CN108892793B - Preparation method of green degradable high-barrier high-transparency nanocellulose composite membrane - Google Patents
Preparation method of green degradable high-barrier high-transparency nanocellulose composite membrane Download PDFInfo
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- C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
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Abstract
The invention relates to the field of packaging materials, and discloses a preparation method of a green degradable high-barrier high-transparency nanocellulose composite membrane, which comprises the following steps: 1) preparing nano cellulose water dispersion; 2) preparing a nano clay suspension; 3) preparing a nano-cellulose/PVA/nano-clay composite liquid; 4) standing and defoaming the nano-cellulose/PVA/nano-clay composite liquid, pouring the nano-cellulose/PVA/nano-clay composite liquid into a mold for leveling, and performing vacuum drying to prepare a nano-cellulose/PVA/nano-clay composite film; 5) and (3) placing the composite membrane in an acyl chloride/petroleum ether mixed solution for dipping treatment, and then heating for reaction to complete the acyl chlorination hydrophobic treatment of the composite membrane. The composite film material prepared by the invention has excellent oxygen and water vapor barrier property, mechanical property and good biodegradability, and the light transmittance is up to 89%, so that the composite film material has wide commercial application potential in the fields of food fresh-keeping packaging, medicine packaging, green degradable packaging materials and the like.
Description
Technical Field
The invention relates to the field of packaging materials, in particular to a preparation method of a green degradable high-barrier high-transparency nano cellulose composite film.
Background
Since the 21 st century, plastic packaging materials made from petroleum products have produced a large amount of non-degradable packaging waste, causing global environmental problems. In recent years, in order to meet new demands for packaging materials in various fields, packaging materials have been developed toward high quality, high strength, multiple functions, new processes, light weight, and the like. The development of the world economy, the shortage of environmental resources and the transformation of life concepts lead people to increasingly strengthened environmental protection consciousness, and the concept of green degradable environment-friendly materials is brought forward.
The currently studied green barrier packaging materials are classified into the following four major categories according to the types of raw materials: (1) natural biodegradable materials, such as cellulose, starch, lignin, chitosan, etc., have the advantages of rich sources, low price, etc.; (2) chemically synthesized degradable materials such as polylactic acid (PLA), polyvinyl alcohol (PVA, PVOH), polycarbonate, polyurethane, and the like; (3) microbial synthetic degradable materials such as Polyhydroxybutyrate (PHB) and the like; (4) a mixed degradable high polymer material prepared by blending or copolymerizing two or more natural or synthetic degradable materials, such as Novon starch mixed material of Warner-Lambert company in the United states. However, the green barrier packaging materials generally have the problems of unsatisfactory mechanical properties, imperfect barrier properties, insufficient transparency and the like.
Disclosure of Invention
In order to solve the technical problems, the invention provides a preparation method of a green degradable high-barrier high-transparency nano cellulose composite film, which is characterized in that nano cellulose and nano clay are added into PVA to prepare the composite film, so that the oxygen barrier property and the strength property of the composite film are improved by utilizing the synergistic effect of the nano cellulose and the nano clay, and the water vapor barrier property of the composite film is improved by utilizing subsequent acyl chlorination treatment to replace the existing petroleum-based polymer plastic film. The method has low cost, and the prepared composite film is green and degradable, and has high barrier capability, high light transmittance and excellent mechanical property.
The specific technical scheme of the invention is as follows: a preparation method of a green degradable high-barrier high-transparency nanocellulose composite membrane comprises the following steps:
1) adding the nano-cellulose gel into water for dilution and dispersion treatment to obtain the nano-cellulose aqueous dispersion.
2) Adding the inorganic particles of the nano clay into water, and dispersing to obtain a nano clay suspension.
3) Preparing PVA solution, adding nano cellulose dispersion liquid, heating, stirring and mixing, then adding nano clay suspension, and continuously stirring and mixing to obtain the nano cellulose/PVA/nano clay composite liquid.
4) And standing and defoaming the nano-cellulose/PVA/nano-clay composite liquid, pouring the nano-cellulose/PVA/nano-clay composite liquid into a mold for leveling, and performing vacuum drying to obtain the nano-cellulose/PVA/nano-clay composite film.
5) And (3) placing the composite membrane in an acyl chloride/petroleum ether mixed solution for dipping treatment, and then heating for reaction to complete the acyl chlorination hydrophobic treatment of the composite membrane.
