A heat-resistant and high-strength polylactic acid composite material and its preparation method

Abstract

The present invention discloses a heat-resistant, high-strength polylactic acid composite material and a preparation method thereof. The preparation method comprises: mixing and melt-extruding polylactic acid, a bio-based furan polyester, and an antioxidant through a twin-screw extruder, water-cooling and drawing to obtain a PLA / bio-based furan polyester composite strip having a draw ratio of 100 to 1500:1, and then heat-treating the strip at 90 to 130°C for 10 seconds to 5 minutes to obtain the heat-resistant, high-strength polylactic acid composite material. The twin-screw extruder comprises an extrusion screw conveying section, an extrusion screw melting section, a mixing section, a venting section, and a homogenizing section, arranged in sequence along the extrusion direction. The temperatures of the extrusion screw melting section and the mixing section are 2 to 10°C higher than the highest melting point of the polylactic acid and the bio-based furan polyester. Based on the total mass of the polylactic acid, the bio-based furan polyester, and the antioxidant as 100%, the mass proportion of the polylactic acid is 83% to 99.85%, the mass proportion of the bio-based furan polyester is 0.1% to 15%, and the mass proportion of the antioxidant is 0.05% to 2.0%.

Description

Technical Field

[0001] The present invention relates to the field of polylactic acid composite materials, and in particular to a heat-resistant and high-strength polylactic acid composite material and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA) is an environmentally friendly polymer made from renewable resources, which is fully biodegradable and has good biocompatibility. It is known as the bio-based polymer material with the most development potential.

[0003] However, PLA's slow crystallization rate leads to a long molding cycle, increased energy consumption, and higher production costs. In addition, PLA has poor heat resistance (only around 55°C), which seriously limits its large-scale application. Increasing PLA's crystallization rate and improving its heat resistance can broaden its application in areas such as food tableware.

[0004] Chinese invention patent application CN 110452330 A discloses a method for preparing a PLA composite material by radiation cross-linking. However, radiation cross-linking makes the cross-linked molecular chains difficult to degrade, affecting the degradation performance of the material.

[0005] Chinese invention patent application CN201810044643.4 discloses a polylactic acid-polypropylene carbonate composite material and its preparation method. Although the heat resistance of the modified PLA-based composite material is improved, the Vicat softening temperature is difficult to be higher than 110°C.

[0006] Therefore, there is an urgent need to seek a heat-resistant, high-strength, fully biodegradable PLA-based composite material to broaden the practical application range of PLA. Summary of the Invention

[0007] In response to the above technical problems and the shortcomings in the art, the present invention provides a method for preparing a heat-resistant and high-strength polylactic acid composite material. The process is simple, and the prepared polylactic acid composite material has excellent heat resistance and tensile strength.

[0008] A method for preparing a heat-resistant and high-strength polylactic acid composite material comprises: mixing polylactic acid, bio-based furan polyester, and an antioxidant through a twin-screw extruder, melt-extruding, water-cooling and drawing to obtain a PLA / bio-based furan polyester composite material strip having a draw ratio (i.e., the ratio of the cross-sectional area of the twin-screw extruder outlet to the cross-sectional area of the PLA / bio-based furan polyester composite material strip) of 100 to 1500:1, and then heat-treating at 90 to 130° C. for 10 seconds to 5 minutes to obtain the heat-resistant and high-strength polylactic acid composite material;

[0009] The twin-screw extruder includes an extrusion screw conveying section, an extrusion screw melting section, a mixing section, a venting section, and a homogenizing section, which are sequentially arranged along the extrusion direction. The temperatures of the extrusion screw melting section and the mixing section are 2 to 10°C higher than the highest melting point of polylactic acid and bio-based furan polyester. Based on the total mass of polylactic acid, bio-based furan polyester, and antioxidant being 100%, the mass proportion of polylactic acid is 83% to 99.85%, the mass proportion of bio-based furan polyester is 0.1% to 15%, and the mass proportion of antioxidant is 0.05% to 2.0%.

