1. A method for preparing polylactic resin with high melt strength by two-step reaction is characterized by comprising the following steps:

(1) uniformly stirring 100 parts by weight of polylactic acid and 0.5-3 parts by weight of glycidyl methacrylate in a high-speed mixer to obtain a premixed material;

uniformly mixing 0.2-4 parts by weight of polyfunctional group reactive monomer, 0.1-0.5 part by weight of peroxide initiator and 10-30 parts by weight of organic solvent to obtain a monomer mixed solution;

(2) adding the premixed material and the monomer mixed solution into a screw extruder in sections, and carrying out melting, blending, extruding, water cooling, grain cutting and drying to obtain the high-melt-strength polylactic resin;

the premixed material is added from a hopper of the extruder, and the monomer mixed solution is added from an air outlet at a sixth temperature zone of the extruder.

2. The method for preparing a high melt strength polylactic acid resin according to claim 1, wherein the polyfunctional reactive monomer of step (1) is at least one of 1, 6-hexanediol diacrylate, 1, 4-butanediol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate;

the peroxide initiator in the step (1) is at least one of dibenzoyl peroxide, ditert-amyl peroxide, dicumyl peroxide, bis (tert-butylperoxyisopropyl) benzene, 2, 5-di-tert-butylperoxy-2, 5-dimethylhexane, tert-butylperoxycumene, di-tert-butyl peroxide, dicumyl hydroperoxide, cumene hydroperoxide and tert-amyl hydroperoxide.

3. The method for preparing high melt strength polylactic acid resin according to claim 2, wherein the polyfunctional reactive monomer in step (1) is trimethylolpropane triacrylate; the peroxide initiator is dicumyl peroxide.

4. The method for preparing a high melt strength polylactic acid resin according to the claim 1, wherein the screw extruder of the step (2) comprises 8 temperature zones: the temperature of the first zone is 140-160 ℃, the temperature of the second zone is 160-180 ℃, and the temperature of the third zone to the eighth zone is 180-200 ℃.

5. The method for preparing a high melt strength polylactic acid resin according to claim 1, wherein the polylactic acid is 100 parts by weight, the glycidyl methacrylate is 1.5 parts by weight, the polyfunctional reactive monomer is 0.5-3 parts by weight, the peroxide initiator is 0.1 part by weight, and the organic solvent is 10 parts by weight.

6. The method for preparing a high melt strength polylactic acid resin according to the claim 1, wherein the monomer mixture of the step (2) is added into the extruder through a micro-injector from the vent at the sixth temperature zone of the extruder.

7. The method for preparing the polylactic resin with high melt strength by the two-step reaction according to claim 1, wherein the stirring speed of the high-speed mixer in the step (1) is 80-120 rpm, and the stirring time is 8-15 min;

and (3) the rotating speed of a feeding screw of the screw extruder in the step (2) is 5-10 rpm, and the rotating speed of a main machine screw is 150-180 rpm.

8. The method for preparing a high melt strength polylactic acid resin according to the two-step reaction of claim 7, wherein the screw extruder of step (2) has a feeding screw rotating speed of 5rpm and a main machine screw rotating speed of 150 rpm.

9. The method for preparing a high melt strength polylactic acid resin according to the claim 1, wherein the screw extruder of the step (2) is a double or single screw extruder.

10. The method for preparing the polylactic acid resin with high melt strength by the two-step reaction according to claim 1, wherein the polylactic acid in the step (1) is further dried by air blowing at 80-100 ℃ for 4-8 hours before being mixed;

the organic solvent in the step (1) is at least one of acetone, tetrahydrofuran, dichloromethane and trichloromethane.

Background

Polylactic acid (PLA) is a green polymer material that is most promising to replace petroleum-based polymers because of its wide and renewable raw material sources, no pollution during the whole production process, and full biodegradation of the end products. In addition, as the country comes out of the plastic restriction order and the plastic prohibition order successively, the high performance of PLA is important as the most mature, the most productive and the most widely used biodegradable material in the current industrialization. At present, PLA can be made into different types of plastic products by processing methods such as extrusion, injection molding and the like, and is widely applied to the fields of biomedicine, industry and agriculture, food packaging and the like. However, because PLA is a linear molecular chain, PLA has the defects of low melt strength, insufficient strain hardening, and the like, which severely limits its large-scale popularization and application in some fields, such as film blowing, foaming, and the like.

