Degradable PVA composite material based on deep eutectic solvent plasticized microcrystalline cellulose and preparation method thereof

Abstract

The invention provides a degradable PVA composite material based on deep eutectic solvent plasticized microcrystalline cellulose and a preparation method of the degradable PVA composite material, and relates to the field of biodegradable composite materials. The preparation method comprises the following steps: stirring citric acid and choline chloride at 70 DEG C for 15-30 minutes to form transparent liquid, so as to obtain DES liquid; boiling MCC in water for 2-3 hours to remove impurities, and drying at 65-70 DEG C until the weight is constant; mCC is added into DES, and the mixture is placed in an oil bath at 85-90 DEG C to be stirred for 90-100 min; diluting, performing suction filtration, washing and drying; dissolving PVA in water to prepare a solution, and stirring at 60-70 DEG C until the solution is transparent to obtain a PVA solution; adding the plasticized MCC into the PVA solution, and uniformly stirring to obtain mixed slurry; pouring the mixed slurry into a mold; and drying to obtain the PVA composite membrane material. The DES is used as a solvent to plasticize the MCC, so that the affinity of the MCC and the PVA is improved, and the prepared PVA composite material is good in interface and excellent in performance.

Description

Technical Field

[0001] This invention relates to the field of biodegradable composite materials, and more specifically, to a biodegradable PVA composite material based on deep eutectic solvent plasticized microcrystalline cellulose and its preparation method. Background Technology

[0002] Polyvinyl alcohol (PVA), a typical biodegradable water-soluble polymer, possesses excellent film-forming properties, biocompatibility, and mechanical properties, and is widely used in packaging, biomedical materials, and other fields. Microcrystalline cellulose (MCC) is a preferred natural reinforcing filler due to its wide availability, high rigidity, and biodegradability. However, the significant polarity difference and interfacial incompatibility between MCC and PVA limit their uniform dispersion and performance in blend systems.

[0003] Traditional physical mixing methods or chemically modified MCCs have problems such as harsh reaction conditions, high costs, or poor controllability. Summary of the Invention

[0004] The purpose of this invention is to provide a biodegradable PVA composite material based on deep eutectic solvent plasticization of microcrystalline cellulose. DES is used as a solvent to plasticize MCC, which improves the affinity between MCC and PVA. The resulting PVA composite material has good interface and excellent performance.

[0005] Another objective of this invention is to provide a method for preparing a biodegradable PVA composite material based on deep eutectic solvent plasticized microcrystalline cellulose, using DES as a solvent to plasticize and modify MCC, and the modified MCC is used to prepare PVA. The preparation process is simple and the reaction conditions are mild.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] On one hand, embodiments of the present invention provide a biodegradable PVA composite material based on deep eutectic solvent-plasticized microcrystalline cellulose, which includes the following steps:

[0008] Preparation of S1, DES: Citric acid and choline chloride are stirred at 70°C for 15-30 minutes until a transparent liquid is formed, thus obtaining DES liquid;

[0009] S2, MCC pretreatment: Boil the MCC in water for 2-3 hours to remove impurities, and dry it at 65-70℃ to constant weight;

[0010] S3, MCC plasticizing treatment: Add MCC to DES, stir in an oil bath at 85-90℃ for 90-100 min; dilute, filter, wash, and dry;

[0011] S4, PVA solution preparation and blending: PVA is dissolved in water to make a solution, and stirred at 60-70℃ until transparent to obtain a PVA solution; then the plasticized MCC is added to the PVA solution and stirred evenly to obtain a mixed slurry;

[0012] S5, Molding and Drying: Pour the mixed slurry into the mold; dry it to obtain the PVA composite film material.

[0013] In some embodiments of the present invention, in step S1, the molar ratio of citric acid to choline chloride is 1:1.

[0014] In some embodiments of the present invention, in step S3, the mass ratio of DES to MCC is 7:1.

[0015] In some embodiments of the present invention, in step S4, the mass fraction of the PVA solution is 4-6%.

