Degradable polylactic acid pearlescent film and preparation and application thereof

Abstract

The application belongs to the technical field of polymer material processing and preparation, and discloses a degradable polylactic acid pearlescent film and a preparation and application thereof.The degradable polylactic acid pearlescent film comprises 1-3 layers, and each layer independently comprises the following components by mass fraction: 100 parts of polylactic acid, 0-1 parts of an antioxidant, and 0-1 parts of a functional additive.The degradable polylactic acid pearlescent film is obtained by extruding granulation, casting a sheet, and bidirectional stretching.The polylactic acid pearlescent film is synchronously or asynchronously bidirectionally stretched at a stretching temperature of 65-85 DEG C and a stretching ratio of 3-5, a large number of mesophase is induced to form, the light transmittance of the polylactic acid is greatly reduced, and the polylactic acid pearlescent film has high glossiness of the pearlescent effect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polymer material processing and preparation, and particularly relates to a degradable polylactic acid pearlescent film and a preparation and application thereof. BACKGROUND

[0002] Pearlescent film is widely used in various packaging materials due to its unique pearlescent effect. At present, the main method for preparing pearlescent film on the market is to use polypropylene (PP) as raw material, add calcium carbonate and inorganic fillers such as pearlescent pigment, and then extrude and stretch bidirectionally to form the film. Stretching can form countless uniform cavities, when light enters the cavities, interference occurs, and multiple interference lights finally form a pearlescent effect.

[0003] However, polypropylene is a non-degradable material, and its use will cause serious environmental problems. According to the "Opinions on Further Strengthening the Governance of Plastic Pollution" issued by the National Development and Reform Commission and the Ministry of Ecology and Environment in January 2020, it is required to gradually limit the use of disposable non-degradable plastics by 2025. Traditional pearlescent film used for packaging or decoration is mainly prepared from non-degradable polypropylene resin, which takes more than 200 years to degrade under natural conditions, and is basically not recyclable, which is one of the main components of white pollution.

[0004] In recent years, with the emphasis on environmental protection, biodegradable materials have developed rapidly. Among them, polylactic acid (PLA) is a relatively mature biodegradable resin, which is derived from renewable natural resources, has good biocompatibility, mechanical strength and transparency, and is abundant in raw materials and renewable. It is considered as the most promising biodegradable plastic, which can be used to replace polypropylene and polyethylene to prepare packaging materials. Chinese patent publication CN102453319A provides a polylactic acid biaxially stretched frosted film, which comprises the following components blended: 100 parts by weight of polylactic acid resin, 0.2-10 parts of modification aid; after melt blending and granulation of each component, the film is obtained by casting and pressing, and then biaxial stretching at a higher temperature. The polylactic acid biaxially stretched frosted film has a pearlescent luster and a frosted texture, a light transmittance ≥93%, a haze ≥70%, and a surface gloss ≤10, and can be used for packaging and film pasting. However, the modification aid added in the formula is an oily substance with low molecular weight, which is easy to precipitate from the inside to the surface of the film, and there is a hidden danger of contamination of the contacted objects during the use of the film. Chinese patent publications CN112976735A and CN114106535A use PLA and PBAT to prepare degradable pearlescent film by adding a large amount of inorganic fillers such as calcium carbonate and titanium dioxide. However, the above methods all obtain the pearlescent effect by adding pearlescent fillers, and a large amount of pearlescent fillers not only need to consider the toxicity and cost of the fillers, but also will reduce the strength of polylactic acid. SUMMARY

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary purpose of the present application is to provide a degradable polylactic acid pearlescent film.

[0006] Another purpose of the present application is to provide a preparation method of the above-mentioned degradable polylactic acid pearlescent film.

[0007] Still another purpose of the present application is to provide an application of the above-mentioned degradable polylactic acid pearlescent film in packaging materials.

