A completely degradable toughened polylactic acid material and preparation method thereof

Abstract

The purpose of the present invention is to provide a completely degradable toughened polylactic acid material and a preparation method thereof. By weight, it comprises: 5-40 parts of a bio-based degradable thermoplastic elastomer, 57-94.5 parts of polylactic acid, and 0.5-3 parts of other processing aids. The method provided by the present invention has the following benefits: 1) The toughening agent used is a bio-based degradable thermoplastic elastomer material, the raw material is derived from biomass, and can be completely degraded under natural conditions. The polylactic acid composite material obtained by toughening and modifying it can be completely degraded under natural conditions; 2) Adding a small amount of bio-based degradable thermoplastic elastomer can significantly increase the elongation at break and notched impact strength of PLA.

Description

Technical Field

[0001] The present invention relates to the fields of polymer materials and chemical engineering, and in particular to a completely degradable toughened polylactic acid material and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA) is an aliphatic polyester whose monomers can be prepared from renewable biomass such as corn, cassava, sugarcane and sugar beet. Polylactic acid has good biocompatibility, easy processability and degradability, and is widely used in medicine and plastic products. The final products of PLA degradation are carbon dioxide and water, which can be reabsorbed and utilized by plants, reducing pollution to the ecological environment and can replace traditional petroleum-based non-degradable plastics. However, PLA has many performance defects, such as low elongation at break, poor toughness, low impact strength, etc., which greatly limit its large-scale application.

[0003] Toughening modification of PLA materials has attracted more and more attention, mainly through physical or chemical means to improve the brittleness of PLA and improve its mechanical properties. The most commonly used method at present is to use polyesters such as PBAT and PBS to blend and modify polylactic acid. However, PBAT and PBS are incompatible with PLA, so epoxy chain extenders are needed to extend the system chain to improve the incompatibility problem. However, the styrene content of most epoxy chain extenders exceeds the standard, resulting in the prepared plastic products not meeting the food safety contact standards. The introduction of PBS and PBAT will also cause PLA to lose transparency and gloss, and its application in transparent and high-strength products is limited.

[0004] Thermoplastic elastomer (TPE) is a polymer material that exhibits rubber elasticity at room temperature, can be re-plasticized and molded at high temperatures, has excellent flexibility, and is an ideal material for toughening PLA. Patent CN113402864B discloses a method for toughening and modifying polylactic acid using polyamide thermoplastic elastomer, wherein the polyamide thermoplastic elastomer phase is dispersed in the polylactic acid resin matrix phase in an island shape; the polyamide thermoplastic elastomer includes a block copolymer formed by an AABB-type polyamide hard segment and a polyether diol soft segment. Patent CN111534068 discloses a method for modifying polylactic acid using a toughening agent, wherein the toughening agent is selected from ethylene-methyl acrylate-glycidyl methacrylate random copolymer, hydrogenated polystyrene-polybutadiene-polystyrene triblock copolymer, natural rubber, and polycaprolactone plastic. The above patents all use petroleum-based non-degradable elastomers as toughening agents to modify polylactic acid, which will affect the degradation performance of the final material.

[0005] In view of this, the present invention provides a completely degradable toughened polylactic acid material and a preparation method thereof. In parts by weight, it comprises: 5-40 parts of a bio-based degradable thermoplastic elastomer, 57-94.5 parts of polylactic acid, and 0.5-3 parts of other processing aids. The method provided by the present invention has the following benefits: 1) The toughening agent used is a bio-based degradable thermoplastic elastomer material, the raw material is derived from biomass, and can be completely degraded under natural conditions. The polylactic acid composite material obtained by toughening and modifying it can be completely degraded under natural conditions; 2) Adding a small amount of bio-based degradable thermoplastic elastomer can significantly increase the elongation at break and notched impact strength of PLA. Summary of the invention

[0006] The purpose of the present invention is to provide a completely degradable toughened polylactic acid material and a preparation method thereof.

[0007] The present invention provides a completely degradable toughened polylactic acid material, characterized in that the components of the toughened polylactic acid material, measured by weight, include:

[0008] (1) 5-40 parts of biodegradable thermoplastic elastomer

[0009] (2) 57-94.5 parts of polylactic acid

[0010] (3) Processing aids 0.5-3 parts

[0011] The bio-based degradable thermoplastic elastomer has a multi-arm block copolymer structure as shown in formula (I), wherein A is an amorphous aliphatic polyester segment with a glass transition temperature below -20°C, and B is a polylactide segment, wherein the polylactide segment is at least one of poly(L-lactide), poly(D-lactide) and poly(rac-lactide).

[0012] R-(AbB) x

[0013] (I)

[0014] The number of arms x of the multi-arm block copolymer is 2-8, and the R group has one of the following structures:

[0015]

[0016] The processing aid is selected from at least one of an antioxidant, a dispersant, a colorant or a lubricant.

