Preparation method and application of high-transparency regenerated PET composite material based on PTW modification

Abstract

The invention belongs to a preparation method and application of a PTW modification-based high-transparency regenerated PET composite material, and the method comprises the following steps: S1, pretreatment of recycled PET: crushing the recycled PET material into sheets, soaking the sheets in a NaOH solution, washing the sheets with deionized water after soaking until the sheets are neutral, and drying the sheets for later use; s2, 100 parts of a new PET material, 15-50 parts of the recycled PET material treated in the step S1, 1-8 parts of ethylene-butyl acrylate-glycidyl methacrylate (PTW) and 0.1-5 parts of an antioxidant are weighed for standby application; s3, uniformly mixing the materials weighed in the S2, performing melt blending and segmented extrusion on sheets through a single-screw extruder, and performing shock cooling on the extruded melt sheets through liquid nitrogen injection at an outlet of a die head during extrusion; and S4, the extruded sheet is subjected to preheating treatment and then is rapidly formed through a mold. By adopting the method to modify and recycle the PET material, the mechanical property of the PET material is ensured, the transparency of the material is close to that of a new PET material, and the PET material can be widely applied to the fields of disposable tableware and transparent food packaging materials.

Description

Technical Field

[0001] This invention belongs to the field of polymer material recycling technology, and specifically relates to a method for preparing and applying a highly transparent recycled PET composite material based on PTW modification. Background Technology

[0002] Polyethylene terephthalate (PET) is a widely used thermoplastic polyester material. It possesses good heat resistance and rigidity, as well as excellent mechanical properties. In particular, its excellent transparency without any fillers makes it widely used in packaging materials such as films and sheets. Currently, high-end disposable tableware primarily uses PET. With the deepening of sustainable development concepts and the requirements of green environmental protection, adding a certain proportion of recycled PET to PET tableware has gradually become a trend. However, in existing technologies, the transparency of PET tableware decreases significantly after adding a certain amount of recycled PET. Reports indicate that adding certain transparent agents, such as MBS (methyl methacrylate-butadiene-styrene copolymer), can improve the transparency of recycled PET, but some mechanical properties will decrease, adversely affecting the use of PET in disposable tableware. How to achieve a transparency level close to or reaching that of virgin PET after adding a significant amount of recycled PET, while maintaining essentially unchanged mechanical properties, is a technical challenge and presents considerable difficulties.

[0003] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying a highly transparent recycled PET composite material based on PTW modification, thereby overcoming the defects in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for preparing a highly transparent recycled PET composite material based on PTW modification, comprising the following steps: S1: Pre-treatment of recycled PET: Crush the recycled PET material into flakes, soak them in NaOH solution, wash them with deionized water until neutral, and then dry them for later use. S2: Weigh 100 parts of virgin PET, 15-50 parts of recycled PET treated with S1, 1-8 parts of ethylene-butyl acrylate-glycidyl methacrylate (PTW), and 0.1-5 parts of antioxidant for later use; S3: After the materials weighed in S2 are mixed evenly, they are melt-blended and extruded into sheets through a single screw extruder. During extrusion, the extruded melt sheet is rapidly cooled by liquid nitrogen spray at the die outlet. S4: The extruded sheet is preheated and then quickly shaped through a mold.

[0006] Furthermore, in step S2, the mass of PTW accounts for 6%-25% of the mass of the recycled PET material.

[0007] Furthermore, as a preferred embodiment, in step S1, the PET powder is immersed in a 0.05-0.5 mol / L NaOH solution at 60°C.

[0008] Furthermore, as a more preferred embodiment, in step S1, the PET powder is immersed in a 0.2 mol / L NaOH solution at 60°C, stirred for 2-3 hours, washed with deionized water until neutral, and then vacuum dried at 80°C for 18 hours.

[0009] Furthermore, as a more preferred embodiment, in step S2, 100 parts of virgin PET material, 15-50 parts of recycled PET material treated in S1, 2-7 parts of ethylene-butyl acrylate-glycidyl methacrylate (PTW), and 0.5-2 parts of antioxidant are weighed out for later use.

