Carboxymethyl hemicellulose composite thin film and preparation method therefor

Abstract

The present invention relates to a carboxymethyl hemicellulose composite thin film and a preparation method therefor. The composite thin film comprises 95-100 parts by weight of carboxymethyl hemicellulose, 1-5 parts by weight of gallic acid, and 50-60 parts by weight of sorbitol, wherein the carboxymethyl hemicellulose is obtained after etherifying bamboo hemicellulose with chloroacetic acid under alkaline condition, and the degree of substitution of the carboxymethyl hemicellulose is 0.17-0.59. The preparation method of the present invention comprises: mixing carboxymethyl hemicellulose with deionized water, gallic acid, and sorbitol in sequence to obtain a composite thin film liquid; and then slowly pouring the composite thin film liquid into a mold and drying to obtain the required composite thin film. By preparing the carboxymethyl hemicellulose from the bamboo hemicellulose, and then on this basis, preparing the carboxymethyl hemicellulose composite thin film, the present invention has not only antimicrobial characteristics but also the characteristics of environmental friendliness, a low price, etc.

Description

A carboxymethyl hemicellulose composite film and preparation method thereof Technical Field

[0001] The invention belongs to the technical field of composite film preparation, and in particular relates to a carboxymethyl hemicellulose composite film and a preparation method thereof. Background Art

[0002] Hemicellulose is abundant in source, has good degradability and biocompatibility, and can be used in food packaging, medicine, papermaking additives and other fields. However, hemicellulose has poor solubility in water and strong intermolecular hydrogen bonding forces, so the mechanical properties of hemicellulose film materials are poor. By chemically modifying hemicellulose and adding plasticizers, antibacterial agents and other methods, the film-forming and antibacterial properties of hemicellulose-based film materials can be effectively improved, thereby improving their overall performance. During storage and transportation, fruits and vegetables need to be isolated from air and microorganisms to extend their shelf life. Traditional packaging film materials are mostly derived from non-renewable fossil resources, so the research and development of environmentally friendly packaging film materials with good preservation effects will be of great significance.

[0003] Meanwhile, bamboo, a biomass resource with broad development prospects, accounts for 72.96% of China's total bamboo planting area. Bamboo's main components are cellulose, hemicellulose, and lignin, with hemicellulose accounting for 20-30%. Separating and purifying hemicellulose from bamboo raw materials and converting it into high-value-added products holds broad market potential.

[0004] Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a carboxymethyl hemicellulose composite film and a preparation method thereof, wherein carboxymethyl hemicellulose is prepared from bamboo hemicellulose, and then the carboxymethyl hemicellulose composite film is prepared based on the carboxymethyl hemicellulose composite film, which not only has antibacterial properties, but also is environmentally friendly and inexpensive.

[0006] The present invention is achieved by providing a carboxymethyl hemicellulose composite film and a preparation method thereof, comprising 95 to 100 parts by weight of carboxymethyl hemicellulose, 1 to 5 parts by weight of gallic acid, and 50 to 60 parts by weight of sorbitol, wherein the carboxymethyl hemicellulose is obtained by etherifying bamboo hemicellulose with chloroacetic acid under alkaline conditions, and the degree of substitution DS of the carboxymethyl hemicellulose is 0.17 to 0.59.

[0007] Because hemicellulose has a low solubility in water, resulting in poor film-forming properties, hemicellulose is carboxymethylated. This not only improves the solubility of carboxymethyl hemicellulose in water, but also enhances the bioactivity of the composite film. Hemicellulose extracted from bamboo is carboxymethylated. After the hydroxyl groups on the hemicellulose molecular chains undergo carboxymethylation, the physicochemical properties of the hemicellulose are effectively improved and its bioactivity is enhanced. Carboxymethyl hemicellulose is negatively charged and can be adsorbed on the surface of cells, disrupting bacterial physiological activities and hindering their reproduction while preventing bacteria from absorbing nutrients. Sorbitol, a functional sugar alcohol, is a food-grade plasticizer that can improve film-forming properties. Gallic acid, as an antibacterial agent, can inhibit the synthesis of polysaccharides in bacterial biofilms, thereby hindering bacterial growth and achieving an antibacterial effect. The present invention combines carboxymethyl hemicellulose, sorbitol, and gallic acid to form a composite film, coordinating the properties of the three, giving full play to their respective advantages. The resulting composite film not only has good film-forming properties but also has antibacterial characteristics.