[0017] Preferably, the segment A has one of the following structures:

[0018]

[0019] The segment B has the following structure:

[0020]

[0021] The invention is characterized in that y is a natural number from 2 to 8, m is a natural number from 50 to 1000, and n is a natural number from 50 to 1000.

[0022] Another object of the present invention is to provide a method for preparing the toughened polylactic acid material, comprising the following steps:

[0023] (1) fully drying the bio-based degradable thermoplastic elastomer, polylactic acid and processing aid in a drying device, and fully mixing them in proportion;

[0024] (2) The mixture obtained in step (1) is extruded into pellets through a twin-screw extruder at an extruder temperature of 120 to 195° C. and an extruder speed of 300 to 350 rpm, and pelletized to obtain toughened polylactic acid pellets. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The uniaxial stretching spectra of the composite materials prepared in Example 1 and Example 2 are shown.

[0026] Figure 2 1 is the uniaxial stretching spectrum of the composite materials prepared in Examples 3 to 5.

[0027] Figure 3 The DSC spectrum of the composite material prepared in Example 1 at a scanning rate of 10°C / min.

[0028] Figure 4 This is the DSC spectrum of the composite material prepared in Example 6 at a scanning rate of 10°C / min.

[0029] Figure 5 This is a graph of the notched impact strength of the composite materials prepared in Examples 3 to 5 at an impact speed of 3.5 m / s.

[0030] Figure 6 This is the uniaxial stretching spectrum of the composite material prepared in Example 6. DETAILED DESCRIPTION

[0031] The present invention is described in detail with reference to the following embodiments, but the present invention is not limited to these embodiments.

[0032] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0033] Comparative Example 1

[0034] (1) Preparation of poly(L-lactide)-b-poly(ε-caprolactone)-b-poly(L-lactide) triblock copolymer (two-arm block copolymer)

[0035] (0.06 mmol, 8.29 mg) 1,4-p-phenylenedimethanol, (0.06 mmol, 22.05 mg) phosphazene ligand P2-tert-butyl, (0.06 mmol, 37.78 mg) 1,1'-(oxybis(ethylene))bis(3-(3,5-bis(trifluoromethyl)phenyl)urea) Dissolve in 1.3 mL tetrahydrofuran, mix and stir at room temperature for 10 min, add (24 mmol, 2.7 mL) ε-caprolactone to the reaction tube, and react at room temperature for 30 min under nitrogen protection. Then dissolve (18 mmol, 2.59 g) L-lactide in 12 mL tetrahydrofuran and add to the above reaction system, react at room temperature for 20 min under nitrogen protection, and add 10 drops of benzoic acid to terminate the reaction. Pour the reaction mixture into 50 mL methanol, centrifuge and separate the precipitate to obtain poly(L-lactide)-b-poly(ε-caprolactone)-b-poly(L-lactide) triblock copolymer.

[0036] (2) Preparation of composite materials

[0037] By weight, 5 parts of poly(L-lactide)-b-poly(ε-caprolactone)-b-poly(L-lactide) triblock copolymer, 94 parts of polylactic acid and 1 part of antioxidant 1010 were fully dried and mixed uniformly, and extruded and granulated using a twin-screw extruder to obtain a toughened polylactic acid composite material. The composite material has a low elongation at break (<10%) and a poor toughening effect.

[0038] Comparative Example 2

[0039] (1) Preparation of poly(δ-caprolactone)-b-poly(L-lactide) diblock copolymers (single-arm block copolymers)

[0040] (0.06 mmol, 6.48 mg) benzyl alcohol, (0.06 mmol, 22.05 mg) phosphazene ligand P2-tert-butyl, (0.06 mmol, 37.78 mg) 1,1'-(oxybis(ethylene))bis(3-(3,5-bis(trifluoromethyl)phenyl)urea) Dissolve in 1.3 mL tetrahydrofuran, mix and stir at room temperature for 10 min, add (24 mmol, 2.7 mL) δ-caprolactone to the reaction tube, and react at room temperature for 30 min under nitrogen protection. Then dissolve (18 mmol, 2.59 g) L-lactide in 12 mL tetrahydrofuran and add to the above reaction system, react at room temperature for 20 min under nitrogen protection, and add 10 drops of benzoic acid to terminate the reaction. Pour the reaction mixture into 50 mL methanol, centrifuge and separate the precipitation to obtain poly(δ-caprolactone)-b-poly(L-lactide) diblock copolymer.

[0041] (2) Preparation of composite materials

[0042] 5 parts of poly(δ-caprolactone)-b-poly(L-lactide) diblock copolymer, 94 parts of polylactic acid and 1 part of antioxidant 1010 were fully dried and mixed uniformly, and extruded and granulated using a twin-screw extruder to obtain a toughened polylactic acid composite material. The elongation at break of the composite material was low (<10%), and the toughening effect was poor.

