Method for upgrading and recycling polyethylene glycol terephthalate waste into foamable material

Abstract

The invention discloses an upgrading and recycling method of PET (Polyethylene Terephthalate) waste. A foamable material is synthesized by using aliphatic diacid containing branched chains and the PET waste. According to the method disclosed by the invention, the molecular chain entanglement degree in the PET melt is improved by introducing the aliphatic diacid which is derived from a biological source and has a long branch chain into a PET chain, the melt strength and viscoelasticity of the PET are remarkably improved, and the requirement of preparing a foaming material can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene terephthalate (PET) recycling and foaming, and particularly relates to an upgraded recycling method for PET waste materials. Background Art

[0002] Due to its excellent properties and low cost, polyethylene terephthalate is widely used in daily production and life nowadays. The global annual output of bottle-grade PET exceeds 31 million tons, accounting for about 10% of the total plastic production. The global annual output of PET fibers is even more than 72 million tons, accounting for 52% of the total global fiber production, making it the largest fiber category. In recent years, due to the popularity of fast fashion products globally and the widespread use of disposable plastic products, the lifespan of PET products has been greatly shortened, and the corresponding large amount of waste has posed a severe challenge to the waste management and recycling of the polyester industry. Although the recovery rate of bottle-grade PET is relatively high, reaching 50% - 60%, most of it is downgraded and recycled into fiber products, while the recovery rate of PET textiles is less than 13%. A large number of textiles are landfilled or incinerated, leading to serious environmental problems. The mainstream recycling method in the industry is to downgrade and recycle PET into low-value materials (such as sofa fillers, automotive heat insulation materials, or carpet underlays). Another widely concerned recycling method is to recycle PET into small molecule raw materials. However, since textiles are often composed of a mixture of various fibers and contain a large amount of additives such as dyes, this method requires a cumbersome purification and separation process later and is difficult to obtain good economic benefits. Therefore, a strategy for upgrading and recycling PET waste materials is needed to produce high-value recycled products to achieve the sustainable development of the PET industry.

[0003] PET foam has excellent properties such as high-temperature dimensional stability, heat insulation, and chemical resistance. Moreover, as a widely used structural material, PET foam materials have relatively low requirements for product color, which can effectively avoid the problem of difficult decolorization during the PET recycling process. Currently, PET foam has been widely used in industries such as construction, aerospace, modern automotive, shipbuilding, and food packaging. Especially in the wind power field, the sandwich material with PET foam as the core accounts for about 72% of the blade mass. The use of PET foam can replace polycarbonate foam, which is beneficial to reducing the use of fossil resources and protecting the environment.

[0004] The patent specification with the publication number CN119638563A discloses a method for degrading PET to recycle TPA. The steps include adding the PET waste to be treated into an aqueous polyethylene glycol solution containing an alkaline reagent, carrying out a depolymerization reaction at 70 - 110°C and normal pressure. After the reaction, solid-liquid separation is carried out while it is hot. The obtained solid phase is dissolved in water, the residue is filtered off, and the pH of the obtained solution is adjusted to precipitate the TPA monomer. This method has cumbersome steps, consumes a large amount of chemical reagents, and requires a separation and purification process later, which is not conducive to industrial production and will have a greater negative impact on the environment. The patent specification with the publication number CN114805779A discloses a method for preparing an aromatic-aliphatic copolyester. The reaction temperature of the carboxy-ester exchange reaction is 150 - 300°C, the reaction pressure is below 100 Pa, and the reaction time is 2 - 24 hours. It actually synthesizes the copolyester through a melt polycondensation process, which not only has high requirements for the reaction device but also consumes a large amount of energy, significantly increasing the production cost. Summary of the Invention

[0005] The present invention provides an upgraded recycling method for PET waste, which synthesizes a foamable material using a branched aliphatic diacid and PET waste. Commonly used bottle-grade and fiber-grade PET have low melt strength, and there are problems such as cell rupture and coalescence during the foaming process, and a regular foam structure cannot be formed. The method of the present invention introduces a bio-derived aliphatic diacid with long branched chains into the PET chain, increasing the degree of molecular chain entanglement in the PET melt, significantly improving the melt strength and viscoelasticity of PET, meeting the requirements for preparing foamable materials.

