A high-performance polylactic acid biaxially oriented film and its preparation method

Abstract

The invention discloses a high-performance polylactic acid biaxially oriented film, which is prepared by a two-step biaxially oriented process by polylactic acid, poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), an epoxy compatibilizer and a processing aid; its raw materials include 80-95 parts of polylactic acid (PLA), 5-20 parts of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), 0.1-2 parts of epoxy compatibilizer, and 0.1-3 parts of processing aid; each raw material is measured in parts by mass. The present invention successfully solves one of the industrial problems of unstable film formation and poor toughness at a large ratio and low strength at a low ratio in the preparation process of polylactic acid biaxially oriented film. Finally, high-performance polylactic acid biaxially oriented film is successfully prepared under the synergistic effect of PHBH toughening PLA and two-step stretching process to improve the content of polylactic acid mesophase.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and in particular relates to a high-performance polylactic acid biaxially stretched film prepared by a pre-stretching process. Background Art

[0002] With the increasing plastic pollution, packaging materials, as indispensable plastic products, have to pursue the full biodegradability of raw materials. Polylactic acid (PLA) is an environmentally renewable resource with good degradability, mechanical strength and good processability. It is considered to be a good substitute for traditional petroleum-based polymers. However, due to its inherent brittleness and other shortcomings, its application in the packaging industry is limited. The inherent brittleness of PLA is often overcome by orientation through blow molding and biaxial stretching processes. The biaxial stretching process regulates the chain segment movement ability through thermal stretching to customize the oriented microcrystals and amorphous structure. It is an effective way to improve the comprehensive performance of polymers. For example, the publication number CN117801488 A's prior art discloses a transparent polylactic acid film with high heat resistance and a balance of rigidity and toughness, as well as its preparation method and application. However, since the strength and ductility of a single-component polylactic acid biaxially stretched film after hot stretching are limited, polymer blends can combine the advantages of a single polymer to effectively solve this problem. During the hot stretching process, the strength of the polylactic acid blended biaxially stretched film is greatly improved with high orientation at a certain stretching ratio, but the ductility is often reduced. In industrial processing at ultra-large ratios, performance deterioration or poor film-forming rate are often caused due to the compatibility of the blend. How to prepare a transparent polylactic acid biaxially stretched film with high strength and toughness at a low ratio in industrial production is one of the current industrial problems. Summary of the Invention

[0003] To address the aforementioned issues in the existing technology, the present invention provides a high-performance polylactic acid biaxially oriented film and a method for preparing the same. This method utilizes a two-step biaxially oriented process to produce the polylactic acid biaxially oriented film, further enhancing its strength, toughness, and transparency while reducing haze. This method can effectively expand the application areas of the blended film.

[0004] The technical solutions of the present invention are as follows:

[0005] The first object of the present invention is to provide a high-performance polylactic acid biaxially oriented film, which is prepared by a two-step biaxially oriented process of polylactic acid, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), an epoxy compatibilizer and a processing aid; the raw materials include 80-95 parts of polylactic acid (PLA), 5-20 parts of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), 0.1-2 parts of epoxy compatibilizer, and 0.1-3 parts of processing aid; each raw material is measured in parts by weight.

[0006] In one embodiment of the present invention, the optical purity of the polylactic acid is 97.5%.

[0007] In one embodiment of the present invention, the HH content in the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is 6-11%.

[0008] In one embodiment of the present invention, the epoxy compatibilizer is one or more of ADR4468 and ADR4400.

[0009] In one embodiment of the present invention, the processing aid is one or more of an anti-hydrolysis agent, an antioxidant, and a lubricant.

[0010] In one embodiment of the present invention, the antioxidant is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris[2,4-di-tert-butylphenyl]phosphite.

[0011] In one embodiment of the present invention, the anti-hydrolysis agent is a carbodiimide anti-hydrolysis agent.

[0012] In one embodiment of the present invention, the lubricant is one or more of liquid paraffin and stearamide.

