CN116253911A - Preparation method of ultrathin high-strength high-light-transmittance biodegradable food inner packaging film - Google Patents
Preparation method of ultrathin high-strength high-light-transmittance biodegradable food inner packaging film Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W90/00—Enabling technologies or technologies with a potential or indirect contribution to greenhouse gas [GHG] emissions mitigation
- Y02W90/10—Bio-packaging, e.g. packing containers made from renewable resources or bio-plastics
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Abstract
The invention discloses a preparation method of an ultrathin high-strength high-light-transmittance biodegradable food package inner film, which comprises the following steps: dissolving PLA in dichloromethane to obtain a solution I; dissolving methyl cellulose, carboxymethyl chitosan and plasticizer in glacial acetic acid to obtain a solution II; and mixing the solution I and the solution II to obtain a solution III, pouring the solution III into a mold, and naturally airing after the dichloromethane volatilizes to form a film, thus obtaining the high-strength biodegradable food-grade film packaging material. The PLA/MC/CMCS blend film prepared by the solvent evaporation film forming method has good uniformity, the performances of materials are mutually complemented and cooperatively promoted, the film preparation method is simple, the prepared film has the characteristics of good mechanical performance, light transmittance, green safety, biodegradability and the like, has excellent antibacterial performance, can be used as a packaging film directly contacted with food, and reduces the use of food preservatives.
Description
Technical Field
The invention relates to a preparation method of an ultrathin high-strength high-light-transmittance biodegradable food package inner film, belonging to the fields of food packaging materials and biomedical packaging materials.
Background
Food packaging is critical to food safety, and as consumer demand for food hygiene safety increases, development of safe green food packaging materials is urgent. Currently, a great challenge facing the food industry is to develop safe and environmentally friendly food packaging materials to ensure food safety and quality. The development of green, safe, renewable and biodegradable food packaging film materials has important significance for food safety.
Polylactic acid (PLA) can be made of starch of plant resources, has good biodegradability, can be completely degraded into carbon dioxide and water by microorganisms in the nature after being used, and has very good market prospect as packaging food. However, research shows that PLA has defects in performance, in order to improve the performance of the material, an auxiliary agent is added to improve the performance of the PLA material, but the auxiliary agent and PLA are mixed in a melting way, so that the material cannot be fully mixed due to the influences of surface tension, surface energy and compatibility, and the auxiliary agent is difficult to uniformly distribute into a polymer, so that the introduction of the auxiliary agent into the modified performance is influenced. In addition, the prior art is mostly prepared by adopting a melting method, the required temperature is higher, the energy consumption is high, the process is complex, and the method is not suitable for industrial popularization. As disclosed in patent 202110627876.9, the tear strength of the polylactic acid packaging film can be obviously improved by adding the composite cross-linked particles into the polylactic acid, and the packaging film has good degradation capability, but the process for preparing the composite cross-linked particles in the process of preparing the food packaging film is too complex, meanwhile, high-temperature reaction is required in the preparation process of the composite cross-linked particles, chloroform is used as a solvent in the preparation process of the polylactic acid film, and a certain temperature is required in the volatilization and drying of the solvent, so that the polylactic acid packaging film is not suitable for industrial production. In view of the defects of the existing film preparation, the inventor designs a solvent evaporation film forming method to prepare a PLA composite film, and the preparation method has the advantages of mild preparation conditions, simplicity, safety, reliability, edibility, easy tearing and good antibacterial effect.
