Foaming PGA as well as preparation method, system and application thereof

Abstract

The invention relates to foamed PGA (polyglycolic acid) as well as a preparation method, system and application thereof, the preparation method comprises the following steps: (1) performing pyrolytic reaction on polyglycolic acid under the conditions that the temperature is 230-270 DEG C and the absolute pressure is 0.1-2kPa, and ending the reaction when the reaction conversion rate of the polyglycolic acid reaches a preset value which is less than 60% to obtain a melt material; and (2) cooling the melt material at a cooling rate of 2-10 DEG C / min to obtain the solid foaming material. Compared with the prior art, the polyglycolic acid is subjected to partial pyrolytic reaction, and the residual melt material is regularly cooled to obtain the foaming material with micro holes.

Description

Technical Field

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

[0002] Foam materials are a type of material with lightweight, low density, and porous structure. They have excellent cushioning, thermal insulation, and flame retardancy, and are now widely used in the electronics industry, home appliance packaging, automobiles, sporting goods, and other fields. Traditional foam materials are plastics such as polyethylene, polypropylene, polyvinyl chloride, and polystyrene. The incineration or landfill treatment methods used after use will cause serious environmental pollution and waste of resources.

[0003] Developing biodegradable foaming materials is an important way to solve "white pollution". Currently, common biodegradable materials are mainly aliphatic polyesters, including polylactic acid (PLA), polyhydroxyalkanoates (PHA), polyphenylene esters (PHB) and polyglycolic acid (PGA). At present, biodegradable foaming materials are made by physical or chemical foaming. The physical foaming method mainly includes supercritical carbon dioxide foaming, which has high requirements for equipment and high process costs; the chemical foaming method is mainly through the addition of foaming agents, and the residual chemical substances are prone to secondary pollution. Summary of the invention

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

[0005] The object of the present invention can be achieved by the following technical scheme: A method for preparing foamed PGA, comprising the following steps:

[0006] (1) subjecting polyglycolic acid to partial pyrolysis reaction at a temperature of 230 to 270° C. and an absolute pressure of 0.1 kPa to 2 kPa to obtain a molten material;

[0007] (2) Cooling the molten material to room temperature at a cooling rate of 2 to 10° C. / min to obtain a solid foaming material.

[0008] Preferably, the weight average molecular weight of the polyglycolic acid used as the raw material in step (1) is between 10,000 and 50,000 g / mol.

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

[0010] More preferably, the preset value is 20% to 40%.

[0011] Preferably, after step (1), the method further comprises 1b) subjecting the remaining polyglycolic acid to further thermal decomposition reaction at a temperature of 200 to 230° C. and normal pressure for a reaction time of 0.1 to 1 h to obtain a molten material.

[0012] Further preferably, step (1) is carried out in a vacuum reactor, and step 1b) is carried out in a normal pressure reactor. When the reaction conversion rate of the polyglycolic acid reaches a preset value, the remaining polyglycolic acid is discharged from the vacuum reactor and enters the normal pressure reactor for further pyrolysis in the normal pressure reactor. As the reaction proceeds, the pyrolysis rate of the polyglycolic acid accelerates. When the reaction proceeds to a certain extent in the vacuum reactor, the generation rate of small molecules is too fast, which easily causes the collapse of unformed bubble pores and makes it difficult to form new bubble pores. Therefore, the remaining polyglycolic acid is discharged from the vacuum reactor and enters the normal pressure reactor for further pyrolysis in the normal pressure reactor. The boiling point of glycolide at normal pressure is 330°C. In this pyrolysis stage, the small molecules generated and gasified by pyrolysis are mainly water and carbon oxides. A small amount of gas continues to be generated in the melt during pyrolysis, but the conversion rate of polyglycolic acid will not be significantly improved.

[0013] More preferably, the vacuum reactor and the atmospheric pressure reactor are both selected from a vertical stirring reactor or a horizontal stirring reactor, the viscosity of the melt in the vacuum reactor and the atmospheric pressure reactor is 300 to 10,000 centipoise, and the rotation speed is 3 to 15 rpm.

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

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

[0016] More preferably, the catalyst is selected from metal oxides, rare earth metal inorganic salts or rare earth metal complexes of lanthanum (La), cerium (Ce), scandium (Sc) or a combination thereof. The catalytic action of the catalyst accelerates the thermal decomposition of polyglycolic acid to generate glycolide, H2O, CO, CO2 and other small molecules, which form bubbles in the melt and further volatilize and gasify to form bubble holes; after the reaction is completed, the melt material is discharged, and the bubble holes in the melt are retained in the subsequent cooling and solidification process to form uniform micropores.

