CN113087957A - High-power foaming polylactic acid bead and preparation method thereof - Google Patents
High-power foaming polylactic acid bead and preparation method thereof Download PDFInfo
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- CN113087957A CN113087957A CN202110558691.7A CN202110558691A CN113087957A CN 113087957 A CN113087957 A CN 113087957A CN 202110558691 A CN202110558691 A CN 202110558691A CN 113087957 A CN113087957 A CN 113087957A
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- 229920000747 poly(lactic acid) Polymers 0.000 title claims abstract description 188
- 239000004626 polylactic acid Substances 0.000 title claims abstract description 188
- 239000011324 bead Substances 0.000 title claims abstract description 123
- 238000005187 foaming Methods 0.000 title claims abstract description 84
- 238000002360 preparation method Methods 0.000 title claims abstract description 17
- 239000012530 fluid Substances 0.000 claims abstract description 39
- 238000000034 method Methods 0.000 claims abstract description 26
- 238000004519 manufacturing process Methods 0.000 claims abstract description 15
- 239000006260 foam Substances 0.000 claims abstract description 13
- 239000002245 particle Substances 0.000 claims description 76
- 239000011347 resin Substances 0.000 claims description 64
- 229920005989 resin Polymers 0.000 claims description 64
- 238000001816 cooling Methods 0.000 claims description 28
- 238000010438 heat treatment Methods 0.000 claims description 27
- 230000008961 swelling Effects 0.000 claims description 21
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- 238000001125 extrusion Methods 0.000 claims description 14
- 239000000155 melt Substances 0.000 claims description 13
- 229920006395 saturated elastomer Polymers 0.000 claims description 12
- 238000009835 boiling Methods 0.000 claims description 10
- 238000005469 granulation Methods 0.000 claims description 9
- 230000003179 granulation Effects 0.000 claims description 9
- 238000002844 melting Methods 0.000 claims description 6
- 230000008018 melting Effects 0.000 claims description 6
- 238000009826 distribution Methods 0.000 claims description 5
- 238000011049 filling Methods 0.000 claims description 5
- 239000002131 composite material Substances 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 18
- 230000008569 process Effects 0.000 abstract description 16
- 239000002994 raw material Substances 0.000 abstract description 12
- 230000035484 reaction time Effects 0.000 abstract description 5
- 230000000052 comparative effect Effects 0.000 description 13
- 229910002092 carbon dioxide Inorganic materials 0.000 description 10
- 238000001878 scanning electron micrograph Methods 0.000 description 10
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- 239000000498 cooling water Substances 0.000 description 4
- 238000002425 crystallisation Methods 0.000 description 4
- 230000008025 crystallization Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 230000009471 action Effects 0.000 description 3
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- 230000007062 hydrolysis Effects 0.000 description 3
- 238000006460 hydrolysis reaction Methods 0.000 description 3
- 230000008595 infiltration Effects 0.000 description 3
- 238000001764 infiltration Methods 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 2
- 238000012668 chain scission Methods 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000006261 foam material Substances 0.000 description 2
- 238000013012 foaming technology Methods 0.000 description 2
- 238000005470 impregnation Methods 0.000 description 2
- 238000004806 packaging method and process Methods 0.000 description 2
- 239000008188 pellet Substances 0.000 description 2
- 239000012466 permeate Substances 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000003672 processing method Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 239000002028 Biomass Substances 0.000 description 1
- 241001391944 Commicarpus scandens Species 0.000 description 1
- 239000012620 biological material Substances 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 229940079593 drug Drugs 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/16—Making expandable particles
- C08J9/18—Making expandable particles by impregnating polymer particles with the blowing agent
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
- C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
- C08J9/122—Hydrogen, oxygen, CO2, nitrogen or noble gases
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2203/00—Foams characterized by the expanding agent
- C08J2203/06—CO2, N2 or noble gases
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2203/00—Foams characterized by the expanding agent
- C08J2203/08—Supercritical fluid
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
- C08J2367/04—Polyesters derived from hydroxy carboxylic acids, e.g. lactones
Abstract
The invention provides polylactic acid foamed beads, which have a foaming ratio of 20-40 times; the diameter of the foam hole of the polylactic acid foaming bead is 80-150 mu m. The high-magnification polylactic acid expanded bead prepared by the invention has a specific structure, particularly has a uniform cell structure from the center to the edge, and is an ultra-light material with excellent performance. In addition, the invention only adopts polylactic acid with a general grade as a raw material, namely, the polylactic acid expanded beads with high magnification can be obtained. According to the preparation method of the polylactic acid foaming bead, the supercritical fluid is adopted, the specific foaming process is combined, the process is simple, the reaction time is short, the control is easy, the production efficiency is high, the prepared foaming bead meets the steam forming process, the foaming bead can be used for a long time at the temperature of-50-120 ℃, the foaming process is green and environment-friendly, the application range is wide, and the industrial scale production and application are favorably realized.