[0013] A second object of the present invention is to provide a method for preparing a high-performance polylactic acid biaxially oriented film, comprising the following steps:

[0014] (1) feeding 0.1-2 parts of epoxy compatibilizer, 0.1-3 parts of processing aid, 80-95 parts of polylactic acid and 5-20 parts of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) into a twin-screw extruder for melt extrusion and casting to form a film, which is then rapidly cooled by a casting roller to control the initial crystallinity of the PLA film to below 5%;

[0015] (2) The cooled film is subjected to two-step biaxial stretching at 60-100° C. using a biaxial stretching process, and then subjected to heat treatment at 60-100° C. for shaping, thereby obtaining the high-performance polylactic acid biaxially stretched film.

[0016] In one embodiment of the present invention, in step (1), polylactic acid and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) are dried at 70° C. before use.

[0017] In one embodiment of the present invention, in step (1), the temperature of melt blending is 170-200°C.

[0018] The setting of the melt blending temperature not only maintains the full reaction between the epoxy groups and the two components, but also avoids the partial degradation of PHBH at high temperature.

[0019] In one embodiment of the present invention, in step (1), the temperatures of the casting roller are set to 50°C, 50°C, and 20°C in sequence.

[0020] In one embodiment of the present invention, in step (2), the two-step biaxial stretching process is: simultaneous initial pre-stretching at 60-80°C at a constant stretching rate, and then a second stretching at 80-100°C at a constant stretching rate.

[0021] In one embodiment of the present invention, the stretching rate of the initial pre-stretching is 30-240 mms / s. Preferably, the stretching rate of the initial pre-stretching is 70 mm / s or 140 mm / s.

[0022] In one embodiment of the present invention, the stretching rate of the second stretching is 30-240 mm / s. Preferably, the stretching rate of the second stretching is 70 mm / s.

[0023] In one embodiment of the present invention, in step (2), the stretching ratio of the initial pre-stretching is 2×2, 2.5×2.5 or 3×3; the stretching ratio of the second stretching is 3×3, 4×4, 5×5 or 6×6.

[0024] In one embodiment of the present invention, in step (2), the stretching ratio of the initial pre-stretching is 2×2; and the stretching ratio of the second stretching is 3×3.

[0025] The third object of the present invention is to provide an application of a high-performance polylactic acid biaxially oriented film for use in the fields of daily necessities, chemical industry, food, agriculture or pharmaceutical packaging.

[0026] The beneficial technical effects of the present invention are:

[0027] In the present invention, the relatively low addition amount of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) as the dispersed phase cannot crystallize in the matrix, thereby avoiding the performance deterioration caused by the slow crystallization of PHBH itself and the significant reduction in the optical properties of the film caused by the introduction of the blend. Moreover, after pre-stretching, the secondary stretching will not result in the inability to form a film due to the crystallization of the dispersed phase and the matrix.

[0028] The present invention collaboratively prepares a strong, transparent, low-haze polylactic acid biaxially stretched film through melt blending and a two-step biaxial stretching process. First, a relatively low content of PHBH is added as a toughening component for melt blending and casting, and then biaxially stretched at low temperature and low ratio for pre-stretching, and then a high-temperature secondary stretching is performed to obtain the final biaxially stretched film. First, the low content of PHBH cannot crystallize in the matrix, which successfully suppresses its disadvantage of slow crystallization, so that only the evolution of the mesophase occurs during the pre-stretching of the PLA / PHBH blend film. Secondly, the non-crystallized PHBH ensures that the final blend film still maintains excellent optical properties comparable to those of pure PLA. Secondly, through the low-temperature and low-ratio pre-stretching process, the polylactic acid biaxially stretched film produces a rich PLA mesophase, which is then secondary stretched to the final film. During the secondary stretching process, the mesophase content is further increased. The mesophase content of the final film after pre-stretching is approximately twice that of the film that has not been pre-stretched. The mesophase plays a role similar to a "physical cross-linking point" in the PLA chain structure, which plays a role in stress transmission during the stretching process, eliminates stress concentration, and prepares a high-strength and high-toughness polylactic acid double-stretch film at a lower ratio.

