Cooking-resistant PE suction nozzle cover and preparation method thereof

Abstract

The preparation method comprises the following steps: stirring and mixing a chitosan solution, a polyvinyl alcohol aqueous solution and cellulose hydrogel, adding a glutaraldehyde aqueous solution, performing stirring, performing freeze drying to obtain composite aerogel powder, melting activated PE powder, adding the composite aerogel powder, polypropylene and an antioxidant, and performing extrusion molding to obtain the cooking-resistant PE suction nozzle cover. Transferring into a charging barrel of an injection molding machine, uniformly mixing, performing injection molding, and demolding to obtain the steaming-resistant PE suction nozzle cover. According to the preparation method, the composite aerogel powder containing the graphene nanosheets is mixed with the polyethylene material, the heat resistance of the PE suction nozzle cover is improved through cellulose in the graphene nanosheets and the composite aerogel powder, and the bonding strength of the PE powder is improved through the porous structure of the composite aerogel powder; the mechanical strength of the PE suction nozzle cover is improved through the synergistic effect with the graphene nanosheets, and the prepared PE suction nozzle cover can resist the high temperature of a high-temperature cooking process and also can keep good mechanical strength at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer compounds and relates to a PE nozzle cover, in particular to a boiling-resistant PE nozzle cover and a preparation method thereof. Background Art

[0002] A nozzle is a tube cover assembly used on a packaging bag to achieve sealing. It is mainly used in liquid packaging bag products such as food and daily chemical products. The product is made by injecting molten plastic particles into a mold cavity by an injection molding machine and cooling and forming them. In the prior art, high-density polyethylene is usually used as a material to prepare the nozzle material. When the nozzle material is used to package fresh food or food, a high-temperature cooking process is required to be sterilized and disinfected. However, high-density polyethylene is not resistant to high temperatures and is easily decomposed when cooked at a high temperature of up to 120°C, which causes the nozzle cover to crack, affects the sealing, and cannot be used.

[0003] Patent CN108790004A discloses a retort-resistant suction nozzle and a production method thereof, wherein homopolymer polypropylene and masterbatch are added into the barrel of an injection molding machine and mixed evenly, and then heated and melted and injected into a mold cavity and pressure maintained, and then cooled and formed and then demolded by rotation. The obtained suction nozzle product has high temperature resistance. However, in this scheme, the masterbatch has little effect on improving the mechanical strength of the obtained milk retort suction nozzle, and only homopolymer polyethylene is used as the raw material. The obtained suction nozzle has low mechanical strength, and the mechanical strength is significantly reduced after multiple retorts, which is not conducive to packaging and transportation.

[0004] Patent CN107151366A discloses a high temperature, high pressure and crack resistant suction nozzle and its production method. The high temperature resistance and compressive strength of the suction nozzle are improved by melt mixing high-density polyethylene, linear low-density polyethylene, metallocene PE and masterbatch. However, the suction nozzle in this solution can only withstand a high temperature of 80°C and cannot withstand a high temperature of 120°C in the high temperature cooking process. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of how to improve the high temperature resistance and mechanical strength of PE materials, and to provide a boiling-resistant PE nozzle cover and a preparation method thereof.

[0006] The present invention mixes composite aerogel powder containing graphene nanosheets with polyethylene material, improves heat resistance through cellulose in graphene nanosheets and composite aerogel powder, improves bonding strength through the porous structure of composite aerogel powder, and synergizes with graphene nanosheets to improve the mechanical strength of PE nozzle cover.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for preparing a boiling-resistant PE nozzle cover comprises the following steps:

[0009] Step 1: Mix the chitosan solution and 1 wt% polyvinyl alcohol aqueous solution in a reactor, add the cellulose hydrogel into the reactor, stir and mix for 2-3 hours, add 20-25% by volume glutaraldehyde aqueous solution to initiate crosslinking, stir until a gel state is formed, freeze-dry the gel, and crush and sieve to obtain a composite aerogel powder.

[0010] Step 2: Melt the activated PE powder in a reactor, add the composite aerogel powder, polypropylene and antioxidant after cooling to 110-130°C, transfer to the barrel of the injection molding machine and mix evenly, inject the molten pellets into the mold cavity and hold the pressure for 1-2s, cool for 6-8s, and then rotate and demold to obtain a cooking-resistant PE nozzle cover.

[0011] The antioxidant is astaxanthin.

[0012] Furthermore, the activated PE powder is prepared by the following steps: PE powder is activated and treated at 35-40° C. for 30-40 minutes using an ultraviolet ozone generator.

