A method for improving the foaming properties of PLA materials

Abstract

The application relates to a method for improving the foaming performance of PLA material, belonging to the field of degradable foaming materials.The preparation steps are as follows: after adding a semi-aromatic carbon dioxide-based copolymer into PLA raw materials, the PLA raw materials are extruded, blended and granulated to obtain modified PLA; the modified PLA is uniformly mixed with a foaming aid, and then is extruded by an extruder to form pre-foaming particles or plates; the particles or plates are transferred into a foaming device to be heated and foamed; the foamed foaming material is cured by using hot air to obtain a cured material; and the cured material is shaped to obtain the product.The PLA is modified by PPCP, PPCEP or / and PPCCP; the addition of the PPCP, the PPCEP or / and the PPCCP increases the foaming ratio of the PLA material; and the strength of the PLA foaming material is obviously increased.Both of them are degradable materials, and the foaming material obtained after foaming also maintains the degradable performance.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable foamed materials, specifically relating to a method for improving the foaming ratio of PLA materials using carbon dioxide-based biodegradable materials. Background Technology

[0002] Currently, biodegradable bio-based foaming materials are mainly polylactic acid (PLA). However, due to the insufficient gas barrier properties of PLA itself, the gas escape rate during foaming is relatively high, resulting in insufficient foaming ratio during the foaming process.

[0003] For example, Chinese patent CN112961395B discloses a high-expansion-ratio PLA / PBAT / Talc composite foamed oil-absorbing material. This material is made by melt-blending PLA, PBAT, Talc, and additives, pressing them into thin sheets, placing the sheets in a reactor, heating them to 130℃~145℃, and after the temperature stabilizes, introducing supercritical gas at a controlled pressure range of 1600psi~1800psi, then continuing to raise the temperature to 160℃~180℃ and holding it for 3~5 minutes. After holding, the temperature is lowered to 100℃~115℃ and saturated at this temperature for 0.5h~1h. After saturation, the sheets are ultrasonically treated. After ultrasonic treatment, supercritical fluid is released into the reactor at atmospheric pressure, and then the temperature is lowered to 0~5℃. After cooling, the sheets are removed and dried. This material, through PBAT modification of PLA and ultrasonic treatment during the foaming process, successfully achieves a PLA material expansion ratio of 20~40 times. However, this expansion ratio is still insufficient for foamed materials, and the preparation process requires high precision. Therefore, how to further improve the expansion ratio of PLA materials remains a problem that needs to be solved in this field. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for improving the foaming performance of PLA materials with simple process requirements and higher foaming ratio.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for improving the foaming performance of PLA material, characterized in that the preparation steps are as follows:

[0006] 1) Modified PLA is obtained by extruding and granulating a semi-aromatic carbon dioxide-based copolymer after adding it to PLA raw material; the mass ratio of PLA raw material to semi-aromatic carbon dioxide-based copolymer is 100:0.1~60; the semi-aromatic carbon dioxide-based copolymer is PPCP, PPCEP or / and PPCCP;

[0007] 2) Modified PLA and foaming agent are mixed evenly at a mass ratio of 100:1~4 and then extruded using an extruder to form pre-foamed granules or boards; the foaming agent is a premix of crosslinking agent, nucleating agent and foaming agent;

[0008] 3) Transfer the granules or boards into the foamer and heat them to 135°C to foam. After foaming, the foamed material is cured with hot air to obtain cured material. The cured material is then formed.

[0009] PPCP is a terpolymer of phthalic anhydride, propylene oxide, and carbon dioxide; PPCEP is a quaternary copolymer of phthalic anhydride, propylene oxide, ethylene oxide, and carbon dioxide; and PPCCP is a quaternary copolymer of phthalic anhydride, propylene oxide, cyclohexane oxide, and carbon dioxide.

[0010] To improve the foaming ratio of PLA material, this invention first modifies it with PPCP, PPCEP, and / or PPCCP. The selected PPCP, PPCEP, and PPCCP are well-compatible with PLA material, and compatibilizers can be omitted during the blending process. As the amount of PPCP, PPCEP, and PPCCP added increases, the foaming ratio of PLA material also increases. Furthermore, PPCP, PPCEP, and PPCCP modification of PLA significantly increases the strength of the PLA foam material. Both are biodegradable materials, and the foamed material retains its biodegradable properties after foaming.

