A PLA / PCL / rubber heat shrinkable film based on dynamic vulcanization technology and its preparation method

Abstract

The present invention discloses a PLA / PCL / rubber heat shrinkable film based on dynamic vulcanization technology and its preparation method. According to parts by mass, the raw material ratio is composed of: 60-80 parts of polylactic acid, 10-20 parts of polycaprolactone, 3-20 parts of rubber, 0.2-2 parts of antioxidant, and 0.015-0.6 parts of cross-linking agent. During preparation, the raw materials are dynamically vulcanized in a twin-screw extruder to make a PLA / PCL / rubber TPV masterbatch, and then the masterbatch is blown into a film with heat shrinkage performance in a single-screw film blowing machine. The phase state of the PLA / PCL / rubber composite film is a bicontinuous phase, and both rubber and PLA are continuous three-dimensional network structures. The three-dimensional network structure of the cross-linked rubber gives the film excellent heat shrinkage performance. The PLA / PCL / rubber film prepared by the present invention has high tensile strength, elongation at break, excellent heat shrinkage performance and degradable characteristics.

Description

Technical Field

[0001] The invention belongs to the field of PLA composite film preparation, and particularly relates to a PLA / PCL / rubber heat shrinkable film based on dynamic vulcanization technology and a preparation method thereof. Background Art

[0002] There are many different types of plastic packaging films, but the market demand for heat-shrinkable films is growing at an astonishing rate, making them a hot topic in the plastic packaging industry. Heat-shrinkable films are a type of polymer shape-memory film that shrinks by utilizing the transition between the stationary and reversible phases within the polymer. Currently, commonly used heat-shrinkable films include PVC, PE, PP, PVDC, OPS, and PET. However, heat-shrinkable films made from these materials are difficult to degrade, pose a significant threat to the environment, and are not in line with the concept of green and environmentally friendly development. Furthermore, these heat-shrinkable films typically utilize unidirectional and bidirectional stretching, resulting in complex manufacturing processes and high costs. Therefore, the industry urgently needs to develop a new type of heat-shrinkable film material that is both biodegradable and easy to process.

[0003] The biodegradability of polylactic acid (PLA) gives it enormous potential for application in a variety of fields, particularly packaging materials. In the production of packaging materials, blown film technology is widely popular due to its high production efficiency and ability to produce polymer films with excellent macroscopic properties. However, unmodified commercial PLA resins have low molecular chain entanglement, resulting in relatively low melt strength, making them difficult to stably blown into films. Furthermore, PLA's brittleness further limits its practicality in the plastics market. Precisely because of these issues, PLA has yet to replace petroleum-based polymers, such as low-density polyethylene (LDPE), which are currently widely used in blown film processes.

[0004] Chinese patent CN115891367A discloses a PBAT-PLA composite material and its application in a biodegradable heat-shrinkable film. The PBAT-PLA composite material is produced by three-layer co-extrusion blow molding, using PBAT as the inner and outer layers and PLA-crosslinked PBAT as the middle layer. The resulting biodegradable heat-shrinkable film exhibits excellent tensile properties and impact resistance. However, this invention utilizes a three-layer co-extrusion blow molding process to produce a heat-shrinkable film, resulting in a cumbersome production process and high costs. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a PLA / PCL / rubber heat shrinkable film based on dynamic vulcanization technology and a preparation method thereof, wherein the film has high strength, high ductility, and excellent heat shrinkage performance.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A PLA / PCL / rubber heat shrinkable film based on dynamic vulcanization technology and a preparation method thereof. The raw material ratio composition, calculated by mass, is: 60-80 parts of polylactic acid, 10-20 parts of polycaprolactone, 3-20 parts of rubber, 0.2-2 parts of antioxidant, and 0.015-0.6 parts of cross-linking agent.

[0008] Furthermore, the polylactic acid is one or more of poly-L-lactic acid, poly-D-lactic acid and racemic polylactic acid.

[0009] Furthermore, the rubber is one or more of natural rubber, epoxy natural rubber, and nitrile rubber.

