CN116284718A - A kind of high melt strength polylactic acid and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of polymer materials, and in particular relates to a high-melt-strength polylactic acid and a preparation method thereof. The present invention adopts organic cyclic peroxide as tackifier, and polylactic acid and branching aid as raw materials for blending, and uses an improved twin-screw extruder to prepare polylactic acid with high melt strength, wherein the mass ratio of raw materials is: Polylactic acid 96‑98.9%, tackifier 0.1‑2%, branching aid 1‑2%. The high melt strength polylactic acid obtained by the invention has excellent melt strength and good processing fluidity. The invention has simple process, common equipment and easy realization of industrialized production, wherein the source of the used raw material polylactic acid is extensive and renewable.

Description

A kind of high melt strength polylactic acid and preparation method thereof

technical field

The invention belongs to the technical field of polymer materials, in particular to a polylactic acid with high melt strength and a preparation method thereof.

Background technique

Polylactic acid (PLA) is a kind of aliphatic polyester obtained by chemical synthesis from crop fruits or crop stalks, which is extracted and fermented to obtain lactic acid monomers. It has good biocompatibility and can be used in nature. The final products of degradation are water and carbon dioxide, which will not pollute the environment. At the same time, it has high tensile strength (>60MPa), easy to process and shape, and the price is relatively reasonable. The melt strength of pure polylactic acid is very low, and it can be processed by injection molding and tape casting. However, when preparing foamed materials, the gas escape rate is too fast due to the low melt strength, so it is not easy to prepare foamed plastics. This low melt strength characteristic limits the application of polylactic acid in fields such as foam plastics.

In today's related fields of polymer materials, some blending modification technologies have been found to improve the melt strength of polylactic acid. Chinese patent (CN113265129A) discloses a method for modifying polylactic acid by utilizing organic peroxides and regulators, wherein the content of organic peroxides is 0.1-2%, and the content of regulators and lubricants is 0.1- 3% and the content of nucleating agent is 0.1-5%, and the rest is polylactic acid. Through the modification of organic peroxides and regulators, the melt strength of the modified sample has been enhanced to a certain extent, but the operation steps are more cumbersome, the modified components are more numerous and the fluidity of the modified sample has decreased to a certain extent. And disclose a kind of polylactic acid mixture in Chinese patent (CN113929831A), with dibenzoyl peroxide as initiator, with trifunctional group acrylate blend modification improve the melt strength of polylactic acid, the prepared polylactic acid branched Higher degree of entanglement, higher melt strength and better cell properties. Chinese patent (CN109575196B) blends polylactic acid and chain extender glycidyl methacrylate in a twin-screw extruder, and the increase in the maximum torque of the twin-screw extruder reflects the increase in melt strength. Chinese patent (CN113265029A) discloses a long-chain branched polylactic acid with high melt strength and excellent processing fluidity, which is extruded in the polylactic acid molecular chain through the reaction of polylactic acid, organic peroxide and branching regulator The introduction of long-chain branched structure makes it have both excellent melt strength and processing fluidity. These blending methods have all modified polylactic acid, but the compatibility of the material is relatively low, and the melt strength is still not up to the ideal level.

While improving the melt strength of polylactic acid, its processing capacity will also be reduced to a certain extent. How to greatly improve the melt strength while ensuring its fluidity can meet the normal processing requirements is a polylactic acid melt strength modification technology. most critical issues in the field.

Contents of the invention

In order to solve the above problems, the present invention proposes a high melt strength polylactic acid and a preparation method thereof.

Technical scheme of the present invention is as follows:

A high-melt-strength polylactic acid, the ratio of raw materials by weight is: polylactic acid 96-98.9%, organic cyclic peroxide tackifier 0.1-2%, branching aid 1-2%; wherein, The organic cyclic peroxide is one or a combination of cyclic ketone peroxide and 1,2,4-trioxetane peroxide.

Preferably, the structural formula of cyclic ketone peroxide is shown in formula (1) or (2):

Wherein R ₁ -R ₄ are any one of methyl, ethyl or isopropyl.

Preferably, the structural formula of 1,2,4-trioxetane peroxide is shown in formula (3):

Wherein R ¹ -R ³ are any one of methyl, ethyl or isopropyl.

