CN117187974A - Cellulose nanofibrils prepared from seaweed waste residues as raw materials and low-cost preparation method thereof - Google Patents

Abstract

The invention discloses cellulose nanofibrils prepared from seaweed waste residues and a low-cost preparation method thereof. The method comprises the following steps: (1) Synthesizing proton type ionic liquid PILs by taking alcohol amine and oxalic acid as raw materials; (2) Uniformly mixing PILs with water to obtain a PILs aqueous solution, adding seaweed waste residues into the PILs aqueous solution, continuously stirring to pretreat the seaweed waste residues, filtering, washing with water, and washing the pretreated seaweed waste residues to be neutral; (3) Dispersing seaweed waste residues into deionized water, carrying out ultrasonic treatment, and freeze-drying to obtain cellulose nanofibrils. According to the invention, the synthesized low-cost PILs are used as a swelling agent and a hydrolysis catalyst for preprocessing seaweed waste residues to prepare the cellulose nanofibrils, and the PILs have the advantages of low vapor pressure, stable chemical property and recycling, so that the preparation method further reduces the preparation cost of the cellulose nanofibrils, and is energy-saving, environment-friendly and pollution-free.

Description

A kind of cellulose nanofibrils prepared from seaweed waste residue and its low-cost preparation Preparation method

Technical field

The invention belongs to the technical field of nanocellulose, and specifically relates to a cellulose nanofibril prepared from seaweed waste residue as raw material and a low-cost preparation method thereof.

Background technique

Cellulose nanofibrils are nanocellulose materials in the form of filaments, with a diameter of less than 100nm at the nanometer level and a length of more than 500nm at the nanometer or micron level. Compared with other members of the nanocellulose family, its aspect ratio is higher, and its structure consists of a crystalline region and a small amount of amorphous region, which improves the stability and flexibility of cellulose nanofibrils. On the one hand, cellulose nanofibrils have the typical characteristics of nanomaterials. The interface effect, small size effect, and quantum tunneling effect make them exhibit high specific surface area, high mechanical strength, light weight, low density, strong adsorption capacity, and high hydrophilicity. etc.; on the other hand, due to the presence of a large number of reactive hydroxyl functional groups on the surface, it has good affinity for reactions and is easier to modify than natural cellulose. Based on this, cellulose nanofibrils are widely used in the fields of architectural coatings, papermaking, automobile manufacturing, and new energy; and the characteristics of green materials such as non-toxic and degradable also make it show great potential in fine chemicals, medicine, food and other industries. development potential.

The current raw materials for preparing cellulose nanofibrils are mainly agricultural and forestry wastes and paper pulp. The collection cost of agricultural and forestry wastes is too high, and pulp is not only relatively expensive but also requires the consumption of forest resources, which greatly limits cellulose nanofibrils. Large-scale preparation and application.

Seaweed is a low-grade cryptophyte that grows in the ocean. It is the original producer of organic matter and a natural enricher of inorganic matter in the ocean. It is closely related to human life and economic development and plays an increasingly important role in human life. important role. Most seaweeds are used to extract seaweed polysaccharides, such as carrageenan, sodium alginate, agar, dietary fiber, etc. After these seaweeds are processed and utilized, a large amount of waste is produced - seaweed waste. Considering that seaweed waste residue contains 50-60% cellulose, which is large in quantity and has a stable source, if cellulose nanofibrils can be prepared from seaweed waste residue as raw material, it is expected to solve its industrialization bottleneck from the raw material and promote its true commercialization. .

The preparation methods of cellulose nanofibrils mainly include mechanical, chemical and biological methods. The mechanical method uses the impact and shearing of mechanical force to separate and crack the fibers. This method consumes a lot of energy and has low yield. The size of the prepared nanofibrils is extremely uneven and causes great damage to the cellulose structure. Chemical methods include TEMPO oxidation. and acid hydrolysis, etc. This method has high requirements for production equipment, is difficult to recycle production residues, and harms the environment. The biological method uses a series of cellulose active enzymes to enzymatically hydrolyze cellulose. The process is complex, time-consuming, and costly. higher. In summary, a low-energy-consuming and environmentally friendly preparation method is urgently needed for large-scale production of cellulose nanofibrils.