[0017] More preferably, the catalyst is used in an amount of 0.001 to 5 wt % of the polyglycolic acid.

[0018] Preferably, in step (1), the gaseous material generated during the pyrolysis of polyglycolic acid is collected. Specifically, the gaseous material generated during the pyrolysis of 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 in step (2), so that the overall cooling rate tends to be uniform. If the thickness is too thick, the surface of the material solidifies first, while the middle is still molten, which easily forms larger voids.

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

[0021] A system used in the preparation method of the above-mentioned foamed PGA includes a reaction device and a continuous cooling device arranged in sequence along the material conveying direction. The thermal decomposition reaction of polyglycolic acid is carried out in the reaction device to obtain a molten material, and the molten material is cooled in the continuous cooling device.

[0022] Preferably, the reaction equipment is a continuous reaction equipment, and the pyrolysis reaction is carried out in the continuous reaction equipment, that is, after the reaction is completed, the melt material is introduced into the next processing equipment, and the next batch of materials is added to the continuous reaction equipment to continue the pyrolysis reaction.

[0023] More preferably, the continuous reaction equipment comprises a vacuum reactor and a normal pressure reactor which are arranged in sequence.

[0024] Preferably, the continuous cooling equipment includes multiple parallel conveyor belts, a material stop block is provided next to the input end of each conveyor belt, a material thickness homogenizing device and a feed port are provided above the input end of each conveyor belt, the molten material is cooled on the conveyor belt in the continuous cooling equipment, and the thickness of the molten material on the conveyor belt is controlled by adjusting the distance between the material thickness homogenizing device and the conveyor belt surface.

[0025] Specifically, the molten material outputted from the reaction equipment is transported to each transmission belt through each feed port, and the stopper blocks fixed on the sides of the bottom of the input end of the transmission belt can prevent the molten material from leaking from the sides.

[0026] Further preferably, the continuous cooling equipment adopts an air-cooling cooling method and also includes an air-cooling unit, and cold air enters into the equipment through a cold air duct to cool the material on the surface of the conveyor belt.

[0027] Further preferably, a plurality of infrared thermometers are provided at intervals on the side of the conveyor belt along the material conveying direction, and the temperature measuring end of the infrared thermometer faces the surface of the conveyor belt. There is a section between adjacent infrared thermometers, and the cooling rate of each section = the temperature difference between the temperature measurements of two adjacent infrared thermometers / time difference. The cooling rate of each section is 2-10°C / min, and the time difference is calculated based on the ratio of the distance between two adjacent infrared thermometers to the conveyor belt speed.

[0028] More preferably, infrared thermometers are provided at the middle and end (i.e., output end) of the conveyor belt, wherein the temperature detected at the end is the discharge temperature of the solid foaming material, and the discharge temperature is preferably below 80° C. (e.g., 60° C.). By controlling the temperature of the solid foaming material when it is output from the continuous cooling device, potential safety hazards in the production process can be reduced.

[0029] More preferably, an infrared thermometer is also provided at the front end of the conveyor belt, and the temperature detected at the front end is the starting temperature of the molten material in the continuous cooling device.

[0030] In the present invention, the molten material is gradually cooled in a continuous cooling device to form a solid foaming material, and the cooling rate is maintained at 2-10°C / min. Preferably, before the molten material is solidified, the cooling rate of the molten material is 5-8°C / min. If the cooling rate is too fast, the bubble pores in the molten material are prone to collapse during the rapid solidification of the molten material. If the cooling rate is too slow, in the initial cooling stage, the molten material has a certain fluidity and cannot be quickly preformed. The surface of the material solidifies first, and the intermediate melt is prone to form larger voids 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 foaming material can be further cooled to near room temperature (for example, 30° C.) during the process of traveling. The traction mechanism can adopt a conventional belt conveyor symmetrically arranged up and down, and the cutting unit can adopt a conventional cutting knife.

[0032] Preferably, the system further comprises a condensation unit for collecting gaseous materials 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 which are arranged in sequence.

