High-strength biodegradable express bag material and manufacturing process thereof

Abstract

The application belongs to the field of degradable packaging film materials, and provides a high-strength biodegradable express bag material and a manufacturing process thereof. The application forms a compatible film system capable of heat sealing and bag making through the single-layer blown film design of the PBAT continuous phase and the PLA dispersed phase, the adjustment of the interfacial compatibility state by an epoxy ring-opening reaction agent, the anti-blocking of silicon dioxide, the lubrication of calcium stearate, and the smoothness adjustment of erucic acid amide, so that the material maintains coordination between the bearing strength, elongation at break, heat sealing strength, opening smoothness, and controlled compost degradation evaluation, solves the problem that the strength of the PBAT / PLA express bag is difficult to be compatible with degradation, heat sealing, and opening, and is suitable for degradable express packaging bags and related film products.

Description

Technical Field

[0001] This invention relates to the field of biodegradable packaging film materials, specifically to a high-strength biodegradable express delivery bag material and its manufacturing process. Background Technology

[0002] With the continuous expansion of express delivery, instant delivery, and e-commerce retail, express delivery bags have transformed from simple packaging carriers into packaging materials that combine load-bearing capacity, protection, reliable sealing, easy opening, and environmental friendliness. Traditional non-degradable plastic express delivery bags have a mature foundation in terms of transport strength, heat sealing processing, and cost, but their high environmental burden after disposal makes it difficult to meet the application requirements of green packaging and circular low-carbon development. PBAT and PLA are both important polyester materials that can be used in the field of biodegradable packaging. Blending and blowing film of the two can take advantage of the flexibility of PBAT in film formation and the rigidity and sourcing advantages of PLA to form single-layer films or heat-sealed bags suitable for express delivery bags. For express delivery bag applications, the material needs to maintain longitudinal and transverse tensile strength and elongation at break during loading, sorting, handling, and extrusion, and also needs to form a stable heat-sealed edge during bag making, while also possessing smooth opening and film thickness stability. Therefore, comprehensive requirements are placed on interfacial compatibility, phase morphology, rheological window, and heat sealing processing.

[0003] Existing PBAT / PLA biodegradable membrane materials typically improve mechanical properties and processing stability through blending, toughening, filler modification, or chain extension compatibility. However, problems such as phase separation, excessively large dispersed phase size, insufficient blown film traction orientation, and narrowed melt flow window may still occur between PBAT and PLA, making it difficult to balance strength, toughness, heat sealing, and opening performance. Publicly available research indicates that incompatible PBAT / PLA blends may exhibit phase separation characteristics in DSC, SEM, and rheological characterization, and changes in PLA content can affect elongation at break and tear-related properties. For example, Chinese patent CN113045879A discloses a high tear-resistant PLA-PBAT composite biodegradable resin, its preparation method, and its application. This scheme improves tear resistance through multi-component formulation, but its focus is on the composite resin and negative ion functional formulation, without systematically limiting the coupling control between reactive compatibility structure, PLA dispersed phase orientation, heat seal integrity, and opening slip components in single-layer blown film for express delivery bags. Therefore, a PBAT / PLA material system suitable for blown film and heat-sealing of express delivery bags is still needed. Summary of the Invention

[0004] The purpose of this invention is to provide a high-strength biodegradable express delivery bag material and its manufacturing process, which solves the pain points of current PBAT / PLA biodegradable express delivery bag materials, which are difficult to balance mechanical strength and biodegradability, and where the integrity of the heat-sealed structure and the smoothness of the opening are mutually constrained.

[0005] This invention combines the reinforcement of PLA dispersed phase with the continuous phase of PBAT to support the film formation and the interfacial compatibility of epoxy ring-opening reactant. It also uses calcium stearate of silica and erucamide to regulate the anti-adhesion, lubrication and slip state, so that the interfacial constraints caused by reinforcement and the heat sealing weakening that the slip component may cause are mutually mitigated, thereby taking into account both strength degradation, heat sealing and opening performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A high-strength biodegradable express delivery bag material, comprising a single-layer film formed by blown film, or comprising a bag body formed by heat sealing the single-layer film, wherein the raw materials for preparing the high-strength biodegradable express delivery bag material include, by weight, the following: Polybutylene adipate / butylene terephthalate copolymer, abbreviated as PBAT, 55-70 parts by weight; Polylactic acid, abbreviated as PLA, 20-35 parts by weight; 0.20-0.80 parts by weight of epoxy ring-opening reagent; 0.20-0.80 parts by weight of silicon dioxide; 0.05-0.30 parts by weight of calcium stearate; Erucamide 0.03-0.20 parts by weight; The PBAT forms a continuous PBAT phase, the PLA forms a dispersed PLA phase dispersed in the continuous PBAT phase, and the nominal thickness of the monolayer membrane is 0.030-0.080 mm.

[0007] Furthermore, the epoxy ring-opening agent is 1,4-butanediol diglycidyl ether, or a mixture of 1,4-butanediol diglycidyl ether and trimethylolpropane triglycidyl ether; the D50 of the PLA dispersed phase is 0.20-1.50 μm, the PLA dispersed phase is oriented along the blown film traction direction, and the aspect ratio of the PLA dispersed phase along the blown film traction direction is 3-15.

[0008] Furthermore, the single-layer film in the high-strength biodegradable express bag material is formed by blown film production from PBAT / PLA reactive compatibility masterbatch, which is prepared through the following steps: A1. Raw material drying: PBAT and PLA are dried separately to achieve a moisture content of 0.02-0.15 wt% for both. A2. Raw material premixing: PBAT, PLA, the epoxy ring-opening agent, silica, calcium stearate and erucamide are mixed according to the mass parts of the raw materials to obtain a premix; A3. Reactive extrusion: The premixed material is fed into a twin-screw extruder and reactively extruded at 150-185°C to obtain the extrudate; A4. Post-processing: The extrudate is cooled, pelletized and dried to obtain the PBAT / PLA reaction-compatible masterbatch.

[0009] Furthermore, in step A3, the epoxy ring-opening reactant is used to participate in the reaction of the terminal carboxyl or terminal hydroxyl groups of PBAT and / or PLA and to adjust the compatibility state of the PBAT / PLA phase interface; the reaction extrusion conditions in step A3 are controlled so that the melt flow rate of the extrudate is 2-8 g / 10 min, the gel point area ratio is 0.00-0.50%, and the D50 of the PLA dispersed phase is 0.20-1.50 μm.

[0010] Furthermore, in the epoxy ring-opening reagent, the mass fraction of trimethylolpropane triglycidyl ether is 0-40 wt%, and the balance is 1,4-butanediol diglycidyl ether.

[0011] Furthermore, the melt flow rate of the PBAT is 2-10 g / 10 min.

[0012] Furthermore, in step A2, the epoxy ring-opening reactant is first premixed with PLA, and then PBAT, silica, calcium stearate and erucamide are added for further premixing.

[0013] Furthermore, in step A3, the twin-screw extruder is equipped with four temperature zones from the feed section to the die head section, with temperatures of 150-165℃, 160-175℃, 170-185℃ and 165-180℃ respectively.

[0014] Furthermore, the melt flow rate of the high-strength biodegradable express bag material is 2-8 g / 10 min, and the gel point area ratio is 0.00-0.50%.

[0015] Furthermore, the D50 of the silica is 1-8 μm, and in the mass ratio of silica, calcium stearate and erucamide, the silica corresponds to 100 parts, the calcium stearate corresponds to 6-38 parts, and the erucamide corresponds to 4-25 parts.

[0016] Furthermore, the longitudinal tensile strength of the monolayer membrane is 25-45 MPa, the transverse tensile strength is 22-38 MPa, the longitudinal fracture nominal strain is 250-650%, the transverse fracture nominal strain is 250-600%, and the heat-sealing strength is 6-12 N / 15 mm.

[0017] As a concept of this invention, it employs a design combining a continuous PBAT phase, a dispersed PLA phase, and an epoxy ring-opening reactant to regulate interfacial compatibility. This design primarily aims to achieve a synergistic balance between the load-bearing strength and biodegradability of express delivery bags. Existing PBAT / PLA films, while generally improving strength and dimensional stability by simply increasing the rigid PLA phase or enhancing interfacial constraints, may become brittle and narrow the blown film processing window. Conversely, simply increasing the proportion of flexible components or pursuing a higher proportion of degradable materials may weaken the load-bearing structure and reduce heat-sealing stability. This invention provides film-forming toughness through the continuous PBAT phase, structural reinforcement through the dispersed PLA phase, and participates in end-group reactions and improves interfacial compatibility through the epoxy ring-opening reactant. Simultaneously, stress transfer is controlled by the dispersed phase size and traction orientation, mitigating the embrittlement tendency caused by reinforcement and the insufficient load-bearing capacity caused by the flexible phase. This allows the express delivery bag material to maintain a balance between strength, toughness, processing, and degradation performance.

[0018] This invention also discloses a manufacturing process for any of the aforementioned high-strength biodegradable express delivery bag materials, comprising the following steps: S1. Provide the prepared PBAT / PLA reactive compatibility masterbatch, which is obtained by drying PBAT and PLA separately, mixing the dried PBAT and PLA with the epoxy ring-opening reactant, silica, calcium stearate and erucamide, and then react-extruded, cooled, pelletized and dried by a twin-screw extruder. S2. The PBAT / PLA reactive compatibility masterbatch is blown into a film, and the nominal thickness of the monolayer film is controlled to be 0.030-0.080 mm to obtain a monolayer film; S3. Heat-seal the single-layer film to form a bag, thereby obtaining the high-strength biodegradable express bag material.

