PLA (polylactic acid) and PPC (polypropylene carbonate) copolymerized biaxially oriented film and preparation method thereof

Abstract

The invention discloses a PLA (polylactic acid) and PPC (polypropylene carbonate) copolymerized biaxially oriented film and a preparation method thereof, and aims to solve the application problems of poor heat resistance, low strength, fragility, poor weather resistance, poor antibacterial ability, weak hydrophobic ability and the like of polylactic acid and solve the problem that in a copolymerized biaxially oriented process, the polylactic resin is poor in mechanical property due to roll sticking and fragility, low strength and polymerization molecular weight and poor mechanical property. The invention aims to solve the problems that a polylactic acid base material is easily subjected to film surface adhesion damage, tensile fracture, small width, insufficient smoothness and the like, and adverse effects on subsequent processing and application are caused, improve the formula of main and auxiliary extrusion stretching materials, and add PPC, antistatic master batch, inorganic filler, a folding-resistant modifier, a mixed accelerant, a lubricant and other formula auxiliary materials to improve the performance of the polylactic acid base material. Through a film two-way stretching process, the performance of polylactic resin is overcome, and industrial mass production of the mixed polymerization stretching film which is highly transparent, high in oxygen isolation capacity, harmless to environment, degradable and medium and long in service life is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a PLA and PPC copolymer biaxial stretching film and a preparation method thereof, and belongs to the technical field of material science and engineering. BACKGROUND

[0002] Polylactic acid (PLA) has been widely used in the fields of medicine and food packaging due to its unique biodegradability, biocompatibility, crystallinity, mechanical properties, transparency, and good oxygen barrier properties, and its application prospects are even broader with the deepening of the construction of a green and environmentally friendly society. However, the high brittleness and low heat resistance of polylactic acid seriously limit its performance in some applications.

[0003] In order to overcome the high brittleness and low heat resistance of polylactic acid (PLA), petroleum-based polymers and cellulose-based polymers are often used for modification to enhance its hydrophobicity and mechanical properties. However, the introduction of new groups often weakens the biodegradability and biocompatibility of polylactic acid film, affecting its advantages in the environmental protection field. Therefore, how to improve the molecular structure orientation of polylactic acid (PLA) while retaining its excellent biodegradability, or through new compounding schemes and biaxial stretching processes to improve the toughness, tensile strength, high barrier property, heat sealing performance, etc. of polylactic acid film, has become an urgent need for the development of polylactic acid resin and its products.

[0004] In order to improve the transparency and strength of polylactic acid film, Guangdong University of Technology developed a transparent polylactic acid film (patent number: CN201811554766.9). This patent provides a high levorotatory polylactic acid film based on natural raw materials and a casting film forming process, which achieves good elongation at break (150%~280%), tensile strength (220 MPa), and crystallinity (0%~8%), and has excellent transparency, biocompatibility, and degradation performance, achieving significant results.

[0005] In order to improve the antibacterial performance of polylactic acid film, China Petroleum Chemical Co., Ltd. developed an antibacterial biaxial stretching polylactic acid film (patent number: CN201010519986.5). This patent proposes the use of water-soluble polyguanidine inorganic acid salt as an antibacterial agent and applies it in a biaxial stretching process, and verifies its antibacterial effect before and after boiling. However, this patent does not provide a strength improvement scheme for biaxial stretching film.

[0006] To improve the weather resistance and water-repellent properties of polylactic acid (PLA) films, Fujian Changsu Industrial Co., Ltd. has developed a multi-layer co-extruded biaxially oriented barrier PLA film (patent number: CN202111506114.X). This patent provides a multi-layer co-extruded film stretching scheme consisting of a PLA resin surface layer, a PLA resin layer, an adhesive resin layer, an anti-adhesive agent, and a barrier layer. Oxygen barrier properties and strength are improved; however, this scheme requires sophisticated process equipment and control, making it unsuitable for manufacturing large-width films.