[0006] In some embodiments, the foamable material has the following structure:

[0007]

[0008] Wherein, x is a positive integer, y and z are non-negative integers and not both zero at the same time, R1, R4, R5, and R8 are each independently an alkylene group with 5 - 10 carbon atoms, R2, R6, and R7 are each independently an alkyl group with 5 - 10 carbon atoms, and R3 is a hydrocarbon group with 5 - 10 carbon atoms containing a carbon-carbon double bond.

[0009] Furthermore, (y + z):(x + y + z) is 0.1 - 10:100, such as 1:100, 2.5:100, 5:100, etc., and further can be 1 - 5:100.

[0010] In some embodiments, the number of branched-chain carbon atoms in the branched aliphatic diacid is 5 - 10.

[0011] In some embodiments, the branched aliphatic diacid includes at least one of dodecenedioic acid dimer, tetradecenedioic acid dimer, hexadecenedioic acid dimer, octadecenedioic acid dimer, eicosenedioic acid dimer, docosenedioic acid dimer, hydrogenated dodecenedioic acid dimer, hydrogenated tetradecenedioic acid dimer, hydrogenated hexadecenedioic acid dimer, hydrogenated octadecenedioic acid dimer, hydrogenated eicosenedioic acid dimer, and hydrogenated docosenedioic acid dimer.

[0012] In some embodiments, the PET waste includes one or more of bottle-grade PET waste, PET fiber waste, and blended fiber waste with PET as the main component (e.g., greater than 50 wt%). The blended fiber waste may specifically include one or more of polyester / cotton blended fiber waste, polyester / propylene blended fiber waste, etc.

[0013] In some embodiments, the method for upgrading and recycling the PET waste specifically includes the steps of:

[0014] (1) Reactively extruding the PET waste and the branched aliphatic diacid in a twin-screw extruder to obtain a low-molecular-weight copolyester;

[0015] (2) Solid-phase polycondensing the low-molecular-weight copolyester to obtain a PET-based foamable material.

[0016] In step (1), based on the total molar amount of the branched aliphatic diacid and the terephthalic acid units in the PET waste being 100%, the molar proportion of the branched aliphatic diacid may be 0.1% - 10%, such as 1%, 2.5%, 5%, etc., and further may be 1% - 5%.

[0017] In step (1), the temperature of the reactive extrusion may be 250 - 300 °C, such as 260 °C, 270 °C, 280 °C, 290 °C, etc., and further may be 250 - 290 °C.

[0018] In step (1), the screw speed of the twin-screw extruder may be 5 - 15 Hz, such as 10 Hz, etc.

[0019] In step (1), the reaction extrusion time of the PET waste and the branched aliphatic diacid in the twin-screw extruder may be 50 - 300 s, such as 100 s, 150 s, 200 s, 250 s, etc., and further may be 50 - 150 s.

[0020] In step (1), after the reactive extrusion, pelletizing and drying operations may further be included. The drying may be vacuum drying. The drying temperature may be 40 - 120 °C, such as 60 °C, etc., and the time may be 4 - 24 h, such as 10 h, etc., and further may be 4 - 10 h.

[0021] In step (2), the temperature of the solid-phase polycondensation can be 160 - 210 °C, such as 180 °C, etc., and further can be 180 - 210 °C, the time can be 1 - 24 h, such as 3 h, 6 h, etc., and further can be 3 - 6 h.

[0022] In step (2), the solid-phase polycondensation can be carried out under a vacuum condition of <100 Pa (preferably <50 Pa) or in an inert gas atmosphere. The inert gas referred to in the present invention means a gas that does not participate in the reaction.

[0023] In step (2), the solid-phase polycondensation can be carried out under continuous stirring.

[0024] The present invention also provides a foamable material obtained by the above-mentioned upgrading and recycling method of PET waste.

[0025] Generally, the melt strength and viscoelasticity of PET are relatively low, and problems such as cell rupture will occur during the foaming process, so it is not suitable for direct foaming. By introducing an aliphatic diacid with long branched chains into the PET chain, the melt strength and viscoelasticity are improved through branch entanglement, making the polymer have the ability to be foamed and suitable for preparing foam materials.

[0026] In some embodiments, the melt index of the foamable material under the conditions of 260 °C and 1.2 kg pressure is less than 12 g / 10 min.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. The present invention can be applied to a variety of PET wastes, especially PET fibers without decolorization treatment and blended fiber wastes mainly composed of PET.

[0029] 2. The steps of the present invention are simple, with low energy consumption, no need to add other chemicals additionally, being environmentally friendly, having low cost, and having broad industrial application prospects.