According to the invention, the composite film is prepared by adding the nano-cellulose and the nano-clay into the PVA, so that the oxygen barrier property and the strength property of the composite film are improved by utilizing the synergistic effect of the nano-cellulose and the nano-clay, and meanwhile, the water vapor barrier property of the composite film is improved by utilizing the subsequent acyl chlorination treatment, so that the existing petroleum-based polymer plastic film is replaced. The method has low cost, and the prepared composite film is green and degradable, and has high barrier capability, high light transmittance and excellent mechanical property.
In particular, the amount of the solvent to be used,
nanocellulose is cellulose with one dimension of nanometer level produced from plant cellulose through mechanical, chemical, enzyme treatment and combined treatment or produced by bacteria. Nanocellulose is mainly classified into the following three major categories: the detailed information of the Cellulose nanoparticles include, but are not limited to, Nano-fibrillated Cellulose (NFC, also called Cellulose nanofibrils Nano-fibers (CNF)), Nano-microcrystalline Cellulose (NCC, also called Cellulose nanocrystals Nano-fibers (CNC)), Bacterial nanocellulose (BNC, also called Bacterial Cellulose-BC, for short called BC), and detailed information shown in table 1. The nano-cellulose has higher crystallinity and cohesive energy density, can be used as an efficient oxygen barrier substance, and the reason for improving the oxygen barrier property can be attributed to that the nano-fibrils uniform in the nano-cellulose can form a dense and complex network structure, and the lamination barrier of the nano-cellulose coating can provide the oxygen barrier effect. The use of nanocellulose also brings the advantage that the mechanical properties of the composite material can be greatly improved based on the larger specific surface area and the binding capacity of the nanocellulose.
TABLE 1 preparation methods and Properties of different nanocelluloses
PVA can combine with the hydroxyl on the nano-cellulose to form a dense and complex network structure, and the strength performance of the composite membrane is effectively improved.
The addition of the nano clay can further improve the barrier property of the composite film material, so that the oxygen transmission rate of the composite film material is reduced by orders of magnitude.
The subsequent acyl chlorination treatment can effectively improve the water vapor barrier property of the composite film material.
Preferably, step 1) is specifically: adding 0.5-1.5wt% of nano cellulose gel into water to prepare 0.1-0.8 wt% of nano cellulose solution, and performing dispersion treatment at 10000-15000 r/min for 5-15 min.
Preferably, step 2) is specifically: adding inorganic particles of nano clay into water to prepare nano clay suspension with the concentration of 0.5-5 wt%, and performing dispersion treatment for 2-6 h at 10000-15000 r/min.
Preferably, step 3) is specifically: dissolving solid PVA in water to prepare a 5-10wt% PVA solution, adding a nano-cellulose dispersion solution, heating and stirring in a water bath at 90-100 ℃ for 1-3h, adding a nano-clay suspension, and continuously stirring and mixing for 2-4 h to obtain a nano-cellulose/PVA/nano-clay composite solution, wherein the mass ratio of the PVA to the nano-cellulose to the nano-clay is 70-98: 1-15.
Preferably, the step 4) is specifically: standing and defoaming the nano-cellulose/PVA/nano-clay composite liquid at room temperature for 4-8 h, pouring the nano-cellulose/PVA/nano-clay composite liquid into a polystyrene plastic mold, leveling, and vacuum drying to obtain a composite film with the thickness of 50-100 mu m; wherein the drying temperature is 40-60 ℃, the vacuum degree is-0.1 MPa, and the time is 3-5 d.
Preferably, the step 5) is specifically as follows: the composite film is placed in 1-3 wt% of acyl chloride/petroleum ether mixed solution for dipping treatment for 2-4 min, and then placed at the temperature of 100 ℃ and 110 ℃ for reaction for 2-6 min.
Preferably, the nanocellulose is cellulose with at least one dimension of nanometer level in nano fibrillated cellulose, nano microcrystalline cellulose and bacterial nanocellulose; the nano clay is bentonite, kaolin or vermiculite.
Preferably, the polymerization degree of the PVA is 600-2500, and the alcoholysis degree is 80-98%.
Preferably, the acid chloride is a fatty acid chloride or a hexanoyl chloride.
