A method for preparing nanocellulose by treating bamboo shoot shell with a eutectic solvent

Abstract

The application discloses a method for preparing nanocellulose by treating bamboo shoot shell through a eutectic solvent, and comprises the following steps: S1, configuration of the eutectic solvent: after uniformly mixing a first component, a second component and a third component, the mixture is heated and stirred to obtain a ternary eutectic solvent; S2, configuration of a cosolvent: after uniformly mixing benzyl tripropyl ammonium hydroxide, 1'3-bishydroxymethyl urea and water, the mixture is heated and stirred to obtain the cosolvent; S3, preparation of nanocellulose: after mixing pretreated bamboo shoot shell, the ternary eutectic solvent and the cosolvent, the mixture is heated and stirred, after the reaction is completed, the mixture is washed with water, filtered, dried, and the obtained crude cellulose is configured into a suspension, and then ultrasonic treatment, high-pressure homogenization and freeze-drying are carried out to obtain nanocellulose. The nanocellulose obtained through the method has a high yield (88.36%), a high proportion of cellulose (90.19%) and a size of 58.78 nm.

Description

Technical Field

[0001] This invention relates to the field of cellulose technology, and in particular to a method for preparing nanocellulose by treating bamboo shoot shells with a eutectic solvent. Background Technology

[0002] Nanocellulose, with its unique lignin composition and nanoscale properties, shows broad application prospects in various fields such as automotive lightweighting, papermaking, food packaging, textiles, biomedicine, and lignin modification. It can not only effectively reduce the weight of automotive components and improve paper performance, creating high-strength and high-transparency food packaging, but also endow textiles with multiple functional properties and serve as a carrier for biodegradable materials and drug delivery systems in the biomedical field. Furthermore, nanocellulose has demonstrated significant potential in the field of flexible electronics in terms of electrochemical performance and mechanical stability.

[0003] Bamboo shoots are an important green food and economic crop. my country is rich in bamboo shoot resources, with the southern mountainous area of ​​Anhui Province being one of the main production areas. During the annual bamboo shoot processing season, large quantities of processing byproducts accumulate, going unused and resulting in resource waste. Bamboo shoot husks, a byproduct of bamboo shoot processing, account for 30%-40% of the whole bamboo shoot and are mainly composed of cellulose, hemicellulose, and lignin. Using them as a raw material for extracting nanocellulose represents the utilization of agricultural waste and has a positive role in promoting green environmental protection.

[0004] Currently, methods for extracting nanocellulose from bamboo shoot shells include physical, chemical, biological, and enzymatic methods. Among the physical methods, high-pressure homogenization extraction is the most commonly used, but it has high equipment requirements, high costs, and high energy consumption. Chemical methods mainly use acids, alkalis, and TEMPO for extraction, but the corrosiveness of the solvents makes later recovery impossible and causes significant environmental pollution. Biological methods degrade cellulose in bamboo shoot shells through microbial fermentation, but the operating conditions are complex. Enzymatic methods, while simple to operate and environmentally friendly, have high requirements for reaction solvents and ambient temperature, long reaction times, and high costs. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a method for preparing nanocellulose by treating bamboo shoot shells with a eutectic solvent.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing nanocellulose by treating bamboo shoot shells with a eutectic solvent includes the following steps: S1. Preparation of the eutectic solvent: After the first component, the second component, and the third component are mixed evenly, the mixture is stirred and heated to obtain a ternary eutectic solvent. S2. Preparation of co-solvent: Benzyltripropylammonium hydroxide, 1',3-dihydroxymethylurea, and water are mixed evenly, stirred, and heated to obtain a cosolvent; S3. Preparation of nanocellulose: Pretreated bamboo shoot shells, ternary eutectic solvent, and co-solvent are mixed, stirred, and heated. After the reaction is complete, the mixture is washed with water, filtered, and dried to obtain crude cellulose. The crude cellulose is then prepared into a suspension, sonicated, homogenized under high pressure, and freeze-dried to obtain nanocellulose.

