CN114541169B

CN114541169B - Recoverable composite packaging bag

Info

Publication number: CN114541169B
Application number: CN202210150148.8A
Authority: CN
Inventors: 李志明; 李志勇; 王媛; 潘宣洲; 郭炯; 潘苑杰; 蔡锦恩; 陈银霞; 陈越
Original assignee: Guangdong Baojiali New Material Co ltd
Current assignee: Guangdong Baojiali New Material Co ltd
Priority date: 2022-02-18
Filing date: 2022-02-18
Publication date: 2023-05-16
Anticipated expiration: 2042-02-18
Also published as: CN114541169A

Abstract

The invention discloses a recyclable composite packaging bag, which mainly comprises the steps of preparing hydrophobic paper, preparing a surface coating, coating and forming. In the preparation of the surface coating, hexamethylene diisocyanate and toluene diisocyanate are selected to modify lignin, and silver nano particles are added on the basis. Compared with the prior art, the food packaging bag prepared by the invention has good hydrophobic property, strong mechanical property and thermal stability, and can inhibit food-borne pathogenic bacteria in a limited way.

Description

Recoverable composite packaging bag

Technical Field

The invention relates to the field of food packaging, in particular to a recyclable composite packaging bag.

Background

Food packaging is an important component of the food industry, which can maintain the quality and safety of food during storage and transportation, and can extend the shelf life of the food by preventing adverse factors or conditions (e.g., spoilage microorganisms, chemical contaminants, oxygen, moisture, light, external forces, etc.). To achieve such a function, the packaging material provides physical protection for the product and creates suitable physicochemical conditions, which are critical for ensuring the shelf life of the food and for maintaining the quality and safety of the food. Food packaging should prevent moisture gain or loss, prevent microbial contamination, and should possess some resistance to the transmission of water vapor, oxygen, carbon dioxide and other volatile compounds in addition to the essential properties of the packaging material (e.g., mechanical, optical and thermal properties). Food packaging is used not only as a container, but also as a protective barrier with some innovative functions.

The food packaging materials mainly comprise plastics, glass, metal, wood, paper and the like, and the packaging materials have the characteristics of good packaging effects in aspects of functions, environmental protection and beautiful appearance. With the enhancement of environmental awareness and the enhancement of government management, food packaging is widely paid attention to gradually. The traditional food package exposes a plurality of defects, is not suitable for sustainable development, and becomes the main stream of future development in developing novel, safe and environment-friendly multifunctional food packaging materials. The advantages of different packaging materials are utilized to compound the existing packaging materials to generate new packaging materials, and environmental-friendly packaging materials such as green packaging materials, nano packaging materials and the like are recycled greatly, so that the development direction of future food packaging materials is realized.

Plastic packages have been widely used for food packaging due to their advantages of plasticity, elasticity, insulation, high strength, low specific gravity, light weight, strong corrosion resistance, easy processing, abundant resources, low energy consumption, low cost, protection for food, etc., but in the processing process, in order to improve the application performance of plastic products, many processing aids are often added to petroleum-based materials, and because these aids are mostly endocrine disruptors of human body, they may have a negative effect on health. In recent years, under the requirements of environmental protection and sustainable development, the development direction of plastic food packaging materials is degradable plastic and edible plastic. For example, biodegradable plastics: starch-based plastics, polylactic acid plastics and the like are currently applied to the aspects of candies, edible bottled water, yoghourt, fresh agricultural and sideline products, fruits, vegetables and the like, and replace the traditional disposable and nondegradable plastic packaging products. However, at present, biodegradable packaging materials have some limitations, and those based on biopolymers have relatively poor mechanical properties, high hydrophilicity and poor processability, which limit their application in industry.

