Biodegradable PE foam and preparation method thereof

Abstract

The invention relates to the technical field of PE foam, in particular to biodegradable PE foam and a preparation method thereof.The biodegradable PE foam is prepared from 50 parts to 60 parts of bio-based resin, 5 parts to 15 parts of AC foaming agents, 0.4 part to 0.8 part of peroxide cross-linking agents, 0.3 part to 0.8 part of zinc oxide, 0.75 part to 1.25 parts of zinc stearate, 0.2 part to 0.7 part of antioxidants, 0.5 part to 3 parts of nanometer white carbon black, 23.45 parts to 37.85 parts of PE and 1 part to 5 parts of compatilizers; the preparation method of the biodegradable PE foam comprises the following steps: S1, banburying and granulating; s2, extrusion molding; s3, carrying out radiation crosslinking treatment; s4, gradient foaming; s5, cooling and shaping. The biodegradable PE foam has good biodegradable performance, and the application environmental protection property of the foam is improved; and when the material is used as a cushion packaging material, good buffering and vibration absorption effects can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of PE foam, and in particular to biodegradable PE foam and a preparation method thereof. Background Art

[0002] ‌ PE foam has become a widely used cushioning packaging material due to its good cushioning and vibration absorption properties. Foam is a material made by foaming plastic particles. It has the characteristics of light weight, good elasticity, easy bending, and thin volume. The high molecular polymer can be made into foam after foaming and can be used as a cushioning packaging material. However, there are problems such as the waste cannot be completely degraded and incineration will produce harmful gases. ‌

[0003] However, for the widely used PE foam, there is a large amount of waste, and its degradation mainly depends on the action of microorganisms in the natural environment, but this process is extremely slow, which leads to long-term environmental problems. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a biodegradable PE foam and a preparation method thereof.

[0005] The purpose of the present invention can be achieved by the following technical scheme: a biodegradable PE foam, wherein the raw materials for preparing the biodegradable PE foam include: in parts by weight, 50-60 parts of bio-based resin, 5-15 parts of AC foaming agent, 0.4-0.8 parts of peroxide crosslinking agent, 0.3-0.8 parts of zinc oxide, 0.75-1.25 parts of zinc stearate, 0.2-0.7 parts of antioxidant, 0.5-3 parts of nano-white carbon black, 23.45-37.85 parts of PE, and 1-5 parts of compatibilizer.

[0006] Preferably, the bio-based resin is selected from at least one of polylactic acid, polyhydroxyalkanoate, and polybutylene succinate.

[0007] Preferably, the compatibilizer is maleic anhydride grafted polyethylene.

[0008] Preferably, the peroxide cross-linking agent is dicumyl peroxide.

[0009] Preferably, the nano-white carbon black has a particle size of 50-100 nm, a specific surface area of ​​≥200 m² / g, and a surface modification treatment with a silane coupling agent KH-550.

[0010] The present invention also provides a method for preparing biodegradable PE foam, comprising the following steps: S1. Internal mixing and granulation: add bio-based resin, PE, peroxide crosslinking agent, zinc oxide, zinc stearate, antioxidant and compatibilizer into an internal mixer, mix at 80-120°C for 3-5 minutes, then add AC foaming agent and nano-silica and continue mixing for 1-2 minutes, extrude and pelletize at 130-150°C through a twin-screw extruder to obtain masterbatch; S2, extrusion molding: the masterbatch is put into a single screw extruder, and extruded to obtain a master sheet with a thickness of 1-3 mm; S3, radiation cross-linking treatment: use an electron accelerator to irradiate the master sheet with an electron beam, with a radiation dose of 10-25 Mrad, an energy of 1.5-2.0 MeV, and 3-5 irradiation layers; S4, gradient foaming: the irradiated mother sheet is sent into a vertical foaming furnace, and passes through a horizontal preheating zone and a vertical foaming zone in sequence, and the foaming time is 30-60 seconds; S5. Cooling and shaping: The foamed sheet is cooled and shaped in a 10-15°C water bath, cut and rolled to obtain biodegradable PE foam.

[0011] Preferably, in step S2, the extrusion temperature of the single-screw extruder: the temperature gradient from zone one to zone seven is 90℃±2℃, 97℃±2℃, 106℃±2℃, 111℃±2℃, 116℃±2℃, 117℃±2℃, 120℃±2℃, and the die head temperature is 120±2℃.

[0012] Preferably, in step S3, the relationship between the radiation dose and the mass fraction of the bio-based resin is: radiation dose=0.25×the mass fraction of the bio-based resin+5.

