Recyclable PE wrapping film and preparation method thereof

Abstract

The application relates to the technical field of plastic packaging film, and particularly discloses a recyclable PE wrapping film and a preparation method thereof. The recyclable PE wrapping film comprises the following raw materials: PE recyclable material, ethylene-propylene-diene rubber, active phenolic resin, metal halide, metallocene POE, HDPE resin, tackifying masterbatch, and the balance of LLDPE resin; the preparation method is as follows: the LLDPE resin is mixed with the PE recyclable material and the ethylene-propylene-diene rubber, hot melting, the active phenolic resin and the metal halide are added from the side feeding, hot melting, and a melt is prepared; the melt is cast and cooled to prepare a cast sheet, the cast sheet is drawn and stretched, and then subjected to corona treatment, curling and slitting. The recyclable PE wrapping film does not add opening agents, slip agents and anti-fog agents, ensures that the product is easy to recycle, the recyclable material has high purity, a high content of PE recyclable material is added, and the recyclable PE wrapping film still has relatively high tensile strength, puncture resistance and transparency.

Description

Technical Field

[0001] This application relates to the field of plastic packaging film technology, and more specifically, to a recyclable PE stretch film and a method for preparing the same. Background Technology

[0002] Polyethylene (PE) stretch film, as an important industrial packaging material, has become the preferred choice for unitized and fixed packaging of palletized goods in the logistics and warehousing fields due to its excellent self-adhesion, high tensile strength, good puncture strength, and transparency. By spirally wrapping the goods around their perimeter, it utilizes the film's own recoil stress to tightly bind the goods together, effectively improving transportation efficiency and cargo safety.

[0003] However, the formulation design of traditional stretch films, in order to meet stringent processing and application performance requirements, presents a significant contradiction with the global concept of a circular economy for sustainable development. To achieve smooth winding and unwinding processes, prevent excessive adhesion between film layers, and reduce the coefficient of friction on the film surface, it is typically necessary to add large amounts of inorganic opening agents (such as diatomaceous earth and silica) and organic slip agents (such as erucamide and oleamide) to the raw materials. Furthermore, in certain storage environments, anti-fogging agents are sometimes required to prevent moisture condensation on the film surface from affecting the visibility of goods.

[0004] These functional additives are indispensable in the initial use of stretch film, but they become a major obstacle to its recycling and regeneration at the end of its life cycle. During the recycling and cleaning process, opening agents are difficult to completely separate and remain in the recycled plastic, leading to increased impurities and poor melt flowability. Small-molecule slip agents and anti-fogging agents are prone to thermal decomposition or migration during melt granulation, not only causing unpleasant odors in the recycled material but also severely degrading its performance and processing stability. Ultimately, these recycled materials containing additives have low purity and large quality fluctuations, and are usually unsuitable for the reproduction of high-value products, only suitable for downgraded use, such as in the production of garbage bags and fillers. On the other hand, the current plastic recycling industry suffers from complex recycling sources and inconsistent quality. Therefore, there is an urgent need for a new type of PE stretch film to fundamentally solve the contradiction between recyclability and usability. Summary of the Invention

[0005] To ensure that the product is easy to recycle, the recycled material is highly pure, and has strong mechanical strength and transparency, this application provides a recyclable PE stretch film and its preparation method by adding appropriate PE stretch film recycled material without adding opening agents, slip agents, or anti-fogging agents.

[0006] In the first aspect, this application provides a recyclable PE stretch film, which adopts the following technical solution:

[0007] A recyclable PE stretch film comprises the following raw materials by weight percentage: 5-30% recycled PE, 3-5% EPDM rubber, 4-5% active phenolic resin, 1-2% metal halide, 2-8% metallocene POE, 1-5% HDPE resin, 1-3% tackifying masterbatch, and the balance being LLDPE resin.

[0008] By adopting the above technical solution, using LLDPE resin as the matrix, excellent drawability, toughness and self-adhesion are provided. A certain amount of recycled PE material, EPDM rubber, active phenolic resin and metal halide are added to achieve the effects of opening properties, toughness and easy recyclability without adding additives.

[0009] Ethylene propylene diene monomer (EPDM) rubber serves as the elastomer core. Under the action of metal halides, the active phenolic resin undergoes dynamic vulcanization. The metal halides, acting as Lewis acids, interact with the groups on the active phenolic resin, forming highly reactive intermediates. These intermediates then undergo alkylation with the unsaturated double bonds on the EPDM backbone, forming stable C-C covalent bonds that tightly crosslink multiple EPDM rubber chains. This reaction is highly selective for the unsaturated monomers (ENB, DCPD) in EPDM, but does not react with the saturated PE matrix, thus achieving the goal of crosslinking only the EPDM rubber phase without crosslinking the PE plastic matrix. During melt blending, vulcanization occurs due to shear force and heat. Because of the difference in polarity and compatibility with recycled PE, the vulcanized EPDM rubber forms dispersed particles that are preferentially encapsulated by the recycled PE, forming a core-shell structure of microspheres with vulcanized EPDM as the core and PE as the shell. These microspheres are dispersed in the matrix, resulting in a composite material that possesses both the elasticity of rubber and the thermoplastic processing properties of plastic.

