Preparation process of high-toughness environment-friendly plastic bag

Abstract

This application relates to the field of environmentally friendly plastic bag manufacturing technology, and discloses a manufacturing process for high-toughness environmentally friendly plastic bags. The process involves mixing anhydrous citric acid, zinc ricinoleate, trimellitic anhydride, hydrophilic fumed silica, and epoxidized soybean oil to prepare a dry-water reactive core powder. Poly(butylene adipate / terephthalate), polylactic acid, talc, and ethylene bis-stearamide are blended and melted, and the core powder is fed into the rear section of an extruder. Coordination masking prevents early cross-linking and gelation of the matrix, and the mixture is granulated to obtain latent masterbatch. Subsequently, an inverted temperature gradient is used for blown film production. The high-temperature section promotes the unmasking of the active core and in-situ branching and chain extension. A low-temperature die section constructs a multi-hydrogen bond network between molecules to physically anchor the slip agent. The bag is then wound and heat-sealed. This invention solves the problems of easy crystal point formation during blend granulation and bubble breakage during blown film production, improves the longitudinal and transverse mechanical toughness of the plastic bag, and avoids the heat-sealing strength reduction caused by slip agent surface precipitation.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly plastic bag manufacturing technology, specifically a manufacturing process for a high-toughness environmentally friendly plastic bag. Background Technology

[0002] Currently, environmentally friendly plastic bags are typically made by blending poly(butylene adipate / terephthalate) and polylactic acid (PLA) to balance the material's flexibility and basic stiffness. However, in actual production, these two polymers exhibit inherent thermodynamic incompatibility, resulting in weak interfacial bonding and a generally low melt strength in the blend. When materials containing this low-strength melt are subjected to a high tensile force at the die opening of a blown film machine, the film bubble struggles to maintain a stable expansion shape, easily exhibiting vibration or even localized bubble rupture, thus affecting continuous production.

[0003] To improve resin compatibility and increase melt viscosity, reactive crosslinking agents or chain extenders are typically added to the formulation for reactive compatibilization. Conventional mixing and granulation processes often involve direct contact between the crosslinking agent and the bulk resin. Under the high-temperature shear environment of twin-screw extrusion, the crosslinking agent can prematurely initiate disordered coupling of the polymer backbone in areas of locally high concentration, generating over-crosslinked gel microparticles. These unmelted microparticles can cause rapid clogging of the extruder filter and remain on the surface of the final film, forming crystalline defects and reducing the surface quality of the packaging bag.

[0004] Besides defects in the processing stage, the performance of the formed film also has limitations. Due to the unidirectional stretching effect during the blown film traction process, the polymer molecular chains exhibit significant anisotropy, leading to an imbalance in the transverse and longitudinal mechanical properties of the resulting packaging bags. This makes them highly susceptible to tearing and splitting along the longitudinal direction during use. Simultaneously, to reduce the frictional resistance of the processing equipment and improve the film's opening properties, small-molecule slip agents such as amides are typically added to the formulation. These small molecules lack effective spatial anchoring in the matrix resin and spontaneously migrate and precipitate to the material surface during film storage. The slip agents enriched on the surface form a weak boundary layer with low surface energy. In the subsequent heat-sealing bag-making process, this severely hinders the diffusion and interpenetration of the heated and molten polymer chains across the interface between the two film layers. This results in limited initial heat-sealing strength of the finished product, and irreversible decay of the heat-sealing bond after long-term storage, causing the packaging bag seal to crack and fail. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a manufacturing process for high-toughness environmentally friendly plastic bags, which solves the problems of existing polyester blend modified materials being prone to gel crystal points during granulation and extrusion, having low melt strength and easy bubble breakage during the blown film stage, and having longitudinal tearing and long-term heat-sealing strength decay caused by excessive molecular chain orientation and surface precipitation of slip agents in the molded packaging bags.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a process for preparing a high-toughness environmentally friendly plastic bag, comprising: The latent masterbatch is added to a single-screw blown film mill, and the heating temperature from the feeding section to the die head section is controlled to decrease sequentially to form an inverted temperature gradient; the melt is extruded through the die head and blown to form an annular film bubble, which is then cooled, flattened and wound up to obtain a continuous cylindrical film; High-toughness environmentally friendly plastic bags are produced by bottom sealing, side sealing and heat cutting of continuous tubular films; The latent masterbatch comprises the following components by weight: Poly(butylene adipate) 60.0-70.0 parts, polylactic acid 20.0-30.0 parts, talc 2.0-5.0 parts, ethylene bis-stearamide 1.0-2.0 parts, epoxidized soybean oil 3.5-6.5 parts, and dry aqueous reaction core powder; The dry-water reaction core powder comprises the following components by weight: 0.5-1.5 parts anhydrous citric acid, 0.3-0.8 parts zinc ricinoleate, 0.3-0.8 parts trimellitic anhydride, 0.5-1.2 parts hydrophilic fumed silica, and 0.5-1.5 parts epoxidized soybean oil.

[0007] By employing the above technical solution, and utilizing the chemical interactions between the formulation components in conjunction with the temperature and flow channel range of the extrusion blown film equipment, the rheological and crosslinking reactions within the material are carried out in stages. The specific reaction mechanism and effects are as follows: Coordination masking and spatial isolation of the reaction components. In the early stage of extrusion granulation, the high specific surface area of ​​fumed silica is used as a powder carrier to adsorb an appropriate amount of epoxidized soybean oil to form a micro-droplet dispersion phase. The frictional heating caused by mixing promotes the coordination complexation of the oxygen-containing functional groups of anhydrous citric acid with the zinc ions dissociated from zinc ricinoleate, causing the catalyst to temporarily lose its free activity in the subsequent extrusion stage. The dry powder reaction core is fed into the side feed port in the middle and rear section of the extruder. At this time, the silanol groups on the surface of silica act as competitive binding sites, generating a weak interaction with the highly active trimellitic anhydride. Furthermore, the physical feeding position and heating time isolate the active crosslinking agent from the blended resin main material, reducing the probability of disordered coupling of polymer chains during the extrusion granulation stage, thereby effectively controlling the formation of gel crystals.

[0008] As the latent masterbatch enters the high-temperature feeding and compression sections of the blown film machine, external heat gradually disrupts the coordination equilibrium between citric acid and zinc ions. The zinc ions, now in a free state, begin to catalyze the previously dispersed epoxidized soybean oil, causing its epoxy groups to open and undergo transesterification with the end groups of polylactic acid and the polyester matrix. At this point, the freed tetrafunctional citric acid molecules act as multi-arm crosslinking centers, undergoing polycondensation reactions with the ring-opened groups to construct a micro-crosslinked structure between the two incompatible host resins, improving interfacial compatibility and increasing the entanglement density of the chain segments.