[0013] Preferably, the temperature gradient of the horizontal preheating zone is: preheating zone 1 115°C±2°C, preheating zone 2 120°C±2°C, preheating zone 3 125°C±2°C.

[0014] Preferably, the temperature gradient of the vertical foaming zone is: Foaming zone 1: 200-220℃, residence time 10-15 seconds; Foaming zone 2: 230-250°C, residence time 20-30 seconds; Foaming zone three: 180-200℃, residence time 5-10 seconds.

[0015] Preferably, the biodegradable PE foam has an open porosity of 35-45%, a density of 0.05-0.15 g / cm³, and a specific surface area of ​​20-50 m2 / g.

[0016] The beneficial effects of the present invention are: 1. The biodegradable PE foam of the present invention is prepared by combining bio-based resin with PE and other raw materials, with an open porosity of 35-45%, a density of 0.05-0.15g / cm³, and a specific surface area of ​​20-50㎡ / g. Compared with conventional products, it has a high open porosity and a large specific surface area, is conducive to decomposition in a natural environment, and has good impact resistance. It can be better used as a cushioning packaging material, and has the advantages of being green, environmentally friendly, lightweight, and shock-absorbing.

[0017] 2. The biodegradable PE foam preparation method of the present invention achieves the following breakthrough advantages through the design of bio-based / PE composite system, compatibilizer interface enhancement and radiation-gradient foaming synergistic process: ① Efficient degradation: 90-day composting degradation rate ≥ 60%, solving the problem of plastic pollution; ② Mechanical balance: compression strength ≥50kPa, meeting industrial packaging requirements; ③ Reduce production: compatible with existing equipment, reducing production costs by more than 30%; ④ Environmentally friendly: Carbon emissions over the entire life cycle are reduced by 60-70%. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0019] Example 1 The raw material ratio for preparing the biodegradable PE foam in this embodiment is as follows: 55 parts of polylactic acid (PLA), 30 parts of PE, 0.6 parts of dicumyl peroxide (DCP), 10 parts of AC foaming agent, 0.5 parts of zinc oxide, 1.0 parts of zinc stearate, 0.5 parts of antioxidant, 2 parts of nano-silica (KH-550 modified), and 3 parts of maleic anhydride grafted polyethylene (MAH-g-PE).

[0020] Preparation process of biodegradable PE foam in this embodiment: S1. Internal mixing and granulation: Add polylactic acid (PLA), PE, maleic anhydride grafted polyethylene, zinc oxide, zinc stearate, antioxidant 1010 and dicumyl peroxide (DCP) into an internal mixer, set the temperature to 100°C, the speed to 50 rpm, and mix for 4 minutes; add AC foaming agent and nano-silica (KH-550 modified), and continue mixing for 1.5 minutes; extrusion and pelletization at 140°C by a twin-screw extruder, the pellet diameter is 3 mm; S2, Extrusion molding: The masterbatch was put into a single screw extruder, and melt-extruded at a temperature gradient of 90°C, 97°C, 106°C, 111°C, 116°C, 117°C, and 120°C from zone 1 to zone 7, and the die temperature was 120°C to obtain a master sheet with a thickness of 2.0±0.2mm and a width of 300mm; S3, Radiation cross-linking: An electron accelerator is used to irradiate the master sheet with electron beam. The relationship between the radiation dose and the mass fraction of bio-based resin is: radiation measurement = 0.25 × bio-based resin fraction + 5. The radiation dose is calculated according to the formula: 0.25 × 55 + 5 = 18.75 Mrad, and 18 Mrad is actually used; the energy is 1.8 MeV, 4 layers are irradiated, and the transmission speed is 2 m / min.

[0021] S4, gradient foaming: The irradiated mother sheet is sent into the vertical foaming furnace, and passes through the horizontal preheating zone: 115℃ (10s) → 120℃ (10s) → 125℃ (10s) and the vertical foaming zone: (foaming zone 1: 210℃ (staying 15s), foaming zone 2: 240℃ (staying 25s), foaming zone 3: 190℃ (staying 8s); S5, cooling and shaping: The foamed sheet was cooled in a 12°C water bath to be shaped, cut and rolled (thickness 10 mm, width 250 mm) to obtain biodegradable PE foam.

[0022] Embodiment 2: The raw material ratios for preparing the biodegradable PE foam in this embodiment are adjusted as follows: polylactic acid (PLA) is increased to 60 parts, PE is reduced to 23.45 parts, nano-silica (KH-550 modified) is increased to 3 parts, and the remaining components and ratios are the same as those in Example 1.