[0007] Preferably, the first component is choline chloride, the second component is glycerol or oxalic acid, and the third component is any one of aluminum chloride hexahydrate, ferric chloride hexahydrate, and zinc chloride hexahydrate.

[0008] Preferably, the molar ratio of the first component, the second component, and the third component is 1:1:(0.1-0.3).

[0009] Preferably, the mass ratio of benzyltripropylammonium hydroxide, 1'3-dihydroxymethylurea, and water is 1:1:(10-20).

[0010] The preferred method for pre-treating bamboo shoot shells is as follows: Clean the bamboo shoot shells, dry them, cut them, and crush them through an 80-mesh sieve. This is the original sample, referred to as OS. OS was mixed with deionized water at a mass ratio of 1:10 and stirred continuously at 90°C for 2 hours at a speed of 800 rpm. The mixture was then filtered through a 200-mesh sieve. The solid insoluble matter was placed in an oven and dried at 60°C for 5 hours. The pre-treated dried powder was mixed with a 1% NaOH solution at a mass ratio of 1:10 and stirred continuously at 90°C for 2 hours at a speed of 800 rpm. After stirring, the mixture was filtered through a 200-mesh sieve and washed with deionized water until the pH of the filtrate was close to neutral. The solid was then dried at 60°C for 5 hours and subsequently pulverized through an 80-mesh sieve to obtain the pre-treated bamboo shoot shell, abbreviated as PS.

[0011] Preferably, the mass ratio of the pretreated bamboo shoot shell, ternary eutectic solvent, and co-solvent is (1-10):100:(10-20).

[0012] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a ternary eutectic solvent and a co-solvent in synergistic action for the extraction of nanocellulose. Compared to existing binary eutectic solvents, this invention introduces a third component, a metal salt, which, through metal coordination, improves the removal rate of lignin and hemicellulose, thereby increasing the yield of nanocellulose from bamboo shoot shells. Smaller nanocellulose crystals can be obtained at lower temperatures in a shorter time. Compared to binary eutectic solvents, the ternary eutectic solvent has a lower eutectic point, which can improve the reaction rate and yield. Because of its more components, the ternary eutectic solvent can reach its melting point at low temperatures, exhibiting better conductivity and solubility, and facilitating subsequent solvent recovery and reuse.

[0013] 2. This invention also introduces benzyltripropylammonium hydroxide and 1'3-dihydroxymethylurea. The hydroxide ions on benzyltripropylammonium hydroxide can form hydrogen bonds with the hydroxyl groups on cellulose, thereby changing the original intermolecular and intramolecular hydrogen bonds of cellulose. The amino and hydroxyl groups on the 1'3-dihydroxymethylurea molecule can form hydrogen bonds with benzyltripropylammonium hydroxide, and then the complex hydrated ions formed together with water molecules coat the surface of the cellulose molecular chain, thereby preventing the aggregation of cellulose molecular chains and promoting the dispersion of cellulose.

[0014] 3. The nanocellulose obtained by the method of the present invention has a high yield (88.36%), a high cellulose content (90.19%), and a size of up to 58.78 nm. Attached Figure Description

[0015] Figure 1 This is a transmission electron microscope image of Example 1 (CGF); Figure 2 This is a transmission electron microscope image of Example 2 (COF); Figure 3 This is a transmission electron microscope image of Example 3 (COA); Figure 4 This is a transmission electron microscope image of Example 4 (COZ). Detailed Implementation

[0016] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods.

[0017] The method for pre-treating bamboo shoot shells is as follows: Clean the bamboo shoot shells, dry them, cut them, and crush them through an 80-mesh sieve. This is the original sample, referred to as OS. OS was mixed with deionized water at a mass ratio of 1:10 and stirred continuously at 90°C for 2 hours at a speed of 800 rpm. The mixture was then filtered through a 200-mesh sieve. The solid insoluble matter was placed in an oven and dried at 60°C for 5 hours. The pre-treated dried powder was mixed with a 1% NaOH solution at a mass ratio of 1:10 and stirred continuously at 90°C for 2 hours at a speed of 800 rpm. After stirring, the mixture was filtered through a 200-mesh sieve and washed with deionized water until the pH of the filtrate was close to neutral. The solid was then dried at 60°C for 5 hours and subsequently pulverized through an 80-mesh sieve to obtain the pre-treated bamboo shoot shell, abbreviated as PS. Example 1