Preferably, the organic cyclic peroxide tackifier is 3,3,6,6-tetramethyl-1,2-dioxane, 3,3,6,6-tetramethyl-1,2 , 4,5-tetraoxocyclohexane, 7,7-dimethyl-2,3,5,6-tetraoxabicyclo[2.2.1]heptane (CA-1) or 3,3,5, The combination of one or more of 7,7-pentamethyl-1,2,4-trioxepane (CA-2); the structural formula of said CA-1, CA-2 is as formula (4 )-(5) as shown:

Preferably, the branching aid is butyl acrylate, 1,5-pentanediol diacrylate, pentaerythritol triacrylate, pentaerythritol acrylate, trimethylolpropane triacrylate, three (2,3-epoxypropylene base) isocyanurate, tris(4-hydroxyphenyl)methane triglycidyl ether, trimethylolpropane triglycidyl ether, 1,4-butanediol diglycidyl ether, phthalic anhydride, A combination of one or more of terephthalic anhydride, 4-hydroxybutyl acrylate glycidyl ether or glycidyl methacrylate.

The preparation method of high melt strength polylactic acid comprises the following steps:

(1) By weight, the ratio of raw materials is: 96-98.9% of polylactic acid, 0.1-2% of organic cyclic peroxide tackifier, and 1-2% of branching aid;

(2) Dry the polylactic acid in a vacuum oven at 70°C for 2 hours, then cool to room temperature;

(3) The dry polylactic acid is fed into the extruder from the feeding port of the improved twin-screw extruder, and a tackifier and a branching aid are added at the liquid feeding port, and extruded to obtain polylactic acid with high melt strength ;The extruder screw temperature is set at 140°C-190°C, of which the first section of the forward conveying element is 140-180°C, the mixing element and the reverse conveying element are both 180°C, and the last section of the forward conveying element is Gradually raise the temperature from 180°C to 190°C at the die; the length-to-diameter ratio of the screw of the extruder is above 64:1, and the screw speed is 50-400rpm.

Preferably, the improved twin-screw extruder is provided with a group of mixing elements at a place where the length-to-diameter ratio of the screw to the feeding port is 30-40 times, and the staggered angle of the mixing elements is 60°; Set a set of reverse conveying elements at -50 times, and the helix angle of the elements is 30°.

It can be understood that such an improvement to the twin-screw extruder has the following advantages:

(1) Set a set of mixing elements with a staggered angle of 60° at a place where the length-to-diameter ratio of the screw distance from the feeding port is 30-40 times. The advantage is that the tackifier and branching aid can be evenly distributed in the polylactic acid before the polymerization reaction. In the matrix, avoid the waste of additives and low branching efficiency due to uneven distribution and insufficient participation in the reaction.

(2) Set a set of reverse conveying elements with a helix angle of 30° at a place where the length-to-diameter ratio of the screw to the feeding port is 40-50 times. The advantage of the reverse conveying element is to prolong the residence time of polylactic acid, tackifier and branching aid in the screw. Sufficient residence time can ensure that the polymerization branching reaction can be carried out to the end, so that polylactic acid, tackifier and branching agent The chemical additives can react completely under high temperature conditions, which greatly improves the modification efficiency.

The beneficial effects of the present invention are as follows:

1. The present invention uses organic cyclic peroxides as tackifiers. Due to the unique structural properties of organic cyclic peroxides, the modified polylactic acid molecular segments will produce more branched chains and reduce crosslinking. To a certain extent, more branched chain structures will significantly enhance the melt strength of polylactic acid and maintain good processing fluidity. At the same time, the organic cyclic peroxide can effectively regulate the free radical activity under the synergistic effect of the branching auxiliaries after adding the branching auxiliaries, thereby improving the utilization efficiency of the organic cyclic peroxides. In addition, it can also make the polylactic acid terminal The group participates in the reaction, further reduces the degree of crosslinking, increases the degree of branching and branching efficiency, thereby optimizing the topology of the polylactic acid molecular chain.

2. The combination of polylactic acid/organic cyclic peroxide tackifier/branching aid selected in the present invention can still have flow properties that meet processing requirements while greatly improving melt strength.