[0019] Furthermore, step S2 also includes online monitoring of blown film extrusion pressure and film thickness, wherein the blown film extrusion pressure fluctuates within a range of -10% to +10% relative to a set extrusion pressure, and the average deviation of the film thickness relative to a target film thickness is -10% to +10%.

[0020] Furthermore, in the raw material drying step, PBAT is dried at 45-60℃ for 3-5 hours, and PLA is dried at 50-65℃ for 4-6 hours. The dried PBAT and PLA are then introduced into the raw material premixing step. The moisture content after drying is determined by using the dried PBAT and PLA samples as test objects, and the moisture content is taken as the percentage of the sample moisture mass to the total sample mass.

[0021] Furthermore, in the raw material premixing step, the epoxy ring-opening reactant is first premixed with PLA for 3-8 minutes, and then PBAT, silica, calcium stearate and erucamide are added and premixed for another 7-12 minutes. The total premixing time is 10-20 minutes, and the premixed material is then obtained for the reaction extrusion step.

[0022] Furthermore, when the epoxy ring-opening agent contains trimethylolpropane triglycidyl ether, the trimethylolpropane triglycidyl ether accounts for 0-40 wt% of the epoxy ring-opening agent, with the remainder being 1,4-butanediol diglycidyl ether. The epoxy ring-opening agent is first premixed with PLA and then mixed with PBAT, silica, calcium stearate, and erucamide. The resulting premix is ​​then reacted and extruded, with melt flow rate and gel point area ratio used as release quality control indicators.

[0023] Furthermore, in the reactive extrusion step, the twin-screw extruder is equipped with four temperature zones from the feed section to the die head section. The temperatures of the four temperature zones are 150-165℃, 160-175℃, 170-185℃ and 165-180℃ respectively. The screw speed of the twin-screw extruder is 120-250 r / min, the effective residence time is 1-4 min, and the melt pressure is 5-15 MPa. The premixed material is melt-mixed and reactive extruded to form the extrudate.

[0024] Furthermore, in the post-processing step, the extrudate is cooled by air cooling and then pelletized. The pellets are dried at 45-60℃ for 2-4 hours to obtain PBAT / PLA reaction-compatible masterbatch for the blown film step.

[0025] Furthermore, the interfacial compatibility state of PBAT / PLA was characterized using the extrudate obtained in step A3, the PBAT / PLA reactive compatibility masterbatch, or the monolayer film obtained by blown film production from the masterbatch as test samples. FTIR, DSC, and microstructure detection were performed on the test samples. FTIR recorded the characteristic peaks of epoxy, ester absorption peaks, and hydroxyl absorption peaks. DSC recorded the thermal transition temperatures of PBAT and PLA. Microstructure detection recorded the D50 and aspect ratio of the PLA dispersed phase. The obtained data were used together to describe the interfacial compatibility state after the participation of the epoxy ring-opening reactant.

[0026] Furthermore, the melt flow rate was tested using PBAT raw materials, extrudates, PBAT / PLA reaction-compatible masterbatches, or high-strength biodegradable express bag materials. After drying, the test samples were tested at 190℃ and 2.16kg according to GB / T 3682.1-2018. The mass of the extrudate within 10 minutes was recorded, and the data was expressed in g / 10min.

[0027] Furthermore, the gel point mentioned in this invention refers to an opaque or semi-transparent granular defect area in the extruded tablet sample or monolayer film sample, which is identified by an optical microscope. The gel point area ratio is calculated by taking the extruded tablet sample or monolayer film sample as the test sample, placing the test sample under an optical microscope and acquiring at least 5 non-overlapping field-of-view images, and performing binarization identification on the gel point projection area in the field-of-view images. The gel point area ratio is calculated by multiplying the ratio of the total gel point projection area to the total area of ​​the statistical field of view by 100%. The obtained gel point area ratio is used for quality control of extruded materials, PBAT / PLA reaction-compatible masterbatch, or high-strength biodegradable express bag materials. When no gel point area meeting the above identification conditions is observed in at least 5 fields of view, the gel point area ratio is recorded as 0.00%.

[0028] Furthermore, the D50 and aspect ratio of the PLA dispersed phase were determined using the cross-section of the monolayer film along the blown film traction direction as the test area. Low-temperature brittle fracture was used to form the cross-section and microscopic images were acquired. At least 200 PLA ​​dispersed phases were counted for each sample. The projected area of ​​each PLA dispersed phase was converted into the equivalent circle diameter, and the median value of the number distribution of the equivalent circle diameter was used as the D50. The ratio of the maximum length of each PLA dispersed phase along the blown film traction direction to the maximum width perpendicular to the blown film traction direction was used as the aspect ratio. The obtained D50 and aspect ratio were used to characterize the size and orientation state of the PLA dispersed phase.

[0029] Furthermore, the D50 of silica was determined by using silica raw material as the test object. The silica raw material was dispersed in anhydrous ethanol and ultrasonically dispersed for 5-10 minutes. The particle size distribution of silica was recorded by laser particle size distribution method, and the median diameter of the volume distribution was used as the D50 of silica.

[0030] Furthermore, in the blown film step, after the PBAT / PLA reactive compatibility masterbatch enters the blown film equipment, it is melted, plasticized, and extruded through a die to form a film bubble. The die temperature is 145-175℃, the blow-up ratio is 2.0-3.5, the draw ratio is 5-15, and after cooling and shaping, a single-layer film with a nominal thickness of 0.030-0.080mm is obtained.

[0031] Furthermore, in the blown film online monitoring step, the extrusion pressure and target film thickness are set as reference values. The blown film extrusion pressure and film thickness data are collected, and the blown film extrusion pressure fluctuation and film thickness deviation are calculated as a percentage of the difference between the real-time collected value and the corresponding reference value divided by the corresponding reference value. When the blown film extrusion pressure fluctuation is maintained between -10% and +10% and the average film thickness deviation is maintained between -10% and +10%, the obtained single-layer film enters the heat-sealing bag making step, and the nominal thickness of the single-layer film corresponds to the target film thickness.

[0032] Furthermore, in the heat-sealing bag-making step, the single-layer film is heat-sealed at a heat-sealing temperature of 120-160℃, a heat-sealing time of 0.2-0.8s, and a heat-sealing pressure of 0.2-0.5MPa. After heat-sealing, a heat-sealed edge of the bag body is formed, resulting in a bag body formed by heat-sealing the single-layer film.

[0033] Furthermore, the thickness of the single-layer membrane is measured at no less than 5 measurement points along the width of the membrane, and the arithmetic mean is recorded as the measured thickness. The measured thickness is used to calculate the membrane thickness deviation, and the target membrane thickness is used to determine the nominal thickness of the single-layer membrane.

[0034] Furthermore, the mechanical properties test used a single-layer film as the test sample. Tensile specimens were cut along the blown film traction direction and perpendicular to the blown film traction direction, respectively. The longitudinal tensile strength, transverse tensile strength, longitudinal nominal strain at break and transverse nominal strain at break were determined according to GB / T 1040.3-2006. The specimen thickness, specimen width, gauge length, test speed, maximum force and fracture displacement were recorded. The heat seal strength test used the heat-sealed edge of the heat-sealed bag as the test sample and was determined according to QB / T2358-1998. The obtained data were used to characterize the mechanical properties of the single-layer film and the heat-sealing structure of the bag.

[0035] Furthermore, the biodegradability was tested using samples cut from single-layer membranes or bags. The final aerobic biodegradation capacity under controlled composting conditions was tested according to GB / T 19277.1-2025. The organic carbon content, carbon dioxide release, and test time of the samples were recorded, and the biodegradation rate calculated from the carbon dioxide release was used as the evaluation data for biodegradability.

[0036] Furthermore, in this invention, the ranges of melt flow rate, gel point area ratio, PLA dispersed phase D50, PLA dispersed phase aspect ratio, tensile strength, nominal fracture strain, heat-sealing strength, dynamic friction coefficient, and controlled compost biodegradation rate are determined by the arithmetic mean of the test results of the corresponding test items (n=3), and the standard deviation is used to characterize repeatability.

[0037] As another aspect of this invention, the present invention employs a blown film preparation process using PBAT / PLA reactive compatible masterbatch followed by heat sealing to form bags. This process is primarily used to achieve, maintain, or amplify the aforementioned synergistic effects. Existing bag-making processes, if only the melt-fusion capability is improved, generally benefit the integrity of the heat-sealed edges, but may increase film adhesion and reduce opening slipperiness; if only slippery and anti-adhesion components are added, the bonding at the heat-sealed interface may be weakened. This invention, by first preparing the reactive compatible masterbatch, and then controlling the film thickness, bubble formation, extrusion pressure, and traction orientation during the blown film process, ensures that the continuous PBAT phase and the dispersed PLA phase maintain a stable distribution during film formation. Furthermore, by controlling the subsequent heat-sealing temperature, time, and pressure, a repeatable bonding structure is formed at the heat-sealed edges of the bag, thereby achieving a stable balance between heat-sealed integrity, opening slipperiness, and film mechanical load-bearing capacity.