[0007] Analysis of the above patents and related technical solutions shows that there is a lack of an industrial solution for biaxial stretching film forming that can simultaneously improve the strength, transparency, and antibacterial properties of polylactic acid films and has large-width production capacity.

[0008] Polypropylene carbonate (PPC) is a fully biodegradable and environmentally friendly plastic synthesized from carbon dioxide and propylene oxide. It possesses excellent biodegradability, biocompatibility, impact resistance, transparency, non-toxicity, and superior barrier properties. Therefore, the melt-coating of PLA and PPC can effectively improve the flexibility and gas barrier properties of PLA while maintaining its biodegradability. In recent years, the application prospects of PLA and PPC as fully biodegradable materials in various fields have attracted attention.

[0009] Currently, only Beijing Technology and Business University and Tongji University have been granted patents related to PLA / PPC composite films. Tongji University's patent (patent number: CN201810072208.2) proposes a method for preparing PLA / PPC biodegradable composite films based on blown film technology, achieving a biodegradability rate of 94% and a tensile strength of 85 MPa. Although this method has achieved certain results in improving the biodegradability and strength of the material, its applicability to large-scale industrial production and its integration with biaxial stretching processes remain insufficient due to the use of blown film technology.

[0010] Based on the above technological developments and application cases, although various solutions have been proposed to improve the performance of polylactic acid (PLA) films through different formulations, there are still insufficient industry reports or patent authorizations for comprehensive solutions that simultaneously possess strength, transparency, antibacterial properties, and large-width biaxially stretched film formation capabilities for PLA films. With the increasing industrial demand, effectively combining the advantages of PLA and polypropylene carbonate composites and using biaxial stretching technology to overcome the performance bottlenecks of existing films has become crucial for improving the application performance of PLA films. Summary of the Invention

[0011] This invention relates to a biaxially oriented film modified from a blend of polylactic acid (PLA) and polypropylene carbonate (PPC) and its preparation method. The aim is to overcome many problems associated with PLA in practical applications, such as poor heat resistance, low strength, brittleness, poor weather resistance, poor hydrophobicity, and weak antibacterial ability. This invention improves the properties of the PLA substrate by adding polypropylene carbonate (PPC) and other auxiliary materials, such as antistatic masterbatch, inorganic fillers, folding modifiers, mixing accelerators, and lubricants, to the PLA resin. This results in excellent mechanical and processing properties during biaxial film stretching, meeting the demands of industrial mass production.

[0012] This invention is achieved through the following scheme: a PLA and PPC copolymer biaxially oriented film, the film comprising the following components: Biaxially oriented polylactic acid film (PLA), polypropylene carbonate (PPC), antibacterial agents, chain extenders, antistatic agents, flexural modifiers, lubricants, and inorganic fillers; The biodegradable resin comprises 200 parts by weight, consisting of polylactic acid resin (PLA) and polypropylene carbonate (PPC), with the specific composition as follows: Polylactic acid resin (PLA): 150-180 parts by weight; Polypropylene carbonate (PPC): 20-50 parts by weight.

[0013] The total weight of the excipients is 20-50 parts by weight, specifically including: Antibacterial agent: 2-6 parts by weight; Chain extender: 2-6 parts by weight; Antistatic agent: 5-10 parts by weight; Flexural strength modifier: 10-20 parts by weight; Lubricant: 10-20 parts by weight; Inorganic filler: 10-20 parts by weight.

[0014] The film is prepared by a biaxial stretching process with a width of 3 meters or more, and the resulting film has the following properties: Stretch film thickness: 5–100 μm; Biodegradation period: 1.5–3 years; Biodegradation rate: >94%; Tensile strength: 100–250 MPa; Elongation at break: 108–280%; Bacterial count per unit: ≤100 CFU / cm²; Transparency (light transmittance): >90%.