[0010] When the material is subjected to external impact or tension, these rigid core-soft shell microspheres dispersed in the matrix can act as effective stress concentration points. They can induce a large number of crazes and shear bands in the matrix, thereby absorbing a large amount of impact energy, preventing crack propagation, and achieving a more significant toughening effect. This effectively compensates for the increased brittleness caused by the addition of recycled PE, and improves the puncture strength and tear resistance of the film. In addition, during the film-making process, these microspheres will form tiny, uniform protrusions or phase regions on the film surface, thereby changing the microscopic topology of the film surface and acting as an inorganic opening agent. They form tiny air gaps between the wound film layers, effectively reducing the contact area and electrostatic force, thereby preventing adhesion. This is more permanent than adding small molecule slip agents and will not migrate or precipitate. LLDPE resin, recycled PE, and EPDM are all polyolefins with good compatibility. Moreover, no non-olefin components are introduced, and there are no foreign contaminants. During recycling and granulation, these microspheres can melt together with the matrix without causing serious negative impacts on the purity of the recycled material and reprocessing.

[0011] Preferably, the raw materials are in the following weight percentages: 30% recycled PE, 4% EPDM rubber, 4.5-5% active phenolic resin, 1-1.5% metal halide, 6% metallocene POE, 3% HDPE resin, 1% tackifying masterbatch, and the balance being LLDPE resin.

[0012] By adopting the above technical solutions, the raw materials of PE stretch film are more precise, thereby reducing brittleness, improving the toughness of PE stretch film, and giving the stretch film better transparency.

[0013] Preferably, the active phenolic resin is selected from at least one of p-tert-butylphenol formaldehyde resin, octylphenol formaldehyde resin, bromomethyl p-tert-octylphenol formaldehyde resin, and chloromethylphenol formaldehyde resin;

[0014] The metal halide is selected from at least one of stannous chloride, ferric chloride, aluminum chloride, and zinc bromide.

[0015] By adopting the above technical solution, the above phenolic resin provides alkyl groups for the alkylation crosslinking reaction, while EPDM accepts alkyl groups. Metal halides act as catalysts to catalyze the entire reaction. p-tert-butylphenol formaldehyde resin and octylphenol formaldehyde resin are hydroxymethyl type phenolic resins with hydroxymethyl groups at their ends. Bromomethyl p-tert-octylphenol formaldehyde resin and chloromethyl phenolic resin are halomethyl type phenolic resins. Under the catalysis of metal halides, the EPDM chain undergoes an alkylation crosslinking reaction.

[0016] Preferably, the mass ratio of the EPDM rubber, p-tert-butylphenol formaldehyde resin, and stannous chloride is 4:4.5:1.5.

[0017] Preferably, the mass ratio of the EPDM rubber, p-tert-butylphenol formaldehyde resin, and stannous chloride is 4:5:1.

[0018] By adopting the above technical solution, p-tert-butylphenol formaldehyde resin is used as the active phenolic resin, and stannous chloride is used as the metal halide. The introduction of tert-butyl groups into the active phenolic resin has strong non-polarity, which can reduce the polarity of the resin and improve its compatibility with EPDM rubber, thereby ensuring uniform dispersion and effective crosslinking. Moreover, it can also reduce the brittleness of the resin. Furthermore, although tert-butyl groups are electron-donating groups, they are located at the para position of the benzene ring, and have a relatively small impact on the reactivity of phenolic hydroxyl and hydroxymethyl groups. Therefore, the resin can still maintain sufficient crosslinking ability, thereby retaining its reactivity.

[0019] Preferably, the method for preparing the recycled PE material is as follows: recycled PE stretch film is sorted, washed, and granulated to obtain recycled PE material.

[0020] Optionally, the recycled PE material has a melt flow index of 5-10 g / 10 min and a density of 0.945-0.955 g / cm³ at 190℃ and 2.16 kg. 3 ;

[0021] The LLDPE resin has a melt flow index of 1.8-2.5 g / 10 min at 190℃ and 2.16 kg, and a density of 0.916-0.92 g / cm³. 3 .

[0022] By adopting the above technical solution, the recycled granules have a high melt index, which helps to improve the processing fluidity of the system containing recycled materials. The melt index of the recycled granules is greater than that of LLDPE resin, which can make the blend melt flow uniform, the processing stable, and the surface of the stretch film smooth. Therefore, the low density and moderate melt index of LLDPE resin can provide the stretch film with a flexible base and self-adhesion and tensile properties, while the high density and matching melt index of PE recycled materials can provide rigidity and strength. When combined with EPDM, a stretch film with high tear resistance, impact resistance, and puncture resistance is formed.