Glass packaging is also one of the commonly used food packaging, glass being made of a melt of silicate, metal oxide, etc., and its main safety problem is migration of dissolved out substances from the glass, such as added lead compounds and silica, etc., into the food. The glaze on enamel and ceramic is mainly composed of lead, zinc, fu, sb, ba, cu, cr, drill and other metal oxides and salts thereof, and basically contains harmful substances. Enamels and ceramics are relatively hot when fired, and if fired at low temperatures insoluble silicates cannot be formed, and if used to contain acidic foods, these materials can easily dissolve out of the food causing safety problems.

Paper food packaging material is made of paper pulp and paper board as main raw materials, the raw materials of wood, bamboo and the like are renewable plants, and reed, bagasse, cotton stalk, wheat straw and the like are wastes, which are recyclable resources. Paper packaging materials offer advantages over other materials such as plastics in terms of resources. The paper food packaging material has the advantages of low price, economy, good protection, flexible production, good air permeability, convenient storage and transportation, good softness, easy modeling, no pollution to the content, easy recycling and wide application in the food packaging industry.

The most abundant biopolymer in the biosphere is a carbohydrate polymer, accounting for 75% of the available biomass worldwide. Cellulose, which is the most abundant and widely spread carbohydrate polymer so far and is also the first renewable organic substance, is the most basic constituent of paper packaging material in excess of 750 million tons per year, is widely used in packaging materials, is biodegradable and thus is completely environmentally safe. Paper is composed of a porous fibrous structure of microfibrils, consisting of long-chain cellulose molecules having a crystalline state that regularly breaks down the amorphous regions of the crystalline structure. The OH sites and the fiber network in the basic unit of cellulose have relatively large pores, so that the fibers have natural hydrophilicity, and the unmodified paper packaging material has strong hygroscopicity. Paper packaging also tends to absorb moisture from the environment or food and lose its physical and mechanical strength properties. For food packaging, penetration of grease through the paper packaging can affect the appearance of the product. In addition, the substantial exchange (increase or loss) of moisture and oxygen accelerates the physical, chemical and microbiological changes of the surrounding environment, thus shortening the shelf life of the food product.

Chinese patent CN 108149512A discloses paper nut packing bag and its preparation method, comprising: mixing raw wood pulp, bark, hemp, straw, mica flakes, reinforcing filler and lime water according to a certain proportion, and then washing, sun-drying, beating, fishing out paper, squeezing and baking to obtain the paper nut packaging bag. The paper nut packaging bag prepared by the preparation method has high strength, and is wear-resistant and burst-resistant; chinese patent CN 102370211A discloses a paper-plastic composite packaging bag, which comprises a matte film layer, a composite aluminum film layer, a PE layer, a kraft paper layer and a PET film layer, wherein the matte film layer, the composite aluminum film layer, the PE layer, the kraft paper layer and the PET film layer are sequentially distributed from top to bottom. The paper-plastic composite packaging bag is high in structural strength, firm and durable, is made of environment-friendly materials, and can reduce pollution. The existing food packaging paper bag raw materials are environment-friendly, partial filler is generally added in the preparation process to achieve the effect of increasing the strength of the packaging bag, and most of the packaging bags are poor in waterproof performance, especially the packaging materials which take fiber as a base material are paper, so that the application of the packaging bags in food packaging is limited due to the hydrophilicity of the packaging materials. Therefore, the preparation of the food packaging bag which is environment-friendly, recyclable, good in mechanical strength and waterproof and antibacterial is particularly important.

Disclosure of Invention

In order to solve the technical problems, the invention provides a recyclable composite packaging bag, which has the following technical scheme:

s1, preparing hydrophobic paper: weighing carnauba wax, adding the carnauba wax into chloroform to prepare 2-4wt% solution of carnauba wax, and heating to 50-60 ℃; then placing filter paper into carnauba wax solution, soaking for 2-4 h, taking out, placing into ethanol water solution with the volume fraction of 75-85% for solidification for 2-3 h, taking out, and naturally drying to obtain hydrophobic paper;

s2, preparing a surface coating: 30-50 parts by weight of lignin is dissolved in dimethyl sulfoxide, then a curing agent and a catalyst are added for reaction to form a prepolymer, and polyethylene glycol is added for uniform mixing to obtain a surface coating solution;

