Polylactic acid heat shrink film and preparation method thereof

Abstract

The invention discloses a polylactic acid heat shrink film and a preparation method thereof, and the polylactic acid heat shrink film is prepared by melt blending and biaxial stretching of the following raw materials: 86-92 parts by weight of a polylactic acid modified material, 4-6 parts by weight of a blend of poly (adipic acid) / butylene terephthalate, polycarbonate and poly (butylene succinate), 1-2 parts by weight of poly (adipic acid)-1, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate), 1-2 parts by weight of a compatilizer, 1-2 parts by weight of an antioxidant and 1-2 parts by weight of a lubricant. The composite material is prepared from the following components in parts by weight: 1 to 3 parts of 1, 2-propylene glycol ester, 1.5 to 3 parts of nano organic modified montmorillonite, 0.5 to 1 part of nano silicon dioxide, 2 to 4 parts of bio-based citrate plasticizer, 0.5 to 0.8 part of polymeric epoxy functionalized chain extender, and 0.3 to 0.6 part of hindered phenol antioxidant. Through blending modification of the raw materials and accurate regulation and control of the processing technology, the contradiction between the brittleness and the thermal shrinkage performance of the polylactic acid film is solved, and meanwhile the polylactic acid film has good mechanical performance and high barrier performance.

Description

A polylactic acid heat shrink film and its preparation method Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a polylactic acid heat shrink film with excellent heat shrinkage properties, mechanical properties and barrier properties, and its preparation method. Background Technology

[0002] Traditional petroleum-based plastic films (such as PET and PVC) suffer from problems such as non-degradability and environmental pollution. While polylactic acid (PLA), as a biodegradable material, offers environmental advantages, it suffers from drawbacks such as high brittleness and poor thermal stability. Existing technologies can improve PLA performance through blending modification of raw materials, but problems such as imprecise shrinkage control and insufficient barrier properties remain. This invention achieves the preparation of high-performance polylactic acid heat-shrinkable films through material modification and processing optimization. Summary of the Invention

[0003] In view of this, the present invention provides a polylactic acid heat shrink film and its preparation method. By blending and modifying the raw materials and precisely controlling the processing technology, the contradiction between the brittleness and heat shrinkability of polylactic acid film is resolved. At the same time, it also has good mechanical properties and high barrier properties. Its biodegradability meets the requirements of sustainable development. The processing technology is compatible with existing plastic processing equipment and has high industrialization value.

[0004] The technical solution of this invention is as follows:

[0005] A polylactic acid heat-shrinkable film is prepared by melt blending and biaxial stretching of the following raw materials: 86-92 parts by weight of modified polylactic acid, 4-6 parts by weight of a blend of poly(butylene adipate / terephthalate), polycarbonate, and polybutylene succinate, 1-3 parts by weight of poly(1,2-propanediol adipate), 1.5-3 parts by weight of nano-organic modified montmorillonite, 0.5-1 parts by weight of nano-silica, and 2-4 parts by weight of bio-based citrate plasticizer. The polymeric epoxy functionalized chain extender comprises 0.5-0.8 parts by weight, and the phenolic antioxidant comprises 0.3-0.6 parts by weight; the polylactic acid modified material is a polyracemic lactic acid prepolymer with a number average molecular weight of 5000-7000 g / mol, a poly-L-lactic acid prepolymer with a number average molecular weight of 3000-5000 g / mol, and polycaprolactone with a number average molecular weight of 3500-5000 g / mol, which are prepared by using the polymeric epoxy functionalized chain extender.

[0006] More preferably, in the polylactic acid modified material, the polyracemic lactic acid prepolymer is 70-80 parts by weight, the poly-L-lactic acid prepolymer is 8-12 parts by weight, and the polycaprolactone is 20-30 parts by weight; the crystallinity of the polylactic acid modified material is 10-20%, and the number average molecular weight is 120,000-150,000 g / mol.

[0007] More preferably, the poly(butylene adipate), polycarbonate, and polybutylene succinate blend are blended in a weight ratio of 1:1:2.