[0011] Preferably, in the above method for improving the foaming performance of PLA material, the semi-aromatic carbon dioxide-based copolymer mentioned in step 1) is a mixture of PPCP and PPCCP in a mass ratio of 10:0.5~3. The preferred semi-aromatic carbon dioxide-based copolymer used for modification is mainly PPCP, with a small amount of PPCCP added for adjustment. This mixture has good compatibility with PLA, effectively increasing the strength and toughness of the PLA material while preventing excessive brittleness. It also further improves the gas encapsulation during the foaming process, better preventing gas escape and increasing the foaming ratio.

[0012] Preferably, in the above-described method for improving the foaming properties of PLA materials, the mass ratio of PLA raw material to semi-aromatic carbon dioxide-based copolymer in step 1) is 100:5~30. This preferred addition amount better simultaneously regulates the foaming properties and strength of the PLA material. More preferably, the mass ratio of PLA raw material to semi-aromatic carbon dioxide-based copolymer in step 1) is 100:12~17; this achieves the optimal modification effect of the present invention.

[0013] Preferably, in the above method for improving the foaming properties of PLA materials, the extrusion blending temperature in step 1) is 160℃~170℃.

[0014] Preferably, in the above-mentioned method for improving the foaming performance of PLA materials, the foaming aid mentioned in step 2) is a premixture of crosslinking agent, nucleating agent, and foaming agent in a mass ratio of 1~3:1~2:0.5~1.5. The PPCP, PPCEP, and PPCCP used in this invention are non-crystalline materials. Only a small amount of the crosslinking agent, nucleating agent, and foaming agent necessary for material foaming needs to be added. Uniform mixing can be achieved without adding compatibilizers, and the foaming aid can be uniformly dispersed, thereby obtaining a foamed material with uniform performance.

[0015] Specifically, the crosslinking agent is benzoyl peroxide or dicumyl peroxide. Preferred crosslinking agents can achieve uniform crosslinking of PPCP, PPCEP, PPCCP, and PLA, better ensuring the toughness and strength of the foamed material.

[0016] Specifically, the nucleating agent is one of talc, silicon dioxide, titanium dioxide, and magnesium oxide. All of the above nucleating agents can disperse well and uniformly in the material of the present invention, achieving a good nucleation effect. Preferably, the nucleating agent is toluene diisocyanate-modified talc. Toluene diisocyanate itself can act as a chain extender; by using it to modify talc and then as a nucleating agent, the resulting foamed material can better maintain its strength after high-ratio foaming.

[0017] Specifically, the foaming agent is carbon dioxide or azodicarbonamide.

[0018] Preferably, in the above method for improving the foaming performance of PLA material, the extrusion method in step 2) is to use a twin-screw extruder and a single-screw extruder in series.

[0019] Specifically, the temperature settings for the twin-screw extruder are: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, and Zone 4 145℃~155℃; the temperature settings for the single-screw extruder are: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, and Zone 4 135℃~145℃.

[0020] When a twin-screw extruder is connected in series with a single-screw extruder and a set temperature control, it can not only quickly and evenly mix the materials, but also effectively control the foaming by controlling the melt state, thus achieving high-ratio foaming of PLA materials.

[0021] Preferably, in the above method for improving the foaming performance of PLA materials, the hot air curing in step 3) involves placing the foaming material in flowing hot air at 35°C to 40°C for 2 to 4 hours. Under this preferred curing process, the foamed material can better maintain its strength and toughness.

[0022] Compared with existing technologies, the method for improving the foaming performance of PLA materials according to the present invention has the following beneficial effects: To improve the foaming ratio of PLA materials, the present invention first modifies them with PPCP, PPCEP, or / and PPCCP. The semi-aromatic carbon dioxide-based copolymer used for modification is mainly PPCP, with a small amount of PPCCP added for adjustment. This mixture has good compatibility with PLA, effectively increasing the strength and toughness of the PLA material while preventing excessive brittleness. It also further improves the gas encapsulation during the foaming process, better preventing gas escape and increasing the foaming ratio. PPCP, PPCEP, and PPCCP are all well-compatible with PLA materials, and compatibilizers are not required during blending. As the amount of PPCP, PPCEP, or / and PPCCP added increases, the foaming ratio of the PLA material also increases accordingly. PPCP, PPCEP, or / and PPCCP modification of PLA also significantly increases the strength of the PLA foam material. Furthermore, both are biodegradable materials, and the foamed material retains its biodegradable properties after foaming. Detailed Implementation

[0023] The present invention will be specifically described below through examples. PPCP and PPCCP were prepared in-house by Shandong Lianxin Environmental Protection Technology Co., Ltd. PLA was purchased from Anhui Fengyuan Futailai Polylactic Acid Co., Ltd., model FY601. Toluene diisocyanate modified talc was obtained by soaking commercially available talc in toluene diisocyanate for 10 hours, followed by solid-liquid separation and drying of the solid. Other auxiliary materials were also commercially available and will not be described in detail here. For ease of comparison of component dosages in the examples, the extrusion process was the same; similarly, for ease of performance testing comparison, samples from each example were prepared as foamed boards of the same size (50cm*30cm*10cm). Unless otherwise specified, all raw materials used were commercially available. Toluene diisocyanate modified talc.

