Foamed PGA, preparation method therefor, system and use thereof

Abstract

The present invention relates to a foamed PGA, a preparation method therefor, a system and the use thereof. The preparation method comprises the following steps: (1) subjecting polyglycolic acid to pyrolysis under the conditions of a temperature of 230-270°C and an absolute pressure of 0.1 kPa-2 kPa, and when the reaction conversion rate of the polyglycolic acid reaches a preset value, ending the reaction to obtain a melt material, the preset value being less than 60%; and (2) cooling the melt material at a cooling rate of 2-10°C / min to obtain a solid foamed material. Compared with the prior art, in the present invention polyglycolic acid is subjected to partial pyrolysis and the remaining melt material is cooled in a regulated manner to obtain foamed material with micropores.

Description

Foamed PGA and preparation method, system and application thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of degradable foamed materials, in particular to a foamed PGA and preparation method, system and application thereof. BACKGROUND

[0002] Foamed materials are a class of materials with the structural characteristics of light weight, low density and porous, which have excellent buffering, thermal insulation, flame retardant and other properties, and have been widely used in electronic industry, home appliance packaging, automobile, sports goods and other fields. Traditional foamed materials are polyethylene, polypropylene, polyvinyl chloride, polystyrene and other plastics, and the disposal methods of incineration or landfill after use will cause serious environmental pollution and resource waste problems.

[0003] Developing biodegradable foamed materials is an important way to solve the "white pollution", and the common degradable materials at present are mainly aliphatic polyesters, including polylactic acid (PLA), polyhydroxyalkanoate (PHA), polyphenyl ester (PHB) and polyglycolic acid (PGA). At present, biodegradable foamed materials are prepared by physical or chemical foaming. The physical foaming method mainly includes supercritical carbon dioxide foaming method, which has high requirements for equipment and high process cost; the chemical foaming method mainly adds foaming agent, and the residual chemical substances are easy to cause secondary pollution. SUMMARY

[0004] The purpose of the present application is to provide a foamed PGA and preparation method, system and application thereof, which has low cost and can reduce secondary pollution.

[0005] The purpose of the present application can be achieved by the following technical scheme: a preparation method of foamed PGA, comprising the following steps:

[0006] (1) partially pyrolyzing polyglycolic acid under the condition of temperature 230-270℃ and absolute pressure 0.1kPa-2kPa to obtain a melt material;

[0007] (2) cooling the melt material to room temperature at a cooling rate of 2-10℃ / min to obtain a solid foamed material.

[0008] Preferably, the weight average molecular weight of the raw material polyglycolic acid in step (1) is 10000-50000g / mol.

[0009] Preferably, the reaction of step (1) is ended when the reaction conversion rate of the polyglycolic acid reaches a preset value, and the melt material is obtained, and the preset value is less than 60%.

[0010] Further preferably, the preset value is 20%-40%.

[0011] Preferably, after step (1), the method further comprises 1b) continuing the pyrolysis reaction of the remaining polyglycolic acid at a temperature of 200-230°C under normal pressure, for a reaction time of 0.1-1h, to obtain a melt material.

[0012] Further preferably, step (1) is performed in a vacuum reactor, and step 1b) is performed in a normal pressure reactor, and the remaining polyglycolic acid is discharged from the vacuum reactor into the normal pressure reactor when the reaction conversion rate of the polyglycolic acid reaches a preset value, and is further pyrolyzed in the normal pressure reactor. As the reaction proceeds, the pyrolysis rate of the polyglycolic acid increases, and when the reaction in the vacuum reactor proceeds to a certain extent, the generation rate of small molecule substances is too fast, which can easily cause the collapse of unformed bubble pores and the formation of new bubble pores, and therefore the remaining polyglycolic acid is discharged from the vacuum reactor into the normal pressure reactor, and is further pyrolyzed in the normal pressure reactor. The boiling point of glycolide under normal pressure is 330°C, and in this pyrolysis stage, the small molecule substances generated and vaporized by pyrolysis are mainly water and carbon oxides, and a small amount of gas is continuously generated in the melt during pyrolysis, but the conversion rate of the polyglycolic acid does not increase significantly.