[0013] Furthermore, in step 1, the dosage ratio of the chitosan solution, the polyvinyl alcohol aqueous solution, the cellulose hydrogel and the glutaraldehyde aqueous solution is 200-250 mL: 100-150 mL: 20-30 g: 40-50 mL.

[0014] Furthermore, in step 1, the concentration of the chitosan solution is 1-1.5 wt%, and the solvent is 2 wt% acetic acid aqueous solution.

[0015] Furthermore, in step 2, the dosage ratio of activated PE powder, composite aerogel powder, polypropylene and antioxidant is 60-80g: 10-15g: 10-15g: 1-2g.

[0016] Further, the cellulose hydrogel is prepared by the following steps:

[0017] In a reaction kettle, sodium carboxymethyl cellulose is added into deionized water, citric acid is added, the temperature is raised to 180-190° C., and the reaction is stirred for 15-20 minutes. The modified graphene nanosheets are dispersed in deionized water to obtain a 1wt% graphene dispersion, and the graphene dispersion is added into the reaction kettle, and the reaction is stirred at 70-80° C. for 60-80 minutes to obtain a cellulose hydrogel.

[0018] Furthermore, the dosage ratio of sodium carboxymethyl cellulose, deionized water, citric acid and graphene dispersion is 1-2 g: 30-40 mL: 0.1-0.2 g: 40-60 mL.

[0019] Further, the modified graphene nanosheets are prepared by the following steps:

[0020] The graphene nanosheets are dissolved in dimethyl sulfoxide in a reaction kettle, N, N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine are added into the reaction kettle, stirred and mixed for 1-2 hours, polyvinyl pyrrolidone solution is added, the temperature is raised to 40-50°C and stirred for 20-24 hours, the precipitate is collected by centrifugation, washed and vacuum dried to obtain the modified graphene nanosheets.

[0021] Further, the amount ratio of graphene nanosheets, dimethyl sulfoxide, N,N'-dicyclohexylcarbodiimide, 4-dimethylaminopyridine and polyvinylpyrrolidone solution is 0.2-0.3 g: 80-100 mL: 12-14 g: 1.2-1.4 g: 30-40 mL;

[0022] Furthermore, the concentration of the polyvinyl pyrrolidone solution is 100 mg / mL, and the solvent is dimethyl sulfoxide.

[0023] Beneficial effects of the present invention:

[0024] (1) The preparation method of the present invention mixes a composite aerogel powder containing graphene nanosheets with a polyethylene material, and improves the heat resistance of the PE nozzle cover through the graphene nanosheets and the cellulose in the composite aerogel powder. The porous structure of the composite aerogel powder improves the bonding strength of the PE powder, and the mechanical strength of the PE nozzle cover is improved by synergistic action with the graphene nanosheets. The prepared PE nozzle cover can withstand the high temperature of the high-temperature cooking process and can also maintain good mechanical strength.

[0025] (2) The preparation method of the present invention utilizes the dispersibility of polyvinyl pyrrolidone-modified graphene nanosheets while maintaining their hydrophobicity to enhance the bonding strength between the graphene nanosheets and the hydrophobic PE powder; utilizes polyvinyl pyrrolidone to disperse the modified graphene nanosheets in the cellulose hydrogel; obtains a composite hydrogel containing chitosan by blending the cellulose hydrogel and the chitosan hydrogel, and fixes the modified graphene nanosheets dispersed in the composite hydrogel in the composite hydrogel powder after freeze-drying; utilizes the chitosan in the composite hydrogel powder to enhance the bonding strength between the PE powder and the composite aerogel powder, thereby enhancing the mechanical strength of the PE nozzle cover. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Embodiment 1: A method for preparing a boiling-resistant PE nozzle cover, comprising the following steps:

[0028] S1. Dissolve 0.4 g of graphene nanosheets in 160 mL of dimethyl sulfoxide in a reactor, add 24 g of N, N'-dicyclohexylcarbodiimide and 2.4 g of 4-dimethylaminopyridine into the reactor, stir and mix for 1 h, add 60 mL of 100 mg / mL polyvinyl pyrrolidone solution, the solvent of the polyvinyl pyrrolidone solution is dimethyl sulfoxide, heat to 40 ° C and stir for 20 h, collect the precipitate by centrifugation, wash with N, N-dimethylacetamide, acetone and hot water, and vacuum dry to obtain modified graphene nanosheets.

[0029] S2. Add 1 g of sodium carboxymethyl cellulose to 30 mL of deionized water in a reactor, add 0.1 g of citric acid, heat to 180° C., stir and react for 15 min, disperse the modified graphene nanosheets in deionized water to obtain a 1 wt% graphene dispersion, add 40 mL of the graphene dispersion to the reactor, stir and react at 70° C. for 60 min, and obtain a cellulose hydrogel.