[0018] A method for preparing nanocellulose by treating bamboo shoot shells with a eutectic solvent, characterized by comprising the following steps: S1. Preparation of the eutectic solvent: Choline chloride, glycerol, and ferric chloride hexahydrate were mixed evenly in a molar ratio of 1:1:0.2 and stirred at 80°C until a uniform and transparent solution was obtained, thus yielding a ternary eutectic solvent. S2. Preparation of co-solvent: Benzyltripropylammonium hydroxide, 1'3-dihydroxymethylurea and water were mixed evenly in a mass ratio of 1:1:15 and stirred at 60°C until a uniform and transparent solution was obtained to obtain a cosolvent. S3. Preparation of nanocellulose: Pretreated bamboo shoot shells, ternary eutectic solvent, and co-solvent were mixed in a mass ratio of 5:100:15, stirred at 90°C for 2 hours, washed with water and filtered, and dried at 60°C to obtain crude cellulose. The crude cellulose was prepared into a 0.5 wt% suspension, ultrasonicated at 700 W for 30 min, and homogenized under high pressure at 400 MPa for 5 min to obtain nanocellulose suspension. The nanocellulose, abbreviated as CGF, was freeze-dried using a freeze dryer. Example 2

[0019] The difference between this embodiment and the previous embodiment is as follows: Choline chloride, oxalic acid, and ferric chloride hexahydrate were mixed evenly in a molar ratio of 1:1:0.2 and stirred at 80°C until a uniform and transparent solution was obtained, thus yielding a ternary eutectic solvent. The rest is exactly the same as in Example 1; The resulting nanocellulose is abbreviated as COF. Example 3

[0020] The difference between this embodiment and the previous embodiment is as follows: Choline chloride, oxalic acid, and aluminum chloride hexahydrate were mixed evenly in a molar ratio of 1:1:0.2 and stirred at 80°C until a uniform and transparent solution was obtained, thus yielding a ternary eutectic solvent. The rest is exactly the same as in Example 1; The resulting nanocellulose is abbreviated as COA. Example 4

[0021] The difference between this embodiment and the previous embodiment is as follows: Choline chloride, oxalic acid, and zinc chloride hexahydrate were mixed evenly in a molar ratio of 1:1:0.2 and stirred at 80°C until a uniform and transparent solution was obtained, thus yielding a ternary eutectic solvent. The rest is exactly the same as in Example 1; The resulting nanocellulose is abbreviated as COZ.

[0022] Results and Detection Analysis of nanocellulose yield and chemical composition Using the weighing method, the mass of the pretreated bamboo shoot shell (m0) and the mass of the bamboo shoot shell after treatment with the eutectic solvent (m1) were weighed respectively. The yield was calculated using the formula C=(m1 / m0)*100%. The chemical composition of bamboo shoot shells was analyzed using an ultraviolet spectrophotometer, referring to the U.S. Department of Energy Renewable Energy Laboratory Method (NREL, 2008) and reagent kit. The morphology of the bamboo shoot shells was observed using transmission electron microscopy, and the grain size was calculated. The results are shown in Table 1.

[0023] Table 1

[0024] Application of preparing nanocellulose by treating bamboo shoot shells with eutectic solvent The preparation of a modified PVA composite film includes the following steps: Preparation of modified nanocellulose: The nanocellulose (CGF) prepared in Example 1 and water were homogenized by ultrasound to form a suspension with a mass fraction of 5%. The pH of the suspension was adjusted to 4 by preparing 0.1 mol / L HCl. After stirring in a water bath at 100 °C for 10 min, a citric acid solution with a mass fraction of 2% was added to control the pH to 3-4. The suspension was stirred in a water bath at 100 °C for 2 h. After cooling to room temperature, the suspension was dialyzed to neutral using a dialysis bag. Modified PVA composite film PVA particles and water were stirred at 95°C for 2 hours to prepare a 3% PVA solution. Then, acid-modified nanocellulose suspension was added to the PVA solution at a mass ratio of 1:0.6. Subsequently, vinyltriethoxysilane (KH151) was added to the mixture at 2% of the total mass. The mixture was stirred at 55°C for 30 minutes to obtain the membrane solution.