[0013] Still further preferably, the vacuum reactor and the normal pressure reactor are selected from vertical stirred tanks or horizontal stirred tanks, and the viscosity of the melt material in the vacuum reactor and the normal pressure reactor is 300-10000 centipoise, and the rotation speed is 3-15 revolutions per minute.

[0014] Preferably, step (1) is performed in the presence of a catalyst.

[0015] Further preferably, the catalyst is a rare earth metal catalyst.

[0016] Still further preferably, the catalyst is selected from metal oxides of lanthanum (La), cerium (Ce), scandium (Sc), or a combination thereof, rare earth metal inorganic salts, or rare earth metal complexes. The catalyst accelerates the pyrolysis of the polyglycolic acid to generate small molecule substances such as glycolide, H2O, CO, CO2, etc., and the small molecule substances form bubbles in the melt, and further vaporize to form bubble pores; after the reaction is completed, the melt material is discharged, and the bubble pores in the melt are retained to form uniform micropores during the subsequent cooling and solidification process.

[0017] Further preferably, the amount of the catalyst is 0.001-5wt% of the polyglycolic acid.

[0018] Preferably, in step (1), the gas phase material generated in the pyrolysis process of the polyglycolic acid is collected. Specifically, the gas phase material generated in the pyrolysis process of the polyglycolic acid under vacuum is introduced into a condensation unit for condensation and collection, to obtain crude glycolide.

[0019] Preferably, the thickness of the melt material is controlled to be 1-5 cm during the cooling process of step (2) so that the overall cooling rate is uniform. If the thickness is too large, the surface of the material solidifies first and the middle is still a melt, which is prone to form large cavities.

[0020] Preferably, the cooling rate of the melt material is 5-8 ℃ / min before the melt material solidifies in step (2).

[0021] A system for preparing the foamed PGA described above, the system comprising a reaction device and a continuous cooling device arranged in sequence along the material conveying direction, the pyrolysis reaction of polyglycolic acid is carried out in the reaction device to obtain a melt material, and the cooling of the melt material is carried out in the continuous cooling device.

[0022] Preferably, the reaction device is a continuous reaction device, and the pyrolysis reaction is carried out in the continuous reaction device, that is, after the reaction is completed, the melt material is introduced into the next processing device, and the next batch of material is continuously introduced into the continuous reaction device for pyrolysis reaction.

[0023] More preferably, the continuous reaction device comprises a vacuum reaction kettle and an atmospheric pressure reaction kettle arranged in sequence.

[0024] Preferably, the continuous cooling device comprises a plurality of parallel conveying belts, a material blocking block is arranged beside the input end of each conveying belt, a material thickness homogenizing device and a feeding port are arranged above the input end of each conveying belt, the melt material is cooled on the conveying belt in the continuous cooling device, and the thickness of the melt material on the conveying belt is controlled by adjusting the distance between the material thickness homogenizing device and the surface of the conveying belt.

[0025] Specifically, the melt material output from the reaction device is conveyed to the conveying belts through the feeding ports, and the material blocking block fixed beside the bottom of the input end of the conveying belt can prevent the melt material from leaking from the side.

[0026] Further preferably, the continuous cooling device adopts a wind cooling type cooling method and further comprises an air cooling unit, and cold air enters the inside of the device through an air cooling pipeline to cool the material on the surface of the conveying belt.

[0027] Further preferably, a plurality of infrared temperature measuring instruments are arranged at intervals along the side edges of the conveying belt along the material conveying direction, and the temperature measuring end of the infrared temperature measuring instrument faces the surface of the conveying belt. The temperature difference between adjacent infrared temperature measuring instruments is a section, and the cooling rate of each section is the temperature difference between the temperature measurements of adjacent two infrared temperature measuring instruments / time difference, the cooling rate of each section is 2-10 ℃ / min, and the time difference is calculated according to the ratio of the distance between adjacent two infrared temperature measuring instruments and the conveying belt speed.

[0028] Further preferably, infrared temperature detectors are arranged at the middle and the end (i.e. the output end) of the conveying belt, wherein the temperature detected at the end is the discharge temperature of the solid foamed material, which is preferably below 80℃ (e.g. 60℃). By controlling the temperature of the solid foamed material when it is discharged from the continuous cooling device, the safety hazard in the production process is reduced.