s3, coating and forming: uniformly coating the surface coating solution prepared in the step S2 on the surface of the hydrophobic paper prepared in the step S1, drying at 103-108 ℃ for 12-20 hours to obtain composite hydrophobic paper, and further cutting and forming the composite hydrophobic paper to obtain a composite packaging bag;

further preferably, the technical scheme of the recyclable composite packaging bag is as follows:

s2, preparing a surface coating: 30 to 50 weight parts of lignin is dissolved in dimethyl sulfoxide, then a curing agent and a catalyst are added for reaction to form a prepolymer, and then polyethylene glycol and 0.15 to 0.3 weight part of silver nano particles are added for uniform mixing to obtain a surface coating solution;

further, the mass-volume ratio of the solidification ratio filter paper to the ethanol in the step S1 is 25: (65-80) g/mL.

Further, the mass ratio of polyethylene glycol to lignin in step S2 is 1: (1-1.2).

Lignin is an amorphous aromatic polymer widely existing in plants, has biodegradability and non-toxic properties in natural environment, and has great functional modification potential due to abundant hydroxyl groups. In recent years, biodegradable, low cost paper-based packaging materials have attracted attention as alternatives to petroleum-based packaging in order to relieve severe environmental stresses. Lignin-based polyurethanes as coating agents impart excellent mechanical properties, especially hydrophobicity and barrier properties to gases, to paper packaging the inventors have found that the use of lignin and polyols as raw materials for the synthesis of polyurethanes results in polyurethanes with good recyclability and other excellent properties. However, in order to further increase the reactivity of lignin, the present inventors modified lignin by a prepolymerization reaction of isocyanate and lignin, without complicated separation and purification in the modification process, in the prepolymerization reaction, hydroxyl groups in lignin react with an excessive amount of isocyanate to form a terminal isocyanate prepolymer having a much higher reactivity than that of lignin. The prepolymerization ensures that lignin, in the form of the active segments, participates as much as possible in the synthesis of the bio-coating, rather than the filler.

Further, the curing agent in the step S2 is a mixture of hexamethylene diisocyanate and toluene diisocyanate.

Preferably, the mass ratio of hexamethylene diisocyanate to toluene diisocyanate is 3: (5-6).

Further, the catalyst in the step S2 is dibutyl tin dilaurate, and the addition amount of the dibutyl tin dilaurate is 0.5-2 parts by weight.

The silver nano-particles are prepared by the following method: taking 2-4 mL of iturin A aqueous solution with the concentration of 1mg/mL, adding 1-2 mL of silver nitrate aqueous solution with the concentration of 0.1mg/mL into the iturin A aqueous solution, radiating the aqueous solution for 30-35 min under the ultraviolet light with the wavelength of 365-370 nm, centrifuging the aqueous solution for 30-35 min at 8000-10000 rpm, collecting particles, and washing the particles for 2-3 times with water to obtain the silver nano particles.

The hydroxyl and carbonyl groups in lignin can also chelate metal ions, making lignin a natural ligand for metal coordination bonds. The inventor discovers that the electrostatic crosslinking exists between the modified lignin and the silver nano particles, so that the modified lignin can be an effective capping agent, and the mechanical strength of the packaging bag can be effectively improved. Silver is also an effective antibacterial agent, and the inventor utilizes the metal coordination advantage of lignin to introduce silver nano particles into lignin-based polyurethane paint, which is beneficial to further improving packaging performance.

In addition, the inventor finds through experiments that under the catalysis of catalyst dibutyl tin dilaurate, the-OH in lignin and polyethylene glycol is condensed with-NCO in toluene diisocyanate to form a carbamate bond (-COONH-) but further adding hexamethylene diisocyanate in the process of modifying lignin can improve the thermal stability of the surface coating, the lignin and the hexamethylene diisocyanate both contain a large amount of aromatic structures, so that a large amount of carbon residues can be generated after pyrolysis, and the high reactivity of the hexamethylene diisocyanate and the coordination of silver nano particles and-OH enable the crosslinking to be more compact, thereby playing the effect of improving the thermal stability of the packaging bag.

