Biodegradable polylactic acid blister tray and preparation process thereof

Abstract

The invention provides a biodegradable polylactic acid blister tray and a preparation process thereof, and belongs to the technical field of high polymer materials, polylactic acid (PLA) is used as a matrix, and the biodegradable polylactic acid blister tray is prepared by mixing poly (butylene adipate-co-terephthalate) (PBAT), polyethylene glycol (PEG) and dicumyl peroxide (DCP) through melt blending, extrusion granulation and casting extrusion processes. The PLA film materials with different proportions are prepared by using the PLA as a raw material, and the mechanical property, the transparent property and the crystallization property of the materials are systematically analyzed, so that the processing technological parameters are optimized, and the comprehensive performance of the film is ensured; pBAT, PEG and DCP are introduced into a PLA matrix, the ratio of all the components and the processing technology are optimized through a system test, compatibilization and toughening of the film are achieved, the material has biodegradability and good processing adaptability and application prospects, and a new technical path is provided for development of environment-friendly materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a biodegradable polylactic acid blister tray and a preparation process thereof. Background Art

[0002] With the increasingly serious environmental pollution and resource waste problems caused by the large-scale application of non-degradable plastics, the development of environmentally friendly biodegradable alternative materials has become a global consensus. Polylactic acid (PLA), as a typical bio-based polymer material, uses lactic acid monomers from renewable resources such as corn and sugarcane as raw materials, and is prepared into linear aliphatic polyesters through polycondensation or ring-opening polymerization processes. It can be completely degraded into carbon dioxide and water through the action of microorganisms in the natural environment, and does not release toxic gases during the incineration process, having both ecological safety and sustainable development characteristics. Butylene terephthalate (PBAT) is a semi-aromatic biodegradable polyester, whose mechanical properties can be comparable to those of low-density polyethylene (LDPE), suitable for blown film extrusion in the packaging industry, having good ductility and elongation at break, as well as good heat resistance and impact resistance, and also having excellent biodegradability.

[0003] In the prior art, the Chinese invention patent with the application number: 202010189309 and the patent name: A preparation method of a biaxially stretched polylactic acid packaging film improves the orientation degree of the PLA film through a biaxial stretching process. However, due to the internal reasons of the PLA molecular chain structure and aggregation state, the obtained products still have technical bottlenecks such as low elongation at break and insufficient impact resistance. To solve this problem, the composite modification technology constructs multi-level interfacial interactions in the PLA matrix by introducing various interfacial compatibilizers such as reactive compatibilizers or polar / rigid substance fillers, increases the interaction between the molecular chains of the PLA blend, and realizes the synergistic compatibilization and toughening effect. Summary of the Invention

[0004] The purpose of the present invention is to address the above problems existing in the prior art and propose a biodegradable polylactic acid blister tray and a preparation process thereof.

[0005] The purpose of the present invention can be achieved by the following technical solutions: A biodegradable polylactic acid blister tray, comprising: 75 - 95% of polylactic acid (PLA), 5 - 25% of poly(butylene adipate-co-terephthalate) (PBAT), 5 - 15% of polyethylene glycol (PEG), and 0.01 - 0.1% of dicumyl peroxide (DCP), wherein: The polylactic acid (PLA) is the main matrix material for providing rigidity; The poly(butylene adipate-co-terephthalate) (PBAT) is a toughening agent for improving flexibility and impact resistance; The polyethylene glycol (PEG) is a plasticizer used to improve the processing fluidity of the PLA / PBAT blend system, reduce the melt viscosity, and facilitate thermoforming; The dicumyl peroxide (DCP) is a crosslinking agent that enhances the intermolecular force and is used to enhance the mechanical properties of the material, such as tensile strength and heat resistance.

[0006] Preferably, the melt flow rate (MFR) of the polylactic acid (PLA) is 10.0 g / 10 min. The MFR is moderate (the standard MFR range of PLA is 5 - 30 g / 10 min), which can not only ensure the melt fluidity for extrusion and thermoforming but also avoid collapse or loose structure during forming due to excessive fluidity. When the MFR is low, the molecular chains are longer and the crystallinity is higher, which helps to maintain the rigidity of the PLA matrix.

[0007] Preferably, the melt flow rate of the poly(butylene adipate-co-terephthalate) (PBAT) is 4.0 g / 10 min. The MFR of PBAT is close to that of PLA (10 g / 10 min), which is beneficial to optimizing the compatibility, reducing the viscosity difference between the two phases, reducing phase separation during blending, and enhancing the interfacial bonding force. The viscosity of PBAT is moderate, which can be evenly dispersed in the PLA matrix to form a continuous phase or a sea-island structure, effectively absorb the impact energy, and make the toughening effect stable.

[0008] Preferably, the polyethylene glycol (PEG) is of analytical purity. The analytical purity PEG has low impurity content, which can effectively avoid the thermal degradation or crosslinking side reactions of PLA caused by impurities (such as metal ions). Moreover, the high-purity PEG has a narrow molecular weight distribution, better compatibility with PLA / PBAT, and is beneficial to uniformly reducing the glass transition temperature (tg) of the system.

[0009] Preferably, the dicumyl peroxide (DCP) is of analytical purity. The high-purity DCP ensures the crosslinking reaction efficiency, avoids impurity interference in the free radical initiation process, prevents over-crosslinking (resulting in brittleness) or under-crosslinking (insufficient mechanical properties), and is convenient for reducing the impact of by-products (such as residual peroxides) on the biodegradability of the material, thus improving the safety.