[0015] The mass ratio of polylactic acid resin (PLA) to polypropylene carbonate (PPC) is from 3:1 to 9:1.

[0016] The antibacterial agent is a water-soluble polyguanidine inorganic acid salt, the chain extender is polyvinyl alcohol, the antistatic agent is an inorganic or organosilicon compound, the lubricant is polytetrafluoroethylene or wax, and the inorganic filler is nano-sized silica, calcium carbonate, or talc.

[0017] A method for preparing a PLA and PPC copolymer biaxially oriented film, the preparation process includes the following steps: According to the above-mentioned mass ratio of components, polylactic acid resin (PLA), polypropylene carbonate (PPC) and auxiliary materials are mixed evenly to obtain a raw material mixture; the raw material mixture is melted and extruded through a melt blending process; the melt is prepared into a film through an extrusion die; the film is subjected to a wide-width (over 3 meters) biaxial stretching treatment; after the stretched film is cooled and cured, the final PLA and PPC copolymer biaxially stretched film is obtained.

[0018] The biaxial stretching ratio is 2 to 5 times.

[0019] The stretching process employs a combination of hot and cold stretching to optimize the mechanical and biodegradability of the film.

[0020] The final thickness of the film is between 5 μm and 100 μm, and can be adjusted according to actual needs.

[0021] The film surface has excellent antibacterial properties and can maintain a long-term antibacterial effect under different environments (such as humid heat, refrigeration, etc.).

[0022] The beneficial effects of this invention are as follows: 1. The addition of PPC improves the mechanical properties of polylactic acid film, resulting in biaxially oriented films with high strength, high toughness, and high transparency.

[0023] 2. The addition of antibacterial agents can effectively inhibit the growth of bacteria on the film surface, enhancing its application in fields such as medical and food packaging.

[0024] Oxygen barrier performance: PPC has excellent oxygen barrier performance, which effectively extends the medium and long-term service life of the film (200-300 days) and the stacking degradation time is 100-200 days.

[0025] 3. The film is recyclable and can be reused after depolymerization and polycondensation, which meets the requirements of sustainable development.

[0026] 4. The film of the present invention is applicable to multiple fields such as food packaging, fresh food isolation covering film and medical film, and has broad application prospects.

[0027] 5. The biaxial stretching process ensures uniform stress on the film during stretching, is suitable for a variety of stretching materials, and has similar process conditions to those for polypropylene film production, making it easy to achieve industrial production. Detailed Implementation

[0028] The present invention will be further described below, but the scope of protection of the present invention is not limited to the content described.

[0029] Example 1: Formulas with proportions within a relatively small range A biaxially oriented film modified by blending polylactic acid (PLA) and polypropylene carbonate (PPC) and its preparation method thereof, comprising the following components: 1. Polylactic acid (PLA): 150 parts by weight 2. Polypropylene carbonate (PPC): 20 parts by weight 3. Antibacterial agent: 2 parts by weight 4. Chain extender: 2 parts by weight 5. Antistatic agent: 5 parts by weight 6. Flexural strength modifier: 10 parts by weight 7. Lubricant: 10 parts by weight 8. Inorganic filler: 10 parts by weight The mass ratio is: PLA : PPC : Antibacterial agent : Chain extender : Antistatic agent : Flexural strength modifier : Lubricant : Inorganic filler = 150 : 20 : 2 : 2 : 5 : 10 : 10 : 10 In this embodiment, the mass ratio of polylactic acid to polypropylene carbonate is 150:20, and the proportion of auxiliary materials in the formulation is relatively low, mainly used to improve the antibacterial properties, mechanical properties, and processing performance of the film. Through biaxial stretching, the film maintains good transparency and antibacterial properties under high temperature and humidity changes, making it suitable for food packaging and medical films, and possessing a long service life and excellent oxygen barrier properties.