[0023] Preferably, the method for preparing the recycled PE material is as follows:

[0024] Recycled PE stretch film is sorted, cleaned, and granulated to obtain recycled granules, which are then divided into recycled granules A and recycled granules B.

[0025] Mix recycled granules A with maleic anhydride, styrene and dicumyl peroxide evenly, heat to 180-190℃ for 10-20 minutes for hot melting, granulate, and mix with recycled granules B to obtain recycled PE material.

[0026] By employing the above technical solution, recycled PE stretch film is granulated to obtain recycled granules. These granules are then grafted with maleic anhydride. After grafting maleic anhydride onto the recycled granules, the molecular chains of these granules possess highly reactive anhydride groups. During dynamic vulcanization, under the influence of metal halides and shear forces, the EPDM molecular chains generate a small number of free radicals or polar sites. At this point, the anhydride groups on the maleic anhydride-grafted PE exhibit stronger chemical or physical interactions with these sites than van der Waals forces. Therefore, maleic anhydride-grafted PE has a stronger affinity for EPDM than PE in the recycled granules. During phase recombination, it can preferentially and more firmly migrate and anchor at the interface of the EPDM phase, enhancing the interfacial strength. This results in a microsphere structure with maleic anhydride as the shell and vulcanized EPDM as the core. The ungrafted recycled granules prevent the shell from becoming too rigid and the compatibility with the LLDPE matrix from changing due to grafting. Consequently, the core-shell structure of the microspheres remains as a whole, integrating with the LLDPE. The weakening of the interfacial bonding between the matrix and the phase interface results in a thinner phase interface, making it difficult for stress to be effectively transferred and prone to delamination at the interface, leading to brittle fracture. Recycled pellets grafted with maleic anhydride can preferentially and firmly anchor to the EPDM surface, forming a tightly bonded inner shell. Ungrafted recycled pellets, due to their good compatibility with the maleic anhydride-grafted polyethylene main chain, continue to be wrapped in the outer layer, forming a thick outer shell, thus achieving perfect compatibility with the LLDPE matrix. The inner shell ensures effective stress transfer between the toughening phase EPDM and the shell layer, while the outer shell ensures perfect fusion of the entire core-shell structure with the LLDPE matrix. This gradient interfacial structure effectively absorbs impact energy, thereby maximizing the toughening effect. Furthermore, the grafting of maleic anhydride onto the recycled pellets does not introduce difficult-to-separate heterogeneous components during the recycling process, improving the phase structure of the blend. This results in better material compatibility and a lower tendency for phase separation during recycling and regranulation, leading to a more stable and uniform recycled material.

[0027] Preferably, the amount of recycled granules A is 30-50% EPDM rubber.

[0028] By adopting the above technical solution, grafting maleic anhydride onto the surface of an appropriate amount of recycled granules A can completely cover the surface of EPDM particles with a layer of maleic anhydride-grafted PE, forming a strong core-shell structure with strong interfacial bonding, resulting in good toughness improvement and high impact strength. If the amount of recycled granules grafted with maleic anhydride is small, the surface coverage of EPDM particles is small, the interfacial bonding is incomplete, and the improvement in toughness is not obvious. If the amount of recycled granules grafted with maleic anhydride is too large, the EPDM will be completely covered, and the excess maleic anhydride-grafted PE will form an island phase in the LLDPE matrix. Due to the different polarity from the matrix, new stress defects will be generated, leading to brittleness of the material and poor processing performance.

[0029] Preferably, the stannous chloride is pretreated by the following method: stannous chloride is mixed with calcium stearate and an antioxidant, and stirred for 5-10 minutes. The mass ratio of stannous chloride, calcium stearate and antioxidant is 1:0.5-1:0.2-0.5.

[0030] By adopting the above technical solution, stannous chloride easily generates yellow tin oxide or tin complexes when heated or oxidized, resulting in slight yellowing. Dry mixing of stannous chloride with calcium stearate and antioxidants addresses this issue. Calcium stearate, as a weakly basic metal soap, neutralizes the free acid produced by stannous chloride upon heating, thus mitigating polymer degradation and yellowing caused by catalysis at the source. Furthermore, calcium ions interact with tin ions, stabilizing them and slowing down the rate of the coloring side reactions they trigger. Calcium stearate also increases lubricity, aiding processing. The antioxidant terminates free radical reactions, breaking the yellowing reaction chain, resulting in a whiter, more transparent stretch film without affecting the dynamic vulcanization toughening effect, achieving excellent and reliable mechanical properties. Simultaneously, it does not affect the recyclability of the stretch film and will not negatively impact the closed-loop recycling of the product.