[0010] A preparation process of a biodegradable polylactic acid thermoformed tray includes: S1. Placing the polylactic acid (PLA) pellets and the poly(butylene adipate-co-terephthalate) (PBAT) pellets in a drying oven and drying them for 12 - 24 h to reduce the water content to <0.02%, avoiding hydrolysis degradation during processing (PLA is sensitive to humidity), and ensuring the melt stability; S2. Weigh the components according to the addition ratio. Place the dried polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polyethylene glycol (PEG), and dicumyl peroxide (DCP) pellets in a high-speed mixer and premix for 5 - 10 minutes to evenly disperse each component and reduce phase separation during subsequent processing. S3. Twin-screw extrusion granulation. Mix the above substances and place them in an extruder for melt extrusion. After extrusion, cool the extruded sample with water at a temperature of 20 - 25°C, and use a pelletizer for cutting granulation. Shearing force promotes the compatibility of PLA / PBAT blends, and melt blending makes DCP evenly distributed to achieve controllable cross-linking. S4. Use a casting machine. Place the extruded masterbatch in the casting machine to extrude a film, and then place the prepared film sheet in a dryer to eliminate concentrated stress and avoid cracking or warping due to stress concentration during film thermoforming. S5. Preheat the sheet to the softening temperature using an infrared heating furnace and prepare a thermoformed tray using vacuum thermoforming equipment. S6. The thermoformed tray after forming is naturally cooled in the mold. After demolding, it enters a water cooling tank for rapid shaping. Rapid cooling can reduce the crystallization time and improve the surface smoothness. Mechanical trimming removes burrs to keep the surface of the thermoformed tray smooth and facilitate improving the appearance quality of the finished product.

[0011] Preferably, in step S2, the rotation speed of the high-speed mixer is 500 - 800 rpm, and the mixing temperature is 40 - 50°C. Among them, the mixing temperature is used to avoid premature decomposition of DCP. High-speed shearing is convenient to ensure the full dispersion of powders / pellets, avoid uneven local concentration, and low-temperature mixing prevents premature decomposition of DCP (the decomposition temperature of DCP is about 120°C), which is convenient to retain the cross-linking activity for the subsequent extrusion stage.

[0012] Preferably, in step S3, the temperatures of each section of the extruder are 155, 170, 175, 180, 185, 180°C (die head) respectively, and the temperature is gradually increased (155 → 185°C) to avoid thermal degradation of PLA and ensure sufficient melting of PBAT. The screw rotation speed is 70 r / min, and the rotation speed is convenient to balance the residence time and shearing force, ensuring both the blending uniformity and avoiding molecular chain breakage caused by excessive shearing.

[0013] Preferably, in step S4, the temperature for eliminating concentrated stress is set at 70 - 90°C, and the time for eliminating concentrated stress is 10 - 14 h. Annealing above the glass transition temperature promotes molecular chain relaxation, eliminates internal stress, and prevents subsequent thermoforming deformation. 10 - 14 h ensures sufficient stress release and avoids embrittlement of the film caused by excessive crystallization.

[0014] Preferably, in step S6, after the finished plastic suction tray is formed, the cooling time in the mold is 30 - 60 s for preliminary shaping to avoid deformation during demolding. Among them, the temperature inside the water cooling tank is 10 - 15 °C, which is convenient for rapid cooling to lock the shape and improve dimensional stability. An antistatic agent is sprayed on the surface of the plastic suction tray to reduce the surface resistance of the plastic suction tray, prevent the plastic suction tray from adsorbing dust or particles, and meet the usage requirements in a clean environment, such as medical or electronic packaging.

[0015] Compared with the prior art, the biodegradable polylactic acid plastic suction tray and its preparation process have the following beneficial effects: 1. A biodegradable polylactic acid plastic suction tray and its preparation process provided by the present invention use polylactic acid (PLA) as the main matrix material. By mixing polybutylene adipate - terephthalate (PBAT), polyethylene glycol (PEG), and dicumyl peroxide (DCP), and utilizing the synergistic effect among the components, the compatibility and toughness of the film are significantly improved, and a biodegradable film with excellent properties is prepared.

[0016] 2. A biodegradable polylactic acid plastic suction tray and its preparation process provided by the present invention introduce PBAT, PEG, and DCP into the PLA matrix, and through melt blending, extrusion granulation, and cast extrusion processes, PLA film materials with different ratios are prepared. By systematically analyzing the mechanical properties, transparency, and crystallization properties of the materials, the processing process parameters are optimized to ensure the comprehensive performance of the film.

[0017] 3. A biodegradable polylactic acid plastic suction tray and its preparation process provided by the present invention systematically study the influence of the PBAT addition amount on the mechanical properties and transparency of the PLA / PBAT film through single - factor experiments, determine the optimal addition amount of PBAT, and provide a scientific basis for the performance optimization of the film.

[0018] 4. A biodegradable polylactic acid plastic suction tray and its preparation process provided by the present invention introduce PEG into the PLA / PBAT film. By systematically detecting the mechanical properties and transparency of the film, the optimal addition amount of PEG is determined, significantly improving the hydrophilicity and mechanical properties of PLA and further enhancing the comprehensive performance of the film.

[0019] 5. A biodegradable polylactic acid plastic suction tray and its preparation process provided by the present invention add DCP to the PLA / PBAT / PEG film, achieve synergistic compatibilization by adding different contents of DCP, detect the mechanical properties and transparency of the film, obtain the optimal addition amount of DCP, and ensure the stability and processing performance of the film.

[0020] 6. A biodegradable polylactic acid blister tray and its preparation process provided by the present invention deeply study the crystallization properties of the PLA / PBAT / PEG / DCP film, systematically explore the thermodynamic behavior of the film, and provide important theoretical support for the processing and application of the material.