[0030] S3. Dissolve chitosan with a deacetylation degree of 80% in a 2wt% acetic acid aqueous solution to prepare a 1wt% chitosan solution, mix 200mL of the chitosan solution and 100mL of a 1wt% polyvinyl alcohol aqueous solution in a reactor, add 20g of cellulose hydrogel into the reactor, stir and mix for 2h, add 40mL of a 20% by volume glutaraldehyde aqueous solution to initiate crosslinking, stir until a gel state is formed, freeze-dry the gel, and grind and sieve to obtain a composite aerogel powder.

[0031] S4. Use an ultraviolet ozone generator to activate the PE powder at 35°C for 30 minutes, melt 60g of the activated PE powder in a reactor, cool to 110°C, add 10g of composite aerogel powder, 10g of polypropylene and 1g of astaxanthin, add to the injection molding machine barrel and mix evenly, inject the molten pellets into the mold cavity in four stages and hold the pressure for 1s, cool for 6s and then rotate to demold to obtain a cooking-resistant PE nozzle cover.

[0032] Embodiment 2: A method for preparing a boiling-resistant PE nozzle cover, comprising the following steps:

[0033] S1. Dissolve 0.5 g of graphene nanosheets in 180 mL of dimethyl sulfoxide in a reactor, add 26 g of N, N'-dicyclohexylcarbodiimide and 2.6 g of 4-dimethylaminopyridine into the reactor, stir and mix for 1.5 h, add 70 mL of 100 mg / mL polyvinyl pyrrolidone solution, the solvent of the polyvinyl pyrrolidone solution is dimethyl sulfoxide, heat to 45 ° C and stir for 22 h, collect the precipitate by centrifugation, wash with N, N-dimethylacetamide, acetone and hot water, and vacuum dry to obtain modified graphene nanosheets.

[0034] S2. In a reactor, add 1.5 g of sodium carboxymethyl cellulose to 35 mL of deionized water, add 0.15 g of citric acid, heat to 185 ° C, stir and react for 17 min, disperse the modified graphene nanosheets in deionized water to obtain a 1 wt% graphene dispersion, add 50 mL of the graphene dispersion to the reactor, stir and react at 75 ° C for 70 min to obtain a cellulose hydrogel.

[0035] S3, dissolving chitosan with a deacetylation degree of 90% in a 2wt% acetic acid aqueous solution to prepare a 1.25wt% chitosan solution, mixing 225mL of the chitosan solution and 125mL of a 1wt% polyvinyl alcohol aqueous solution in a reactor, adding 25g of cellulose hydrogel into the reactor, stirring and mixing for 2.5h, adding 45mL of a 22.5% by volume glutaraldehyde aqueous solution to initiate crosslinking, stirring until a gel state is formed, freeze-drying the gel, and crushing and sieving to obtain a composite aerogel powder.

[0036] S4. Use an ultraviolet ozone generator to activate the PE powder at 37°C for 35 minutes, melt 70g of the activated PE powder in a reactor, cool to 120°C, add 12.5g of composite aerogel powder, 12.5g of polypropylene and 1.5g of astaxanthin, add to the injection molding machine barrel and mix evenly, inject the molten pellets into the mold cavity in four stages and hold the pressure for 1s, cool for 7s and then rotate to demold to obtain a cooking-resistant PE nozzle cover.

[0037] Embodiment 3: A method for preparing a boiling-resistant PE nozzle cover, comprising the following steps:

[0038] S1. Dissolve 0.6 g of graphene nanosheets in 200 mL of dimethyl sulfoxide in a reactor, add 28 g of N, N'-dicyclohexylcarbodiimide and 2.8 g of 4-dimethylaminopyridine into the reactor, stir and mix for 2 h, add 80 mL of a 100 mg / mL polyvinyl pyrrolidone solution, the solvent of the polyvinyl pyrrolidone solution is dimethyl sulfoxide, heat to 50 ° C and stir for 24 h, collect the precipitate by centrifugation, wash with N, N-dimethylacetamide, acetone and hot water, and vacuum dry to obtain modified graphene nanosheets.

[0039] Graphene nanosheets have a hydrophobic base plane and hydrophilic groups on the edges, and are not easily dispersed in aqueous solutions. Polyvinyl pyrrolidone is adsorbed on the surface of graphene nanosheets to modify them and improve their water dispersibility.

