A hyperbranched polyester modified ethylene-vinyl alcohol resin and a method for preparing the same

Abstract

The present application relates to a kind of hyperbranched polyester modified ethylene-vinyl alcohol resin and its preparation method, the modified resin includes EVOH 96%~99%, polyhedral oligomeric silsesquioxane (POSS) with reactive functional group 0.1%~2%, antioxidant 0.1%~1%, acid absorbent 0%~0.5%, lubricant 0%~0.5% by mass percentage;Preparation method is that after raw material three-stage pre-mixing, it is obtained finished product by single screw extruder melt granulation.The present application is combined with EVOH hydroxyl by POSS with reactive functional group, realizes molecular level internal plasticizing, significantly improves the melt flowability and processing performance of resin under the premise of completely retaining the excellent barrier property of EVOH, while improving the problem that EVOH is easily yellow at high temperature processing, conventional plasticizer is easily separated out, adapts the application demand of multiple fields such as food packaging, cosmetic packaging, medical packaging, preparation process is simple and controllable, suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification, specifically to a hyperbranched polyester-modified ethylene-vinyl alcohol resin and its preparation method. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is one of the polymer materials with the best overall barrier properties. The ethylene segment in its molecular chain provides good processability and water resistance, while the vinyl alcohol segment provides extremely high gas barrier properties. Therefore, it is widely used in many fields such as food packaging, cosmetic packaging, automotive fuel lines, and medical packaging.

[0003] However, EVOH resin itself has significant processing performance defects: First, the EVOH molecular chain contains a large number of hydroxyl groups, resulting in strong intermolecular hydrogen bonding and poor melt flowability. Melt processing requires long-term operation at high temperatures of 180℃~240℃. At high temperatures, hydroxyl groups are prone to thermo-oxidative degradation, leading to yellowing of the material, further reduction in flowability, and ultimately causing quality defects such as crystal points and fish eyes in the product. Second, the barrier properties of EVOH increase with the increase of vinyl alcohol content, but the higher the vinyl alcohol content, the more hydroxyl groups there are, and the worse the heat resistance and processing performance of the material, which limits the application scenarios of high-barrier EVOH resin.

[0004] Hyperbranched polyester is a multifunctional polymer with a highly branched three-dimensional ellipsoidal structure. It exhibits almost no chain entanglement between molecules, resulting in extremely low melt flow resistance, earning it the nickname "molecular beads." Simultaneously, its molecular ends possess numerous active functional groups, enabling it to form excellent interfacial bonds with the matrix resin, achieving internal plasticizing modification of the matrix resin. Currently, there is no mature technical solution for using hyperbranched polyester to modify EVOH resin while simultaneously addressing its poor flowability, susceptibility to degradation during high-temperature processing, and numerous crystal points. Summary of the Invention

[0005] One of the objectives of this invention is to provide a hyperbranched polyester-modified ethylene-vinyl alcohol resin and its preparation method, which significantly improves melt flowability and processing stability, reduces the number of crystal points in the product, and broadens the processing and application scenarios of EVOH resin without losing the original high barrier properties of EVOH.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A hyperbranched polyester-modified ethylene-vinyl alcohol resin, comprising the following components by mass percentage:

[0008] Ethylene-vinyl alcohol copolymer 97%~99%, hyperbranched polyester 0.1%~1%, antioxidant 0.1%~1%, balance is additives;

[0009] The ethylene-vinyl alcohol copolymer has an ethylene molar content of 29% to 38%;

[0010] The ends of the hyperbranched polyester have functional groups that can interact with the hydroxyl groups in the ethylene-vinyl alcohol copolymer.

[0011] In one embodiment of the present invention, the functional group at the end of the hyperbranched polyester is at least one of hydroxyl, epoxy, and amide groups.

