A crosslinked polyurethane, citrus packaging material, and method of making the same

Abstract

The application discloses a crosslinking type polyurethane, a citrus packaging material and a preparation method thereof, and belongs to the technical field of high polymer polymers, and the preparation raw materials of the crosslinking type polyurethane comprise a polyester polymer, an ethylene-vinyl alcohol copolymer and an isocyanate component, a proper crosslinking network structure is constructed between the polyester polymer and the ethylene-vinyl alcohol copolymer, the advantages of various polymers are integrated, the compactness of the system is improved, the barrier properties to oxygen and water vapor can be effectively improved and stably maintained, and the crosslinking type polyurethane is suitable for being used as the citrus packaging material which is obviously changed in storage environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high molecular polymers, and particularly relates to a cross-linked polyurethane, a citrus packaging material and a preparation method thereof. BACKGROUND

[0002] Conventionally, when preparing pericarpium citri reticulatae from Citrus sinensis, in order to reduce the difficulty of subsequent manual peeling operation, effectively maintain the integrity of the pericarp, and improve the average utilization rate of the production line and the processing efficiency, it is usually necessary to "peel at different peaks" and "process at different peaks", and the picked fresh fruits are placed in a ventilated place for a short period of time for temporary storage, so that the fresh fruits are moderately dehydrated and the pericarp is softened. However, the traditional "spreading" process has the following problems: while the fresh fruits are naturally dehydrated in the air, the fruits will continue to undergo aerobic respiration, which will continuously consume the flavor substances such as sugars and organic acids in the fruits, thereby directly affecting the flavor quality and the aging potential of the final pericarp, and the heat generated by respiration will also accelerate the decay of the fruits.

[0003] In order to overcome this technical problem, the existing technology uses a fresh-keeping bag with a specific air permeability to seal and store the fresh fruits, aiming to inhibit the respiration of the fresh fruits, slow down the consumption of nutrients, and at the same time allow water to continue to evaporate, so as to achieve the purpose of softening the pericarp while maintaining the quality. However, under the typical high-temperature and high-humidity climate conditions in Xinhui, Guangdong, the air permeability and moisture permeability of the existing packaging materials often change significantly, and it is difficult to stably maintain the required oxygen and humidity balance in the bag.

[0004] Therefore, it has become a key technical problem to be solved in the field to develop a packaging material that can still maintain high and stable water vapor transmission rate under complex environmental conditions, while having good sealing property to effectively block oxygen. SUMMARY

[0005] In view of the deficiencies in the prior art, a cross-linked polyurethane and a citrus packaging material having excellent and stable oxygen barrier property and water vapor transmission property, and a preparation method thereof are provided. The cross-linked polyurethane builds a proper cross-linked network structure between a polyester polymer and an ethylene-vinyl alcohol copolymer, adjusts the compactness of the system and integrates the advantages of each polymer, thereby being able to improve and stably maintain the oxygen barrier property and the water vapor transmission property, and being suitable as a citrus packaging material for storage in an environment with significant changes.

[0006] The first object of the present application is to provide a cross-linked polyurethane, the preparation raw materials of which include a polyester polymer, an ethylene-vinyl alcohol copolymer and an isocyanate component, wherein the preparation raw materials of the polyester polymer include at least one of terephthalic acid, phthalic acid and naphthalene dicarboxylic acid.

[0007] The aforementioned cross-linked polyurethane is essentially a polymer obtained by cross-linking a polyester polymer with an ethylene-vinyl alcohol copolymer through an isocyanate component. The rigid benzene and naphthalene ring structures in the polyester polymer structure facilitate the crystallization of the polyester polymer to form a dense structure, providing basic support and strength for the packaging material. At the same time, the ethylene-vinyl alcohol copolymer, which has excellent oxygen barrier properties and water vapor permeability, is "inserted" into the polyester polymer structure through covalent bonds. The two can interact to improve the oxygen barrier properties and water vapor permeability. Furthermore, the stability of the cross-linked network structure is also beneficial for maintaining its performance under high temperature and high humidity environments, thus achieving good oxygen barrier properties and water vapor permeability under different environments.

[0008] In some embodiments of the present invention, the mass ratio of the polyester polymer, the ethylene-vinyl alcohol copolymer, and the isocyanate component is 1:0.05~0.2:0.05~0.2. By controlling the mass ratio in the above reaction, it is beneficial to control the degree of crosslinking, thereby helping to maintain the mechanical strength and toughness of the crosslinked polyurethane.