[0040] S2. Add 2 g of sodium carboxymethyl cellulose to 40 mL of deionized water in a reactor, add 0.2 g of citric acid, heat to 190° C., stir and react for 20 min, disperse the modified graphene nanosheets in deionized water to obtain a 1 wt% graphene dispersion, add 60 mL of the graphene dispersion into the reactor, stir and react at 80° C. for 80 min, and obtain a cellulose hydrogel.

[0041] Sodium carboxymethyl cellulose is dissolved in water and then cross-linked with citric acid to form a hydrogel. Graphene dispersion is added during the formation of the hydrogel, and modified graphene nanosheets are dispersed in the hydrogel under the action of polyvinyl pyrrolidone on its surface. The decomposition temperature of cellulose is relatively high, which helps to improve the heat resistance of the PE nozzle cover.

[0042] S3. Dissolve chitosan with a deacetylation degree of 95% in a 2wt% acetic acid aqueous solution to prepare a 1.5wt% chitosan solution, mix 250mL of the chitosan solution and 150mL of a 1wt% polyvinyl alcohol aqueous solution in a reactor, add 30g of cellulose hydrogel into the reactor, stir and mix for 3h, add 50mL of a 25% by volume glutaraldehyde aqueous solution to initiate crosslinking, stir until a gel state is formed, freeze-dry the gel, and grind and sieve to obtain a composite aerogel powder.

[0043] Chitosan is dissolved in acetic acid solution to prepare chitosan solution. After cross-linking with polyvinyl alcohol, the cross-linking density and thermal stability of the chitosan solution are improved, and the dispersibility of cellulose hydrogel can be improved. The hydroxyl groups on the surface of the modified graphene nanosheets in the cellulose hydrogel are combined with the amino groups on the chitosan. The modified graphene nanosheets are dispersed in the chitosan solution, and cross-linking is initiated by glutaraldehyde to form a gel state. Then, aerogel is prepared. The dispersed modified graphene nanosheets are coated and fixed with the cross-linked gel of chitosan and polyvinyl alcohol and the cellulose hydrogel to facilitate melt blending with PE powder.

[0044] S4. Use an ultraviolet ozone generator to activate the PE powder at 40°C for 40 minutes, melt 80g of the activated PE powder in a reactor, cool to 130°C, add 15g of composite aerogel powder, 15g of polypropylene and 2g of astaxanthin, add to the injection molding machine barrel and mix evenly, inject the molten pellets into the mold cavity in four stages and maintain the pressure for 2s, cool for 8s and then rotate to demold to obtain a cooking-resistant PE nozzle cover.

[0045] The surface of PE powder is activated by hydroxylation using an ultraviolet ozone generator, so that the PE powder can be more tightly cross-linked with the chitosan in the composite aerogel powder. The cross-linking of PE powder and chitosan is used to improve the bonding strength between cellulose and graphene nanosheets in the composite aerogel powder and PE powder, thereby improving the heat resistance of the prepared PE nozzle cover. The porous structure of the composite aerogel powder enhances its bonding strength with PE powder, and synergizes with the graphene nanosheets to improve the physical strength of the prepared PE nozzle cover.

[0046] Comparative Example 1: The difference from Example 1 is that in S2, the modified graphene nanosheets are replaced by graphene nanosheets to prepare a boiling-resistant PE nozzle cover.

[0047] Comparative Example 2: The difference from Example 1 is that in S3, the cellulose hydrogel is replaced by a graphene dispersion to prepare a cooking-resistant PE nozzle cover.

[0048] Comparative Example 3: The difference from Example 1 is that in S4, the composite aerogel powder is replaced by the cellulose aerogel powder obtained by freeze-drying, crushing and sieving the cellulose hydrogel to prepare the cooking-resistant PE nozzle cover.

[0049] The performance test of the retort-resistant PE nozzle covers prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was performed. The breaking strength of the PE nozzle covers was tested after being treated by a high-temperature retort process for 1 time and 10 times. The condition of the high-temperature retort process was retort at 121° C. for 30 minutes.

[0050] The sealing performance of the PE nozzle cover was tested after being treated with the high-temperature cooking process for 1 time and 10 times. The leakage was observed at a constant pressure of 80kg for 3 minutes. After leakage, the length of the crack was measured and the crack rate was calculated. The results are shown in Table 1:

[0051] Table 1 Performance test table of PE nozzle cover after high temperature cooking process

[0052]

[0053] The breaking strength of the retort-resistant PE nozzle covers prepared in Examples 1 to 3 of the present invention is only slightly reduced after being treated by the high-temperature retort process 10 times, and there is no leakage or cracking, which does not affect repeated use, indicating that the retort-resistant PE nozzle covers prepared in the present invention have good high-temperature resistance and good mechanical strength.