[0023] The difference between the preparation process of this embodiment and that of embodiment 1 is that the radiation dose is: 0.25×60+5=20 Mrad, the temperature of the second foaming zone of the vertical foaming furnace is increased to 250° C., and the remaining steps are the same as those of embodiment 1.

[0024] Comparative Example 1: The raw materials for the preparation of this example are adjusted: the compatibilizer maleic anhydride grafted polyethylene MAH-g-PE is removed, and the remaining components and proportions are the same as those in Example 1, and the preparation process is the same as that in Example 1.

[0025] Comparative Example 2: The raw materials and proportions of the preparation of this embodiment are the same as those of Example 1, except that the radiation dose is increased to 35 Mrad (far exceeding the value calculated by the formula) during the preparation process, and the remaining steps are the same as those of Example 1.

[0026] The performance test results of the PE foam finally obtained in the above-mentioned Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are as follows: Industrial application examples: The foam obtained in Example 1 was used for electronic product packaging, and the performance test was compared with that of petroleum-based PE foam as follows: Through the comparative experimental data of Example 1, Example 2, Comparative Example 1, Comparative Example 2 and industrial application examples, the scheme of the present invention shows significant advantages in degradation performance, mechanical strength and process controllability, which are specifically reflected in the following aspects: 1. Core advantage of biodegradability: significantly improved degradation performance Example 1: The 90-day composting degradation rate reached 61.3%, far exceeding that of traditional PE foam and higher than that of pure PLA foam material (degradation rate of about 50%).

[0027] Example 2: By increasing the PLA content (60 parts) and specific surface area (46.8 m2 / g), the degradation rate was further improved to 67.8%, verifying the synergistic degradation mechanism of bio-based resin and cellular structure.

[0028] Comparative analysis: Comparative Example 1 (without compatibilizer): The degradation rate is only 37.4%, which proves that the compatibilizer (MAH-g-PE) improves the PLA / PE interface bonding and prevents PE from encapsulating PLA and hindering degradation; Comparative Example 2 (excessive radiation dose): the degradation rate was artificially high to 70.3%, but the material actually failed due to molecular chain breakage (compression strength 40 kPa), which illustrates the rationality of the radiation dose formula of the present invention.

[0029] Degradation mechanism: PLA preferentially hydrolyzes: The PLA phase hydrolyzes rapidly in the compost, forming a porous structure (scanning electron microscopy shows that the pore size increases by 2 times in 30 days), accelerating PE exposure; PE oxidation breakage: The enzymatic reaction produced by microbial metabolism combined with Fe³⁺ (iron-containing substances in compost) triggers PE oxidation chain breakage.

[0030] 2. Balance optimization between mechanical properties and degradability Example 1: The compression strength is 57 kPa, which is close to the traditional PE foam (60-70 kPa), while maintaining a high degradation rate (61.3%), solving the contradiction of bio-based materials that "strong but difficult to degrade, and degradable but easy to break".

[0031] Key technical support: Compatibilizer MAH-g-PE: The interfacial shear strength is increased by 70% (DMA test), and phase separation is inhibited (compression strength of comparative example 1 is reduced by 45%); Gradient foaming process: Through the three-zone temperature control of foaming (210℃→240℃→190℃), the cell diameter is evenly distributed to avoid stress concentration.

[0032] Trade-off verification of Example 2: The degradation rate increased to 67.8%, but the compression strength dropped to 48 kPa, proving that the PLA / PE ratio can be adjusted to meet the needs of different scenarios, such as disposable packaging vs. durable cushioning.

[0033] 3. Radiation cross-linking and foaming work together to improve process controllability ①Dynamic control of radiation dose: According to the radiation dose formula = 0.25 × the number of bio-based resins + 5, the radiation dose of Example 1 (55 parts of PLA) is 18 Mrad, and the radiation dose of Example 2 (60 parts of PLA) is 20 Mrad, which accurately matches the cross-linking requirements; In Comparative Example 2, the PLA molecular weight decreased by 40% due to excessive radiation at 35 Mrad, verifying the necessity of the radiation dose formula.

[0034] ② Gradient foaming temperature optimization: The temperature of the second foaming zone is 240℃, which makes the decomposition rate of AC foaming agent >95%, and the foaming efficiency is increased by 40% compared with the constant temperature process; The three foaming zones were quickly set at 190°C to avoid cell collapse (compared with comparative example 2, where cell collapse caused the density to increase to 0.17 g / cm³).