Description
Technical Field
The invention belongs to the technical field of polylactic acid foamed beads, relates to polylactic acid foamed beads and a preparation method thereof, and particularly relates to high-power foamed polylactic acid beads and a preparation method thereof.
Background
The polylactic resin is a biodegradable material, can be degraded into water and carbon dioxide due to biomass, is an environment-friendly green renewable material, and is widely applied to the fields of medicines, packaging, consumer products and the like. The polylactic acid resin is highly favored by the application market end due to the advantages of degradable materials. At present, polylactic acid resin is relatively high in price and cannot be widely used as a general material, so that the polylactic acid resin is one of the key points of current research, and the polylactic acid resin is foamed to save materials and further reduce cost. In particular, the EPS foam which is used in a large amount in the field of packaging causes the environmental problem of white pollution and is gradually eliminated. The polylactic resin has the advantages of self degradable materials, can save materials after foaming, reduce the cost and is deeply favored by application market ends.
However, polylactic acid resin has high crystallinity, the melt strength of the molten polylactic acid resin is very low, the polylactic acid resin cannot be directly made into a foaming material, and the polylactic acid is not resistant to hydrolysis, and molecules are easy to break chains under the action of a trace amount of water, so that the foaming technology of the polylactic acid is always a technical problem in the field.
Therefore, how to find a suitable method to solve the above problems in the polylactic acid foaming technical field, especially to obtain polylactic acid foaming beads suitable for application and to widen the application depth and width of the polylactic acid foaming material, has become one of the focuses of great attention of many research and development manufacturers and first-line researchers.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a polylactic acid expanded bead and a preparation method thereof, and particularly to a high-power expanded polylactic acid bead, wherein the polylactic acid expanded bead provided by the present invention only uses a general grade polylactic acid as a raw material, i.e. an available high-power polylactic acid expanded bead; and the process is simple and easy to control, and is favorable for realizing industrial scale production and application.
The invention provides polylactic acid foamed beads, which have a foaming ratio of 20-40 times;
the diameter of the foam hole of the polylactic acid foaming bead is 80-150 mu m.
Preferably, the particle size of the polylactic acid expanded beads is 3-10 mm;
the polylactic acid expanded beads have a uniform cell distribution;
the cells are closed cell structures.
Preferably, the density of the polylactic acid expanded beads is 30-60 kg/m3；
The polylactic acid foaming beads are high-power foaming polylactic acid beads;
the polylactic acid expanded beads have a uniform cell structure from the center to the edges.
The invention provides a preparation method of polylactic acid foaming beads, which comprises the following steps:
1) extruding, granulating and rapidly cooling polylactic acid resin to obtain non-crystalline polylactic acid particles;
2) placing the amorphous polylactic acid particles obtained in the step into a die cavity at a first temperature, filling a supercritical fluid, and obtaining a polymer-supercritical fluid homogeneous phase system after balancing;
3) decompressing the polymer-supercritical fluid homogeneous system obtained in the step to obtain saturated swelling polylactic acid particles;
4) and heating the saturated swelling polylactic acid particles obtained in the step at a second temperature, and foaming and expanding the particles to obtain the polylactic acid expanded beads.
Preferably, the melt index of the polylactic resin is 3-10 g/10 min;
the melt strength of the polylactic resin is 1-10 cN;
the particle size of the polylactic resin is 1-3 mm;
the polylactic resin is dried polylactic resin.
Preferably, the polylactic acid resin has a water content of 100ppm or less;
the extrusion temperature is 160-190 ℃;
the rapid cooling comprises water cooling;
the cooling temperature of the rapid cooling is less than or equal to 5 ℃.
Preferably, the extrusion granulation rapid cooling mode comprises twin-screw extrusion water-cooling ribbing granulation;
the proportion of the total volume of the polylactic resin to the volume of the die cavity is 90-99 percent;
the supercritical fluid comprises supercritical N2And/or supercritical CO2；
The pressure of the supercritical fluid is 7.2-20 MPa.
Preferably, the first temperature is lower than the second temperature;
the time for reaching the equilibrium is 15-30 min;
the pressure after pressure relief is normal pressure;
the pressure relief is slow pressure relief;
the pressure relief rate is 0.1-20 MPa/s.
Preferably, the first temperature is higher than the critical temperature of the supercritical fluid and lower than the softening temperature of the polylactic acid resin;
the second temperature is higher than the softening temperature of the polylactic acid resin and lower than the melting temperature of the polylactic acid resin;
the first temperature is 35-80 ℃;
the second temperature is 80-160 ℃.