[0009] Construction of the physical hydrogen bond network and anchoring of the slip agent. Tripterygium anhydride undergoes asymmetric grafting at higher temperatures, with its anhydride groups attaching to the polyester backbone, while the free carboxyl groups retained on one side dangle from the molecular chain. As the melt moves to the inverted die section with a lower set temperature, the cooling of the system reduces the thermal motion of the macromolecules. Multiple intermolecular hydrogen bonds are established between the grafted free carboxyl groups, the silanol groups on the silica surface, and the amide bonds in the middle of the ethylene bis-stearamide molecule due to hydrogen bond donor-acceptor relationships. This significantly increases the viscoelastic modulus of the melt at the die exit, providing structural support to maintain the stability of the film bubble. At the same time, the ethylene bis-stearamide is confined within the polymer matrix by this hydrogen bond network, inhibiting its ability to migrate to the film surface, avoiding excessive enrichment of the surface precipitate, and thus ensuring the heat-sealing interface adhesion of the finished plastic bag.

[0010] The preparation steps of the dry aqueous reaction core powder include: Anhydrous citric acid, zinc ricinoleate, trimellitic anhydride, and hydrophilic fumed silica are placed in a high-speed mixer and the speed is set to 1500-2000 r / min to dry-mix and fluidize the materials. Then, epoxidized soybean oil is sprayed in according to the formula. The system temperature is maintained at 70-85℃ by shear friction self-heating. After continuous mixing for 10-20 min, the dry water-state reaction core powder is discharged.

[0011] By employing the above technical solution, the set high rotation speed can provide a strong mechanical shearing effect, prompting the atomized epoxidized soybean oil to enter the pores of the fumed silica. The frictional self-heating temperature of the system is controlled between 70 and 85°C. This temperature condition satisfies the activation energy required for coordination between citric acid and zinc ions, and is below the critical temperature for the epoxy groups to initiate a large-scale chain extension reaction in the polymer, thus maintaining the chemical stability of the reaction components at the current stage.

[0012] Preferably, the hydrophilic fumed silica has a silica content >99.8%, a primary particle size of 12–20 nm, and a specific surface area of ​​150–200 m² as measured by the BET method. 2 / g, and the surface has not undergone hydrophobic modification treatment.

[0013] By adopting the above technical solution, the hydrophilic fumed silica without hydrophobic modification retains a large number of polar silanol groups on its surface. These polar groups serve as important sites for adsorbing trimellitic anhydride at the microscopic level and participate in the construction of intermolecular hydrogen bond networks during film cooling and molding. The temperature section from the side feed point to the extruder die head is set to 155–160°C. By controlling the screw speed, the residence time of the dry aqueous reactive core powder from the side feed port to the extrusion outlet is controlled to be 15–25 seconds. Preferably, in step (2), the barrel temperature from the main feed port area to the middle section of the extruder is set to 160–170°C. The injection pressure of the middle section liquid injection pump is set to 4.0–8.0 MPa. By adopting the above technical solution, the temperature range is higher than the melting temperature of the main resin, which ensures the normal plasticization of the material in the screw shear section. The moderate processing temperature also helps to slow down the thermal degradation rate of polyester molecular chains in the high shear section of the screw and maintain the basic molecular weight of the blend.

[0014] High-pressure injection enables room-temperature liquid epoxidized soybean oil to overcome the back pressure of the polymer melt inside the barrel, dispersing it into the higher viscosity melt in the form of fine droplets. This prevents the liquid additives from slipping on the inner wall of the barrel and affecting the mixing effect of the screw.

[0015] The shorter residence time constitutes a supplementary measure to physical isolation. When the reactive powder is dispersed into the homogeneous melt and before a large amount of heat is absorbed and desorption occurs, the material is extruded through a die and rapidly cooled by water ring pelletizing. The active additives are fixed inside the matrix particles by rapid cooling.

[0016] The specific process parameters for the inverted temperature gradient of the single-screw blown film machine are as follows: the barrel temperature in the feeding and compression section is set to 185–195℃; the barrel temperature in the homogenization section is set to 165–175℃; and the die head section temperature is set to 155–165℃. The blow-up ratio for blown film formation is controlled to be 2.5–3.0, and the traction ratio is 3.0–4.0.

[0017] By employing the above technical solution, a processing heat field higher than conventionally set is applied in the initial stage of blown film production. This thermodynamic condition causes the reaction nuclei latent in the masterbatch to unmask, and the released active centers drive the polymer chain segments to complete cross-linking and chain extension during screw extrusion, thereby compensating for insufficient interfacial bonding during the flow of the two-phase blend.

[0018] As the material moves towards the die head, the flow channel temperature gradually decreases. Within this temperature range, the thermal motion of molecules relatively weakens, allowing the spontaneous hydrogen bonding between the pendant carboxyl groups, silanol groups, and ethylene bis-stearamide to become dominant. The viscosity and elasticity of the melt at the extrusion die are increased, providing support for the bubble to resist the disturbance of the blown airflow.

[0019] An appropriate biaxial stretching field causes the polymer molecular chains containing cross-linked structures to orient themselves both longitudinally and transversely. Due to the combined effects of chemical chain extension and physical cross-linking within the system, the molecular chains cannot slip indefinitely, thereby improving the balance of mechanical properties in both longitudinal and transverse directions after film formation.

[0020] Preferably, the talc powder contains more than 60.0% silica and more than 30.0% magnesium oxide.

[0021] By employing the above technical solution, talc powder with a layered structure acts as a heterogeneous nucleating agent during the film cooling and forming stage, which is beneficial to improving the crystallization rate and grain distribution density of the polymer. The formation of micro-grains further restricts the activity space of polymer chain segments in the amorphous region, and, together with the air ring cooling system, solidifies the restricted orientation state of the material, thereby improving the tear resistance of the finished plastic bag.

[0022] This invention provides a process for preparing high-toughness, environmentally friendly plastic bags. It offers the following advantages: 1. This invention avoids gel crystal point problems during extrusion granulation by constructing a dry-water reactive core powder and combining it with side feeding and temperature control in the processing section of a twin-screw extruder. Furthermore, it utilizes the early coordination complexation of citric acid and zinc ions, as well as the physical adsorption on the surface of fumed silica, to mask and spatially isolate the highly active crosslinking system during the granulation stage. This suppresses early disordered coupling of the polymer backbone caused by the crosslinking agent under high-temperature shear, ensuring the unobstructed flow of the extrusion filter and thus eliminating crystal point defects on the surface of the finished film.

[0023] 2. This invention sets an inverted temperature gradient in the blown film forming stage, so that the latent masterbatch undergoes catalytic demasking and polycondensation chain extension in the high-temperature feeding section. Subsequently, in the die cooling section, it promotes the spontaneous establishment of a multiple hydrogen bond physical network between the molecular chain side groups and the lubricant, thereby improving the viscoelasticity of the melt exiting the die and providing the structural support required for the film bubble to maintain its shape, thus solving the common problems of bubble breaking and film bubble vibration in conventional processing.