[0031] Secondly, this application provides a method for preparing recyclable PE stretch film, employing the following technical solution:

[0032] A method for preparing recyclable PE stretch film includes the following steps:

[0033] LLDPE resin is mixed with recycled PE, EPDM rubber, tackifying masterbatch, metallocene POE and HDPE resin for 5-8 minutes, hot-melted, and active phenolic resin and metal halide are added from the side feed. The mixture is then extruded to obtain the melt.

[0034] The melt is cast and cooled to obtain a casting sheet. The casting sheet is then drawn, stretched, corona-electrode, rolled, and cut to obtain a recyclable PE stretch film.

[0035] By adopting the above technical solution, the active phenolic resin and metal halide are added from the side feed port, which can avoid premature cross-linking. After being sheared by the screw, the cross-linked EPDM phase is broken into micron-sized particles. After being processed by casting, cooling, stretching and other processes, a wrapping film is obtained.

[0036] Preferably, the temperatures of each zone during the extrusion granulation are: Zone 1 160-170℃, Zone 2 180-190℃, Zone 3 190-200℃, Zone 4 195-205℃, and Die head 200-210℃.

[0037] By adopting the above technical solution, the extrusion temperature is higher than the melting point of LLDPE, which can make the recycled PE material completely melt and plasticize, avoid the formation of crystal points, and ensure that the components are evenly dispersed.

[0038] In summary, this application has the following beneficial effects:

[0039] 1. Because the EPDM in this application reacts with active phenolic resin and metal halide, EPDM can selectively crosslink in the composite melt of LLDPE and recycled PE. In the composite material, the crosslinked EPDM phase forms dispersed particles, which are then encapsulated by the recycled PE, resulting in microspheres with EPDM as the core and recycled PE as the shell. The microspheres are uniformly dispersed in the LLDPE matrix, thereby compensating for the brittleness of the recycled PE. Its own elastomeric properties effectively prevent the film roll from sticking together, provide a physical opening effect, prevent mutual adhesion, and are free of foreign contaminants, making them pure and recyclable.

[0040] 2. This application preferably uses recycled PE stretch film to prepare PE recycled material, realizing the closed-loop application of plastic packaging, responding to environmental protection policies and brand owners' requirements for recyclable contents, and fundamentally solving the problem of difficult recycling of traditional stretch film by discarding opening agents, slip agents, anti-fogging agents and other pollutants. The resulting recycled material has high purity and high value.

[0041] 3. In this application, it is preferred to graft a specific amount of maleic anhydride onto the recycled material prepared from recycled PE stretch film, which is preferentially anchored on the interface of the EPDM phase, thereby enhancing the interfacial strength. The ungrafted PE recycled material continues to be wrapped in the outer layer, improving the compatibility with the LLDPE matrix, thus forming a gradient interface structure, improving the toughening effect, and enhancing the impact resistance, tear resistance, and tensile strength of the stretch film. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the embodiments.

[0043] The sources of each raw material in the example are as follows: density is 0.92 g / cm³. 3 The LLDPE resin with a melt index of 2 g / 10 min was selected from Sinopec, model DFDA-7042, and density of 0.918 g / cm³. 3 The LLDPE with a melt index of 2 g / 10 min was selected from Sinopec, grade DFDC-7050H; the EPDM rubber was selected from DowDuPont, grade 4570; the p-tert-butylphenol-formaldehyde resin was selected from Hubei Xingyan New Materials; the octylphenol-formaldehyde resin was selected from Santec, model SP-1045P; the metallocene POE was selected from Dongguan Chuangshi Plastics, grade ExxonMobil 6202FL; the HDPE resin was selected from Philips, model HMW5060; and the tackifying masterbatch was selected from Tianjin Zeheng Packaging Products, model ZH-60, with a density of 0.88 g / cm³. 3 .

[0044] Example 1: A recyclable PE stretch film, the raw material amounts of which are shown in Table 1, wherein the density of LLDPE resin is 0.92 g / cm³. 3 The melt flow index at 190℃ and 2.16 kg is 2 g / 10 min. The active phenolic resin is p-tert-butylphenol formaldehyde resin with a density of 1.379 g / cm³. 3 The metal halide is stannous chloride, and the density of HDPE resin is 0.95 g / cm³. 3 The melt flow index at 190℃ and 2.16kg is 5g / 10min. The recycled PE material is obtained by sorting, washing, hot-melting at 160℃, and granulating recycled PE stretch film collected by Sam. The main material of the recycled PE stretch film is HDPE or a blend of HDPE and MDPE. The melt flow index of the recycled PE material at 190℃ and 2.16kg is 8g / 10min, and the density is 0.95g / cm³. 3 .

[0045] The above-mentioned method for preparing recyclable PE stretch film includes the following steps:

[0046] S1. Mix LLDP resin with recycled PE, EPDM rubber, tackifying masterbatch, metallocene POE and HDPE resin for 8 minutes, heat melt, and add active phenolic resin and metal halide from the side feed. Extrude to obtain melt. The temperature of each zone during extrusion granulation is: zone 1 170℃, zone 2 190℃, zone 3 200℃, zone 4 205℃, die head 210℃, and screw speed is 80r / min.