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

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

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

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

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

[0039] 3. The gaseous materials produced in the vacuum pyrolysis process of the present invention can be collected by a condensation unit to obtain crude glycolide (after refining, refined glycolide products can be obtained), and no pollutants are generated in the entire production process;

[0040] 4. The preparation of the foamed PGA of the present invention can adopt a conventional vertical stirring tank or horizontal stirring tank and a conveyor belt, which has lower requirements on equipment and lower process cost than the traditional supercritical carbon dioxide physical foaming method;

[0041] 5. The present invention accelerates the thermal decomposition of polyglycolic acid to generate glycolide, H2O, CO, CO2 and other small molecules through the catalytic action of the catalyst. The above small molecules form bubbles in the melt, which further volatilize and gasify to form bubble holes. Compared with the traditional chemical foaming method of adding a foaming agent, it is not easy to cause secondary pollution by residual chemical substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a partial structural schematic diagram of the system of the present invention;

[0043] Figure 2 is a cross-sectional view of the foamed PGA prepared in Example 3;

[0044] In the figure: 1-continuous cooling equipment, 11-blocking block, 12-material thickness homogenizing device, 13-feeding port, 14-air cooling unit, 2-traction unit, 3-cutting unit. DETAILED DESCRIPTION

[0045] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0046] In the present invention:

[0047] Reaction conversion rate = mass of remaining polyglycolic acid / mass of initial polyglycolic acid.

[0048] The test method for foaming materials is as follows:

[0049] 1) The density of the foaming material is weighed using a standard block and the volume is calculated using the weight / volume method;

[0050] 2) The compressive strength of the foamed material is measured using the compression mode of a universal material testing machine;

[0051] 3) The thermal conductivity of the foaming material is measured using a thermal conductivity meter;

[0052] 4) Test of hydrolysis performance of foaming material: The foaming material was crushed by a pulverizer, and particles of 20-40 mesh were screened out using a vibrating screen. After the particles were dried, 2 parts of the test samples, both of which had a mass of M0, were weighed and respectively mixed with water to form a sample with a concentration of 5wt%, and the test was carried out at 90°C. After 2 days, the remaining solid phase was separated, and the masses of the remaining solid phase were recorded after drying as M1 and M2, respectively. The hydrolysis degradation rates of the test samples were (M0-M1) / M0 and (M0-M2) / M0, respectively, and the average of the two was taken.

[0053] The system used in the present invention includes not only a vacuum reactor and a normal pressure reactor, but also Figure 1 The continuous cooling device 1, the traction unit 2 and the cutting unit 3 are shown.

[0054] The continuous cooling device 1 includes a plurality of parallel conveyor belts, a material stopper 11 is provided next to the input end of each conveyor belt, and a material thickness homogenizing device 12 and a feed port 13 are provided above the input end of each conveyor belt. The molten material is transported to the conveyor belt through the feed port 13, and the thickness of the molten material on the conveyor belt is controlled by adjusting the distance between the material thickness homogenizing device 12 and the conveyor belt surface. The material stopper 11 can prevent the material from scattering during the feeding process. The continuous cooling device 1 also includes an air cooling unit 14, and cold air enters the interior of the device through a cold air duct to cool the material on the surface of the conveyor belt.

[0055] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention 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.

[0056] Example 1

[0057] 10 kg of polyglycolic acid with a weight average molecular weight of about 2.6W is put into a vacuum reactor, and 1 g of catalyst La2O3 is added. The pyrolysis reaction is carried out at a temperature of 230°C and an absolute pressure of 100 Pa. The reaction is terminated when the reaction conversion rate of the polyglycolic acid reaches 40%. The remaining polyglycolic acid is discharged from the vacuum reactor and introduced into a normal pressure reactor. The pyrolysis reaction is continued at a temperature of 220°C and normal pressure for about 30 minutes to obtain a molten material. The gaseous material produced during the vacuum reaction is collected in turn through a hot water heat exchanger and a cold water condenser.

[0058] The molten material is introduced into the continuous cooling equipment, the distance between the material thickness homogenization device and the conveyor belt surface is adjusted in advance, the thickness of the molten material on the conveyor belt is controlled to be 2 cm, and the air cooling unit (power: 5 kW) is turned on in advance to make the temperature in the continuous cooling equipment about 10°C. The length of the transmission belt is 10 meters. Infrared thermometers are fixed at the front end, middle part and end of the transmission belt. The residence time of the molten material in the continuous cooling equipment is 30 minutes. The discharge temperature of the solid foaming material is controlled to be 65±1°C. The average cooling rate in the first stage is about 6.8°C / min, and the average cooling rate in the second stage is about 3.5°C / min. The finished product is obtained after cutting.