[0016] On the other hand, embodiments of the present invention provide a biodegradable PVA composite material based on deep eutectic solvent plasticized microcrystalline cellulose, which is prepared by the above method.

[0017] In PVA composite materials, the amounts of each raw material, by mass fraction, are as follows: MCC 5%-20wt%, DES 35-50wt%, PVA 10wt%, and the remainder is water.

[0018] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0019] The method for preparing PVA composite materials provided by this invention utilizes DES to plasticize MCC, making it easier to disperse in the PVA matrix; it improves the mechanical strength of the composite material, with tensile strength increasing by 20-50%; it significantly improves thermal stability, making it suitable for packaging, electrospinning, hot pressing, and other applications; this method is green and environmentally friendly, operates under mild conditions, requires no complex reaction system, and has good prospects for industrialization.

[0020] Secondly, the preparation method is simple, the reaction conditions are mild, no high temperature and high pressure are required, and the requirements for production equipment are low. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1SEM images showing the swelling of cellulose in DES solutions with different molar ratios;

[0023] Figure 2 Images showing the swelling of cellulose in DES solutions with different molar ratios;

[0024] Figure 3 Heat flow temperature curves for different samples;

[0025] Figure 4 Thermogravimetric analysis graphs of different samples;

[0026] Figure 5 Images of DES solutions with different molar ratios. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to specific embodiments.

[0029] This invention provides a biodegradable PVA composite material based on deep eutectic solvent-plasticized microcrystalline cellulose, comprising the following steps:

[0030] S1, Preparation of DES: Weigh citric acid and choline chloride according to a molar ratio of 1:1, stir at 70℃ for 15-30 minutes until completely dissolved to form a transparent liquid, and obtain DES liquid.

[0031] S2, MCC pretreatment: Boil the MCC in water for 2-3 hours to remove impurities, and dry it at 65-70℃ to constant weight;

[0032] S3, plasticizing treatment of MCC: Add MCC to DES at a mass ratio of 7:1, stir in an oil bath at 85-90℃ for 90-100 min; dilute, filter, wash alternately with water and ethanol, dry at 65℃, and set aside.

[0033] S4, PVA solution preparation and blending: PVA is dissolved in water to make a solution, and stirred at 60-70℃ until transparent to obtain a PVA solution; then the plasticized MCC is added to the PVA solution with a mass fraction of 4-6%, and stirred evenly to obtain a mixed slurry;

[0034] S5, Molding and Drying: Pour the mixed slurry into the mold; dry at room temperature or at a constant temperature of 60℃ to obtain the PVA composite film material.

[0035] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0036] Example 1

[0037] The PVA composite material of this embodiment was prepared according to the following method:

[0038] Preparation of S1 and DES: Weigh citric acid and choline chloride in a molar ratio of 1:1, and stir at 70°C for 15-30 minutes until completely melted to form a transparent liquid.

[0039] S2, MCC pretreatment: Boil the MCC in water for 2 hours to remove impurities, and dry it at 65℃ to constant weight.

[0040] Plasticizing treatment of S3 and MCC: Add DES to MCC at a ratio of 7:1 (by mass), place in an oil bath at 85°C and stir for 90 minutes; after treatment, dilute and filter, wash alternately with water and ethanol, and dry at 65°C for later use.

[0041] S4, PVA solution preparation and blending: Set up multiple groups (MCC content 0-100wt%) according to a total mass ratio of 2.0g of PVA and MCC; dissolve PVA in water to make a 4% solution, stir at 60℃ until transparent; add plasticized MCC to the PVA solution and stir evenly.

[0042] S5, Molding and Drying: Pour the slurry into the mold; dry at room temperature or at a constant temperature of 60℃ to obtain the composite membrane material.

[0043] Example 2

[0044] Effect of DES solution plasticizing microcrystalline cellulose with different molar ratios on the properties of PVA composites

[0045] I. Experimental Objective

[0046] The study investigated the plasticizing effect of citric acid / choline chloride DES solvent on microcrystalline cellulose (MCC) and systematically characterized MCC treated with different molar ratios (7:3, 3:2, 1:1, 2:3, 3:7) to optimize its application performance in biodegradable materials.