[0010] Furthermore, the amount of the antioxidant is 0.2%-2% of the total mass of the rubber and plastic, and the antioxidant is one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant CA, antioxidant B900, antioxidant BHT, antioxidant 264, and antioxidant DLTP.

[0011] Furthermore, the crosslinking agent is a peroxide, and the amount of the peroxide is 0.5%-3% of the rubber mass; the peroxide is one or more of dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide and tert-butyl perbenzoate.

[0012] A method for preparing a PLA / PCL / rubber heat shrinkable film based on dynamic vulcanization technology comprises the following steps:

[0013] Step 1: First, mix polycaprolactone, rubber, cross-linking agent and antioxidant in an internal mixer and then crush them into small particles.

[0014] Step 2: melt-blending the blend obtained in step 1 with PLA in a twin-screw according to a certain ratio, and extruding and granulating to obtain a blown film masterbatch.

[0015] Step 3: Add the film blowing masterbatch obtained in step 2 into a single-screw film blowing machine, and blow-mold to obtain an ultra-tough PLA / PCL / rubber bio-based degradable film with heat shrinkage performance.

[0016] In the above method, the temperature of the internal mixer in step 1 is 60-110° C., and the blending time is about 3-10 minutes.

[0017] In the above method, in step 2, the temperature of the twin-screw extruder is 150° C.-190° C., and the screw speed is 50-400 r / min.

[0018] In the above method, in step 2, PLA, PCL and rubber are sheared and vulcanized under the action of a cross-linking agent to prepare a PLA / PCL / rubber TPV blown film masterbatch through dynamic vulcanization.

[0019] In the above method, in step 3, the temperature of the single-screw film blowing machine is 150° C.-180° C., and the screw speed is 50-400 r / min.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1) The present invention uses PCL and rubber as toughening agents for PLA. Under the synergistic effect of PCL and rubber, the brittleness of PLA can be effectively improved, and the PLA / PCL / rubber film has excellent tear strength and elongation at break.

[0022] 2) For blends, the compatibility between different phases directly impacts material performance. This invention uses peroxide as a crosslinking agent and employs dynamic vulcanization to prepare a PLA / PCL / rubber TPV blown film masterbatch. The peroxide not only decomposes to produce free radicals that initiate crosslinking of the rubber but also triggers a grafting reaction between the plastic and rubber, significantly improving interfacial compatibility between the plastic and rubber phases and imparting superior mechanical properties to the material.

[0023] 4) The PLA / PCL / rubber TPV material obtained by dynamic vulcanization in the present invention has a co-continuous phase structure, which can significantly improve the melt strength of the material and make the blow molding process more stable and efficient.

[0024] 5) The PLA / PCL / rubber TPV material obtained by dynamic vulcanization in the present invention has a co-continuous phase structure, that is, both PLA and cross-linked rubber are continuous phase structures, and the film obtained after the blown film forming process still has a co-continuous phase structure. Excellent heat shrinkage function can be achieved through a simple film blowing process, thereby avoiding the complex unidirectional and bidirectional stretching processes required for conventional heat shrinkable films. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope image of the PLA / PCL / rubber TPV blown film masterbatch in Example 4 after being etched with dichloromethane.

[0026] Figure 2 This is a scanning electron microscope image of the surface of the PLA / PCL / rubber film obtained in Example 4 after being etched with dichloromethane. DETAILED DESCRIPTION

[0027] The following examples and accompanying drawings provide a clear and complete description of the technical solutions in the embodiments of the present invention. However, the embodiments described herein represent only a portion of the present invention, not all of it. In both the examples and the comparative examples, PLA and PCL were dried in a 60°C oven for 8 hours before use, and the rubber was masticated on an open mill before use.

[0028] The raw materials and sources of the following reference examples and embodiments:

[0029] Polylactic acid (PLA) was selected as the matrix resin (REVODE 110, Zhejiang Hisun Biomaterials Co., Ltd.). PCL (Capa 6800) was purchased from Solvay, USA. Natural rubber was purchased from the Guangzhou Rubber Industry Research Institute. DCP was used as the crosslinker, and antioxidant 1010 was used as the antioxidant.