[0030] 3. The PET-based foamable material prepared by the present invention contains aliphatic chain segments, which can significantly improve its biodegradability and has wide applications. Description of the Drawings

[0031] Figure 1 It is the nuclear magnetic resonance hydrogen spectrum of the PET foamable material synthesized in Example 1.

[0032] Figure 2 It is the heat flow curve of the PET foamable material synthesized in Example 1. Detailed Embodiments

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The operating methods without specific conditions noted in the following embodiments are generally in accordance with conventional conditions or the conditions recommended by the manufacturer.

[0034] The melt index test conditions in the following examples are all 260 °C and 1.2 kg pressure.

[0035] Example 1

[0036] (1) 1000 g of bottle-grade PET chips and 29.19 g of octadecane diacid (dimeric octadecenoic acid) (the molar proportion of dimeric octadecenoic acid units is 1%, and the molar ratio of dimeric octadecenoic acid units to terephthalic acid units = 1:99) were mixed and then added into a twin-screw extruder. They were kneaded and reacted and extruded at 260 °C and a screw speed of 10 Hz. After pelletizing the obtained low-molecular-weight copolyester, it was dried in a vacuum oven at 60 °C for 10 h.

[0037] (2) The dried low-molecular-weight copolyester (50 g) was added into a flask. The pressure in the flask was evacuated to <50 Pa, and the temperature was raised to 210 °C, and stirring was continued for 6 h to obtain a PET foamable material.

[0038] After testing, the melt index of the PET foamable material obtained in Example 1 was 6.26 g / 10 min.

[0039] Figure 1 The nuclear magnetic resonance hydrogen spectrum of the PET foamable material obtained in Example 1 is shown, and the signals of terephthalic acid units, ethylene glycol units, and dimeric octadecenoic acid units can be observed. Figure 2 The heat flow curve of the PET foamable material obtained in Example 1 is shown. It can be seen that the glass transition temperature is about 78 °C and the melting point is about 248 °C.

[0040] Example 2

[0041] The synthesis process was the same as that in Example 1, except that 72.97 g of octadecane diacid (dimeric octadecenoic acid) (the molar proportion of dimeric octadecenoic acid units is 2.5%, and the molar ratio of dimeric octadecenoic acid units to terephthalic acid units = 2.5:97.5) was added.

[0042] After testing, the melt index of the PET foamable material obtained in Example 2 was 5.35 g / 10 min.

[0043] Example 3

[0044] The synthesis process was the same as that in Example 1, except that 145.93 g of octadecane diacid (dimeric octadecenoic acid) (the molar proportion of dimeric octadecenoic acid units is 5%, and the molar ratio of dimeric octadecenoic acid units to terephthalic acid units = 5:95) was added.

[0045] After testing, the melt index of the PET foamable material obtained in Example 3 is 3.96 g / 10 min.

[0046] Example 4

[0047] The synthesis process is the same as that of Example 1, except that the octadecadienoic acid is replaced with an equimolar amount of octadecane hydrogenated dimer acid (hydrogenated dimer octadecenoic acid).

[0048] After testing, the melt index of the PET foamable material obtained in Example 4 is 6.62 g / 10 min.

[0049] Example 5

[0050] The synthesis process is the same as that of Example 1, except that the octadecadienoic acid is replaced with an equimolar amount of docosadienoic acid (dimer docosenoic acid).

[0051] After testing, the melt index of the PET foamable material obtained in Example 5 is 5.38 g / 10 min.

[0052] Example 6

[0053] The synthesis process is the same as that of Example 1, except that the octadecadienoic acid is replaced with an equimolar amount of docosane hydrogenated dimer acid (hydrogenated dimer docosenoic acid).

[0054] After testing, the melt index of the PET foamable material obtained in Example 6 is 5.94 g / 10 min.

[0055] Example 7

[0056] The synthesis process is the same as that of Example 1, except that the bottle-grade PET chips are replaced with an equal mass of fiber-grade PET chips.

[0057] After testing, the melt index of the PET foamable material obtained in Example 7 is 6.01 g / 10 min.

[0058] Example 8

[0059] The synthesis process is the same as that of Example 1, except that the bottle-grade PET chips are replaced with an equal mass of bottle-grade PET waste.

[0060] After testing, the melt index of the PET foamable material obtained in Example 8 is 6.21 g / 10 min.