[0047] II. Experimental Materials and Equipment

[0048] 1. Materials:

[0049] Microcrystalline cellulose Type 101 (MCC), analytical grade; citric acid, analytical grade, dried before use; choline chloride, analytical grade, dried before use; deionized water or distilled water, for pretreatment.

[0050] 2. Main equipment: magnetic stirrer, heating plate, oil bath (temperature controlled at 80-85℃); vacuum filter / vacuum filter (for cellulose extraction), constant temperature oven (65℃ drying), slanted flask, analytical balance, glassware, stirring rod, etc.; characterization instruments such as FTIR, XRD, SEM, TGA / DSC, etc.

[0051] III. Experimental Procedure

[0052] 1. DES Preparation: Weigh out citric acid and choline chloride according to different molar ratios (7:3, 3:2, 1:1, 2:3, 3:7). Specific steps: Before use, citric acid and choline chloride should be dried at 50-60℃ for at least 2 hours to remove adsorbed water. Choline chloride is highly hygroscopic; the relative humidity of the operating environment should be <60%. Stir and melt at 70℃ until completely liquefied to form transparent DES. The solubility of different molar ratios without adding water is shown in the attached figure. Figure 2 As shown, for opaque materials, a small amount of water, ≤5wt%, can be added. Figure 2 It can be concluded that in systems with different proportions of choline chloride and citric acid, DES with a higher proportion of choline chloride is more transparent but less effective in promoting the swelling of cotton linters. Conversely, increasing the proportion of citric acid is more conducive to promoting the swelling of cotton linters. However, an excessively high proportion of citric acid results in a large number of residual crystal particles in the DES, affecting the transparency of the DES mixed solution.

[0053] Prepare 50 mL of DES; Table 1 shows the raw material mass required for each of the five conventional molar ratios (with the total number of moles fixed at 0.2 mol).

[0054] Table 1

[0055]

[0056] Table 2

[0057]

[0058] Converted to volume (assuming water density is 1 g / mL): Add a maximum of 1.56-1.76 mL of deionized water. Initially add no more than 1 mL of water, observing changes in transparency as you add. Adding excessive water will reduce the DES melting point control capability, affect swelling properties, and impair the accuracy of structural characterization.

[0059] 2. MCC pretreatment: Weigh 3g of MCC, boil it in water for 2 hours, wash it with deionized water, and dry it at 65℃ to constant weight.

[0060] 3. MCC plasticizing treatment: Take 0.5g of MCC from each group, add 3.5g of the corresponding DES, and place in an oil bath at 85℃ with stirring for 90 minutes. Vacuum is applied but heating is not performed. The swelling of cellulose in each group is then observed, and the results are shown in the attached figure. Figure 1 As shown. From Figure 1 It can be concluded that DES with a high choline chloride ratio exhibits better uniformity and stability, and has a smoother surface in SEM images, while DES with a high citric acid ratio may show crystal precipitation and an uneven granular structure in SEM images.

[0061] IV. Extraction methods of plasticized cellulose

[0062] 1. Cooling and sedimentation: Cool the reaction flask to room temperature and let it stand or centrifuge at low speed to precipitate cellulose.

[0063] 2. Dilution and Filtration: Dilute with 20 mL of deionized water and filter. Wash three times alternately with water and ethanol to remove residual DES. Dry the filter paper or transfer it to a glass dish and dry at 65°C for 12 hours. Grind the cellulose sample through a 200-mesh sieve (average particle size 20 μm, DP≈200) and dry it for later use. Reserve 3 g for tableting.

[0064] V. Preparation of PVA composite film materials

[0065] PVA solution preparation and blending: PVA is dissolved in water to prepare a solution (mass fraction 4%), and stirred at 60-70℃ until transparent to obtain a PVA solution; then, plasticized MCC is added to the PVA solution and stirred evenly to obtain a mixed slurry;

[0066] Molding and drying: Pour the mixed slurry into a mold; dry at a constant temperature of 60℃ to obtain the PVA composite film material.