Preferably, in step 1), the nanocellulose is subjected to a modification treatment: adding nanometer cellulose into 8-12 times of mixed bacteria solution containing lactobacillus, photosynthetic bacteria and yeast with total bacteria concentration of 0.01-0.02wt%, heating to 30-40 deg.C, and fermenting for 1-2 days; then preparing the nano-cellulose into an aqueous solution, dropwise adding 3-5mol/L NaOH solution while stirring, and adjusting the pH to be neutral; then placing the mixture in a water bath at the temperature of 25-35 ℃, stirring at the speed of 250-350rpm/min, adding 2.5-3.5wt% of NaOH solution while adjusting the pH value to 8-9, dropwise adding a modifier, adding the NaOH solution to keep the pH value of the system at 8-9, repeatedly adding for 4 times in the above way, wherein the total adding amount of the modifier is 8-12wt% of the mass of the nano-cellulose, and reacting for 50-70min to obtain the modified nano-cellulose; the modifier is anhydride.
The nanocellulose molecule contains abundant hydroxyl groups, can generate abundant hydrogen bonding, but the excessive hydroxyl groups bring negative effects: the hydrophilicity of the composite membrane is too high. After the fermentation treatment of the mixed bacteria, hydroxyl groups on a part of the nano-cellulose can be reduced under the action of microorganisms, and then the nano-cellulose is secondarily modified by a modifier so as to further adjust the hydrophobicity of the nano-cellulose.
Preferably, the nanoclay inorganic particles are subjected to a modification treatment: mixing inorganic particles of nano clay with 0.1-0.3 times of octadecyl trimethyl ammonium bromide and 4-6 times of water, stirring, heating to 35-45 deg.C, ball milling for 40-80min, centrifuging, filtering, washing solid, and drying.
The nanoclay inorganic particles are microscopically in a tightly stacked lamellar structure, so that the dispersibility of the nanoclay inorganic particles is poor and an agglomeration phenomenon is easily generated when the nanoclay inorganic particles are added into an aqueous solution. In the present invention, if the nanoclay inorganic particles are not uniformly dispersed, the uniformity of film formation may be deteriorated. In the modification process, the octadecyl trimethyl ammonium bromide can perform ion exchange with the nano clay inorganic particles, and the octadecyl trimethyl ammonium bromide penetrates into the interlayers of the nano clay inorganic particles to prop open the adjacent layered structures, increase the distance between the layers and improve the dispersibility of the nano clay inorganic particles in water. After being subsequently mixed with the nano-cellulose and the PVA, the nano-cellulose and the PVA can enter the layers of the nano-cellulose and the PVA to form a three-dimensional interaction network, so that the interlayer spacing of the nano-clay inorganic particles is further increased, and the single-layer nano-clay inorganic particles can be locked between complex three-dimensional network structures, thereby exerting the barrier property of the nano-clay inorganic particles to the utmost extent.
Preferably, 0.2-0.4 wt% of organic water-resistant adhesion promoter can be further added into the nano-cellulose/PVA/nano-clay composite liquid, and the preparation method of the organic water-resistant adhesion promoter comprises the following steps: mixing a resin compound containing at least two epoxy groups with diphenol propane, adding cyclohexanone as a solvent, adding triphenyl butyl phosphonium bromide as a catalyst, heating to 130-150 ℃, reacting for 1-3h, and finally filtering and drying to obtain the organic water-resistant adhesive; wherein the molar ratio of epoxy groups in the resin compound containing at least two epoxy groups to phenolic hydroxyl groups in the diphenol propane is 1: 1.3-1.5.
The organic water-resistant adhesion promoter prepared by the invention has the characteristics of good adhesiveness and water resistance, and can enhance the crosslinking degree and the water resistance of the composite film. The organic water-resistant adhesion promoter contains excessive phenolic hydroxyl in the preparation process, and can be in hydrogen bond combination with nano cellulose and polyvinyl alcohol to form a three-dimensional network structure.
Compared with the prior art, the invention has the beneficial effects that:
(1) the adopted raw materials PVA and nano-cellulose have green and completely biodegradable performance, and the nano-clay belongs to inorganic particles, so that the environment is not polluted, and the nano-clay is completely a green environment-friendly composite material.
(2) The nano-cellulose and the nano-clay are both in nano-scale, and the addition of the nano-cellulose and the nano-clay does not have great influence on the light transmittance of the composite film.
(3) The uniform nanocellulose and the fibrils with the nanometer scale can form a dense and complex network structure, so that the permeation path of oxygen molecules is increased (as shown in figure 1), and meanwhile, the addition of the nanoclay can further improve the barrier property of the composite membrane material, so that the oxygen transmission rate is reduced by orders of magnitude; meanwhile, hydroxyl groups on the nano-cellulose can form hydrogen bond combination with hydroxyl groups on the PVA, and the strength performance of the composite membrane is effectively improved.
(4) The subsequent acyl chlorination treatment condition is mild, the operation is simple, and the water vapor barrier property of the composite film material can be effectively improved.