[0024] Example 1

[0025] 1) PPCP and PPCCP are prepared at a mass ratio of 10:1.5 and then mixed evenly to obtain a mixture of semi-aromatic carbon dioxide-based copolymers. The mixture of PLA raw material and semi-aromatic carbon dioxide-based copolymers is then prepared at a mass ratio of 100:14 and extruded and blended into granules at 165℃ (outlet temperature) to obtain modified PLA.

[0026] 2) A foaming agent is obtained by mixing benzoyl peroxide, toluene diisocyanate-modified talc, and azodicarbonamide at a mass ratio of 2:1.5:1. Modified PLA and the foaming agent are then mixed evenly at a mass ratio of 100:2.5 and extruded using a twin-screw extruder and a single-screw extruder connected in series to form pre-foamed granules. The twin-screw extruder has an aspect ratio of 36:1 and its temperature settings are: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, and Zone 4 145℃~155℃. The single-screw extruder has an aspect ratio of 30:1 and its temperature settings are: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, and Zone 4 135℃~145℃.

[0027] 3) Transfer the granules to the foaming cylinder and heat them to 135°C to foam. After foaming, place the foamed material in flowing hot air at 38°C for 3 hours to mature and obtain matured material. Transfer the matured material to the molding machine and heat it to 110°C to press it into foamed board.

[0028] Example 2

[0029] 1) PPCP and PPCCP are prepared at a mass ratio of 10:1 and then mixed evenly to obtain a mixture of semi-aromatic carbon dioxide-based copolymers. The mixture of PLA raw material and semi-aromatic carbon dioxide-based copolymers is then prepared at a mass ratio of 100:17 and extruded and blended into granules at 163℃ (outlet temperature) to obtain modified PLA.

[0030] 2) A foaming agent is obtained by mixing benzoyl peroxide, toluene diisocyanate-modified talc, and critical carbon dioxide at a mass ratio of 2.5:1.2:1.2. Modified PLA and the foaming agent are then mixed evenly at a mass ratio of 100:2 and extruded using a twin-screw extruder and a single-screw extruder connected in series to form pre-foamed granules. The twin-screw extruder has an aspect ratio of 36:1, and the temperature settings are: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, and Zone 4 145℃~155℃. The single-screw extruder has an aspect ratio of 30:1, and the temperature settings are: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, and Zone 4 135℃~145℃.

[0031] 3) Transfer the granules to a foaming cylinder and heat them to 135°C to foam. After foaming, place the foamed material in flowing hot air at 36°C for 3.5 hours to mature it and obtain matured material. Transfer the matured material to a molding machine and heat it to 110°C to press it into foamed board.

[0032] Example 3

[0033] 1) PPCP and PPCCP are prepared at a mass ratio of 10:2.5 and then mixed evenly to obtain a mixture of semi-aromatic carbon dioxide-based copolymers. The mixture of PLA raw material and semi-aromatic carbon dioxide-based copolymers is then prepared at a mass ratio of 100:12 and extruded and blended into granules at 167℃ (outlet temperature) to obtain modified PLA.

[0034] 2) A foaming agent is obtained by mixing dicumyl peroxide, toluene diisocyanate-modified talc, and azodicarbonamide at a mass ratio of 1.5:1.7:0.8. Modified PLA and the foaming agent are then mixed evenly at a mass ratio of 100:3 and extruded using a twin-screw extruder and a single-screw extruder connected in series to form pre-foamed granules. The twin-screw extruder has an aspect ratio of 36:1, and the temperature settings are: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, and Zone 4 145℃~155℃. The single-screw extruder has an aspect ratio of 30:1, and the temperature settings are: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, and Zone 4 135℃~145℃.

[0035] 3) Transfer the granules to a foaming cylinder and heat them to 135°C for foaming. Place the foamed material in flowing hot air at 39°C for 2.5 hours to mature it and obtain matured material. Transfer the matured material to a molding machine and heat it to 110°C to press it into foamed board.