[0008] The present invention is achieved by providing a method for preparing the carboxymethyl hemicellulose composite film, comprising the following steps:

[0009] Step 1: mixing carboxymethyl hemicellulose with deionized water, gallic acid and sorbitol in sequence to obtain a composite film solution;

[0010] Step 2: slowly pour the composite film liquid into the mold and dry it to obtain the desired composite film.

[0011] The present invention has a simple operation process and a short preparation time, and effectively solves the problem of poor film-forming effect of hemicellulose, thereby synergistically improving the dispersibility among carboxymethyl hemicellulose, sorbitol and gallic acid, and greatly improving the antibacterial performance of the composite film.

[0012] Furthermore, in the step 2, before drying to form a film, the composite membrane liquid is subjected to ultrasonic treatment for more than 10 minutes to remove bubbles.

[0013] Furthermore, in the step 2, the composite film is dried in a forced air drying oven at 40° C. for 48 hours.

[0014] Compared with the prior art, the carboxymethyl hemicellulose composite film and its preparation method of the present invention have the following characteristics:

[0015] (1) The composite film has good gas barrier properties and has a good preservation effect on fruits.

[0016] (2) The operation is convenient and the experimental cycle is short. The raw materials for preparation are all derived from nature and are renewable resources. Therefore, the composite film is a degradable material and can be widely used in various biofunctional materials and packaging materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1 is a comparison diagram of the dissolution effect of carboxymethyl hemicellulose in water;

[0018] FIG2 is a transparency picture showing the macroscopic morphology of the composite film of the present invention;

[0019] FIG3 is a SEM image of the microscopic morphology of the composite film of the present invention, including a to f;

[0020] FIG4 is a schematic diagram showing the effect of the degree of substitution of carboxymethyl hemicellulose on the air permeability of the composite film of the present invention;

[0021] FIG5 is a graph showing the effect of the degree of substitution of carboxymethyl hemicellulose on the antibacterial properties of the composite film of the present invention;

[0022] FIG6 is a test curve showing the effect of the composite film of the present invention on the weight loss rate of blueberries. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] A preferred embodiment of the carboxymethyl hemicellulose composite film of the present invention comprises 95 to 100 parts by weight of carboxymethyl hemicellulose, 1 to 5 parts by weight of gallic acid, and 50 to 60 parts by weight of sorbitol, wherein the carboxymethyl hemicellulose is obtained by etherifying bamboo hemicellulose with chloroacetic acid under alkaline conditions, and the degree of substitution DS of the carboxymethyl hemicellulose is 0.17 to 0.59.

[0025] The present invention also discloses a method for preparing the above carboxymethyl hemicellulose composite film, comprising the following steps:

[0026] Step 1: Carboxymethyl hemicellulose is mixed with deionized water, gallic acid and sorbitol in sequence to obtain a composite film liquid.

[0027] Step 2: slowly pour the composite film liquid into the mold and dry it to obtain the desired composite film.

[0028] In the second step, before drying and forming the film, the composite film solution is subjected to ultrasonic treatment for more than 10 minutes to remove bubbles. The drying conditions of the composite film are: drying in a forced air drying oven at 40° C. for 48 hours.

[0029] The carboxymethyl hemicellulose composite film and its preparation method of the present invention are further illustrated by specific examples below.