[0021] In summary, the present invention provides a biodegradable polylactic acid blister tray and its preparation process. By introducing PBAT, PEG, and DCP into the PLA matrix and optimizing the ratio of each component and the processing technology through systematic experiments, the mechanical properties, transparency, and crystallization properties of the film are significantly improved, and the film is compatibilized and toughened. It not only realizes the biodegradability of the material but also has good processing adaptability and application prospects, providing a new technical path for the development of environmental protection materials. Description of the Drawings

[0022] Figure 1 It is a schematic three-dimensional structure diagram of the blister tray in Specific Example Two. Detailed Embodiments

[0023] The following are specific examples of the present invention and in combination with the drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these examples. Specific Example One:

[0024] The embodiment of the present invention provides a biodegradable polylactic acid blister tray, including: 75 - 95% of polylactic acid (PLA), 5 - 25% of polybutylene adipate-co-terephthalate (PBAT), 5 - 15% of polyethylene glycol (PEG), and 0.01 - 0.1% of dicumyl peroxide (DCP), where: The polylactic acid (PLA) is the main matrix material, used to provide rigidity; The polybutylene adipate-co-terephthalate (PBAT) is a toughening agent, used to improve flexibility and impact resistance; The polyethylene glycol (PEG) is a plasticizer, used to improve the processing fluidity of the PLA / PBAT blend system, reduce the melt viscosity, and facilitate thermoforming; The dicumyl peroxide (DCP) is a crosslinking agent to enhance the intermolecular force, used to enhance the mechanical properties of the material, such as tensile strength and heat resistance.

[0025] The melt flow rate (MFR) of the polylactic acid (PLA) is 10.0 g / 10 min, and the MFR is moderate (the standard MFR range of PLA is 5 - 30 g / 10 min). It can not only ensure the melt fluidity, facilitate extrusion and thermoforming, but also avoid collapse or loose structure during forming due to excessive fluidity. When the MFR is lower, the molecular chain is longer and the crystallinity is higher, which helps to maintain the rigidity of the PLA matrix.

[0026] The melt flow rate of the poly(butylene adipate-co-terephthalate) (PBAT) is 4.0 g / 10 min. The MFR of PBAT is close to that of PLA (10 g / 10 min), which is beneficial to optimizing compatibility, reducing the viscosity difference between the two phases, reducing phase separation during blending, and enhancing the interfacial bonding force. The viscosity of PBAT is moderate, which can be evenly dispersed in the PLA matrix to form a continuous phase or a sea-island structure, effectively absorbing impact energy and making the toughening effect stable.

[0027] The polyethylene glycol (PEG) is of analytical purity. The impurity content of analytical purity PEG is low, which can effectively avoid side reactions such as thermal degradation or crosslinking of PLA caused by impurities (such as metal ions). Moreover, the high-purity PEG has a narrow molecular weight distribution and better compatibility with PLA / PBAT, which is beneficial to uniformly reducing the glass transition temperature (tg) of the system.

[0028] The dicumyl peroxide (DCP) is of analytical purity. The high-purity DCP ensures the efficiency of the crosslinking reaction, avoids the interference of impurities in the free radical initiation process, prevents over-crosslinking (resulting in brittleness) or under-crosslinking (insufficient mechanical properties), and is convenient for reducing the influence of by-products (such as residual peroxides) on the biodegradability of the material, thus improving the safety. Specific Example Two:

[0029] The embodiment of the present invention provides a preparation process of a biodegradable polylactic acid blister tray, including: S1. Place the polylactic acid (PLA) pellets and poly(butylene adipate-co-terephthalate) (PBAT) pellets in a drying oven and dry them for 12 - 24 h to reduce the water content to <0.02%, avoiding hydrolysis degradation during processing (PLA is sensitive to humidity) and ensuring melt stability. S2. Weigh the components according to the addition ratio, and place the dried polylactic acid (PLA), poly(butylene adipate-co-terephthalate) (PBAT), polyethylene glycol (PEG), and dicumyl peroxide (DCP) pellets in a high-speed mixer and premix for 5 - 10 min to evenly disperse each component and reduce phase separation during subsequent processing. S3. Twin-screw extrusion granulation: Mix the above substances, place them in an extruder, carry out melt extrusion, and cool the extruded sample with water at a temperature of 20 - 25 °C after extrusion, and use a pelletizer for cutting granulation. The shear force promotes the blending compatibility of PLA / PBAT, and the melt blending makes DCP evenly distributed to achieve controllable crosslinking. S4. Use a casting machine to place the extruded masterbatch in the casting machine to extrude a film, and then place the prepared film sheet in a dryer to eliminate the concentrated stress and avoid cracking or warping of the film during blistering due to stress concentration. S5. Preheat the sheet to the softening temperature using an infrared heating furnace, and use a vacuum blistering device to prepare a blister tray (such asFigure 1 ); S6. The formed plastic suction tray is naturally cooled in the mold and enters the water cooling tank for rapid shaping after demolding. Rapid cooling can reduce the crystallization time and improve the surface smoothness; mechanical trimming removes burrs to keep the surface of the plastic suction tray smooth, which is convenient for improving the appearance quality of the finished product.

[0030] In step S2, the rotation speed of the high-speed mixer is 500 - 800 rpm, and the mixing temperature is 40 - 50 °C; Among them, the mixing temperature is used to avoid the premature decomposition of DCP. High-speed shearing is convenient to ensure the full dispersion of powders / granules, avoid uneven local concentration, and low-temperature mixing prevents the premature decomposition of DCP (the decomposition temperature of DCP is about 120 °C), which is convenient to retain the cross-linking activity for the subsequent extrusion stage.

[0031] In step S3, the temperatures of each section of the extruder are 155, 170, 175, 180, 185, 180 °C (die head) respectively, and the temperature is gradually increased (155 → 180 °C) to avoid the thermal degradation of PLA and ensure the full melting of PBAT at the same time; the screw rotation speed is 70 r / min, and the rotation speed is convenient to balance the residence time and shear force, which can not only ensure the blending uniformity but also avoid the molecular chain breakage caused by excessive shearing.

