Preparation method of regenerated plastic

Abstract

The invention discloses a regenerated plastic preparation method, the mechanical property is obviously enhanced, the improvement is derived from ordered arrangement of molecular chains induced by a layered structure of nano montmorillonite, and molecular chain damage control of a two-stage temperature control process is combined; the anti-aging performance is improved in a breakthrough manner, and the effect is benefited from that the ultraviolet absorptivity of the nano-montmorillonite at the wave band of 280-400 nm is improved by 35%, and the yellowing index delta E of the nano-montmorillonite after UV accelerated aging for 500 hours is only 1.8; the melt index fluctuation rate is controlled within + / -6.5%, and the fluctuation range is reduced by 65% compared with that of a traditional process; and the emission amount of volatile organic compounds is reduced to 42 [mu] gC / g.

Description

Technical Field

[0001] The present invention relates to the field of recycling of polymer materials, and particularly to a method for preparing recycled plastics. Background Art

[0002] Approximately 300 million tons of plastic waste are generated globally each year. Traditional landfill / incineration treatment causes environmental problems such as soil pollution and marine ecological damage. Recycled plastics have become a key link in the circular economy, but existing technologies are difficult to balance environmental protection requirements and material properties. The performance defects of recycled plastics are significant. The mechanical properties are insufficient: the flexural modulus of conventional recycled materials is generally lower than 60 MPa, which cannot meet the high-end requirements such as automotive parts. The thermal stability is poor: single-stage high-temperature processing results in a molecular weight reduction rate of over 25%, and the melt index fluctuates by more than ±18%. The weather resistance is low: the yellowing index ΔE≥4.0 after 500 hours of UV aging, and there is a lack of an effective ultraviolet shielding mechanism. The processing technology bottleneck is prominent. The pretreatment defects include low sorting and cleaning efficiency, and the removal rate of microplastic impurities is less than 65%, which affects the purity of recycled materials. The process adaptability is poor: traditional melt granulation processes have high energy consumption (large water consumption in the wet method and high impurity removal cost in the dry method), and it is difficult to achieve oriented intercalation of fillers. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a method for preparing recycled plastics.

[0004] To solve the above technical problems, the present invention provides the following technical solutions: A method for preparing recycled plastics according to the present invention includes the following steps: (a) Premixing recycled plastic particles with 0.1-0.5 wt% of nanoclay at 185±5°C for 10-15 minutes; (b) Performing final mixing on the mixture obtained in step (a) at 215±5°C, and maintaining the mixing pressure at 2-4 MPa; (c) Extrusion molding the final mixing product in the range of 240-280°C.

[0005] As a preferred technical solution of the present invention, the layer spacing of the nanoclay is 1.2-1.5 nm, and the cation exchange capacity ≥100 mmol / 100 g.

[0006] As a preferred technical solution of the present invention, the premixing in step (a) is carried out using a twin-screw extruder, the screw length-diameter ratio L / D is 40:1-48:1, and the rotation speed is 300-500 rpm.

[0007] As a preferred technical solution of the present invention, the pressure gradient control of the final mixing in step (b) is: maintaining 2 MPa for the first 5 minutes, and then increasing by 0.4 MPa per minute to 4 MPa.

[0008] As a preferred technical solution of the present invention, after the extrusion molding in step (c), it further includes: As a preferred technical solution of the present invention, the recycled plastic particles contain a mixture with the following mass ratios: polyester plastics (PET / PBT) 50 - 80%, polyolefin plastics (PE / PP) 20 - 50%, and the impurity content ≤ 3%; 0.01 - 0.1 wt% of hindered amine light stabilizer with a molecular weight range of 2000 - 4000 g / mol (HALS) is introduced in the premixing and kneading stage.

[0009] A nano - montmorillonite of the present invention is characterized in that its surface is modified by a silane coupling agent KH - 550, and the grafting rate is 1.2 - 1.8 mol / g.

[0010] The recycled plastic prepared by the method for preparing recycled plastic of the present invention is characterized in that: The flexural modulus ≥ 65 MPa; The yellowness index ΔE ≤ 2.5; The melt index volatility ≤ ± 8%.

[0011] It is applicable to the injection molding of automotive interior parts and meets the following requirements: The volatile organic compound emission ≤ 50 μgC / g; The color difference ΔE ≤ 3.0 after 1000 - hour xenon lamp aging.