[0067] VI. Performance Testing

[0068] PVA composite film materials prepared in different batches 1-7 were tested for their mechanical properties according to the test methods in GB / T 1040.1-2006 / ISO 527-1:1993; "Determination of tensile properties of plastics - Part 1: General", with a common material speed of 5 mm / min. The results are shown in Table 3.

[0069] Table 3

[0070] Mole ratio Batch 1 Batch 2 Batch 3 Batch 4 Batch 5 Batch 6 Batch 7 Blank group 55 54 59 40 57.5 48 47 7：3 58 60.5 56 55 58 61 62 3：2 56 62 60 66 68 64 59 1：1 109 112 108 107 114 121 118 2：3 132 140 138 132 129 131 133 3：7 86 94 82 88 83 84 99

[0071] Table 4 Tensile properties (citric acid to choline chloride molar ratio 7:3)

[0072]

[0073] Table 5 Tensile properties (molar ratio 3:2)

[0074]

[0075]

[0076] Table 6 Tensile properties (citric acid to choline chloride molar ratio 1:1)

[0077] batch Maximum force (N) Elongation (%) Tensile strength 1 126.716 3.624 10.24 2 100.535 6.662 8.932 3 65.813 9.645 5.318 4 89.775 3.753 7.255 5 110.063 3.385 8.894 6 89.087 3.901 7.199 7 69.146 9.785 5.588

[0078] Table 7 Tensile properties (citric acid to choline chloride molar ratio 2:3)

[0079] batch Maximum force (N) Elongation (%) Tensile strength 1 142.039 6.379 11.478 2 155.556 8.266 12.57 3 139.916 6.582 11.306 4 137.889 7.464 11.143 5 150.224 8.537 12.139 6 106.611 4.817 8.618

[0080] Table 8 Tensile properties (citric acid to choline chloride molar ratio 3:7)

[0081] batch Maximum force (N) Elongation (%) Tensile strength 1 130.259 13.52 10.526 2 111.704 6.381 9.027 3 103.377 5.97 8.354 4 107.182 6.092 8.661 5 82.004 5.115 6.627 6 135.124 25.602 10.919

[0082] Table 9 Tensile Properties (Blank Group)

[0083] batch Maximum force (N) elongation Tensile strength 1 117.528 3.335 9.497 2 115.903 7.985 9.366 3 168.116 6.605 13.585 4 116.754 4.991 9.435 5 180.321 10.488 14.545 6 143.946 7.379 11.632 7 116.082 7.872 9.38

[0084] The blank group refers to PVA composite membrane material without the addition of modified MCC. The maximum tensile force is the tensile force at which the membrane breaks during the tensile test.

[0085] The tensile properties in Table 3-9 are the test results of the mechanical properties of PVA / MCC composite films under different molar ratios.

[0086] Each group has multiple repeated spline tests, and a final average is calculated. Maximum force refers to the maximum force a material can withstand before it breaks; elongation refers to the material's extension rate before it breaks; tensile strength is the maximum force divided by the cross-sectional area, representing the strength of its tensile ability.

[0087] From Table 3-9, we can conclude that: 1. Blank group (without DES): maximum force range: -115–180N; elongation is low: average 7.6%; tensile strength is high: average 11.3MPa. This indicates that the film is brittle but hard, with poor toughness and high rigidity.

[0088] In the 2.7:3 molar ratio group, the maximum force increased slightly, with some samples reaching over 130N, and the elongation was significantly improved: averaging 24.8%. The tensile strength decreased slightly: averaging 9.8MPa. This indicates that the plasticizing effect is beginning to show, the ductility is improved, the strength is slightly reduced, but the overall performance is improved.