3. The present invention improves the structure of the twin-screw extruder to prolong the residence time of polylactic acid in the screw, so that the polylactic acid matrix is evenly mixed with the organic cyclic peroxide tackifier and branching auxiliary agent, and the reaction is more complete. At the same time, the problems of waste of additives and low reaction efficiency caused by the failure of some reactants to fully participate in the reaction are avoided.

Description of drawings:

Fig. 1 is the chemical reaction schematic diagram of organic cyclic peroxide tackifier and branching aid and polylactic acid;

Fig. 2 is the structural representation of the improved twin-screw extruder in the embodiment; Wherein the reference numerals are: 1. Feed port, 2. Screw, 2-1. Forward conveying element, 2-2. Mixing element, 2- 3. Reverse conveying element, 3. Liquid feed port;

Fig. 3 is a schematic diagram of forward conveying elements of the screw in Fig. 2;

Fig. 4 is a schematic diagram of the mixing element of the screw in Fig. 2;

Fig. 5 is a schematic diagram of the reverse conveying element of the screw in Fig. 2 .

Detailed ways

The twin-screw extruder used in the following examples, see Fig. 2 to Fig. 5, is provided with screw rod, and feed port 1 and liquid feed port 3 that are arranged at intervals along the axial direction, screw rod comprises two sections of forward conveying elements 2- 1 and a mixing element 2-2 and a reverse conveying element 2-3 arranged between two sections of forward conveying element 2-1, wherein one section of forward conveying element 2-1 is located at the outlet of the screw extruder, and the other A section of forward conveying element 2-1 extends from the feeding port 1 to the liquid feeding port 3. The mixing element 2-2 is located at a place where the length-to-diameter ratio of the screw is 30-40 times from the feeding port, and the staggered angle of the mixing elements is 60°. The reverse conveying element 2-3 is located at a place where the aspect ratio of the screw rod is 40-50 times from the feeding port, and the helix angle of the reverse conveying element is 30°. The feed material from the feed port 1 and the liquid feed port 3 is transported to the mixing element 2-2 through another forward conveying element 2-1, and enters the reverse conveying element 2-3 after being mixed.

Example 1

(1) By weight, the ratio of raw materials is: polylactic acid: 1.96kg, tackifier (CA-1 accounts for 100%): 0.02kg, branching aid (4-hydroxybutyl acrylate glycidyl ether): 0.02kg.

(2) The polylactic acid was dried in a vacuum drying oven at a temperature of 70° C. for 2 hours and then cooled to room temperature.

(3) Add the dried polylactic acid into the improved twin-screw extruder through the feeding port, then add the tackifier liquid and the branching auxiliary agent into the extruder at the liquid feeding port for reaction and mixing, and extrude , Pelletizing to obtain polylactic acid with high melt strength. The screw temperature of the improved screw extruder is set at 140-190°C, of which the first section of the forward conveying element is 140-180°C, the mixing element and the reverse conveying element are both 180°C, and the last section of the forward conveying element From 180°C to 190°C gradually from part to die. The screw speed was set at 280rpm, and the aspect ratio was set at 68:1.

Example 2

Change the ratio of raw materials in Example 1, polylactic acid: 1.96kg, tackifier (CA-2 accounts for 100%): 0.02kg, branching aid (4-hydroxybutyl acrylate glycidyl ether): 0.02kg . Other steps are identical with embodiment 1.

Example 3

Change the ratio of raw materials in Example 1, polylactic acid: 1.978kg, tackifier (CA-1 and CA-2 each account for 50%): 0.002kg, branching aid (4-hydroxybutyl acrylate glycidyl ether ): 0.02kg. Other steps are identical with embodiment 1.

Example 4

Change the ratio of raw materials in Example 1, polylactic acid: 1.96kg, tackifier (CA-1 and CA-2 each account for 50%): 0.02kg, branching aid (4-hydroxybutyl acrylate glycidyl ether ): 0.02kg. Other steps are identical with embodiment 1.