Preferably, the heating comprises hot air heating;
the heating mode comprises boiling bed heating;
the foaming and expanding time of the particles is 30-90 s.
The invention provides polylactic acid foamed beads, which have a foaming ratio of 20-40 times; the diameter of the foam hole of the polylactic acid foaming bead is 80-150 mu m. Compared with the prior art, the invention is based on the research that the supercritical fluid (SCF, which refers to the fluid above the critical temperature and the critical pressure) can be used for preparing the polymer foaming material by utilizing the advantages of high diffusion rate, high solubility and the like of the supercritical fluid in the polymer because the viscosity and the diffusion coefficient are close to gas, and the density and the solvation capacity are close to liquid, and the supercritical fluid foaming technology is clean in the whole foaming process and can not pollute the environment and foaming products.
The high-magnification polylactic acid foamed bead prepared by the invention has a specific structure, the foaming magnification can reach 20-40 times, the pore diameter of the foamed bead is 80-150 mu m, and particularly, the foamed bead has a uniform cell structure from the center to the edge and is an ultra-light material with excellent performance. The polylactic acid foaming bead provided by the invention only adopts the polylactic acid with a general grade as a raw material, namely the available high-magnification polylactic acid foaming bead, effectively solves the limitation that the polylactic acid resin foaming material in the prior art has high requirements on polylactic acid materials, especially high requirements on melt strength, and further solves the defect that the conventional kettle pressure foaming form cannot be adopted to prepare the foaming bead because the polylactic acid melt has low strength and is not resistant to hydrolysis and molecules are easy to chain scission under the action of trace water.
According to the polylactic acid foaming bead and the preparation method thereof provided by the invention, the used polylactic acid resin raw material is a general brand, a supercritical fluid is adopted, a specific foaming process is combined, the process is simple, the reaction time is short, the control is easy, the production efficiency is high, the prepared foaming bead meets the steam forming process, the polylactic acid foaming bead can be used for a long time at the temperature of-50-120 ℃, the foaming process is green and environment-friendly, the high-power foaming polylactic acid bead can be prepared, the application range is wide, and the industrial scale production and application are favorably realized.
Experimental results show that the preparation method provided by the invention can be combined with the production process of amorphous modification, low-temperature impregnation and heating foaming to realize the foaming of the general polylactic resin with the melt index of 3-10 g/10min and the melt strength of 1-10 cN; the whole reaction time is short for 15-30 min, and the production efficiency is high. The prepared foaming bead closed-cell structure has uniform cells, the diameter of each cell is small by 80-150 mu m, the foaming ratio is high and reaches 20-40 times, and the foaming bead closed-cell structure is easy to form by water vapor and is a degradable foam material with ultra-light weight and excellent performance.
Drawings
FIG. 1 is a scanning electron micrograph of a section of polylactic acid expanded beads prepared according to the present invention;
FIG. 2 is a scanning electron micrograph of a section of polylactic acid expanded beads prepared in example 1 of the present invention;
FIG. 3 is a SEM photograph of a section of polylactic acid expanded beads prepared in example 2 of the present invention;
FIG. 4 is a SEM photograph of a cut surface of polylactic acid expanded beads prepared in comparative example 1 according to the present invention;
FIG. 5 is a SEM photograph of a cut surface of polylactic acid expanded beads prepared in comparative example 2 of the present invention.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
All of the starting materials of the present invention, without particular limitation as to their source, may be purchased commercially or prepared according to conventional methods well known to those skilled in the art.
All the raw materials of the invention are not particularly limited in purity, and the invention preferably adopts the purity requirements of analytical purity or the purity requirements of the polylactic acid foaming material preparation field.
All the raw materials, the marks and the acronyms thereof belong to the conventional marks and acronyms in the field, each mark and acronym is clear and definite in the field of related application, and the raw materials can be purchased from the market or prepared by a conventional method by the technical staff in the field according to the marks, the acronyms and the corresponding application.
The invention provides polylactic acid foamed beads, which have a foaming ratio of 20-40 times;
the diameter of the foam hole of the polylactic acid foaming bead is 80-150 mu m.
In the present invention, the polylactic acid expanded beads are high-expansion polylactic acid beads. The expansion ratio of the polylactic acid expanded beads is 20 to 40 times, preferably 22 to 38 times, more preferably 25 to 35 times, and still more preferably 28 to 32 times.
In the invention, the diameter of the foam hole of the polylactic acid expanded bead is 80-150 μm, preferably 90-140 μm, and more preferably 100-130 μm.
In the present invention, the polylactic acid expanded beads have a porous structure. In particular, the cells are preferably of closed cell structure.
In the present invention, the polylactic acid expanded beads are preferably high-expansion polylactic acid beads.