[0032] In step S4, the temperature for eliminating the concentrated stress is set at 70 - 90 °C, and the time for eliminating the concentrated stress is 10 - 14 h. Annealing above the glass transition temperature promotes the relaxation of molecular chains, eliminates the internal stress in the cast film, and prevents subsequent plastic suction deformation; 10 - 14 h ensures the full release of stress and avoids the embrittlement of the film caused by excessive crystallization at the same time.

[0033] In step S6, after the finished plastic suction tray is formed, the cooling time in the mold is 30 - 60 s for preliminary shaping to avoid deformation during demolding; Among them, the temperature inside the water cooling tank is 10 - 15 °C, which is convenient for rapid cooling to lock the shape and improve the dimensional stability; The surface of the plastic suction tray is sprayed with an antistatic agent to reduce the surface resistance of the plastic suction tray, prevent the plastic suction tray from adsorbing dust or particles, and meet the use requirements of a clean environment, such as medical or electronic packaging. Specific Example Three:

[0034] Specific Example Three is a screening test on the mass ratio of PBAT in the PLA / PBAT film mentioned in Specific Example One and Specific Example Two. The content of Specific Example Three is as follows: 1. The PLA pellets and PBAT pellets were dried in an oven at 80 °C for 24 h. After drying, the PLA and PBAT were pre-mixed evenly in a multi-functional grinder according to a certain ratio and then melt-extruded in an extruder. The temperatures of each section of the extruder were 155, 170, 175, 180, 185, and 180 °C (die head) respectively, and the screw speed was 70 r / min. The extruded samples were cooled by cooling water and then cut into pellets. The extruded masterbatch was made into a film with a thickness of about 120 μm in a casting machine. Finally, the prepared film was placed in a dryer and the concentrated stress was eliminated at 80 °C for 12 h.

[0035] Among them, the mass fractions of PBAT were 5%, 10%, 15%, 20%, and 25% respectively. At the same time, films with PBAT mass fractions of 0 (pure PLA) and 100% (pure PBAT) were used as control groups.

[0036] 2. The mechanical properties of the film samples were tested. Referring to GB / T 1040.3—2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", long strip films with dimensions of 150 mm × 15 mm were cut. The distance between the clamps was 100 mm, and the tensile speed was (100 ± 10) mm / min. The elongation at break and tensile strength of the samples were tested at room temperature by an intelligent electronic tensile testing machine.

[0037] 3. Results Table 1 Mechanical property data of PLA / PBAT films PBAT mass fraction / % Elongation at break (longitudinal / transverse) / % Tensile strength (longitudinal / transverse) / MPa 0 8.11 / 7.82 62.89 / 64.98 5 8.21 / 9.98 62.75 / 53.32 10 8.42 / 14.25 61.11 / 49.76 15 8.67 / 17.53 58.38 / 45.53 20 8.95 / 20.88 53.45 / 38.24 25 8.86 / 22.32 48.23 / 33.25 100 576.52 / 502.55 29.41 / 25.87 As a copolymer of PBA and PBT, PBAT combines the characteristic advantages of both. It not only exhibits excellent ductility and heat resistance but also has good impact resistance and biodegradability. To explore the effect of PBAT content on the mechanical behavior of PLA-based composites, in this study, film samples were prepared by regulating the mass ratio of the PLA / PBAT blend system, and their mechanical properties were systematically characterized (see Table 1).

[0038] As can be seen from Table 1, the pure PLA film exhibits typical brittle characteristics. Its longitudinal elongation at break is only 8.11%, but the tensile strength is as high as 62.89 MPa, showing the intrinsic characteristics of high rigidity and low toughness. In the PLA / PBAT film material, with the increase of the PBAT content, the longitudinal elongation of the PLA / PBAT film increases slightly, indicating that the introduction of PBAT is more conducive to improving the transverse toughness. With the increase of the PBAT content, the PLA / PBAT film becomes softer and the tensile strength gradually decreases. When the mass fraction of PBAT is 25%, compared with the pure PLA, the longitudinal and transverse tensile strengths are reduced by 23.31% and 48.83% respectively. This phenomenon is mainly attributed to two aspects: First, PLA itself has a high tensile strength, while PBAT, as a flexible material, has a low strength, resulting in a decrease in the overall strength after blending the two; Second, the interfacial force between PLA and PBAT is weak, weakening the tensile properties of the material while improving the flexibility. In addition, the longitudinal tensile strength of the PLA / PBAT film is always higher than the transverse, because the molecular chains are arranged parallel to the longitudinal direction during the film processing, forming a higher crystallinity and intermolecular force, thus enhancing the longitudinal mechanical properties. Specific Example 4:

[0039] Specific Example 4 is a screening test on the mass ratio of PBAT in the PLA / PBAT film mentioned in Specific Example 1 and Specific Example 2. The content of Specific Example 4 is as follows: 1. Dry the PLA pellets and PBAT pellets in a drying oven at 80 °C for 24 h. After drying, mix the PLA and PBAT evenly in a multifunctional pulverizer according to a certain ratio, and melt-extrude them in an extruder. The temperatures of each section of the extruder are 155, 170, 175, 180, 185, 180 °C (die head) respectively, and the screw speed is 70 r / min. Cool the extruded sample with cooling water and then cut it into pellets. Place the extruded masterbatch in a casting machine to make a film with a thickness of about 120 μm. Finally, place the made film in a dryer and eliminate the concentrated stress at 80 °C for 12 h.

[0040] Among them, the mass fractions of PBAT are 5%, 10%, 15%, 20%, 25% respectively, and at the same time, the films with PBAT mass fractions of 0 (pure PLA) and 100% (pure PBAT) are used as control groups.