[0008] More preferably, the nano-silica has a particle size of 30-60 nm; the nano-silica is surface modified by a silane coupling agent of grade KH-550.

[0009] More preferably, the polymeric epoxy functionalized chain extender is designated KL-E4370 and is used for molecular chain crosslinking.

[0010] More preferably, the phenolic antioxidant is BHT.

[0011] More preferably, the bio-based citrate plasticizer is tributyl acetylcitrate.

[0012] A method for preparing a polylactic acid heat-shrinkable film includes the following steps:

[0013] Step 1: The components according to the formula ratio are fed into a twin-screw extruder for melt blending and extrusion. After extrusion, the melt flows into the T-die and flows out of the die.

[0014] Step 2: The melt flowing out of the die head is rapidly cooled and cast into sheets, and then subjected to biaxial stretching to obtain polylactic acid heat shrink film.

[0015] The temperature of the melt blending is controlled by four zones: Zone 1 is 140-150℃ (raw material melting), Zone 2 is 160-170℃ (raw material dispersion), Zone 3 is 165-175℃ (chain extension reaction), and Zone 4 is 170-180℃ (homogenization); the screw speed is 200-300 r / min;

[0016] The biaxial stretching process employs a gradient temperature stretching process: a biaxial synchronous stretching method is used, controlling the longitudinal to transverse stretching ratio to be 1:4 to 1:5; a three-level temperature gradient is set: preheating zone: 60-80℃ (to eliminate internal stress), stretching zone: 85-100℃ (to trigger molecular chain orientation), and shaping zone: 60-90℃ (to fix the crystal structure).

[0017] The beneficial effects of this invention are as follows: This invention successfully prepares a polylactic acid heat-shrinkable film with excellent comprehensive properties through the synergistic effect of polylactic acid modified materials and blends of poly(butylene adipate / terephthalate), polycarbonate, and polybutylene succinate, combined with the composite reinforcement of nano-silica and nano-organically modified montmorillonite, and precise control of the gradient temperature biaxial stretching process. This shrinkable film maintains its biodegradable characteristics while significantly improving its heat shrinkage performance, mechanical properties, and barrier properties. Furthermore, through crosslinking with polymeric epoxy functionalized chain extenders and optimization with bio-based citrate plasticizers during processing, it achieves a balance between environmental friendliness and practicality, and can be widely used in food and daily necessities packaging, as well as electronic component encapsulation. Detailed Implementation

[0018] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0019] Example 1

[0020] A polylactic acid heat-shrinkable film is prepared by melt blending and biaxial stretching of the following raw materials: 86 parts by weight of polylactic acid modified material, 4 parts by weight of a blend of poly(butylene adipate / terephthalate), polycarbonate, and poly(butylene succinate), 1 part by weight of poly(1,2-propanediol adipate), 1.5 parts by weight of nano-organic modified montmorillonite, 0.5 parts by weight of nano-silica, 2 parts by weight of bio-based citrate plasticizer, 0.5 parts by weight of polymeric epoxy functionalized chain extender, and 0.3 parts by weight of phenolic antioxidant; the polylactic acid modified material is a polyracemic lactic acid prepolymer with a number average molecular weight of 5000 g / mol, a poly(L-lactic acid) prepolymer with a number average molecular weight of 3000 g / mol, and polycaprolactone with a number average molecular weight of 3500 g / mol, prepared by polymeric epoxy functionalized chain extender.

[0021] In the polylactic acid (PLA) modified material, 70 parts by weight of polyracemic lactic acid prepolymer, 8 parts by weight of poly-L-lactic acid prepolymer, and 20 parts by weight of polycaprolactone are present. The crystallinity of the PLA modified material is 10%, and the number average molecular weight is 120,000 g / mol. A blend of poly(butylene adipate / terephthalate), polycarbonate, and polybutylene succinate is blended in a weight ratio of 1:1:2. The particle size of the nano-silica is 30 nm. The nano-silica is surface modified using a silane coupling agent of grade KH-550. The polymeric epoxy functionalized chain extender of grade KL-E4370 is used for molecular chain crosslinking. The phenol-inhibiting antioxidant is BHT. The bio-based citrate plasticizer is tributyl acetylacetonate.