In response to this deficiency of PLA, some researchers have proposed the introduction of long chain branching structures on linear chains of PLA to improve its melt strength. At present, the main methods for modifying PLA long-chain branching include directional polymerization, high-energy irradiation, melt reaction extrusion and the like. Chinese patent application CN 104448154a discloses a preparation method of radiation grafted long-chain branched polylactic acid. The method comprises the steps of adopting a double-screw extruder to carry out blending treatment on 1, 6-hexanediol diacrylate (HDDA) and PLA in advance, and then utilizing a Co 60 source to carry out irradiation treatment on the PLA/HDDA blend with different doses under the condition of limited oxygen to obtain the irradiated long-chain branched PLA. However, the high-energy rays used in the method have limited penetrating ability, so that the chain extension reaction can only be initiated on the surface of the PLA solid particles, the reaction efficiency is low, and a long irradiation time is needed. In addition, in both of the chinese patent applications CN 103923268A and CN108570145A, dicumyl peroxide (DCP) and polyfunctional reactive monomer pentaerythritol triacrylate are used as an initiator and a crosslinking agent, respectively, and then the long-chain branched PLA is prepared by a melt radical grafting reaction. However, because radical generated by DCP can cause severe degradation of PLA molecules, antioxidant or crosslinking promoter added in the two methods is needed, but other substances can be introduced into the PLA molecules, which is not favorable for ensuring the purity of the final product. Therefore, it is an important task in the art to provide a new preparation method with rapid mass production, simple process flow, controllable reaction and high purity of the product to prepare the polylactic resin with high melt strength.

Disclosure of Invention

In order to solve the defects and shortcomings of the prior art, the invention aims to provide a method for preparing polylactic resin with high melt strength by a two-step reaction.

The method of the invention is suitable for large-scale continuous production, has simple process flow, fast and controllable grafting reaction, and the obtained grafted product is safe, has no residue and has high purity.

The purpose of the invention is realized by the following technical scheme:

a method for preparing high-melt-strength polylactic resin by a two-step reaction comprises the following steps:

(1) uniformly stirring 100 parts by weight of polylactic acid (PLA) and 0.5-3 parts by weight of Glycidyl Methacrylate (GMA) in a high-speed mixer to obtain a premixed material;

uniformly mixing 0.2-4 parts by weight of polyfunctional group reactive monomer, 0.1-0.5 part by weight of peroxide initiator and 10-30 parts by weight of organic solvent to obtain a monomer mixed solution;

(2) adding the premixed material and the monomer mixed solution into a screw extruder in sections, and carrying out melting, blending, extruding, water cooling, grain cutting and drying to obtain the high-melt-strength polylactic resin;

the premixed material is added from a hopper of the extruder, and the monomer mixed solution is added from an air outlet at a sixth temperature zone of the extruder.

Preferably, the polylactic acid in the step (1) is dried by air blowing at 80-100 ℃ for 4-8 hours before mixing.

Preferably, the stirring speed of the high-speed mixer in the step (1) is 80-120 rpm, and the stirring time is 8-15 min.

Preferably, the polyfunctional reactive monomer of step (1) is at least one of 1, 6-hexanediol diacrylate (HDDA), 1, 4-butanediol diacrylate (BDDA), tripropylene glycol diacrylate (TPGDA), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), pentaerythritol tetraacrylate (PET4A), and dipentaerythritol hexaacrylate (DPHA), more preferably trimethylolpropane triacrylate (TMPTA).

Preferably, the peroxide initiator of step (1) is at least one of dibenzoyl peroxide (BPO), ditert-amyl peroxide (DTAP), dicumyl peroxide (DCP), bis (tert-butylperoxyisopropyl) benzene (DPIB), 2, 5-di-tert-butylperoxy-2, 5-dimethylhexane (BPDH), tert-butylperoxycumene (TBCP), di-tert-butyl peroxide (DTBP), dicumyl peroxide (DBHP), Cumene Hydroperoxide (CHP) and tert-amyl hydroperoxide (TAHP), more preferably dicumyl peroxide (DCP).