[0008] The purposes of the present application are achieved by the following solutions:

[0009] A degradable polylactic acid pearlescent film comprises 1-3 layers, each layer independently comprising the following components by mass fraction:

[0010] 100 parts of polylactic acid,

[0011] 0-1 parts of antioxidant,

[0012] 0-1 parts of functional aid.

[0013] The molecular weight of the polylactic acid is 100-250,000; the melt index of the polylactic acid is MFR=6-7 g / 10 min (210°C, 2.16 Kg); and the molar content of D-lactic acid is 1.4-12%.

[0014] The antioxidant comprises at least one of phosphite antioxidants and hindered phenolic antioxidants; and is preferably at least one of YIPHOS2010, YIPHOS2012, YIPHOS2013, YIPHOS2103, YIPHOS2105, YIPHOS3010, YIPHOS3019, antioxidant 1010, and antioxidant 2246.

[0015] The functional aid comprises at least one of antibacterial agents and antistatic agents.

[0016] The antibacterial agent is at least one of KP-J81, inorganic metal ion antibacterial agent; and the antistatic agent is at least one of Basionics LQ 01 and Irgastat P18 of BASF.

[0017] The degradable polylactic acid pearlescent film contains a mesogen; and the molar content of the mesogen is 8-12%.

[0018] The preparation method of the above-mentioned degradable polylactic acid pearlescent film comprises the following steps:

[0019] (1) Polylactic acid, antioxidant, and functional aid are weighed according to the formula, extruded and granulated, and cast into a thick sheet;

[0020] (2) the thick sheet obtained in step (1) is subjected to bidirectional stretching to obtain the degradable polylactic acid pearlescent film.

[0021] The polylactic acid in step (1) is dried at 50-80℃ for 5-12h before weighing.

[0022] The extrusion granulation in step (1) is specifically as follows: the polylactic acid, antioxidant and functional additive are extruded and granulated through a double-screw extruder, and the temperature of each section of the double-screw extruder is 155-170℃.

[0023] The casting sheet in step (1) is specifically as follows: the granulated product is sent into a screw extruder, melted and plasticized at 155-170℃, and then enters the independent flow channel of the die, and the casting sheet is obtained at 25-55℃; when the degradable polylactic acid pearlescent film is 1 layer, a single-layer casting thick sheet is obtained after casting sheet; when the degradable polylactic acid pearlescent film is 2-3 layers, a multi-layer co-extruded casting thick sheet is obtained after casting sheet.

[0024] The screw extruder used is a three-layer co-extrusion casting film machine; the speed ratio of the fixed roller and the traction roller in the casting process is controlled to be 1:1-0.9:1, and the screw rotation speed of the screw extruder is 30-80r / min.

[0025] The bidirectional stretching in step (2) is synchronous bidirectional stretching or asynchronous bidirectional stretching; the stretching temperature is 65-85℃, the transverse and longitudinal stretching ratios are independently 3-5, and the holding time is 30-60s; the heat setting temperature is 60-85℃, and the setting time is 2-10s.

[0026] The above degradable polylactic acid pearlescent film is applied in packaging materials.

[0027] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0028] The polylactic acid pearlescent film of the present application is induced to form a large number of mesophases through synchronous or asynchronous bidirectional stretching at a stretching temperature of 65-85℃ and a stretching ratio of 3-5, which greatly reduces the light transmittance of the polylactic acid and has high glossiness of the pearlescent effect; at the same time, the prepared polylactic acid pearlescent film has high transverse and longitudinal tensile strength and elongation at break; no pearl pigment or other additives are added in the present technology, which reduces the cost and eliminates the influence on the mechanical properties; the prepared film is completely biodegradable, the preparation technology is continuous, the process is simple, safe and environmentally friendly, and the prepared film can be widely applied in the packaging field of food, medicine and decorations. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 DSC curves of Examples 6-8 and Comparative Example 2. DETAILED DESCRIPTION

[0030] The present application will be further described in detail by the following examples and drawings, but the embodiments of the present application are not limited thereto. The specific conditions not mentioned in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0031] The reagents used in the examples are all commercially available unless otherwise specified.