[0043] Example 1

[0044] The difference from Comparative Example 1 is that segment A is poly(δ-caprolactone), and the difference from Comparative Example 2 is that the toughening agent is a triblock copolymer:

[0045] 5 parts of poly(L-lactide)-b-poly(δ-caprolactone)-b-poly(L-lactide) triblock copolymer, 94 parts of polylactic acid and 1 part of antioxidant 1010 were fully dried and mixed evenly, and extruded and granulated using a twin-screw extruder to obtain a toughened polylactic acid composite material. The tensile curve of the composite material is shown in Figure 1 As shown, the DSC curve is Figure 3 shown.

[0046] Example 2

[0047] The difference from Comparative Example 1 is that segment A is poly(δ-octyl lactone):

[0048] 5 parts of poly(L-lactide)-b-poly(δ-octyrolactone)-b-poly(L-lactide) triblock copolymer, 94 parts of polylactic acid and 1 part of antioxidant 1010 were fully dried and mixed evenly, and extruded and granulated using a twin-screw extruder to obtain a toughened polylactic acid composite material. The tensile curve of the composite material is shown in Figure 1 shown.

[0049] Example 3

[0050] Using trimethylolpropane as an initiator, a poly(δ-caprolactone)-b-poly(L-lactide) three-arm block copolymer was prepared. 5 parts of poly(δ-caprolactone)-b-poly(L-lactide) three-arm block copolymer, 94 parts of polylactic acid and 1 part of

[0051] The antioxidant 1010 is fully dried and mixed evenly, and then extruded and granulated using a twin-screw extruder to obtain a toughened polylactic acid composite material. The tensile curve of the composite material is as follows: Figure 2 shown.

[0052] Example 4

[0053] Pentaerythritol was used as an initiator to obtain a poly(δ-caprolactone)-b-poly(L-lactide) four-arm block copolymer. Five parts of poly(δ-caprolactone)-b-poly(L-lactide) four-arm block copolymer, 94 parts of polylactic acid and 1 part of antioxidant 1010 were fully dried and mixed evenly, and extruded and granulated using a twin-screw extruder to obtain a toughened polylactic acid composite material. The tensile curve of the composite material is shown in FIG. Figure 2 shown.

[0054] Example 5

[0055] Pentaerythritol was used as an initiator to obtain a poly(δ-undecalactone)-b-poly(L-lactide) four-arm block copolymer. Five parts of poly(δ-undecalactone)-b-poly(L-lactide) four-arm block copolymer, 94 parts of polylactic acid and 1 part of antioxidant 1010 were fully dried and mixed evenly, and extruded and granulated using a twin-screw extruder to obtain a toughened polylactic acid composite material. The tensile curve of the composite material is shown in FIG. Figure 2 shown.

[0056] Example 6

[0057] Different from Example 1, D-lactide was used as a raw material to prepare a poly(D-lactide)-b-poly(δ-caprolactone)-b-poly(D-lactide) triblock copolymer.

[0058] 5 parts of poly (D-lactide) -b-poly (δ-caprolactone) -b-poly (D-lactide) triblock copolymer, 94 parts of polylactic acid and 1 part of antioxidant 1010 were fully dried and mixed evenly, and extruded and granulated using a twin-screw extruder to obtain a toughened polylactic acid composite material. The DSC curve of the composite material is shown in Figure 4 As shown, the stretching curve is Figure 6 As shown in the DSC curve, it can be seen that by using poly (D-lactide) as a block, stereocomplex crystals can be formed between the toughening agent and polylactic acid, which can not only toughen polylactic acid, but also increase the use temperature of polylactic acid.

Claims

1. A completely degradable toughened polylactic acid material, characterized in that: The components of the toughened polylactic acid material include, by weight: (1) 5-40 parts of biodegradable thermoplastic elastomer (2) 57-94.5 parts of polylactic acid (3) Processing aids 0.5-3 parts The bio-based degradable thermoplastic elastomer has a multi-arm block copolymer structure as shown in formula (I), R-(A-b-B) x (I) Wherein A is an amorphous aliphatic polyester segment with a glass transition temperature lower than -20°C, and B is a polylactide segment; the number of arms x of the multi-arm block copolymer is 2-8; and the R group has one of the following structures:

2. The toughened polylactic acid material according to claim 1, characterized in that: The polylactide segment is at least one of poly(L-lactide), poly(D-lactide) and poly(rac-lactide).

3. The toughened polylactic acid material according to claim 1, characterized in that: The processing aid is selected from at least one of an antioxidant, a dispersant, a colorant or a lubricant.

4. The toughened polylactic acid material according to claim 1, characterized in that: The segment A has one of the following structures: The segment B has the following structure: The invention is characterized in that y is a natural number from 2 to 8, m is a natural number from 50 to 1000, and n is a natural number from 50 to 1000.

5. The method for preparing the toughened polylactic acid material according to claim 1, characterized in that: The steps include: (1) fully drying the bio-based degradable thermoplastic elastomer, polylactic acid and processing aid in a drying device, and fully mixing them in proportion; (2) The mixture obtained in step (1) is extruded into pellets through a twin-screw extruder at an extruder temperature of 120 to 195° C. and an extruder speed of 300 to 350 rpm, and pelletized to obtain toughened polylactic acid pellets.

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