The antibacterial effect of the nano silver and the effect produced by compounding the nano silver with other raw materials are in direct proportion to the addition amount of the nano silver, but the content of the nano silver in the food packaging material is not too high, so that on the basis, the nano silver particles are modified, the nano silver is compounded by using the iturin A and the silver nitrate, and the addition of the nano silver can be reduced while the same effect is achieved. Iturin a is a cyclic lipopeptide having fatty acid chains and phenolic groups that can generate superoxide radicals through the phenolic groups and then aid in the formation of silver nanoparticles by silver ions under the mediation of ultraviolet radiation. The nano silver particles prepared by the method can be applied to paper packaging to effectively inhibit food-borne pathogenic bacteria and fungi, and compared with the common nano silver particles, the nano silver particles have higher antibacterial activity, lower silver concentration and wider antibacterial spectrum.

Detailed Description

The following description of the technical solution in the embodiments of the present invention is clear and complete. The following examples are illustrative of the invention and are not intended to limit the scope of the invention. The operations referred to in the examples, unless otherwise specified, are all conventional in the art.

The comparative example and the examples of the present invention have the following parameters of part of raw materials:

carnauba wax, CAS:8015-86-9, available from Shanghai Yuan Ye Biotechnology Co., ltd;

DMSO, dimethyl sulfoxide, CAS:67-68-5, available from sigma aldrich (Shanghai) trade limited;

hexamethylene diisocyanate, CAS:822-06-0, available from Shandong Jiayi chemical technology Co., ltd;

toluene diisocyanate, CAS:26471-46-5, available from Hubei Xinming Tai chemical Co., ltd;

dibutyl tin dilaurate, CAS:77-58-7, available from Jinan Huijun chemical Co., ltd.

Example 1

The preparation of the recyclable composite packaging bag comprises the following steps:

s1, preparing hydrophobic paper: weighing 15g of carnauba wax, adding the carnauba wax into 500mL of chloroform, uniformly mixing to obtain a carnauba wax solution, heating to 50 ℃ until the carnauba wax solution is completely dissolved, then placing 25g of filter paper into the molten carnauba wax solution, soaking the filter paper for 3 hours at 50 ℃, taking out the filter paper, spreading the filter paper, solidifying the filter paper in 75mL of ethanol water solution with the volume fraction of 85% for 2 hours, taking out a sample, and naturally drying the sample at room temperature;

s2, preparing a surface coating: dissolving 40 parts by weight of lignin in DMSO, adding 3 parts by weight of hexamethylene diisocyanate, 5 parts by weight of toluene diisocyanate and 0.5 part by weight of dibutyltin dilaurate for curing reaction to form a prepolymer, and adding 40 parts by weight of polyethylene glycol into the prepolymer for further crosslinking and mixing uniformly to obtain a surface coating solution;

s3, coating and forming: and (3) uniformly coating the surface coating solution prepared in the step (S2) on the surface of the hydrophobic paper prepared in the step (S1) by using a ZY-TB-B4 wire rod scraper in an integrated manner, drying at 108 ℃ for 12 hours to obtain composite hydrophobic paper, and further cutting and forming the composite hydrophobic paper to obtain the composite packaging bag.

Example 2

s2, preparing a surface coating: dissolving 40 parts by weight of lignin in DMSO, adding 3 parts by weight of hexamethylene diisocyanate, 5 parts by weight of toluene diisocyanate and 0.5 part by weight of dibutyltin dilaurate for curing reaction to form a prepolymer, adding 40 parts by weight of polyethylene glycol into the prepolymer for further crosslinking, adding 0.15 part by weight of silver nanoparticles into the mixture, and uniformly mixing to obtain a surface coating solution;

The silver nano-particles are prepared by the following method: 2mL of 1mg/mL aqueous solution of iturin A was taken, 1mL of 0.1mg/mL aqueous solution of silver nitrate was added thereto, then irradiated with ultraviolet light at a wavelength of 365nm for 30min, centrifuged at 10000rpm for 30min, and then the particles were collected and washed with water 3 times to obtain silver nanoparticles.