[0029] Further preferably, an infrared temperature detector is arranged at the front end of the conveying belt, and the temperature detected at the front end is the initial temperature of the melt material in the continuous cooling device.

[0030] In the present application, the melt material is gradually cooled in the continuous cooling device to form a solid foamed material, and the cooling rate is maintained at 2-10℃ / min. Preferably, the cooling rate of the melt material is 5-8℃ / min before the melt material solidifies. If the cooling rate is too fast, the bubble holes in the melt material are prone to collapse during the rapid solidification of the melt material. If the cooling rate is too slow, the melt material has a certain flowability in the initial cooling stage, which cannot be quickly preformed, and the surface of the material solidifies first, and the intermediate melt is prone to form larger cavities during the delayed solidification process.

[0031] Preferably, the system further comprises a traction unit and a cutting unit arranged after the continuous cooling device. Under the traction of the traction unit, the solid foamed material can be further cooled to near room temperature (e.g. 30℃) during the travel. The traction mechanism can adopt a conventional belt conveyor arranged symmetrically above and below, and the cutting unit can adopt a conventional cutting knife.

[0032] Preferably, the system further comprises a condensing unit for collecting the gas phase material generated during the pyrolysis of polyglycolic acid under vacuum.

[0033] Further preferably, the condensing unit comprises a hot water heat exchanger and a cold water condenser arranged in sequence.

[0034] A foamed PGA prepared by the above preparation method.

[0035] The application of the above foamed PGA in the field of packaging, degradable thermal insulation materials or degradable flame-retardant materials.

[0036] Compared with the prior art, the present application has the following beneficial effects:

[0037] 1. The present application allows polyglycolic acid to undergo partial pyrolysis, and the remaining melt material is cooled regularly to obtain a foamed material with micro-holes;

[0038] 2. The foamed material obtained by the present application has good thermal insulation, water vapor barrier and air barrier effects, reduced bulk density, accelerated and adjustable hydrolysis and degradation rate;

[0039] 3. The gas phase material generated in the vacuum pyrolysis process of the present application can be collected by a condensation unit to obtain crude glycolide (after refining, refined glycolide product can be obtained), and the entire production process does not produce pollutants;

[0040] 4. The preparation of foamed PGA in the present application can use conventional vertical stirred tank or horizontal stirred tank and conveyor belt, which has lower requirements for equipment and lower process cost compared with traditional supercritical carbon dioxide physical foaming method;

[0041] 5. The present application accelerates the pyrolysis of polyglycolic acid to generate glycolide, H2O, CO, CO2 and other small molecule substances through the catalysis of the catalyst, and the above small molecule substances form bubbles in the melt, and further volatilize and gasify to form bubble holes, which is not easy to produce secondary pollution caused by residual chemicals compared with the traditional chemical foaming method of adding foaming agent.

[0042] BRIEF DESCRIPTION OF DRAWINGS

[0043] Fig. 1 is a partial structure schematic diagram of the system of the present application;

[0044] Fig. 2 is a cross-sectional view of the foamed PGA prepared in Example 3;

[0045] In the figure: 1-continuous cooling equipment, 11-material blocking block, 12-material thickness homogenizing device, 13-feeding port, 14-air cooling unit, 2-drawing machine unit, 3-cutting unit. DETAILED DESCRIPTION

[0046] The present application will be described in detail below in combination with the drawings and specific examples. The present embodiment is implemented on the premise of the technical scheme of the present application, and gives detailed implementation mode and specific operation process, but the protection scope of the present application is not limited to the following examples.

[0047] In the present application:

[0048] Reaction conversion rate = mass of residual polyglycolic acid / mass of initial polyglycolic acid.