[0010] Furthermore, as a more preferred embodiment, the virgin PET material used in step S2 is CR-8633 from China Resources, with an integration index of 10-20 g / 10 min (260℃ / 2.16 kg), a tensile strength of 60-65 MPa, an elongation at break of 92-99%, and a notched impact strength (23℃) of 5-10 kJ / m. 2 Light transmittance ≥90%, haze ≤2%, intrinsic viscosity 0.5-1.0 dl / g.

[0011] Furthermore, as a more preferred embodiment, the PET recycled material in step S2 has a tensile strength of 40-50 MPa, an elongation at break of 50-60%, and a notched impact strength (23°C) of 3-5 kJ / m. 2 Light transmittance ≥74%, haze ≤5%, intrinsic viscosity 0.2-0.7dl / g.

[0012] Furthermore, as a preferred embodiment, in step S3, the flow rate of liquid nitrogen is 5-15 L / min, the cooling distance is 80-280 mm, and the cooling time is 1-8 s.

[0013] Furthermore, as a more preferred embodiment, in step S3, the flow rate of liquid nitrogen is 8-12 L / min, the cooling distance is 100-150 mm, and the cooling time is 2-3 s.

[0014] Furthermore, preferably, the single-screw extruder in step S3 is divided into a feeding section, a compression section, a melting section, a homogenization section, and a die section for temperature control.

[0015] Furthermore, as a more preferred method, the temperature control of the single-screw extruder in step S3 is as follows: 220-230℃ in the feeding section, 235-245℃ in the compression section, 245-255℃ in the melting section, 255-265℃ in the homogenization section, and 250-260℃ in the die section.

[0016] Furthermore, preferably, the sheet extruded by the single-screw extruder in step S3 has a thickness of 0.8 mm.

[0017] Furthermore, preferably, the preheating temperature in step S4 is 100-150℃ and the preheating time is 20-40 min.

[0018] Furthermore, as a more preferred embodiment, the preheating temperature in step S4 is 120-130°C, and the preheating time is 30 minutes.

[0019] Furthermore, as a preferred embodiment, in step S4, the mold temperature is 20-40℃ during molding, the mold pressure drops to -0.05-0.1MPa within 0.1-0.3s, and the mold is demolded and cooled after holding the pressure for 10-15s.

[0020] Furthermore, as a more preferred embodiment, in step S4, the mold temperature is maintained at 30°C during molding, the mold pressure drops to -0.05-0.1MPa within 0.1-0.3s, and the mold is demolded and cooled after holding the pressure for 10-15s.

[0021] Furthermore, preferably, the mold in step S4 has dual cooling channels, namely a liquid nitrogen cooling channel and a water cooling channel.

[0022] Furthermore, preferably, the diameter of both the liquid nitrogen cooling channel and the water cooling channel is 1.0-2.0 mm.

[0023] Furthermore, as a more preferred embodiment, the diameter of both the liquid nitrogen cooling channel and the water cooling channel is 1.5 mm.

[0024] Furthermore, as a preferred embodiment, the liquid nitrogen flow rate of the liquid nitrogen cooling channel is 1-10 L / min, the cooling water flow rate of the water cooling channel is 5-15 L / min, and the cooling time is 5-20 s.

[0025] Furthermore, as a more preferred embodiment, the liquid nitrogen flow rate of the liquid nitrogen cooling channel is 2-5 L / min, the cooling water flow rate of the water cooling channel is 8-12 L / min, and the cooling time is 10-15 s.

[0026] Furthermore, as a more preferred embodiment, the distance between the liquid nitrogen cooling channel and the water cooling channel is 8-10 mm.

[0027] The present invention also provides an application of a PTW-modified high-transparency recycled PET composite material, which is made by the above method and is used for disposable tableware and transparent food packaging materials.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a specific ratio of PTW modified recycled PET and a specific process to obtain recycled materials with high transparency and low haze.