Disclosure of Invention
The invention provides a preparation method of a high-strength ultrathin light-transmitting biodegradable food inner packaging film, which overcomes the defects of uneven dispersion of an auxiliary agent, complex process, high energy consumption and the like of a PLA melt blending film, and does not need to adopt fluorine-containing compounds and the like which are harmful to the environment. The PLA-MC-CMCS blend film prepared by the solvent volatilization film forming method under mild conditions has the characteristics of high strength, ultra-thin, light transmission, green safety and biodegradability, can be used as an inner food packaging film to be in direct contact with food, has excellent antibacterial effect, and the whole preparation process is completed at room temperature without heating or special equipment, has low cost, is used as a food packaging material, and is more suitable for industrial production and commercial use.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
the preparation method of the ultrathin high-strength high-light-transmittance biodegradable food inner packaging film adopts a solvent evaporation film forming method, and comprises the following steps:
1) Dissolving PLA in dichloromethane to obtain a solution I;
2) Dissolving methyl cellulose, carboxymethyl chitosan and plasticizer in glacial acetic acid to obtain a solution II;
3) And mixing the solution I and the solution II to obtain a solution III, pouring the solution III into a mold, and naturally airing after the dichloromethane volatilizes to form a film, thus obtaining the high-strength biodegradable food-grade film packaging material.
The steps are operated at room temperature, heating is not needed, special equipment is not needed, the energy consumption is low, the cost is low, the process is simple, the implementation is easy, and the method is suitable for large-scale industrial production. The obtained film has no harmful substances and solvent residues, is extremely easy to degrade, can obtain packaging films with any size, and is suitable for food packaging.
The adoption of the methylene dichloride and the glacial acetic acid as the solvents can ensure the compatibility of materials, facilitate the film formation and drying at room temperature, avoid the solvent residue, avoid any heating operation and ensure the performance of the product.
When the film is naturally dried, the film can be placed at a ventilation position, so that the drying speed is increased, and the film is naturally dried to constant weight.
The method takes polylactic acid (PLA) as a main material, environment-friendly polyethylene glycol as a plasticizer, food-grade Methylcellulose (MC) and food-grade carboxymethyl chitosan (CMCS) as modified materials, and the PLA/MC/CMCS blend film prepared by a solvent evaporation film forming method has good uniformity, so that the performances of the materials are mutually supplemented and synergistically improved, the film preparation method is simple, and the prepared film has good mechanical properties, light transmittance, green safety and biodegradability, can be used as an edible sugar coating, can also be used as a food inner packaging film for milk tea powder, coffee powder, seasoning bags, cake packages, meat packages, snack packages and the like, is directly contacted with food, and has excellent antibacterial performance.
The thickness of the film is preferably 5 to 8. Mu.m, and the thickness of the film is preferably 20 to 35. Mu.m, when the film is used as a peel-off food packaging film which is in direct contact with food.
In the prior art, materials such as pp are mostly adopted in food inner packaging, so that degradation is difficult, light transmittance is poor, and when the packaging film is used for directly contacting food such as seasoning bags or instant food bags, even if a notch for tearing is reserved on the packaging film, the phenomenon that the packaging film is difficult to tear often occurs due to overlarge toughness of the packaging film. As the food inner packaging film, the breaking elongation and the maximum pulling force of the film need to fall within a certain range (the reasonable range of the breaking elongation is about 10-20%, and the reasonable range of the maximum pulling force is 5-8N), so that the film can be torn along a notch when being eaten conveniently on the basis of ensuring the package integrity requirement, and the film obtained by the application has the breaking elongation and the maximum pulling force which fall within the reasonable range, is high in strength and high in light transmittance, can well ensure the requirements of the integrity and the like of the food inner packaging film, is torn when being eaten conveniently, and is the food inner packaging film easy to tear.
The method prepares the blend membrane by a solvent evaporation membrane forming method, has simple operation and lower solution mixing viscosity, and the substances are dispersed and dissolved in the solution in a molecular form, so that the dispersion is more uniform, the dispersion effect is better, and the mutual restriction effect of the substances is enhanced; meanwhile, the auxiliary agent is mixed with PLA through the solution state, so that the auxiliary agent and the polymer are more fully and uniformly mixed.
In order to ensure the properties of the film obtained, in step 1), the mass ratio of PLA is (7-9): 2; the concentration of the first solution is 6-8g/100g, i.e. 6-8g PLA is dissolved in every 100g dichloromethane. More preferably, the concentration of the first solution is 6-6.5g/100g, which ensures higher light transmittance and better mechanical properties.