[0059] Example 2

[0060] 10 kg of polyglycolic acid with a weight average molecular weight of about 2.6W was put into a vacuum reactor, 2 g of catalyst La2O3 was added, and a pyrolysis reaction was carried out at a temperature of 240°C and an absolute pressure of 1000 Pa. When the reaction conversion rate of the polyglycolic acid reached 25%, the reaction was terminated to obtain a molten material; the gaseous material produced during the vacuum reaction was collected in turn through a hot water heat exchanger and a cold water condenser.

[0061] The molten material is introduced into the continuous cooling equipment, the distance between the material thickness homogenization device and the conveyor belt surface is adjusted in advance, the thickness of the molten material on the conveyor 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 equipment is maintained at about 15°C, the length of the transmission belt is 10 meters, and infrared thermometers are fixed at the front end, middle part and end of the transmission belt. The residence time of the molten material in the continuous cooling equipment is 30 minutes, the discharge temperature of the solid foaming material is controlled to be 70±1°C, the average cooling rate in the first stage is about 7.6°C / min, and the average cooling rate in the second stage is about 3.8°C / min; the finished product is obtained after cutting.

[0062] Example 3

[0063] 10 kg of polyglycolic acid with a weight average molecular weight of about 2.6W is put into a vacuum reactor, and 1 g of catalyst La2O3 is added. The pyrolysis reaction is carried out at a temperature of 250°C and an absolute pressure of 500 Pa. The reaction is terminated when the reaction conversion rate of the polyglycolic acid reaches 30%. The remaining polyglycolic acid is discharged from the vacuum reactor and introduced into a normal pressure reactor. The pyrolysis reaction is continued at a temperature of 210°C and normal pressure for about 30 minutes to obtain a molten material. The gaseous material produced during the vacuum reaction is collected in turn through a hot water heat exchanger and a cold water condenser.

[0064] The molten material is introduced into the continuous cooling equipment, the distance between the material thickness homogenization device and the conveyor belt surface is adjusted in advance, the thickness of the molten material on the conveyor 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 equipment is maintained at about 10°C, the length of the transmission belt is 10 meters, and infrared thermometers are fixed at the front end, middle part and end of the transmission belt. The residence time of the molten material in the continuous cooling equipment is 30 minutes, the discharge temperature of the solid foaming material is controlled to be 60±1°C, the average cooling rate in the first stage is about 6.7°C / min, and the average cooling rate in the second stage is about 3.3°C / min; the finished product is obtained after cutting.

[0065] Example 4

[0066] 10 kg of polyglycolic acid with a weight average molecular weight of 3.5W is put into a vacuum reactor, 45 g of catalyst Ce (HCO3) is added, and a pyrolysis reaction is carried out at a temperature of 240°C and an absolute pressure of 1000 Pa. The reaction is terminated when the reaction conversion rate of the polyglycolic acid reaches 60%; the remaining polyglycolic acid is discharged from the vacuum reactor and introduced into a normal pressure reactor, and the pyrolysis reaction is continued at a temperature of 200°C and normal pressure for about 30 minutes to obtain a molten material; the gaseous material produced during the vacuum reaction is collected in turn through a hot water heat exchanger and a cold water condenser.

[0067] The molten material is introduced into the continuous cooling equipment, the distance between the material thickness homogenization device and the conveyor belt surface is adjusted in advance, the thickness of the molten material on the conveyor belt is controlled to be 5 cm, and the air cooling unit (power: 5 kW) is turned on in advance to make the temperature in the continuous cooling equipment about 10°C. The length of the transmission belt is 10 meters. Infrared thermometers are fixed at the front end, middle part and end of the transmission belt. The residence time of the molten material in the continuous cooling equipment is 30 minutes. The discharge temperature of the solid foaming material is controlled to be 60±1°C. The average cooling rate in the first stage is about 6.2°C / min, and the average cooling rate in the second stage is about 3.2°C / min. The finished product is obtained after cutting.

[0068] Comparative Example 1

[0069] The same as Example 1, except that: when the reaction conversion rate of polyglycolic acid reaches 70%, the reaction is terminated, and the remaining polyglycolic acid is discharged from the vacuum reactor and introduced into a normal pressure reactor for subsequent operation steps.