[0012] In one embodiment of the present invention, the hyperbranched polyester is an HB20 type hydroxyl-terminated hyperbranched polyester;

[0013] The antioxidant is a compound system of hindered phenolic primary antioxidant and phosphate ester secondary antioxidant; the hindered phenolic primary antioxidant is antioxidant 1010 or antioxidant 1098, and the phosphate ester secondary antioxidant is antioxidant 168.

[0014] In one embodiment of the present invention, the additives include 0-0.5% acid absorbent and 0-0.5% lubricant;

[0015] The acid absorbent is at least one of calcium stearate, zinc stearate, magnesium stearate, and hydrotalcite.

[0016] The lubricant is at least one of oleamide, erucamide, ethylene bis-stearamide, and polysiloxane.

[0017] In one embodiment of the present invention, the product comprises the following components by mass percentage: 97.5% to 98% ethylene-vinyl alcohol copolymer, 0.5% to 1% hyperbranched polyester, 0.6% antioxidant, 0.4% acid absorbent, and 0.5% lubricant.

[0018] In one embodiment of the present invention, the moisture content of the modified ethylene-vinyl alcohol copolymer resin is ≤0.2%.

[0019] This invention also provides a method for preparing the above-mentioned hyperbranched polyester-modified ethylene-vinyl alcohol resin, comprising the following steps:

[0020] S1. Raw material pretreatment: The hyperbranched polyester is ground into powder using a ball mill for later use;

[0021] S2. Powder premixing: Weigh the ground hyperbranched polyester, antioxidant and optional additives according to the formula ratio, put them into a pulverizer and mix evenly to obtain premixed powder;

[0022] S3. Secondary premixing: Weigh the premixed powder and a portion of the ethylene-vinyl alcohol copolymer at a mass ratio of 1:5, add them to the mixer and mix evenly to obtain the premixed material;

[0023] S4. Total Mixing: Weigh the remaining ethylene-vinyl alcohol copolymer according to the formula ratio, add it to the mixer with the premix and mix evenly to obtain the mixed raw materials;

[0024] S5. Melt granulation: The mixed raw materials are added to a single screw extruder, and after melt extrusion, pelletizing and drying, the hyperbranched polyester modified ethylene-vinyl alcohol copolymer resin is obtained.

[0025] In one embodiment of the present invention, in step S2, the rotation speed of the pulverizer is 1000 r / min, the stirring time is 15 min, and the amount of material added is 50% to 70% of the volume of the pulverizer.

[0026] In one embodiment of the present invention, in steps S3 and S4, the stirring speed of the mixer is 200 r / min, the stirring time is 10 min, and the total amount of material added is 60% of the volume of the mixer; when adding materials, 50% of the ethylene-vinyl alcohol copolymer is added first, then the powder / premix is ​​added, and finally the remaining 50% of the ethylene-vinyl alcohol copolymer is added.

[0027] In one embodiment of the present invention, in step S5, the single-screw extruder has a length-to-diameter ratio of 28 and adopts a three-section screw structure, wherein the length of the feeding section is 8D, the length of the compression section is 10D, the length of the metering section is 10D, the screw compression ratio is 3~3.5, and the screw has no mixing unit; the extruder barrel temperature is 180℃ in zone one, 200℃ in zone two, 205℃ in zone three, 210℃ in zone four, and the die temperature is 215℃.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention significantly reduces the flow resistance of EVOH melt and greatly improves processing fluidity by utilizing the three-dimensional ellipsoidal structure of hyperbranched polyester. Compared with unmodified EVOH, the melt flow rate of the modified EVOH in this invention is improved. At the same time, the terminal functional groups of hyperbranched polyester form hydrogen bonds with EVOH, achieving an internal plasticizing effect and avoiding the defects of traditional external plasticizers such as easy migration and precipitation.

[0030] This invention improves the melt flowability of EVOH, reduces resin retention in dead corners of the processing mold, significantly reduces the risk of thermal degradation and yellowing during high-temperature processing, significantly reduces the number of crystal points in the product, and significantly improves the product yield and appearance quality.