In order to further improve the uniformity of material dispersion, step 1) is to add PLA into methylene dichloride, and to stir and disperse the PLA for 4 to 6 hours by using a dispersing machine at a stirring speed of 1000rpm to 1500rpm to obtain a solution I. The step 1) is completed in a dispersing machine, and the stainless steel charging barrel of the dispersing machine is controlled at 20-25 ℃ by condensed water. The methylene dichloride is extremely volatile, so that the solution I is quickly sealed by a preservative film after being poured out, and the volatilization of the methylene dichloride is reduced.
In order to improve the modification effect, in the step 2), the plasticizer is polyethylene glycol 600; the mass ratio of the methyl cellulose to the carboxymethyl chitosan is 1 (0.9-1.1);
in order to improve the uniformity of material dispersion and improve the product performance, in the step 2), the preparation of the solution II is as follows: dissolving methyl cellulose and carboxymethyl chitosan in glacial acetic acid to prepare methyl cellulose and carboxymethyl chitosan glacial acetic acid solution with the concentration of 30mg/g-40mg/g (the sum of the concentration of the methyl cellulose and the carboxymethyl chitosan is 30mg/g-40 mg/g); and adding the methyl cellulose and carboxymethyl chitosan glacial acetic acid solution into the plasticizer polyethylene glycol 600 for more than two times, and stirring while adding to obtain a solution II.
In order to improve the uniformity of material dispersion, in the step 2), the stirring speed is 800rpm-1000rpm, the stirring is carried out for 5min-10min after each time of adding methyl cellulose and carboxymethyl chitosan glacial acetic acid solution, the next batch is added, and the stirring is carried out for 10min-15min after the last batch of methyl cellulose and carboxymethyl chitosan glacial acetic acid solution is added, thus obtaining a solution II.
In order to further improve the uniformity of material dispersion, in the step 3), the solution is added into the solution I for more than two times, and the solution III is obtained by stirring while adding.
In order to better ensure the uniformity of material dispersion, in the step 3), the stirring speed is 800rpm-1000rpm, the stirring time is 8min-10min after adding the second solution each time, the next batch is added, and the stirring is 20min-30min after the last batch of the second solution is added, so as to obtain a third solution.
To further ensure the quality of the modification, in step 3), in solution three, the ratio of the sum of the methylcellulose and carboxymethyl chitosan mass to the PLA mass is 1: (40-60), preferably 1: (55-60), wherein the mass of the plasticizer is 1/10 of the total mass of the solution III.
In order to further ensure the uniformity of the materials, in the step 3), pouring the solution III into a die with the depth of 250-300 mu m, scraping the film by an automatic film scraping machine, placing the film on a film scraping plate for 5-8 minutes after scraping the film, then removing the film from the film scraping plate, and drying in a fume hood for 6-8 hours to obtain the high-strength biodegradable food-grade film packaging material.
The technology not mentioned in the present invention refers to the prior art.
The preparation method of the ultrathin high-strength high-light-transmittance biodegradable food inner packaging film comprises the steps of selecting environment-friendly materials from all materials, degrading PLA (polylactic acid) as a main material of the film, selecting environment-friendly polyethylene glycol (PEG-600) as a plasticizer, selecting food-grade chitosan and sodium carboxymethyl cellulose as additives, improving the performance of the PLA film through a solvent volatilization film forming method, effectively controlling the proportion of PLA and an auxiliary agent, further improving the performance of a polymer blend, preparing the polymer blend film through the solvent volatilization film forming method, and dispersing and dissolving substances in a liquid in a molecular form to ensure that the substances are dispersed more uniformly, the dispersing effect is better, the mutual restriction effect of the substances is stronger, and the auxiliary agent is mixed with the PLA through a solution state to ensure that the auxiliary agent and the polymer are more fully and uniformly mixed; the raw materials are green, safe, renewable and biodegradable materials, and can be used as packaging materials to directly contact food; the PLA composite film is prepared by volatilizing the solvent, is simple, novel, practical and easy to repeat, simplifies the film preparation steps, saves the production cost, improves the film quality, has adjustable thickness (1 mu m to any thickness), is suitable for standard industrial production, can be used for easily torn food packages such as sugar coats, milk tea powder, coffee powder, seasoning bags, pancake packages, meat product packages, snack packages and various food inner packaging films, has the advantages of high strength, high light transmittance and the like, has moderate toughness and is convenient to tear; meanwhile, the antibacterial agent has excellent antibacterial performance, and the use of food preservatives is reduced.