[0030] Comparative Example 1

[0031] 20 parts of PCL were added to a torque rheometer at 70°C and a rotor speed of 60 r / min. After melting, 0.2 parts of antioxidant 1010 were added. After mixing evenly, the PCL blend was discharged. The sample was crushed into fine particles using a crusher.

[0032] The PCL blend obtained in the above steps was mixed with 80 parts of PLA and then added to a twin-screw extruder for melt plasticization, blending, and extrusion pelletization to obtain a PLA / PCL blown film masterbatch. The twin-screw extruder parameters were as follows: zone 1 temperature of 130-160°C, zone 2 temperature of 170-180°C, zone 3 temperature of 180-190°C, zone 4 temperature of 180-185°C, and die head temperature of 180°C. The screw speed was 150 rpm.

[0033] The film blowing masterbatch was blown into a film by a single-screw film blowing machine to obtain a PLA / PCL blown film. The temperature of the single-screw film blowing machine was 165°C-175°C, and the head temperature was 170°C.

[0034] Comparative Example 2

[0035] 20 parts of PCL and 15 parts of natural rubber were added to a torque rheometer at 70°C and a rotor speed of 60 r / min. After mixing, 0.23 parts of antioxidant 1010 were added. After mixing, the PCL / natural rubber blend was discharged. The blend was crushed into fine particles using a crusher.

[0036] The PCL / natural rubber blend obtained in the above steps was mixed with 80 parts of PLA and then added to a twin-screw extruder for melt plasticization, blending, and extrusion pelletization to obtain a PLA / PCL / natural rubber blown film masterbatch. The twin-screw extruder parameters were: zone 1 temperature of 130-160°C, zone 2 temperature of 170-180°C, zone 3 temperature of 180-190°C, zone 4 temperature of 180-185°C, and die head temperature of 180°C. The screw speed was 150 rpm.

[0037] The film-blowing masterbatch is blown into a film through a single-screw film-blowing machine to obtain a PLA / PCL / rubber heat-shrinkable film based on dynamic vulcanization technology and a preparation method thereof. The temperature of the single-screw film-blowing machine is 165°C-175°C, and the head temperature is 170°C.

[0038] Example 1

[0039] 20 parts PCL and 3 parts natural rubber were added to a torque rheometer at 70°C and a rotor speed of 60 r / min. After mixing, 0.206 parts of antioxidant 1010 and 0.045 parts of crosslinker DCP were added. After mixing, the PCL / natural rubber blend was discharged. The blend was crushed into fine particles using a crusher.

[0040] The PCL / natural rubber blend obtained in the above steps was mixed with 80 parts of PLA and then added to a twin-screw extruder for melt plasticization, blending, dynamic vulcanization, and extrusion pelletization to produce a PLA / PCL / natural rubber blown film masterbatch. The twin-screw extruder parameters were: zone 1 temperature of 130-160°C, zone 2 temperature of 170-180°C, zone 3 temperature of 180-190°C, zone 4 temperature of 180-185°C, and die head temperature of 180°C. The screw speed was 150 rpm.

[0041] The film-blowing masterbatch is blown into a film through a single-screw film-blowing machine to obtain a PLA / PCL / rubber heat-shrinkable film based on dynamic vulcanization technology and a preparation method thereof. The temperature of the single-screw film-blowing machine is 165°C-175°C, and the head temperature is 170°C.

[0042] Example 2

[0043] 20 parts PCL and 5 parts natural rubber were added to a torque rheometer at 70°C and a rotor speed of 60 r / min. After mixing, 0.210 parts of antioxidant 1010 and 0.075 parts of crosslinker DCP were added. After mixing, the PCL / natural rubber blend was discharged. The blend was crushed into fine particles using a crusher.

[0044] The PCL / natural rubber blend obtained in the above steps was mixed with 80 parts of PLA and then added to a twin-screw extruder for melt plasticization, blending, dynamic vulcanization, and extrusion pelletization to produce a PLA / PCL / natural rubber blown film masterbatch. The twin-screw extruder parameters were: zone 1 temperature of 130-160°C, zone 2 temperature of 170-180°C, zone 3 temperature of 180-190°C, zone 4 temperature of 180-185°C, and die head temperature of 180°C. The screw speed was 150 rpm.