The iturin A is a cyclic lipopeptide antibiotic produced by bacillus bacteria, CAS:52229-90-0 available from Shanghai Biotech (Shanghai) Inc.

Example 3

s2, preparing a surface coating: dissolving 40 parts by weight of lignin in DMSO, adding 8 parts by weight of hexamethylene diisocyanate and 0.5 part by weight of dibutyltin dilaurate for curing reaction to form a prepolymer, adding 40 parts by weight of polyethylene glycol into the prepolymer for further crosslinking, adding 0.15 part by weight of silver nanoparticles into the mixture, and uniformly mixing to obtain a surface coating solution;

Example 4

s2, preparing a surface coating: dissolving 40 parts by weight of lignin in DMSO, adding 8 parts by weight of toluene diisocyanate and 0.5 part by weight of dibutyltin dilaurate for curing reaction to form a prepolymer, adding 40 parts by weight of polyethylene glycol into the prepolymer for further crosslinking, adding 0.15 part by weight of silver nanoparticles into the mixture, and uniformly mixing to obtain a surface coating solution;

The silver nano-particles are prepared by the following method: taking 2mL of 1mg/mL aqueous solution of iturin A, adding 1mL of 0.1mg/mL aqueous solution of silver nitrate into the aqueous solution, radiating the aqueous solution by ultraviolet light with the wavelength of 365nm for 30min, centrifuging the aqueous solution at 10000rpm for 30min, collecting particles, and washing the particles with water for 3 times to obtain silver nano particles, wherein the iturin A is a cyclic lipopeptide antibiotic produced by bacillus bacteria and is purchased from Shanghai, inc.

Example 5

The silver nanoparticles (50 nm-80 nm) were purchased from wuhan rana white pharmaceutical chemicals limited.

Comparative example 1

s2, preparing a surface coating: dissolving 40 parts by weight of lignin in DMSO, then adding 0.5 part by weight of dibutyltin dilaurate and 40 parts by weight of polyethylene glycol, and uniformly mixing to obtain a surface coating solution;

Comparative example 2

s2, preparing a surface coating: dissolving 40 parts by weight of lignin in DMSO, adding 0.5 part by weight of dibutyltin dilaurate, 40 parts by weight of polyethylene glycol and 0.15 part by weight of silver nanoparticles into the mixture, and uniformly mixing to obtain a surface coating solution;

Test example 1

The composite hydrophobic papers obtained in examples 1 to 5 and comparative examples 1 to 2 were subjected to an antibacterial test by: single colonies of E.coli (ATCC 8739), staphylococcus aureus (ATCC 25923) and Salmonella typhimurium (ATCC 14028) were picked up and cultured in the sterilized meat peptone medium at 37℃for 12 hours at 180r/min, respectively, to obtain a test bacterial liquid. The composite hydrophobic paper sheet (0.1 g/sheet) subjected to autoclaving at 121℃was sterilized with 5mL of test bacterial liquid (about 10 ⁶ cfu/mL) and allowed to act for 3h at 180r/min at 37 ℃. Thereafter, the bacterial liquid which has been acted is subjected to a series of dilutions, and the dilutions are spread on LB solid medium for colony counting. At least three replicates were performed for each sample.

The inhibition ratio (GI) for E.coli, staphylococcus aureus and Salmonella typhimurium can be calculated by the following formula:

wherein A represents the colony count of the blank control, and B represents the colony count of the test sample.