Drawings
Fig. 1: and (3) preparing a composite membrane.
Fig. 2: light transmittance of the composite films of examples 1-5.
Detailed Description
For a better understanding of the present invention, the following examples are further illustrated, but are not limited to the following examples.
Each example was operated at room temperature (15 to 25 ℃ C.) unless otherwise specified.
Example 1
The preparation of the ultra-thin high-strength light-transmitting biodegradable food inner packaging material comprises the following steps:
1) Placing PLA (microphone P890263, mw-110,000, which are the same in each of the following examples) into a stainless steel charging barrel of a dispersing machine by taking methylene dichloride as a solvent, controlling the condensed water at 20 ℃, controlling the rotating speed at 1500rpm, continuously dispersing for 4 hours to obtain PLA methylene dichloride solution with the mass ratio of PLA to methylene dichloride of 6g/100g, pouring the PLA methylene dichloride solution into a conical flask, rapidly sealing the conical flask by using a preservative film, and storing the conical flask at about 10 ℃ for standby to reduce volatilization of the methylene dichloride, and marking as solution I;
2) Dissolving methyl cellulose and carboxymethyl chitosan with the mass ratio of 1:1 in glacial acetic acid solution to prepare methyl cellulose and carboxymethyl chitosan glacial acetic acid solution with the concentration of 30 mg/g; adding methyl cellulose and carboxymethyl chitosan glacial acetic acid solution into polyethylene glycol 600 plasticizer while stirring for three times (equal amount) to obtain solution two, wherein the stirring speed is 800rpm, stirring is carried out for 5min after each addition, the next addition operation is carried out, and the stirring time of the last addition is 10min;
3) Adding the solution into the solution I for three times (equal amount) while stirring, wherein the stirring speed is 800rpm, stirring for 8min after each addition, and then carrying out the next addition operation, and stirring for 20min after the last addition to obtain a solution III, wherein the mass ratio of the mass sum of the methylcellulose and the carboxymethyl chitosan to the mass of PLA is 1/40, and the mass of the polyethylene glycol 600 is 1/10 of the mass of the solution III. Pouring the solution III into a mould with the thickness of 250 mu m of an automatic film scraping machine, scraping the film at the temperature of about 30 ℃, placing the film on a film scraping plate for 6 minutes after scraping the film, then removing the film from the film scraping plate, attaching a label, drying in a fume hood for 8 hours, cutting edges to obtain a PLA/MC/CMCS blended composite film, and filling the PLA/MC/CMCS blended composite film into a sealing bag for standby.
Example 2
The preparation of the high-strength ultrathin light-transmitting biodegradable food packaging material comprises the following steps:
1) Placing PLA into a stainless steel charging barrel of a dispersing machine by taking methylene dichloride as a solvent, controlling the condensed water at 20 ℃, controlling the rotating speed at 1500rpm, continuously dispersing for 4 hours to obtain PLA methylene dichloride solution with the mass ratio of PLA to methylene dichloride of 6g/100g, pouring the PLA methylene dichloride solution into a conical flask, rapidly sealing with a preservative film, and storing at about 10 ℃ for standby in order to reduce methylene dichloride volatilization, and marking as solution I;
2) Dissolving methyl cellulose and carboxymethyl chitosan with the mass ratio of 1:1 in glacial acetic acid solution to prepare methyl cellulose and carboxymethyl chitosan glacial acetic acid solution with the concentration of 40 mg/g; adding methyl cellulose and carboxymethyl chitosan glacial acetic acid solution into polyethylene glycol 600 plasticizer while stirring for three times to obtain solution two, stirring at 800rpm for 5min after each addition, and stirring for 10min.