[0038] The continuous PBAT phase primarily addresses the issues of flexible film formation and heat sealing in monolayer films, while the dispersed PLA phase mainly addresses the load-bearing strength and rigid support of express delivery bags. Excessive PBAT ratio can lead to a softer film, resulting in insufficient load-bearing capacity and dimensional stability. Conversely, excessive PLA ratio can cause film embrittlement and narrow the blown film processing window. Increasing interfacial constraint solely with epoxy ring-opening agents may decrease melt flowability or increase the gel point. While excessive amounts of silica, calcium stearate, and erucamide may improve anti-blocking and opening smoothness, they may weaken the heat-sealing interface bonding. This invention achieves a balance between interfacial compatibility, melt flow, film surface smoothness, and heat-sealing bonding through PBAT and PLA ratio matching, interfacial compatibility adjustment after the epoxy ring-opening agent contacts PLA first, and the synergistic effects of silica, calcium stearate, and erucamide in anti-blocking, lubrication, and smoothness.

[0039] Beneficial technical effects 1. By constructing an interfacial compatibility adjustment system using PBAT continuous phase, PLA dispersed phase, and epoxy ring-opening reactant, the interfacial bonding and stress transfer between the two polyester phases are improved, reducing the tendency for embrittlement caused by uncontrolled dispersed phase size during simple blending. This improves the load-bearing stability of the single-layer film of the express delivery bag while maintaining the properties of biodegradable materials.

[0040] 2. By controlling the PLA dispersed phase D50, traction direction orientation, and aspect ratio, the PLA dispersed phase can form a structural distribution in the PBAT continuous phase that is more suitable for the direction of blown film stress, reducing local stress concentration and achieving a balance between longitudinal and transverse tensile strength and nominal strain at break, which is beneficial to meeting the tensile resistance requirements during express sorting, handling, and loading processes.

[0041] 3. By matching the proportions of silica, calcium stearate, and erucamide, the anti-adhesion, lubrication, and slip properties are simultaneously adjusted on the film surface and during melt processing, reducing the heat-sealing weakening that may be caused by adding slip components alone, and achieving a more stable balance between opening operability and heat-sealing edge integrity.

[0042] 4. By first preparing PBAT / PLA reaction-compatible masterbatch and then performing blown film and heat-sealing bag making, and by monitoring the blown film extrusion pressure and film thickness deviation online, a continuous quality control chain is formed for material melt flow, gel point area ratio, film thickness stability and heat-sealing processing conditions, which is beneficial to improving the batch repeatability and industrial bag making adaptability of express bag materials. Attached Figure Description

[0043] Figure 1 This diagram illustrates the effect of the mass fraction of the epoxy ring-opening reactant on the longitudinal tensile strength and heat-sealing strength in this scheme.

[0044] Figure 2 This diagram illustrates the effect of PLA mass fraction on longitudinal tensile strength and heat-sealing strength in this scheme.

[0045] Figure 3 This diagram illustrates the effect of silica mass fraction on longitudinal tensile strength and heat-sealing strength in this scheme.

[0046] Figure 4 This diagram shows the effect of the traction ratio on the longitudinal tensile strength and heat-sealing strength of this scheme.

[0047] Figure 5 The diagram shows the difference in the equivalent circle diameter of the PLA dispersed phase in Example 1 and Comparative Examples 3, 9, and 10.

[0048] Figure 6 The cumulative distribution diagram of the equivalent circle diameter of PLA dispersed phase in Example 1 and Comparative Examples 3, 9 and 10 is shown.

[0049] Figure 7 The figure shows the aspect ratio distribution of the PLA dispersed phase in Example 1 and Comparative Examples 3, 9 and 10.

[0050] Figure 8 This is a superimposed diagram of the FTIR absorption spectra of Example 1, Comparative Example 9, and Comparative Example 10.

[0051] Figure 9 The DSC heat flow-temperature curves for Example 1 and Comparative Examples 9 and 10 are shown.

[0052] Figure 10 The graph shows the melt flow rate and gel point area ratio of Example 1 and Comparative Examples 3, 9, and 10.

[0053] Figure 11 The graph shows the relationship between heat-sealing strength and dynamic friction coefficient for Example 1, Comparative Example 4, and Comparative Example 11.

[0054] Figure 12This is a scatter plot showing the average percentage of effective particle area on the membrane surface for Example 1, Comparative Example 4, and Comparative Example 11.

[0055] Figure 13 The images show a comparison of macroscopic optical photographs of the final product of Example 1 and the final product of Comparative Example 9. In example a, macroscopic optical photograph of the final product of Example 1, the sample being a PBAT / PLA reaction-compatible monolayer film and a heat-sealed bag; and in example b, macroscopic optical photograph of the final product of Comparative Example 9, the sample being a PBAT / PLA monolayer film and a heat-sealed bag prepared without the addition of 1,4-butanediol diglycidyl ether.

[0056] Figure 14 The images show a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 9; where a is a low-magnification SEM image of the final product of Example 1; b is a low-magnification SEM image of the final product of Comparative Example 9; c is a medium-magnification SEM low-temperature brittle fracture cross-section of the final product of Example 1; d is a medium-magnification SEM low-temperature brittle fracture cross-section of the final product of Comparative Example 9; e is a high-magnification SEM cross-section of the final product of Example 1; and f is a high-magnification SEM cross-section of the final product of Comparative Example 9.

[0057] Figure 15 The images show a comparison of the TEM characterization of the final product of Example 1 and the final product of Comparative Example 9; where a is a bright-field TEM image of the final product of Example 1; b is a bright-field TEM image of the final product of Comparative Example 9; c is an HRTEM or locally high-resolution TEM image of the final product of Example 1; and d is an HRTEM or locally high-resolution TEM image of the final product of Comparative Example 9. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0059] Example 1 S1: Raw material preparation and drying. Based on a base batch size of approximately 10 kg PBAT / PLA reaction-compatible masterbatch, commercially available PBAT was selected with a melt flow rate of 2 g / 10 min; commercially available PLA was selected with a supplier-specified number-average molecular weight of 6.0 × 10⁻⁶. 4 g / mol; commercially available 1,4-butanediol diglycidyl ether was selected as the epoxy ring-opening agent; commercially available silica with a D50 of 1 μm was selected; commercially available calcium stearate and commercially available erucamide were selected. PBAT was dried at 45℃ for 3 h, and PLA was dried at 50℃ for 4 h. After drying, the moisture content of both PBAT and PLA was 0.15 wt%. The median diameter of the volume distribution was confirmed by laser particle size distribution method after ultrasonic dispersion of silica in anhydrous ethanol for 5 min.

[0060] S2: Raw material premixing. Weigh out 55 parts by weight of PBAT, 20 parts by weight of PLA, 0.20 parts by weight of 1,4-butanediol diglycidyl ether, 0.20 parts by weight of silica, 0.05 parts by weight of calcium stearate, and 0.03 parts by weight of erucamide, based on the weight of the input materials. First, premix 1,4-butanediol diglycidyl ether and PLA at 120 rpm for 3 minutes at 25°C, normal pressure, and in air. Then add PBAT, silica, calcium stearate, and erucamide, and continue premixing at 180 rpm for 7 minutes, for a total premixing time of 10 minutes. The premixing is considered complete when the premixing time reaches the set time and the mixture appears uniform, with no visible liquid phase aggregation and no particle clumping.

[0061] S3: Reactive Extrusion and Masterbatch Post-processing. The premixed material was fed into a twin-screw extruder. The four temperature zones of the twin-screw extruder from the feed section to the die head section were 150℃, 160℃, 170℃, and 165℃ respectively. The screw speed was 120 r / min, the effective residence time was 1 min, the melt pressure was 5 MPa, and the extrusion was carried out under atmospheric pressure. After air cooling to 25℃, the extruded material was pelletized. The pellets were then dried at 45℃ for 2 h to obtain PBAT / PLA reactive compatibility masterbatch. The criteria for successful reactive extrusion were continuous extrusion, no obvious breakage, and uniform pellet appearance.

[0062] S4: Film blowing and heat sealing for bag making. PBAT / PLA reactive compatibility masterbatch is added to the film blowing equipment. The die temperature is 145℃, the blow-up ratio is 2.0, and the draw ratio is 5. After cooling and setting, a single-layer film with a nominal thickness of 0.030mm is obtained. During the film blowing process, the extrusion pressure is set to 8MPa, and the pressure and film thickness are collected online. The fluctuation of the extrusion pressure relative to the set extrusion pressure is -10%, and the average deviation of the film thickness relative to the target film thickness is -10%. The single-layer film is heat-sealed at a heat-sealing temperature of 120℃, a heat-sealing time of 0.2s, and a heat-sealing pressure of 0.2MPa to form a heat-sealed bag edge.

[0063] S5: Quality Inspection Methods and Results. After drying the masterbatch, the melt flow rate was measured at 190℃ and 2.16 kg, resulting in 8.0±0.2 g / 10 min (n=3). The gel point area ratio was statistically analyzed using microscopic images of the single-layer film, resulting in 0.00±0.00% (n=3). Microscopic images were collected after low-temperature brittle fracture of the single-layer film cross-section. Each sample contained at least 200 PLA ​​dispersed phases, with a PLA dispersed phase D50 of 1.50±0.04 μm and an aspect ratio of 3.0±0.2 along the blown film traction direction (n=3). Samples were cut along and perpendicular to the blown film traction direction. The longitudinal tensile strength was 25.0±0.8 MPa, the transverse tensile strength was 22.0±0.7 MPa, the longitudinal nominal strain at break was 250±12%, the transverse nominal strain at break was 250±10%, and the heat-sealing strength was 6.0±0.3 N / 15 mm (n=3). Controlled composting evaluation was conducted using samples cut from a single-layer membrane. Organic carbon content, carbon dioxide release, and testing time were recorded. The records were used for quality retention of biodegradable properties.