[0009] In some embodiments of the present invention, the raw materials for preparing the polyester polymer further include at least one of ethylene glycol, propylene glycol, and butanediol.

[0010] In some embodiments of the present invention, the number-average molecular weight of the polyester polymer is 5kDa to 50kDa.

[0011] In some embodiments of the present invention, the ethylene content of the ethylene-vinyl alcohol copolymer is 30 wt% or more, preferably 30 wt% to 60 wt%. By controlling the ethylene content within the above range, it is beneficial to control the hydrogen bond network structure and crystallinity of the system, thereby improving oxygen barrier properties and water vapor permeability.

[0012] In some embodiments of the present invention, the melt index of the ethylene-vinyl alcohol copolymer at 210°C and 2.16 kg is 1 to 18 g / 10 min.

[0013] In some embodiments of the present invention, the isocyanate component includes at least one of isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, polyphenyl polymethylene polyisocyanate, and terephthalic diisocyanate.

[0014] A second objective of the present invention is to provide a method for preparing the above-mentioned cross-linked polyurethane, which includes the step of melt extruding raw materials of polyester polymer, ethylene-vinyl alcohol copolymer and isocyanate component.

[0015] In some embodiments of the present invention, the temperature range of the melt extrusion is 160~265°C.

[0016] In some embodiments of the present invention, the preparation method further includes a ripening step.

[0017] In some embodiments of the present invention, the curing conditions are 50~80°C and the time is 6~24h.

[0018] A third objective of this invention is to provide the application of the above-mentioned cross-linked polyurethane in the preparation of citrus packaging materials.

[0019] A fourth objective of this invention is to provide a citrus packaging material, the raw materials of which include the aforementioned cross-linked polyurethane.

[0020] In some embodiments of the present invention, the raw materials for preparation also include nano-inorganic powder. Adding the aforementioned nano-inorganic powder facilitates obtaining superior oxygen barrier properties under high temperature and high humidity conditions.

[0021] In some embodiments of the present invention, the nano-inorganic powder includes at least one of nano-alumina and nano-zinc oxide.

[0022] In some embodiments of the present invention, the nano-inorganic powder comprises nano-alumina with an average particle size of 10-50 nm and nano-alumina with an average particle size of 80-300 nm, in a mass ratio of 1:0.2-0.5.

[0023] In some embodiments of the present invention, the mass ratio of the cross-linked polyurethane to the nano-inorganic powder is 100:2~15.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The raw materials for preparing the cross-linked polyurethane of the present invention are cheap and readily available, and the preparation method is simple, which is conducive to industrial production.

[0026] (2) By constructing an appropriate cross-linking network structure between polyester polymers and ethylene-vinyl alcohol copolymers, the present invention improves the compactness of the material and the advantages of each polymer, thereby obtaining a cross-linked polyurethane with excellent and stable oxygen barrier properties and water vapor permeability, which is suitable as a packaging material for citrus fruits with significant changes in storage environment. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0028] Unless otherwise specified, all raw materials used in this invention are derived from commercially available products and are expressed in parts by weight.

[0029] The following are the polymer raw materials used in the examples:

[0030] PET: Changzhou Huarun Composite Materials, with a number average molecular weight of 25kDa;

[0031] EVOH: Soarnol series products from Nippon Synthetic Chemicals, including V2504R (vinyl content 25wt%), DC3205HB (vinyl content 32wt%), ET3803 (vinyl content 38wt%), and H4815 (vinyl content 48wt%).

[0032] Example 1

[0033] This embodiment provides a cross-linked polyurethane film, which is prepared from the following raw materials: 100 parts PET, 5 parts V2504R, and 5 parts isophorone diisocyanate.

[0034] Its preparation method is as follows:

[0035] After mixing the above-mentioned raw materials, they were added to a casting extruder. The extruder speed was 40 r / min and the speed was 4.5 kg / h. The temperatures of each section were 160℃, 230℃, 265℃, 260℃, 255℃ and 245℃, respectively, to obtain a film with a thickness of 50 μm. The film was then cured at 60℃ for 12 h to obtain a cross-linked polyurethane film.

[0036] Example 2

[0037] This embodiment provides a cross-linked polyurethane film, which differs from Example 1 only in that the raw materials used for preparation are: 100 parts PET, 10 parts DC3205HB, and 10 parts isophorone diisocyanate. All other aspects remain the same as in Example 1.