[0030] Example 2: Formulas with proportions within a wide range A biaxially oriented film modified by blending polylactic acid (PLA) and polypropylene carbonate (PPC) and its preparation method thereof, comprising the following components: 1. Polylactic acid (PLA): 180 parts by weight 2. Polypropylene carbonate (PPC): 50 parts by weight 3. Antibacterial agent: 6 parts by weight 4. Chain extender: 6 parts by weight 5. Antistatic agent: 10 parts by weight 6. Flexural strength modifier: 20 parts by weight 7. Lubricant: 20 parts by weight 8. Inorganic filler: 20 parts by weight The mass ratio is: PLA : PPC : Antibacterial agent : Chain extender : Antistatic agent : Flexural strength modifier : Lubricant : Inorganic filler = 180 : 50 : 6 : 6 : 10 : 20 : 20 : 20 In this embodiment, the mass ratio of polylactic acid to polypropylene carbonate is 180:50, with a relatively high proportion of auxiliary materials, which is used to further improve the strength, transparency, antibacterial properties, and weather resistance of the film. After biaxial stretching, the film exhibits extremely high transparency, high strength, and high toughness, and has a longer service life and stronger antibacterial properties, making it particularly suitable for long-term use and for medical and food packaging applications with high antibacterial requirements.

[0031] Example 3: Intermediate Value Formulation Example A biaxially oriented film modified by blending polylactic acid (PLA) and polypropylene carbonate (PPC) and its preparation method thereof, comprising the following components: 1. Polylactic acid (PLA): 165 parts by weight 2. Polypropylene carbonate (PPC): 35 parts by weight 3. Antibacterial agent: 4 parts by weight 4. Chain extender: 4 parts by weight 5. Antistatic agent: 7 parts by weight 6. Flexural strength modifier: 15 parts by weight 7. Lubricant: 15 parts by weight 8. Inorganic filler: 15 parts by weight The mass ratio is: PLA : PPC : Antibacterial agent : Chain extender : Antistatic agent : Flexural strength modifier : Lubricant : Inorganic filler = 165 : 35 : 4 : 4 : 7 : 15 : 15 : 15 In this embodiment, the mass ratio of polylactic acid to polypropylene carbonate is 165:35, and the auxiliary material ratio is within a moderate range to balance the film's strength, antibacterial properties, and processability. Through biaxial stretching, this film exhibits excellent performance in terms of light transmittance, antioxidant capacity, and mechanical strength, making it suitable for various applications and providing good antibacterial properties and a medium- to long-term service life. Example

[0032] Comparative Examples of Existing Technologies: To compare the differences between existing technologies and this invention, we selected the performance test results of traditional PLA films and PLA / PPC blend films under the same conditions. The test data are as follows: Test item Existing PLA film PLA-PPC film of the present invention Tensile strength (MPa) 20 35 Elongation at break (%) 6 10 Oxygen permeability (cc / m²·d) 300 150 Antibacterial property None Strong Weather resistance Poor Excellent Transparency 80% 95% Service life 150 days 250 days The comparative data shows that the PLA-PPC blend biaxially oriented film of the present invention is significantly superior to existing PLA films in terms of tensile strength, ductility, oxygen permeability, transparency, antibacterial properties, and service life, demonstrating the advantages of the present invention.

[0033] Alternative solutions In addition to the formulations and embodiments listed above, the present invention can also employ the following alternatives: 1. Alternative raw materials: If the grain fermentation method is not used to prepare polylactic acid (PLA), other renewable resources of lactic acid or its derivatives can be used as raw materials, such as extracting lactic acid from plant starches such as sugarcane and cassava.

[0034] 2. Alternative catalysts: Other catalysts with similar catalytic effects can be selected for the ring-opening polymerization (ROP) process of lactide, such as organometallic catalysts and titanium-based catalysts.

[0035] 3. Other blended resins: If PPC is not suitable for certain special applications, other copolymer resins with similar functions (such as polycarbonate, polyester, etc.) can be used as substitutes to maintain the performance of the film.