Preferably, the organic solvent in step (1) is at least one of acetone, tetrahydrofuran, dichloromethane and chloroform, and more preferably acetone.

Preferably, the screw extruder of step (2) comprises 8 temperature zones: the temperature of the first zone is 140-160 ℃, the temperature of the second zone is 160-180 ℃, and the temperature of the third zone to the eighth zone is 180-200 ℃.

Preferably, the rotation speed of the feeding screw of the screw extruder in the step (2) is 5-10 rpm, the rotation speed of the main machine screw is 150-180 rpm, more preferably the rotation speed of the feeding screw is 5rpm, and the rotation speed of the main machine screw is 150 rpm.

Preferably, the monomer mixed solution in the step (2) is added into the extruder from an air outlet at the sixth temperature zone of the extruder through a micro-injector.

Preferably, the screw extruder in step (2) is a double or single screw extruder.

Preferably, the polylactic acid comprises 100 parts by weight of polylactic acid, 1.5 parts by weight of glycidyl methacrylate, 0.5-3 parts by weight of polyfunctional group reactive monomer, 0.1 part by weight of peroxide initiator and 10 parts by weight of organic solvent.

More preferably, the polyfunctional reactive monomer is 2 to 3 parts by weight.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. according to the invention, the rapid end capping is carried out on the PLA molecular chain by adopting GMA, unsaturated double bonds with high reaction activity can be introduced at the tail end of the PLA molecular chain, and in the free radical chain reaction initiated by peroxide at the tail end of an extruder, the unsaturated double bonds with high reaction activity are easy to carry out graft reaction with a polyfunctional group reactive monomer to generate the PLA with high melt strength.

2. In the free radical chain reaction at the tail end of the extruder, free radicals can preferentially attack unsaturated double bonds with high reaction activity on a PLA molecular chain blocked by GMA, so that the violent breakage of the PLA molecular main chain can be avoided, and simultaneously, no antioxidant or crosslinking promoter needs to be additionally added, and the obtained final product has high purity.

3. The preparation method has simple process flow, is suitable for industrial mass production, has quick and controllable grafting reaction, and the obtained product has high purity, thereby being more beneficial to widening the application field of the PLA material.

Drawings

FIG. 1 is a graph of melt index MFI of PLA prepared in examples 1 to 6 of the present invention and comparative examples 1 to 6.

FIG. 2 is a graph of complex viscosity η × S (Pa · s) versus frequency ω (rad/s) for PLA made in examples 1-6 of the present invention.

FIG. 3 is a graph of complex viscosity η × S (Pa · s) versus frequency ω (rad/s) for PLA made according to comparative examples 1-6 of the present invention.

FIG. 4 is a graph of storage modulus G' (Pa) versus frequency ω (rad/s) for PLA made in examples 1-6 of the present invention.

FIG. 5 is a graph of storage modulus G' (Pa) versus frequency ω (rad/s) for PLA made according to comparative examples 1-6 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

Those who do not specify specific conditions in the examples of the present invention follow conventional conditions or conditions recommended by the manufacturer. The raw materials, reagents and the like which are not indicated for manufacturers are all conventional products which can be obtained by commercial purchase.

Example 1

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) adding 100 parts of dried PLA and 1.5 parts of Glycidyl Methacrylate (GMA) into a high-speed mixer with the rotating speed of 100rpm and stirring for 10min to form a premixed material;

(3) 0.5 part of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into 10 parts of acetone to form a diluted TMPTA/DCP solution;

(4) adding a PLA/GMA premixed material into a double-screw extruder from a hopper of the extruder, adding a TMPTA/DCP dilute solution into the double-screw extruder from an air outlet at a sixth temperature zone of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain a product; wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Example 2

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) adding 100 parts of dried PLA and 1.5 parts of Glycidyl Methacrylate (GMA) into a high-speed mixer with the rotating speed of 100rpm and stirring for 10min to form a premixed material;

(3) 1.0 part of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into 10 parts of acetone to form a diluted TMPTA/DCP solution;

(4) adding a PLA/GMA premixed material into a double-screw extruder from a hopper of the extruder, adding a TMPTA/DCP dilute solution into the double-screw extruder from an air outlet at a sixth temperature zone of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain a product; wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Example 3