[0038] Example 3

[0039] This embodiment provides a cross-linked polyurethane film, which differs from Example 1 only in that the raw materials used for preparation are: 100 parts PET, 15 parts ET3803, and 15 parts isophorone diisocyanate. All other aspects remain the same as in Example 1.

[0040] Example 4

[0041] This embodiment provides a cross-linked polyurethane film, which differs from Example 1 only in that the raw materials used for preparation are: 100 parts PET, 20 parts H4815, and 20 parts isophorone diisocyanate. All other aspects remain the same as in Example 1.

[0042] Example 5

[0043] This embodiment provides a cross-linked polyurethane film, which differs from Example 1 only in that the raw materials used for preparation are: 100 parts PET, 5 parts DC3205HB, and 5 parts isophorone diisocyanate. All other aspects remain the same as in Example 1.

[0044] Example 6

[0045] This embodiment provides a cross-linked polyurethane film, which differs from Example 1 only in that the raw materials used for preparation are: 100 parts PET, 5 parts ET3803, and 10 parts isophorone diisocyanate, while the rest remains the same as in Example 1.

[0046] Example 7

[0047] This embodiment provides a cross-linked polyurethane film, which differs from Example 1 only in that the raw materials used for preparation are: 100 parts PET, 5 parts H4815, and 15 parts isophorone diisocyanate, while the rest remains the same as in Example 1.

[0048] Example 8

[0049] This embodiment provides a cross-linked polyurethane film, which differs from Example 1 only in that the raw materials used for preparation are: 100 parts PET, 10 parts V2504R, and 10 parts isophorone diisocyanate. All other aspects remain the same as in Example 1.

[0050] Example 9

[0051] This embodiment provides a citrus packaging material, the raw materials for which are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, and 5 parts nano-alumina with an average particle size of 20nm.

[0052] Its preparation method is as follows:

[0053] After mixing the above-mentioned raw materials, they were added to a casting extruder. The extruder was set at 40 r / min and 4.5 kg / h. The temperatures of each section were 160℃, 230℃, 265℃, 260℃, 255℃, and 245℃, respectively, to obtain a film with a thickness of 50 μm. The film was then aged at 60℃ for 12 h to obtain citrus packaging material.

[0054] Example 10

[0055] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, and 12 parts nano-alumina with an average particle size of 20 nm. All other aspects are the same as in Example 9.

[0056] Example 11

[0057] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, and 12 parts nano-alumina with an average particle size of 150 nm. All other aspects remain the same as in Example 9.

[0058] Example 12

[0059] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, and 12 parts nano zinc oxide with an average particle size of 20 nm. The rest is the same as in Example 9.

[0060] Example 13

[0061] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, and 12 parts nano zinc oxide with an average particle size of 150 nm. All other aspects are the same as in Example 9.

[0062] Example 14

[0063] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, 10 parts nano-alumina with an average particle size of 20 nm and 2 parts nano-alumina with an average particle size of 150 nm. All other aspects are the same as in Example 9.

[0064] Example 15

[0065] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, 8 parts nano-alumina with an average particle size of 20 nm and 4 parts nano-alumina with an average particle size of 150 nm. All other aspects are the same as in Example 9.

[0066] Example 16

[0067] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, 6 parts nano-alumina with an average particle size of 20 nm and 6 parts nano-alumina with an average particle size of 150 nm. All other aspects are the same as in Example 9.

[0068] Example 17

[0069] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, 9 parts nano zinc oxide with an average particle size of 20 nm and 3 parts nano zinc oxide with an average particle size of 150 nm. All other aspects are the same as in Example 9.

[0070] Example 18

[0071] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, 9 parts nano-alumina with an average particle size of 20 nm and 3 parts nano-zinc oxide with an average particle size of 150 nm. All other aspects are the same as in Example 9.

[0072] Example 19

[0073] This embodiment provides a citrus packaging material, which differs from Example 9 only in that the raw materials used are: 100 parts PET, 10 parts DC3205HB, 10 parts isophorone diisocyanate, 9 parts nano zinc oxide with an average particle size of 20 nm and 3 parts nano aluminum oxide with an average particle size of 150 nm. All other aspects are the same as in Example 9.

[0074] Comparative Example 1

[0075] This comparative example provides a film of a blend, the raw materials for which are: 100 parts PET and 10 parts DC3205HB; the preparation method is as follows:

[0076] After mixing the above-mentioned raw materials, they were added to a casting extruder. The extruder was set at 40 r / min and 4.5 kg / h. The temperatures of each section were 160℃, 230℃, 265℃, 260℃, 255℃, and 245℃, respectively, to obtain a film of blend with a thickness of 50 μm.