Example 5

Change the ratio of raw materials in Example 1, polylactic acid: 1.95kg, tackifier (CA-1 and CA-2 each account for 50%): 0.02kg, branching aid (4-hydroxybutyl acrylate glycidyl ether ): 0.03kg. Other steps are identical with embodiment 1.

Example 6

Change the ratio of raw materials in Example 1, polylactic acid: 1.93kg, tackifier (CA-1 and CA-2 each account for 50%): 0.04kg, branching aid (4-hydroxybutyl acrylate glycidyl ether ): 0.03kg. Other steps are identical with embodiment 1.

Example 7

Change the ratio of raw materials in Example 1, polylactic acid: 1.92kg, tackifier (CA-1 and CA-2 each account for 50%): 0.04kg, branching aid (4-hydroxybutyl acrylate glycidyl ether ): 0.04kg. Other steps are identical with embodiment 1.

Example 8

Change the ratio of raw materials in Example 1, polylactic acid: 1.9kg, tackifier (CA-1 and CA-2 each account for 50%): 0.04kg, branching aid (4-hydroxybutyl acrylate glycidyl ether ): 0.06kg. Other steps are identical with embodiment 1.

Example 9

Change the ratio of raw materials in Example 1, polylactic acid: 1.88kg, tackifier (CA-1 and CA-2 each account for 50%): 0.06kg, branching aid (4-hydroxybutyl acrylate glycidyl ether ): 0.06kg. Other steps are identical with embodiment 1.

Comparative example 1

Change the ratio of raw materials in Example 1, polylactic acid: 2kg. Other steps are identical with embodiment 1.

Comparative example 2

The ratio of raw materials in Example 1 was changed, polylactic acid: 1.96kg, thickener (CA-1 and CA-2 each accounting for 50%): 0.04kg, and other steps were the same as in Example 1.

Comparative example 3

Change the ratio of raw materials in Example 1, polylactic acid: 1.96kg, branching aid (4-hydroxybutyl acrylate glycidyl ether): 0.04kg. Other steps are identical with embodiment 1.

Comparative example 4

Add the dried polylactic acid, tackifier and branching aid together into a conventional screw extruder, extrude and pelletize to obtain polylactic acid with high melt strength. The temperature of the screw extruder was set at 180° C., the screw speed was set at 280 rpm, and the aspect ratio was set at 68:1. Other steps were the same as in Example 1.

Comparative example 5

Change the raw material composition and proportioning in Example 1, polylactic acid: 1.92kg, tackifier (3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triple pass Oxynonane): 0.04 kg, branching aid (4-hydroxybutyl acrylate glycidyl ether): 0.04 kg. Other steps are identical with embodiment 1.

Table 1 shows the maximum torque and zero shear viscosity obtained in Examples 1-9 and Comparative Examples 1-5 and the test results of melt flow rate index (MFR) at 210°C and 2.16kg.

Table 1: Maximum Torque, Zero Shear Viscosity and MFR of Examples and Comparative Examples

In the present invention, as the addition amount of organic cyclic peroxide tackifier and branching aid gradually increases, the maximum torque and zero-shear viscosity of high-melt strength polylactic acid continue to increase, and the MFR value decreases slightly . However, it can be seen from Examples 8 and 9 that if the organic cyclic peroxide tackifier and branching aid are added too much, the MFR value of high melt strength polylactic acid will be greatly reduced, which will seriously affect its processing fluidity .

As can be seen from Table 1, the maximum torque and zero shear viscosity of the high melt strength polylactic acid prepared in Examples 1-7 are much higher than the pure polylactic acid of Comparative Example 1, indicating that the high melt strength polylactic acid prepared in Examples 1-7 Melt Strength PLA has a higher melt strength.

In comparative example 2, due to the lack of branching aids, the improvement effect of the maximum torque and zero-shear viscosity is not obvious.

Comparative example 3 lacks the addition of organic cyclic peroxide tackifier, and its test result is similar to comparative example 1, as can be seen, in the absence of organic cyclic peroxide tackifier, the branching aid is almost Not involved in the reaction.

Comparative Example 4 uses a common twin-screw extruder, because the modifier and the polylactic acid in the extruder react insufficiently, so that its measurement result is lower than that of Example 7 under the same raw material ratio, which also shows the improved The advanced screw is conducive to the full reaction of raw materials.