[0030] Example 1

[0031] An embodiment of the method for preparing the first carboxymethyl hemicellulose composite film of the present invention comprises the following steps:

[0032] Step (11): Preparation of hemicellulose-based composite film liquid: 0.35 g of carboxymethyl hemicellulose with a degree of substitution of 0.17, 12.5 g of deionized water, 0.7 mL of 0.037 g / mL gallic acid, and 0.2 g of sorbitol were added to a 50 mL beaker in sequence and stirred at 50°C and 500 rpm for 2 h to obtain a composite film liquid of carboxymethyl hemicellulose, sorbitol, and gallic acid.

[0033] Step (12): Preparation of hemicellulose-based composite film: The composite film solution was ultrasonicated for 10 minutes to remove bubbles, slowly poured into a 3.5 cm × 3.5 cm silica gel mold, and dried in a forced air drying oven at 40°C for 48 hours to obtain a carboxymethyl hemicellulose composite film.

[0034] Example 2

[0035] An embodiment of the method for preparing the second carboxymethyl hemicellulose composite film of the present invention comprises the following steps:

[0036] Step (21): Preparation of hemicellulose-based composite film liquid: 0.35 g of carboxymethyl hemicellulose with a degree of substitution of 0.33, 12.5 g of deionized water, 0.7 mL of 0.037 g / mL gallic acid, and 0.2 g of sorbitol were sequentially added to a 50 mL beaker and stirred at 50°C and 500 rpm for 2 h to obtain a composite film liquid of carboxymethyl hemicellulose, sorbitol, and gallic acid.

[0037] Step (22): Preparation of hemicellulose-based composite film: The composite film solution was ultrasonicated for 10 minutes to remove bubbles, slowly poured into a 3.5 cm × 3.5 cm silica gel mold, and dried in a forced air drying oven at 40°C for 48 hours to obtain a carboxymethyl hemicellulose composite film.

[0038] Example 3

[0039] An embodiment of a method for preparing a third carboxymethyl hemicellulose composite film of the present invention comprises the following steps:

[0040] Step (31): Preparation of a hemicellulose-based composite film liquid. 0.35 g of carboxymethyl hemicellulose with a degree of substitution of 0.46, 12.5 g of deionized water, 0.7 mL of 0.037 g / mL gallic acid, and 0.2 g of sorbitol were sequentially added to a 50 mL beaker and stirred at 50°C and 500 rpm for 2 h to obtain a composite film liquid of carboxymethyl hemicellulose, sorbitol, and gallic acid.

[0041] Step (32): Preparation of hemicellulose-based composite film: The composite film solution was ultrasonicated for 10 minutes to remove bubbles, slowly poured into a 3.5 cm × 3.5 cm silica gel mold, and dried in a forced air drying oven at 40°C for 48 hours to obtain a carboxymethyl hemicellulose composite film.

[0042] Example 4

[0043] An embodiment of a fourth method for preparing a carboxymethyl hemicellulose composite film of the present invention comprises the following steps:

[0044] Step (41): Preparation of a hemicellulose-based composite film liquid. 0.35 g of carboxymethyl hemicellulose with a degree of substitution of 0.59, 12.5 g of deionized water, 0.7 mL of 0.037 g / mL gallic acid, and 0.2 g of sorbitol were sequentially added to a 50 mL beaker and stirred at 50° C. and 500 rpm for 2 h to obtain a composite film liquid of carboxymethyl hemicellulose, sorbitol, and gallic acid.

[0045] Step (42): Preparation of hemicellulose-based composite film: The composite film solution was ultrasonically treated for 10 minutes to remove bubbles, slowly poured into a 3.5 cm × 3.5 cm silica gel mold, and dried in a forced air drying oven at 40°C for 48 hours to obtain a carboxymethyl hemicellulose composite film.

[0046] Comparative Example 1

[0047] The first comparative example of the present invention comprises the following steps:

[0048] Step (51): Preparation of a hemicellulose-based composite film liquid. Hemicellulose, 12.5 g of deionized water, 0.7 mL of 0.037 g / mL gallic acid, and 0.2 g of sorbitol were sequentially added to a 50 mL beaker and stirred at 50° C. and 500 rpm for 2 h to obtain a composite film liquid of hemicellulose, sorbitol, and gallic acid.