[0010] Bio-based furan polyester is a bio-based polymer that is recyclable and degradable and has a wide range of applications. The present invention introduces bio-based furan polyester into PLA without affecting the degradation performance of the material.

[0011] The key to the preparation method of the present invention is that the melt processing temperature of the twin-screw extruder must be higher than the melting point of the bio-based furan polyester to completely melt the bio-based furan polyester. The extruded sample must be pulled to a draft ratio of 100 to 1500:1. This results in the bio-based furan polyester being dispersed in the polylactic acid (PLA) as fibrous rods with a diameter range of 0.1 to 30 μm. Finally, after a short heat treatment at a specific temperature, the PLA crystallizes to form a network, significantly improving its heat resistance. During the preparation process of the present invention, the formation of the bio-based furan polyester fibrous rods and the PLA crystalline network significantly improve the tensile strength of the resulting polylactic acid composite material.

[0012] In a preferred embodiment, the method for preparing the heat-resistant and high-strength polylactic acid composite material, the weight average molecular weight of the polylactic acid is 1×10 4 ~1×10 6 g / mol, and a melting point range of 150-170°C. Polylactic acid with this weight-average molecular weight and melting point range can better match the processing temperature window of bio-based furan polyester.

[0013] The preparation method of the heat-resistant and high-strength polylactic acid composite material, the bio-based furan polyester is degradable, preferably including polyethylene 2,5-furandicarboxylate (PEF), polypropylene 2,5-furandicarboxylate (PBF), polybutylene 2,5-furandicarboxylate (PPF), poly neopentyl 2,5-furandicarboxylate (PNF), poly hexane 2,5-furandicarboxylate (PHF), poly octanediol 2,5-furandicarboxylate (POF), poly decanediol 2,5-furandicarboxylate (PDeF), poly dodecanediol 2,5-furandicarboxylate (PDoF), poly 1,20-furandicarboxylate (PEF), poly propylene glycol 2,5-furandicarboxylate (PBF), poly butylene 2,5-furandicarboxylate (PPF), poly neopentyl 2,5-furandicarboxylate (PNF), poly hexanediol 2,5-furandicarboxylate (PHF), poly octanediol 2,5-furandicarboxylate (POF), poly decanediol 2,5-furandicarboxylate (PDeF), poly dodecanediol 2,5-furandicarboxylate (PDoF), poly 1,20-furandicarboxylate (PEF), poly 1,20-furandicarboxylate (PEF), poly propylene glycol 2,5-furandicarboxylate (PBF), poly butylene 2,5-furandicarboxylate (PPF), poly neopentyl 2,5-furandicarboxylate (PNF), poly hexanediol 2,5-furandicarboxylate (PHF), poly octanediol 2,5-furandicarboxylate (POF), poly 20F), poly-2,5-furandicarboxylic acid-2-methyl-1,3-propylene glycol ester (PMePF), poly-2,5-furandicarboxylic acid cyclohexanedimethanol ester (PCF), poly-2,5-furandicarboxylic acid isosorbide ester (PIsF), poly-2,5-furandicarboxylic acid pentanediol ester (PPeF), poly-2,5-furandicarboxylic acid heptanediol ester (PHepF), poly-2,5-furandicarboxylic acid nonanediol ester (PNoF), poly(terephthalate) At least one of polyethylene glycol-2,5-furandicarboxylate copolyester (PEFT), polyethylene glycol cyclohexanedimethanol furandicarboxylate (PECF), polyethylene glycol-2,2,4,4-tetramethyl-1,3-cyclobutanediol poly-2,5-furandicarboxylate (PETF), polyester elastomer based on 2,5-furandicarboxylic acid, poly-2,5-furandicarboxylic acid-based aromatic polyester, and poly-2,5-furandicarboxylic acid-based aliphatic aromatic copolyester.