[0036] Example 4

[0037] 1) PPCP and PPCCP are prepared at a mass ratio of 10:1.5 and then mixed evenly to obtain a mixture of semi-aromatic carbon dioxide-based copolymers. The mixture of PLA raw material and semi-aromatic carbon dioxide-based copolymers is then prepared at a mass ratio of 100:30 and extruded and blended at 165℃ (outlet temperature) to obtain modified PLA.

[0038] 2) Benzoyl peroxide, titanium dioxide, and critical carbon dioxide were mixed at a mass ratio of 2:1.5:1 to obtain a foaming agent; modified PLA and the foaming agent were then mixed evenly at a mass ratio of 100:2.5 and extruded using a twin-screw extruder and a single-screw extruder connected in series to form pre-foamed granules; the twin-screw extruder had an aspect ratio of 36:1, and the temperature settings were: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, Zone 4 145℃~155℃; the single-screw extruder had an aspect ratio of 30:1, and the temperature settings were: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, Zone 4 135℃~145℃.

[0039] 3) Transfer the granules to the foaming cylinder and heat them to 135°C to foam. After foaming, place the foamed material in flowing hot air at 38°C for 3 hours to mature and obtain matured material. Transfer the matured material to the molding machine and heat it to 110°C to press it into foamed board.

[0040] Example 5

[0041] 1) PPCP and PPCCP are prepared at a mass ratio of 10:1.5 and then mixed evenly to obtain a mixture of semi-aromatic carbon dioxide-based copolymers. The mixture of PLA raw material and semi-aromatic carbon dioxide-based copolymers is then prepared at a mass ratio of 100:5 and extruded and blended into granules at 165℃ (outlet temperature) to obtain modified PLA.

[0042] 2) A foaming agent is obtained by mixing dicumyl peroxide, magnesium oxide, and azodicarbonamide at a mass ratio of 2:1.5:1. Modified PLA and the foaming agent are then mixed evenly at a mass ratio of 100:2.5 and extruded using a twin-screw extruder and a single-screw extruder connected in series to form pre-foamed granules. The twin-screw extruder has an aspect ratio of 36:1 and its temperature settings are: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, and Zone 4 145℃~155℃. The single-screw extruder has an aspect ratio of 30:1 and its temperature settings are: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, and Zone 4 135℃~145℃.

[0043] 3) Transfer the granules to a foaming machine and heat them to 135°C to foam. After foaming, place the foamed material in flowing hot air at 35°C for 4 hours to mature it and obtain matured material. Transfer the matured material to a molding machine and heat it to 110°C to press it into foamed board.

[0044] Example 6

[0045] 1) PPCP and PPCCP are prepared at a mass ratio of 10:0.5 and then mixed evenly to obtain a mixture of semi-aromatic carbon dioxide-based copolymers. The mixture of PLA raw material and semi-aromatic carbon dioxide-based copolymers is then prepared at a mass ratio of 100:0.1 and extruded and granulated at 160℃ (outlet temperature) to obtain modified PLA.

[0046] 2) A foaming agent is obtained by mixing dicumyl peroxide, silica, and azodicarbonamide at a mass ratio of 1:2:0.5. Modified PLA and the foaming agent are then mixed evenly at a mass ratio of 100:4 and extruded using a twin-screw extruder and a single-screw extruder connected in series to form a pre-foamed board. The twin-screw extruder has an aspect ratio of 36:1 and its temperature settings are: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, and Zone 4 145℃~155℃. The single-screw extruder has an aspect ratio of 30:1 and its temperature settings are: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, and Zone 4 135℃~145℃.

[0047] 3) Transfer the board to the foaming machine and heat it to 135°C to foam. After foaming, place the foamed material in flowing hot air at 40°C for 6 hours to mature it and obtain mature material. Transfer the mature material to the molding machine and heat it to 110°C to press it to maintain the shape of the board. After cooling, the foamed board is obtained.

[0048] Example 7

[0049] 1) PPCP and PPCCP are prepared at a mass ratio of 10:3 and then mixed evenly to obtain a mixture of semi-aromatic carbon dioxide-based copolymers. The mixture of PLA raw material and semi-aromatic carbon dioxide-based copolymers is then prepared at a mass ratio of 100:60 and extruded and blended at 170℃ (outlet temperature) to obtain modified PLA.