[0029] The biaxially oriented film of the invention has high strength (100-150 MPa), high elongation at break (60%-150%), high transparency and low haze. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The stress-strain curves of the films obtained in Example 2 and Comparative Example 1 are shown.

[0031] Figure 2 The UV-visible light transmittance of the film obtained in Example 2 and its digital photograph. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0033] The raw materials used in the examples of the present invention are all commercially available unless otherwise specified. The optical purity of polylactic acid is 97.5%, and the HH content of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is 6-11%.

[0034] Example 1

[0035] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0036] 95 parts of PLA, 5 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190°C to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200°C, and rapidly cooled by a casting roller, with the casting roller temperatures set to 50°C, 50°C, and 20°C in sequence; an initial film material (X PLA =4%);

[0037] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0038] Example 2

[0039] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0040] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C., to obtain an initial film material (X PLA =2%);

[0041] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0042] Example 3

[0043] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0044] 85 parts of PLA, 15 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C. in sequence; an initial film material (X PLA =1%);

[0045] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0046] Example 4

[0047] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0048] 80 parts of PLA, 20 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C. in sequence; and an initial film material (X PLA =2%);

[0049] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0050] Example 5

[0051] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0052] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C., to obtain an initial film material (X PLA =0);

[0053] The initial film material is pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 80° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0054] Example 6

[0055] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0056] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C., to obtain an initial film material (X PLA =2%);

[0057] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 140 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0058] Example 7

[0059] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0060] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C., to obtain an initial film material (X PLA =1%);

[0061] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 210 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0062] Example 8

[0063] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0064] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C., to obtain an initial film material (X PLA =0);

[0065] The initial film material was pre-stretched to a ratio of 2.5×2.5 at a stretching rate of 30 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0066] Example 9

[0067] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0068] 90 parts of PLA, 10 parts of PHBH, 1.2 parts of epoxy compatibilizer ADR4468, 0.5 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester, 0.2 parts of carbodiimide anti-hydrolysis agent, and 0.1 parts of lubricant liquid paraffin were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C. in sequence; and an initial film material (X PLA =3%);

[0069] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 30 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0070] Example 10

[0071] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0072] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4400, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, 0.2 parts of tris[2,4-di-tert-butylphenyl]phosphite, 0.2 parts of carbodiimide anti-hydrolysis agent, and 0.3 parts of lubricant liquid paraffin were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C., and the mixture was rapidly cooled by a casting roller, and the casting roller temperatures were sequentially set to 50° C., 50° C., and 20° C.; an initial film material (X PLA =1%);

[0073] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 4×4 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0074] Example 11

[0075] A method for preparing a high-performance polylactic acid biaxially oriented film comprises the following steps:

[0076] 90 parts of PLA, 10 parts of PHBH, 0.4 parts of epoxy compatibilizer ADR4468, 0.2 parts of ADR4400, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, 0.2 parts of tris[2,4-di-tert-butylphenyl]phosphite, 0.2 parts of carbodiimide anti-hydrolysis agent, and 0.3 parts of lubricant liquid paraffin were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C. in sequence; an initial film material (X PLA =1%);

[0077] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 60° C. using a biaxial stretching process, and then secondary stretched to a ratio of 6×6 at a stretching rate of 70 mm / s at 80° C. to obtain the high-performance polylactic acid biaxially stretched film.

[0078] Comparative Example 1

[0079] A method for preparing a polylactic acid biaxially oriented film comprises the following steps:

[0080] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C., to obtain an initial film material (X PLA =2%);

[0081] The initial film material was stretched once to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. using a biaxial stretching process to obtain the polylactic acid biaxially stretched film.