[0089] The 3.3:2 molar ratio group had a maximum force similar to or slightly lower than the blank group, moderate elongation (average 7.3%), and tensile strength (average 7.1 MPa). This indicates that the plasticizer was not ideal, the flexibility was not further improved, and the performance was mediocre.

[0090] 4.1:1 molar ratio group, the maximum force fluctuates greatly, and some samples are lower (65–126 N), the elongation is lower: average 6.2%, tensile strength: average 7.7 MPa. This indicates that the DES ratio is critical, the system may be unstable, and the membrane structure is non-uniform.

[0091] The 5.2:3 molar ratio group has the highest maximum force (up to 155N), moderate elongation (average 7%), and the best tensile strength (average 11.2MPa), making it the group with the best tensile strength. This indicates that the PVA and MCC composite structure is the most ideal under the 2:3 molar ratio.

[0092] The 6.3:7 molar ratio group has moderate maximum force and tensile strength, high elongation (average 10.4%), and tensile strength (9 MPa), indicating that while excessive DES improves flexibility, it reduces strength, resulting in a balanced performance.

[0093] Example 3

[0094] To determine the optimal mass ratio between citrate-choline chloride (DES) and microcrystalline cellulose (MCC), the following experiment was designed to screen the optimal ratio by evaluating swelling effect, processing uniformity, and post-plasticization properties.

[0095] I. Experimental Objective

[0096] By setting different DES:MCC mass ratios (mass ratio g / g), the optimal ratio of swelling and plasticizing effect can be determined for subsequent blending, electrospinning, or hot pressing applications.

[0097] 1. Setting experimental variables

[0098] Variable 1: Mass ratio setting (gDES / gMCC), with a fixed MCC feed amount of 0.5g, set the following 5 sets of DES addition amounts:

[0099] Table 3

[0100] serial number DES addition amount (g) Mass ratio (DES: MCC) A 1.5 3:1 B 2.5 5:1 C 3.5 7:1 D 4.5 9:1 E 6.0 12:1

[0101] II. Experimental Procedure

[0102] 1. Material preparation: Citric acid-choline chloride DES was prepared in a 1:1 molar ratio; MCC was pretreated (washed with boiling water and dried);

[0103] 2. Swelling experiment: Add 0.5g of MCC to a 100mL slanted flask; add different masses of DES (e.g., 3.5g corresponds to a mass ratio of 7:1); heat to an oil bath at 85℃ and stir for 90min; observe the swelling state (swelling rate, color, uniformity) after cooling, as shown in Figure 5.

[0104] Example 4

[0105] The effect of MCC content variation on the properties of PVA composites in MCC / PVA composite systems

[0106] I. Experimental Objective

[0107] This study explores the effects of varying MCC content (0%, 20%, 40%, 60%, 80%, 100%) on the structure and performance of the composite material, under the condition that the total mass of MCC and PVA remains constant. The optimal mass ratio of DES selected in previous experiments is used to plasticize MCC, and the compatibility and structural changes of MCC-PVA are investigated.

[0108] II. Setting Experimental Variables

[0109] With a fixed total mass of MCC + PVA = 2.0g, 6 groups of experiments were set up. The MCC ratio is as follows, and the amount of DES added is set to the optimal mass ratio (7:1 = DES:MCC).

[0110] Table 4

[0111] serial number MCC content (wt%) MCC mass (g) PVA mass (g) A 0 0 2 B 20 0.4 1.6 C 40 0.8 1.2 D 60 1.2 0.8 E 80 1.6 0.4 F 100 2 0

[0112] III. Experimental Procedure

[0113] PVA solution preparation: Weigh 1799g of PVA according to the required mass, add water (approximately 4% w / v concentration), stir at 95℃ to dissolve and form a uniform and transparent PVA solution, then cool and set aside.

[0114] MCC pretreatment and plasticizing: Weigh the dried MCC according to the set MCC mass;

[0115] Add DES (at a mass ratio of 7:1, e.g., 5.6g DES for 0.8g MCC), stir in an oil bath at 85℃ for 90min to allow swelling; after cooling, dilute with water, filter, wash, and dry to obtain plasticized MCC;

[0116] MCC and PVA blending: Add the dried MCC to the PVA solution and stir at 60–70℃ for 30 minutes to form a homogeneous mixture; if it is a full MCC group (100%), it can be directly dispersed with DES treatment solution.