3) Adding the solution into the solution I for three times, stirring at the speed of 800rpm, stirring for 8min after each addition, and stirring for 20min after the last addition to obtain solution III, wherein the mass ratio of the mass sum of methylcellulose and carboxymethyl chitosan to the mass of PLA is 1/60, and the mass of polyethylene glycol 600 is 1/10 of the mass of the solution III. Pouring the solution III into a mould with the thickness of 250 mu m of an automatic film scraping machine, scraping the film at the temperature of about 30 ℃, placing the film on a film scraping plate for 6 minutes after scraping the film, then removing the film from the film scraping plate, attaching a label, drying in a fume hood for 8 hours, cutting edges to obtain a PLA/MC/CMCS blended composite film, and filling the PLA/MC/CMCS blended composite film into a sealing bag for standby.
Example 3
The preparation of the high-strength ultrathin light-transmitting biodegradable food packaging material comprises the following steps:
1) Placing PLA into a stainless steel charging barrel of a dispersing machine by taking methylene dichloride as a solvent, controlling the condensed water at 20 ℃, controlling the rotating speed at 1500rpm, continuously dispersing for 4 hours to obtain PLA methylene dichloride solution with the mass ratio of PLA to methylene dichloride of 8g/100g, pouring the PLA methylene dichloride solution into a conical flask, rapidly sealing with a preservative film, and storing at about 10 ℃ for standby in order to reduce methylene dichloride volatilization, and marking as solution I;
2) Dissolving methyl cellulose and carboxymethyl chitosan with the mass ratio of 1:1 in glacial acetic acid solution, and preparing methyl cellulose and carboxymethyl chitosan glacial acetic acid solution with the mass ratio of 30 mg/g; adding methyl cellulose and carboxymethyl chitosan glacial acetic acid solution into polyethylene glycol 600 plasticizer while stirring for three times to obtain solution two, wherein the stirring speed is 800rpm, stirring is carried out for 5min each time, the next adding operation is carried out, and the stirring time of the last adding operation is 10min.
3) Adding the solution into the solution I for three times, stirring at the speed of 800rpm, stirring for 8min after each addition, and stirring for 20min after the last addition to obtain solution III, wherein the mass ratio of the mass sum of methylcellulose and carboxymethyl chitosan to the mass of PLA is 1/40, and the mass of polyethylene glycol 600 is 10/three of the mass of the solution. Pouring the solution III into a mould with the thickness of 250 mu m of an automatic film scraping machine, scraping the film at the temperature of about 30 ℃, placing the film on a film scraping plate for 6 minutes after scraping the film, then removing the film from the film scraping plate, attaching a label, drying in a fume hood for 8 hours, cutting edges to obtain a PLA/MC/CMCS blended composite film, and filling the PLA/MC/CMCS blended composite film into a sealing bag for standby.