[0024] 3. This invention anchors ethylene bis-stearamide in the polymer matrix through the internal hydrogen bond network formed during the cooling film-forming stage. This restricts the long-range spontaneous migration of the slip agent to the film surface, blocks the formation pathway of low surface energy weak boundary layers, and ensures the heat-sealing strength of the packaging bag after long-term storage. At the same time, the nucleation effect of talc and the restriction of internal cross-linking nodes prevent unidirectional over-orientation of molecular chains under traction and stretching, and improves the balance of longitudinal and transverse tear toughness of the film. Attached Figure Description

[0025] Figure 1 This is a graph showing the change in melt mass flow rate under continuous extrusion thermal cycling according to the present invention. Figure 2 This is a bar chart showing the number of dead crosslinking crystal points in the thin film of the present invention; Figure 3 The following are verification test diagrams of the dynamic formation of supramolecular hydrogen bond network and the change of melt strength of the present invention. Among them, (a) is a comparison diagram of the characteristic peaks of the variable temperature Fourier transform infrared spectrum of the sample of Example 1 at 190℃ and 160℃, and (b) is a comparison bar chart of the maximum melt traction force of Example 1 and Comparative Example 4 at the two temperatures. Figure 4 The following is a test graph of the processing stability of the thin film preparation process of the present invention, wherein (a) is a real-time torque change curve collected in the twin-screw extrusion granulation stage of Example 1, Comparative Example 1 and Comparative Example 5, and (b) is a bar chart comparing the continuous stabilization time of blown film bubbles of each test sample. Figure 5 The diagram shows a comparison of the mechanical properties and isotropic verification tests of the packaging film of the present invention. (a) is a stress-strain simulation curve of Example 1 and Comparative Example 4 during longitudinal and transverse tensile processes, and (b) is a bar chart showing the distribution of longitudinal and transverse right-angle tear strength of the samples of Example 1, Comparative Example 3, Comparative Example 4 and Comparative Example 5. Figure 6 The graph shows a comparison of the anti-migration properties and long-term heat-sealing stability of the thin film of the present invention. (a) is a bar chart comparing the heat-sealing strength of Example 1, Comparative Example 4 and Comparative Example 5 in the initial state and after accelerated aging at 40°C for 30 days. (b) is a graph showing the trend of the static friction coefficient of the surface of the three groups of thin film samples with the accelerated aging time. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0028] Epoxidized soybean oil, CAS No. 8013-07-8. A commercially available industrial-grade product, it is a pale yellow to slightly yellow transparent liquid at room temperature, with an epoxy value of not less than 6.0% and an iodine value of not more than 6.0 gI. 2 / 100g, acid value not higher than 0.5mgKOH / g.

[0029] Trimeric tricarboxylic anhydride, chemically known as 1,2,4-phenyltricarboxylic anhydride, CAS number 552-30-7. A commercially available industrial-grade product with a purity greater than 99.0% and a melting point of 164–166°C.

[0030] Anhydrous citric acid, CAS No. 77-92-9. Commercially available industrial grade product, purity greater than 99.5%, moisture content less than 0.5%.

[0031] Zinc ricinoleate, CAS No. 13040-19-2. Commercially available industrial-grade powder with a zinc content of 8.0-10.0% and a melting point of 70-75℃.

[0032] Ethylene bis-stearamide, CAS No. 110-30-5. Commercially available industrial grade product, purity greater than 98.0%, melting point 140-145℃, acid value not exceeding 10.0 mg KOH / g.

[0033] Talc, CAS No. 14807-96-6. A commercially available submicron-sized inorganic powder product with a silica content greater than 60.0%, a magnesium oxide content greater than 30.0%, and an average particle size D50 of 800 nm.

[0034] Hydrophilic fumed silica, CAS No. 112945-52-5. A commercially available nano-sized inorganic powder product with a silica content greater than 99.8%, an original particle size of 12–20 nm, and a specific surface area of ​​150–200 m² / g (measured by the BET method). 2 / g, the surface has not undergone hydrophobic modification treatment.

[0035] Preparation Example 1: This preparation example provides a method for preparing dry aqueous reaction core powder, including the following steps: Weigh out 1.0 part anhydrous citric acid, 0.55 part zinc ricinoleate, 0.55 part trimellitic anhydride, and 0.85 part hydrophilic fumed silica and add them to a high-speed mixer. Turn on the high-speed mixer and set the speed to 1750 r / min. While the materials are in a high-speed dry-mixing fluidized state, spray 1.0 part epoxidized soybean oil into the mixer chamber through an atomizing nozzle within 3 minutes. Utilize the self-heating generated by the strong shear friction of the impeller blades to maintain the temperature of the material system at 77℃, and continue mixing for 15 minutes. Discharge the material to obtain a solid dry powder with good flowability, i.e., the dry-water reaction core powder, and seal it for later use at room temperature.

[0036] Preparation Example 2: This preparation example provides a method for preparing dry aqueous reaction core powder, including the following steps: Weigh out 0.5 parts anhydrous citric acid, 0.3 parts zinc ricinoleate, 0.3 parts trimellitic anhydride, and 0.5 parts hydrophilic fumed silica and add them to a high-speed mixer. Turn on the high-speed mixer and set the speed to 1500 r / min. While the materials are in a high-speed dry-mixing fluidized state, spray 0.5 parts epoxidized soybean oil into the mixer chamber through an atomizing nozzle within 2 minutes. Utilize the self-heating generated by the strong shear friction of the impeller blades to maintain the temperature of the material system at 70℃, and continue mixing for 10 minutes. Discharge the material to obtain a solid dry powder with good flowability, i.e., the dry-water reaction core powder, and seal it for later use at room temperature.

[0037] Preparation Example 3: This preparation example provides a method for preparing dry aqueous reaction core powder, including the following steps: Weigh out 1.5 parts anhydrous citric acid, 0.8 parts zinc ricinoleate, 0.8 parts trimellitic anhydride, and 1.2 parts hydrophilic fumed silica and add them to a high-speed mixer. Turn on the high-speed mixer and set the speed to 2000 r / min. While the materials are in a high-speed dry-mixing fluidized state, spray 1.5 parts epoxidized soybean oil into the mixer chamber through an atomizing nozzle within 4 minutes. Utilize the self-heating generated by the strong shear friction of the impeller blades to maintain the temperature of the material system at 85℃, and continue mixing for 20 minutes. Discharge the material to obtain a free-flowing solid dry powder, i.e., the dry-water reaction core powder, and seal it for later use at room temperature.