[0014] In a preferred embodiment, in the method for preparing a heat-resistant, high-strength polylactic acid composite material, the bio-based furan polyester is polyethylene 2,5-furandicarboxylate, which has a melting point of 212°C. Accordingly, the temperature of the twin-screw extruder's extrusion screw conveying section is 205-215°C, the temperature of the extrusion screw's melting and mixing sections is 215-225°C, and the temperature of the venting and homogenizing sections is 205-220°C.

[0015] In a preferred embodiment, in the method for preparing the heat-resistant and high-strength polylactic acid composite material, the draw ratio of the PLA / bio-based furan polyester composite material strip is 300 to 800:1.

[0016] According to the required draw ratio, the corresponding discharge port diameter and traction rate of the twin-screw extruder can be selected.

[0017] In a preferred embodiment, in the method for preparing the heat-resistant and high-strength polylactic acid composite material, the discharge port diameter of the twin-screw extruder is 0.1 to 3 mm, and the pulling speed is 5 to 100 m / min.

[0018] Further preferably, in the method for preparing the heat-resistant and high-strength polylactic acid composite material, the discharge port diameter of the twin-screw extruder is 0.5-1 mm, and the pulling speed is 10-50 m / min.

[0019] The preparation method of the heat-resistant and high-strength polylactic acid composite material is that the crystallinity of the PLA / bio-based furan polyester composite material strip is greater than 40%.

[0020] The method for preparing the heat-resistant and high-strength polylactic acid composite material is as follows: in the PLA / bio-based furan polyester composite material strip, the dispersion state of polyethylene 2,5-furandicarboxylate in the polylactic acid is in the form of fiber rods with a diameter ranging from 0.1 to 30 μm.

[0021] The addition of antioxidants is mainly to prevent the degradation of PLA during high-temperature melt extrusion, and conventional antioxidants can be used.

[0022] In a preferred example, in the method for preparing the heat-resistant and high-strength polylactic acid composite material, the antioxidant is antioxidant 168.

[0023] The present invention also provides a heat-resistant and high-strength polylactic acid composite material prepared by the preparation method.

[0024] In a preferred embodiment, the heat-resistant and high-strength polylactic acid composite material has a Vicat softening temperature of 135 to 160° C. and a tensile strength of 60 to 82 MPa.

[0025] Compared with the prior art, the present invention has the following main advantages:

[0026] The preparation method of the present invention has simple process, and the prepared polylactic acid composite material is degradable and has excellent heat resistance and tensile strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a photograph of the dispersed morphology of PEF in PLA in the PLA / PEF composite material obtained in Example 1;

[0028] Figure 2 is a DSC curve diagram of isothermal crystallization of PLA and the PLA / PEF composite material obtained in Example 1;

[0029] Figure 3 This is a photograph of the dispersed morphology of PEF in PLA in the PLA / PEF composite material obtained in Comparative Example 1. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are intended to illustrate the present invention and are not intended to limit the scope of the invention. The operating methods in the following examples where no specific conditions are specified are generally performed under conventional conditions or as recommended by the manufacturer.

[0031] The crystallinity determination method is: according to the American standard ASTM D3418, a differential scanning calorimeter (DSC) is used to test the crystallinity and isothermal crystallization time of the composite material.

[0032] The weight average molecular weight of the polylactic acid used in each embodiment and comparative example is 1×10 4 ~1×10 6 g / mol.

[0033] Example 1

[0034] 96.9 wt% of PLA (melting point 165°C), 3 wt% of PEF and 0.1 wt% of antioxidant 168 were extruded through a twin-screw extruder (the temperature of the extrusion screw conveying section was 210°C, the temperature of the extrusion screw melting section was 215°C, the temperature of the mixing section was 215°C, the temperature of the exhaust section was 210°C, the temperature of the homogenization section was 205°C, and the discharge port diameter was 1 mm), cooled underwater, and pulled (pulling rate was 20 m / min) to obtain a PLA / PEF composite material (draw-down ratio of 400:1).

[0035] Prepared PLA / PEF composite materials, the dispersion state of PEF in PLA is as follows Figure 1 As shown in the figure, PEF is in the form of fiber rods with a diameter of about 0.5 μm. PEF is in the form of fiber rods in PLA, which can promote the crystallization of PLA, with a crystallinity of 59.6%.