[0050] 2) Benzoyl peroxide, titanium dioxide, and critical carbon dioxide are mixed at a mass ratio of 3:1:1.5 to obtain a foaming agent; modified PLA and the foaming agent are then mixed evenly at a mass ratio of 100:1 and extruded using a twin-screw extruder and a single-screw extruder connected in series to form pre-foamed granules or sheets; wherein the length-to-diameter ratio of the twin-screw extruder is 36:1, and the temperature settings of the twin-screw extruder are: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, Zone 4 145℃~155℃; the length-to-diameter ratio of the single-screw extruder is 30:1, and the temperature settings of the single-screw extruder are: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, Zone 4 135℃~145℃;

[0051] 3) Transfer the granules or boards to the foamer and heat them to 135°C to foam. After foaming, place the foamed material in flowing hot air at 40°C for 2 hours to mature it and obtain matured material. Transfer the matured material to the molding machine and heat it to 110°C to press it into foamed boards.

[0052] Example 8

[0053] Replace the PPCCP in Example 1 with an equal amount of PPCEP, and keep the other steps and process conditions the same as in Example 1.

[0054] Example 9

[0055] The mixture of semi-aromatic carbon dioxide-based copolymers in Example 1 was replaced with an equal amount of PPCCP, and the other steps and process conditions were the same as in Example 1.

[0056] Performance testing:

[0057] 1. Maximum bending angle of the sample: The maximum bending angle that the sample in each embodiment can achieve when bent. This angle is the interior angle formed by the sample itself.

[0058] 2. Biodegradation rate: Analyzed and tested according to GB / T19277.1 and GB / T19277.2.

[0059] Threshing rate refers to the percentage of grains threshed per 1 dm³. 3 The mass loss rate of a cubic sample after dragging it for 10m on a pine board with a friction coefficient of 0.2 with a 0.5kg weight placed on top.

[0060] Table 1 compares the properties of the foamed materials prepared in Examples 1 to 7 of this invention:

[0061] Table 1 Performance Test Results

[0062] Example Maximum bending angle of the sample (°) Biodegradation rate % Compressive strength kPa threshing rate % Foaming ratio Example 1 112 93.4 168 1.27 62.1 Example 2 114 93.4 164 1.29 62.3 Example 3 113 93.3 165 1.31 61.7 Example 4 123 92.5 171 1.17 62.8 Example 5 109 93.2 153 1.89 48.3 Example 6 102 93.8 134 - 44.7 Example 7 128 91.5 173 1.03 65.3 Example 8 97 93.7 139 1.15 63.4 Example 9 121 92.4 172 1.32 58.1

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for improving the foaming properties of PLA materials, characterized in that, The preparation steps are as follows: 1) Modified PLA is obtained by extruding and granulating a semi-aromatic carbon dioxide-based copolymer after adding it to PLA raw material; the mass ratio of PLA raw material to semi-aromatic carbon dioxide-based copolymer is 100:12~30; the semi-aromatic carbon dioxide-based copolymer is a mixture of PPCP and PPCCP in a mass ratio of 10:0.5~3. 2) Modified PLA and foaming agent are mixed evenly at a mass ratio of 100:1~4 and then extruded using an extruder to form pre-foamed granules or boards; the foaming agent is a premix of crosslinking agent, nucleating agent and foaming agent; 3) Transfer the granules or boards into the foamer and heat them to 135°C to foam. After foaming, the foamed material is cured with hot air to obtain cured material. The cured material is then formed.

2. The method for improving the foaming properties of PLA material according to claim 1, characterized in that: The extrusion blending temperature in step 1) is 160℃~170℃.

3. The method for improving the foaming properties of PLA material according to claim 1, characterized in that: The foaming agent mentioned in step 2) is a premixture of crosslinking agent, nucleating agent and foaming agent in a mass ratio of 1~3:1~2:0.5~1.

5.

4. The method for improving the foaming properties of PLA material according to claim 3, characterized in that: The crosslinking agent is benzoyl peroxide or dicumyl peroxide.

5. The method for improving the foaming properties of PLA material according to claim 3, characterized in that: The nucleating agent is toluene diisocyanate-modified talc.

6. The method for improving the foaming properties of PLA material according to claim 1, characterized in that: The extrusion method described in step 2) refers to the extrusion using a twin-screw extruder and a single-screw extruder connected in series.

7. The method for improving the foaming properties of PLA material according to claim 6, characterized in that: The temperature settings for the twin-screw extruder are: Zone 1 40℃~100℃, Zone 2 130℃~140℃, Zone 3 135℃~145℃, and Zone 4 145℃~155℃; the temperature settings for the single-screw extruder are: Zone 1 145℃~155℃, Zone 2 140℃~150℃, Zone 3 135℃~145℃, and Zone 4 135℃~145℃.

8. The method for improving the foaming properties of PLA material according to claim 1, characterized in that: The hot air curing mentioned in step 3) involves placing the foaming material in flowing hot air at 35℃~40℃ for 2h~4h.