[0036] Although the technical solutions of the present invention have been described and enumerated in detail, it should be understood that modifications to the above embodiments or the adoption of equivalent alternatives are obvious to those skilled in the art. Such modifications or improvements made without departing from the spirit of the present invention are all within the scope of protection claimed by the present invention.

Claims

1. A PLA and PPC copolymer biaxially oriented film, characterized in that, The film comprises the following components: Biaxially oriented polylactic acid film (PLA), polypropylene carbonate (PPC), antibacterial agents, chain extenders, antistatic agents, flexural modifiers, lubricants, and inorganic fillers; The biodegradable resin comprises 200 parts by weight, consisting of polylactic acid resin (PLA) and polypropylene carbonate (PPC), with the specific composition as follows: Polylactic acid resin (PLA): 150-180 parts by weight; Polypropylene carbonate (PPC): 20-50 parts by weight.

2. The PLA and PPC copolymer biaxially oriented film according to claim 1, characterized in that, The total weight of the excipients is 20-50 parts by weight, specifically including: Antibacterial agent: 2-6 parts by weight; Chain extender: 2-6 parts by weight; Antistatic agent: 5-10 parts by weight; Flexural strength modifier: 10-20 parts by weight; Lubricant: 10-20 parts by weight; Inorganic filler: 10-20 parts by weight.

3. A PLA and PPC copolymer biaxially oriented film according to claim 1 or 2, characterized in that, The film is prepared by a biaxial stretching process with a width of 3 meters or more, and the resulting film has the following properties: Stretch film thickness: 5–100 μm; Biodegradation period: 1.5–3 years; Biodegradation rate: >94%; Tensile strength: 100–250 MPa; Elongation at break: 108–280%; Bacterial count per unit: ≤100 CFU / cm²; Transparency (light transmittance): >90%.

4. A PLA and PPC copolymer biaxially oriented film according to claim 1 or 2, characterized in that, The mass ratio of polylactic acid resin (PLA) to polypropylene carbonate (PPC) is from 3:1 to 9:

1.

5. A PLA and PPC copolymer biaxially oriented film according to claim 1 or 2, characterized in that, The antibacterial agent is a water-soluble polyguanidine inorganic acid salt, the chain extender is polyvinyl alcohol, the antistatic agent is an inorganic or organosilicon compound, the lubricant is polytetrafluoroethylene or wax, and the inorganic filler is nano-sized silica, calcium carbonate, or talc.

6. A method for preparing a PLA and PPC copolymer biaxially oriented film, characterized in that, The preparation process includes the following steps: According to the above-mentioned mass ratio of components, polylactic acid resin (PLA), polypropylene carbonate (PPC) and auxiliary materials are mixed evenly to obtain a raw material mixture; the raw material mixture is melted and extruded through a melt blending process; the melt is prepared into a film through an extrusion die; the film is subjected to a wide-width (over 3 meters) biaxial stretching treatment; after the stretched film is cooled and cured, the final PLA and PPC copolymer biaxially stretched film is obtained.

7. The method for preparing a PLA and PPC copolymer biaxially oriented film according to claim 6, characterized in that, The biaxial stretching ratio is 2 to 5 times.

8. The method for preparing a PLA and PPC copolymer biaxially oriented film according to claim 6, characterized in that, The stretching process employs a combination of hot and cold stretching to optimize the mechanical and biodegradability of the film.

9. The method for preparing a PLA and PPC copolymer biaxially oriented film according to claim 6, characterized in that... The final thickness of the film is between 5 μm and 100 μm, and can be adjusted according to actual needs.

10. The method for preparing a PLA and PPC copolymer biaxially oriented film according to claim 6, characterized in that, The film surface has excellent antibacterial properties and can maintain a long-term antibacterial effect under different environments (such as humid heat, refrigeration, etc.).