[0064] Features and application scenarios of this embodiment. This embodiment adopts a relatively conservative low-ratio scheme and mild processing conditions, resulting in a thinner film thickness, lower dosage of anti-blocking, lubricating and slip components, and higher melt flowability. It is suitable for lightweight express inner packaging bags, low-load e-commerce small package packaging, and biodegradable packaging scenarios with strict control over material usage.

[0065] Example 2 Raw materials and proportions: For a batch size of approximately 10 kg of PBAT / PLA reaction-compatible masterbatch, commercially available PBAT with a melt flow rate of 10 g / 10 min was used; commercially available PLA with a supplier-specified number-average molecular weight of 2.0 × 10⁻⁶ was also used. 5 g / mol; commercially available 1,4-butanediol diglycidyl ether and commercially available trimethylolpropane triglycidyl ether were selected as epoxy ring-opening agents; commercially available silica with a D50 of 8 μm was selected; commercially available calcium stearate and commercially available erucamide were selected. By mass percentage of the input materials, PBAT was 70 parts by mass, PLA was 35 parts by mass, and epoxy ring-opening agent was 0.80 parts by mass, of which 1,4-butanediol diglycidyl ether was 0.48 parts by mass and trimethylolpropane triglycidyl ether was 0.32 parts by mass, with mass fractions of 60 wt% and 40 wt%, respectively; silica was 0.80 parts by mass, calcium stearate was 0.30 parts by mass, and erucamide was 0.20 parts by mass.

[0066] Preparation process: PBAT was dried at 60℃ for 5 hours, and PLA was dried at 65℃ for 6 hours. After drying, the moisture content of both PBAT and PLA was 0.02 wt%. First, the epoxy ring-opening reactant and PLA were premixed at 150 r / min for 8 minutes at 25℃, normal pressure, and air atmosphere. Then, PBAT, silica, calcium stearate, and erucamide were added, and premixing continued at 220 r / min for 12 minutes, for a total premixing time of 20 minutes. The premixed material was fed into a twin-screw extruder with four temperature zones of 165℃, 175℃, 185℃, and 180℃, a screw speed of 250 r / min, an effective residence time of 4 minutes, and a melt pressure of 15 MPa. After extrusion, the extrudate was air-cooled to 25℃, pelletized, and dried at 60℃ for 4 hours to obtain PBAT / PLA reactive compatibility masterbatch.

[0067] Film Formation and Bag Making: PBAT / PLA reactive compatibility masterbatch is added to a blown film equipment, melt-plasticized, and extruded through a die to form a film bubble. The die temperature is 175℃, the blow-up ratio is 3.5, and the draw ratio is 15. After cooling and setting, a single-layer film with a nominal thickness of 0.080mm is obtained. During the blown film process, the extrusion pressure is set at 12MPa, the fluctuation of the blown film extrusion pressure relative to the set extrusion pressure is +10%, and the average deviation of the film thickness relative to the target film thickness is +10%. The single-layer film is heat-sealed at a heat-sealing temperature of 160℃, a heat-sealing time of 0.8s, and a heat-sealing pressure of 0.5MPa to form a bag.

[0068] Quality testing methods and results: The melt flow rate of the masterbatch was 2.0±0.1 g / 10 min, n=3; the gel point area ratio of the monolayer film was 0.50±0.03%, n=3; the D50 of the PLA dispersed phase was 0.20±0.02 μm, and the aspect ratio along the blown film traction direction was 15.0±0.6, n=3. The longitudinal tensile strength of the monolayer film was 45.0±1.2 MPa, the transverse tensile strength was 38.0±1.0 MPa, the longitudinal nominal strain at break was 650±22%, the transverse nominal strain at break was 600±18%, and the thermal bonding strength was 12.0±0.4 N / 15 mm, n=3. FTIR was used to record the characteristic peaks of epoxy, ester group absorption peaks, and hydroxyl group absorption peaks; DSC was used to record the thermal transition temperatures of PBAT and PLA; and microscopic morphology analysis was used to record the size and orientation state of the PLA dispersed phase. Controlled composting evaluation was conducted by cutting samples from the bag, recording the carbon dioxide release and converting it to biodegradability. The resulting records were retained as samples for biodegradability quality.

[0069] Features of this embodiment: This embodiment adopts an optimized scheme with a high load, and the ratios of PBAT, PLA, epoxy ring-opening reactant and additives are all in the high value range, resulting in a larger film thickness and stronger blown film traction and heat sealing conditions. It is suitable for express delivery outer packaging bags and multi-category logistics packaging scenarios with high load-bearing requirements and high heat sealing edge reliability requirements.

[0070] Example 3 In this embodiment, medium-batch continuous blown film production is used as the application. Approximately 20 kg of PBAT / PLA reactive compatibility masterbatch is prepared and further formed into a single-layer film bag. Commercially available PBAT is used, with a melt flow rate of 6 g / 10 min; commercially available PLA is used, with a supplier-specified number-average molecular weight of 1.2 × 10⁻⁶. 5 g / mol; a mixture of 1,4-butanediol diglycidyl ether and trimethylolpropane triglycidyl ether was used as the epoxy ring-opening agent, wherein the mass fraction of trimethylolpropane triglycidyl ether was 20 wt%. The raw material ratio was 62 parts by mass of PBAT, 28 parts by mass of PLA, 0.50 parts by mass of epoxy ring-opening agent, 0.75 parts by mass of silica, 0.05 parts by mass of calcium stearate, and 0.03 parts by mass of erucamide. The D50 of silica was 4 μm. For every 100 parts of silica, the amount of calcium stearate was approximately 6.7 parts, and for every 100 parts of silica, the amount of erucamide was approximately 4 parts.

[0071] In the preparation process, PBAT was first dried at 52℃ for 4 hours, and PLA was dried at 58℃ for 5 hours. After drying, the moisture content of both PBAT and PLA was 0.08 wt%. The epoxy ring-opening agent and PLA were premixed with each other at 25℃, atmospheric pressure, and air atmosphere for 5 minutes at a stirring speed of 140 r / min. Then, PBAT, silica, calcium stearate, and erucamide were added, and the mixture was premixed for another 10 minutes at a stirring speed of 200 r / min, for a total premixing time of 15 minutes. The premixed material was fed into a twin-screw extruder with four temperature zones of 155℃, 168℃, 175℃, and 170℃, a screw speed of 180 r / min, an effective residence time of 2.5 minutes, and a melt pressure of 9 MPa. The extrudate was air-cooled to 25℃, pelletized, and then dried at 52℃ for 3 hours.

[0072] The obtained PBAT / PLA reactive compatibility masterbatch was fed into a blown film equipment with a die temperature of 160℃, a blow-up ratio of 2.8, and a draw ratio of 10. After cooling and setting, a single-layer film with a nominal thickness of 0.050mm was obtained. During the blown film process, the extrusion pressure was set to 10MPa, the fluctuation of the blown film extrusion pressure relative to the set extrusion pressure was 0%, and the average deviation of the film thickness relative to the target film thickness was 0%. Subsequently, the single-layer film was heat-sealed at a heat-sealing temperature of 140℃, a heat-sealing time of 0.5s, and a heat-sealing pressure of 0.35MPa to form bags.

[0073] The prepared samples underwent quality testing. The melt flow rate was 5.0±0.2 g / 10 min, n=3; the gel point area ratio was 0.20±0.02%, n=3; the PLA dispersed phase D50 was 0.85±0.03 μm, and the aspect ratio along the blown film traction direction was 9.0±0.5, n=3. The longitudinal tensile strength was 34.0±1.0 MPa, the transverse tensile strength was 30.0±0.9 MPa, the longitudinal nominal strain at break was 460±16%, the transverse nominal strain at break was 420±15%, and the heat-sealing strength was 9.0±0.3 N / 15 mm, n=3. The silica raw material was dispersed in anhydrous ethanol and sonicated for 7 min before laser particle size analysis to confirm that its D50 was consistent with the feed specifications. Single-layer film or bag samples were cut for controlled composting evaluation, and biodegradability records were generated.

[0074] Applicable scenarios for this embodiment: This embodiment uses a medium ratio and medium process intensity. The combination of silica, calcium stearate and erucamide is biased towards the low lubrication and smoothness area, which is suitable for the preparation of daily express bags that take into account the opening feel, heat sealing stability and film bubble processing stability.

[0075] Example 4 I. Preparation Target and Raw Material State: The preparation scale is approximately 15 kg of PBAT / PLA reactive compatibility masterbatch. The target product is a bag formed by heat sealing a single-layer film. PBAT is a commercially available material with a melt flow rate of 8 g / 10 min; PLA is a commercially available material with a supplier-specified number-average molecular weight of 1.6 × 10⁻⁶. 5 g / mol; the epoxy ring-opening reagent consisted of 1,4-butanediol diglycidyl ether and trimethylolpropane triglycidyl ether, with a mass fraction of 10 wt% for trimethylolpropane triglycidyl ether; silica was a commercially available material with a D50 of 6 μm; calcium stearate and erucamide were also commercially available materials. PBAT was dried at 45°C for 5 h, and PLA was dried at 65°C for 4 h. After drying, the moisture content of PBAT and PLA was 0.05 wt%.