In the present invention, the polylactic acid expanded beads preferably have a uniform cell distribution. In particular, the polylactic acid expanded beads preferably have a uniform cell structure from the center of the beads to the edge of the beads. That is, the polylactic acid expanded beads have a uniform cell distribution throughout the whole.
In the invention, the particle size of the polylactic acid expanded beads is preferably 3-10 mm, more preferably 4-9 mm, more preferably 5-8 mm, and more preferably 6-7 mm.
In the present invention, the density of the polylactic acid expanded beads is preferably 30 to 60kg/m3More preferably 35 to 55kg/m3More preferably 40 to 50kg/m3。
Referring to fig. 1, fig. 1 is a scanning electron micrograph of a section of the polylactic acid expanded bead prepared according to the present invention.
As can be seen from FIG. 1, the polylactic acid expanded bead prepared by the invention is a high-power expanded polylactic acid bead, has a porous structure and a closed cell structure, has a cell diameter of 80-150 μm, is uniform in cell distribution, and has a uniform cell structure from the center of the bead to the edge of the bead.
The invention also provides a preparation method of the polylactic acid expanded bead, which comprises the following steps:
1) extruding, granulating and rapidly cooling polylactic acid resin to obtain non-crystalline polylactic acid particles;
2) placing the amorphous polylactic acid particles obtained in the step into a die cavity at a first temperature, filling a supercritical fluid, and obtaining a polymer-supercritical fluid homogeneous phase system after balancing;
3) decompressing the polymer-supercritical fluid homogeneous system obtained in the step to obtain saturated swelling polylactic acid particles;
4) and heating the saturated swelling polylactic acid particles obtained in the step at a second temperature, and foaming and expanding the particles to obtain the polylactic acid expanded beads.
The invention firstly obtains non-crystalline polylactic acid particles after extrusion granulation and rapid cooling of polylactic acid resin.
In the invention, the grade of the polylactic resin raw material is not specially limited, the polylactic resin can be prepared by using the polylactic resin with a general grade, the requirements on the melt strength and the like of the polylactic resin raw material are also lower, the cost of the polylactic resin raw material is greatly reduced, and the application width and the application range are improved.
In the invention, the melt index of the polylactic acid resin is preferably 3-10 g/10min, more preferably 4-9 g/10min, more preferably 5-8 g/10min, and more preferably 6-7 g/10 min. Wherein the melt index MI is measured with a 2.16kg weight at 190 ℃.
In the invention, the melt strength of the polylactic acid resin is preferably 1-10 cN, more preferably 3-8 cN, and more preferably 5-6 cN.
In the present invention, the polylactic acid resin preferably includes polylactic acid resin particles. The particle size of the polylactic resin particles is preferably 1-3 mm, more preferably 1.2-2.8 mm, more preferably 1.5-2.5 mm, and more preferably 1.8-2.3 mm.
In the present invention, the polylactic acid resin is preferably a dried polylactic acid resin. Specifically, the polylactic acid resin is preferably dried under vacuum at 80 ℃.
In the present invention, the water content of the polylactic acid resin is preferably 100ppm or less, more preferably 50ppm or less, and still more preferably 50ppm or less.
In the invention, the extrusion temperature is preferably 160-190 ℃, more preferably 165-185 ℃, and more preferably 170-180 ℃.
In the present invention, the rapid cooling includes water cooling. Specifically, the cooling temperature of the rapid cooling is preferably 5 ℃ or lower, more preferably 3 ℃ or lower, and still more preferably 1 ℃ or lower.
In the present invention, the extrusion granulation rapid cooling mode preferably comprises twin-screw extrusion water-cooling strand granulation. Namely, granulating after water-cooling bracing and cooling after double-screw extrusion.
The invention relates to a complete and refined integral preparation process, which better ensures the structure, the appearance and the parameters of polylactic acid foaming beads, and the twin-screw extrusion water-cooling brace granulation can be more specifically as follows:
the method comprises the following steps of extruding and granulating through a double-screw extruder, wherein the temperature of an feeding section of the extruder is preferably 160-170 ℃ (more preferably 162-168 ℃, and more preferably 164-166 ℃), the temperature of a melting section is preferably 170-185 ℃ (more preferably 172-183 ℃, and more preferably 175-180 ℃), the temperature of a homogenizing section is preferably 185-190 ℃ (more preferably 186-189 ℃, and more preferably 187-188 ℃), and the temperature of a die is preferably 190 ℃. And (3) carrying out water bracing granulation, controlling the temperature of cooling water by a refrigerator, wherein the temperature of the cooling water is less than 5 ℃, and inhibiting the crystallization of the polylactic acid by a rapid cooling process to prepare non-crystallization foaming particles with the particle size of 1.5-2 mm (more preferably 1.6-1.9 mm, and more preferably 1.7-1.8 mm).