[0047] S2. The melt is cast and cooled to obtain a casting sheet. The casting sheet is then traction, stretched, corona-electrode, rolled, and slit to obtain a recyclable PE stretch film. The speed of the casting roller is 1m / min, the speed of the traction roller is 1.2m / min, the synchronization coefficient of the traction roller is 1.5, the tension of the take-up roller is 3.5kg, the synchronization coefficient of the take-up roller is 0.4, and the temperature of the cooling roller is 20℃.

[0048] Table 1. Raw material consumption of recyclable PE stretch film in Examples 1-6

[0049]

[0050] Example 2: A recyclable PE stretch film, the raw material amounts are shown in Table 1, and the density of LLDPE resin is 0.918 g / cm³. 3 The melt flow index at 190℃ and 2.16 kg is 2 g / 10 min. The active phenolic resin is p-tert-butylphenol formaldehyde resin with a density of 1.379 g / cm³. 3 The metal halide is stannous chloride, and the density of HDPE resin is 0.95 g / cm³. 3The melt flow index at 190℃ and 2.16kg is 5g / 10min. The recycled PE material is obtained by sorting, washing, hot-melting at 160℃, and granulating recycled PE stretch film collected by Sam. The main material of the recycled PE stretch film is HDPE or a blend of HDPE and MDPE. The melt flow index of the recycled PE material at 190℃ and 2.16kg is 8g / 10min, and the density is 0.95g / cm³. 3 .

[0051] The above-mentioned method for preparing recyclable PE stretch film includes the following steps:

[0052] S1. Mix LLDP resin with recycled PE, EPDM rubber, tackifying masterbatch, metallocene POE and HDPE resin for 5 min, heat melt, and add active phenolic resin and metal halide from the side feed. Extrude to obtain melt. The temperature of each zone during extrusion granulation is: zone 1 160℃, zone 2 180℃, zone 3 190℃, zone 4 200℃, die head 200℃, and screw speed is 90 r / min.

[0053] S2. The melt is cast and cooled to obtain a casting sheet. The casting sheet is then traction, stretched, corona-electrode, rolled, and cut to obtain a recyclable PE stretch film. The speed of the casting roller is 0.9 m / min, the speed of the traction roller is 1.1 m / min, the synchronization coefficient of the traction roller is 1.4, the tension of the take-up roller is 3.4 kg, the synchronization coefficient of the take-up roller is 0.5, and the temperature of the cooling roller is 30℃.

[0054] Examples 3-6: A recyclable PE stretch film, which differs from Example 1 in that the raw material usage is as shown in Table 1.

[0055] Example 7: A recyclable PE stretch film, which differs from Example 1 in that the active phenolic resin is selected from octylphenol formaldehyde resin.

[0056] Example 8: A recyclable PE stretch film, which differs from Example 1 in that stannous chloride is pretreated as follows: stannous chloride, calcium stearate, and antioxidant 1010 are mixed in a mass ratio of 1:1:0.5 and dry-mixed at 800 r / min for 10 min.

[0057] Example 9: A recyclable PE stretch film, which differs from Example 1 in that stannous chloride is pretreated as follows: stannous chloride, calcium stearate, and antioxidant 1010 are mixed at a mass ratio of 1:0.5:0.2 and dry-mixed at 1200 r / min for 5 min.

[0058] Example 10: A recyclable PE stretch film, differing from Example 8 in that the recycled PE material is prepared using the following method:

[0059] The recycled PE stretch film collected by Sam was sorted, washed, hot-melted at 160℃, and granulated to produce the final product. The main material of the recycled PE stretch film is HDPE or a blend of HDPE and MDPE. The melt flow index of the recycled PE material at 190℃ and 2.16kg is 8g / 10min, and the density is 0.95g / cm³. 3 Take 30kg of recycled granules and divide them into 2kg of recycled granules A and 28kg of recycled granules B;

[0060] The recycled granules A are mixed evenly with 0.06 kg maleic anhydride, 0.02 kg styrene and 0.006 kg dicumyl peroxide, heated to 190°C, hot-melted for 10 min, granulated, and then mixed with recycled granules B to obtain recycled PE material.

[0061] Example 11: A recyclable PE stretch film, differing from Example 8 in that the recycled PE material is prepared using the following method:

[0062] The recycled PE stretch film collected by Sam was sorted, washed, hot-melted at 160℃, and granulated to produce the final product. The main material of the recycled PE stretch film is HDPE or a blend of HDPE and MDPE. The melt flow index of the recycled PE material at 190℃ and 2.16kg is 8g / 10min, and the density is 0.95g / cm³. 3 Take 30 kg of recycled granules and divide them into 1.2 kg of recycled granules A and 28.8 kg of recycled granules B;

[0063] The recycled granules A are mixed evenly with 0.036 kg maleic anhydride, 0.012 kg styrene and 0.0036 kg dicumyl peroxide, heated to 180°C, hot-melted for 20 min, granulated, and then mixed with recycled granules B to obtain recycled PE material.