[0022] A method for preparing a polylactic acid heat-shrinkable film includes the following steps:

[0023] Step 1: The components according to the formula ratio are fed into a twin-screw extruder for melt blending and extrusion. After extrusion, the melt flows into the T-die and flows out of the die.

[0024] Step 2: The melt flowing out of the die head is rapidly cooled and cast into sheets, and then subjected to biaxial stretching to obtain polylactic acid heat shrink film.

[0025] The temperature of the melt blending is controlled by four zones: zone 1 is 145℃, zone 2 is 165℃, zone 3 is 165℃, and zone 4 is 175℃; the screw speed is 250 r / min.

[0026] The biaxial stretching process adopts a gradient temperature stretching process: the biaxial synchronous stretching method is used, and the longitudinal: transverse stretching ratio is controlled to be 1:4; three temperature gradients are set: preheating zone: 70℃, stretching zone: 90℃, and setting zone: 60℃.

[0027] Example 2

[0028] A polylactic acid heat-shrinkable film is prepared by melt blending and biaxial stretching of the following raw materials: 92 parts by weight of polylactic acid modifier, 6 parts by weight of a blend of poly(butylene adipate / terephthalate), polycarbonate, and poly(butylene succinate), 3 parts by weight of poly(1,2-propanediol adipate), 3 parts by weight of nano-organic modified montmorillonite, 1 part by weight of nano-silica, 4 parts by weight of bio-based citrate plasticizer, 0.8 parts by weight of polymeric epoxy functionalized chain extender, and 0.6 parts by weight of phenolic antioxidant; the polylactic acid modifier is a polyracemic lactic acid prepolymer with a number average molecular weight of 7000 g / mol, a poly(L-lactic acid) prepolymer with a number average molecular weight of 5000 g / mol, and polycaprolactone with a number average molecular weight of 5000 g / mol, prepared by polymeric epoxy functionalized chain extender.

[0029] In the polylactic acid (PLA) modified material, 80 parts by weight of polyracemic lactic acid prepolymer, 12 parts by weight of poly-L-lactic acid prepolymer, and 30 parts by weight of polycaprolactone are present. The crystallinity of the PLA modified material is 20%, and the number average molecular weight is 150,000 g / mol. A blend of poly(butylene adipate / terephthalate), polycarbonate, and polybutylene succinate is blended in a weight ratio of 1:1:2. The particle size of the nano-silica is 60 nm. The nano-silica is surface modified using a silane coupling agent of grade KH-550. The polymeric epoxy functionalized chain extender of grade KL-E4370 is used for molecular chain crosslinking. The phenol-inhibiting antioxidant is BHT. The bio-based citrate plasticizer is tributyl acetylacetonate.

[0030] The preparation method of the polylactic acid heat shrink film is the same as that in Example 1.

[0031] Comparative Example 1

[0032] The polylactic acid modifier in the heat-shrinkable film raw material of Example 1 was replaced with L-polylactic acid with a molecular weight of 120,000 g / mol. The remaining raw materials and preparation method remained unchanged.

[0033] Comparative Example 2

[0034] The polybutylene adipate / terephthalate, polycarbonate, polybutylene succinate blend, polymeric epoxy functionalized chain extender, and bio-based citrate plasticizer were removed from the heat shrink film raw material of Example 1. The remaining raw materials and preparation method remained unchanged.

[0035] Comparative Example 3

[0036] The nano-organic modified montmorillonite in the heat shrink film raw material of Example 1 was removed. The remaining raw materials and preparation method remained unchanged.

[0037] The thin films prepared in each embodiment and comparative example were subjected to performance tests. The test items and test standards are shown in Table 1, and the test results are shown in Table 2.