The amorphous polylactic acid particles obtained in the step are placed in a die cavity at a first temperature, supercritical fluid is filled in the die cavity, and a polymer-supercritical fluid homogeneous phase system is obtained after equilibrium is reached.
In the present invention, the first temperature is preferably lower than the second temperature. The first temperature is more preferably higher than the critical temperature of the supercritical fluid and lower than the softening temperature of the polylactic acid resin. Specifically, the first temperature may be 35 to 80 ℃, more preferably 45 to 70 ℃, and more preferably 55 to 60 ℃.
In the present invention, the ratio of the total volume of the polylactic acid resin particles to the volume of the cavity is preferably 90% to 99%, more preferably 92% to 97%, and still more preferably 94% to 95%.
In the present invention, the supercritical fluid preferably includes supercritical N2And/or supercritical CO2More preferably supercritical N2Or supercritical CO2. Specifically, the CO content may be 32 ℃ to 7.3MPa2Or N of more than-147 ℃ and more than 3.4MPa2。
In the invention, the pressure of the supercritical fluid is preferably 7.2-20 MPa, more preferably 10-17 MPa, and more preferably 13-16 MPa.
In the invention, the time for reaching the equilibrium is preferably 15-30 min, more preferably 18-27 min, and more preferably 21-24 min.
The supercritical fluid adopted by the invention swells and permeates the non-crystalline polylactic acid particles to saturation at a first temperature (T1 temperature). The temperature T1 is above the critical temperature of carbon dioxide and below the softening temperature of polylactic acid, which can ensure the rapid permeation of supercritical fluid and prevent the mutual migration and adhesion of polylactic acid particle surface molecules caused by heating.
According to the invention, the polymer-supercritical fluid homogeneous system obtained in the above step is decompressed, and the swelling saturated polylactic acid particles are obtained.
In the invention, the pressure after the pressure relief is normal pressure. In the invention, the normal pressure can be 0.8-1.2 bar, can also be 0.9-1.1 bar, and can be 1bar specifically.
In the present invention, the pressure relief preferably comprises slow pressure relief. The pressure relief rate is preferably 0.1-20 MPa/s, more preferably 1-15 MPa/s, and more preferably 5-10 MPa/s. Specifically, it may be less than 20 MPa/s.
The invention slowly releases the pressure to 0 (normal pressure), and takes out the polylactic acid particles after the swelling saturation. The invention controls the pressure release rate to be lower than 20MPa/s, and further inhibits the foaming of particles at a low pressure release rate.
Finally, heating the saturated swelling polylactic acid particles obtained in the step at a second temperature, and foaming and expanding the particles to obtain the polylactic acid expanded beads.
In the present invention, the second temperature is preferably higher than the softening temperature of the polylactic acid resin and lower than the melting temperature of the polylactic acid resin. The second temperature may be 80 to 160 ℃, more preferably 90 to 150 ℃, more preferably 100 to 140 ℃, and more preferably 110 to 130 ℃.
In the present invention, the heating preferably includes hot air heating. More particularly, the heating means preferably comprises ebullated bed heating. I.e. in the case of a bubbling bed, the boiling heating is carried out by hot air having a second temperature.
In the invention, the time for the foaming and expansion of the particles is preferably 30-90 s, more preferably 40-80 s, and more preferably 50-70 s.
The invention controls the temperature of the hot air (second temperature) within a range of T2 by heating and foaming the hot air by the hot air boiling bed. The temperature of the hot air is higher than the softening temperature of the polylactic acid and lower than the melting temperature.
The invention is a complete and refined integral preparation scheme, better ensures the foaming rate and the appearance of polylactic acid beads, and improves the performance of the polylactic acid beads, and the preparation method of the polylactic acid expanded beads can specifically comprise the following steps:
(1) extruding and granulating the general polylactic resin, and quickly cooling to prepare non-crystalline polylactic acid particles;
(2) placing amorphous polylactic acid particles in a container with a constant temperature T1 (first temperature), filling supercritical fluid for permeation and swelling to reach a saturated state, and forming a polymer-supercritical fluid homogeneous phase system;
(3) after the balance is achieved, slowly releasing the pressure to 0 (normal pressure), and taking out the polylactic acid particles with saturated swelling;
(4) and finally, placing the polylactic acid particles on a boiling bed, heating the polylactic acid particles by hot air at a temperature T2 (a second temperature), and foaming and expanding the particles to obtain the polylactic acid foamed beads with the diameter of cells of 80-150 mu m and the foaming ratio of 20-40 times.