Comparative Example 5 uses a cyclic peroxide disclosed in the prior art as a tackifier. Compared with Example 7, under the same mass ratio, the degree of improvement in its melt strength is not as high as that of the organic ring selected in the present invention. The effect of peroxide is good.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Equivalent replacements or changes to the concepts thereof shall fall within the protection scope of the present invention.

Claims (7)

1. The high melt strength polylactic acid is characterized by comprising the following raw materials in parts by weight: 96-98.9% of polylactic acid, 0.1-2% of organic cyclic peroxide tackifier and 1-2% of branching auxiliary agent; wherein the organic cyclic peroxide is one or two of cyclic ketone peroxide and 1,2, 4-trioxane peroxide.

2. The high melt strength polylactic acid according to claim 1, wherein the cyclic ketone peroxide has a structural formula represented by formula (1) or (2):

wherein R is ₁ -R ₄ Is any one of methyl, ethyl or isopropyl.

3. The high melt strength polylactic acid according to claim 1, wherein the structural formula of the 1,2, 4-trioxane peroxide is represented by formula (3):

wherein R is ¹ -R ³ Is any one of methyl, ethyl or isopropyl.

4. The high melt strength polylactic acid according to claim 1, wherein, the organic cyclic peroxide tackifier is 3, 6-tetramethyl-1, 2-dioxane, 3, 6-tetramethyl-1, 2,4, 5-tetraoxy cyclohexane a combination of one or more of 7, 7-dimethyl-2, 3,5, 6-tetraoxabicyclo [2.2.1] heptane or 3,5, 7-pentamethyl-1, 2, 4-trioxepane; wherein, the structural formulas of the 7, 7-dimethyl-2, 3,5, 6-tetraoxabicyclo [2.2.1] heptane and the 3,5, 7-pentamethyl-1, 2, 4-trioxepan are shown in formulas (4) - (5):

5. the high melt strength polylactic acid of claim 1, wherein the branching aid is one or more of butyl acrylate, 1, 5-pentanediol diacrylate, pentaerythritol triacrylate, pentaerythritol acrylate, trimethylolpropane triacrylate, tris (2, 3-epoxypropyl) isocyanurate, tris (4-hydroxyphenyl) methane triglycidyl ether, trimethylolpropane triglycidyl ether, 1, 4-butanediol diglycidyl ether, phthalic anhydride, terephthalic anhydride, 4-hydroxybutyl glycidyl acrylate, or glycidyl methacrylate.

6. The method for producing a high melt strength polylactic acid according to any one of claims 1 to 5, comprising the steps of:

(1) The raw materials are as follows by weight: 96-98.9% of polylactic acid, 0.1-2% of organic cyclic peroxide tackifier and 1-2% of branching auxiliary agent;

(2) Placing polylactic acid in a vacuum drying oven to be dried for 2 hours at 70 ℃, and then cooling to room temperature;

(3) Feeding the dried polylactic acid into an extruder from a feed inlet of an improved double-screw extruder, adding an organic annular peroxide tackifier and a branching auxiliary agent at a liquid feed inlet, and performing extrusion molding to obtain high-melt-strength polylactic acid; the temperature of a screw rod of the extruder is set to 140-190 ℃, wherein the temperature of a first section of forward conveying element part is 140-180 ℃, the temperature of a mixing element and a reverse conveying element part are 180 ℃, and the temperature of the last section of forward conveying element part to a die is gradually increased from 180 ℃ to 190 ℃; the length-diameter ratio of the screw rod of the extruder is more than 64:1, and the rotating speed of the screw rod is 50-400rpm.

7. The method for producing high melt strength polylactic acid according to claim 6, wherein the twin-screw extruder modified in step (3) is provided with 1 set of mixing elements at a position where the length-diameter ratio of the screw to the feed port is 30 to 40 times, and the staggering angle of the mixing elements is 60 °; and 1 group of reverse conveying elements are arranged at the position of the screw rod, which is 40-50 times of the length-diameter ratio of the screw rod to the charging hole, and the helix angle of the elements is 30 degrees.

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