[0012] As a preferred technical solution of the present invention, the method for testing the yellowness index includes: Using a QUV accelerated aging tester (UVA - 340 lamp tube, 0.76 W / m² @ 340 nm); Sampling and measuring the Lab value every 250 hours, and the total test duration ≥ 1000 hours; The ΔE value is calculated according to the CIE2000 color difference formula.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The mechanical properties are significantly enhanced. This improvement is due to the ordered arrangement of molecular chains induced by the layered structure of nano - montmorillonite and the control of molecular chain damage by the two - stage temperature control process; (2) The anti - aging performance is improved breakthroughly. This effect benefits from: the ultraviolet absorption rate of nano - montmorillonite in the 280 - 400 nm wavelength band is increased by 35%, and the yellowness index ΔE after 500 - hour UV accelerated aging is only 1.8; (3) The processing stability is greatly improved. The melt index volatility of the present invention is controlled within ± 6.5%, and the fluctuation range is reduced by 65% compared with the traditional process; (4) The advantage of environmental protection compliance, and the volatile organic compound emission is reduced to 42 μgC / g. Description of the Drawings

[0014] The accompanying drawings are used to provide a further understanding of the present invention and form a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the accompanying drawings: Figure 1 is a flowchart of the steps of the present invention. Detailed implementation manners

[0015] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0016] Among them, the same reference numerals in the accompanying drawings all refer to the same components.

[0017] As Figure 1 shown, the present invention provides a method for preparing recycled plastics, including the following steps: (a) Premix recycled plastic particles with 0.1 - 0.5 wt% of nano-montmorillonite at 185 ± 5 °C for 10 - 15 minutes; (b) Carry out final mixing of the mixture obtained in step (a) at 215 ± 5 °C, and keep the mixing pressure at 2 - 4 MPa; (c) Extrusion mold the final mixing product in the range of 240 - 280 °C.

[0018] Furthermore, the layer spacing of the nano-montmorillonite is 1.2 - 1.5 nm, and the cation exchange capacity ≥ 100 mmol / 100 g.

[0019] Furthermore, the premixing in step (a) is carried out using a twin-screw extruder, the length-diameter ratio L / D of the screw is 40:1 - 48:1, and the rotational speed is 300 - 500 rpm.

[0020] Furthermore, the pressure gradient control of the final mixing in step (b) is: keep 2 MPa for the first 5 minutes, and then increase by 0.4 MPa per minute to 4 MPa.

[0021] Furthermore, after the extrusion molding in step (c), it further includes: (d) Heat-treat the molded product in a vacuum environment at 80 - 100 °C for 2 - 4 hours, and the heating rate ≤ 5 °C / min.

[0022] Furthermore, the recycled plastic particles contain a mixture with the following mass ratios: polyester plastics (PET / PBT) 50 - 80%, polyolefin plastics (PE / PP) 20 - 50%, and the impurity content ≤ 3%; Introduce 0.01 - 0.1 wt% of hindered amine light stabilizer (HALS) with a molecular weight range of 2000 - 4000 g / mol in the premixing stage.

[0023] The present invention provides a nano-montmorillonite, characterized in that its surface is modified by a silane coupling agent KH-550, and the grafting rate is 1.2-1.8 mol / g.

[0024] The present invention provides a recycled plastic prepared by a method for preparing recycled plastics, characterized in that: The flexural modulus ≥ 65 MPa; The yellowness index ΔE ≤ 2.5; The melt index volatility ≤ ±8%.

[0025] It is applicable to the injection molding of automotive interior parts and meets: The volatile organic compound emission ≤ 50 μgC / g; The color difference ΔE ≤ 3.0 after 1000 hours of xenon lamp aging.

[0026] The test method for its yellowness index includes: Using a QUV accelerated aging tester (UVA-340 lamp tube, 0.76 W / m² @ 340 nm); Sampling and measuring the Lab value every 250 hours, and the total test duration ≥ 1000 hours; The ΔE value is calculated according to the CIE2000 color difference formula.

[0027] Example 1: Raw materials: 70% post-consumer PET bottle chips + 30% industrial waste PE film; Process parameters: Premixing: 185 °C / 12 minutes, screw speed 400 rpm; Final mixing: 210 °C / pressure gradient 2 → 4 MPa; Heat treatment: 90 °C vacuum treatment for 3 hours.

[0028] Example 2: Raw materials: 70% post-consumer PET bottle chips + 30% industrial waste PE film; Process parameters: Premixing: 180 °C / 15 minutes, screw speed 500 rpm; Final mixing: 220 °C / pressure gradient 2 → 4 MPa; Heat treatment: 100 °C vacuum treatment for 4 hours.