(5) The composite film material prepared by the invention has excellent oxygen and water vapor barrier property, mechanical property and good biodegradability, and the light transmittance is up to 89%, so that the composite film material has wide commercial application potential in the fields of food fresh-keeping packaging, medicine packaging, green degradable packaging materials and the like.
Drawings
FIG. 1 is a schematic diagram of nanocellulose to increase the oxygen molecule permeation path;
FIG. 2 shows the transmittance measurements of the pure PVA film and the nanocellulose/PVA/nanoclay composite film.
Detailed Description
The present invention will be further described with reference to the following examples.
General examples
A preparation method of a green degradable high-barrier high-transparency nanocellulose composite membrane comprises the following steps:
1) adding 0.5-1.5wt% of nano cellulose gel into water to prepare 0.1-0.8 wt% of nano cellulose solution, and performing dispersion treatment at 10000-15000 r/min for 5-15 min.
2) Adding inorganic particles of nano clay into water to prepare nano clay suspension with the concentration of 0.5-5 wt%, and performing dispersion treatment for 2-6 h at 10000-15000 r/min.
3) Dissolving solid PVA in water to prepare a 5-10wt% PVA solution, adding a nano-cellulose dispersion solution, heating and stirring in a water bath at 90-100 ℃ for 1-3h, adding a nano-clay suspension, and continuously stirring and mixing for 2-4 h to obtain a nano-cellulose/PVA/nano-clay composite solution, wherein the mass ratio of the PVA to the nano-cellulose to the nano-clay is 70-98: 1-15.
4) Standing and defoaming the nano-cellulose/PVA/nano-clay composite liquid at room temperature for 4-8 h, pouring the nano-cellulose/PVA/nano-clay composite liquid into a polystyrene plastic mold, leveling, and vacuum drying to obtain a composite film with the thickness of 50-100 mu m; wherein the drying temperature is 40-60 ℃, the vacuum degree is-0.1 MPa, and the time is 3-5 d.
5) The composite film is placed in 1-3 wt% of acyl chloride/petroleum ether mixed solution for dipping treatment for 2-4 min, and then placed at the temperature of 100 ℃ and 110 ℃ for reaction for 2-6 min.
Wherein the nano-cellulose is cellulose with at least one dimension of nano-scale in nano-fibrillated cellulose, nano-microcrystalline cellulose and bacterial nano-cellulose; the nano clay is bentonite, kaolin or vermiculite. The polymerization degree of the PVA is 600-2500, and the alcoholysis degree is 80-98%. The acyl chloride is fatty acyl chloride or caproyl chloride.
Optionally, the nanocellulose is subjected to a modification treatment: adding nanometer cellulose into 8-12 times of mixed bacteria solution containing lactobacillus, photosynthetic bacteria and yeast with total bacteria concentration of 0.01-0.02wt%, heating to 30-40 deg.C, and fermenting for 1-2 days; then preparing the nano-cellulose into an aqueous solution, dropwise adding 3-5mol/L NaOH solution while stirring, and adjusting the pH to be neutral; then placing the mixture in a water bath at the temperature of 25-35 ℃, stirring at the speed of 250-350rpm/min, adding 2.5-3.5wt% of NaOH solution while adjusting the pH value to 8-9, dropwise adding a modifier, adding the NaOH solution to keep the pH value of the system at 8-9, repeatedly adding for 4 times in the above way, wherein the total adding amount of the modifier is 8-12wt% of the mass of the nano-cellulose, and reacting for 50-70min to obtain the modified nano-cellulose; the modifier is anhydride.
Optionally, the nanoclay inorganic particles are modified: mixing inorganic particles of nano clay with 0.1-0.3 times of octadecyl trimethyl ammonium bromide and 4-6 times of water, stirring, heating to 35-45 deg.C, ball milling for 40-80min, centrifuging, filtering, washing solid, and drying.
Optionally, 0.2-0.4 wt% of organic water-resistant adhesion promoter can be added into the nano-cellulose/PVA/nano-clay composite liquid, and the preparation method of the organic water-resistant adhesion promoter comprises the following steps: mixing a resin compound containing at least two epoxy groups with diphenol propane, adding cyclohexanone as a solvent, adding triphenyl butyl phosphonium bromide as a catalyst, heating to 130-150 ℃, reacting for 1-3h, and finally filtering and drying to obtain the organic water-resistant adhesive; wherein the molar ratio of epoxy groups in the resin compound containing at least two epoxy groups to phenolic hydroxyl groups in the diphenol propane is 1: 1.3-1.5.