In 2002, Swatloski et al. discovered that ionic liquids have excellent solubility for cellulose. Studies have shown that ionic liquids (IL) can serve as catalysts, reaction media, swelling agents or solvents in pretreatment systems. Not only do they have significant reaction effects, but also because of their extremely low vapor pressure and good thermal stability, they can be used through distillation. It can be almost completely recycled. In addition, IL not only has a good swelling effect on cellulose, destroys the complex structure of cellulose due to van der Waals forces and hydrogen bonding effects, which is beneficial to subsequent mechanical processing, but can also appropriately introduce acidic functional groups into its structure to avoid the hydrolysis of the fiber by a single acid. The disadvantages of reduced thermal stability of plain nanofibrils. It can be seen that using IL to pretreat cellulose to prepare cellulose nanofibrils is an ideal method. However, the price of conventional imidazole ionic liquids is relatively high, which is not conducive to reducing the cost of cellulose nanofibrils. Therefore, it is necessary to develop a low-cost ionic liquid for treating cellulose in order to maximize the realization of a low-cost, low-energy-consuming and green and environmentally friendly preparation method of cellulose nanofibrils.

Contents of the invention

In view of the problems existing in the prior art, the present invention provides a cellulose nanofibril prepared from seaweed waste residue as raw material and a low-cost preparation method thereof.

The present invention is realized through the following technical solutions:

In one aspect, the present invention provides a method for preparing cellulose nanofibrils prepared from seaweed waste residue. The method includes the following steps:

(1) Synthesis of PILs: Use alcoholamine and oxalic acid as raw materials to synthesize protonic ionic liquid PILs;

(2) Pretreatment of seaweed waste residue: Mix PILs and water to obtain a PILs aqueous solution. Add the seaweed waste residue to the PILs aqueous solution. Continue stirring to perform swelling and hydrolysis pretreatment of the seaweed waste residue. After the pretreatment is completed, filter and wash the pretreated seaweed residue. The treated seaweed waste residue is washed until neutral;

(3) Preparation of cellulose nanofibrils by ultrasonic disintegration: first disperse the seaweed waste residue obtained in step (2) into deionized water, then ultrasonic treat it, and finally freeze-dry the suspension. The resulting powder is cellulose nanofibrils. Filaments.

In the above technical solution, further, in step (1), the alcoholamine is ethanolamine, diethanolamine or triethanolamine, the molar ratio of alcoholamine to oxalic acid is 0.8~1.2:1~3, and the reaction temperature is 0~70 ℃.

In the above technical solution, further, in step (2), the water content in the PILs aqueous solution is 10-70wt%, the solid-liquid mass ratio of the seaweed waste residue and the PILs aqueous solution is 1:50-150, and the pretreatment temperature The temperature is 20~110℃, and the stirring time is 1~5 hours.

In the above technical solution, further, in step (3), the solid-liquid mass ratio of the seaweed waste residue and deionized water is 1:100~1000, the ultrasonic output power is 500~1500W, and the ultrasonic frequency is 10~30kHz. Ultrasound time is 10~25min.

In the above technical solution, further, the method further includes the step of recovering PILs, and rotary evaporating the filtrate obtained in step (2) to obtain PILs for reuse.

In the above technical solution, further, the rotary evaporation temperature is 30 to 70°C.

Another aspect of the present invention provides cellulose nanofibrils prepared by the above preparation method and using seaweed waste residue as raw material.

In the above technical solution, further, the diameter distribution of the cellulose nanofibrils is 20-30 nm, the length distribution is 2-6 μm, and the aspect ratio is 100-200.

Compared with the prior art, the present invention has the following beneficial effects:

The cellulose raw material used in the present invention is industrial waste residue after degumming of seaweed. Compared with paper pulp, it reduces the cost of raw materials by "turning waste into treasure" and reduces the consumption of forest resources as the main raw material of paper pulp.

The cost of the protic ionic liquid PILs generated by the reaction of ethanolamine and oxalic acid used in the present invention is only 2 to 3 yuan/kg, while the price of conventional imidazole ionic liquids is more than ten times or even dozens of times that. In addition, in order to enhance the fluidity of PILs, promote the cleavage of glucosidic bonds in cellulose, and improve the pretreatment effect, water is also added to PIL in the present invention, which further reduces the cost.

In the present invention, the PILs in the filtrate can be completely steamed out, recycled and reused by rotary evaporating the filtrate at low temperature, which not only reduces energy consumption again, but also achieves truly green, environmentally friendly and pollution-free properties.

The present invention uses ultrasonic disintegration technology to mechanically peel pretreated seaweed waste residue into cellulose nanofibrils. The process is simple and easy to operate, and the obtained cellulose nanofibrils have good and stable properties.