[0070] Comparative Example 2

[0071] The same as Example 1, except that: before the molten material is fed, the temperature in the continuous cooling equipment is about 5°C, the residence time of the molten material in the continuous cooling equipment is 20 minutes, the discharge temperature of the solid foaming material is controlled at 60±1°C, the average cooling rate in the first stage is about 10.6°C / min, and the average cooling rate in the second stage is about 5.4°C / min.

[0072] Table 1 Test results of various embodiments and comparative examples

[0073] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 <![CDATA[Density (kg / m 3 )]]> 628 801 763 630 867 634 Compression strength(kPa) 412 373 522 840 1156 256 Thermal conductivity W / (m·K) 0.040 0.051 0.032 0.073 0.097 0.082 Hydrolytic degradability 55％ 45％ 51％ 53％ 37％ 52％

[0074] As shown in Table 1, compared with Example 1, the reaction conversion rate of polyglycolic acid during pyrolysis reaction in Comparative Example 1 is higher than 60%. Although the compressive strength is improved, the density and thermal conductivity of the product are also significantly increased, while the hydrolysis degradation is significantly reduced, which is not conducive to its application as a foaming material in the fields of packaging, degradable thermal insulation materials or degradable flame retardant materials. Compared with Example 1, the compressive strength of Comparative Example 2 is reduced and the thermal conductivity is significantly increased. It is speculated that this may be due to the fact that the cooling rate of the melt material is too fast, and the bubble pores 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 foaming material, affecting its compressive strength and thermal conductivity. Comprehensive comparison, the present invention is conducive to maintaining the performance of the obtained foaming material at a better level by controlling the pyrolysis reaction conversion rate and the cooling rate of the melt material.

[0075] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing foamed PGA, characterized in that: The following steps are involved: (1) subjecting polyglycolic acid to a pyrolysis reaction at a temperature of 230 to 270° C. and an absolute pressure of 0.1 kPa to 2 kPa, and terminating the reaction when the reaction conversion rate of the polyglycolic acid reaches a preset value to obtain a molten material, wherein the preset value is less than 60%; (2) The molten material is cooled at a cooling rate of 2 to 10° C. / min to obtain a solid foaming material.

2. The method for preparing foamed PGA according to claim 1, characterized in that: After step (1), the method further comprises 1b) continuing to pyrolyze the remaining polyglycolic acid at a temperature of 200 to 230° C. and normal pressure for a reaction time of 0.1 to 1 h to obtain a molten material.

3. The method for preparing foamed PGA according to claim 2, characterized in that: Step (1) is carried out in a vacuum reactor in the presence of a catalyst, and step 1b) is carried out in a normal pressure reactor. When the reaction conversion rate of the polyglycolic acid reaches a preset value, the remaining polyglycolic acid is discharged from the vacuum reactor and enters a normal pressure reactor for further pyrolysis in the normal pressure reactor.

4. The method for preparing foamed PGA according to claim 3, characterized in that: The vacuum reactor and the atmospheric pressure reactor are both selected from vertical stirring reactors or horizontal stirring reactors. The viscosity of the melt material in the vacuum reactor and the atmospheric pressure reactor is 300-10000 centipoise, and the rotation speed is 3-15 rpm.

5. The method for preparing foamed PGA according to claim 1, characterized in that: During the cooling process of step (2), the thickness of the molten material is controlled to be 1 to 5 cm, and before the molten material solidifies, the cooling rate of the molten material is controlled to be 5 to 8° C. / min.

6. The method for preparing foamed PGA according to any one of claims 1 to 5, characterized in that: The preset value is between 20% and 40%. Step (1) further comprises: collecting gaseous materials generated during the pyrolysis of polyglycolic acid to obtain crude glycolide.

7. A system used in the preparation method 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 equipment includes multiple parallel conveyor belts, a material stop block is arranged next to the input end of each conveyor belt, and a material thickness homogenizing device and a feed port are arranged above the input end of each conveyor belt. The molten material is cooled in the continuous cooling equipment, and the thickness of the molten material on the conveyor belt is controlled by adjusting the distance between the material thickness homogenizing device and the conveyor belt surface.

8. The system used in the preparation method according to claim 7, characterized in that: The reaction equipment includes a vacuum reactor and a normal pressure reactor; and / or, a plurality of infrared thermometers are fixed on the sides of the conveyor belt; And / or, the continuous cooling device adopts an air-cooled cooling method.

9. A foamed PGA, characterized in that: The preparation method is described in any one of claims 1 to 6.

10. Use of the foamed PGA according to claim 9 in the fields of packaging, degradable thermal insulation materials or degradable flame retardant materials.

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