[0038] Example 1: This embodiment provides a process for preparing a high-toughness, environmentally friendly plastic bag, including the following steps: A co-rotating twin-screw extruder with a main feed port, a mid-section liquid injection pump, and a mid-to-rear-section side feeder was used. 65.0 parts of poly(butylene adipate / terephthalate), 25.0 parts of polylactic acid, 3.5 parts of talc, and 1.5 parts of ethylene bis-stearamide were mixed evenly and fed into the extruder through the main feed port. The barrel temperature from the main feed port to the mid-section of the extruder was set at 165°C to melt the material. 5.0 parts of epoxidized soybean oil were injected under high pressure (5.0 MPa) into the polymer melt via the mid-section liquid injection pump for shear mixing. Subsequently, the dry aqueous reactive core powder prepared in Preparation Example 1 was fed into the melt inside the extruder through the side feeder located before the homogenization section. The temperature from the side feed point to the extruder die head was set at 158°C, and the screw speed was controlled to ensure that the residence time of the dry aqueous reactive core powder from the side feed port to the extrusion outlet was 20 s. The extruded material is pelletized in a water ring and then centrifuged and dried to obtain latent masterbatch.

[0039] The latent masterbatch is added to a single-screw blown film mill. The barrel temperature of the feeding and compression section of the single-screw blown film mill is set at 190℃, the barrel temperature of the homogenization section at 170℃, and the die head section at 160℃, forming an inverted temperature gradient that decreases from high to low. After the melt is extruded through the die head to form an annular film bubble, it is subjected to forced cooling with a large volume of air using a dual-nozzle air ring. The blow-up ratio is controlled at 2.8 and the draw ratio at 3.5 to flatten the film bubble and wind it up to obtain a continuous tubular film.

[0040] A continuous tubular film is loaded into a fully automatic bag-making machine, and the hot cutting blade temperature is set to 138°C. The film is then bottom-sealed, side-sealed, and cut to produce a high-toughness, environmentally friendly plastic bag.

[0041] Example 2: This embodiment provides a process for preparing a high-toughness, environmentally friendly plastic bag, including the following steps: A co-rotating twin-screw extruder with a main feed port, a mid-section liquid injection pump, and a mid-to-rear-section side feeder was used. 60.0 parts of poly(butylene adipate / terephthalate), 20.0 parts of polylactic acid, 2.0 parts of talc, and 1.0 part of ethylene bis-stearamide were mixed evenly and fed into the extruder through the main feed port. The barrel temperature from the main feed port to the mid-section of the extruder was set at 160°C to melt the material. 3.5 parts of epoxidized soybean oil were injected under high pressure (4.5 MPa) into the polymer melt via the mid-section liquid injection pump for shear mixing. Subsequently, 2.1 parts of the dry aqueous reactive core powder prepared in Preparation Example 2 were fed into the melt in the extruder at a constant rate through the side feeder located before the homogenization section. The temperature from the side feed point to the extruder die head was set at 155°C, and the screw speed was controlled to ensure that the residence time of the dry aqueous reactive core powder from the side feed port to the extrusion outlet was 15 s. The extruded material is pelletized in a water ring and then centrifuged and dried to obtain latent masterbatch.

[0042] Latent masterbatch is added to a single-screw blown film mill. The barrel temperature of the feeding and compression section of the single-screw blown film mill is set at 185℃, the barrel temperature of the homogenization section at 165℃, and the die head temperature at 155℃, forming an inverted temperature gradient that decreases from high to low. After the melt is extruded through the die head to form an annular film bubble, it is subjected to forced cooling with a large volume of air using a dual-nozzle air ring. The blow-up ratio is controlled at 2.5 and the draw ratio at 3.0 to flatten the film bubble and wind it up to obtain a continuous tubular film.

[0043] A continuous tubular film is loaded into a fully automatic bag-making machine, and the hot cutting blade temperature is set to 130°C. The film is then bottom-sealed, side-sealed, and cut to produce a high-toughness, environmentally friendly plastic bag.

[0044] Example 3: This embodiment provides a process for preparing a high-toughness, environmentally friendly plastic bag, including the following steps: A co-rotating twin-screw extruder with a main feed port, a mid-section liquid injection pump, and a mid-to-rear-section side feeder was used. 70.0 parts of poly(butylene adipate / terephthalate), 30.0 parts of polylactic acid, 5.0 parts of talc, and 2.0 parts of ethylene bis-stearamide were mixed evenly and fed into the extruder through the main feed port. The barrel temperature from the main feed port to the mid-section of the extruder was set at 170°C to melt the material. 6.5 parts of epoxidized soybean oil were injected under high pressure (6.0 MPa) into the polymer melt via the mid-section liquid injection pump for shear mixing. Subsequently, 5.8 parts of the dry aqueous reactive core powder prepared in Preparation Example 3 were fed into the melt in the extruder at a constant rate through the side feeder located before the homogenization section. The temperature from the side feed point to the extruder die head was set at 160°C, and the screw speed was controlled to ensure that the residence time of the dry aqueous reactive core powder from the side feed port to the extrusion outlet was 25 s. The extruded material is pelletized in a water ring and then centrifuged and dried to obtain latent masterbatch.

[0045] Latent masterbatch is added to a single-screw blown film mill. The barrel temperature of the feeding and compression section of the single-screw blown film mill is set at 195℃, the barrel temperature of the homogenization section at 175℃, and the die head temperature at 165℃, forming an inverted temperature gradient that decreases from high to low. After the melt is extruded through the die head to form an annular film bubble, it is subjected to forced cooling with a large volume of air using a dual-nozzle air ring. The blow-up ratio is controlled at 3.0 and the draw ratio at 4.0 to flatten the film bubble and wind it up to obtain a continuous tubular film.

[0046] A continuous tubular film is loaded into a fully automatic bag-making machine, and the hot cutting blade temperature is set to 145°C. The film is then bottom-sealed, side-sealed, and cut to produce a high-toughness, environmentally friendly plastic bag.

[0047] Example 4: This embodiment provides a process for preparing a high-toughness, environmentally friendly plastic bag, including the following steps: A co-rotating twin-screw extruder with a main feed port, a mid-section liquid injection pump, and a mid-to-rear-section side feeder was used. 60.0 parts of poly(butylene adipate / terephthalate), 30.0 parts of polylactic acid, 4.5 parts of talc, and 1.2 parts of ethylene bis-stearamide were mixed evenly and fed into the extruder through the main feed port. The barrel temperature from the main feed port to the mid-section of the extruder was set at 168°C to melt the material. 4.0 parts of epoxidized soybean oil were injected under high pressure (8.0 MPa) into the polymer melt via the mid-section liquid injection pump for shear mixing. Subsequently, 3.95 parts of the dry aqueous reactive core powder prepared in Preparation Example 1 were fed into the melt in the extruder at a constant rate through the side feeder located before the homogenization section. The temperature from the side feed point to the extruder die head was set at 158°C, and the screw speed was controlled to ensure that the residence time of the dry aqueous reactive core powder from the side feed port to the extrusion outlet was 22 s. The extruded material is pelletized in a water ring and then centrifuged and dried to obtain latent masterbatch.