[0029] (2) The present invention uses PTW modified recycled PET to fully utilize its chemical compatibilization and physical filling characteristics to achieve the integrity of the recycled PET molecular chain. It can inhibit the crystallization of recycled PET, reduce the entanglement of PET molecular chains, and enhance the lubrication effect and shear thinning behavior, so that recycled PET has good processing performance. (3) The present invention features segmented temperature control during single-screw extrusion and rapid cooling with liquid nitrogen. By integrating a liquid nitrogen spray device into the die head, PET is cooled to below its glass transition temperature in a very short time, overcoming the crystallization limitation caused by slow cooling and directly freezing PET in an amorphous structure, thereby helping to improve the transparency of PET. (4) The present invention uses dual cooling channels to cool during the molding process, which can further reduce the phenomenon of stress-induced crystallization during the molding process and improve the transparency of the molded product. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the mold used in step S4 of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the tableware made in Embodiment 1 of the present invention. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0032] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0033] Example 1: A method for preparing a highly transparent recycled PET composite material based on PTW modification includes the following steps: S1: Pre-treatment of recycled PET: First, wash the recycled PET material with deionized water, then soak and wash it with detergent. After washing, crush the PET material into flakes, soak it in 0.2mol / L NaOH solution at 60℃ and stir for 2-3 hours. Wash it with deionized water until neutral, and dry it in a vacuum environment at 80℃ for 18 hours before use. S2: Weigh 100kg of virgin PET, 30kg of recycled PET treated in S1, 2kg of ethylene-butyl acrylate-glycidyl methacrylate (PTW), and 0.5kg of antioxidant for later use; S3: After the materials weighed in S2 are mixed evenly at high speed, they are melt-blended and extruded in stages through a single-screw extruder to form sheets with a thickness of 0.80 mm. A liquid nitrogen injection device is installed at the die outlet of the extruder to directly quench the extruded molten sheet. The segment parameters of the single-screw extrusion are as follows: feed section temperature 220-230℃, compression section temperature 235-245℃, melting section temperature 245-255℃, homogenization section temperature 255-265℃, and die section temperature 250-260℃. The screw speed is adjusted in real time according to the die resistance. The liquid nitrogen flow rate is 8-12 L / min, the cooling distance is 100-150 mm, and the cooling time is 2-3 s. S4: The sheet extruded from S3 is preheated (120-130℃, 30min). When the mold temperature is 30℃, the mold is quickly lowered to cover the sheet. The pressure inside the mold is reduced to -0.05-0.1MPa within 0.1-0.3s. After holding the pressure for 10-15s, the sheet is demolded and cooled to produce tableware of 200×200×40mm or other sizes. The mold contains a φ1.5mm stainless steel micro dual channel. The cooling media are liquid nitrogen (transparent zone) and cooling water at 2-5℃ (structural zone). The liquid nitrogen flow rate in the transparent zone is 2-5L / min, and the cooling water flow rate in the structural zone is 8-12L / min. The channel spacing between the liquid nitrogen and cooling water is 8-10mm, and the cooling time is 10-15s.

[0034] The properties of the recycled PET material in S1 are as follows: tensile strength 44 MPa, elongation at break 56%, notched impact strength (23℃) 4.7 kJ / m. 2 Light transmittance ≥74%, haze ≤5%, intrinsic viscosity 0.42dl / g.

[0035] The virgin PET material used in S2 is CR-8633 from China Resources, with the following properties: melt flow index 10-20 g / 10 min (260℃ / 2.16 kg), tensile strength 62 MPa, elongation at break 98%, and notched impact strength (23℃) 8 kJ / m. 2 Light transmittance ≥90%, haze ≤2%, intrinsic viscosity 0.84 dl / g; The antioxidants used are Doverphos S-9288 (bis(2,4-dicumylphenyl) diphosphite) and antioxidant 1010, which are a compound antioxidant, with 0.3 kg of Doverphos S-9288 and 0.2 kg of antioxidant 1010.