Example 1
1) Preparing nano cellulose water dispersion liquid:
adding 200g of 1% nanocellulose (nano fibrillated cellulose) gel into 200g of deionized water to prepare 0.5% nanocellulose solution, and dispersing for 15min at 10000r/min by using a high-speed disperser.
2) Preparation of nanoclay suspension: 10g of nano clay inorganic particles (bentonite) are added into 200g of deionized water to prepare nano clay suspension with the concentration of 0.5 percent, and a high-speed dispersion machine is adopted to perform dispersion treatment for 2 hours at the revolution of 10000 r/min.
3) Preparing a nano-cellulose/PVA/nano-clay composite liquid: weighing 8g of solid PVA (with the polymerization degree of 600-2500 and the alcoholysis degree of 80-98%) and dissolving in 100g of deionized water, then adding a certain proportion of nano-cellulose water dispersion, placing in a 90 ℃ constant-temperature water bath kettle, heating, stirring and mixing for 2h, then adding a certain proportion of nano-clay suspension, and continuously stirring and mixing for 4h to obtain a nano-cellulose/PVA/nano-clay composite liquid mixed according to different proportions, wherein the mass ratio of the PVA, the nano-cellulose and the nano-clay is 70: 15.
4) Preparing a nano-cellulose/PVA/nano-clay composite film: and (3) standing and defoaming the nano-cellulose/PVA/nano-clay composite solution obtained in the step (3) at room temperature for 4 hours, pouring the solution into a polystyrene plastic mold for leveling, and drying the composite film material by using a constant-temperature vacuum drying oven under the drying condition of 40 ℃, the vacuum degree of-0.1 MPa and the drying time of 3 days to prepare the nano-cellulose/PVA/nano-clay composite film with the film thickness of 50 microns.
5) Acyl chlorination treatment of the composite film: and (3) placing the composite film prepared in the step (4) in a mixed solution of 1% of fatty acyl chloride and petroleum ether for dipping treatment for 2min, and then placing the composite film in a constant temperature forced air drying oven for reaction at 105 ℃ for 2min to finish the acyl chlorination hydrophobic treatment of the composite film.
Example 2
A preparation method of a green degradable high-barrier high-transparency nanocellulose composite membrane comprises the following steps:
1) inoculating Acetobacter xylinum strain into seed culture medium, plugging the bottle mouth with sterilized cotton, shaking gently to disperse the seeds in the culture medium, and culturing in a constant temperature incubator at 25 deg.C for 3 days. Inoculating the activated strain into a slant culture medium, and performing shake culture in a constant temperature shaker at 30 ℃ and 150rpm for 24 hours. And then inoculating 15mL of cultured seeds into 200mL of fermentation medium, fully shaking to separate and fully disperse the strains in the fermentation medium, and then carrying out shaking culture in a constant temperature shaking table at 30 ℃ and 150rpm for 7 days to obtain the bacterial cellulose membrane. And taking out the bacterial cellulose membrane from the fermentation medium, filtering, washing with deionized water, soaking in a 4% NaOH solution, heating in a boiling water bath at 100 ℃ for 1h to remove residual culture medium and mycoprotein, neutralizing with dilute hydrochloric acid, and washing with deionized water to neutrality to obtain the bacterial nano-cellulose. Adding 0.5 wt% of bacterial nano-cellulose into water to prepare 0.1 wt% of nano-cellulose solution, and performing dispersion treatment for 10min at 12500 r/min.
Wherein, the seed culture medium and the fermentation culture medium comprise: 5 w/v% of glucose, 0.5 w/v% of peptone, 0.1 w/v% of citric acid, 0.2 w/v% of disodium hydrogen phosphate, 0.1 w/v% of potassium dihydrogen phosphate and 0.5 w/v% of yeast extract; the composition of the slant culture medium is as follows: glucose 5 w/v%, peptone 0.5 w/v%, citric acid 0.1 w/v%, agar 2.0 w/v%, calcium carbonate 0.05 w/v%. The culture medium has pH of 6.0 + -0.2, and is sterilized at 121 deg.C under 0.1MPa for 30 min.
The embodiment aims at the specific application of the bacterial nano-cellulose in the invention, the bacterial nano-cellulose is produced by fermentation by using the dynamic three-stage culture method in a targeted manner, the cultured bacterial nano-cellulose is snowflake-shaped, namely, a plurality of plush-shaped fine short fibers are attached to the periphery of each long main cellulose fiber, and the diameters and the lengths of the cellulose fibers are different, so that the connection among the fibers is favorably enhanced, the formation of network connection is promoted, and the strength performance of the composite membrane is improved. Meanwhile, the method is simple to operate, high in yield, capable of realizing continuous production and suitable for industrial production requirements.