[0048] Latent masterbatch is added to a single-screw blown film mill. The barrel temperature of the feeding and compression section of the single-screw blown film mill is set at 192℃, the barrel temperature of the homogenization section at 172℃, and the die head temperature at 162℃, forming an inverted temperature gradient that decreases from high to low. After the melt is extruded through the die head to form an annular film bubble, it is subjected to forced cooling with a large volume of air using a dual-nozzle air ring. The blow-up ratio is controlled at 2.6, and the draw ratio at 3.2 to flatten the film bubble and wind it up to obtain a continuous tubular film.

[0049] A continuous tubular film is loaded into a fully automatic bag-making machine, and the hot cutting blade temperature is set to 140°C. The film is then bottom-sealed, side-sealed, and cut to produce a high-toughness, environmentally friendly plastic bag.

[0050] Example 5: This embodiment provides a process for preparing a high-toughness, environmentally friendly plastic bag, including the following steps: A co-rotating twin-screw extruder with a main feed port, a mid-section liquid injection pump, and a mid-to-rear-section side feeder was used. 70.0 parts of poly(butylene adipate / terephthalate), 20.0 parts of polylactic acid, 2.5 parts of talc, and 1.8 parts of ethylene bis-stearamide were mixed evenly and fed into the extruder through the main feed port. The barrel temperature from the main feed port to the mid-section of the extruder was set at 162°C to melt the material. 6.0 parts of epoxidized soybean oil were injected under high pressure (4.0 MPa) into the polymer melt via the mid-section liquid injection pump for shear mixing. Subsequently, 3.95 parts of the dry aqueous reactive core powder prepared in Preparation Example 1 were fed into the melt in the extruder at a constant rate through the side feeder located before the homogenization section. The temperature from the side feed point to the extruder die head was set at 156°C, and the screw speed was controlled to ensure that the residence time of the dry aqueous reactive core powder from the side feed port to the extrusion outlet was 18 s. The extruded material is pelletized in a water ring and then centrifuged and dried to obtain latent masterbatch.

[0051] Latent masterbatch is added to a single-screw blown film mill. The barrel temperature of the feeding and compression section of the single-screw blown film mill is set at 188℃, the barrel temperature of the homogenization section at 168℃, and the die head temperature at 158℃, forming an inverted temperature gradient that decreases from high to low. After the melt is extruded through the die head to form an annular film bubble, it is subjected to forced cooling with a large volume of air using a dual-nozzle air ring. The blow-up ratio is controlled at 2.9 and the draw ratio at 3.8 to flatten the film bubble and wind it up to obtain a continuous tubular film.

[0052] A continuous tubular film is loaded into a fully automatic bag-making machine, and the hot cutting blade temperature is set to 135°C. The film is then bottom-sealed, side-sealed, and cut to produce a high-toughness, environmentally friendly plastic bag.

[0053] Comparative Example 1: Compared with Example 1, the difference is that liquid diversion and side feeding isolation are not performed. Instead, all the raw materials in the formula (including a total of 6.0 parts of epoxidized soybean oil) are added to the high-speed mixer at one time and mixed. Then, all of them are directly fed into the main feed port of the extruder for granulation. Everything else is the same.

[0054] Comparative Example 2: Compared with Example 1, the difference is that the single-screw blown film machine adopts the traditional positive temperature gradient of low temperature first and high temperature later, that is, the temperature of the feeding and compression section barrel is set to 160°C, the temperature of the homogenization section barrel is set to 175°C, and the temperature of the die head section is set to 190°C, and the rest are the same.

[0055] Comparative Example 3: Compared with Example 1, the difference is that hydrophilic fumed silica was removed from the formulation, but all other aspects are the same.

[0056] Comparative Example 4: Compared with Example 1, the difference is that trimellitic anhydride and anhydrous citric acid have been removed from the formulation, while the rest are the same.

[0057] Comparative Example 5: The difference from Example 1 is that ethylene bis-stearamide has been removed from the formulation; otherwise, they are the same.

[0058] Test Example 1: 1. Sample setup: The latent masterbatches obtained after the twin-screw extrusion granulation stage of Examples 1, 1, and 3 were selected as test subjects. The three types of masterbatches were placed in a vacuum drying oven, and the temperature was set at 80°C for 8 hours to remove residual moisture from the system.

[0059] 2. Test steps: 2.1 A melt flow rate tester was used, and the test was performed according to the current standard GB / T 3682.2-2018 "Determination of melt mass flow rate (MFR) and melt volumetric flow rate (MVR) of thermoplastics - Part 2: Test methods for materials sensitive to time-temperature history and / or humidity". The barrel test temperature was set to 190℃, and the nominal load was 2.16kg. The dried batch of masterbatch was added to the barrel, preheated at a constant temperature for 5 minutes, and then extruded for the first time. The extruded parts were cut and weighed to calculate the initial melt mass flow rate (MFR, unit: g / 10min).

[0060] 2.2 Collect the extruded samples from the initial MFR test, and re-crush them to particles smaller than 3 mm using a micro-grinder. Then, place them again in a vacuum drying oven for dehumidification under the same conditions. Re-introduce the dried recycled material into the melt flow rate analyzer for a second measurement under the same temperature and load. Repeat this crushing, drying, and extrusion process until the third thermal cycle test is completed. Record the MFR value after each cycle to assess the extent of rheological property degradation of the blend system under multiple intense thermal-shear histories.

[0061] 2.3 The remaining sample after the third thermal cycle was extracted and extruded into a film with a thickness of approximately 0.05 mm using a laboratory-scale small-scale casting film machine under uniform temperature conditions of 190℃. A 1 square meter area of ​​the film was cut off, and irreversible solid gel points (crystal points) with a diameter greater than 0.1 mm were identified and counted using a high-definition thin film crystal point detector (or manually assisted under a strong light transmission backplane). The number of crystal points per unit area was recorded. The test results are shown in Table 1: Table 1: Test Records of In-situ Coordination Masking and Side-feeding Processes for Preventing Early Crosslinking

[0062] According to Table 1, Figure 1 and Figure 2 The data shows that the initial melt mass flow rate in Example 1 was 4.86 g / 10 min. After three consecutive thermal cycling tests, this value only decreased to 4.29 g / 10 min, and the number of irreversible crosslinking crystal points on the film surface remained at 7 per m. 2 The rheological properties of the comparative example 1, produced using a one-pot process, were extremely poor. Its initial flow rate was only 1.15 g / 10 min, and by the third cycle, the resin melt had completely lost its macroscopic flowability, with the number of gel crystals on the film surface surging to 1459 / m. 2 Test results show that when all the components of the formulation are directly mixed and heated in an extruder, the highly active epoxy groups of epoxidized soybean oil and the terminal carboxyl groups of polyester undergo an irreversible early cross-linking reaction under the catalysis of zinc ions. The microscopically generated three-dimensional network cross-linked structure leads to a sharp increase in the viscosity of the macroscopic system and the formation of a large-area solid gel.