[0036] Example 2: Unlike Example 1, the weights of the raw materials in S2 are as follows: 100kg virgin PET, 30kg recycled PET treated in S1, 4kg PTW, 0.3kg Doverphos S-9288, and 0.2kg antioxidant 1010.

[0037] Example 3: Unlike Example 1, the weights of the raw materials in S2 are as follows: 100kg virgin PET, 30kg recycled PET treated in S1, 5kg PTW, 0.3kg Doverphos S-9288, and 0.2kg antioxidant 1010.

[0038] Example 4: Unlike Example 1, the weights of the raw materials in S2 are as follows: 100 kg of virgin PET, 30 kg of recycled PET treated in S1, 6 kg of PTW, 0.3 kg of Doverphos S-9288, and 0.2 kg of antioxidant 1010.

[0039] Example 5: Unlike Example 1, the weights of the raw materials in S2 are as follows: 100 kg of virgin PET, 30 kg of recycled PET treated in S1, 7 kg of PTW, 0.3 kg of Doverphos S-9288, and 0.2 kg of antioxidant 1010.

[0040] Comparative Example 1: Unlike Example 1, PTW was not added to the raw materials in S2.

[0041] Comparative Example 2: Unlike Example 1, the amount of PTW added in S2 is 1 kg.

[0042] Comparative Example 3: Unlike Example 1, the amount of PTW added in S2 is 9 kg.

[0043] Comparative Example 4: Unlike Example 4, S4 is cooled by only a single cooling water during molding.

[0044] Comparative Example 5: Unlike Example 4, in S3, liquid nitrogen is not used for rapid cooling during extrusion; instead, ordinary cooling water is used.

[0045] Comparative Example 6: Unlike Example 5, in S2, the raw material PTW is replaced with the general-purpose transparent agent MBS (methyl methacrylate-butadiene-styrene terpolymer).

[0046] Table 1 below shows the raw material formulas for Examples 1-5, and Table 2 shows the raw material formulas for Comparative Examples 1-5. The materials prepared in Examples 1-5 and Comparative Examples 1-5 were tested, and the test performance is shown in Table 3 below.

[0047] The above testing standards are as follows: viscosity is tested according to GB / T1632.1-2008 standard, tensile strength and elongation at break are tested according to ISO527-2 standard, notched impact strength is tested according to ISO179 / 1eA standard, and transparency and haze are tested according to ASTM D1003-13.

[0048] The test results above show that: 1. The transparency of Examples 1-5 is all >88.6%, which is significantly higher than that of Comparative Example 1 (>65.4%) and Comparative Example 2 (>76.6%), and is basically close to that of new PET (>90%). Moreover, the higher the PTW content, especially when the amount of PTW accounts for more than 6% of the amount of waste PET, the more obvious the improvement in transparency is, indicating that PTW modification greatly improves the transparency of recycled PET. 2. In terms of mechanical properties, the tensile strength of Examples 1-5 was 58.5-60.1 MPa, far exceeding the 44 MPa of recycled PET, and superior to Comparative Example 1 (52.6 MPa); in terms of elongation at break, Examples 1-5 reached 80.2-94.1%, close to the 98% of virgin PET, and significantly higher than the 56% of recycled PET; in terms of notched impact strength, Examples 1-5 reached 7.4-8.2 kJ / m. 2 Compared with 8.0kJ / m of virgin PET material 2 Basically equivalent, comparison ratio 15.8 kJ / m 2 Even better; 3. The viscosity of Examples 1-5 is basically the same as that of virgin PET. Therefore, the modification of PTW successfully achieved the goal of high transparency while maintaining stable mechanical properties. The principle is as follows: (1) PTW reacts with the terminal carboxyl or terminal hydroxyl groups of PET through epoxy groups, reconnects the broken molecular chains, reduces chain segment defects, strengthens the integrity of the molecular chains, thereby reducing light scattering and improving transparency; (2) The chain extension effect of PTW can increase the molecular weight of PET, making the molecular chains more compact but increasing the amorphous region and reducing the crystallinity, thereby improving transparency; (3) PET repairs the molecular chains, ensuring the integrity of the molecular chains, and the viscosity increases significantly, thereby ensuring that the mechanical properties are maintained while improving transparency. More specifically, PTW stands for ethylene-butyl acrylate-glycidyl methacrylate. The ethylene segment can regulate melt flowability, reducing melt cracking, streaks, or bubbles caused by high viscosity. The elasticity of the butyl acrylate segment can alleviate stress whitening caused by stress concentration during processing or use, and can also interfere with PET crystallization, reducing crystallinity and light scattering caused by crystallization. The epoxy groups contained in glycidyl methacrylate can react with the end groups of PET to form chemical bonds, thereby greatly improving the compatibility between new and old PET, eliminating defects at the interface between new and old PET, significantly reducing phase separation, reducing light scattering and improving transparency. Unlike traditional transparent agent modifications, PTW is a multifunctional modifier. Through improved compatibility and toughness, it not only improves the transparency of new and old PET, but also has virtually no impact on the mechanical properties of modified PET.