[0076] II. Formulation Composition and Premixing Control: By mass of the ingredients, PBAT is 65 parts by mass, PLA is 30 parts by mass, and epoxy ring-opening agent is 0.60 parts by mass, including 0.54 parts by mass of 1,4-butanediol diglycidyl ether and 0.06 parts by mass of trimethylolpropane triglycidyl ether; silica is 0.80 parts by mass, calcium stearate is 0.05 parts by mass, and erucamide is 0.032 parts by mass. For every 100 parts of silica, calcium stearate is 6.25 parts, and for every 100 parts of silica, erucamide is 4 parts. First, premix the epoxy ring-opening agent and PLA at 130 rpm for 6 minutes. Then add PBAT, silica, calcium stearate, and erucamide, and continue premixing at 210 rpm for 9 minutes. The total premixing time is 15 minutes. The premixing environment is 25°C, normal pressure, and air atmosphere.

[0077] III. Reactive Extrusion and Post-processing: The premixed material was fed into a twin-screw extruder with four temperature zones set at 162℃, 172℃, 182℃, and 178℃ respectively. The screw speed was 220 r / min, the effective residence time was 3.5 min, and the melt pressure was 13 MPa. The extrudate was cooled to 25℃ by air cooling and then pelleted. The pellets were dried at 60℃ for 2 h to obtain PBAT / PLA reactive compatibility masterbatch for the blown film step. The quality criteria for the output were continuous strips, no obvious melt adhesion on the pellet surface, and the masterbatch moisture content meeting the requirements for subsequent blown film production.

[0078] IV. Blown Film Heat Sealing and Online Control: After the PBAT / PLA reactive compatible masterbatch enters the blown film equipment, it is melted, plasticized, and extruded through a die to form a film bubble. The die temperature is 170℃, the blow-up ratio is 3.2, and the draw ratio is 12. After cooling and shaping, a single-layer film with a nominal thickness of 0.060mm is obtained. The blown film extrusion pressure is set to 11MPa. The actual online monitoring pressure fluctuation relative to the set extrusion pressure is +5%, and the average deviation of the film thickness relative to the target film thickness is -5%. The single-layer film is heat-sealed at a heat-sealing temperature of 150℃, a heat-sealing time of 0.6s, and a heat-sealing pressure of 0.4MPa, forming a heat-sealed edge of the bag.

[0079] V. Quality Testing Methods and Results: The melt flow rate of the PBAT / PLA reactive compatibility masterbatch was 6.5±0.2 g / 10 min, n=3; the gel point area ratio was 0.35±0.02%, n=3. Microscopic morphology analysis of the monolayer film cross-section showed that the PLA dispersed phase D50 was 0.60±0.03 μm, and the aspect ratio along the blown film traction direction was 12.0±0.5, n=3. The longitudinal tensile strength of the monolayer film was 40.0±1.1 MPa, the transverse tensile strength was 34.0±0.9 MPa, the longitudinal nominal strain at break was 520±18%, the transverse nominal strain at break was 500±16%, and the heat-sealing strength was 10.5±0.4 N / 15 mm, n=3. FTIR, DSC, and microscopic morphology detection are used together to record the interfacial compatibility state of the samples; controlled compost evaluation records organic carbon content, carbon dioxide release, and test time, and uses the converted data as the quality retention data for biodegradability attributes.

[0080] The process features and application directions of this embodiment. This embodiment uses a lower proportion of lubricating and slipping agents with a higher silica content, combined with a higher draw ratio and medium-high heat sealing conditions, to demonstrate feasibility under a wider process window. It is suitable for express delivery bag products that require smooth film opening, stable heat-sealed edges, and a certain load-bearing capacity.

[0081] Comparative Example 1 The comparative example is basically the same as Example 1, except that the amount of PBAT added in step S2 is 50 parts by mass, while other conditions remain unchanged.

[0082] Comparative Example 2: It is basically the same as Example 1, except that the amount of PLA fed in step S2 is 15 parts by mass, and other conditions remain unchanged.

[0083] Comparative Example 3: It is basically the same as Example 1, except that the amount of 1,4-butanediol diglycidyl ether added in step S2 is 0.10 parts by mass, and other conditions remain unchanged.

[0084] Comparative Example 4: It is basically the same as Example 1, except that the amount of silicon dioxide fed in step S2 is 0.10 parts by mass, and other conditions remain unchanged.

[0085] Comparative Example 5: It is basically the same as Example 1, except that the amount of calcium stearate added in step S2 is 0.02 parts by mass, and other conditions remain unchanged.

[0086] Comparative Example 6: It is basically the same as Example 1, except that the amount of erucamide added in step S2 is 0.01 parts by mass, and other conditions remain unchanged.

[0087] Comparative Example 7: Basically the same as Example 1, except that in step S1, PBAT was dried at 40°C for 1 hour and PLA was dried at 45°C for 1 hour, and the moisture content of PBAT and PLA after drying was controlled to be 0.25 wt%, with other conditions remaining unchanged.

[0088] Comparative Example 8: It is basically the same as Example 1, except that in step S3, the temperatures of the four temperature zones of the twin-screw extruder from the feed section to the die head section are 140°C, 150°C, 160°C and 155°C respectively, while other conditions remain unchanged.

[0089] Comparative Example 9: Essentially the same as Example 1, except that 1,4-butanediol diglycidyl ether was not added in step S2, and PLA was premixed as in Example 1, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect of 1,4-butanediol diglycidyl ether on the PBAT / PLA phase interface construction method.

[0090] Comparative Example 10: Essentially the same as Example 1, except that in step S2, the sequential control of premixing 1,4-butanediol diglycidyl ether with PLA for 3 min was omitted. Instead, PBAT, PLA, 1,4-butanediol diglycidyl ether, silica, calcium stearate, and erucamide were premixed all at once for 10 min at 180 rpm under air conditions at 25°C and atmospheric pressure, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect of the premixing order of 1,4-butanediol diglycidyl ether and PLA on the construction of the PBAT / PLA phase interface.

[0091] Comparative Example 11: This example is essentially the same as Example 1, except that silica is not added in step S2; instead, 0.05 parts by weight of calcium stearate and 0.03 parts by weight of erucamide are added, while other conditions remain unchanged. This comparative example is used to verify the synergistic effect of silica, calcium stearate, and erucamide.

[0092] Characterization and performance testing: The range of test data is determined by the arithmetic mean of the n=3 test results, and repeatability is characterized by the standard deviation.

[0093] Using PBAT / PLA reactive compatibility masterbatch as the test object, the effect of melt flow rate on the blown film processing window was evaluated. After drying the samples at 45℃ for 2 hours, they were tested according to GB / T 3682.1-2018 "Plastics - Determination of melt mass flow rate and melt volumetric flow rate - Part 1: Standard Method" at 190℃ and 2.16 kg. The extrusion mass was recorded for 10 minutes, n=3, and the mean and standard deviation were calculated. The fields represent the mean melt flow rate and the standard deviation of the melt flow rate, in g / 10min. Values ​​within the range of 2-8 indicate better processing compatibility and are entered into the experimental data table.

[0094] Using extruded tablets or monolayer films as samples, the proportion of gel dots in the area was evaluated. The samples were placed under an optical microscope, and at least five non-overlapping fields of view were acquired. Binarization was performed using the same threshold, and the percentage of the total projected area of ​​gel dots in the statistical field of view was calculated (n=3). The fields are the average and standard deviation of the gel dot area proportion, in %. Lower values ​​indicate better melt homogeneity. When no gel dot region meeting the identification criteria was observed within the acquired field of view, the gel dot area proportion was recorded as 0.00%.

[0095] The size and orientation of the PLA dispersed phase were evaluated using the low-temperature brittle fracture cross-section of a single-layer film along the blown film traction direction. After acquiring microscopic images, at least 200 PLA ​​dispersed phases were counted for each sample. The projected area was converted to the equivalent circle diameter, and the median of the number distribution was taken as D50. Simultaneously, the aspect ratio was calculated as the ratio of the maximum length in the traction direction to the maximum width in the vertical direction, with n=3. The fields are the mean D50, standard deviation of D50, mean aspect ratio, and standard deviation of aspect ratio for the PLA dispersed phases, in μm and dimensionless. Figure 5 and Figure 6 The distribution curve shown is based on the equivalent circle diameter data obtained from the above statistics. Figure 7 The distribution curves shown are based on the aspect ratio data obtained from the above statistics and are used to represent the relative distribution trends among different samples; D50 and aspect ratio in Table 1 are the statistical results for the corresponding sample n=3.

[0096] Using single-layer films as the research object, the longitudinal and transverse tensile properties were evaluated. Samples were cut along both the traction direction and perpendicular to the traction direction. Films with a thickness less than 1 mm were tested according to GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets". Sample thickness, width, gauge length, test speed, maximum force, and breaking displacement were recorded, with n=3. The fields are longitudinal tensile strength, transverse tensile strength, longitudinal nominal strain at break, transverse nominal strain at break, and their standard deviation, in MPa and %. Higher values ​​indicate better load-bearing capacity.