[0064] Example 12: A recyclable PE stretch film, differing from Example 10 in that the recycled PE material is prepared using the following method:

[0065] The recycled PE stretch film collected by Sam was sorted, washed, hot-melted at 160℃, and granulated to produce the final product. The main material of the recycled PE stretch film is HDPE or a blend of HDPE and MDPE. The melt flow index of the recycled PE material at 190℃ and 2.16kg is 8g / 10min, and the density is 0.95g / cm³. 3 Take 30 kg of recycled granules and divide them into 0.4 kg of recycled granules A and 29.6 kg of recycled granules B;

[0066] The recycled granules A are mixed evenly with 0.012 kg maleic anhydride, 0.004 kg styrene and 0.0012 kg dicumyl peroxide, heated to 190°C, hot-melted for 10 min, granulated, and then mixed with recycled granules B to obtain recycled PE material.

[0067] Example 13: A recyclable PE stretch film, differing from Example 10 in that the recycled PE material is prepared using the following method:

[0068] The recycled PE stretch film collected by Sam was sorted, washed, hot-melted at 160℃, and granulated to produce the final product. The main material of the recycled PE stretch film is HDPE or a blend of HDPE and MDPE. The melt flow index of the recycled PE material at 190℃ and 2.16kg is 8g / 10min, and the density is 0.95g / cm³. 3 Take 30kg of recycled granules and divide them into 4kg of recycled granules A and 26kg of recycled granules B;

[0069] The recycled granules A are mixed evenly with 0.12 kg maleic anhydride, 0.04 kg styrene and 0.012 kg dicumyl peroxide, heated to 190°C, hot-melted for 10 min, granulated, and then mixed with recycled granules B to obtain recycled PE material.

[0070] Comparative Example 1: A recyclable PE stretch film, differing from Example 1 in that it uses a melt flow index of 3.5 g / 10 min and a density of 0.959 g / cm³. 3 HB0035 type HDPE can replace LLDPE in equal amounts.

[0071] Comparative Example 2: A recyclable PE stretch film, which differs from Example 1 in that the amount of recycled PE added is 40 kg and the amount of LLDPE added is 50 kg.

[0072] Comparative Example 3: A recyclable PE stretch film, which differs from Example 1 in that it does not contain EPDM rubber, active phenolic resin and metal halides, but only 30 kg of recycled PE material and 70 kg of LLDPE.

[0073] Comparative Example 4: A recyclable PE stretch film, which differs from Example 1 in that an equal amount of LLDPE is used to replace the active phenolic resin and metal halide.

[0074] Performance testing

[0075] I. Mechanical and Transparency Tests of PE Stretch Film

[0076] Recyclable PE stretch film was prepared according to the methods in the examples and comparative examples. Commercially available PE stretch film was used as a control group. The commercially available PE stretch film was selected from Wuxi Kuaile Packaging Products Co., Ltd., model KLBZ-50. The performance was tested according to the following methods, and the test results are recorded in Table 2.

[0077] 1. Thickness: Tested in accordance with GB / T6672-2001 "Mechanical Measurement Method for Determination of Thickness of Plastic Films and Sheets".

[0078] 2. Puncture resistance: Tested in accordance with GB / T10004-2008 "Test method for puncture resistance of plastic composite film for packaging".

[0079] 3. Tensile strength and elongation at break: Tested in accordance with GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Tests on films and sheets", a 15*1.5cm sample was cut for testing, the clamp distance was 50mm, and the speed was 250mm / min.

[0080] 4. Haze: The haze shall be determined according to the method in GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics".

[0081] Table 2 Performance test results of PE stretch film

[0082]

[0083] Combining the data in Table 2 and the raw material usage in Examples 1-6, it can be seen that the PE stretch film produced by using a specific amount of recycled PE material in Examples 1-6, and using a specific ratio of EPDM rubber and p-tert-butylphenol formaldehyde resin as active phenolic resin, with stannous chloride as a catalyst, has the advantages of thinness, strong puncture resistance, high tensile strength, low haze, and high transparency. This indicates that the PE stretch film produced by using a specific amount of recycled PE material, EPDM rubber, active phenolic resin, etc., not only has good toughness but also high transparency and is easy to recycle.

[0084] Compared with Example 1, Example 7 uses octylphenol formaldehyde resin as the active phenolic resin. As shown in Table 2, the tensile and puncture resistance of the PE stretch film prepared using EPDM rubber, octylphenol formaldehyde resin and stannous chloride in a mass ratio of 4:4.5:1.5 is reduced.