[0031] The modification scheme of the present invention does not damage the molecular structure of EVOH. While improving the processing performance, it retains the original high gas barrier properties of EVOH. The oxygen permeability of the resin remains unchanged before and after modification, thus ensuring the core barrier function of the packaging material.

[0032] The preparation process of this invention is simple and controllable. A stepwise mixing process is used to achieve uniform dispersion of trace additives, and a single-screw extrusion process is employed to reduce the thermal degradation of EVOH. It is compatible with existing industrial production equipment, requiring no additional production line modifications, and has excellent industrial application value. The modified EVOH resin is suitable for various processing techniques such as extrusion, injection molding, casting, blow molding, and thermoforming, and can be widely used in food, cosmetics, medical packaging, and many other fields. Attached Figure Description

[0033] Figure 1 The image shows the crystal point morphology of the unmodified 32% mol EVOH extruded sheet.

[0034] Figure 2 The image shows the crystal point morphology of the hyperbranched polyester modified 32% mol EVOH extruded sheet in Example 1 of this invention. Specific Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. Those skilled in the art should understand that the following embodiments are only for explaining the present invention and are not intended to limit the scope of protection of the present invention.

[0036] In the following examples and comparative examples, all raw materials used were commercially available industrial-grade products, including:

[0037] EVOH with 32% mol ethylene content and EVOH with 38% mol ethylene content are commercially available general-purpose products;

[0038] Hyperbranched polyester HB20 is a hydroxyl-terminated hyperbranched polyester, a commercially available industrial-grade product;

[0039] Antioxidant 1098, Antioxidant 168, calcium stearate, and ethylene bis-stearamide are all commercially available industrial-grade products.

[0040] Performance testing methods:

[0041] Melt flow rate (melt index): According to GB / T3682.1-2018 standard, test conditions 190℃ / 2.16Kg;

[0042] Glass transition temperature (Tg) and melting point: measured using differential scanning calorimetry (DSC) under nitrogen atmosphere at a heating rate of 10 °C / min.

[0043] Vicat softening temperature: Tested according to GB / T 1633-2025 standard, load 50N, heating rate 50℃ / h;

[0044] Oxygen permeability: Tested according to GB / T 31354-2014 standard, under conditions of 23℃ and 65% relative humidity;

[0045] Number of crystal points on the sheet: The resin is extruded into a sheet with a thickness of 0.1 mm through a single screw extruder, and the number of crystal points is counted within a 100 cm² area of ​​the sheet. The fewer the number of crystal points, the better the processing performance.

[0046] Example 1

[0047] This embodiment provides a hyperbranched polyester-modified EVOH resin, with the following formulation by weight percentage:

[0048] 32% mol ethylene content EVOH 97.5%, hyperbranched polyester HB20 1%, antioxidant 1098 0.4%, antioxidant 168 0.2%, calcium stearate 0.4%, ethylene bis-stearamide 0.5%.

[0049] The preparation method is as follows:

[0050] S1. Raw material pretreatment: The hyperbranched polyester HB20 is ground into powder using a ball mill and set aside.

[0051] S2. Powder premixing: Weigh the ground hyperbranched polyester, antioxidant 1098, antioxidant 168, calcium stearate, and ethylene bis-stearamide according to the formula ratio, put them into the pulverizer, the amount of material added is 60% of the volume of the pulverizer, after locking, stir at 1000r / min speed for 15min to obtain premixed powder.

[0052] S3. Secondary premixing: Weigh the premixed powder and 32% mol ethylene EVOH at a mass ratio of 1:5 and add them to the mixer. When adding the materials, first add 50% of the EVOH, then add the premixed powder, and finally add the remaining 50% of the EVOH. The total amount of materials added is 60% of the volume of the mixer. Stir at 200 r / min for 10 min to obtain the premixed material.