[0063] Furthermore, Comparative Example 3, with fumed silica removed, also exhibited a significant tendency for crosslinking. Its flow rate decreased from 2.97 g / 10 min to 0.82 g / 10 min after three thermal cycles, and the number of crystal points on the film surface reached 312 per m. 2 Data confirms that, in the absence of a spatially confined environment provided by fumed silica nanopores, the coordination structure formed by citric acid and zinc ricinoleate undergoes premature dissociation in the extrusion homogenization stage. The released catalytic activity leads to branching and mild cross-linking of polymer segments.

[0064] The rheological and film-forming stability results of Example 1 validated the reliability of the masking process described in this scheme. The mesoporous physical adsorption of epoxidized soybean oil by fumed silica, combined with side-feeding technology, strictly controls the mixing residence time of the reaction powder to within 20 seconds, limiting the energy input required for thermodynamic unmasking of the in-situ coordination structure. Simultaneously, the silanol groups on the surface of the inorganic powder play a competitive bonding role, delaying the construction of complex topological cross-linking nodes until the film-forming die stage, thereby ensuring the processing thermoplasticity and rheological stability of the masterbatch during granulation and extrusion.

[0065] Test Example 2: 1. Sample setup: The latent masterbatches obtained after pelleting and drying in Example 1 and Comparative Example 4 after the twin-screw extrusion process were extracted as test samples. A portion of the masterbatch was hot-pressed at 170°C and 10MPa for 3 minutes using a flat vulcanizing press, and then transferred to a cold press for cooling and shaping to prepare uniform sheets with a thickness of about 0.1 mm for subsequent spectral testing.

[0066] 2. Test steps: 2.1 A Fourier Transform Infrared Spectrometer (FTIR) equipped with a temperature-controlled heating stage was used for temperature-variable spectral acquisition. The prepared thin-slice sample was fixed in the optical path, and the heating rate was set to 10℃ / min. The temperature of the test chamber was stabilized at 160℃ and 190℃, and held at each temperature for 10 min to ensure thermal equilibrium was reached within the sample. The infrared absorption spectrum of the sample was scanned and recorded under nitrogen purging, with a focus on extracting and comparing the 1600 cm⁻¹ spectrum. -1 ~1750cm -1 The positions of characteristic absorption peaks of the carboxyl group (C=O) and amide I band within the band.

[0067] 2.2 The melt traction force of the sample was determined using a high-pressure capillary rheometer equipped with a melt tension testing component. The dried masterbatch was added to the barrel, and the test temperatures for the barrel and capillary die were set to 160℃ and 190℃, respectively. The temperature was maintained at the set test temperatures for 5 minutes. The plunger was controlled to extrude the melt into the capillary at a constant rate, and the extruded melt filament was stretched by the traction roller below. During the test, the rotational speed of the traction roller was increased with a constant acceleration, and the maximum traction force transmitted by the force sensor at the moment the melt filament broke was recorded. The test results are shown in Table 2. Table 2: Data Recorded on Infrared Characteristic Peak Positions and Melt Strength Tests under Variable Temperature Conditions

[0068] According to Table 2 and Figure 3 The data shows that, at 190°C, the stretching vibration peak of the free carboxyl group in the infrared spectrum of the test sample in Example 1 is located at 1731.5 cm⁻¹.-1 The amide I band absorption peak characterizing ethylene bis-stearamide is located at 1652.8 cm⁻¹. -1 At this point, the measured melt drag force was 2.1 cN. After cooling to 160℃, the absorption peaks of the carboxyl group and amide I band shifted red-shifted to 1705.2 cm⁻¹. -1 and 1638.4cm -1 Meanwhile, the maximum melt drag force increased significantly to 18.7 cN. In contrast, Comparative Example 4, within the same cooling test range, did not exhibit a significant red shift in its amide absorption peak (only increasing from 1651.9 cm⁻¹). -1 Offset to 1648.7cm -1 The melt traction force increased slightly from 1.8 cN to 4.3 cN.

[0069] The shift of the spectral absorption peak to the lower wavenumber region indicates the formation of hydrogen bonds between the proton donor and acceptor within the system. Under cooling conditions of 160℃, the thermal motion within the system weakens, and a hydrogen bond network forms between the free carboxyl groups of trimellitic anhydride grafted onto the polyester backbone, the silanol groups on the fumed silica surface, and the amide bonds of ethylene bis-stearamide. Previously free lubricant molecules are anchored as physical crosslinking nodes during this process, directly manifesting as a significant increase in melt tension in the macroscopic rheological behavior. In Comparative Example 4, due to the removal of trimellitic anhydride and anhydrous citric acid, the system lacks the corresponding carboxyl proton donors; the cooling process only causes the conventional contraction of the free volume of the polymer chain segments and an increase in fluid friction resistance, without the formation of the corresponding physical crosslinking structure.

[0070] Test results verified the actual effect of the inverted temperature gradient process of the present invention: the high temperature of 190°C in the feeding section of the blown film machine limited the formation of hydrogen bonds and maintained the free lubrication state of ethylene bis-stearamide to reduce extrusion resistance; the low temperature of 160°C in the die section promoted the establishment of supramolecular hydrogen bond network, improved the apparent viscosity and strength of the extruded melt, and provided the necessary structural support for film blow molding.

[0071] Test Example 3: 1. Sample setup: Raw materials or mixtures corresponding to Examples 1 to 5 and Comparative Examples 1, 2, 4, and 5 were selected and fed into a co-rotating twin-screw extruder for granulation. The extruder's data acquisition and monitoring system was turned on, and data recording was initiated after the feeding and melt extrusion states stabilized. The real-time torque of the extruder's main motor was continuously recorded for 60 minutes, and the average torque during this test period was calculated. Simultaneously, the torque fluctuation rate was calculated by dividing the standard deviation of the torque by the average value, thereby evaluating the rheological properties of the material and the stability of internal crosslinking during the granulation stage.

[0072] 2. Test steps: 2.1 Collect the latent masterbatches from each group (except for Comparative Example 1, which could not be pelletized and discharged normally due to severe gelation) after pelletizing and centrifugal drying. Feed these masterbatches into a single-screw blown film machine and perform blown film forming operations strictly according to the equipment section temperature gradient, screw speed, and blow-up traction ratio set in each example and comparative example.