[0029] Example 3: Raw materials: 60% waste automotive bumper (PP / EPDM 70 / 30) + 40% household appliance shell (ABS); Process parameters: Premixing: 190 °C / 14 minutes, screw speed 450 rpm; Final mixing: 220 °C / pressure gradient 2 → 4 MPa (increasing by 0.4 MPa per minute); Heat treatment: Vacuum treatment at 100°C for 4 hours.

[0030] Example 4: Raw materials: Ocean-recycled PET flakes (containing 5% sea salt sediment); Pretreatment: Supercritical CO2 cleaning (35 MPa, 50°C, 2 hours) Process parameters: Premixing: 190°C / 14 minutes, screw speed 450 rpm; Final mixing: 220°C / Pressure gradient 2 → 4 MPa ( + 0.4 MPa per minute); Heat treatment: Vacuum treatment at 100°C for 4 hours.

[0031] Comparative example 1 (unmodified montmorillonite, single-stage process): Yellowing index ΔE = 4.3, flexural modulus 50 MPa; Comparative example 2 (single-stage process): Agglomeration of montmorillonite resulted in ΔE = 3.9, flexural modulus 55 MPa; Comparative example 3 (two-stage process): Agglomeration of montmorillonite resulted in ΔE = 3.2, flexural modulus 58 MPa.

[0032] Comparison: 1. Yellowing index determination (three-reference color correction method): Reference 1: Unaged specimen; Reference 2: 500h xenon lamp-aged PP standard sheet; Reference 3: 1000h outdoor-exposed recycled PET.

[0033] 2. Molecular weight test - Gel Permeation Chromatography (GPC) protocol: Mobile phase: Trichlorobenzene (135°C); Standard sample: Narrow-distribution polystyrene; After testing and comparison, Table 1 was obtained

[0034] Table 1 According to Table 1, it can be seen that the ΔE value of the montmorillonite group is reduced by 42% compared with the traditional antioxidant, and the two-stage process reduces the molecular chain breakage rate to 9.8%.

[0035] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing recycled plastics, characterized in that, It includes the following steps: (a) Premix the recycled plastic particles with 0.1 - 0.5 wt% of nano - montmorillonite at 185 ± 5 °C for 10 - 15 minutes; (b) Carry out final mixing of the mixture obtained in step (a) at 215 ± 5 °C, and keep the mixing pressure at 2 - 4 MPa; (c) Extrusion - mold the final - mixed product in the temperature range of 240 - 280 °C.

2. The method according to claim 1, wherein The layer spacing of the nano - montmorillonite is 1.2 - 1.5 nm, and the cation exchange capacity ≥ 100 mmol / 100 g.

3. The method according to claim 1, wherein The premixing in step (a) is carried out using a twin - screw extruder with a screw length - to - diameter ratio L / D of 40:1 - 48:1 and a rotation speed of 300 - 500 rpm.

4. The method according to claim 1, characterized in that The pressure gradient control of the final mixing in step (b) is: keep 2 MPa for the first 5 minutes, and then increase by 0.4 MPa per minute until 4 MPa.

5. The method according to claim 1, wherein After the extrusion - molding in step (c), it also includes: (d) Heat - treat the molded product in a vacuum environment at 80 - 100 °C for 2 - 4 hours, and the heating rate ≤ 5 °C / min.

6. The method according to claim 1, characterized in that, The recycled plastic particles contain a mixture with the following mass ratios: polyester plastics (PET / PBT) 50 - 80%, polyolefin plastics (PE / PP) 20 - 50%, and the impurity content ≤ 3%; 0.01 - 0.1 wt% of hindered amine light stabilizer (HALS) with a molecular weight range of 2000 - 4000 g / mol is introduced in the premixing stage.

7. The nano-montmorillonite according to claim 2, wherein Its surface is modified by silane coupling agent KH - 550 with a grafting rate of 1.2 - 1.8 mol / g.

8. The recycled plastic prepared by the method according to claim 1, wherein: The flexural modulus ≥ 65 MPa; the yellowing index ΔE ≤ 2.5; the melt index volatility ≤ ±8%.

9. The recycled plastic according to claim 7, wherein It is applicable to the injection molding of automotive interior parts, meeting the requirements: volatile organic compound emissions ≤ 50 μgC / g; color difference ΔE ≤ 3.0 after 1000 - hour xenon lamp aging.

10. The recycled plastic according to claim 6, characterized in that, The test method for its yellowing index includes: using a QUV accelerated aging tester (UVA - 340 lamp tube, 0.76 W / m²@340 nm); sampling and measuring the Lab value every 250 hours, and the total test duration ≥ 1000 hours; the ΔE value is calculated according to the CIE2000 color - difference formula.

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