[0117] Film-forming or molding process: Pour the mixture into a petri dish or mold and dry it, such as drying at 60°C to form a film.

[0118] Example 5

[0119] Plasticizing behavior of PVA with different degrees of polymerization and DES with citrate-choline chloride and its effect on the processing performance of composite with MCC

[0120] I. Experimental Variable Design

[0121] Table 5

[0122] experimental group PVA aggregation degree Degree of alcoholysis Sample number A 500 98-99 PVA0599 B 1000 98-99 PVA1099 C 1700 98-99 PVA1799 D 2400 98-99 PVA2499 E 2800 98-99 PVA2899

[0123] II. Experimental Materials

[0124] PVA (different degrees of polymerization, degree of alcoholysis ≥95%), citric acid (AR), choline chloride (AR), microcrystalline cellulose Type 101 (MCC), deionized water, laboratory glassware, stirring rods, magnetic stirrers, constant temperature ovens, vacuum dryers, hot press molds, electrospinning equipment, etc.

[0125] III. Experimental Procedure

[0126] Step 1: DES Configuration

[0127] 1. Weigh out 5 mmol of citric acid and choline chloride in a 1:1 molar ratio (corresponding to 0.96 g of citric acid and 0.70 g of choline chloride).

[0128] 2. Mix the two in a dry beaker and heat at 70-80℃ with magnetic stirring for 15-20 minutes to form a transparent DES liquid.

[0129] 3. Cool to room temperature before use.

[0130] Step 2: Preparation of PVA aqueous solution

[0131] 1. Weigh 10g of PVA sample and add it to 100mL of deionized water;

[0132] 2. Heat and stir at 90-95℃ until completely dissolved to form a 10wt%-23wt% transparent PVA aqueous solution;

[0133] 3. Cool to room temperature before use.

[0134] Step 3: MCC Preprocessing

[0135] 1. Take 0.5g of MCC and add it to 3.5g of prepared DES. Soak the mixture in an oil bath at 85℃ for 90min.

[0136] 2. After cooling, dilute with water, filter and wash several times to remove residual DES;

[0137] 3. Vacuum dry to constant weight for later use.

[0138] Step 4: Preparation of PVA-MCC blends

[0139] 1. Add dried MCC (content 2%, 3%, 5%, etc.) to the PVA solution and mix by ultrasonication and high-speed shearing for 30 min (MCC content 5wt%).

[0140] 2. Add an equal mass of DES as a plasticizer, and stir for another 15 minutes to form a uniformly mixed solution;

[0141] IV. Processing Methods and Performance Testing

[0142] (1) Hot pressing and thermoplastic processing

[0143] Pour the mixture into the mold and pre-dry at 80℃ for 8 hours to remove most of the moisture; use a hot press molding machine, set the temperature to 130-150℃, press for 5 minutes, and then cool and demold.

[0144] (2) Electrospinning

[0145] Dilute the PVA-MCC-DES system to a suitable concentration (8-10wt%); set the voltage to 15-20kV, the collection distance to 15cm, and the spinning speed to 0.2-0.5mL / h; collect the membrane material and vacuum dry it.

[0146] Thermogravimetric analysis was performed on the above samples, as shown in the attached figure. Figure 4 As shown, the thermogravimetric analysis (TGA) plot illustrates the mass change trend of different samples during the heating process. The X-axis represents temperature (°C), and the Y-axis represents the percentage of remaining mass (%). Figure 4 It includes the following 6 groups of samples:

[0147] MCC (untreated microcrystalline cellulose), MCC11, MCC23, MCC32, MCC37, and MCC73 are MCC samples treated with different molar ratios of DES (citric acid:choline chloride).