The high-power polylactic acid foamed bead has a specific structure, the foaming ratio can reach 20-40 times, the pore diameter of the foamed bead is 80-150 mu m, particularly the foamed bead has a uniform cell structure from the center to the edge, and the foamed bead is an ultra-light material with excellent performance. The polylactic acid foaming bead provided by the invention only adopts the polylactic acid with a general grade as a raw material, namely the available high-magnification polylactic acid foaming bead, effectively solves the limitation that the polylactic acid resin foaming material in the prior art has high requirements on polylactic acid materials, especially high requirements on melt strength, and further solves the defect that the conventional kettle pressure foaming form cannot be adopted to prepare the foaming bead because the polylactic acid melt has low strength and is not resistant to hydrolysis and molecules are easy to chain scission under the action of trace water.
According to the polylactic acid foaming bead and the preparation method thereof provided by the invention, the used polylactic acid resin raw material is a general brand, a supercritical fluid is adopted, a specific foaming process is combined, the process is simple, the reaction time is short, the control is easy, the production efficiency is high, the prepared foaming bead meets the steam forming process, the polylactic acid foaming bead can be used for a long time at the temperature of-50-120 ℃, the foaming process is green and environment-friendly, the high-power foaming polylactic acid bead can be prepared, the application range is wide, and the industrial scale production and application are favorably realized.
Experimental results show that the preparation method provided by the invention can be combined with the production process of amorphous modification, low-temperature impregnation and heating foaming to realize the foaming of the general polylactic resin with the melt index of 3-10 g/10min and the melt strength of 1-10 cN; the whole reaction time is short for 15-30 min, and the production efficiency is high. The prepared foaming bead closed-cell structure has uniform cells, the diameter of each cell is small by 80-150 mu m, the foaming ratio is high and reaches 20-40 times, and the foaming bead closed-cell structure is easy to form by water vapor and is a degradable foam material with ultra-light weight and excellent performance.
For further illustration of the present invention, a polylactic acid expanded bead and a method for preparing the same are described in detail with reference to the following examples, but it should be understood that the examples are carried out on the premise of the technical solution of the present invention, and the detailed embodiments and specific procedures are given only for further illustration of the features and advantages of the present invention, not for limitation of the claims of the present invention, and the scope of the present invention is not limited to the following examples.
Example a general purpose polylactic acid resin, a commercially available Hainan biomaterial, under the trade designation REVODE 190, was selected.
Example 1
Firstly, drying general polylactic resin particles for later use, wherein the drying conditions are vacuum drying at 80 ℃ and the water content is less than 100 ppm.
Then, extruding and granulating through a double-screw extruder, wherein the feeding section of the extruder is 160 ℃ plus 170 ℃, the melting section is 170 ℃ plus 185 ℃, the homogenizing section is 185 ℃ plus 190 ℃, and the die temperature is 190 ℃. The water bracing and granulating is adopted, the temperature of cooling water is controlled by a refrigerator, the temperature of the cooling water is less than 5 ℃, the crystallization of polylactic acid is inhibited by a rapid cooling process, and the non-crystallization foaming particles with the particle size of 1.5mm are prepared.
Then, the particles to be foamed are placed in a high-pressure container thermostatically maintained at T1, and are charged with 5:1 supercritical N2And CO2The supercritical fluid pressure is 16MPa, the temperature T1 is 60 ℃, and the swelling and infiltration are carried out for 180min until the supercritical fluid is saturated.
And then, slowly relieving the pressure in the high-pressure container from 16MPa to 0 at a pressure relief rate of 20MPa/s, and taking out the polylactic acid particles after swelling and saturation.
Finally, the particles are heated to foam through a boiling bed of hot air, wherein the temperature T2 is 135 ℃ and the heating time is 90 s.
The polylactic acid expanded beads prepared in example 1 of the present invention were examined and characterized.
The results show that the polylactic acid particles are foamed and expanded to obtain the bulk density of 30kg/m3The expanded beads of (2) were expanded 40 times as much as the original beads, and the scanning electron micrograph of the section of the expanded beads is shown in FIG. 2.
Referring to fig. 2, fig. 2 is a scanning electron micrograph of a section of the polylactic acid expanded beads prepared in example 1 of the present invention.
As can be seen from FIG. 2, the diameter of the cells is between 100 and 150 μm.
Example 2
First, general-purpose polylactic acid resin pellets were prepared into noncrystalline particles to be foamed having a particle diameter of 2mm by the extrusion processing method of example 1.
Then, the particles to be foamed are placed in a high-pressure container thermostatically maintained at T1 and charged with 1:5 supercritical N2And CO2The supercritical fluid pressure is 13MPa, the temperature T1 is 40 ℃, and the swelling permeation is carried out for 360min until the supercritical fluid is saturated.