2) Adding inorganic particles of nano clay (kaolin) into water to prepare nano clay suspension with the concentration of 0.5 wt%, and dispersing for 4h at 12500 r/min.
3) Dissolving solid PVA (with the polymerization degree of 600-2500 and the alcoholysis degree of 80-98%) in water to prepare a PVA solution with the concentration of 5wt%, adding a nano-cellulose dispersion solution, heating and stirring in a water bath at 90 ℃ for 3 hours, adding a nano-clay suspension, and continuously stirring and mixing for 2 hours to obtain a nano-cellulose/PVA/nano-clay composite solution, wherein the mass ratio of the PVA to the nano-cellulose to the nano-clay is 85: 7.5.
4) Standing and defoaming the nano-cellulose/PVA/nano-clay composite liquid at room temperature for 6 hours, pouring the liquid into a polystyrene plastic mold for leveling, and performing vacuum drying to obtain a composite film with the thickness of 75 microns; wherein the drying temperature is 50 ℃, the vacuum degree is-0.1 MPa, and the time is 4 d.
5) The composite film is put into a 2wt% hexanoyl chloride/petroleum ether mixed solution for immersion treatment for 3min, and then is put at 110 ℃ for reaction for 2 min.
Wherein the nanocellulose is subjected to modification treatment: adding nano-cellulose into a mixed bacterial solution which is 10 times of the nano-cellulose in mass, contains lactic acid bacteria, photosynthetic bacteria and saccharomycetes and has the total bacterial concentration of 0.015 wt%, heating to 35 ℃, and fermenting for 1.5 days; then preparing the nano-cellulose into an aqueous solution, dropwise adding 4mol/L NaOH solution while stirring, and adjusting the pH to be neutral; then placing the mixture in a water bath at 30 ℃, stirring at the speed of 300rpm/min, adding 3wt% of NaOH solution while adjusting the pH to 8.5, dropwise adding a modifier, adding the NaOH solution to keep the pH of the system at 8.5, repeatedly adding the modifier for 4 times in the above way, wherein the total addition of the modifier is 10wt% of the mass of the nano-cellulose, and reacting for 60min to obtain the modified nano-cellulose; the modifier is acetic anhydride.
The nano clay inorganic particles are subjected to modification treatment: mixing the nano clay with 0.2 times of octadecyl trimethyl ammonium bromide and 5 times of water, stirring uniformly, heating to 40 ℃, ball-milling for 60min, centrifuging, filtering, cleaning the solid, and drying.
Example 3
A preparation method of a green degradable high-barrier high-transparency nanocellulose composite membrane comprises the following steps:
1) adding 1.5wt% nanocellulose (nanocrystalline cellulose) gel into water to obtain 0.8wt% nanocellulose solution, and dispersing at 15000r/min for 5 min.
2) Adding inorganic particles (vermiculite) of nano clay into water to prepare nano clay suspension with the concentration of 5wt%, and performing dispersion treatment for 2 hours at 15000 r/min.
3) Dissolving solid PVA (with the polymerization degree of 600-2500 and the alcoholysis degree of 80-98%) in water to prepare a 10wt% PVA solution, adding a nano-cellulose dispersion solution, heating and stirring in a water bath at 90 ℃ for 3 hours, adding a nano-clay suspension, and continuously stirring and mixing for 4 hours to obtain a nano-cellulose/PVA/nano-clay composite solution, wherein the mass ratio of the PVA to the nano-cellulose to the nano-clay is 98: 1.
4) Standing and defoaming the nano-cellulose/PVA/nano-clay composite liquid at room temperature for 4 hours, pouring the liquid into a polystyrene plastic mold for leveling, and performing vacuum drying to obtain a composite film with the thickness of 50 microns; wherein the drying temperature is 40 ℃, the vacuum degree is-0.1 MPa, and the time is 5 d.
5) The composite film is put into a 3wt% hexanoyl chloride/petroleum ether mixed solution for immersion treatment for 4min, and then placed at 100 ℃ for reaction for 6 min.