[0041] 2. Detect the transparency of the film samples. Refer to GB / T 2410—2008 "Determination of Light Transmittance and Haze of Transparent Plastics", cut a square film with a size of 50 mm × 50 mm, and test the light transmittance of the sample with a light transmittance / haze meter at room temperature.

[0042] 3. Results Table 2 Data Sheet of Transparency Performance of PLA / PBAT Films PBAT mass fraction / % Light transmittance / % 0 94.38 5 82.67 10 71.21 15 65.24 20 62.23 25 56.54 100 35.55 As can be seen from Table 2, with the increase of the PBAT content, the light transmittance of the PLA / PBAT film gradually decreases. When the mass fraction of PBAT is 25%, the light transmittance of the PLA / PBAT film is 56.54%. Since the transparency of PBAT is relatively low, the light transmittance is only about 35%. When PLA and PBAT are mixed, phase separation occurs. The refractive indices of the two polymers are different, and light scattering occurs at the formed interface, resulting in a decrease in transparency.

[0043] Through the data analysis of Table 1 and Table 2, considering the comprehensive mechanical properties and transparency performance, PBAT with a mass fraction of 10% is selected as the reference component for further research. Specific Example Five:

[0044] Specific Example Five is a screening test for the mass fraction of PEG in the PLA / PBAT films mentioned in Specific Examples One, Two, Three, and Four. The content of Specific Example Five is as follows: 1. Dry the PLA pellets and PBAT pellets in an oven at 80 °C for 24 h. After drying, mix the PLA, PBAT, and PEG evenly in a multifunctional pulverizer in a certain proportion, and melt-extrude them in an extruder. The temperatures of each section of the extruder are 155, 170, 175, 180, 185, and 180 °C (die head) respectively, and the screw speed is 70 r / min. Cut the extruded sample into pellets after cooling with cooling water. Place the extruded masterbatch in a casting machine to make a film with a thickness of about 120 μm. Finally, place the made film in a dryer and eliminate the concentrated stress at 80 °C for 12 h.

[0045] Among them, the mass fractions of PEG are 2%, 4%, 6%, 8%, 10%, 12%, and 14% respectively.

[0046] 2. Detect the mechanical properties of the film samples. Refer to GB / T 1040.3—2006 "Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets". Cut a long strip of film with a size of 150 mm × 15 mm, with a clamp spacing of 100 mm and a tensile speed of (100 ± 10) mm / min. Test the elongation at break and tensile strength of the samples at room temperature through an intelligent electronic tensile testing machine.

[0047] 3. Results Table 3 Data Sheet of Mechanical Properties of PLA / PBAT / PEG Films PLA / PBAT / PEG mass ratio Elongation at break (longitudinal / transverse) / % Tensile strength (longitudinal / transverse) / MPa 88 / 10 / 2 8.67 / 17.82 58.89 / 48.78 86 / 10 / 4 8.91 / 23.98 56.65 / 53.32 84 / 10 / 6 8.99 / 25.25 54.21 / 47.36 82 / 10 / 8 8.67 / 26.23 50.36 / 45.53 80 / 10 / 10 9.85 / 27.08 46.45 / 44.04 78 / 10 / 12 8.46 / 24.32 45.22 / 40.25 76 / 10 / 14 8.02 / 12.51 44.46 / 39.87 PEG has good adhesion and wettability, can effectively improve the compatibility of PLA, thereby enhancing the hydrophilicity and mechanical properties of PLA, and accelerating its biodegradation rate. PEG was introduced into the PLA / PBAT blend system as a compatibilizer, and its mass fractions were 2%, 4%, 6%, 8%, 10%, 12% and 14% respectively. The mechanical property test results are shown in Table 3.

[0048] With the increase of PEG content, the elongation at break of the PLA / PBAT / PEG film first increases and then decreases, and the improvement of the transverse elongation rate is particularly significant; when the PEG mass fraction is 8% - 10%, the longitudinal and transverse elongation rates of the film reach the maximum. This phenomenon is mainly attributed to the dual role of PEG: on the one hand, as a plasticizer, PEG promotes the stretching of PLA molecular chains, and its end groups are coupled with the carboxyl groups at the ends of PLA macromolecular chains, increasing the spatial volume of PLA molecules and weakening the interaction between adjacent molecular chains, thus significantly enhancing the toughness of the material; on the other hand, when the PEG mass fraction exceeds 10%, due to excessive dispersion and increased size of PEG, a large number of defects are generated inside the blend material, leading to stress concentration, and then the elongation at break decreases. In addition, the addition of PEG significantly reduces the tensile strength of the PLA / PBAT / PEG film, which is mainly because PEG molecules are inserted between PLA macromolecular chains, shielding the entanglement points of PLA molecular chains and reducing the secondary valence force between molecules, thus weakening the tensile strength of the material while improving its flexibility.

[0049] In addition, the addition of PEG significantly reduces the tensile strength of the PLA / PBAT / PEG film, which is mainly because PEG molecules are inserted between PLA macromolecular chains, shielding the entanglement points of PLA molecular chains and reducing the secondary valence force between molecules, thus weakening the tensile strength of the material while improving its flexibility. Specific Example Six:

[0050] Specific Example Six is a screening test on the mass ratio of PEG in the PLA / PBAT / PEG film mentioned in Specific Examples One, Two, Three, and Four. The content of Specific Example Six is as follows: 1. Dry the PLA pellets and PBAT pellets in an oven at 80°C for 24 h. After drying, mix the dried PLA, PBAT, and PEG evenly in a multi-functional pulverizer in a certain proportion, and melt-extrude them in an extruder. The temperatures of each section of the extruder are 155, 170, 175, 180, 185, 180°C (die head) respectively, and the screw speed is 70 r / min. Cool the extruded sample with cooling water and then cut it into pellets. Place the extruded masterbatch in a casting machine to make a film with a thickness of about 120 μm. Finally, place the made film in a dryer and eliminate the concentrated stress at 80°C for 12 h.