[0148] from Figure 4 It can be concluded that the thermal decomposition behavior of each sample is similar, mainly divided into two stages: the initial stage (room temperature - 280℃): the mass loss is minimal, mainly due to the volatilization of moisture or residual low-boiling-point substances; the main decomposition stage (approximately 290–370℃): this is the main pyrolysis stage of microcrystalline cellulose, characterized by a sharp decrease in mass, which belongs to the cellulose skeleton breakage and carbonization reaction; the residual mass (approximately 380–400℃): basically tends to be stable, indicating that the carbonization residue is stable.

[0149] Differences in thermal stability: MCC73 (black line) started degrading slightly earlier, which may indicate a decrease in thermal stability after treatment; MCC23 and MCC32 had slightly higher degradation initiation temperatures, indicating that they may have relatively better thermal stability; the original MCCs had similar or slightly worse degradation temperatures compared to most treated samples, indicating that DES treatment had no significant effect on thermal stability or only slightly improved it.

[0150] Residual mass differences: The residual mass of each group is similar, basically around 10%, indicating that the main decomposition mechanism is the same.

[0151] The main decomposition temperature range is between 290 and 370 °C, which is consistent with the thermal decomposition characteristics of microcrystalline cellulose. DES treatment did not significantly reduce thermal stability, and some samples such as MCC23 and MCC32 showed higher thermal stability. MCC73 had slightly poor thermal stability, possibly due to its higher molar ratio of citric acid leading to over-plasticization or structural damage. That is, appropriate DES treatment may improve thermal stability.

[0152] In summary, the method for preparing PVA composite materials provided in this invention utilizes DES to plasticize MCC, making it easier to disperse in the PVA matrix; it improves the mechanical strength of the composite material, with tensile strength increasing by 20–50%; it significantly improves thermal stability, making it suitable for packaging, electrospinning, hot pressing, and other applications; this method is green and environmentally friendly, operates under mild conditions, requires no complex reaction system, and has good prospects for industrialization.

[0153] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a biodegradable PVA composite material based on deep eutectic solvent plasticized microcrystalline cellulose, characterized in that, It includes the following steps: Preparation of S1, DES: Citric acid and choline chloride are stirred at 70°C for 15-30 minutes until a transparent liquid is formed, thus obtaining DES liquid; S2, MCC pretreatment: Boil the MCC in water for 2-3 hours to remove impurities, and dry it at 65-70℃ to constant weight; S3, plasticizing treatment of MCC: Add MCC to DES and stir in an oil bath at 85-90℃ for 90-100 minutes; Dilution, filtration, washing, drying; S4, PVA solution preparation and blending: PVA is dissolved in water to make a solution, and stirred at 60-70℃ until transparent to obtain a PVA solution; then the plasticized MCC is added to the PVA solution and stirred evenly to obtain a mixed slurry; S5, Molding and Drying: Pour the mixed slurry into the mold; dry it to obtain the PVA composite film material.

2. The method for preparing biodegradable PVA composite material based on deep eutectic solvent-plasticized microcrystalline cellulose according to claim 1, characterized in that, In step S1, the molar ratio of citric acid to choline chloride is 1:

1.

3. The method for preparing biodegradable PVA composite material based on deep eutectic solvent-plasticized microcrystalline cellulose according to claim 1, characterized in that, In step S3, the mass ratio of DES to MCC is 7:

1.

4. The method for preparing biodegradable PVA composite material based on deep eutectic solvent-plasticized microcrystalline cellulose according to claim 1, characterized in that, In step S4, the mass fraction of the PVA solution is 4-6%.

5. A biodegradable PVA composite material based on deep eutectic solvent-plasticized microcrystalline cellulose, characterized in that, It is prepared by the method described in any one of claims 1-4.

6. The biodegradable PVA composite material based on deep eutectic solvent-plasticized microcrystalline cellulose according to claim 1, characterized in that, The mass fraction of MCC is 5%-20wt%, the mass fraction of DES is 35-50wt%, the mass fraction of PVA is 10wt%, and the balance is water.

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