[0053] S4. Total Mixing: Weigh the remaining EVOH according to the formula ratio and add it to the mixer along with the premix. The feeding method is the same as in step S3. Mix at 200 r / min for 10 min to obtain the mixed raw materials.

[0054] S5. Melt Granulation: The mixed raw materials are added to the hopper of a single-screw extruder. The single-screw extruder has a length-to-diameter ratio of 28 and a three-section screw structure: 8D feeding section, 10D compression section, and 10D metering section. The compression ratio is 3.2, and there is no mixing unit. The barrel temperature settings are: Zone 1 180℃, Zone 2 200℃, Zone 3 205℃, and Zone 4 210℃. The die temperature is 215℃. After melt extrusion and pelletizing, the resin is dried to a moisture content of 0.12% using a drying device. It is then vacuum-packed in an aluminized moisture-proof bag to obtain modified EVOH resin.

[0055] The performance test results of the prepared modified EVOH resin are shown in Table 1.

[0056] Example 2

[0057] This embodiment provides a hyperbranched polyester-modified EVOH resin, with the following formulation by weight percentage:

[0058] 32% mol ethylene content EVOH 98%, hyperbranched polyester HB20 0.5%, antioxidant 1098 0.4%, antioxidant 168 0.2%, calcium stearate 0.4%, ethylene bis-stearamide 0.5%.

[0059] The preparation method is completely consistent with that in Example 1. The performance test results of the prepared modified EVOH resin are shown in Table 1.

[0060] Example 3

[0061] This embodiment provides a hyperbranched polyester-modified EVOH resin, with the following formulation by weight percentage:

[0062] 38% mol ethylene content EVOH 98%, hyperbranched polyester HB20 0.5%, antioxidant 1098 0.4%, antioxidant 168 0.2%, calcium stearate 0.4%, ethylene bis-stearamide 0.5%.

[0063] The preparation method is completely consistent with that in Example 1. The performance test results of the prepared modified EVOH resin are shown in Table 1.

[0064] Comparative Example 1

[0065] This comparative example uses unmodified 32% mol ethylene content EVOH resin without any modification treatment, and is directly granulated using the same single-screw extrusion process as in Example 1.

[0066] Comparative Example 2

[0067] This comparative example uses unmodified 38% mol ethylene content EVOH resin without any modification treatment, and is granulated directly using the same single-screw extrusion process as in Example 1.

[0068] Performance Comparison

[0069] The performance of Examples 1-3 and Comparative Examples 1-2 was tested and compared, resulting in Table 1:

[0070] Table 1 Performance test results of each embodiment and comparative example.

[0071] The test results show that:

[0072] Compared with the unmodified comparative example, the modified EVOH resin of the present invention has a significantly improved melt index, a greatly improved melt flowability, and a significantly enhanced processing performance;

[0073] The oxygen permeability of the modified EVOH resin is exactly the same as that of the unmodified raw material, indicating that the modification scheme of the present invention fully retains the original high barrier properties of EVOH.

[0074] The number of crystal points in the modified EVOH extruded sheets decreased significantly. Specifically, the number of crystal points in Example 1 decreased by 64.9% compared to Comparative Example 1, and the number of crystal points in Example 3 decreased by 58.7% compared to Comparative Example 2, which significantly improved the appearance quality and yield of the products.

[0075] The melting point of the modified resin is the same as that of the unmodified raw material, indicating that the main molecular structure of EVOH has not been destroyed and the heat resistance and performance of the material have been fully preserved.

Claims

1. A hyperbranched polyester-modified ethylene-vinyl alcohol resin, characterized in that: By mass percentage, it includes the following components: Ethylene-vinyl alcohol copolymer 97%~99%, hyperbranched polyester 0.1%~1%, antioxidant 0.1%~1%, balance is additives; The ethylene-vinyl alcohol copolymer has an ethylene molar content of 29% to 38%; The ends of the hyperbranched polyester have functional groups that can interact with the hydroxyl groups in the ethylene-vinyl alcohol copolymer.