[0077] Comparative Example 2

[0078] This comparative example provides a packaging material, the raw materials of which are: 100 parts PET, 10 parts DC3205HB, and 12 parts nano-alumina with an average particle size of 20 nm; the preparation method is as follows:

[0079] After mixing the above-mentioned raw materials, they were added to a casting extruder. The extruder had a rotation speed of 40 r / min and a speed of 4.5 kg / h. The temperatures of each section were 160℃, 230℃, 265℃, 260℃, 255℃, and 245℃, respectively, to obtain a packaging material with a thickness of 50 μm.

[0080] Performance testing:

[0081] 1. Oxygen barrier properties

[0082] According to GB / T 19789-2021 "Packaging Materials - Plastic Films and Sheets - Oxygen Permeability Test - Coulometric Method", the oxygen permeability of the films / packaging materials obtained in the above examples and comparative examples was measured. The test area was 50 cm². 2 The carrier gas (N2) flow rate was 100 mL / min, and the test conditions were set as follows: temperature 25 ℃ / relative humidity 40% (condition 1), temperature 50 ℃ / relative humidity 90% (condition 2). The results are shown in Table 1.

[0083] 2. Water vapor permeability

[0084] According to GB / T 26253-2010 "Determination of Water Vapor Transmission Rate of Plastic Films and Sheets - Infrared Detector Method", the water vapor transmission rate of the films / packaging materials obtained in the above examples and comparative examples was measured, with a test area of ​​50 cm². 2 The carrier gas (N2) flow rate was 100 mL / min, and the test conditions were set as follows: temperature 25 ℃ / relative humidity 90% (condition 1) and temperature 50 ℃ / relative humidity 90% (condition 2). The results are shown in Table 1.

[0085] 3. Corruption rate

[0086] One hundred newly harvested citrus fruits in July were sealed and packaged with the film / packaging materials obtained in the above examples and comparative examples, respectively, and placed in a warehouse in Xinhui, Guangdong. In addition, 100 citrus fruits were left to naturally pile up in the warehouse, and the spoilage of the citrus fruits was recorded after 7 days and 14 days. The results are shown in Table 1.

[0087] Table 1

[0088]

[0089] As shown in Table 1, the cross-linked polyurethane film prepared by this invention has excellent oxygen barrier properties and water vapor permeability. Even under high temperature and high humidity conditions, it can stably maintain excellent performance and has a low spoilage rate when packaging citrus fruits, which is significantly better than the effect of natural stacking. In contrast, the film obtained by blending polyester polymers and ethylene-vinyl alcohol copolymers in the comparative example has significantly poor oxygen barrier properties, and its oxygen barrier properties and water vapor permeability change significantly under high temperature and high humidity conditions, resulting in unstable performance and a high spoilage rate when packaging citrus fruits.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading this application specification, they can still modify or make equivalent substitutions to the specific implementation of the present invention, but these modifications or changes do not depart from the protection scope of the pending claims of the present invention.

Claims

1. A citrus packaging material, characterized in that, Its preparation raw materials include cross-linked polyurethane and nano-inorganic powder in a mass ratio of 100:2~15; The raw materials for preparing the crosslinked polyurethane include polyester polymers, ethylene-vinyl alcohol copolymers, and isocyanate components in a mass ratio of 1:0.05~0.2:0.05~0.2, wherein the raw materials for preparing the polyester polymers include at least one of terephthalic acid, phthalic acid, and naphthalic acid. The cross-linked polyurethane is a polymer obtained by cross-linking a polyester polymer with an ethylene-vinyl alcohol copolymer through an isocyanate component; The nano-inorganic powder is selected from nano-alumina with an average particle size of 20 nm and nano-alumina with an average particle size of 150 nm, with a mass ratio of 1:0.2~0.

5.

2. The citrus packaging material according to claim 1, characterized in that, The number-average molecular weight of the polyester polymer is 5kDa to 50kDa.

3. The citrus packaging material according to claim 1, characterized in that, The ethylene-vinyl alcohol copolymer has an ethylene content of 30 wt% or more.

4. The citrus packaging material according to claim 1, characterized in that, The ethylene-vinyl alcohol copolymer has a melt index of 1~18 g / 10min at 210℃ and 2.16kg.

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