[0049] Step (52): Preparation of hemicellulose-based composite film. The composite film solution was ultrasonicated for 10 minutes to remove bubbles, slowly poured into a 3.5 cm × 3.5 cm silica gel mold, and dried in a forced air drying oven at 40°C for 48 hours to obtain a composite film of hemicellulose, sorbitol, and gallic acid.

[0050] Supplementary explanation of the accompanying drawings of the present invention:

[0051] In accompanying drawing 1, the solubility of hemicellulose extracted from moso bamboo under the conditions of substitution degree DS of 0, 0.17, 0.33, 0.46 and 0.59 is compared with the initial state and the state after 10 minutes of ultrasound. The solubility of hemicellulose extracted from moso bamboo (DS=0) in water is poor, and the solution is turbid after 10 minutes of ultrasound, indicating that more hemicellulose is still undissolved. As the degree of carboxymethylation modification of hemicellulose increases, its solubility in water gradually improves. When the substitution degree DS of carboxymethyl hemicellulose is 0.33, after 10 minutes of ultrasound, the solution is only slightly turbid, indicating that most of the carboxymethyl cellulose can be dissolved in water at this time. When the substitution degree DS of carboxymethyl hemicellulose reaches 0.46 and 0.59, it is completely dissolved in water, the solution is clear and transparent, and there is no obvious precipitation at the bottom of the bottle, further illustrating that the solubility of hemicellulose in water is significantly improved after carboxymethylation modification.

[0052] Figure 2 shows images of the composite film of the present invention at degrees of substitution of 0, 0.33, and 0.59, respectively. The composite film prepared with hemicellulose (DS=0) exhibits an uneven surface and low transparency. When carboxymethyl-modified hemicellulose (DS=0.59) is added to the composite film, the surface becomes smooth and flat, with high transparency. Furthermore, the surface smoothness and transparency of the composite film significantly improve with increasing degree of substitution (DS) of carboxymethyl hemicellulose. This is related to the significantly improved hydrophilicity of hemicellulose after carboxymethylation.

[0053] In accompanying drawing 3, a, d are SEM images of the composite film containing hemicellulose, and its surface is rough, which is related to the poor dispersibility and film-forming property of hemicellulose being slightly soluble in water before modification. b, e are SEM images of the composite film containing carboxymethyl hemicellulose (DS=0.33), and its composite film surface roughness is reduced. c, f are SEM images of the composite film containing carboxymethyl hemicellulose (DS=0.59), and its composite film surface roughness is further reduced, indicating that as the degree of substitution DS of carboxymethyl hemicellulose increases, the surface of the composite film becomes smoother and flatter.

[0054] In Figure 4, there are schematic diagrams showing thickness test comparisons and air permeability test comparisons of the composite film of the present invention under the conditions of substitution degrees of 0, 0.17, 0.33, 0.46 and 0.59, respectively. The degree of substitution DS of carboxymethyl hemicellulose has no significant effect on the thickness of the composite film, and the thickness of the composite film is about 0.14 mm. When hemicellulose is added (DS=0), the air permeability of the composite film is 5.03 μm / Pa·s. As the degree of substitution DS of carboxymethyl hemicellulose increases, the air permeability of the composite film decreases significantly. When carboxymethyl hemicellulose with a degree of substitution DS of 0.59 is added, the air permeability of the composite film is 2.60 μm / Pa·s, and the air permeability decreases by 48.31%. This indicates that as the degree of substitution DS increases, the air barrier performance of the composite film is significantly improved.