[0049] 4. As can be seen from Comparative Example 3, when the PTW content is relatively high (approximately 30%), high viscosity and high notched impact strength (8.0 kJ / m) occur. 2 However, the transparency did not improve significantly. The main reason is that when the amount of PTW is large, the epoxy groups react excessively with the end groups of PET, leading to branching of the molecular chain or slight cross-linking, which increases the melt strength. A small amount of cross-linking can improve toughness, resulting in increased notch strength. However, when the amount of PTW increases, unreacted epoxy groups self-polymerize, forming a PTW-enriched phase, which interferes with the regularity of PET chain segments, triggers light scattering, and leads to crystallization, thus resulting in no improvement in transparency. This shows that when the amount of PTW exceeds 30%, local cross-linking will increase the impact strength, but phase separation will reduce the transparency.

[0050] 5. As can be seen from Example 4 and Comparative Example 4, when dual microchannels are not used for zoned cooling during molding, the transparency and haze of the molded product are significantly worse. The main reason is that ordinary cooling water, although faster than room temperature air cooling, cannot achieve gradient temperature control of dual microchannels, resulting in uneven temperature distribution of the molded product, causing local crystallization and deterioration of transparency and haze. The mechanical properties of the molded product also decrease to some extent. Due to poor cooling effect, the surface is brittle while the core is not sufficiently cooled, which generates internal stress and leads to the generation of microcracks.

[0051] 6. As can be seen from Example 4 and Comparative Example 5, when there is no liquid nitrogen for rapid cooling during the extrusion stage, the transparency and haze of the molded product also deteriorate significantly. The main reason is that when ordinary water is used for cooling, the PET melt cools slowly, and the molecular chains have enough time to arrange into crystalline regions. The difference in refractive index between the crystalline and amorphous regions leads to light scattering, resulting in decreased transparency and increased haze. The mechanical properties also decrease to varying degrees. The main reason is still the stress caused by the internal temperature difference of the product due to slow cooling.

[0052] 7. As can be seen from Example 4 and Comparative Examples 4 and 5, neither rapid cooling with liquid nitrogen in the extrusion stage nor dual microchannel partitioned cooling in the blow molding stage can make recycled PET have both high transparency and maintain its basic mechanical properties. Only the synergistic effect of the two can achieve the goal of balancing transparency and mechanical properties. Rapid cooling with liquid nitrogen in the extrusion stage instantly drops the PET below the glass transition temperature, freezing the movement of molecular chains and causing synchronous amorphization from the core to the surface, greatly reducing the possibility of crystallization. The dual microchannel, through gradient temperature control of liquid nitrogen and water, further reduces the internal stress caused by uneven cooling shrinkage, thereby basically ensuring that the mechanical properties do not change significantly.