[0073] 2.2 The extruded melt is formed into an annular membrane bubble through the die, cooled by the air ring, and flattened by the traction roller. Timing begins after the overall membrane bubble morphology has stabilized. The holding time of the membrane bubble without human intervention is observed and recorded. To standardize the test time span, 120 minutes is set as the upper limit. A test duration of more than 120 minutes without rupture when the upper limit is reached is recorded. The test results are shown in Table 3. Table 3: Data Recorded on Stability Tests of Continuous Extrusion Granulation and Blown Film Molding Processes

[0074] According to Table 3 and Figure 4 The data shows that the average torque in the granulation extrusion stage of Examples 1 to 5 ranged from 178.6 N·m to 192.1 N·m, with a torque fluctuation rate of less than 3.5%. Furthermore, in the subsequent blown film process, continuous bubble-free operation for over 120 minutes was achieved, demonstrating excellent processing tolerance. In contrast, Comparative Example 1, using a one-pot method, saw its torque rise to 312.5 N·m in the initial extrusion stage, with a fluctuation rate as high as 18.6%. Uncontrolled early cross-linking of the melt caused equipment overload, ultimately leading to granulation interruption. Moreover, Comparative Example 5, without the addition of ethylene bis-stearamide, saw its granulation torque increase to 245.7 N·m, confirming that this component did not participate in cross-linking and anchoring under the high-temperature environment of the granulation stage, but rather remained in a free state to reduce internal melt friction and shear resistance at the screw interface.

[0075] After entering the film-forming process, insufficient melt strength directly led to the molding failure of the corresponding test group. In Comparative Example 2, which used an upright temperature gradient (i.e., high temperature at the die head), the formed film bubble broke and fractured after only 14 minutes because the high temperature hindered the formation of hydrogen bond networks. In Comparative Example 4, which removed trimellitic anhydride and anhydrous citric acid, the lack of cross-linking reaction nuclei in the system resulted in poor film-forming stability of the blended melt. Tension fluctuations caused the film bubble to rupture after 22 minutes of continuous operation, which could not meet the requirements of long-term continuous industrial production.

[0076] By combining the differences in various processing indicators, the actual effectiveness of the linkage between chemical formulation and thermodynamic process in this solution was verified. The medium-high temperature range maintained by the extruder ensured the free state and low viscosity rheological characteristics of the lubricant, avoiding abnormal torque caused by premature crosslinking; while the inverted cooling at the die head triggered the reconstruction of the supramolecular physical crosslinking network, enabling the melt exiting the die to instantly acquire the critical tension for rapid cooling of the air ring and traction blowing, thus opening up a process path for the continuous processing of heterogeneous biodegradable polyester with high stability from an engineering implementation perspective.

[0077] Test Example 4: 1. Sample setup: The films prepared in Examples 1 to 5, as well as Comparative Examples 3, 4, and 5 from which effective film samples could be obtained, were selected as test objects. The sampled films were placed in a standard constant temperature and humidity environment with a temperature of 23±2℃ and a relative humidity of 50±5% for conditioning for no less than 40 hours to eliminate residual internal stress inside the film.

[0078] According to GB / T 1040.3 standard, five standard dumbbell-shaped specimens were cut from each group of films in both the longitudinal (MD, i.e., machine running direction) and transverse (TD, i.e., perpendicular to the machine running direction) directions using a punching machine. Tensile tests were performed using a computer-controlled electronic universal testing machine, with the initial gauge length set to 50 mm and the tensile speed kept constant at 500 mm / min. The maximum tensile force and gauge length elongation at fracture were recorded, and the longitudinal and transverse tensile strengths and elongation at break were calculated. The results were taken as the arithmetic mean of the five specimens.

[0079] According to the QB / T-1130 standard, five right-angle tear test specimens were cut along both the longitudinal and transverse directions of the film. The universal testing machine's fixtures were changed, and the tensile speed was adjusted to 200 mm / min. The specimens were then subjected to tear tests. The highest load required for the specimen to break during the tearing process was recorded, and this value was divided by the nominal thickness of the specimen to obtain the right-angle tear strength values ​​in both the longitudinal and transverse directions. The arithmetic mean of these values ​​was then recorded. The test results are shown in Table 4. Table 4: Test Data Records of Mechanical Properties and Isotropic Properties of Packaging Films

[0080] According to Table 4 and Figure 5The data shows that the films of Examples 1 to 5 exhibit good longitudinal and transverse (MD / TD) isotropy while maintaining high mechanical strength. Taking Example 1 as an example, its MD and TD tensile strengths reached 23.4 MPa and 21.8 MPa, respectively, and the elongation at break remained in the excellent range of 415% and 432%, respectively. Moreover, the TD right-angle tear strength (91.2 N / mm) was slightly higher than that of MD (85.6 N / mm). In contrast, the overall mechanical properties of Comparative Example 4, which did not contain trimellitic anhydride and anhydrous citric acid, were significantly reduced. The MD tensile strength dropped to 12.1 MPa, and the TD elongation at break was much lower than that of MD, showing obvious anisotropic defects. In addition, the TD tear strength of Comparative Example 5, which lacked ethylene bis-stearamide, dropped to 58.3 N / mm. The mismatch between the longitudinal and transverse mechanical properties also reflects the non-uniformity of the tensile orientation within the film.

[0081] The differences in mechanical properties and isotropy mentioned above mainly stem from the different phase structures and molecular chain orientation states within the blend system. In Comparative Example 4, due to the lack of reactive chain extenders, the interfacial adhesion between polylactic acid and polyester is weak. Under the unidirectional traction force during the blown film process, the dispersed phase is prone to over-orientation and even interfacial slip along the machine's running direction, directly resulting in insufficient transverse chain segment entanglement density in the film. In the Example system, after releasing catalytic activity during the film-forming stage, epoxidized soybean oil and free citric acid construct a star-shaped topological micro-crosslinked structure in situ, improving the interfacial compatibility between heterogeneous matrices. Subsequently, the melt enters the inverted temperature drop region of the die head, where the rapidly established supramolecular hydrogen bond network acts as a physical crosslinking node, effectively restricting the free slippage of polymeric chain segments under the traction tensile force field. Combined with the rapid cooling of the air ring and heterogeneous nucleation, this three-dimensional network, synergistic between chemical micro-crosslinking and physical hydrogen bonding, rapidly freezes the spatial conformation of the macromolecular chains, inhibiting excessive chain segment deentanglement induced by unidirectional stretching, and ensuring the balance of longitudinal and transverse mechanical properties of the film from a structural perspective.

[0082] Test Example 5: 1. Sample setup: The packaging films prepared in Example 1, Comparative Example 4 (with trimellitic anhydride and anhydrous citric acid removed), and Comparative Example 5 (without ethylene bis-stearamide) were selected as test objects. A 100mm × 15mm strip of film was cut, two samples were overlapped, and a constant-temperature heat sealer was used to perform partial heat sealing at a set parameters of 140℃, 0.5MPa, and 1.0s to prepare an initial heat-sealed sample.

[0083] 2. Test steps: 2.1 According to QB / T-2358 standard, clamp both ends of the heat-sealed specimen into the upper and lower fixtures of a computer-controlled electronic universal testing machine. Set the tensile speed to 300 mm / min and perform a T-shaped peel test. Record the maximum load at which the heat-sealed interface separates or the specimen breaks as the initial heat-sealing strength. Simultaneously record the initial static friction coefficient using a friction coefficient measuring instrument for films from the same batch.

