid from lactic acid in one step according to claim 1, wherein the reaction temperature in the secondary reaction kettle is 150-180 ℃ and the pressure is 100-500 Pa.
9. The method for synthesizing polylactic acid from lactic acid in one step according to claim 3, wherein the reaction temperature in the three-stage reaction kettle is 150-180 ℃ and the pressure is below 300 Pa.
10. The polylactic acid prepared by the method for synthesizing the polylactic acid from the lactic acid in one step according to any one of claims 1 to 9, which is characterized in that: the weight average molecular weight of the polylactic acid is 6-12 ten thousand g/mol, the melting point is 165-175 ℃, the melting enthalpy is 42-51J/g, and the crystallinity is 45-55%.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101153070A (en) * | 2006-09-28 | 2008-04-02 | 东丽纤维研究所（中国）有限公司 | High melting point polylactic acid by direct condensation and polymerization of lactic acid, and method of producing the same |
| CN103254411A (en) * | 2013-06-07 | 2013-08-21 | 北京理工大学 | Method for preparing high-molecular-weight polylactic acid through direct polycondensation and chain extension |
| WO2013184014A1 (en) * | 2012-06-06 | 2013-12-12 | Universidade De Coimbra | Process for preparing high molecular weight poly(lactic acid) by melt polycondensation |
| CN109432810A (en) * | 2018-12-05 | 2019-03-08 | 杭州索孚机械有限公司 | Horizontal single self-cleaning film evaporator |
| CN209957681U (en) * | 2019-02-20 | 2020-01-17 | 中粮集团有限公司 | Polylactic acid devolatilization device |
-
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- 2021-11-16 CN CN202111351511.4A patent/CN113896867B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101153070A (en) * | 2006-09-28 | 2008-04-02 | 东丽纤维研究所（中国）有限公司 | High melting point polylactic acid by direct condensation and polymerization of lactic acid, and method of producing the same |
| WO2013184014A1 (en) * | 2012-06-06 | 2013-12-12 | Universidade De Coimbra | Process for preparing high molecular weight poly(lactic acid) by melt polycondensation |
| CN103254411A (en) * | 2013-06-07 | 2013-08-21 | 北京理工大学 | Method for preparing high-molecular-weight polylactic acid through direct polycondensation and chain extension |
| CN109432810A (en) * | 2018-12-05 | 2019-03-08 | 杭州索孚机械有限公司 | Horizontal single self-cleaning film evaporator |
| CN209957681U (en) * | 2019-02-20 | 2020-01-17 | 中粮集团有限公司 | Polylactic acid devolatilization device |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114213634A (en) * | 2022-01-11 | 2022-03-22 | 内蒙古久泰新材料有限公司 | Process for continuously preparing alkyd oligomer |
| CN114213634B (en) * | 2022-01-11 | 2023-08-11 | 内蒙古久泰新材料有限公司 | Continuous preparation process of alkyd oligomer |
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