[0051] Among them, the mass fractions of PEG are 2%, 4%, 6%, 8%, 10%, 12%, and 14% respectively.

[0052] 2. Detect the transparency of the thin film samples. Refer to GB / T 2410—2008 "Determination of Light Transmittance and Haze of Transparent Plastics". Cut square thin films with a size of 50 mm × 50 mm, and test the light transmittance of the samples at room temperature through a light transmittance / haze meter.

[0053] 3. Results Table 4 Data Sheet of Transparency of PLA / PBAT / PEG Thin Films PLA / PBAT / PEG mass ratio Light transmittance / % 88 / 10 / 2 74.34 86 / 10 / 4 79.57 84 / 10 / 6 81.51 82 / 10 / 8 82.04 80 / 10 / 10 84.23 78 / 10 / 12 83.01 76 / 10 / 14 79.34 It can be seen from Table 4 that the light transmittance of the PLA / PBAT / PEG thin film first increases and then decreases with the increase of the PEG content, and reaches the maximum value when the mass fraction of PEG is 10%, showing excellent transparency. In summary, the optimal mass fraction of PEG is 10%. Specific Example Seven:

[0054] Specific Example Seven is a screening test for the mass ratio of DCP in the PLA / PBAT / PEG thin films mentioned in Specific Examples One, Two, Three, Four, Five, and Six. The content of Specific Example Seven is as follows: 1. Dry the PLA pellets and PBAT pellets in an oven at 80 °C for 24 h. After drying, mix the PLA, PBAT, PEG, and DCP evenly in a multi-functional grinder in a certain proportion, and melt and extrude them in an extruder. The temperatures of each section of the extruder are 155, 170, 175, 180, 185, and 180 °C (die head) respectively, and the screw speed is 70 r / min. Cool the extruded sample with cooling water and then cut it into pellets. Place the extruded masterbatch in a casting machine to make a thin film with a thickness of about 120 μm. Finally, place the made thin film in a dryer and eliminate the concentrated stress at 80 °C for 12 h.

[0055] Among them, the mass fractions of DCP are 0.01%, 0.03%, 0.05%, 0.07%, and 0.09% respectively. At the same time, thin films with a PBAT mass fraction of 0 (pure PLA) and 10% (PLA / PBAT / PEG = 80 / 10 / 10) are used as control groups.

[0056] 2. Detect the mechanical properties of the thin film samples. Refer to GB / T 1040.3—2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets". Cut long strip thin films with a size of 150 mm × 15 mm, the distance between the clamps is 100 mm, the tensile speed is (100 ± 10) mm / min, and test the elongation at break and tensile strength of the samples at room temperature through an intelligent electronic tensile testing machine.

[0057] 3. Results Table 5 Mechanical properties of PLA / PBAT / PEG films PLA / PBAT / PEG / DCP mass ratio Elongation at break (longitudinal / transverse) / % Tensile strength (longitudinal / transverse) / MPa 100 / 0 / 0 / 0 8.11 / 7.82 62.89 / 64.98 80 / 10 / 10 / 0 9.85 / 27.08 46.45 / 44.04 80 / 10 / 10 / 0.01 230.19 / 178.65 44.21 / 37.66 80 / 10 / 10 / 0.03 348.67 / 326.43 36.36 / 33.53 80 / 10 / 10 / 0.05 299.75 / 267.08 29.45 / 29.14 80 / 10 / 10 / 0.07 308.46 / 248.32 29.12 / 28.95 80 / 10 / 10 / 0.09 299.12 / 222.31 28.96 / 28.47 The results of the modification study show that in the PLA / PBAT / PEG (80 / 10 / 10) blend system, DCP as a reactive compatibilizer has a significant regulatory effect on the material multiphase interface engineering. Systematic research shows (Table 5) that when the DCP addition amount varies in the range of 0.01%~0.09%, the elongation at break of the film shows a parabolic evolution law of first rising and then falling. Especially when the mass proportion of DCP is 0.03%, the longitudinal and transverse elongation at break of the material reach the peak value simultaneously, showing excellent ductility.

[0058] The intrinsic mechanism of this phenomenon can be analyzed through interfacial action: the introduction of an appropriate amount of DCP triggers an in-situ volume expansion reaction during the processing, significantly enhancing the interfacial adhesion energy between the three phases of PLA-PBAT-PEG. This interfacial strengthening effect brings double gains: on the one hand, a more effective stress transfer network is constructed, allowing the material to consume more energy through multi-phase synergistic deformation when subjected to stress; on the other hand, the improvement of interfacial compatibility promotes the mobility of the PEG elastic chain segments, thereby forming high toughness characteristics. It is worth noting that when the DCP addition exceeds the critical value of 0.03%, excessive cross-linking reaction leads to excessive rigidification of the interface layer, which in turn weakens the stress buffering capacity of the multi-phase system, resulting in a significant drop in the elongation at break. In addition, with the increase of DCP content, the longitudinal and transverse tensile strengths of the film show a downward trend. Specific embodiment eight:

[0059] Specific Example 8 is a screening test for the mass fraction of DCP in the PLA / PBAT / PEG / DCP films mentioned in Specific Examples 1, 2, 3, 4, 5 and 6. The content of Specific Example 8 is as follows: 1. The PLA pellets and PBAT pellets were dried in a drying oven at 80°C for 24 hours. The dried PLA, PBAT, PEG, and DCP were pre-mixed in a multifunctional pulverizer in a certain proportion and melt-extruded in an extruder. The temperatures of each section of the extruder were 155, 170, 175, 180, 185, and 180°C (die head), respectively. The screw speed was 70 r / min. The extruded sample was cooled with cooling water and then cut and granulated. The extruded masterbatch was placed in a casting machine to make a film with a thickness of about 120 μm. Finally, the prepared film was placed in a dryer to eliminate concentrated stress at 80°C for 12 hours.