[0082] Comparative Example 2

[0083] A method for preparing a polylactic acid biaxially oriented film comprises the following steps:

[0084] PLA 80 parts, PHBH 20 parts, epoxy compatibilizer ADR4468 0.6 parts, antioxidant tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester 0.3 parts, carbodiimide anti-hydrolysis agent 0.2 parts, after fully drying, were added into a twin-screw extruder at 190 ° C to prepare polylactic acid based blend pellets, and finally cast at 200 ° C, and quickly cooled by casting roller, and the casting roller temperature was set to 50 ° C, 50 ° C, and 20 ° C in sequence; the initial film material (X PLA =3%);

[0085] The initial film material was stretched once to a ratio of 3×3 at a stretching rate of 70 mm / s at 80° C. using a biaxial stretching process to obtain the polylactic acid biaxially stretched film.

[0086] Comparative Example 3

[0087] A method for preparing a polylactic acid biaxially oriented film comprises the following steps:

[0088] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, and 0.2 parts of carbodiimide anti-hydrolysis agent were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures being set to 50° C., 50° C., and 20° C., to obtain an initial film material (X PLA =1%);

[0089] The initial film material was stretched once to a ratio of 3×3 at a stretching rate of 140 mm / s at 80° C. using a biaxial stretching process to obtain the polylactic acid biaxially stretched film.

[0090] Comparative Example 4

[0091] A method for preparing a polylactic acid biaxially oriented film comprises the following steps:

[0092] 90 parts of PLA, 10 parts of PHBH, 0.6 parts of epoxy compatibilizer ADR4468, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester, 0.2 parts of carbodiimide anti-hydrolysis agent, and 0.1 parts of lubricant liquid paraffin were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, with the casting roller temperatures set to 50° C., 50° C., and 20° C. in sequence; an initial film material (X PLA =2%);

[0093] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 90° C. using a biaxial stretching process, and then secondary stretched to a ratio of 3×3 at a stretching rate of 70 mm / s at 90° C. to obtain the polylactic acid biaxially stretched film.

[0094] Comparative Example 5

[0095] A method for preparing a polylactic acid biaxially oriented film comprises the following steps:

[0096] 90 parts of PLA, 10 parts of PHBH, 0.4 parts of epoxy compatibilizer ADR4468, 0.2 parts of ADR4400, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, 0.2 parts of tris[2,4-di-tert-butylphenyl] phosphite, 0.3 parts of antioxidant tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, 0.2 parts of carbodiimide anti-hydrolysis agent, and 0.1 parts of lubricant liquid paraffin were fully dried and added into a twin-screw extruder at 190° C. to prepare polylactic acid-based blend pellets; then, the mixture was cast at 200° C. and rapidly cooled by a casting roller, and the casting roller temperatures were set to 50° C., 50° C., and 20° C. in sequence; an initial film material (X PLA =2%);

[0097] The initial film material was pre-stretched to a ratio of 2×2 at a stretching rate of 70 mm / s at 80° C. using a biaxial stretching process, and then secondary stretched to a ratio of 4×4 at a stretching rate of 70 mm / s at 120° C. to obtain the polylactic acid biaxially stretched film.

[0098] The polylactic acid-based biaxially stretched films obtained in Examples 1-7 were tested for tensile properties at room temperature according to the GB / T 1040-2006 standard method, with a tensile rate of 10 mm / min. At least five specimens were tested for each sample, and the average value was calculated. The light transmittance and haze of the materials were also tested according to the GB / T 2410-2008 standard method. The results are shown in Table 1.

[0099] Table 1

[0100]

[0101]

[0102] The performance quality of the polylactic acid-based biaxially stretched films obtained in the above comparative examples 1-4 was measured using the same measurement process. The results are shown in Table 2.