Example 4
The preparation of the high-strength ultrathin light-transmitting biodegradable food packaging material comprises the following steps:
1) Placing PLA into a stainless steel charging barrel of a dispersing machine by taking methylene dichloride as a solvent, controlling the condensed water at 20 ℃, controlling the rotating speed at 1500rpm, continuously dispersing for 4 hours to obtain PLA methylene dichloride solution with the mass ratio of PLA to methylene dichloride of 6g/100g, pouring the PLA methylene dichloride solution into a conical flask, rapidly sealing with a preservative film, and storing at about 10 ℃ for standby in order to reduce methylene dichloride volatilization, and marking as solution I;
2) Dissolving methyl cellulose and carboxymethyl chitosan with the mass ratio of 1:1.5 in glacial acetic acid solution, and preparing methyl cellulose and carboxymethyl chitosan glacial acetic acid solution with the mass ratio of 40 mg/g; adding methyl cellulose and carboxymethyl chitosan glacial acetic acid solution into polyethylene glycol 600 plasticizer while stirring for three times to obtain solution II, wherein the stirring speed is 800rpm, stirring is carried out for 5min after each addition, the next addition operation is carried out, and the stirring time of the last addition is 10min;
3) Adding the solution into the solution I for three times, stirring at the speed of 800rpm, stirring for 8min after each addition, and stirring for 20min after the last addition to obtain solution III, wherein the mass ratio of the mass sum of methylcellulose and carboxymethyl chitosan to the mass of PLA is 1/40 of the solution, and the mass of polyethylene glycol 600 is 1/10 of the mass of the solution III. Pouring the solution III into a mould with the thickness of 250 mu m of an automatic film scraping machine, scraping the film at the temperature of about 30 ℃, placing the film on a film scraping plate for 6 minutes after scraping the film, then removing the film from the film scraping plate, attaching a label, drying in a fume hood for 8 hours, cutting edges to obtain a PLA/MC/CMCS blended composite film, and filling the PLA/MC/CMCS blended composite film into a sealing bag for standby.
Example 5
The preparation of the high-strength ultrathin light-transmitting biodegradable food packaging material comprises the following steps:
1) Placing PLA into a stainless steel charging barrel of a dispersing machine by taking methylene dichloride as a solvent, controlling the condensed water at 20 ℃, controlling the rotating speed at 1500rpm, continuously dispersing for 5 hours to obtain PLA methylene dichloride solution with the mass ratio of PLA to methylene dichloride of 6g/100g, pouring the PLA methylene dichloride solution into a conical flask, rapidly sealing with a preservative film, and storing at about 10 ℃ for standby in order to reduce volatilization of the methylene dichloride, and marking as solution I;
2) Dissolving methyl cellulose and carboxymethyl chitosan with the mass ratio of 1:1 in glacial acetic acid solution to prepare methyl cellulose and carboxymethyl chitosan glacial acetic acid solution with the concentration of 30 mg/g; adding methyl cellulose and carboxymethyl chitosan glacial acetic acid solution into polyethylene glycol 600 plasticizer while stirring for three times to obtain solution II, wherein the stirring speed is 800rpm, stirring is carried out for 5min after each addition, the next addition operation is carried out, and the stirring time of the last addition is 10min;
3) Adding the solution into the solution I for three times, stirring at the speed of 800rpm, stirring for 8min after each addition, and stirring for 20min after the last addition to obtain solution III, wherein the mass ratio of the mass sum of methylcellulose and carboxymethyl chitosan to the mass of PLA is 1/40, and the mass of polyethylene glycol 600 is 1/10 of the mass of the solution III. Pouring the solution III into a mould with the thickness of 50 mu m of an automatic film scraping machine, scraping the film at the temperature of about 30 ℃, placing the film on a film scraping plate for 6 minutes after scraping the film, then removing the film from the film scraping plate, attaching a label, drying in a fume hood for 8 hours, cutting edges to obtain a PLA/MC/CMCS blended composite film, and filling the PLA/MC/CMCS blended composite film into a sealing bag for standby.
Comparative example 1
The first solution was prepared in accordance with example 1, and was directly poured into a 250 μm thick mold of an automatic film-scraping machine, scraped at about 30 c, placed on a film-scraping plate for 6 minutes after scraping, then peeled off from the film-scraping plate, labeled, dried in a hood for 8 hours, cut at the edges to give a PLA film, and filled into a sealed bag for use.
Comparative example 2
The dichloromethane in the step 1) of the example 1 is replaced by N, N-dimethylacetamide, and the rest refers to the example 1, wherein the film is obtained by adopting a non-solvent induced phase separation method, and is dried for 3 hours at 50 ℃ for standby.