[0036] The introduction of PEF can shorten the isothermal crystallization time of PLA, such as Figure 2 shown.

[0037] After isothermal treatment at 105°C for 1 min, the Vicat softening temperature of the PLA / PEF composite material was 143.7°C and the tensile strength was 67 MPa.

[0038] Example 2

[0039] Polylactic acid (PLA) with a mass fraction of 87.9wt%, PEF 12wt% and antioxidant 168 0.1wt% were extruded through a twin-screw extruder (the temperature of the extrusion screw conveying section was 212°C, the temperature of the extrusion screw melting section was 217°C, the temperature of the mixing section was 220°C, the temperature of the exhaust section was 215°C, the temperature of the homogenization section was 210°C, and the discharge port diameter was 1mm), cooled underwater, and pulled (the pulling rate was 20m / min) to obtain a PLA / PEF composite material (draw-down ratio of 400:1).

[0040] In the prepared PLA / PEF composite material, PEF is in the form of fiber rods with a diameter of about 0.5 μm and a crystallinity of 50.7%.

[0041] After isothermal treatment at 105°C for 1 min, the Vicat softening temperature of the PLA / PEF composite material was 155.7°C and the tensile strength was 80 MPa.

[0042] Example 3

[0043] The only difference from Example 1 was that the draw-down ratio was 1000. The resulting PLA / PEF composite had a crystallinity of 62.1%. The PEF was in the form of fiber rods with a diameter of approximately 0.2 μm. After isothermal treatment at 105°C for 1 minute, the PLA / PEF composite had a Vicat softening temperature of 145.3°C and a tensile strength of 61 MPa.

[0044] Example 4

[0045] The only difference from Example 1 is that the temperature of the isothermal treatment of the PLA / PEF composite material is 125° C., the treatment time is 5 min, and the Vicat softening temperature of the polylactic acid composite material obtained after the isothermal treatment is 137.1° C. and the tensile strength is 67 MPa.

[0046] Example 5

[0047] The only difference from Example 1 is that the selected PLA has a melting point of 155°C, and the selected bio-based furan polyester is poly (2,5-dodecyl furandicarboxylate) (PDoF), which has a melting point of 127°C, lower than that of PLA. The temperature of the twin-screw extruder's extrusion screw conveying section is 153°C, the temperature of the extrusion screw melting section is 160°C, the temperature of the mixing section is 165°C, the temperature of the venting section is 160°C, and the temperature of the homogenization section is 155°C. All other conditions are the same as in Example 1. The prepared PLA / PDoF composite material has a crystallinity of 51.7%, a Vicat softening temperature of 137.8°C, and a tensile strength of 61 MPa after isothermal treatment at 100°C for 1 minute.

[0048] Comparative Example 1

[0049] The preparation process of the PLA substrate in this comparative example is the same as that in Example 1, except that the temperature of the extrusion screw conveying section is 190°C, the temperature of the extrusion screw melting section is 195°C, the temperature of the mixing section is 200°C, the temperature of the exhaust section is 195°C, the temperature of the homogenization section is 190°C, and there is no pulling step. The dispersion state of PEF in PLA in the obtained PLA / PEF composite material is in the form of granular balls, as shown in FIG. Figure 3 shown.

[0050] After isothermal treatment at 105°C for 1 min, the Vicat softening temperature of the PLA / PEF composite material was 87.2°C and the tensile strength was 56 MPa.

[0051] Comparative Example 2

[0052] The only difference between this comparative example and Example 1 is that the PLA / PEF composite material was not subjected to isothermal treatment, and its Vicat softening temperature was 60.8° C. and its tensile strength was 67 MPa.