And then, slowly relieving the pressure in the high-pressure container from 13MPa to 0 at a pressure relief rate of 10MPa/s, and taking out the polylactic acid particles after swelling and saturation.
Finally, the particles are heated to foam by a boiling bed of hot air, the temperature T2 is 120 ℃, and the heating time is 60 s.
The polylactic acid expanded beads prepared in example 2 of the present invention were examined and characterized.
The results show that the polylactic acid particles are foamed and expanded to obtain the bulk density of 63kg/m3The expanded beads of (2) were expanded 20 times as much as the original beads, and the scanning electron micrograph of the section of the expanded beads is shown in FIG. 3.
Referring to fig. 3, fig. 3 is a scanning electron micrograph of a section of the polylactic acid expanded beads prepared in example 2 of the present invention.
As can be seen from FIG. 3, the diameter of the cells is between 80 and 100 μm.
Example 3
First, general-purpose polylactic acid resin pellets were prepared into non-crystalline particles to be foamed having a particle diameter of 1.8mm by the extrusion processing method of example 1.
Then, the particles to be foamed are placed in a high-pressure container thermostatically maintained at T1, and 2:3 of supercritical N is charged2And CO2The supercritical fluid pressure is 15MPa, the temperature T1 is 50 ℃, and the swelling permeation is 240min to saturation.
And then, slowly relieving the pressure in the high-pressure container from 15MPa to 0 at a pressure relief rate of 5MPa/s, and taking out the polylactic acid particles after swelling and saturation.
Finally, the particles are heated to foam by a boiling bed of hot air, the temperature T2 is 130 ℃, and the heating time is 30 s.
The polylactic acid expanded beads prepared in example 3 of the present invention were examined.
The results show that the polylactic acid particles are foamed and expanded to obtain the polylactic acid particles with the bulk density of 42kg/m3The expanded beads of (2) are expanded by a factor of 30 with respect to the original particles.
Comparative example 1
Comparative example 1 is a comparative example of example 1, and it was tried whether the general polylactic acid particles could successfully complete foaming.
First, by the foaming method of example 1, general polylactic acid resin particles were dried and placed in a high-pressure vessel maintained at a constant temperature of T1, and 5:1 supercritical N was charged2And CO2The supercritical fluid pressure is 16MPa, the temperature T1 is 60 ℃, and the swelling and infiltration are carried out for 180 min.
And then, slowly relieving the pressure in the high-pressure container from 16MPa to 0 at a pressure relief rate of 20MPa/s, and taking out the polylactic acid particles after swelling and saturation.
Finally, the particles are heated to foam through a boiling bed of hot air, wherein the temperature T2 is 135 ℃ and the heating time is 90 s.
The polylactic acid expanded beads prepared in comparative example 1 of the present invention were examined and characterized.
The results show that the polylactic acid particles expand and foam unevenly, and the bulk density is 100kg/m3The expanded beads of (2) were expanded by about 10 times, and the scanning electron micrograph of the section of the expanded beads is shown in FIG. 4.
Referring to fig. 4, fig. 4 is a scanning electron micrograph of a cut surface of the polylactic acid expanded beads prepared in comparative example 1 according to the present invention.
As can be seen from FIG. 4, the foaming of the inner cells is varied mainly because the original polylactic acid particles have high crystallinity and the crystalline regions are difficult to swell and penetrate.
Comparative example 2
Comparative example 2 is a comparative example of example 1, and attempts were made to successfully complete foaming by further extending the saturation time based on comparative example 1.
Firstly, drying general polylactic resin particles, placing the particles into a high-pressure container with constant temperature of T1, and filling 5:1 of supercritical N2And CO2The supercritical fluid pressure is 16MPa, the temperature T1 is 60 ℃, and the swelling and infiltration are carried out for 24 h.
And then, slowly relieving the pressure in the high-pressure container from 16MPa to 0 at a pressure relief rate of 20MPa/s, and taking out the polylactic acid particles after swelling and saturation.
Finally, the particles are heated to foam through a boiling bed of hot air, wherein the temperature T2 is 135 ℃ and the heating time is 90 s.
The polylactic acid expanded beads prepared in comparative example 2 of the present invention were examined and characterized.
The results show that the polylactic acid particles expand and are not foamed uniformly, and the bulk density is 80kg/m3The expanded bead of (2) was expanded by about 16 times, and the photograph of the cross section of the expanded bead is shown in FIG. 5.
Referring to fig. 5, fig. 5 is a scanning electron micrograph of a cut surface of the polylactic acid expanded beads prepared in comparative example 2 according to the present invention.
As can be seen from FIG. 5, the foaming size of the inner cells is different, and the inner crystalline part of the polylactic acid is difficult to permeate.