Comparative example 3
The glacial acetic acid of example 1, step 2) was replaced by ethanol, the remainder being referred to in example 1.
Comparative example 4
The concentration of solution one in step 1) of example 1 was set at 18g/100g, the remainder being referred to example 1.
Comparative example 5
The concentration of solution one in step 1) of example 1 was set to 3g/100g, the remainder being referred to example 1.
Comparative example 6
The mass ratio of methylcellulose to carboxymethyl chitosan in step 2) of example 1 was changed to 2:1, and the remainder was referred to example 1.
Comparative example 7
The mass ratio of methylcellulose to carboxymethyl chitosan in step 2) of example 1 was changed to 0.5:1, and the remainder was referred to example 1.
Comparative example 8
The ratio of the sum of the mass of methylcellulose and carboxymethyl chitosan to the mass of PLA in step 3) of example 1 was replaced by 1:20, the remainder being referred to example 1.
Comparative example 9
The ratio of the sum of the mass of methylcellulose and carboxymethyl chitosan to the mass of PLA in step 3) of example 1 was replaced by 1:80, the remainder being referred to example 1.
Light transmission performance test: the transmittance of the film is tested by an ultraviolet-visible spectrophotometer, and the scanning wavelength is 800-400nm;
mechanical property test: the mechanical properties of the composite film are measured through a stretching experiment, and the indexes of the mechanical properties of the tensile strength and the elongation at break are obtained through a stress-strain curve. The tensile strength and the elongation at break are measured by a tensile strength tester,
cutting the films into 50mm multiplied by 10mm rectangles, smoothly clamping the two ends of the rectangles at the two ends of a miniature electronic universal material tester, setting the initial interval to be 20mm, preparing 6 parallel samples of each film, and respectively calculating the tensile strength (Ts) and the elongation at break (E) of the lower film by a formula, wherein the tensile rate is 60 mm/min.
The formula for tensile strength (Ts):
S＝DW (2)
wherein: ts is the tensile strength (MPa), F is the maximum tensile force (N) at which the film breaks, D is the average thickness (mm) of the film, and W is the width (mm) of the film sample.
The formula of the elongation at break (E) is as follows:
wherein: e is expressed as elongation at break (%); l (L) 0 Expressed as the length (mm) of the film before stretching; l is expressed as the length (mm) of the film after stretching.
Degradation rate test was performed by soil burying method, and the weight (M) of the blend composite film dried to constant weight 1 ) Burying the sample in a container filled with soil, degrading for 100 days, taking out the buried sample, cleaning, and drying to constant weight (M 2 ) And calculating the degradation rate according to a calculation formula: degradation rate= (M 1 -M 2 )/M 1 ×100％)。
Experimental data are shown in the following table:
the wrapper inner envelope is an inner envelope for instant wrapper purchased directly, is made of PP and is easy to tear, but has small strength and is easy to break under severe vibration. The meat product inner envelope is an inner envelope of directly purchased cooked duck legs, is made of PP, has good package integrity, is not easy to tear, and has low light transmittance. The composite films obtained in examples 1-4 are used as easy-to-tear food packages which are in direct contact with food, have high strength and moderate toughness, can meet the integrity requirements of the food packages, and are easy to tear. The composite film obtained in example 5 was used as a sugar coating, both meeting the integrity requirements of the coating and being edible. The composite films obtained in examples 1-5 have high light transmittance, can clearly see the food state, can be completely degraded, and have no residue and no pollution.
Bread packaging experiment:
the preservation experiment result of the self-made bread without the preservative at 37 ℃ in an incubator is compared with the polyethylene preservative film. According to the requirement of GB7099-2003 cake food sanitation standard that the total colony count is less than or equal to 1500cfu/g, the bread wrapped by the preservative film exceeds the national standard requirement index on day 1, and the bread is mildewed on day 4. The bread wrapped by the composite film prepared in the embodiment 1-2 starts to grow microorganisms on the 8 th day, and the total colony count is 800cfu/g and 500cfu/g respectively when the bread is stored to the 15 th day, so that the bread still meets the national standard requirements; the composite film-coated bread prepared in comparative example 1 started microbial growth on day 3 and was stored until the total colony count was 2100cfu/g on day 7.