[0085] Compared with Example 1, Examples 8-9 also used calcium stearate and antioxidants to pretreat stannous chloride. As can be seen from the data in Table 2, the haze of the winding film prepared in Examples 8-9 was reduced, the transparency was slightly improved, and the tensile strength was improved to a certain extent.

[0086] Compared with Example 8, in the preparation of PE recycled materials, a portion of the PE recycled granules in Examples 10 and 11 were subjected to maleic anhydride grafting treatment. The data in Table 2 show that the PE wrapping film prepared in Examples 10 and 11 has enhanced puncture resistance, increased tensile strength and elongation at break, and slightly improved light transmittance.

[0087] Compared to Example 10, Example 12 reduced the amount of maleic anhydride-grafted PE recycled granules, while Example 13 increased the amount of maleic anhydride-grafted PE recycled granules. The PE stretch films prepared in Examples 12 and 13 had reduced tensile and puncture resistance compared to Example 10.

[0088] Compared with Example 1, Comparative Example 1 uses HDPE as the matrix of the stretch film. Although the puncture resistance and tensile strength of the PE stretch film produced therefrom are increased, its thickness is larger and its transparency is reduced.

[0089] In Comparative Example 2, the amount of recycled PE material was increased. Compared with Example 1, the transparency of the PE stretch film produced by this method decreased, as did its tensile strength and puncture resistance. This indicates that increasing the amount of recycled PE material increases the brittleness of the stretch film, reduces its toughness, and affects its transparency.

[0090] In Comparative Example 3, only recycled PE and LLDPE were used as raw materials. Compared with Example 1, the puncture resistance of the PE wrapping film was significantly reduced and the elongation at break was significantly decreased, but the transparency was slightly improved. This indicates that the addition of EPDM, which is incompatible with the matrix, may affect the transparency of the film, but will significantly improve its toughness.

[0091] Comparative Example 4 did not contain any active phenolic resin or metal halides, but only recycled PE, EPDM rubber, and LLDPE. As can be seen, the resulting stretch film showed reduced puncture resistance, decreased tensile strength and elongation at break, and increased transparency compared to Example 1. This indicates that stannous chloride and active phenolic resin can improve the interfacial bonding between EPDM and the matrix and enhance flexibility.

[0092] II. Recyclability Test of PE Stretch Film

[0093] (1) The stretch film prepared in the examples and comparative examples was crushed, hot-melt granulated to obtain material A. Material A was then mixed with LLDPE material (melt index of 1.9 g / 10 min, density of 0.9188 g / cm³). 3 The mixture (selected from Lanzhou Petrochemical DFDA7042N) was mixed in a 50 / 50 ratio, hot-melted at 180℃, and granulated. Material B (melt index 1 g / 10 min, density 0.92 g / cm³) containing an opening agent was used. 3 The materials were selected from Formosa Plastics Group (Taiwan, brand name 3214) and LLDPE (melt index 1.9 g / 10 min, density 0.9188 g / cm³). 3The sample (selected from Lanzhou Petrochemical DFDA7042N) was mixed in a 50 / 50 ratio, melted at 180℃, and granulated to obtain a control group. The color and yellowing of the regenerated particles, as well as the purity and uniformity of the melt, were evaluated for the experimental group and the control group. The specific evaluation criteria are shown in Table 3, and the test results are recorded in Table 4.

[0094] (2) The stretch film prepared in each embodiment and comparative example was crushed, hot-melted and granulated to obtain first-generation particles, and impact strength was tested. Then the first-generation particles were crushed, hot-melted and granulated to obtain first-generation particles, and impact strength was tested. This was recorded as the first-generation test. Then the second-generation recycled particles were crushed, hot-melted and granulated to obtain second-generation recycled particles, and impact strength was tested. This was recorded as the second-generation test. The crushing, hot-melting and granulation were repeated to obtain third-generation recycled particles, and impact strength was tested. The performance retention rate was calculated according to the impact strength of the Nth generation particles / the impact strength of the first generation particles × 100% to verify the resistance of the stretch film to multiple processing and the value of recycled materials. The impact strength was tested according to GB / T1843-2008. The test speed was 3.5m / s. Three samples were tested in each group. The average value of the test results was taken. The test results were recorded in Table 4.

[0095] Table 3 Appearance Evaluation Criteria for Regenerated Particles

[0096]

[0097] Table 4 Recycling performance test of PE stretch film

[0098]

[0099] As can be seen from the data in Tables 3 and 4, the stretch films prepared in Examples 1-6 have little impact on the appearance of the recycled material after recycling, and still have high transparency and uniformity. Moreover, when the stretch films are recycled, the impact strength of the recycled material is high, the surface molecular structure is relatively stable, the resistance to multiple processing is good, and the value of the recycled material is high.

[0100] Compared with Example 1, Example 7 uses octylphenol formaldehyde resin as the active phenolic resin. As can be seen from the data comparison in Table 4, the color and purity are similar to those of Example 1, but its impact strength durability is not as good as that of Example 1.