[0097] The heat seal strength is evaluated using the heat-sealed edge of the bag as the object. A 15mm wide sample is cut from the heat-sealed edge of the bag perpendicular to the heat-sealing direction. A tensile peel test is performed according to QB / T2358-1998 "Test Method for Heat Seal Strength of Plastic Film Packaging Bags". The maximum force or stable peel force is recorded, n=3, and the results are expressed in N / 15mm. The fields are the average heat seal strength and the standard deviation of the heat seal strength, in N / 15mm. Higher values ​​indicate better retention of the heat seal structure.

[0098] The opening slippage was evaluated based on the contact state between the inner surfaces of a single-layer membrane. The samples were equilibrated at 23℃ and 50% relative humidity for 4 hours. A thin-film friction coefficient meter was used with a load of 200g. The contact area of ​​the slider was set according to the fixed value of the instrument fixture. The dynamic friction coefficient of the stable segment during the sliding process was tested, with n=3. The fields are the average dynamic friction coefficient and the standard deviation of the dynamic friction coefficient, in units of 1. The lower the value, the better the opening slippage.

[0099] Using microscopic images of single-layer membrane surfaces, the proportion of effective particle area on the membrane surface was evaluated. After equilibration at 23℃ and 50% relative humidity for 4 hours, membrane surface images were acquired. The identifiable particle regions formed by silica and its combination with lubricating and slip-forming components were segmented using a threshold. The percentage of the total projected area of ​​identifiable particles relative to the total area of ​​the statistical image was calculated (n=3). The fields are the single value, mean, and standard deviation of the proportion of effective particle area on the membrane surface, in %. The obtained data are used to characterize the particle distribution related to membrane surface anti-adhesion and opening slip properties.

[0100] Using samples cut from single-layer membranes or bags, the final aerobic biodegradation capacity under controlled composting conditions was evaluated. Tests were conducted according to GB / T 19277.1-2025, "Determination of final aerobic biodegradation capacity of materials under controlled composting conditions—Method for determining the release of carbon dioxide—Part 1: General Method." The organic carbon content, carbon dioxide release, and test time of the samples were recorded, and the biodegradation rate calculated from the carbon dioxide release was used as the evaluation data.

[0101] To verify the effectiveness of the high-strength biodegradable express bag material and its manufacturing process described in this invention in addressing the challenges of balancing mechanical strength and biodegradability, and the interplay between heat-sealing structural integrity and opening smoothness, the effects of the reactive compatibility component, PLA reinforcing phase, inorganic anti-adhesion reinforcing component, and blown film traction process on the longitudinal tensile strength, heat-sealing strength, dispersed phase morphology, melt processing stability, film surface friction characteristics, and final bag structural integrity were investigated. The results shown in the figures demonstrate that this invention does not rely solely on a single component to improve individual properties. Instead, it achieves a better overall balance between strength, heat sealing, opening smoothness, and the structural stability of the biodegradable structure through the synergistic regulation of the PBAT continuous phase, PLA dispersed reinforcing phase, epoxy ring-opening reactant, silica, calcium stearate, and erucamide.

[0102] like Figure 1As shown, with PLA, silica, draw ratio, and other processing parameters remaining constant, only the amount of epoxy ring-opening agent was adjusted within the range of 0.10-1.00 parts by mass. The results showed that as the amount of epoxy ring-opening agent increased from 0.10 parts by mass to approximately 0.50 parts by mass, both the longitudinal tensile strength and heat-sealing strength of the film increased synchronously; however, when the amount continued to increase, both properties decreased. This indicates that an appropriate amount of epoxy ring-opening agent can improve the interfacial compatibility between PBAT and PLA, increase stress transfer efficiency, and enhance the structural continuity of the heat-sealing region; however, if the agent is excessive, it may cause local over-reaction, inhomogeneous melt structure, or phase disturbance, leading to reduced processing stability and heat-sealing stability. Therefore, the appropriate amount of epoxy ring-opening agent should be controlled within a range that promotes interfacial compatibility without causing excessive cross-linking or gel defects; approximately 0.50 parts by mass corresponds to a better overall effect.

[0103] Based on the established significant contribution of reactive compatibility, the influence of PLA content on the enhanced phase structure and film properties was further investigated. For example... Figure 2 As shown, with the epoxy ring-opening reactant, silica, draw ratio, and other processing parameters remaining constant, the PLA dosage was adjusted within the range of 15-40 parts by mass. The results showed that when the PLA dosage was approximately 28-30 parts by mass, both longitudinal tensile strength and heat-sealing strength remained at a high level, indicating superior overall performance. This phenomenon suggests that when PLA, as a dispersed reinforcing phase, has too low a content, it is difficult to fully exert its rigidity reinforcement and orientation strengthening effects; while when the content is too high, phase region coarsening or interface defect accumulation easily occurs between the dispersed phases, which is detrimental to the continuity of the heat-sealing layer and the maintenance of the film's toughness. Therefore, a moderate PLA content can form a more reasonable dispersed phase network in the PBAT continuous phase, enabling the material to achieve higher mechanical strength and more stable heat-sealing performance while maintaining its biodegradable composition.

[0104] like Figure 3 As shown, with PLA, epoxy ring-opening reactant, traction ratio, and other processing parameters remaining constant, only the amount of silica was adjusted to 0.10-1.00 parts by mass. Test results show that when the silica content is approximately 0.50 parts by mass, the longitudinal tensile strength and heat-sealing strength reach optimal levels. At lower silica content, its contribution to film surface anti-adhesion, nucleation reinforcement, and microstructure support is insufficient; when the content is too high, silica particles may agglomerate, forming localized stress concentration points or interface defects, thereby weakening the film strength and the integrity of the heat-sealed structure. Therefore, an appropriate amount of silica not only helps improve film opening properties and surface microstructure but also, in conjunction with the reactive compatibility system, enhances the mechanical stability of the film without significantly impairing heat-sealing performance.

[0105] Besides formulation factors, the blown film traction process also has a significant impact on the orientation of the dispersed phase and the integrity of the heat-sealed structure. For example... Figure 4 As shown, with PLA, epoxy ring-opening reactant, silica, and other formulation parameters remaining constant, the draw ratio was controlled within the range of 3-18 for comparison. The results show that increasing the draw ratio from a low value to approximately 11 significantly improves both longitudinal tensile strength and heat-sealing strength; however, as the draw ratio continues to increase, both properties decrease. This indicates that moderate draw can promote favorable longitudinal orientation of chain segments and PLA dispersed phase in the PBAT / PLA system, improving load transfer efficiency and overall film strength; however, excessive draw leads to overly strong orientation, localized thinning of the film layer, reduced heat-sealing layer integrity, or increased micro-defects, thereby weakening the heat-sealing strength. Therefore, a draw ratio of approximately 11 achieves a better balance between enhanced orientation and reliable heat sealing.

[0106] The above Figures 1 to 4 From the perspective of formulation and process parameters, this invention, by controlling the amount of epoxy ring-opening agent (approximately 0.50 parts by mass), PLA (approximately 28-30 parts by mass), silica (approximately 0.50 parts by mass), and traction ratio (approximately 11), can simultaneously achieve optimal longitudinal tensile strength and heat-sealing strength. This preliminarily demonstrates that this invention can alleviate the contradiction in traditional PBAT / PLA express bag materials where "reinforcement leads to weakened heat sealing" or "improved heat sealing is accompanied by insufficient mechanical strength."

[0107] To further explain the structural origin of the aforementioned performance improvement, the particle size and morphological distribution of the PLA dispersed phase in Example 1 and Comparative Examples 3, 9, and 10 were analyzed. Figure 5 This is a differential distribution diagram of the equivalent circle diameter of the PLA dispersed phase, where the horizontal axis represents the equivalent circle diameter of PLA, and the vertical axis represents the differential density. Figure 5 As can be seen, the distribution peaks of Example 1 are more concentrated, and the equivalent circle diameter of PLA is mainly concentrated in the smaller particle size range; in contrast, the distribution peaks of the comparative sample shift towards the larger particle size direction and show varying degrees of distribution broadening. This result indicates that the present invention, through the participation of the epoxy ring-opening reactant in interfacial state regulation, and in conjunction with appropriate PLA content and processing traction conditions, can suppress the coarsening of the PLA dispersed phase, enabling PLA to form a finer and more uniform dispersion structure in the PBAT continuous phase.

[0108] Figure 6Further, the cumulative distribution was used to reflect the particle size distribution trends of the PLA dispersed phase, such as D10, D50, and D90. The results showed that the cumulative distribution curve of Example 1 was generally located within a smaller particle size range, and the curve rose faster, indicating a narrower particle size distribution and better dispersed phase uniformity. A narrower particle size distribution helps reduce local stress concentration in large-size PLA phase regions, avoiding interfacial debonding, voids, or crack propagation during stretching or heat sealing, thereby improving the overall mechanical stability and heat sealing reliability of the film. Figure 5 and Figure 6 It can be seen that the control of PLA dispersed phase size in this invention is an important structural basis for achieving both high strength and heat seal integrity.