[0054] In Comparative Example 1, since the graphene nanosheets were not modified, the graphene nanosheets had poor dispersibility in water and were easy to agglomerate, and the degree of dispersion in the cellulose hydrogel was low, and the heat resistance and mechanical properties of the PE nozzle were slightly improved; in Comparative Example 2, since no cellulose hydrogel was added, the heat resistance of the PE nozzle was slightly improved; in Comparative Example 3, since no chitosan hydrogel was added, the bonding strength between the cellulose aerogel powder and the PE powder was low, the cross-linking density was reduced, and the mechanical properties of the prepared PE nozzle were poor.

[0055] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a boiling-resistant PE nozzle cover, characterized in that: The steps include: Step 1: Mix the chitosan solution and 1 wt% polyvinyl alcohol aqueous solution in a reactor, add the cellulose hydrogel into the reactor, stir and mix for 2-3 hours, add 20-25% by volume glutaraldehyde aqueous solution to initiate crosslinking, stir until a gel state is formed, freeze-dry the gel, and crush and sieve to obtain a composite aerogel powder; Step 2: Melt the activated PE powder in a reactor, add the composite aerogel powder, polypropylene and antioxidant after cooling to 110-130°C, transfer to the barrel of the injection molding machine and mix evenly, inject the molten pellets into the mold cavity and hold the pressure for 1-2s, cool for 6-8s and then rotate to demould to obtain a cooking-resistant PE nozzle cover; The antioxidant is astaxanthin.

2. The method for preparing a boiling-resistant PE nozzle cover according to claim 1, characterized in that: The activated PE powder is prepared by the following steps: PE powder is activated and treated at 35-40° C. for 30-40 minutes using an ultraviolet ozone generator.

3. The method for preparing a boiling-resistant PE nozzle cover according to claim 1, characterized in that: The dosage ratio of the chitosan solution, the polyvinyl alcohol aqueous solution, the cellulose hydrogel and the glutaraldehyde aqueous solution in step 1 is 200-250 mL: 100-150 mL: 20-30 g: 40-50 mL.

4. The method for preparing a boiling-resistant PE nozzle cover according to claim 1, characterized in that: The concentration of the chitosan solution in step 1 is 1-1.5 wt %, and the solvent is 2 wt % acetic acid aqueous solution.

5. The method for preparing a boiling-resistant PE nozzle cover according to claim 1, characterized in that: The usage ratio of the activated PE powder, the composite aerogel powder, the polypropylene and the antioxidant in step 2 is 60-80 g: 10-15 g: 10-15 g: 1-2 g.

6. The method for preparing a boiling-resistant PE nozzle cover according to claim 3, characterized in that: The cellulose hydrogel is prepared by the following steps: In a reaction kettle, sodium carboxymethyl cellulose is added into deionized water, citric acid is added, the temperature is raised to 180-190° C., and the reaction is stirred for 15-20 minutes. The modified graphene nanosheets are dispersed in deionized water to obtain a 1wt% graphene dispersion, and the graphene dispersion is added into the reaction kettle, and the reaction is stirred at 70-80° C. for 60-80 minutes to obtain a cellulose hydrogel.

7. The method for preparing a boiling-resistant PE nozzle cover according to claim 6, characterized in that: The dosage ratio of the sodium carboxymethyl cellulose, deionized water, citric acid and graphene dispersion is 1-2 g: 30-40 mL: 0.1-0.2 g: 40-60 mL.

8. The method for preparing a boiling-resistant PE nozzle cover according to claim 6, characterized in that: The modified graphene nanosheet is prepared by the following steps: The graphene nanosheets are dissolved in dimethyl sulfoxide in a reaction kettle, N, N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine are added into the reaction kettle, stirred and mixed for 1-2 hours, polyvinyl pyrrolidone solution is added, the temperature is raised to 40-50°C and stirred for 20-24 hours, the precipitate is collected by centrifugation, washed and vacuum dried to obtain the modified graphene nanosheets.

9. The method for preparing a boiling-resistant PE nozzle cover according to claim 8, characterized in that: The amount ratio of the graphene nanosheets, dimethyl sulfoxide, N,N'-dicyclohexylcarbodiimide, 4-dimethylaminopyridine and polyvinylpyrrolidone solution is 0.2-0.3 g: 80-100 mL: 12-14 g: 1.2-1.4 g: 30-40 mL; The concentration of the polyvinyl pyrrolidone solution is 100 mg / mL, and the solvent is dimethyl sulfoxide.

10. A boiling-resistant PE nozzle cover, characterized in that: The invention is prepared by the preparation method of the boiling-resistant PE nozzle cover according to any one of claims 1 to 9.

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