[0101] Compared with Example 1, Examples 8-9 also used calcium stearate and antioxidants to pretreat stannous chloride. As shown in Table 4, the regenerated particles prepared in Examples 8 and 9 have a cleaner color and better uniformity.

[0102] Compared with Example 8, in the preparation of PE recycled materials, some of the PE recycled granules in Examples 10 and 11 were subjected to maleic anhydride grafting treatment. The data in Table 4 show that the recycled particles have a uniform color and are crystalline, with good surface smoothness, good resistance to multiple processing, and high recycling rate.

[0103] Compared to Example 10, Example 12 shows a reduction in the amount of maleic anhydride-grafted PE recycled granules, while Example 13 shows an increase in the amount of maleic anhydride-grafted PE recycled granules. Compared to Example 10, the PE wrapping films produced in Examples 12 and 13 show a decrease in the strength impact retention rate of the recycled particles.

[0104] Compared with Example 1, Comparative Example 1 uses HDPE as the matrix of the stretch film. It can be seen that the color and purity of the recycled particles produced are similar to those of Example 1, but their durability is reduced.

[0105] In Comparative Example 2, increasing the amount of recycled PE material resulted in a decrease in the color and purity of the recycled particles compared to Example 1, with the particles turning yellow and the recycling efficiency declining.

[0106] In Comparative Example 3, only recycled PE and LLDPE were used as raw materials. Compared with Example 1, the wrapping film prepared in Comparative Example 3 turned yellow when reused, and its uniformity decreased. The impact strength retention rate decreased significantly, the durability and processability were poor, and the value of the recycled material was weakened.

[0107] Comparative Example 4 did not contain any active phenolic resin or metal halides, but only recycled PE, EPDM rubber and LLDPE. Compared with Example 1, the color of the recycled material was the same as that of Example 1, but the purity was reduced and the durability for repeated use was significantly reduced.

[0108] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A recyclable PE stretch film, characterized in that, The raw materials include the following weight percentages: 5-30% recycled PE, 3-5% EPDM rubber, 4-5% active phenolic resin, 1-2% metal halide, 2-8% metallocene POE, 1-5% HDPE resin, 1-3% tackifying masterbatch, and the balance being LLDPE resin. The method for preparing the recycled PE material is as follows: Recycled PE stretch film is sorted, cleaned, and granulated to obtain recycled PE material; The recycled PE material has a melt flow index of 5-10 g / 10 min at 190℃ and 2.16 kg, and a density of 0.945-0.955 g / cm³. 3 The LLDPE resin has a melt index of 1.8-2.5 g / 10 min and a density of 0.916-0.92 g / cm³ at 190℃ and 2.16 kg. 3 .

2. The recyclable PE stretch film according to claim 1, characterized in that: The weight percentages of the raw materials are as follows: 30% recycled PE, 4% EPDM rubber, 4.5-5% active phenolic resin, 1-1.5% metal halide, 6% metallocene POE, 3% HDPE resin, 1% tackifying masterbatch, and the balance being LLDPE resin.

3. The recyclable PE stretch film according to claim 1, characterized in that: The active phenolic resin is selected from at least one of p-tert-butylphenol formaldehyde resin, octylphenol formaldehyde resin, bromomethyl p-tert-octylphenol formaldehyde resin, and chloromethylphenol formaldehyde resin; the metal halide is selected from at least one of stannous chloride, ferric chloride, aluminum chloride, and zinc bromide.

4. The recyclable PE stretch film according to claim 3, characterized in that: The mass ratio of the EPDM rubber, p-tert-butylphenol formaldehyde resin, and stannous chloride is 4:4.5:1.

5.

5. The recyclable PE stretch film according to claim 4, characterized in that: The stannous chloride is pretreated by the following method: stannous chloride is mixed with calcium stearate and an antioxidant, and stirred for 5-10 minutes. The mass ratio of stannous chloride, calcium stearate and antioxidant is 1:0.5-1:0.2-0.

5.

6. A method for preparing a recyclable PE stretch film as described in any one of claims 1-5, characterized in that, Includes the following steps: LLDPE resin is mixed with recycled PE material, EPDM rubber, tackifying masterbatch, metallocene POE and HDPE resin for 5-8 minutes, then hot-melted. Active phenolic resin and metal halide are added from the side feed and extruded to obtain a melt. The melt is cast and cooled to obtain a cast sheet. The cast sheet is then drawn, stretched, corona-electrode, rolled and cut to obtain a recyclable PE stretch film.

7. The method for preparing recyclable PE stretch film according to claim 6, characterized in that: The extrusion temperatures for each zone are as follows: Zone 1: 160-170℃, Zone 2: 180-190℃, Zone 3: 190-200℃, Zone 4: 195-205℃, and Die Head: 200-210℃.

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