Table 1 test results of antibacterial rate of composite hydrophobic paper

The nano silver is an effective antibacterial agent, and the invention utilizes the metal coordination advantage of lignin, and the silver nano particles are introduced into the lignin-based polyurethane coating, which is beneficial to further improving the packaging performance. However, the antibacterial effect of the nano silver is in direct proportion to the addition amount of the nano silver, but the content of the nano silver in the material of the food package is not too high, so that on the basis, the nano silver particles are modified, and the nano silver can be reduced while the same effect is achieved by compounding the iturin A and the silver nitrate. Iturin a is a cyclic lipopeptide having fatty acid chains and phenolic groups that can generate superoxide radicals through the phenolic groups and then aid in the formation of silver nanoparticles by silver ions under the mediation of ultraviolet radiation. The nano silver particles prepared by using the iturin A are applied to paper packaging, so that various food-borne pathogens can be effectively inhibited, and compared with the common nano silver particles, the nano silver particles have higher antibacterial activity, lower silver concentration and wider antibacterial spectrum.

Test example 2

The recoverable composite bags of examples 1-5 and comparative examples 1-2 were subjected to thermogravimetric analysis testing on a TG209F1 thermogravimetric analyzer on an N ₂ Then, the temperature is increased from 30 to 600 ℃ at a speed of 10 ℃/min to obtain a thermal weight curve of the composite packaging bag, and the initial thermal decomposition temperature Ti and the fastest thermal degradation temperature Tmax in thermal decomposition are recorded. The test results are shown in Table 2

Table 2 thermal degradation test results table for package bag

Examples	Ti/℃	Tmax/℃
			Example 1	303.0	360.8
Example 2	320.9	385.3
			Example 3	305.8	361.4
Example 4	307.2	362.5
			Example 5	309.2	370.2
Comparative example 1	251.5	291.2
			Comparative example 2	274.6	305.7

Under the catalysis of catalyst dibutyl tin dilaurate, the condensation of-OH in lignin and polyethylene glycol and-NCO in toluene diisocyanate forms a carbamate bond (-COONH-) and the use of hexamethylene diisocyanate and toluene diisocyanate for compounding in the process of modifying lignin can improve the thermal stability of the surface coating, probably because lignin and hexamethylene diisocyanate both contain a large amount of aromatic structures, a large amount of carbon residues can be generated after pyrolysis, and the high reactivity of hexamethylene diisocyanate and the coordination of silver nanoparticles and-OH further enable the crosslinking to be tighter, so that the effect of improving the thermal stability of the packaging bag can be achieved.

The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.

Claims

1. The recyclable composite packaging bag is characterized by being prepared by the following method:

s1, preparing hydrophobic paper: weighing carnauba wax, adding the carnauba wax into chloroform to prepare 2-4wt% solution of carnauba wax, and heating to 50-60 ℃; then placing filter paper into carnauba wax solution, soaking for 2-4 hours at 50-60 ℃, taking out, placing into ethanol water solution with the volume fraction of 75-85% for solidification for 2-3 hours, taking out, and naturally drying to obtain hydrophobic paper; the mass volume ratio of the filter paper to the ethanol water solution is 25: (65-80) g/mL;

s2, preparing a surface coating: 30 to 50 weight parts of lignin is dissolved in dimethyl sulfoxide, then a curing agent and a catalyst are added to react to form a prepolymer, polyethylene glycol is added into the prepolymer, and then 0.15 to 0.3 weight part of silver nano particles are added to be uniformly mixed to obtain a surface coating solution; the mass ratio of polyethylene glycol to lignin is 1: (1-1.2); the curing agent is a mixture of hexamethylene diisocyanate and toluene diisocyanate; the mass ratio of the hexamethylene diisocyanate to the toluene diisocyanate is 3: (5-6); the catalyst is dibutyl tin dilaurate; the addition amount of the dibutyl tin dilaurate is 0.5-2 parts by weight;

2. The recyclable composite packaging bag as defined in claim 1, wherein: the curing agent is formed by mixing hexamethylene diisocyanate and toluene diisocyanate according to a mass ratio of 3:5.