[0049] The test method of the foamed material is as follows:

[0050] 1) The density of the foamed material is weighed by using standard blocks, and the volume is calculated, and the weight / volume is calculated;

[0051] 2) The compressive strength of the foamed material is measured by using the compression mode of the universal material testing machine;

[0052] 3) The thermal conductivity coefficient of the foamed material is measured by using the thermal conductivity coefficient instrument;

[0053] 4) Hydrolysis performance test of foamed material: the foamed material is crushed by a crusher, and particles of 20-40 mesh are screened out by a vibrating screen. The above particles are dried, and 2 portions of the sample each with a mass of M0 are weighed and configured with water to form a sample with a concentration of 5wt%. The test is carried out at 90℃, and after 2 days, the remaining solid phase is separated. The mass of the remaining solid phase after drying is recorded as M1 and M2. The hydrolysis degradation rate of the sample is (M0-M1) / M0 and (M0-M2) / M0, respectively, and the average value of the two is taken.

[0054] The system used in the application comprises a vacuum reaction kettle and a normal pressure reaction kettle, and further comprises a continuous cooling device 1, a traction machine set 2 and a cutting unit 3 as shown in Fig. 1.

[0055] The continuous cooling device 1 comprises a plurality of parallel conveying belts, a material blocking block 11 is arranged beside the input end of each conveying belt, and a material thickness homogenizing device 12 and a feeding port 13 are arranged above the input end of each conveying belt. The melt material is conveyed onto the conveying belt through the feeding port 13, the thickness of the melt material on the conveying belt is controlled by adjusting the distance between the material thickness homogenizing device 12 and the surface of the conveying belt, and the material blocking block 11 can prevent the material from scattering during the feeding process. The continuous cooling device 1 further comprises an air cooling machine set 14, and cold air enters the inside of the device through a cold air pipeline to cool the material on the surface of the conveying belt.

[0056] Unless otherwise specified, the reagents, methods, instruments and equipment used in the application are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available. Examples

[0057] 10 kg of polyglycolic acid with a weight average molecular weight of about 2.6W is put into a vacuum reaction kettle, 1g of catalyst La2O3 is added, and pyrolysis reaction is carried out at a temperature of 230℃ and an absolute pressure of 100Pa. When the reaction conversion rate of the polyglycolic acid reaches 40%, the reaction is stopped. The remaining polyglycolic acid is discharged from the vacuum reaction kettle and introduced into a normal pressure reaction kettle, and pyrolysis reaction is continued at a temperature of 220℃ and normal pressure. After about 30 minutes of reaction, melt material is obtained. The gas phase material produced in the vacuum reaction process is sequentially collected through a hot water heat exchanger and a cold water condenser.

[0058] The melt material is introduced into the continuous cooling device, the distance between the material thickness homogenizing device and the surface of the conveying belt is adjusted in advance, the thickness of the melt material on the conveying belt is controlled to be 2 cm, the air cooling unit (power: 5 kW) is turned on in advance, the temperature in the continuous cooling device is about 10 ℃, the length of the conveying belt is 10 meters, the infrared temperature measuring instrument is fixed at the front end, the middle and the end of the conveying belt, the residence time of the melt material in the continuous cooling device is 30 min, the discharge temperature of the solid foamed material is controlled to be 65±1 ℃, the average cooling rate of the first stage is about 6.8 ℃ / min, and the average cooling rate of the second stage is about 3.5 ℃ / min; and the finished product is prepared after cutting. Embodiment

[0059] 10 kg of polyglycolic acid with a weight average molecular weight of about 2.6 W is put into a vacuum reaction kettle, 2 g of catalyst La2O3 is added, pyrolysis reaction is carried out under the condition that the temperature is 240 ℃ and the absolute pressure is 1000 Pa, the reaction is ended when the reaction conversion rate of the polyglycolic acid reaches 25%, and the melt material is obtained; the gas phase material produced in the vacuum reaction process is collected in turn through the hot water heat exchanger and the cold water condenser.

[0060] The melt material is introduced into the continuous cooling device, the distance between the material thickness homogenizing device and the surface of the conveying belt is adjusted in advance, the thickness of the melt material on the conveying belt is controlled to be 2 cm, the air cooling unit (power: 5 kW) is turned on in advance, the temperature in the continuous cooling device is about 10 ℃, the length of the conveying belt is 10 meters, the infrared temperature measuring instrument is fixed at the front end, the middle and the end of the conveying belt, the residence time of the melt material in the continuous cooling device is 30 min, the discharge temperature of the solid foamed material is controlled to be 65±1 ℃, the average cooling rate of the first stage is about 6.8 ℃ / min, and the average cooling rate of the second stage is about 3.5 ℃ / min; and the finished product is prepared after cutting. Embodiment