[0061] Example 9

[0062] The synthesis process is the same as that of Example 1, except that the bottle-grade PET chips are replaced with an equal mass of PET fiber waste.

[0063] After testing, the melt index of the PET foaming material obtained in Example 9 was 7.42 g / 10 min.

[0064] Example 10

[0065] The synthesis process was the same as that of Example 1, except that the bottle-grade PET chips were replaced with the same mass of polyester / cotton blended fiber waste, in which the mass fraction of polyester was 80%.

[0066] After testing, the melt index of the PET foaming material obtained in Example 10 was 11.50 g / 10 min.

[0067] Example 11

[0068] The synthesis process was the same as that of Example 1, except that the bottle-grade PET chips were replaced with the same mass of polyester / propylene blended fiber waste, in which the mass fraction of polyester was 80%.

[0069] After testing, the melt index of the PET foaming material obtained in Example 11 was 10.83 g / 10 min.

[0070] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. An upgraded recycling method for PET waste, characterized in that, Synthesis of a foaming material using a branched aliphatic diacid and PET waste 2. The upgrading and recycling method of PET waste according to claim 1, characterized in that, The foaming material has the following structure: Wherein, x is a positive integer, y and z are non-negative integers and not both zero at the same time, R1, R4, R5, and R8 are each independently an alkylene group having 5 to 10 carbon atoms, R2, R6, and R7 are each independently an alkyl group having 5 to 10 carbon atoms, and R3 is a hydrocarbon group having 5 to 10 carbon atoms and containing a carbon-carbon double bond.

3. The upgrading and recycling method of PET waste according to claim 2, wherein, (y + z):(x + y + z) is 0.1 to 10:100, further 1 to 5:

100.

4. The upgrading and recycling method of PET waste according to claim 1, wherein, The number of branched-chain carbon atoms in the branched aliphatic diacid is 5 to 10; or, The branched aliphatic diacid includes at least one of dimeric dodecenoic acid, dimeric tetradecenoic acid, dimeric hexadecenoic acid, dimeric octadecenoic acid, dimeric eicosenoic acid, dimeric docosenoic acid, hydrogenated dimeric dodecenoic acid, hydrogenated dimeric tetradecenoic acid, hydrogenated dimeric hexadecenoic acid, hydrogenated dimeric octadecenoic acid, hydrogenated dimeric eicosenoic acid, and hydrogenated dimeric docosenoic acid.

5. The method for upgrading and recycling PET waste according to claim 1, wherein, The PET waste includes one or more of bottle-grade PET waste, PET fiber waste, and blended fiber waste mainly composed of PET.

6. The upgrading and recycling method of PET waste according to any one of claims 1 to 5, characterized in that, The method for upgrading and recycling the PET waste specifically includes the steps: (1) Adding the PET waste and the branched aliphatic diacid to a twin-screw extruder for reactive extrusion to obtain a low-molecular-weight copolyester; (2) Subjecting the low-molecular-weight copolyester to solid-phase polycondensation to obtain a PET-based foaming material.

7. The method for upgrading and recycling PET waste according to claim 6, characterized in that, In step (1): Based on the total molar amount of the terephthalic acid units in the branched aliphatic diacid and the PET waste being 100%, the molar proportion of the branched aliphatic diacid is 0.1% to 10%, further 1% to 5%; The temperature of the reactive extrusion is 250 to 300 °C, further 250 to 290 °C; The screw speed of the twin-screw extruder is 5 to 15 Hz; The reaction extrusion time of the PET waste and the branched aliphatic diacid in the twin-screw extruder is 50 to 300 s, further 50 to 150 s.

8. The method for upgrading and recycling PET waste according to claim 6, wherein In step (1), after the reactive extrusion, pelletizing and drying operations are also included; The drying is vacuum drying; The temperature of the drying is 40 to 120 °C, and the time is 4 to 24 h, further 4 to 10 h.

9. The method for upgrading and recycling PET waste according to claim 6, characterized in that, In step (2): The temperature of the solid-phase polycondensation is 160 to 210 °C, further 180 to 210 °C, and the time is 1 to 24 h, further 3 to 6 h; The solid-phase polycondensation is carried out under a vacuum condition of <100 Pa, preferably <50 Pa, or in an inert gas atmosphere; The solid-phase polycondensation is carried out under continuous stirring.

10. A foamable material, characterized in that, Obtained by the method for upgrading and recycling PET waste according to any one of claims 1 to 9.

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