Wherein the nanocellulose is subjected to modification treatment: adding the nano-cellulose into 8 times of mixed bacteria liquid which contains lactic acid bacteria, photosynthetic bacteria and saccharomycetes and has the total bacteria concentration of 0.01 wt%, heating to 30 ℃, and fermenting for 2 days; preparing the nano-cellulose into an aqueous solution, heating to 50 ℃, adding 0.05g of ammonium persulfate initiator, stirring, heating to 70 ℃, adding 3.5g of acrylic monomer, carrying out heat preservation reaction for 2 hours, heating to 80 ℃, and carrying out heat preservation reaction for 4 hours. After the reaction is finished, dialyzing the nano-cellulose aqueous solution in flowing deionized water for 3-4 d, removing unreacted acrylic acid monomers, and finishing the modification treatment of the nano-cellulose; the modifier is acrylic acid.
The nano clay inorganic particles are subjected to modification treatment: mixing nano clay with 0.1 times of octadecyl trimethyl ammonium bromide and 4 times of water, stirring, heating to 35 deg.C, ball milling for 80min, centrifuging, filtering, cleaning, and drying.
Example 4
The difference between this example and example 3 is that in this example, 0.3 wt% of organic water-resistant adhesion promoter is added to the nanocellulose/PVA/nanoclay composite liquid, and the preparation method of the organic water-resistant adhesion promoter is as follows: mixing a resin compound containing at least two epoxy groups with diphenol propane, adding cyclohexanone as a solvent, adding triphenyl butyl phosphine bromide as a catalyst, heating to 140 ℃, reacting for 2 hours, and finally filtering and drying to obtain the organic waterproof adhesive; wherein the molar ratio of epoxy groups in the resin compound containing at least two epoxy groups to phenolic hydroxyl groups in the diphenol propane is 1: 1.4.
Measurement of light transmittance
The determination of the light transmittance of the nano-cellulose composite membrane uses an ultraviolet visible spectrophotometer with a thin-film clamp, the wavelength range of the measurement is 200nm to 1000nm, the scanning speed is 300nm/min, the sampling interval is 1nm, the spectral bandwidth is 4nm, the lamp changing wavelength is 340nm, the measurement temperature is 25 ℃, and the sensitivity is 100%. The prepared nanocellulose composite membrane was placed in a sample cell of an ultraviolet-visible spectrometer, and to ensure the accuracy of the test, each sample was measured 3 times repeatedly, and the results are shown in fig. 2.
As can be seen from fig. 2, the transmittance of the nanocellulose/PVA/nanoclay composite film and the transmittance curve of the PVA only film are almost overlapped, and particularly in the visible light region of 400nm or more, the transmittance (89%) of the nanocellulose/PVA/nanoclay composite film is similar to the transmittance (90%) of the PVA only film, and it can be seen that the nanocellulose/PVA/nanoclay composite film has very good transmittance, and can be used for fresh-keeping packaging of food and medicine.
Determination of oxygen Barrier Properties and Water vapor Barrier Properties
The measurement results of the oxygen barrier property and the water vapor barrier property of the composite film material are shown in tables 2 and 3. It can be seen that the oxygen transmission rate of the nanocellulose/PVA/nanoclay is reduced by orders of magnitude compared with the oxygen transmission rate of the pure PVA film, and the composite film added with the nanocellulose and the nanoclay has very excellent oxygen barrier performance, and can almost match with the oxygen high-barrier films such as PVDC and EVOH widely used in the market at present (see the notes in table 2 for the transmission rate data). The nanocellulose and the nanoclay can form a compact network structure under the synergistic effect, the curved path for oxygen molecules to penetrate is increased, and meanwhile, the water vapor barrier property of the film is improved in a magnitude order after the film is subjected to acyl chlorination treatment, so that the effect is obvious.
The nano cellulose-based composite film prepared by the invention has excellent oxygen and water vapor barrier properties and good light transmission performance, and can realize commercial application in the fields of food preservation, medicine packaging, green degradable packaging and the like.
TABLE 2 measurement results of oxygen transmission rate of composite film
TABLE 3 determination of the Water vapor Transmission Rate of the composite Membrane
The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.