[0055] Figure 5 shows comparative images of the antibacterial activity of the composite films of the present invention against S bacteria (i.e., Gram-positive bacteria) and against E bacteria (i.e., Gram-negative bacteria) at degrees of substitution of 0, 0.17, 0.33, 0.46, and 0.59, respectively. Composite films containing hemicellulose and carboxymethyl hemicellulose with varying degrees of substitution (DS) all exhibited antibacterial activity against S bacteria, with distinct zones of inhibition appearing around the films. Sorbitol, as a food-grade antibacterial agent, can effectively inhibit bacterial growth. Gallic acid can also inhibit the synthesis of polysaccharides in bacterial biofilms, thereby hindering bacterial growth. As the degree of substitution of carboxymethyl cellulose increases, the diameter of the zone of inhibition around the film increases, indicating that the antibacterial effect of the composite films against S bacteria increases with increasing carboxymethyl hemicellulose substitution. However, the composite films showed no significant inhibitory effect against E bacteria. Overall, the carboxymethyl hemicellulose / sorbitol / gallic acid composite films exhibit moderate antibacterial activity, with superior antibacterial activity against Gram-positive bacteria over Gram-negative bacteria.

[0056] In FIG5 , the diameters of the inhibition zones of carboxymethyl hemicellulose composite films with different degrees of substitution are shown in Table 1 below:

[0057] Table 1 Diameters of inhibition zones of carboxymethyl hemicellulose composite films with different degrees of substitution

[0058] FIG6 shows a comparative test curve of the weight loss of blueberries in a coating group and a blank group (i.e., not wrapped in plastic wrap) using the composite film of the present invention as a preservative film at a degree of substitution of 0 and 0.59, respectively. Compared with the blank group, the weight loss of blueberries after film preservation was significantly improved. During the first four days of storage, the weight loss of blueberries in the blank group and the coating group (DS=0, 0.59) was relatively similar. After 5 days of storage, the weight loss of blueberries in the blank group was 9.67%, while the weight loss of blueberries in the coating group was 9.11% (DS=0) and 8.27% (DS=0.59), respectively, both lower than the weight loss of blueberries in the blank group. As the number of storage days increased, the difference in weight loss between the blank group and the coating group (DS=0, 0.59) became more pronounced. After 9 days of storage, the weight loss rate of blueberries in the blank group was 20.34%, while the weight loss rates of blueberries in the coating group were 16.90% (DS=0) and 15.36% (DS=0.59), respectively, which were significantly lower than those of the blueberries in the blank group. This indicates that the composite film of the present invention has a certain effect on preserving blueberries, and the preservation effect of the carboxymethyl hemicellulose composite film is better than that of the unmodified hemicellulose composite film.

[0059] In Figure 6, there is a record table showing the preservation effects of the coating group and the blank group on blueberries.

[0060] Table 2: Fresh-keeping effect of coating group and blank group on blueberry

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A carboxymethyl hemicellulose composite film, characterized in that The invention comprises 95 to 100 parts by weight of carboxymethyl hemicellulose, 1 to 5 parts by weight of gallic acid and 50 to 60 parts by weight of sorbitol, wherein the carboxymethyl hemicellulose is obtained by etherifying bamboo hemicellulose with chloroacetic acid under alkaline conditions, and the degree of substitution of the carboxymethyl hemicellulose is 0.17 to 0.

59.

2. A method for preparing a carboxymethyl hemicellulose composite film according to claim 1, characterized in that: The steps include: Step 1, mixing carboxymethyl hemicellulose with deionized water, gallic acid and sorbitol in sequence to obtain a composite film liquid; Step 2: slowly pour the composite film liquid into the mold and dry it to obtain the desired composite film.

3. The method for preparing the carboxymethyl hemicellulose composite film according to claim 2, characterized in that: In the step 2, before drying to form a film, the composite membrane liquid is subjected to ultrasonic treatment for more than 10 minutes to remove bubbles.

4. The method for preparing the carboxymethyl hemicellulose composite film according to claim 2, characterized in that: In the step 2, the composite film is dried in a forced air drying oven at 40° C. for 48 hours.

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