[0053] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a heat-resistant and high-strength polylactic acid composite material, characterized in that: include: Polylactic acid, bio-based furan polyester, and an antioxidant are mixed and melt-extruded through a twin-screw extruder, and water-cooled and drawn to obtain a PLA / bio-based furan polyester composite material strip having a draw ratio of 100 to 1500:

1. The strip is then heat-treated at 90 to 130° C. for 10 seconds to 5 minutes to obtain the heat-resistant and high-strength polylactic acid composite material; in the polylactic acid / bio-based furan polyester composite material strip, the bio-based furan polyester is dispersed in the polylactic acid in a fiber rod-like state; The twin-screw extruder comprises an extrusion screw conveying section, an extrusion screw melting section, a mixing section, a venting section, and a homogenizing section sequentially arranged along the extrusion direction, wherein the temperature of the extrusion screw melting section and the mixing section is 2 to 10° C. higher than the highest melting point of polylactic acid and bio-based furan polyester; Taking the total mass of polylactic acid, bio-based furan polyester and antioxidant as 100%, the mass proportion of polylactic acid is 83% to 99.85%, the mass proportion of bio-based furan polyester is 0.1% to 15%, and the mass proportion of antioxidant is 0.05% to 2.0%.

2. The preparation method according to claim 1, characterized in that The weight average molecular weight of polylactic acid is 1×10 4 ~1×10 6 g / mol, and the melting point range is 150-170°C.

3. The preparation method according to claim 1, characterized in that The bio-based furan polyester is degradable and includes polyethylene 2,5-furandicarboxylate, polypropylene 2,5-furandicarboxylate, polybutylene 2,5-furandicarboxylate, poly neopentyl 2,5-furandicarboxylate, poly hexane 2,5-furandicarboxylate, poly octanediol 2,5-furandicarboxylate, poly decanediol 2,5-furandicarboxylate, poly dodecanediol 2,5-furandicarboxylate, poly 1,20-furandicarboxylate, poly 2,5-furandicarboxylate-2-methyl-1,3-propylene glycol 2,5-furandicarboxylate, and poly cyclohexanedimethanol 2,5-furandicarboxylate. At least one of ester, poly (isosorbide 2,5-furandicarboxylate), poly (pentanediol 2,5-furandicarboxylate), poly (heptanediol 2,5-furandicarboxylate), poly (nonanediol 2,5-furandicarboxylate), polyethylene terephthalate-2,5-furandicarboxylate copolyester, polyethylene cyclohexanedimethanol furandicarboxylate, polyethylene 2,5-furandicarboxylate-2,2,4,4-tetramethyl-1,3-cyclobutanediol furandicarboxylate, polyester elastomer based on 2,5-furandicarboxylic acid, poly (2,5-furandicarboxylic acid-based aromatic polyester), and poly (2,5-furandicarboxylic acid-based aliphatic aromatic copolyester.

4. The preparation method according to claim 3, characterized in that The bio-based furan polyester is polyethylene 2,5-furandicarboxylate; The temperature of the extrusion screw conveying section of the twin-screw extruder is 205-215°C, the temperature of the extrusion screw melting section and the mixing section is 215-225°C, and the temperature of the exhaust section and the homogenizing section is 205-220°C.

5. The preparation method according to claim 1, characterized in that The draw ratio of the PLA / bio-based furan polyester composite material strip is 300 to 800:

1.

6. The preparation method according to claim 1 or 5, characterized in that The discharge port diameter of the twin-screw extruder is 0.1-3 mm, and the pulling speed is 5-100 m / min.

7. The preparation method according to claim 6, characterized in that The discharge port diameter of the twin-screw extruder is 0.5-1 mm, and the pulling speed is 10-50 m / min.

8. The preparation method according to claim 1 or 5, characterized in that The crystallinity of the PLA / bio-based furan polyester composite material strip is greater than 40%; The diameter of the fiber rod is in the range of 0.1 to 30 μm.

9. The preparation method according to claim 1, characterized in that The antioxidant is antioxidant 168.

10. The heat-resistant and high-strength polylactic acid composite material prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The heat-resistant and high-strength polylactic acid composite material has a Vicat softening temperature of 135-160° C. and a tensile strength of 60-82 MPa.

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