[0032] The parts involved in the following examples and comparative examples are all parts by weight, wherein 1 part = 100 g.

[0033] Examples 1-12 and Comparative Examples 1-3:

[0034] (I) Preparation method

[0035] The polylactic acid was dried at 80°C in a forced air drying oven for 5 h, and the raw materials of each layer were extruded and granulated through a twin-screw extruder according to the formulation of Table 1, with the temperature of each section of the twin-screw extruder being 155-170°C. After extrusion and granulation, they were respectively sent into the respective mixing hoppers for uniform mixing, and then respectively sent into different screw extruders of a three-layer co-extrusion casting film machine, melted and plasticized at 155-170°C, and then entered into the respective independent flow channels of the die, and cast into pieces at 55°C, so as to obtain a multi-layer co-extruded thick piece. The speed ratio of the fixed roller and the traction roller was controlled to be 1:1-0.9:1 during the casting process, the screw rotation speed of the screw extruder was 30-80 r / min, and the obtained thick piece was bidirectionally stretched to obtain a degradable polylactic acid pearlescent film with a thickness of 40 μm.

[0036] The parameters of the bidirectional stretching process of each example and comparative example are shown in Table 2.

[0037] (II) Test method:

[0038] (1) Crystallinity: The test method of crystallinity uses a differential scanning calorimeter, and adopts the method of ASTM E-793-95;

[0039] (2) Tensile strength and elongation at break: The mechanical properties use a universal mechanical testing machine, and adopt the method of GB / T 1040-2006;

[0040] (3) Visible light transmittance: A light transmittance and haze tester is used, and the test is carried out according to the method of GB / T 2410-2008;

[0041] (4) Gloss: A specular glossmeter is used, and the test is carried out according to the method of GB / 8807 plastic specular gloss test.

[0042] The properties of the degradable polylactic acid pearlescent film obtained in each example and comparative example are shown in Table 3.

[0043] Table 1 Formulation of examples

[0044]

[0045] In Table 1, PLA1 is produced by naturewors, USA, with the trade name 4060d, and the molecular weight is 180,000; the melt index of polylactic acid is MFR = 7 g / 10 min (210°C / 2.16 Kg); and the molar content of D-lactic acid is 8%; PLA2 is produced by naturewors, USA, with the trade name 4032d, and the molecular weight is 200,000; the melt index of polylactic acid is MFR = 6 g / 10 min (210°C / 2.16 Kg); and the molar content of D-lactic acid is 2%; PLA3 is produced by Zhejiang Haizheng, with the trade name revode 110, and the molecular weight is 188,000; the melt index of polylactic acid is MFR = 6 g / 10 min (210°C / 2.16 Kg); and the molar content of D-lactic acid is 4%.

[0046] The antioxidant is antioxidant 1010; the antibacterial agent is KP-J81; and the antistatic agent is Basionics LQ 01.

[0047] Table 2: Stretch film forming process

[0048]

[0049]

[0050] In Table 2, the formula of Comparative Example 1 is the same as that of Example 1; the formula of Comparative Example 2 is the same as that of Example 5; and the formula of Comparative Example 3 is the same as that of Example 9.

[0051] Table 3: Film properties of examples and comparative examples

[0052]

[0053]

[0054] As shown in Table 3, the polylactic acid films prepared in Examples 1-12 form a large number of mesogens, and the transverse and longitudinal tensile strengths of the films are both greater than 100 MPa, the transverse and longitudinal elongation at break is greater than 100%, the haze is greater than 50%, the gloss is all greater than 80%, and the films have good pearlescent effect. However, the polylactic acid films prepared in Comparative Examples 1-3 do not form mesogens and have no pearlescent effect.