[0060] Among them, the mass fractions of DCP are 0.01%, 0.03%, 0.05%, 0.07%, and 0.09% respectively. At the same time, films with a PBAT mass fraction of 0 (pure PLA) and 10% (PLA / PBAT / PEG = 80 / 10 / 10) are used as control groups.

[0061] 2. Detect the transparency performance of the film samples. Refer to GB / T 2410—2008 "Determination of Light Transmittance and Haze of Transparent Plastics". Cut square films with a size of 50 mm × 50 mm, and test the light transmittance of the samples at room temperature through a light transmittance / haze meter.

[0062] 3. Results Table 6 Data table of transparency performance of PLA / PBAT / PEG films PLA / PBAT / PEG / DCP mass ratio Light transmittance / % 100 / 0 / 0 / 0 94.38 80 / 10 / 10 / 0 84.23 80 / 10 / 10 / 0.01 83.51 80 / 10 / 10 / 0.03 85.04 80 / 10 / 10 / 0.05 84.21 80 / 10 / 10 / 0.07 82.01 80 / 10 / 10 / 0.09 80.34 Optical performance analysis shows that during the change of DCP content, the PLA / PBAT / PEG / DCP film system always maintains excellent optical transparency. As shown in Table 6, the light transmittance of all series of samples is stably maintained in a high-level range above 80%. Among them, when the DCP addition amount is 0.03%, the light transmittance of the film reaches a peak value of 85.04%. This high light transmittance is due to the interfacial compatibilization effect induced by DCP, which effectively inhibits the formation of light-scattering interfaces in the multiphase system while maintaining good crystallization regularity of the polymer matrix.

[0063] 4. Conclusion: Through orthogonal optimization experiments, it is determined that when the material formula reaches PLA / PBAT / PEG / DCP = 80 / 10 / 10 / 0.03 (mass ratio), the system presents the best performance synergy, and its ductility is broken through. Among them, the longitudinal elongation at break reaches 348.67%, and the transverse elongation at break is 326.43%, showing a 42-fold increase compared with pure PLA, demonstrating excellent energy dissipation ability; while significantly improving the toughness, the load-bearing performance of the material is maintained, with a longitudinal tensile strength of 36.36 MPa and a transverse tensile strength of 33.53 MPa; the light transmittance is as high as 84.69%, meeting the application requirements of high-transparency packaging materials. Through multi-scale structure regulation, multi-objective optimization of toughening-reinforcing-transparency is achieved, providing an industrially valuable solution for the development of high-performance biodegradable films. Specific Example Nine:

[0064] Specific Example Nine is a crystallization performance test of the PLA / PBAT / PEG / DCP films mentioned in Specific Examples One, Two, Three, Four, Five, Six, Seven, and Eight. The content of Specific Example Nine is as follows: 1. The PLA pellets and PBAT pellets are dried in an oven at 80 °C for 24 h. After drying, PLA, PBAT, PEG, and DCP are premixed evenly in a multi-functional grinder according to a certain ratio, and then melt-extruded in an extruder. The temperatures of each section of the extruder are 155, 170, 175, 180, 185, and 180 °C (die head) respectively, and the screw speed is 70 r / min. The extruded sample is cooled by cooling water and then cut into pellets. The extruded masterbatch is made into a film with a thickness of about 120 μm in a casting machine. Finally, the prepared film is placed in a dryer and the concentrated stress is eliminated at 80 °C for 12 h.

[0065] Among them, the material ratio is: PLA / PBAT / PEG / DCP = 80 / 10 / 10 / 0.03.

[0066] 2. The differential scanning calorimetry (DSC) analysis is used to detect the crystallization performance of the film sample. Referring to JY / T 0589.3—2020 General Rules for Thermal Analysis Part 3: Differential Scanning Calorimetry, 5 - 8 mg of the PLA / PBAT / PEG / DCP film material is weighed and placed in an aluminum crucible. For the first heating, it is heated from room temperature to 200 °C at a heating rate of 10 °C / min and held at a constant temperature for 3 min to eliminate the thermal history; then it is cooled to -50 °C at a cooling rate of 10 °C / min and held for 2 min; then it is heated to 200 °C at a rate of 10 °C / min; the curve is recorded, and the test atmosphere is N2. The formula for calculating the relative crystallinity of the PLA component in the film material is as follows: X c = (∆H m - ∆H cc ) / (ϕ f × ΔH f 0 ) × 100% In the formula: ∆H m and ∆H cc are the melting enthalpy (J·g –1 ) and crystallization enthalpy (J·g –1 ) of the PLA component in the film material respectively; ΔH f 0 is the melting enthalpy of PLA at 100% crystallization (93.7 J·g –1 ); ϕ f is the mass fraction of the PLA component in the film material.