[0084] 2.2 Place the remaining film samples that have not undergone heat sealing into a constant temperature and humidity aging test chamber, setting the ambient temperature to 40℃ and the relative humidity to 60%. The samples are suspended without overlap in the chamber for accelerated aging treatment, with the aging cycle set to 30 days.

[0085] 2.3 After the aging cycle, the film sample was removed and placed in a standard laboratory for 24 hours to equilibrate the environmental conditions. Then, using the same equipment and parameters as in step 1, the aged film was overlapped and heat-sealed. The heat-sealing strength and static friction coefficient after aging were measured according to the test method in step 2, and the rate of decrease in heat-sealing strength relative to the initial value was calculated. The test results are shown in Table 5: Table 5: Test Data Recordings of Film Migration Resistance and Long-Term Heat Sealing Stability

[0086] According to Table 5 and Figure 6 The data shows that the initial heat seal strength of Example 1 was 16.2 N / 15 mm. After accelerated aging at 40°C for 30 days, this value changed to 15.7 N / 15 mm, with a decay rate of 3.1%. Meanwhile, its surface static friction coefficient remained stable between 0.25 and 0.26 before and after aging. In contrast, Comparative Example 4, lacking a proton donor in the hydrogen bond network, showed significant performance degradation. Its heat seal strength after aging decreased from the initial 14.6 N / 15 mm to 6.1 N / 15 mm, with a decay rate of 58.2%, and its surface static friction coefficient gradually decreased from 0.23 to 0.12. Comparative Example 5, because its formulation did not contain ethylene bis-stearamide, showed no significant decrease in heat seal strength before and after aging, but its static friction coefficient remained consistently higher than 0.72.

[0087] The decline in the long-term heat-sealing strength of polymer films is usually due to the surface migration and enrichment of small-molecule additives. In Comparative Example 4, the free ethylene bis-stearamide molecules in the system exhibit thermodynamic incompatibility with the polyester matrix. Under long-term heat treatment at 40°C, the low-molecular-weight lubricant continuously diffuses to the film surface. The amide molecules enriched on the surface form a low surface energy barrier layer during heat sealing, hindering the interfacial interpenetration and entanglement of polyester macromolecular chains in the molten state, thus leading to a significant decrease in macroscopic heat-sealing strength. In contrast, the formulation in Example 1 constructs a supramolecular hydrogen-bonded network during the film cooling and forming stage through an inverted temperature gradient process. The free carboxyl groups and inorganic silanol groups in the system act as proton donors, forming hydrogen bonds with the amide bonds in the middle of the ethylene bis-stearamide, anchoring them as physical crosslinking nodes in the three-dimensional network. This structure inhibits the long-range migration ability of the lubricating agent in the polymer matrix without changing the lubricating properties of the hydrophobic alkyl chains on the outside. The hydrogen bond constraint remains stable even under accelerated aging conditions, preventing excessive precipitation of additives on the film surface and thus ensuring the heat-sealing interface adhesion of the film after long-term storage.

[0088] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A manufacturing process for a high-toughness, environmentally friendly plastic bag, characterized in that, include: The latent masterbatch is added to a single-screw blown film mill, and the heating temperature from the feeding section to the die head section is controlled to decrease sequentially to form an inverted temperature gradient; the melt is extruded through the die head and blown to form an annular film bubble, which is then cooled, flattened and wound up to obtain a continuous cylindrical film; High-toughness environmentally friendly plastic bags are produced by bottom sealing, side sealing and heat cutting of continuous tubular films; The latent masterbatch comprises the following components in parts by weight: Poly(butylene adipate) 60.0-70.0 parts, polylactic acid 20.0-30.0 parts, talc 2.0-5.0 parts, ethylene bis-stearamide 1.0-2.0 parts, epoxidized soybean oil 3.5-6.5 parts, and dry aqueous reaction core powder; The dry-water reaction core powder comprises the following components by weight: 0.5-1.5 parts anhydrous citric acid, 0.3-0.8 parts zinc ricinoleate, 0.3-0.8 parts trimellitic anhydride, 0.5-1.2 parts hydrophilic fumed silica, and 0.5-1.5 parts epoxidized soybean oil.

2. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 1, characterized in that, The preparation steps of the dry aqueous reaction core powder include: Anhydrous citric acid, zinc ricinoleate, trimellitic anhydride, and hydrophilic fumed silica are placed in a high-speed mixer and the speed is set to 1500-2000 r / min to dry-mix and fluidize the materials. Then, epoxidized soybean oil is sprayed in according to the formula. The system temperature is maintained at 70-85℃ by shear friction self-heating. After continuous mixing for 10-20 min, the dry water-state reaction core powder is discharged.

3. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 2, characterized in that, The time for spraying the formulated amount of epoxidized soybean oil is 2 to 4 minutes.

4. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 1, characterized in that, The preparation steps of the latent masterbatch include: Poly(butylene adipate / terephthalate), polylactic acid, talc, and ethylene bis-stearamide are mixed and then fed into and melted through the main feed port of a twin-screw extruder. Epoxidized soybean oil is injected under high pressure into the polymer melt through a mid-section liquid injection pump for shear mixing. Subsequently, dry-water reactive core powder is fed into the extruder through a mid-to-rear-section side feeder. After homogenization, the powder is extruded, pelletized, and dried to obtain latent masterbatch. The barrel temperature from the main feed port area to the mid-section of the extruder is set to 160–170°C; the injection pressure of the mid-section liquid injection pump is set to 4.0–8.0 MPa; and the temperature from the side feed point to the extruder die head is set to 155–160°C.

5. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 1, characterized in that, The talc powder contains >60.0% silica and >30.0% magnesium oxide.

6. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 1, characterized in that, The hydrophilic fumed silica has a silica content >99.8%, a primary particle size of 12–20 nm, and a specific surface area of ​​150–200 m² / g as measured by the BET method. 2 / g, and the surface has not undergone hydrophobic modification treatment.

7. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 4, characterized in that, By controlling the screw speed, the residence time of the dry-water reaction core powder from the side feed port to the extrusion discharge is controlled to be between 15 and 25 seconds.

8. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 1, characterized in that, The specific process parameters for the inverted temperature gradient of the single-screw blown film machine are as follows: the barrel temperature of the feeding and compression section is set to 185-195℃, the barrel temperature of the homogenization section is set to 165-175℃, and the temperature of the die head section is set to 155-165℃.

9. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 8, characterized in that, The blow-up ratio for blown film forming is 2.5–3.0, and the traction ratio is 3.0–4.

0.

10. The preparation process of the high-toughness environmentally friendly plastic bag according to claim 1, characterized in that, In the hot cutting process, the cutting blade temperature is 130-145℃.

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