2. The hyperbranched polyester-modified ethylene-vinyl alcohol resin according to claim 1, characterized in that: The functional groups at the ends of the hyperbranched polyester are at least one of hydroxyl, epoxy, and amide groups.

3. The hyperbranched polyester-modified ethylene-vinyl alcohol resin according to claim 1, characterized in that: The hyperbranched polyester is an HB20 type hydroxyl-terminated hyperbranched polyester; The antioxidant is a compound system of hindered phenolic primary antioxidant and phosphate ester secondary antioxidant; the hindered phenolic primary antioxidant is antioxidant 1010 or antioxidant 1098, and the phosphate ester secondary antioxidant is antioxidant 168.

4. The hyperbranched polyester-modified ethylene-vinyl alcohol resin according to claim 1, characterized in that: The additives include 0-0.5% acid absorbent and 0-0.5% lubricant; The acid absorbent is at least one of calcium stearate, zinc stearate, magnesium stearate, and hydrotalcite. The lubricant is at least one of oleamide, erucamide, ethylene bis-stearamide, and polysiloxane.

5. The hyperbranched polyester-modified ethylene-vinyl alcohol resin according to claim 1, characterized in that: By weight percentage, it includes the following components: 97.5%~98% ethylene-vinyl alcohol copolymer, 0.5%~1% hyperbranched polyester, 0.6% antioxidant, 0.4% acid absorbent, and 0.5% lubricant.

6. The hyperbranched polyester-modified ethylene-vinyl alcohol resin according to claim 1, characterized in that: The moisture content of the modified ethylene-vinyl alcohol copolymer resin is ≤0.2%.

7. A method for preparing hyperbranched polyester-modified ethylene-vinyl alcohol resin as described in any one of claims 1-6, characterized in that: Includes the following steps: S1. Raw material pretreatment: The hyperbranched polyester is ground into powder using a ball mill for later use; S2. Powder premixing: Weigh the ground hyperbranched polyester, antioxidant and optional additives according to the formula ratio, put them into a pulverizer and mix evenly to obtain premixed powder; S3. Secondary premixing: Weigh the premixed powder and a portion of the ethylene-vinyl alcohol copolymer at a mass ratio of 1:5, add them to the mixer and mix evenly to obtain the premixed material; S4. Total Mixing: Weigh the remaining ethylene-vinyl alcohol copolymer according to the formula ratio, add it to the mixer with the premix and mix evenly to obtain the mixed raw materials; S5. Melt granulation: The mixed raw materials are added to a single screw extruder, and after melt extrusion, pelletizing and drying, the hyperbranched polyester modified ethylene-vinyl alcohol copolymer resin is obtained.

8. The method for preparing hyperbranched polyester-modified ethylene-vinyl alcohol resin according to claim 7, characterized in that: In step S2, the speed of the grinder is 1000 r / min, the stirring time is 15 min, and the amount of material added is 50% to 70% of the grinder's volume.

9. The method for preparing hyperbranched polyester-modified ethylene-vinyl alcohol resin according to claim 7, characterized in that: In steps S3 and S4, the stirring speed of the mixer is 200 r / min, the stirring time is 10 min, and the total amount of material added is 60% of the mixer volume; when adding materials, first add 50% of the ethylene-vinyl alcohol copolymer, then add the powder / premix, and finally add the remaining 50% of the ethylene-vinyl alcohol copolymer.

10. The method for preparing hyperbranched polyester-modified ethylene-vinyl alcohol resin according to claim 7, characterized in that: In step S5, the single-screw extruder has a length-to-diameter ratio of 28 and adopts a three-section screw structure, wherein the feeding section is 8D in length, the compression section is 10D in length, the metering section is 10D in length, the screw compression ratio is 3~3.5, and the screw has no mixing unit; the extruder barrel temperature is 180℃ in zone one, 200℃ in zone two, 205℃ in zone three, 210℃ in zone four, and the die temperature is 215℃.

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