[0061] 10 kg of polyglycolic acid with a weight average molecular weight of about 2.6 W is put into a vacuum reaction kettle, 1 g of catalyst La2O3 is added, pyrolysis reaction is carried out under the condition that the temperature is 250 ℃ and the absolute pressure is 500 Pa, the reaction is ended when the reaction conversion rate of the polyglycolic acid reaches 30%, the remaining polyglycolic acid is discharged from the vacuum reaction kettle and introduced into an atmospheric pressure reaction kettle, pyrolysis reaction is continued under the condition that the temperature is 210 ℃ and the atmospheric pressure, and the melt material is obtained after about 30 minutes of reaction; the gas phase material produced in the vacuum reaction process is collected in turn through the hot water heat exchanger and the cold water condenser.

[0062] The melt material is introduced into the continuous cooling device, the distance between the material thickness homogenizing device and the surface of the conveying belt is adjusted in advance, the thickness of the melt material on the conveying belt is controlled to be 2 cm, the air cooling unit (power: 5 kW) is turned on in advance, the temperature in the continuous cooling device is maintained at about 10 ℃, the length of the conveying belt is 10 meters, the infrared temperature measuring instrument is fixed at the front end, the middle and the end of the conveying belt, the residence time of the melt material in the continuous cooling device is 30 min, the discharge temperature of the solid foamed material is controlled to be 60±1 ℃, the average cooling rate of the first stage is about 6.7 ℃ / min, and the average cooling rate of the second stage is about 3.3 ℃ / min; and the finished product is prepared after cutting. Example

[0063] 10 kg of polyglycolic acid with a weight average molecular weight of 3.5 W is put into a vacuum reaction kettle, 5 g of catalyst Ce(HCO3)4 is added, and pyrolysis reaction is carried out under the condition that the temperature is 240 ℃ and the absolute pressure is 1000 Pa; when the reaction conversion rate of the polyglycolic acid reaches 60%, the reaction is ended; the remaining polyglycolic acid is discharged from the vacuum reaction kettle and introduced into an atmospheric pressure reaction kettle, and pyrolysis reaction is continued under the condition that the temperature is 200 ℃ and the atmospheric pressure; after about 30 minutes of reaction, melt material is obtained; the gas phase material produced in the vacuum reaction process is collected in sequence through a hot water heat exchanger and a cold water condenser.

[0064] The melt material is introduced into the continuous cooling device, the distance between the material thickness homogenizing device and the surface of the conveying belt is adjusted in advance, the thickness of the melt material on the conveying belt is controlled to be 5 cm, the air cooling unit (power: 5 kW) is turned on in advance, the temperature in the continuous cooling device is maintained at about 10 ℃, the length of the conveying belt is 10 meters, the infrared temperature measuring instrument is fixed at the front end, the middle and the end of the conveying belt, the residence time of the melt material in the continuous cooling device is 30 min, the discharge temperature of the solid foamed material is controlled to be 60±1 ℃, the average cooling rate of the first stage is about 6.2 ℃ / min, and the average cooling rate of the second stage is about 3.2 ℃ / min; and the finished product is prepared after cutting.

[0065] Comparative Example 1

[0066] The same as example 1, the difference is that when the reaction conversion rate of the polyglycolic acid reaches 70%, the reaction is ended, the remaining polyglycolic acid is discharged from the vacuum reaction kettle and introduced into an atmospheric pressure reaction kettle, and subsequent operation steps are carried out.

[0067] Comparative Example 2

[0068] The same as example 1, except that the temperature in the continuous cooling device is about 5℃ before the melt material is fed, the residence time of the melt material in the continuous cooling device is 20 min, the discharge temperature of the solid foamed material is controlled at 60±1℃, the average cooling rate in the first stage is about 10.6℃ / min, and the average cooling rate in the second stage is about 5.4℃ / min.