Claims (9)
1. A preparation method of a green degradable high-barrier high-transparency nanocellulose composite membrane is characterized by comprising the following steps:
1) adding the nano-cellulose gel into water for dilution and dispersion treatment to obtain nano-cellulose aqueous dispersion;
2) adding inorganic particles of nano clay into water, and performing dispersion treatment to obtain a nano clay suspension;
3) preparing a PVA solution, adding the nano-cellulose dispersion liquid, heating, stirring and mixing, then adding the nano-clay suspension, and continuously stirring and mixing to obtain a nano-cellulose/PVA/nano-clay composite liquid; wherein the mass ratio of the PVA, the nano-cellulose and the nano-clay is 70-98: 1-15;
4) standing and defoaming the nano-cellulose/PVA/nano-clay composite liquid, pouring the nano-cellulose/PVA/nano-clay composite liquid into a mold for leveling, and performing vacuum drying to prepare a nano-cellulose/PVA/nano-clay composite film;
5) placing the composite membrane in an acyl chloride/petroleum ether mixed solution for dipping treatment, and then heating for reaction to complete the acyl chlorination hydrophobic treatment of the composite membrane;
the nano-cellulose is subjected to modification treatment: adding nanometer cellulose into 8-12 times of mixed bacteria solution containing lactobacillus, photosynthetic bacteria and yeast with total bacteria concentration of 0.01-0.02wt%, heating to 30-40 deg.C, and fermenting for 1-2 days; then preparing the nano-cellulose into an aqueous solution, dropwise adding 3-5mol/L NaOH solution while stirring, and adjusting the pH to be neutral; then placing the mixture in a water bath at the temperature of 25-35 ℃, stirring at the speed of 250-350rpm/min, adding 2.5-3.5wt% of NaOH solution while adjusting the pH value to 8-9, dropwise adding a modifier, adding the NaOH solution to keep the pH value of the system at 8-9, repeatedly adding for 4 times in the above way, wherein the total adding amount of the modifier is 8-12wt% of the mass of the nano-cellulose, and reacting for 50-70min to obtain the modified nano-cellulose; the modifier is anhydride.
2. The preparation method of the green degradable high-barrier high-transparency nanocellulose composite membrane according to claim 1, wherein the step 1) is specifically as follows: adding 0.5-1.5wt% of nano cellulose gel into water to prepare 0.1-0.8 wt% of nano cellulose solution, and performing dispersion treatment at 10000-15000 r/min for 5-15 min.
3. The preparation method of the green degradable high-barrier high-transparency nanocellulose composite membrane according to claim 2, wherein the step 2) is specifically as follows: adding inorganic particles of nano clay into water to prepare nano clay suspension with the concentration of 0.5-5 wt%, and performing dispersion treatment for 2-6 h at 10000-15000 r/min.
4. The preparation method of the green degradable high-barrier high-transparency nanocellulose composite membrane according to claim 3, wherein the step 3) is specifically as follows: dissolving solid PVA in water to prepare a PVA solution with the concentration of 5-10wt%, then adding the nano-cellulose dispersion liquid, heating and stirring the mixture in a water bath at the temperature of 90-100 ℃ for 1-3 hours, then adding the nano-clay suspension, and continuously stirring and mixing the mixture for 2-4 hours to obtain the nano-cellulose/PVA/nano-clay composite liquid.
5. The preparation method of the green degradable high-barrier high-transparency nanocellulose composite membrane as claimed in claim 1, 2, 3 or 4, wherein the step 4) is specifically as follows: standing and defoaming the nano-cellulose/PVA/nano-clay composite liquid at room temperature for 4-8 h, pouring the nano-cellulose/PVA/nano-clay composite liquid into a polystyrene plastic mold, leveling, and vacuum drying to obtain a composite film with the thickness of 50-100 mu m; wherein the drying temperature is 40-60 ℃, the vacuum degree is-0.1 MPa, and the time is 3-5 d.
6. The preparation method of the green degradable high-barrier high-transparency nanocellulose composite membrane as claimed in claim 1, 2, 3 or 4, wherein the step 5) is specifically as follows: the composite film is placed in 1-3 wt% of acyl chloride/petroleum ether mixed solution for dipping treatment for 2-4 min, and then placed at the temperature of 100 ℃ and 110 ℃ for reaction for 2-6 min.
7. The method for preparing the green degradable high-barrier high-transparency nanocellulose composite membrane as claimed in claim 1, 2 or 3, wherein the nanocellulose is cellulose with at least one dimension of nanometer level selected from the group consisting of nano-fibrillated cellulose, nano-microcrystalline cellulose and bacterial nanocellulose; the nano clay is bentonite, kaolin or vermiculite.
8. The preparation method of the green degradable high-barrier high-transparency nanocellulose composite membrane as claimed in claim 1 or 4, wherein the polymerization degree of PVA is 600-2500, and the alcoholysis degree is 80-98%.
9. The method for preparing the green degradable high-barrier high-transparency nanocellulose composite membrane as claimed in claim 1, wherein the acyl chloride is fatty acyl chloride.
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