[0109] While particle size is controlled, the orientation morphology of the PLA dispersed phase also affects the longitudinal reinforcement effect of the film. Figure 7 The figures show the aspect ratio distribution of the PLA dispersed phase in Example 1 and Comparative Examples 3, 9, and 10, with the horizontal axis representing the PLA dispersed phase aspect ratio and the vertical axis representing the differential density. The results show that the aspect ratio distribution in Example 1 is concentrated in a relatively high and moderate range; while the aspect ratio distribution of the comparative examples is lower or more dispersed. This result indicates that the present invention can enable the PLA dispersed phase to form a morphological structure with moderate traction orientation in the PBAT continuous phase. This type of structure can provide reinforcement along the longitudinal direction of the film without compromising the continuity of the heat-sealing layer due to excessive stretching or morphological loss of control, thus explaining... Figures 1 to 4 The phenomenon that longitudinal tensile strength and heat-sealing strength improve simultaneously.

[0110] To illustrate the relationship between the dispersed phase regulation and the reaction compatibility described above, FTIR and DSC analyses were performed on Example 1 and Comparative Examples 9 and 10. Figure 8 As shown, in the FTIR absorption spectrum, the horizontal axis represents wavenumber and the vertical axis represents absorbance. The changes in absorption peaks related to hydroxyl, ester, ether bonds, and epoxy groups are observed. The test results show that Example 1 exhibits peak shape changes in the hydroxyl and ester group related regions; Comparative Example 10 still retains a relatively obvious trend of epoxy characteristic peaks, indicating that the degree of epoxy group consumption and reaction pathway may differ under different premixing sequences, and its interfacial compatibility contribution is related to… Figures 5 to 7 The data correspond to the dispersed phase morphology and performance data shown in Tables 1 and 2; however, Comparative Example 9, lacking the addition of 1,4-butanediol diglycidyl ether, exhibits insufficient related reaction characteristics. These results indicate that the epoxy ring-opening reagent used in this invention participates in end-group-related reactions or interface state regulation in the PBAT / PLA system, thereby improving the compatibility of the two phases and providing characterization evidence for the subsequent formation of fine, uniform, and appropriately oriented PLA dispersed phases.

[0111] Figure 9The DSC heat flow-temperature curves for Example 1, Comparative Examples 9 and 10 are shown to observe the thermal behavior related to glass transition, cold crystallization, and melting. Figure 9 It can be seen that the thermal transition peak shape of Example 1 is more stable and the thermal flow response is more balanced; in contrast, the comparative sample shows a tendency for weaker, wider, or insufficiently transformed peak shapes. This result indicates that the present invention, by adjusting the interfacial compatibility state, improves the thermal behavior coordination between the PLA dispersed phase and the PBAT matrix, which is beneficial for expanding the thermal processing window and improving the melt bonding stability during the heat sealing process. Therefore, Figure 8 FTIR results and Figure 9 The DSC thermal behavior results are consistent with the conclusion that the compatibility of the PBAT / PLA system has improved, and can serve as auxiliary characterization evidence for compatibility design.

[0112] Furthermore, Figure 10 The processing adaptability of the system was evaluated from two dimensions: processing flowability and gel defects. Figure 10 The graph shows the melt flow rate and gel point area ratio for Examples 1 and Comparative Examples 3, 9, and 10, with the left axis representing melt flow rate and the right axis representing gel point area ratio. The results show that Example 1 maintained a moderate melt flow rate and had a gel point area ratio close to its lowest value; while the comparative examples exhibited either high fluidity or an increase in gel points. Excessively high melt flow rate usually indicates insufficient melt strength, which is detrimental to blown film stability; an increased gel point area ratio can cause film surface defects, localized stress concentration, and weak points in heat sealing. Example 1 simultaneously achieved moderate fluidity and low gel defects, demonstrating that the present invention can promote interfacial compatibility while avoiding gelation problems caused by excessive reaction, ensuring continuous film forming and bag heat sealing integrity from a processing perspective. Comparative Example 9 did not contain 1,4-butanediol diglycidyl ether; its gel point area ratio was statistically analyzed as a localized non-uniformity defect during high-temperature extrusion processing and was not used to characterize the degree of gelation caused by the epoxy ring-opening reactant.

[0113] While addressing the issues of strength and heat sealing, biodegradable express delivery bags must also possess good opening properties and a smooth feel. Therefore, the film surface friction behavior and particle microstructure were evaluated. For example... Figure 11As shown, the correlation graph between heat sealing strength and dynamic friction coefficient of Example 1, Comparative Example 4, and Comparative Example 11 uses dynamic friction coefficient as the abscissa and heat sealing strength as the ordinate, and uses a two-way error bar to reflect the fluctuation of heat sealing performance and slip performance. The results show that Example 1 maintains high heat sealing strength at a lower dynamic friction coefficient; although Comparative Example 4 and Comparative Example 11 show different degrees of slip changes, their heat sealing strength does not improve synchronously. This result indicates that the present invention synergistically regulates the anti-adhesion, lubrication, and slip state of the film surface through silica, calcium stearate, and erucamide, while maintaining the structural integrity of the heat-sealing layer by adjusting the interfacial compatibility state, thereby avoiding the problem in traditional systems where "slip agents improve opening performance but weaken heat sealing strength".

[0114] Figure 12 Further, a scatter plot of the effective particle area ratio of Example 1, Comparative Example 4, and Comparative Example 11 is presented. This plot uses the original scatter plot combined with the mean and standard deviation to show the differences in particle distribution on the film surface. The results show that Example 1 has a moderate effective particle area ratio, and the repeated data shows small fluctuations; Comparative Example 4 has insufficient particle contribution, and Comparative Example 11 has a significantly low particle area ratio, both of which are unable to achieve an effective balance between opening resistance, friction performance, and heat-sealing stability. This indicates that the present invention does not reduce friction by simply increasing the amount of slip agent or anti-blocking agent, but rather by rationally controlling the effective particle structure on the film surface to form a stable micro-protrusion and lubrication synergy state, which reduces opening resistance and avoids excessive isolation of the heat-sealing contact interface.

[0115] To further illustrate the effectiveness of the above formulation and process design from a macroscopic appearance perspective, Figure 13 Macroscopic optical photographs were taken comparing the final product of Example 1 with the final product of Comparative Example 9. Figure 13 a is a macroscopic optical photograph of the final product of Example 1. The sample consists of a PBAT / PLA reactive compatibility monolayer film and a heat-sealed bag. The nominal thickness of the monolayer film is 0.030 mm, and the average thickness, calculated based on the online average film thickness deviation, is approximately 0.027 mm. The gel point area ratio is 0.00 ± 0.00%. This demonstrates that even under relatively thin film conditions, Example 1 can still maintain good film surface uniformity and heat-sealed bag integrity. Figure 13 b is a macroscopic optical photograph of the final product of Comparative Example 9, which consists of a PBAT / PLA monolayer film and a heat-sealed bag prepared without the addition of 1,4-butanediol diglycidyl ether, both with a target film thickness of 0.030 mm. The comparison shows that the lack of interfacial compatibility adjustment reduces the film surface uniformity and visible defect control capability. This macroscopically demonstrates that the participation of 1,4-butanediol diglycidyl ether in interfacial state adjustment plays a positive role in obtaining biodegradable express delivery bag materials with uniform appearance, controlled gel points, and intact heat-sealing structures.

[0116] Figure 14 Further comparison of Example 1 and Comparative Example 9 using SEM morphology was conducted to examine the overall morphology of the film surface, the low-temperature brittle fracture section, and the details of the PLA dispersed phase interface. Figure 14 Image a is a low-magnification SEM image of the final product of Example 1. It can be seen that the monolayer film has a continuous observation area over a large area, and the area ratio of gel points is 0.00±0.00%, indicating that the reaction-compatible masterbatch can form a thin film structure with fewer defects after blown film. Figure 14 b is a low-magnification SEM image of the final product of Comparative Example 9, used to compare the differences in film continuity, flow marks, gel points, and local defects with Example 1. The comparison results show that without the addition of 1,4-butanediol diglycidyl ether, the compatibility of the PBAT / PLA system is insufficient, and the overall morphological stability of the film is relatively poor.

[0117] Figure 14 c is a medium-magnification SEM low-temperature brittle fracture cross-section of the final product of Example 1, showing the cross-sectional structure of a single-layer film with a nominal thickness of 0.030 mm and an average thickness of approximately 0.027 mm, indicating that the present invention can obtain a blown film with a thinner thickness and a continuous cross-section. Figure 14 Image d shows a medium-magnification SEM cross-sectional image of the final product of Comparative Example 9 at low temperature, illustrating the cross-sectional state under the same target film thickness conditions. This image serves as a comparison to determine the changes in film cross-sectional continuity and thickness uniformity without the addition of a reactive compatibilizer. Further observation of the high-magnification image is possible. Figure 14 In Example 1, the PLA dispersed phase D50 is 1.50±0.04μm and the aspect ratio along the blown film traction direction is 3.0±0.2, indicating that the present invention can form a size-controlled PLA dispersed phase with traction orientation in a PBAT continuous phase. Figure 14 f is a high-magnification SEM cross-sectional image of the final product of Comparative Example 9, used to show the PLA dispersed phase and PBAT / PLA interface morphology without the addition of 1,4-butanediol diglycidyl ether. Figure 14 e and Figure 14 The comparison shows that adjusting the interface compatibility state can suppress the coarsening of the PLA phase region, reduce the risk of interface debonding, and improve the dispersion stability of the phase region, thus providing a microscopic basis for the mechanical enhancement and heat sealing integrity of the film.