[0045] The film-blowing masterbatch is blown into a film through a single-screw film-blowing machine to obtain a PLA / PCL / rubber heat-shrinkable film based on dynamic vulcanization technology and a preparation method thereof. The temperature of the single-screw film-blowing machine is 165°C-175°C, and the head temperature is 170°C.

[0046] Example 3

[0047] 20 parts PCL and 7 parts natural rubber were added to a torque rheometer at 70°C and a rotor speed of 60 r / min. After uniform mixing, antioxidant 1010 (0.214 parts) and crosslinker DCP (0.105 parts) were added. After uniform mixing, the PCL / natural rubber blend was discharged. The blend was crushed into fine particles using a crusher.

[0048] The PCL / natural rubber blend obtained in the above steps was mixed with 80 parts of PLA and then added to a twin-screw extruder for melt plasticization, blending, dynamic vulcanization, and extrusion pelletization to produce a PLA / PCL / natural rubber blown film masterbatch. The twin-screw extruder parameters were: zone 1 temperature of 130-160°C, zone 2 temperature of 170-180°C, zone 3 temperature of 180-190°C, zone 4 temperature of 180-185°C, and die head temperature of 180°C. The screw speed was 150 rpm.

[0049] The film-blowing masterbatch is blown into a film through a single-screw film-blowing machine to obtain a PLA / PCL / rubber heat-shrinkable film based on dynamic vulcanization technology and a preparation method thereof. The temperature of the single-screw film-blowing machine is 165°C-175°C, and the head temperature is 170°C.

[0050] Example 4

[0051] 20 parts PCL and 10 parts natural rubber were added to a torque rheometer at 70°C and a rotor speed of 60 r / min. After uniform mixing, 0.220 parts of antioxidant 1010 and 0.15 parts of crosslinker DCP were added. After uniform mixing, the PCL / natural rubber blend was discharged. The blend was crushed into fine particles using a crusher.

[0052] The PCL / natural rubber blend obtained in the above steps was mixed with 80 parts of PLA and then added to a twin-screw extruder for melt plasticization, blending, dynamic vulcanization, and extrusion pelletization to produce a PLA / PCL / natural rubber blown film masterbatch. The twin-screw extruder parameters were: zone 1 temperature of 130-160°C, zone 2 temperature of 170-180°C, zone 3 temperature of 180-190°C, zone 4 temperature of 180-185°C, and die head temperature of 180°C. The screw speed was 150 rpm.

[0053] The film-blowing masterbatch is blown into a film through a single-screw film-blowing machine to obtain a PLA / PCL / rubber heat-shrinkable film based on dynamic vulcanization technology and a preparation method thereof. The temperature of the single-screw film-blowing machine is 165°C-175°C, and the head temperature is 170°C.

[0054] Example 5

[0055] 20 parts PCL and 15 parts natural rubber were added to a torque rheometer at 70°C and a rotor speed of 60 r / min. After uniform mixing, 0.23 parts of antioxidant 1010 and 0.225 parts of crosslinker DCP were added. After uniform mixing, the PCL / natural rubber blend was discharged. The blend was crushed into fine particles using a crusher.

[0056] The PCL / natural rubber blend obtained in the above steps was mixed with 80 parts of PLA and then added to a twin-screw extruder for melt plasticization, blending, dynamic vulcanization, and extrusion pelletization to produce a PLA / PCL / natural rubber blown film masterbatch. The twin-screw extruder parameters were: zone 1 temperature of 130-160°C, zone 2 temperature of 170-180°C, zone 3 temperature of 180-190°C, zone 4 temperature of 180-185°C, and die head temperature of 180°C. The screw speed was 150 rpm.

[0057] The film-blowing masterbatch is blown into a film through a single-screw film-blowing machine to obtain a PLA / PCL / rubber heat-shrinkable film based on dynamic vulcanization technology and a preparation method thereof. The temperature of the single-screw film-blowing machine is 165°C-175°C, and the head temperature is 170°C.

[0058] The properties of the control example and the embodiment are shown in Table 1.

[0059] The tensile test is based on GB / T1040-2006 standard.