[0069] Table 1 Test results of each example and comparative example

[0070] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Density (kg / m 3 )628801763630867634 Compression strength (kPa)4123735228401156256 Thermal conductivity W / (m·K)0.0400.0510.0320.0730.0970.082 Hydrolytic degradation 55%45%51%53%37%52%

[0071] As shown in Table 1, compared with example 1, the reaction conversion rate of polyglycolic acid pyrolysis reaction of comparative example 1 is higher than 60%, although the compression strength is increased, the density and thermal conductivity of the product are also significantly increased, and the hydrolytic degradation is significantly reduced, which is not conducive to its application as a foamed material in the fields of packaging, degradable thermal insulation material or degradable flame retardant material. Compared with example 1, the compression strength of comparative example 2 is reduced, and the thermal conductivity is significantly increased, which is presumably due to the fact that the cooling rate of the melt material is too fast, and the bubble holes in the melt material are easy to collapse during the rapid solidification process of the melt material, resulting in uneven distribution of micropores in the foamed material, affecting the compression strength and thermal conductivity. In summary, by controlling the pyrolysis reaction conversion rate and the cooling rate of the melt material, the performance of the obtained foamed material can be maintained at a relatively optimal level.

[0072] The above description of the examples is for the purpose of enabling and using the invention by those of ordinary skill in the art. Those skilled in the art can easily make various modifications to these examples, and apply the general principles described herein to other examples without creative labor. Therefore, the present application is not limited to the above examples, and improvements and modifications made by those skilled in the art based on the disclosure of the present application without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A method of preparing a foamed PGA, characterized by, The method comprises the following steps: (1) pyrolysis of polyglycolic acid at a temperature of 230-270℃ and an absolute pressure of 0.1-2kPa, and the reaction is ended when the reaction conversion rate of the polyglycolic acid reaches a preset value, which is less than 60%, to obtain a melt material; (2) cooling the melt material at a cooling rate of 2-10℃ / min to obtain a solid foamed material.

2. The method of claim 1, wherein the PGA is foamed. After step (1), the method further comprises 1b) continuing the pyrolysis of the remaining polyglycolic acid at a temperature of 200-230℃ and an atmospheric pressure for 0.1-1h to obtain a melt material.

3. The method of claim 2, wherein the PGA is foamed. Step (1) is carried out in a vacuum reactor in the presence of a catalyst, and step 1b) is carried out in an atmospheric pressure reactor, and the remaining polyglycolic acid is discharged from the vacuum reactor into the atmospheric pressure reactor when the reaction conversion rate of the polyglycolic acid reaches a preset value for further pyrolysis.

4. The method of claim 3, wherein the PGA is foamed. The vacuum reactor and the atmospheric pressure reactor are selected from vertical stirred tanks or horizontal stirred tanks, and the viscosity of the melt material in the vacuum reactor and the atmospheric pressure reactor is 300-10000 centipoise, and the rotation speed is 3-15rpm.

5. The method of claim 1, wherein the foamed PGA is prepared by, During the cooling process of step (2), the thickness of the melt material is controlled to be 1-5cm, and the cooling rate of the melt material is controlled to be 5-8℃ / min before the melt material solidifies.

6. The method of claim 1-5, wherein, The preset value is 20%-40%, and step (1) further comprises collecting the gas phase material generated during the pyrolysis of the polyglycolic acid to obtain a crude glycolide.

7. A system for use in the process according to any one of claims 1 to 6, characterized in that The system comprises a reaction device, a continuous cooling device, a traction unit and a cutting unit arranged in sequence along the material conveying direction; The continuous cooling device comprises a plurality of parallel conveying belts, a material blocking block is arranged beside the input end of each conveying belt, a material thickness homogenizing device and a feeding port are arranged above the input end of each conveying belt, the melt material is cooled in the continuous cooling device, and the thickness of the melt material on the conveying belt is controlled by adjusting the distance between the material thickness homogenizing device and the surface of the conveying belt.

8. The system employed in the production method according to claim 7, characterized in that, The reaction device comprises a vacuum reactor and an atmospheric pressure reactor; And / or, a plurality of infrared thermometers are fixed on the side edges of the conveying belts; And / or, the continuous cooling device adopts a air-cooled cooling mode.

9. A foamed PGA characterized in that, The foamed PGA is prepared by the method of any one of claims 1-6.

10. Use of the foamed PGA of claim 9 in the field of packaging, degradable thermal insulation materials or degradable flame-retardant materials.

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