[0118] Figure 15 The TEM scale was then used to further verify the PBAT / PLA phase region profile, local interface state, and silica distribution. Figure 15 Image a is a bright-field TEM image of the final product of Example 1. The sample is a low-temperature ultrathin section or stained section of a PBAT / PLA monolayer film. The PBAT / PLA phase region, the outline of the PLA micron-sized dispersed phase, and the local distribution of silica can be observed, indicating that the PLA dispersed phase and the PBAT matrix in Example 1 have good structural continuity. Figure 15b is a bright-field TEM image of the final product of Comparative Example 9, used to compare and observe the differences in phase region boundaries, local voids, and dispersed phase continuity without the addition of 1,4-butanediol diglycidyl ether. The results show that the phase region boundaries of Comparative Example 9 are more prone to separation characteristics, and the interface continuity is not as good as that of Example 1.

[0119] Figure 15 c is an HRTEM or local high-resolution TEM image of the final product of Example 1, further showing the local morphology or silica edge structure near the interface region. This figure shows the local TEM morphology of Example 1 in the observed area, and its interface morphology differs from that of Comparative Example 9, which can serve as supplementary evidence of phase region distribution and improved interface morphology. Figure 15 Image d is an HRTEM or local high-resolution TEM image of the final product of Comparative Example 9, used to show the local interface structure without the addition of the reactive compatibilizer. Figure 15 c and Figure 15 The comparison shows that, without interfacial compatibility adjustment, the PBAT / PLA phase interface is more prone to voids or boundary demarcation, which is detrimental to load transfer and heat-sealing stability. TEM results and... Figures 5 to 7 Statistical results of dispersed phases Figures 8 to 10 The results of the reaction and processing stability and Figures 13 to 14 The results are consistent with the macroscopic and SEM morphology results, further demonstrating that the present invention can improve the uniformity of phase distribution and the continuity of interface structure in blended systems at the nano to micrometer scale.

[0120] In conclusion, Figures 1 to 15 The effectiveness of the present invention is explained sequentially from aspects such as formulation dosage, process traction, dispersed phase particle size and morphology, interfacial compatibility, thermal behavior, melt processing stability, film surface friction structure, and the macro / micro morphology of the final film and bag. Figures 1 to 4The single-factor analysis showed that when the epoxy ring-opening agent was about 0.50 parts by mass, PLA was about 28-30 parts by mass, silica was about 0.50 parts by mass, and the draw ratio was about 11, the longitudinal tensile strength and heat-sealing strength were in the optimal range. Example 1, as a low-ratio endpoint scheme, under the conditions of 0.20 parts by mass of epoxy ring-opening agent, 20 parts by mass of PLA, 0.20 parts by mass of silica, and a draw ratio of 5, can form a controlled orientation structure with a PLA dispersed phase D50 of about 1.50±0.04μm and an aspect ratio of about 3.0±0.2 along the draw direction. Under the condition of a relatively thin film thickness of 0.030mm and an average equivalent of about 0.027mm, a film surface state with a gel point area ratio of 0.00±0.00% was achieved. Therefore, this invention effectively mitigates the mutual constraints between reinforcement, degradation, heat sealing, and opening performance by using PBAT continuous phase to support film formation, PLA dispersed phase reinforcement, epoxy ring-opening reactant to regulate interfacial compatibility, and silica / calcium stearate / erucamide to synergistically regulate the anti-adhesion and lubrication of the film surface. This results in a courier bag material that combines high mechanical strength, stable heat sealing performance, good film surface lubrication and opening performance, and stable structure of the biodegradable system.

[0121] Table 1. Rheological and micromorphological indices

[0122] Table 2 Mechanical, thermal, frictional and degradation performance indicators

[0123] As can be seen from the performance of the examples and comparative examples in the table, Examples 1-4 achieve a relatively stable overall match between melt flow rate, gel point area ratio, PLA dispersed phase size, orientation state, tensile strength, nominal strain at break, heat sealing strength, and coefficient of dynamic friction. In Examples 2-4, with increases in epoxy ring-opening reactant, traction ratio, film thickness, and heat sealing conditions, the PLA dispersed phase becomes finer and its orientation is enhanced, resulting in an overall improvement in longitudinal and transverse strength and heat sealing strength. Example 1, operating under low formulation and mild conditions, still maintains a basic level of feasibility. In Comparative Examples 1-8, after changing the formulation, additives, or process conditions, at least one core indicator deviates. In Comparative Examples 9-11, after disassembling the synergistic units, the interface morphology, mechanical properties, or opening smoothness-related indicators no longer maintain a synchronous match, indicating that the data trend is consistent with the formulation-interface-film formation-heat sealing logic.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-strength, biodegradable express delivery bag material, characterized in that, The high-strength biodegradable express bag material comprises a single-layer film formed by blown film, or a bag body formed by heat sealing the single-layer film. The raw materials for preparing the high-strength biodegradable express bag material include, by weight, the following: Polybutylene adipate / butylene terephthalate copolymer, abbreviated as PBAT, 55-70 parts by weight; Polylactic acid, abbreviated as PLA, 20-35 parts by weight; 0.20-0.80 parts by weight of epoxy ring-opening reagent; 0.20-0.80 parts by weight of silicon dioxide; 0.05-0.30 parts by weight of calcium stearate; Erucamide 0.03-0.20 parts by weight; The PBAT forms a continuous PBAT phase, the PLA forms a dispersed PLA phase dispersed in the continuous PBAT phase, and the nominal thickness of the monolayer membrane is 0.030-0.080 mm.

2. The high-strength biodegradable express bag material according to claim 1, characterized in that, The epoxy ring-opening agent is 1,4-butanediol diglycidyl ether, or a mixture of 1,4-butanediol diglycidyl ether and trimethylolpropane triglycidyl ether, wherein the mass fraction of trimethylolpropane triglycidyl ether in the epoxy ring-opening agent is 0-40 wt%; the D50 of the PLA dispersed phase is 0.20-1.50 μm, the PLA dispersed phase is oriented along the blown film traction direction, and the aspect ratio of the PLA dispersed phase along the blown film traction direction is 3-15.

3. The high-strength biodegradable express bag material according to claim 1, characterized in that, The single-layer film in the high-strength biodegradable express bag material is formed by blown film production from PBAT / PLA reactive compatibility masterbatch. The PBAT / PLA reactive compatibility masterbatch is prepared through the following steps: A1. Raw material drying: PBAT and PLA are dried separately to achieve a moisture content of 0.02-0.15 wt% for both. A2. Raw material premixing: PBAT, PLA, the epoxy ring-opening agent, silica, calcium stearate and erucamide are mixed according to the mass parts of the raw materials to obtain a premix; A3. Reactive extrusion: The premixed material is fed into a twin-screw extruder and reactively extruded at 150-185°C to obtain the extrudate; A4. Post-processing: The extrudate is cooled, pelletized and dried to obtain the PBAT / PLA reaction-compatible masterbatch.

4. The high-strength biodegradable express bag material according to claim 3, characterized in that, In step A3, the epoxy ring-opening reactant is used to participate in the reaction of the terminal carboxyl or terminal hydroxyl groups of PBAT and / or PLA and to adjust the compatibility state of the PBAT / PLA phase interface; the reaction extrusion conditions in step A3 are controlled so that the melt flow rate of the extrudate is 2-8 g / 10 min, the gel point area ratio is 0.00-0.50%, and the D50 of the PLA dispersed phase is 0.20-1.50 μm.

5. The high-strength biodegradable express bag material according to claim 1, characterized in that, The melt flow rate of the PBAT is 2-10 g / 10 min.

6. The high-strength biodegradable express bag material according to claim 3, characterized in that, In step A3, the twin-screw extruder has four temperature zones from the feed section to the die head section, with temperatures of 150-165℃, 160-175℃, 170-185℃ and 165-180℃ respectively.

7. The high-strength biodegradable express bag material according to claim 1, characterized in that, The high-strength biodegradable express bag material has a melt flow rate of 2-8 g / 10 min and a gel point area ratio of 0.00-0.50%.

8. The high-strength biodegradable express bag material according to claim 1, characterized in that, The silica has a D50 of 1-8 μm. In the mass ratio of silica, calcium stearate and erucamide, the silica corresponds to 100 parts, the calcium stearate corresponds to 6-38 parts, and the erucamide corresponds to 4-25 parts.

9. The high-strength biodegradable express bag material according to claim 1, characterized in that, The longitudinal tensile strength of the single-layer membrane is 25-45 MPa, the transverse tensile strength is 22-38 MPa, the longitudinal fracture nominal strain is 250-650%, the transverse fracture nominal strain is 250-600%, and the heat-sealing strength is 6-12 N / 15 mm.

10. A manufacturing process for a high-strength biodegradable express delivery bag material as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Provide the prepared PBAT / PLA reactive compatibility masterbatch, which is obtained by drying PBAT and PLA separately, mixing the dried PBAT and PLA with the epoxy ring-opening reactant, silica, calcium stearate and erucamide, and then react-extruded, cooled, pelletized and dried by a twin-screw extruder. S2. The PBAT / PLA reactive compatibility masterbatch is blown into a film, and the nominal thickness of the monolayer film is controlled to be 0.030-0.080 mm to obtain a monolayer film; S3. Heat-seal the single-layer film to form a bag, thereby obtaining the high-strength biodegradable express bag material.

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