The present invention provides a high expansion polylactic acid bead and a method for preparing the same, which are described in detail above, and the principle and embodiments of the present invention are explained herein using specific examples, and the above description of the examples is only for helping to understand the method of the present invention and the core concept thereof, including the best mode, and also for enabling anyone skilled in the art to practice the present invention, including making and using any device or system, and implementing any method in combination. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The scope of the invention is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Claims (10)
1. A polylactic acid expanded bead is characterized in that the expansion ratio of the polylactic acid expanded bead is 20-40 times;
the diameter of the foam hole of the polylactic acid foaming bead is 80-150 mu m.
2. The polylactic acid expanded bead according to claim 1, wherein the particle diameter of the polylactic acid expanded bead is 3 to 10 mm;
the polylactic acid expanded beads have a uniform cell distribution;
the cells are closed cell structures.
3. According toThe polylactic acid expanded bead according to claim 1, wherein the density of the polylactic acid expanded bead is 30 to 60kg/m3；
The polylactic acid foaming beads are high-power foaming polylactic acid beads;
the polylactic acid expanded beads have a uniform cell structure from the center to the edges.
4. A preparation method of polylactic acid expanded beads is characterized by comprising the following steps:
1) extruding, granulating and rapidly cooling polylactic acid resin to obtain non-crystalline polylactic acid particles;
2) placing the amorphous polylactic acid particles obtained in the step into a die cavity at a first temperature, filling a supercritical fluid, and obtaining a polymer-supercritical fluid homogeneous phase system after balancing;
3) decompressing the polymer-supercritical fluid homogeneous system obtained in the step to obtain saturated swelling polylactic acid particles;
4) and heating the saturated swelling polylactic acid particles obtained in the step at a second temperature, and foaming and expanding the particles to obtain the polylactic acid expanded beads.
5. The method according to claim 4, wherein the polylactic acid resin has a melt index of 3 to 10g/10 min;
the melt strength of the polylactic resin is 1-10 cN;
the particle size of the polylactic resin is 1-3 mm;
the polylactic resin is dried polylactic resin.
6. The production method according to claim 4, wherein the polylactic acid resin has a water content of 100ppm or less;
the extrusion temperature is 160-190 ℃;
the rapid cooling comprises water cooling;
the cooling temperature of the rapid cooling is less than or equal to 5 ℃.
7. The method for preparing the composite material according to claim 4, wherein the extrusion granulation rapid cooling mode comprises twin-screw extrusion water-cooling strand granulation;
the proportion of the total volume of the polylactic resin to the volume of the die cavity is 90-99 percent;
the supercritical fluid comprises supercritical N2And/or supercritical CO2；
The pressure of the supercritical fluid is 7.2-20 MPa.
8. The method of manufacturing according to claim 4, wherein the first temperature is lower than the second temperature;
the time for reaching the equilibrium is 15-30 min;
the pressure after pressure relief is normal pressure;
the pressure relief is slow pressure relief;
the pressure relief rate is 0.1-20 MPa/s.
9. The production method according to claim 4, wherein the first temperature is higher than a critical temperature of the supercritical fluid and lower than a softening temperature of the polylactic acid resin;
the second temperature is higher than the softening temperature of the polylactic acid resin and lower than the melting temperature of the polylactic acid resin;
the first temperature is 35-80 ℃;
the second temperature is 80-160 ℃.
10. The method of manufacturing according to claim 4, wherein the heating includes hot air heating;
the heating mode comprises boiling bed heating;
the foaming and expanding time of the particles is 30-90 s.
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| US5158986A (en) * | 1991-04-05 | 1992-10-27 | Massachusetts Institute Of Technology | Microcellular thermoplastic foamed with supercritical fluid |
| JP2001164027A (en) * | 1999-09-30 | 2001-06-19 | Kanebo Ltd | Polylactic acid foaming particle and formed product thereof and method for producing the same particle |
| CN106750486A (en) * | 2016-12-06 | 2017-05-31 | 东北林业大学 | A kind of method that supercritical fluid prepares fretting map polylactic wood plastic composite materials |
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|---|---|---|---|---|
| US5158986A (en) * | 1991-04-05 | 1992-10-27 | Massachusetts Institute Of Technology | Microcellular thermoplastic foamed with supercritical fluid |
| JP2001164027A (en) * | 1999-09-30 | 2001-06-19 | Kanebo Ltd | Polylactic acid foaming particle and formed product thereof and method for producing the same particle |
| CN106750486A (en) * | 2016-12-06 | 2017-05-31 | 东北林业大学 | A kind of method that supercritical fluid prepares fretting map polylactic wood plastic composite materials |
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| 杨鸣波等主编: "《塑料成型工艺学》", 北京：中国轻工业出版社, pages: 309 - 310 * |
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