Description of the drawings

Figure 1 is the XRD spectrum of the cellulose nanofibrils obtained in Example 1, Example 2, and Example 3;

Figure 2 is a scanning electron microscope (SEM) photo of the cellulose nanofibrils obtained in Example 2;

Figure 3 is a transmission electron microscope (TEM) photo of the cellulose nanofibrils obtained in Example 2;

Figure 4 is a diameter distribution diagram of cellulose nanofibrils obtained in Example 2.

Detailed ways

The following examples can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

Unless otherwise specified, the materials used in the examples of the present invention can be obtained commercially or prepared according to conventional methods well known to those skilled in the art.

Example 1

(1) Add 250 ml of absolute ethanol to a 500 mL round bottom flask, then add 63.3 g (about 0.5 mol) of oxalic acid dihydrate and stir to dissolve, then add 24.2 g (about 0.16 mol) of triethanolamine dropwise while stirring vigorously. After the dropwise addition is completed, stir continuously at 0°C until the mixture forms a uniform and stable liquid phase. Then, the ethanol is removed by rotary evaporation at 35°C. Finally, the synthesized PILs are placed in a vacuum drying oven at 60°C for 48 hours to remove moisture;

(2) Weigh 90g of PILs into a conical flask, then add 10g of deionized water, stir magnetically to form a homogeneous aqueous solution, then add 2g of seaweed waste residue, stir at 110°C for 1 hour, and finally filter and continue Use deionized water to wash the seaweed waste until neutral;

(3) Use a rotary evaporator to evaporate the PILs from the filtrate in step (2) at 30°C and reserve it for the next pretreatment of raw materials;

(4) Weigh the neutral seaweed waste residue obtained in step (2) and add it to the beaker. Then add deionized water 100 times the mass of the seaweed waste residue into the beaker, and then place the beaker into a 500W, 10kHz ultrasonic cell disrupter. Ultrasonic for 25 minutes, and finally freeze-dry the ultrasonic-treated suspension to obtain cellulose nanofibrils.

Example 2

(1) Add 250 ml of absolute ethanol to a 500 mL round bottom flask, then add 56.2 g (about 0.44 mol) of oxalic acid dihydrate and stir to dissolve, then add 15.3 g (about 0.25 mol) of ethanolamine dropwise while stirring vigorously. After the addition is completed, stir continuously at 35°C until the mixture forms a uniform and stable liquid phase. Then, the ethanol is removed by rotary evaporation at 35°C. Finally, the synthesized PILs are placed in a vacuum drying oven at 60°C for 48 hours to remove moisture;

(2) Weigh 70g of PILs into a conical flask, then add 30g of deionized water, stir magnetically to form a homogeneous aqueous solution, then add 1.5g of seaweed waste residue, stir at 70°C for 3 hours, and finally filter and continue Use deionized water to turn the seaweed waste to neutral;

(3) Use a rotary evaporator to evaporate the PILs from the filtrate in step (2) at 50°C and reserve it for the next pretreatment of raw materials;

(4) Weigh the neutral seaweed waste residue obtained in step (2) and add it to the beaker. Then add deionized water 500 times the mass of the seaweed waste residue into the beaker, and then place the beaker into a 1000W, 20kHz ultrasonic cell disrupter. Ultrasonic for 18 minutes, and finally freeze-dry the ultrasonic-treated suspension to obtain cellulose nanofibrils.

Example 3

(1) Add 250 ml of absolute ethanol to a 500 mL round bottom flask, then add 60.2 g (approximately 0.48 mol) of oxalic acid dihydrate and stir to dissolve, then add 48.5 g (approximately 0.46 mol) of diethanolamine dropwise while stirring vigorously. After the dropwise addition is completed, stir continuously at 70°C until the mixture forms a uniform and stable liquid phase. Then, the ethanol is removed by rotary evaporation at 35°C. Finally, the synthesized PILs are placed in a vacuum drying oven at 60°C for 48 hours to remove moisture;

(2) Weigh 30g of PILs into a conical flask, then add 70g of deionized water, stir magnetically to form a homogeneous aqueous solution, then add 0.7g of seaweed waste residue, stir at 25°C for 5 hours, and finally filter and continue Use deionized water to wash the seaweed waste until neutral;

(3) Use a rotary evaporator to evaporate the PILs from the filtrate in step (2) at 70°C and reserve it for the next pretreatment of raw materials;

(4) Weigh the neutral seaweed waste residue obtained in step (2) and add it to the beaker. Then add deionized water 1000 times the mass of the seaweed waste residue into the beaker, and then place the beaker into a 1500W, 30kHz ultrasonic cell disrupter. Ultrasonic for 10 minutes, and finally freeze-dry the ultrasonic-treated suspension to obtain cellulose nanofibrils.