[0035] 4. Environmental benefits and industrialization potential Carbon emission reduction: Example 1 produces carbon emissions of 1.21 kg CO 2 / t, compared with traditional PE foam (3.85kg CO 2 / t) decreased by 68%; Circular economy compatibility: The foam can be completely degraded in industrial composting facilities after disposal (89.6% degradation rate in 600 days), with no risk of microplastic residues (no PE fragments detected by SEM-EDS); Cost controllability: When the proportion of PLA is ≤60%, the raw material cost is 35-40% lower than that of pure PLA foam, and it is compatible with existing PE foaming equipment without the need to modify the production line.

[0036] In summary, the present invention achieves the following breakthrough advantages through the design of bio-based / PE composite system, compatibilizer interface enhancement and radiation-gradient foaming synergistic process: ① Efficient degradation: 90-day composting degradation rate ≥ 60%, solving the problem of plastic pollution; ② Mechanical balance: compression strength ≥50kPa, meeting industrial packaging requirements; ③ Reduce production: compatible with existing equipment, reducing production costs by more than 30%; ④ Environmentally friendly: Carbon emissions over the entire life cycle are reduced by 60-70%.

[0037] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description here should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in the field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A biodegradable PE foam, characterized in that: The raw materials for preparing the biodegradable PE foam include, by weight, 50-60 parts of bio-based resin, 5-15 parts of AC foaming agent, 0.4-0.8 parts of peroxide crosslinking agent, 0.3-0.8 parts of zinc oxide, 0.75-1.25 parts of zinc stearate, 0.2-0.7 parts of antioxidant, 0.5-3 parts of nano-white carbon black, 23.45-37.85 parts of PE and 1-5 parts of compatibilizer.

2. The biodegradable PE foam according to claim 1, characterized in that: The bio-based resin is selected from at least one of polylactic acid, polyhydroxyalkanoate, and polybutylene succinate.

3. The biodegradable PE foam according to claim 1, characterized in that: The compatibilizer is maleic anhydride grafted polyethylene.

4. The biodegradable PE foam according to claim 1, characterized in that: The peroxide cross-linking agent is dicumyl peroxide.

5. The biodegradable PE foam according to claim 1, characterized in that: The nano-white carbon black has a particle size of 50-100 nm, a specific surface area of ​​≥200 m² / g, and a surface modified by a silane coupling agent KH-550.

6. The method for preparing the biodegradable PE foam according to any one of claims 1 to 4, characterized in that: The steps include: S1. Internal mixing and granulation: add bio-based resin, PE, peroxide crosslinking agent, zinc oxide, zinc stearate, antioxidant and compatibilizer into an internal mixer, mix at 80-120°C for 3-5 minutes, then add AC foaming agent and nano-silica and continue mixing for 1-2 minutes, extrude and pelletize at 130-150°C through a twin-screw extruder to obtain masterbatch; S2, extrusion molding: the masterbatch is put into a single screw extruder, and extruded to obtain a master sheet with a thickness of 1-3 mm; S3, radiation cross-linking treatment: use an electron accelerator to irradiate the master sheet with an electron beam, with a radiation dose of 10-25 Mrad, an energy of 1.5-2.0 MeV, and 3-5 irradiation layers; S4, gradient foaming: the irradiated mother sheet is sent into a vertical foaming furnace, and passes through a horizontal preheating zone and a vertical foaming zone in sequence, and the foaming time is 30-60 seconds; S5. Cooling and shaping: The foamed sheet is cooled and shaped in a 10-15°C water bath, cut and rolled to obtain biodegradable PE foam.

7. The method for preparing the biodegradable PE foam according to claim 6, characterized in that: In step S2, the extrusion temperature of the single-screw extruder: the temperature gradient from zone 1 to zone 7 is 90℃±2℃, 97℃±2℃, 106℃±2℃, 111℃±2℃, 116℃±2℃, 117℃±2℃, 120℃±2℃, and the die head temperature is 120±2℃.

8. The method for preparing the biodegradable PE foam according to claim 6, characterized in that: The temperature gradient of the horizontal preheating zone is: preheating zone 1 115°C ± 2°C, preheating zone 2 120°C ± 2°C, preheating zone 3 125°C ± 2°C.

9. The method for preparing the biodegradable PE foam according to claim 6, characterized in that: The temperature gradient of the vertical foaming zone is: Foaming zone 1: 200-220℃, residence time 10-15 seconds; Foaming zone 2: 230-250°C, residence time 20-30 seconds; Foaming zone three: 180-200℃, residence time 5-10 seconds.

10. The method for preparing the biodegradable PE foam according to claim 6, characterized in that: The biodegradable PE foam has an open porosity of 35-45% and a density of 0.05-0.15 g / cm³.

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