[0053] 8. As can be seen from the comparison between Examples 1-5 and Comparative Example 6, when MBS is used to modify recycled PET, its effect on improving transparency is quite obvious, and the tensile strength and elongation at break can be basically maintained. However, the notched impact strength is significantly reduced. The main reason is that the PMMA shell of MBS matches the refractive index of PET, and the transparency is improved when the dispersion performance is good. However, since MBS is only a physical modification, the low intrinsic viscosity of recycled PET leads to insufficient molecular chain entanglement. The MBS rubber phase cannot effectively induce crazing, and the rubber phase is prone to agglomeration, resulting in weak interfacial bonding. These factors all lead to a significant reduction in notched impact strength. In terms of the mechanical properties of recycled PET, from the perspective of the practical requirements of disposable tableware, ensuring a large notched impact strength is one of the essential properties.

[0054] 9. The following conclusions can be drawn from this: This application achieves improved transparency and ensures a certain mechanical strength by chemically repairing the molecular chain with PTW, especially when the amount of PTW accounts for 6-25% of the waste PET. Furthermore, the rapid cooling with liquid nitrogen during the extrusion stage inhibits crystallization. Finally, the dual microchannels in the blow molding stage further control stress and prevent brittleness. For the first time, this application has achieved a synergistic improvement in high transparency, high strength and high toughness of recycled PET.

[0055] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a highly transparent recycled PET composite material based on PTW modification, characterized in that, Includes the following steps: S1: Pre-treatment of recycled PET: Crush the recycled PET material into flakes, soak them in NaOH solution, wash them with deionized water until neutral, and then dry them for later use. S2: Weigh 100 parts of virgin PET, 15-50 parts of recycled PET treated with S1, 1-8 parts of ethylene-butyl acrylate-glycidyl methacrylate, and 0.1-5 parts of antioxidant for later use; S3: After the materials weighed in S2 are mixed evenly, they are melt-blended and extruded into sheets through a single screw extruder. During extrusion, the extruded melt sheet is rapidly cooled by liquid nitrogen spray at the die outlet. S4: The extruded sheet is preheated and then quickly shaped through a mold.

2. The method for preparing a highly transparent recycled PET composite material based on PTW modification according to claim 1, characterized in that, In step S1, the PET powder is immersed in a 0.05-0.5 mol / L NaOH solution at 60°C.

3. The method for preparing a highly transparent recycled PET composite material based on PTW modification according to claim 1, characterized in that, In step S3, the flow rate of liquid nitrogen is 5-15 L / min, the cooling distance is 80-280 mm, and the cooling time is 1-8 s.

4. The method for preparing a highly transparent recycled PET composite material based on PTW modification according to claim 1, characterized in that, The single-screw extruder in step S3 is divided into a feeding section, a compression section, a melting section, a homogenization section, and a die section for temperature control.

5. The method for preparing a highly transparent recycled PET composite material based on PTW modification according to claim 1, characterized in that, In step S4, the preheating temperature is 100-150℃ and the preheating time is 20-40 minutes.

6. The method for preparing a highly transparent recycled PET composite material based on PTW modification according to claim 1, characterized in that, In step S4, the mold temperature is 20-40℃ during molding, the mold pressure drops to -0.05-0.1MPa within 0.1-0.3s, and the mold is demolded and cooled after holding the pressure for 10-15s.

7. The method for preparing a highly transparent recycled PET composite material based on PTW modification according to claim 1, characterized in that, In step S4, the mold has dual cooling channels, namely a liquid nitrogen cooling channel and a water cooling channel.

8. The method for preparing a highly transparent recycled PET composite material based on PTW modification according to claim 7, characterized in that, The diameters of the liquid nitrogen cooling channel and the water cooling channel are both 1.0-2.0 mm.

9. The method for preparing a highly transparent recycled PET composite material based on PTW modification according to claim 7, characterized in that, The liquid nitrogen flow rate of the liquid nitrogen cooling channel is 1-10 L / min, the cooling water flow rate of the water cooling channel is 5-15 L / min, and the cooling time is 5-20 s.

10. An application of a highly transparent recycled PET composite material prepared by the preparation method according to any one of claims 1-9, characterized in that, Used for disposable tableware and transparent food packaging materials.

Images