Figure 1 is the XRD spectrum of cellulose nanofibrils obtained in Example 1, Example 2, and Example 3; [MEA][(HOA)(H ₂ OA)] represents the use of ethanolamine and oxalic acid dihydrate as raw materials. For synthesized PILs, the subscript percentage indicates the water content of PILs aqueous solution prepared by mixing PILs and water evenly. The bottom one in the figure is the XRD spectrum of the seaweed waste residue cellulose raw material, and the three upper ones are PILs aqueous solutions with different water contents. The XRD spectrum of cellulose nanofibrils obtained by combining pretreated seaweed waste residue with ultrasound. It can be clearly seen from the comparison of the spectra that the cellulose nanofibrils prepared by the method of the present invention retain the complete cellulose structure, and its crystallinity is consistent with the raw material. The cellulose content of seaweed waste residue is significantly higher than that of seaweed residue.

Figures 2 and 3 are respectively scanning electron microscope (SEM) photos and transmission electron microscope (TEM) photos of the cellulose nanofibrils obtained in Example 2. It can be seen from the electron microscope photos that the prepared cellulose nanofibrils exhibit obvious filament branches. Shape, the diameter distribution of vitamin nanofibrils is 20~30nm, and the length distribution is 2~6μm.

Figure 4 is a diameter distribution diagram of the cellulose nanofibrils obtained in Example 2. Most of the diameters are distributed between 20 and 30 nanometers, and the diameter distribution range is narrow.

The above embodiments are only preferred embodiments of the present invention and are not intended to limit the implementation. The protection scope of the present invention shall be subject to the scope defined by the claims. Other changes or changes in different forms can also be made on the basis of the above description. Obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims (8)

1. A method for preparing cellulose nanofibrils prepared from seaweed waste residue, characterized in that: the method includes the following steps: (1) Synthesis of PILs: Use alcoholamine and oxalic acid as raw materials to synthesize protonic ionic liquid PILs; (2) Pretreatment of seaweed waste residue: Mix PILs and water to obtain a PILs aqueous solution. Add the seaweed waste residue to the PILs aqueous solution and continue to stir to pretreat the seaweed waste residue. After the pretreatment is completed, filter and wash with water. Wash the seaweed waste until neutral; (3) Preparation of cellulose nanofibrils by ultrasonic disintegration: first disperse the seaweed waste residue obtained in step (2) into deionized water, then ultrasonic treat it, and finally freeze-dry the suspension. The resulting powder is cellulose nanofibrils. Filaments. 2. The preparation method according to claim 1, characterized in that in step (1), the alcoholamine is ethanolamine, diethanolamine or triethanolamine, and the molar ratio of alcoholamine to oxalic acid is 0.8~1.2:1~ 3. The reaction temperature is 0~70℃. 3. The preparation method according to claim 1, characterized in that in step (2), the water content in the PILs aqueous solution is 10-70wt%, and the solid-liquid mass ratio of the seaweed waste residue and the PILs aqueous solution is 1 : 50~150, the pretreatment temperature is 20~110℃, and the stirring time is 1~5 hours. 4. The preparation method according to claim 1, characterized in that, in step (3), the solid-liquid mass ratio of the seaweed waste residue and deionized water is 1:100~1000, and the ultrasonic output power is 500~1500W. , the ultrasonic frequency is 10~30kHz, and the ultrasonic time is 10~25min. 5. The preparation method according to claim 1, characterized in that the method further includes the step of recovering PILs, and performing rotary evaporation of the filtrate obtained in step (2) to obtain PILs. 6. The preparation method according to claim 5, characterized in that the rotary evaporation temperature is 30-70°C. 7. A cellulose nanofibril prepared from seaweed waste residue, characterized in that it is prepared by the preparation method according to any one of claims 1-6. 8. The cellulose nanofibrils according to claim 7, wherein the cellulose nanofibrils have a diameter distribution of 20-30 nm, a length distribution of 2-6 μm, and an aspect ratio of 100-200.