The present invention is not limited to the above-mentioned embodiments, but is not limited to the above-mentioned embodiments, and any simple modification, equivalent changes and modification made to the above-mentioned embodiments according to the technical matters of the present invention can be made by those skilled in the art without departing from the scope of the present invention.
Claims (9)
1. A preparation method of an ultrathin high-strength high-light-transmittance biodegradable food inner packaging film is characterized by comprising the following steps of: the preparation method adopts a solvent evaporation film forming method and comprises the following steps:
1) Dissolving PLA in dichloromethane to obtain a solution I;
2) Dissolving methyl cellulose, carboxymethyl chitosan and plasticizer in glacial acetic acid to obtain a solution II;
3) And mixing the solution I and the solution II to obtain a solution III, pouring the solution III into a mold, and naturally airing after the dichloromethane volatilizes to form a film, thus obtaining the high-strength biodegradable food-grade film packaging material.
2. The method of manufacturing according to claim 1, wherein: in step 1), the concentration of the first solution is 6-8g/100g.
3. The preparation method according to claim 1 or 2, characterized in that: and 1) adding PLA into dichloromethane, and stirring and dispersing for 4-6h by using a dispersing machine at a stirring speed of 1000rpm-1500rpm to obtain a solution I.
4. The preparation method according to claim 1 or 2, characterized in that: in the step 2), the plasticizer is polyethylene glycol 600; the mass ratio of the methyl cellulose to the carboxymethyl chitosan is 1 (0.9-1.1).
5. The method of manufacturing according to claim 4, wherein: in the step 2), the preparation of the solution II is as follows: firstly, dissolving methyl cellulose and carboxymethyl chitosan in glacial acetic acid by using a food inner packaging film to prepare a methyl cellulose and carboxymethyl chitosan glacial acetic acid solution with the concentration of 30mg/g-40 mg/g; and adding the methyl cellulose and carboxymethyl chitosan glacial acetic acid solution into the plasticizer polyethylene glycol 600 for more than two times, and stirring while adding to obtain a solution II.
6. The method of manufacturing according to claim 5, wherein: in the step 2), the stirring speed is 800rpm-1000rpm, the solution is stirred for 5min-10min after adding methyl cellulose and carboxymethyl chitosan glacial acetic acid solution each time, then the next batch is added, and the solution is stirred for 10min-15min after the last batch of methyl cellulose and carboxymethyl chitosan glacial acetic acid solution is added, thus obtaining the solution II.
7. The preparation method according to claim 1 or 2, characterized in that: in the step 3), in the solution III, the ratio of the sum of the mass of the methylcellulose and the mass of the carboxymethyl chitosan to the mass of the PLA is 1: (40-60), wherein the mass of the plasticizer is 1/10 of the total mass of the solution III.
8. The preparation method according to claim 1 or 2, characterized in that: in the step 3), the solution is added into the solution I for more than two times, the solution is added and stirred simultaneously, the stirring speed is 800rpm-1000rpm, the stirring time is 8min-10min after each time of adding the solution II, the next batch is added, and the stirring time is 20min-30min after the last batch of the solution II is added, so as to obtain the solution III.
9. The preparation method according to claim 1 or 2, characterized in that: in the step 3), pouring the solution III into a mould with the depth of 250-300 mu m, scraping the film by an automatic film scraping machine, placing the film on the film scraping plate for 5-8 minutes after scraping the film, then removing the film from the film scraping plate, and drying in a fume hood for 6-8 hours to obtain the high-strength biodegradable food-grade film packaging material.
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| ZA2023/11155A ZA202311155B (en) | 2023-04-21 | 2023-12-04 | Method for preparing ultrathin, high-strength and high-light-transmitting biodegradable food inner packaging film |
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