[0103] Table 2

[0104] Comparative Example Breaking strength (MPa) Elongation at break (%) Light transmittance (%) Haze (%) Comparative Example 1 93±3 85±6 92.1 8.9 Comparative Example 2 95±3 98±3 91.5 16.8 Comparative Example 3 90±5 89±2 92.4 9.5 Comparative Example 4 85±7 86±4 89.5 14.6

[0105] It can be seen from Table 1 and Table 2 that the breaking strength of polylactic acid and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) biaxial stretch film after two-step stretching process (Examples 1-9) is significantly improved compared with direct biaxial stretching, and the rich mesophase content in the two-step stretching process has a significant effect on the improvement of breaking strength. In addition, in Examples 5-7, the breaking strength slightly decreases by adjusting the pre-stretching rate, and the elongation at break rises thereupon, but compared to Comparative Example 3, both the breaking strength and the elongation at break are greatly improved, which further illustrates that the mesophase content can be effectively regulated by pre-stretching to regulate the PLA biaxial stretch film segment motion, and the PLA brittle-tough transition is achieved, but the change of the stretching rate alone is far from being able to prepare the existing strong and tough balanced polylactic acid biaxial stretch film. The present invention prepares a high-performance polylactic acid biaxial stretch film, which is simple, practical, and easy to industrial production. In addition, low-content PHBH cannot crystallize in the matrix, successfully suppressing the shortcoming of its slow crystallization, and secondly, the non-crystallized PHBH makes the final blend film still maintain excellent optical properties comparable to pure PLA. This invention combines PHBH-toughened PLA with a two-step biaxial stretching process to produce a high-performance polylactic acid biaxially stretched film. This simple, practical, and easily industrially produced film overcomes the lower strength drawback of low-ratio films produced industrially. It has potential applications in film packaging materials, agricultural greenhouse film, and other fields.

[0106] The embodiments provided above are not intended to limit the scope of the present invention, nor are the steps described to limit their execution order. Any obvious improvements to the present invention made by those skilled in the art in combination with existing common knowledge shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A high-performance polylactic acid biaxially oriented film, characterized in that: The invention is prepared by a two-step biaxial stretching process of polylactic acid, poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), epoxy compatibilizer and processing aid; the raw materials include 80-95 parts of polylactic acid, 5-20 parts of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), 0.1-2 parts of epoxy compatibilizer and 0.1-3 parts of processing aid; Each raw material is measured in parts by weight; The method for preparing the high-performance polylactic acid biaxially oriented film comprises the following steps: (1) feeding 0.1-2 parts of epoxy compatibilizer, 0.1-3 parts of processing aid, 80-95 parts of polylactic acid and 5-20 parts of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) into a twin-screw extruder for melt extrusion and casting to form a film, which is then rapidly cooled by a casting roller to control the initial crystallinity of the PLA film to below 5%; (2) performing two-step biaxial stretching on the cooled film at 60-100° C. using a biaxial stretching process, and then performing heat treatment at 60-100° C. for shaping, thereby obtaining the high-performance polylactic acid biaxially stretched film; In step (2), the process of two-step biaxial stretching is: synchronous initial pre-stretching at a constant stretching rate of 60-80°C, and then a second stretching at a constant stretching rate of 80-100°C; the constant stretching rate is 30-240 mm / s; In step (2), the stretching ratio of the initial pre-stretching is 2×2, 2.5×2.5 or 3×3; the stretching ratio of the second stretching is 3×3, 4×4, 5×5 or 6×6.

2. The high-performance polylactic acid biaxially oriented film according to claim 1, characterized in that: The epoxy compatibilizer is one or more of ADR4468 and ADR4400; the processing aid is one or more of anti-hydrolysis agent, antioxidant and lubricant.

3. The high-performance polylactic acid biaxially oriented film according to claim 1, characterized in that: In step (1), polylactic acid and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) are dried at 70° C. before use.

4. The high-performance polylactic acid biaxially oriented film according to claim 1, characterized in that In step (1), the temperature of melt blending is 170-200°C.

5. The high-performance polylactic acid biaxially oriented film according to claim 1, characterized in that: In step (1), the temperatures of the casting roller are set to 50°C, 50°C, and 20°C in sequence.

6. An application of the high-performance polylactic acid biaxially oriented film according to claim 1, characterized in that: Used in the packaging of daily necessities, chemicals, food, agriculture or medicine.

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