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) adding 100 parts of dried PLA and 1.5 parts of Glycidyl Methacrylate (GMA) into a high-speed mixer with the rotating speed of 100rpm and stirring for 10min to form a premixed material;

(3) 1.5 parts of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into 10 parts of acetone to form a diluted TMPTA/DCP solution;

(4) adding a PLA/GMA premixed material into a double-screw extruder from a hopper of the extruder, adding a TMPTA/DCP dilute solution into the double-screw extruder from an air outlet at a sixth temperature zone of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain a product; wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Example 4

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) adding 100 parts of dried PLA and 1.5 parts of Glycidyl Methacrylate (GMA) into a high-speed mixer with the rotating speed of 100rpm and stirring for 10min to form a premixed material;

(3) diluting 2.0 parts of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) into 10 parts of acetone to form a diluted TMPTA/DCP solution;

(4) adding a PLA/GMA premixed material into a double-screw extruder from a hopper of the extruder, adding a TMPTA/DCP dilute solution into the double-screw extruder from an air outlet at a sixth temperature zone of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain a product; wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Example 5

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) adding 100 parts of dried PLA and 1.5 parts of Glycidyl Methacrylate (GMA) into a high-speed mixer with the rotating speed of 100rpm and stirring for 10min to form a premixed material;

(3) diluting 2.5 parts of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) into 10 parts of acetone to form a diluted TMPTA/DCP solution;

(4) adding a PLA/GMA premixed material into a double-screw extruder from a hopper of the extruder, adding a TMPTA/DCP dilute solution into the double-screw extruder from an air outlet at a sixth temperature zone of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain a product; wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Example 6

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) adding 100 parts of dried PLA and 1.5 parts of Glycidyl Methacrylate (GMA) into a high-speed mixer with the rotating speed of 100rpm and stirring for 10min to form a premixed material;

(3) diluting 3.0 parts of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) into 10 parts of acetone to form a diluted TMPTA/DCP solution;

(4) adding a PLA/GMA premixed material into a double-screw extruder from a hopper of the extruder, adding a TMPTA/DCP dilute solution into the double-screw extruder from an air outlet at a sixth temperature zone of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain a product; wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Comparative example 1

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) 100 parts of dried PLA particles, 1.5 parts of Glycidyl Methacrylate (GMA), 0.5 part of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into a dilute solution formed in 10 parts of acetone, and the dilute solution are added into a high-speed mixer with the rotating speed of 100rpm and stirred for 10min, and then solvent volatilization is carried out to form a premixed material;

(3) adding the PLA/GMA/TMPTA/DCP premixed material into a double-screw extruder from a hopper of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain a product; wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Comparative example 2

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) 100 parts of dried PLA particles, 1.5 parts of Glycidyl Methacrylate (GMA), 1.0 part of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into a dilute solution formed in 10 parts of acetone, and the dilute solution are added into a high-speed mixer with the rotating speed of 100rpm and stirred for 10min, and then solvent volatilization is carried out to form a premixed material;

(3) adding the PLA/GMA/TMPTA/DCP premixed material into a double-screw extruder from a hopper of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain the product. Wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Comparative example 3

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) 100 parts of dried PLA particles, 1.5 parts of Glycidyl Methacrylate (GMA), 1.5 parts of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into a dilute solution formed in 10 parts of acetone, and the dilute solution are added into a high-speed mixer with the rotating speed of 100rpm and stirred for 10min, and then solvent volatilization is carried out to form a premixed material;

(3) adding the PLA/GMA/TMPTA/DCP premixed material into a double-screw extruder from a hopper of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain the product. Wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Comparative example 4

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) 100 parts of dried PLA particles, 1.5 parts of Glycidyl Methacrylate (GMA), 2.0 parts of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into a dilute solution formed in 10 parts of acetone, and the dilute solution are added into a high-speed mixer with the rotating speed of 100rpm and stirred for 10min, and then solvent volatilization is carried out to form a premixed material;

(3) adding the PLA/GMA/TMPTA/DCP premixed material into a double-screw extruder from a hopper of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain the product. Wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Comparative example 5