[0060] The calculation of thermal shrinkage is as follows:

[0061]

[0062] Where L0 is the length of the sample before shrinkage, and L is the length of the sample after shrinkage.

[0063] Table 1

[0064]

[0065] As can be seen from Table 1, the addition of rubber can significantly improve the elongation at break of the film, but it will also reduce the tensile strength of the film. As the amount of rubber gradually increases, the thermal shrinkage of the film is significantly improved. This is because the addition of rubber enables the film to form a cross-linked three-dimensional network structure, which provides the film with a strong restoring force, which makes the film have excellent thermal shrinkage properties. The thermal shrinkage of Example 5 with the addition of 15 parts of rubber reached more than 35% in both the transverse and longitudinal directions. Compared with the film without rubber added in Control Example 1, the thermal shrinkage performance is improved by about 12.5 times. It can be seen from the comparison between Control Example 2 and Example 5 that dynamic vulcanization technology can significantly improve the thermal shrinkage of the film. This is because the cross-linked rubber network has a stronger shrinkage recovery force.

[0066] Figure 1 This is a scanning electron microscope image of the PLA / PCL / rubber TPV blown film masterbatch after dichloromethane etching in Example 4. Since both PLA and PCL are etched by dichloromethane, the network structure observed in the SEM image is a rubber cross-linked network structure.

[0067] Figure 2 This is a scanning electron microscope image of the PLA / PCL / rubber film obtained in Example 4 after being etched with dichloromethane. As can be seen, the rubber phase in the film still exhibits a three-dimensional network structure. Therefore, the cocontinuous phase in the PLA / PCL / rubber material was not destroyed during the blown film forming process.

Claims

1. A polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology, characterized in that: The raw material ratio is as follows: 60-80 parts of polylactic acid, 10-20 parts of polycaprolactone, 3-20 parts of rubber, 0.2-2 parts of antioxidant and 0.015-0.6 parts of cross-linking agent by weight; The cross-linking agent is a peroxide; the peroxide is one or more of dicumyl peroxide, di-tert-butyl diisopropyl peroxide, benzoyl peroxide, di-tert-butyl peroxide and tert-butyl perbenzoate.

2. The polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology according to claim 1, characterized in that: The polylactic acid is one or more of poly (L-lactic acid), poly (D-lactic acid) and racemic polylactic acid.

3. The polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology according to claim 1, characterized in that: The rubber is one or more of natural rubber, epoxidized natural rubber, and nitrile rubber.

4. The polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology according to claim 1, characterized in that: The antioxidant is one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant CA, antioxidant B900, antioxidant BHT, antioxidant 264, and antioxidant DLTP.

5. The method for preparing a polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Mix polycaprolactone, rubber, cross-linking agent and antioxidant in an internal mixer and crush them into granules; Step 2: melt blending the blend obtained in step 1 with polylactic acid in a twin-screw extruder, dynamically vulcanizing, and extruding into granules to obtain polylactic acid / polycaprolactone / rubber TPV blown film masterbatch; Step 3: Add the polylactic acid / polycaprolactone / rubber TPV film blowing masterbatch obtained in step 2 into a single-screw film blowing machine, and obtain a polylactic acid / polycaprolactone / rubber bio-based film with heat shrinkage properties by film blowing.

6. The method for preparing a polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology according to claim 5, characterized in that: In step 1, the temperature of the internal mixer is 60-110° C., and the blending time is 3-10 min.

7. The method for preparing a polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology according to claim 5, characterized in that: In step 2, the twin-screw extrusion temperature is 150° C.-190° C., and the screw speed is 50-400 r / min.

8. The method for preparing a polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology according to claim 5, characterized in that: In step 2, polylactic acid, polycaprolactone and rubber are sheared and vulcanized under the action of a cross-linking agent to prepare a polylactic acid / polycaprolactone / rubber TPV blown film masterbatch through dynamic vulcanization.

9. The method for preparing a polylactic acid / polycaprolactone / rubber heat shrinkable film based on dynamic vulcanization technology according to claim 5, characterized in that: In step 3, the temperature of the single-screw film blowing machine is 150° C.-180° C., and the screw speed is 50-400 r / min.

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