[0055] As shown in Table 3, the polylactic acid films prepared in Examples 1-12 form a large number of mesogens, and the transverse and longitudinal tensile strengths of the films are both greater than 100 MPa, the transverse and longitudinal elongation at break is greater than 100%, the haze is greater than 50%, the gloss is all greater than 80%, and the films have good pearlescent effect. However, the polylactic acid films prepared in Comparative Examples 1-3 do not form mesogens and have no pearlescent effect. Figure 1As shown, the DSC curves of Example 6, Example 7, and Example 8 all have obvious exothermic peaks after the glass transition temperature, which indicates that the mesogenic phase is formed in Example 6, 7, and 8. However, the DSC curves of Comparative Example 2-1, Comparative Example 2-2, and Comparative Example 2-3 all do not have obvious exothermic peaks after the glass transition temperature, which also indicates that the mesogenic phase is not formed.

[0056] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and all are included in the protection scope of the present application.

Claims

1. A degradable polylactic acid pearlescent film comprising 1-3 layers, characterized in that, Each layer independently comprises the following components by mass fraction: 100 parts of polylactic acid, 0-1 parts of antioxidant, 0-1 parts of functional additive; The degradable polylactic acid pearlescent film contains mesogens; the molar content of mesogens is 8-12%; The preparation method of the polylactic acid pearlescent film comprises the following steps: (1) Polylactic acid, antioxidant and functional additive are weighed according to the formula, extruded and granulated, and cast into a thick sheet; (2) The thick sheet obtained in step (1) is biaxially stretched to obtain a degradable polylactic acid pearlescent film; The biaxial stretching in step (2) is synchronous biaxial stretching or asynchronous biaxial stretching; wherein the stretching temperature is 65-85℃, the transverse and longitudinal stretching ratio is independently 3-4, and the holding time is 30-60s; the heat setting temperature is 60-85℃, and the setting time is 2-10s.

2. The degradable polylactic acid pearlescent film according to claim 1, wherein: The molecular weight of the polylactic acid is 100-250w; the melt index MFR of the polylactic acid at 210℃ / 2.16Kg is 6-7g / 10min; wherein the molar content of D-lactic acid is 1.4-12%.

3. The degradable polylactic acid pearlescent film of claim 1, wherein: The antioxidant comprises at least one of phosphite antioxidant and hindered phenolic antioxidant.

4. The degradable polylactic acid pearlescent film of claim 3, wherein: The antioxidant is at least one of YIPHOS2010, YIPHOS2012, YIPHOS2013, YIPHOS2103, YIPHOS2105, YIPHOS3010, YIPHOS3019, antioxidant 1010 and antioxidant 2246.

5. The degradable polylactic acid pearlescent film according to claim 1, wherein: The functional additive comprises at least one of antibacterial agent and antistatic agent; Wherein, the antibacterial agent is at least one of KP-J81 and metal ion antibacterial agent; the antistatic agent is at least one of Basf's Basionics LQ 01 and Irgastat P18.

6. The degradable polylactic acid pearlescent film according to claim 1, wherein: In step (1), the polylactic acid is dried at 50-80℃ for 5-12h before weighing; In step (1), the extrusion granulation is specifically: the polylactic acid, antioxidant and functional additive are extruded and granulated through a twin-screw extruder, and the temperature of each section of the twin-screw extruder is 155-170℃.

7. The degradable polylactic acid pearlescent film of claim 1, wherein: In step (1), the cast sheet is specifically: the granulated product is sent into a screw extruder, melted and plasticized at 155-170℃, then enters the independent flow channel of the die, and the cast sheet is obtained at 25-55℃; when the degradable polylactic acid pearlescent film is 1 layer, a single-layer cast thick sheet is obtained after casting; when the degradable polylactic acid pearlescent film is 2-3 layers, a multi-layer co-extruded cast thick sheet is obtained after casting; Wherein, the screw extruder used is a three-layer co-extrusion cast film machine; the speed ratio of the fixed roller and the traction roller in the casting process is controlled to be 1:1-0.9:1, and the screw rotation speed of the screw extruder is 30-80r / min.

8. The degradable polylactic acid pearlescent film according to any one of claims 1-7 for use in packaging materials.

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