[0025] The experimental group used corona-treated PE as the substrate, coated with modified PVA solution, to prepare packaging film; the control group also used corona-treated PE as the substrate, coated with unmodified PVA solution as packaging film. Yellow peaches of similar shape and size from the same batch were prepared into soft-packaged yellow peach products and stored for 60 days at a constant temperature of 25℃ and relative humidity of 50%. Samples were taken on days 0, 15, 30, 45, 60, 75, and 90 to test the changes in the textural properties of the bagged yellow peach flesh. The results are shown in Tables 2 and 3.

[0026] Table 2 Experimental Groups

[0027] Table 3 Control Group

[0028] It is evident from the data in Tables 2 and 3 that, after 90 days of observation, the yellow peaches packaged using the nanocellulose (CGF) prepared in Example 1, further processed into packaging film, maintained a essentially unchanged color. In stark contrast, the yellow peaches in the control group showed a significant decrease in firmness and chewiness within a short period of 45 to 60 days. This result fully validates the significant effect of the present invention—preparing nanocellulose-modified PVA material by treating bamboo shoot shells with a eutectic solvent—on improving the performance of packaging film materials, thereby effectively extending the shelf life of soft-packaged yellow peaches.

[0029] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing nanocellulose by treating bamboo shoot shells with a eutectic solvent, characterized in that, The steps include the following: S1. Preparation of eutectic solvent: After the first component, the second component, and the third component are mixed evenly, the mixture is stirred and heated to obtain a ternary eutectic solvent. S2. Preparation of co-solvent: Benzyltripropylammonium hydroxide, 1',3-dihydroxymethylurea, and water are mixed evenly, stirred, and heated to obtain a cosolvent; S3. Preparation of nanocellulose: After mixing the pretreated bamboo shoot shells, ternary eutectic solvent, and co-solvent, the mixture was stirred and heated. After the reaction was completed, the mixture was washed with water, filtered, and dried to obtain crude cellulose. The crude cellulose was then prepared into a suspension, sonicated, homogenized under high pressure, and freeze-dried to obtain nanocellulose. The first component is choline chloride, the second component is glycerol or oxalic acid, and the third component is any one of aluminum chloride hexahydrate, ferric chloride hexahydrate, and zinc chloride hexahydrate; The mass ratio of benzyltripropylammonium hydroxide, 1'3-dihydroxymethylurea, and water is 1:1:(10-20). The mass ratio of the pretreated bamboo shoot shell, ternary eutectic solvent, and co-solvent is (1-10):100:(10-20).

2. The method for preparing nanocellulose by treating bamboo shoot shells with a eutectic solvent according to claim 1, characterized in that, The molar ratio of the first component, the second component, and the third component is 1:1:(0.1-0.3).

3. The method for preparing nanocellulose by treating bamboo shoot shells with a eutectic solvent according to claim 1, characterized in that, The method for pre-treating bamboo shoot shells is as follows: Clean the bamboo shoot shells, dry them, cut them, and crush them through an 80-mesh sieve. This is the original sample, referred to as OS. OS was mixed with deionized water at a mass ratio of 1:10 and stirred continuously at 90°C for 2 hours at a speed of 800 rpm. The mixture was then filtered through a 200-mesh sieve. The solid insoluble matter was placed in an oven and dried at 60°C for 5 hours. The pre-treated dried powder was mixed with a 1% NaOH solution at a mass ratio of 1:10 and stirred continuously at 90°C for 2 hours at a speed of 800 rpm. After stirring, the mixture was filtered through a 200-mesh sieve and washed with deionized water until the pH of the filtrate was close to neutral. The solid was then dried at 60°C for 5 hours and subsequently pulverized through an 80-mesh sieve to obtain the pre-treated bamboo shoot shell, abbreviated as PS.

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