[0067] 3. Results Table 7 Data Sheet of Melting and Crystallization Parameters of PLA / PBAT / PEG / DCP Films PLA / PBAT / PEG / DCP mass ratio tg / °C <![CDATA[t cc / ℃]]> <![CDATA[t m / ℃]]> <![CDATA[∆H cc / (J·g –1) > <![CDATA[∆H m / (J·g –1) > <![CDATA[X c / % <!-- 10 -->]]> 100 / 0 / 0 / 0 61.0 121.1 155.1 13.0 15.2 2.3 80 / 10 / 10 / 0 59.0 116.8 154.9 14.8 21.0 8.2 80 / 10 / 10 / 0.03 58.2 116.0 152.8 34.0 38.2 5.6 The results of thermal analysis show (Table 7) that the co-modification of PBAT and PEG has a significant impact on the crystallization behavior of PLA. Specifically, the introduction of the toughening phase PBAT and the plasticizer PEG reduces the glass transition temperature (tg) of the PLA component from 61.0 °C of pure PLA to 59.0 °C, and the cold crystallization temperature (t cc ) decreases significantly from 121.1 °C to 116.8 °C, indicating that the interfacial interaction in the blend system is effectively optimized. At the same time, the melting enthalpy (ΔH m ) increases from 15.2 J·g⁻¹ to 21.0 J·g⁻¹, and the crystallinity (X c ) increases from 2.3% to 8.2%. This is mainly attributed to the synergistic enhancement of the movement ability of PLA molecular segments by the heterogeneous nucleation effect of PBAT and the plasticization effect of PEG, which promotes the formation and growth of crystal nuclei. Similar phenomena have also been verified in the system of toughening PLA with polyurethane elastomer.

[0068] After further introducing DCP, the melting temperature (t m ) of the PLA component shows a decrease of 2.1 °C, and the crystallinity decreases to 5.6%. Although the addition of DCP enhances the interaction between PLA molecular chains and restricts its movement ability, resulting in hindered crystallization, the impact on the glass transition temperature and cold crystallization temperature is not significant.

[0069] 4. Conclusion: The research shows that after introducing PBAT and PEG into the PLA matrix, both the glass transition temperature and cold crystallization temperature of the PLA component show a significant trend of shifting towards lower temperatures. At the same time, the melting enthalpy increases and the crystallinity is significantly improved. Specifically, the crystallinity of the PLA component in the film material increases from 2.3% to 8.2%, which confirms that the addition of PBAT and PEG effectively enhances the crystallization ability of PLA; when DCP is introduced into the PLA / PBAT / PEG film material system, the melting temperature of the PLA component decreases from 155.1 °C to 152.8 °C, and the crystallinity also decreases from 8.2% to 5.6%, indicating that the crosslinking effect of DCP triggers the reactive blending between PLA and PBAT, thereby inhibiting the crystallization ability of PLA.

[0070] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to substitute, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A biodegradable polylactic acid blister tray, characterized in that: include: Polylactic acid 75-95%, polybutylene adipate terephthalate 5-25%, polyethylene glycol 5-15%, dicumyl peroxide 0.01-0.1%, of which: The polylactic acid is the main matrix material and is used to provide rigidity; The polybutylene adipate-terephthalate is a toughening agent used to improve flexibility; The polyethylene glycol is a plasticizer used to improve processing fluidity; The dicumyl peroxide is a cross-linking agent and is used to enhance the mechanical properties of the material.

2. The biodegradable polylactic acid blister tray according to claim 1, characterized in that: The melt flow rate of the polylactic acid is 10.0 g / 10 min.

3. The biodegradable polylactic acid blister tray according to claim 1, characterized in that: The melt flow rate of the polybutylene adipate-terephthalate is 4.0 g / 10 min.

4. The biodegradable polylactic acid blister tray according to claim 1, characterized in that: The polyethylene glycol is analytically pure.

5. The biodegradable polylactic acid blister tray according to claim 1, characterized in that: The dicumyl peroxide is analytically pure.

6. A process for preparing the biodegradable polylactic acid blister tray according to claim 1, characterized in that: include: S1. Place the polylactic acid pellets and polybutylene adipate-terephthalate pellets in a drying oven and dry them for 12 to 24 hours to reduce the moisture content to less than 0.02%; S2, weigh the components according to the addition ratio, place the dried polylactic acid, polybutylene adipate-terephthalate, polyethylene glycol and dicumyl peroxide pellets in a high-speed mixer, and premix for 5-10 minutes to evenly disperse the components; S3, twin-screw extrusion granulation, the above substances are mixed, placed in an extruder, and melt extruded, and after extrusion, the extruded sample is cooled with water at a temperature of 20-25°C, and a pelletizer is used for cutting and granulation; S4, using a casting machine, placing the extruded masterbatch in the casting machine, extruding a film, and then placing the prepared film sheet in a dryer to eliminate concentrated stress; S5, using an infrared heating furnace to preheat the sheet to a softening temperature, and using a vacuum blister equipment to prepare a blister tray; S6. The formed blister tray is naturally cooled in the mold, and after demoulding, it enters the water cooling tank for rapid shaping, and mechanical trimming is used to remove burrs to keep the surface of the blister tray smooth.

7. The process for preparing a biodegradable polylactic acid blister tray according to claim 6, characterized in that: In step S2, the speed of the high-speed mixer is 500-800 rpm, and the mixing temperature is 40-50°C; Wherein, the mixing temperature is used to avoid premature decomposition of DCP.

8. The process for preparing a biodegradable polylactic acid blister tray according to claim 6, characterized in that: In step S3, the temperatures of each section of the extruder are 155, 170, 175, 180, 185, and 180°C (die head), and the screw speed is 70 r / min.

9. The process for preparing a biodegradable polylactic acid blister tray according to claim 6, characterized in that: In step S4, the temperature for eliminating concentrated stress is set to 70-90°C, and the time for eliminating concentrated stress is 10-14 hours.

10. The process for preparing a biodegradable polylactic acid blister tray according to claim 6, characterized in that: In step S6, after the finished blister tray is formed, the cooling time in the mold is 30 to 60 seconds; Among them, the temperature inside the water cooling tank is 10~15℃; The surface of the blister tray is sprayed with an antistatic agent to reduce the surface resistance of the blister tray.

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