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) 100 parts of dried PLA particles, 1.5 parts of Glycidyl Methacrylate (GMA), 2.5 parts of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into a dilute solution formed in 10 parts of acetone, and the dilute solution are added into a high-speed mixer with the rotating speed of 100rpm and stirred for 10min, and then solvent volatilization is carried out to form a premixed material;

(3) adding the PLA/GMA/TMPTA/DCP premixed material into a double-screw extruder from a hopper of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain the product. Wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

Comparative example 6

The weight portion is as follows:

(1) air-drying the PLA granules at 80 ℃ for 8 h;

(2) 100 parts of dried PLA particles, 1.5 parts of Glycidyl Methacrylate (GMA), 1.0 part of trimethylolpropane triacrylate (TMPTA) and 0.1 part of dicumyl peroxide (DCP) are diluted into a dilute solution formed in 10 parts of acetone, and the dilute solution are added into a high-speed mixer with the rotating speed of 100rpm and stirred for 10min, and then solvent volatilization is carried out to form a premixed material;

(3) adding the PLA/GMA/TMPTA/DCP premixed material into a double-screw extruder from a hopper of the extruder, and carrying out melting, blending, extruding, water cooling, granulating and drying to obtain the product. Wherein the temperature and the screw rotating speed of each area of the double-screw extruder are respectively as follows: the temperature of the first area is 160 ℃, the temperature of the second area is 180 ℃, and the temperature of the third area to the eighth area is 200 ℃; the feed screw speed was 5rpm and the screw main body speed was 150 rpm.

FIG. 1 is a plot of melt index (MFI) for PLA made in examples 1-6 versus PLA made in comparative examples 1-6. The MFI value of PLA was measured according to GB/T-3682 standard. It is generally considered that there is a mutual dependency between the MFI value of a polymer and the melt strength of the polymer, and the smaller the MFI value, the greater the melt strength of the polymer. As can be seen from FIG. 1, the MFI values of PLA prepared by the present invention in the examples are smaller than those of PLA prepared in the corresponding proportions, which indicates that the preparation method adopted by the present invention is more advantageous for improving the melt strength of PLA.

FIGS. 2-3 are graphs of complex viscosity η x (Pa · s) versus frequency ω (rad/s) for PLA made in examples 1-6 and PLA made in comparative examples 1-6. The test condition is 200 ℃, the strain is 1%, the test frequency range is 0.01-100Hz, and the atmosphere is nitrogen. When a branch chain is introduced into the PLA molecular chain, intermolecular entanglement increases, so that the eta value also increases, and the initial frequency of the shear thinning phenomenon shifts to a low frequency region. As can be seen from fig. 2, in the low frequency region, the values of η of the PLAs produced by the present invention in examples 1-6 were all greater than those of the PLAs produced in the corresponding proportions; and when the amount of TMPTA used reaches a certain level, the platform of the η x- ω curve of the example disappears in the low frequency region, and the curve begins to warp upward, which indicates that there are more long branched chain structures in the PLA prepared by the present invention, so that the molecular entanglement of PLA increases, and the η x value increases.

FIGS. 4-5 are graphs of storage modulus G' (Pa) versus frequency ω (rad/s) for PLA made in examples 1-6 and PLA made in comparative examples 1-6. The test condition is 200 ℃, the strain is 1%, the test frequency range is 0.01-100Hz, and the atmosphere is nitrogen. The higher the E' value, the better the polymer melt elasticity. The melt elasticity of the polymer and the melt strength of the polymer have a dependency relationship, and at a certain temperature, the better the melt elasticity of the polymer is, the higher the melt strength is. As can be seen from FIGS. 4 to 5, the PLA prepared by the present invention of examples 1 to 6 has a larger G 'value than that of the PLA prepared in the corresponding ratio in the low frequency region, and as the amount of TMPTA used is increased, the G' value is also increased and a small plateau region is formed in the low frequency region, which shows that the melt elasticity and melt strength of the PLA prepared by the present invention are significantly improved.

As can be shown in fig. 1 to 5 and the related description, the high melt strength polylactic acid resin can be prepared by using the method of the present invention, and the method greatly expands the application field of the PLA material.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.