[0038] Table 1 Thin Film Test Items and Test Standards

[0039]

[0040] Table 2 Thin Film Test Results

[0041]

[0042] As shown in Table 2, compared with the comparative example, the polylactic acid heat shrink film obtained by the technical solution of the embodiment has good tensile strength and heat shrinkage rate, as well as high barrier properties (oxygen permeability and water vapor permeability), high transparency and low haze. The polylactic acid heat shrink film of the present invention is prepared by a biaxial stretching process, resulting in a beautiful film appearance and strong functionality; it uses degradable raw materials, saving energy and protecting the environment.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art can make various improvements and modifications to the present invention without departing from its technical principles, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A polylactic acid heat-shrinkable film, characterized in that, It is prepared by melt blending and biaxial stretching of the following raw materials: 86-92 parts by weight of polylactic acid modified material, 4-6 parts by weight of poly(butylene adipate / terephthalate), polycarbonate, and polybutylene succinate blend, 1-3 parts by weight of poly(1,2-propanediol adipate), 1.5-3 parts by weight of nano-organic modified montmorillonite, 0.5-1 parts by weight of nano-silica, 2-4 parts by weight of bio-based citrate plasticizer, and polymeric epoxy resin. The functionalized chain extender is 0.5-0.8 parts by weight, and the phenolic antioxidant is 0.3-0.6 parts by weight; the polylactic acid modified material is a polyracemic lactic acid prepolymer with a number average molecular weight of 5000-7000 g / mol, a poly-L-lactic acid prepolymer with a number average molecular weight of 3000-5000 g / mol, and polycaprolactone with a number average molecular weight of 3500-5000 g / mol, which is prepared by using a polymeric epoxy functionalized chain extender.

2. The polylactic acid heat-shrinkable film according to claim 1, characterized in that, In the polylactic acid modified material, the polyracemic lactic acid prepolymer is 70-80 parts by weight, the poly-L-lactic acid prepolymer is 8-12 parts by weight, and the polycaprolactone is 20-30 parts by weight; the crystallinity of the polylactic acid modified material is 10-20%, and the number average molecular weight is 120,000-150,000 g / mol.

3. The polylactic acid heat-shrinkable film according to claim 2, characterized in that, The blend of poly(butylene adipate / terephthalate), polycarbonate, and polybutylene succinate is blended in a weight ratio of 1:1:

2.

4. The polylactic acid heat-shrinkable film according to claim 1, characterized in that, The nano-silica has a particle size of 30-60 nm; the nano-silica is surface modified by a silane coupling agent of grade KH-550.

5. The polylactic acid heat-shrinkable film according to claim 4, characterized in that, The polymeric epoxy functionalized chain extender is designated KL-E4370.

6. The polylactic acid heat-shrinkable film according to claim 5, characterized in that, The phenol-resistant antioxidant is BHT.

7. The polylactic acid heat-shrinkable film according to claim 6, characterized in that, The bio-based citrate plasticizer is tributyl acetylcitrate.

8. The method for preparing a polylactic acid heat-shrinkable film according to claim 1, characterized in that, Includes the following steps: Step 1: The components according to the formula ratio are fed into a twin-screw extruder for melt blending and extrusion. After extrusion, the melt flows into a T-die and exits from the die. Step 2: The melt exiting from the die is rapidly cooled and cast into sheets, and then subjected to biaxial stretching to obtain a polylactic acid heat shrink film. The temperature of the melt blending is controlled by four zones: Zone 1 is 140-150℃, Zone 2 is 160-170℃, Zone 3 is 165-175℃, and Zone 4 is 170-180℃. The screw speed is 200-300 r / min. The biaxial stretching adopts a gradient temperature stretching process: a biaxial synchronous stretching method is used, and the longitudinal: transverse stretching ratio is controlled to be 1:4 to 1:

5. Three temperature gradients are set: preheating zone: 60-80℃, stretching zone: 85-100℃, and setting zone: 60-90℃.

Images