Flame-retardant cellulose based on phosphorus-nitrogen deep-eutectic solvent system as well as preparation method and application of flame-retardant cellulose

Abstract

The invention discloses flame-retardant cellulose based on a phosphorus-nitrogen deep-eutectic solvent system as well as a preparation method and application of the flame-retardant cellulose, and belongs to the field of modified cellulose materials. The preparation method comprises the following steps: respectively stirring guanidine phosphate or urea phosphate with betaine hydrochloride and urea, and stirring urea phosphate and urea to form uniform and transparent liquid, so as to obtain a deep-eutectic solvent containing a phosphorus-nitrogen phosphorylation reagent, adding a cellulose raw material into the deep-eutectic solvent containing the phosphorus-nitrogen phosphorylation reagent at 110-170 DEG C, the flame-retardant cellulose based on the phosphorus-nitrogen-containing eutectic solvent system has an excellent flame-retardant effect, the preparation method is simple to operate and low in cost, meanwhile, energy loss of mechanical treatment in the fiber nanocrystallization process can be effectively reduced, the used eutectic solvent is environmentally friendly and can be recycled to a certain extent, and the cost is low. And industrial production and application of flame-retardant cellulose treatment are facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of modified cellulose materials, and in particular relates to a flame-retardant cellulose based on a phosphorus-nitrogen low eutectic solvent system, and a preparation method and application thereof. Background Art

[0002] Energy is fundamental to human survival and a key driver of modern social progress and economic development. The overexploitation and overuse of traditional fossil fuels, such as coal, oil, and natural gas, has led to increasing resource scarcity and severe environmental pollution. With the growing severity of global climate change and increasing concerns about resource sustainability and environmental protection, the transition from traditional fossil fuel reliance to renewable energy has become a significant global trend.

[0003] Cellulose, one of the most abundant biomass resources on Earth, is found in plants such as wood, bamboo, cotton, and hemp, as well as some marine organisms (such as algae). It possesses outstanding advantages such as being renewable, easily degradable, non-toxic, and biocompatible. With the global emphasis on sustainable development and environmental protection, cellulose-based materials are gradually replacing petroleum-based products, demonstrating enormous potential for application in packaging, electronics, textiles and apparel, architectural decoration, and biomedicine.

[0004] However, as a typical carbohydrate, cellulose is rich in hydroxyl groups in its molecular structure, which makes the material highly flammable, which seriously limits its application in many fields with high fire safety requirements. Untreated cellulose materials not only burn rapidly when exposed to fire, but also release a large amount of heat and smoke, posing a major safety hazard. According to statistics, fires caused by cellulose materials have caused huge casualties and property losses in the fields of construction and transportation. Therefore, the development of cellulose materials with excellent flame retardant properties and the realization of their flame retardant functional modification have become the key technical bottleneck for expanding the high-end application of cellulose. In order to overcome this shortcoming, it is necessary to design and prepare cellulose materials with high thermal stability and excellent flame retardancy.

[0005] Current cellulose flame-retardant modification technologies primarily include physical blending and chemical modification. Physical blending achieves flame retardancy by simply mixing cellulose with a flame retardant. However, this method suffers from issues such as easy migration of the flame retardant, poor durability, and poor compatibility with the cellulose matrix, which severely impacts the material's long-term performance and mechanical strength.

[0006] The chemical modification method introduces flame retardant elements into the cellulose molecular chain through covalent bonds, which can achieve a more lasting flame retardant effect. The most common chemical method for preparing flame retardant cellulose is to modify it by grafting flame retardant groups. Flame retardants commonly used as grafted flame retardant groups include halogen flame retardants, phosphorus flame retardants, boron flame retardants, etc. Among them, phosphorus is the most common flame retardant additive, and the prepared phosphorylated cellulose has the characteristics of low smoke and low toxicity, and good flame retardant effect. For example, although the use of concentrated phosphoric acid to treat cellulose can introduce flame retardant phosphorus elements, it will significantly damage the crystalline structure and mechanical properties of cellulose. In addition, these methods use a large amount of water and organic solvents, generate a large amount of wastewater and waste liquid, and have a heavy environmental burden and are not in line with the principles of green chemistry.

[0007] Deep eutectic solvents (DES), a new class of green solvents, have attracted significant attention in recent years due to their low toxicity, biodegradability, and tunable properties. DES formation is based on the eutectic principle, which involves the formation of a eutectic mixture with a lower melting point than each of its individual components. This reduction in the melting point of the eutectic mixture is due to strong interactions between hydrogen bond acceptors and donors. Compared to traditional ionic liquids, DES do not require complex synthesis and purification steps. Their raw materials are mostly natural compounds or industrial byproducts (such as choline chloride, urea, and organic acids), which are inexpensive and readily available. DES have extremely low vapor pressure, are nonvolatile, and are safe to use. They also possess excellent thermal stability and recyclability, adhering to the principles of green chemistry and atom economy. DES act as both a solvent and a reactant, swelling and even dissolving cellulose while also introducing surface functional groups to modify cellulose. This dual role enables more sustainable, simplified, and efficient synthetic routes while minimizing the use of external reagents and reducing waste generation. The inventors previously studied a method for preparing phosphorylated nanocellulose using a ternary deep eutectic solvent system (publication number CN118165129A). The method first prepares a ternary deep eutectic solvent using phosphorous acid (hydrogen bond donor), choline chloride (hydrogen bond acceptor) and urea (hydrogen bond donor). Then, the cellulose raw material is added to the ternary deep eutectic solvent and a phosphorylation reaction is carried out at 110-170°C to obtain phosphorylated cellulose. Although this method can produce cellulose materials with good flame retardant properties, phosphorous acid is highly acidic and corrodes equipment, destroys the cellulose structure, and reduces the mechanical properties of the cellulose material. Summary of the Invention

[0008] The purpose of the present invention is to provide a flame-retardant cellulose based on a phosphorus-nitrogen deep eutectic solvent system and a preparation method thereof, which solves the problem that phosphorous acid in the existing cellulose phosphorylation deep eutectic solvent system easily destroys the cellulose structure itself and the flame retardant performance needs to be improved.

[0009] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0010] A flame-retardant cellulose based on a phosphorus-nitrogen deep eutectic solvent system, the molecular formula of which is:

[0011]

[0012] Wherein, n is the degree of polymerization, 50≤n<15000.

[0013] A method for preparing flame-retardant cellulose containing a phosphorus-nitrogen deep eutectic solvent system comprises the following steps:

[0014] (1) Synthesis of a deep eutectic solvent: A hydrogen bond donor and a hydrogen bond acceptor are stirred until a uniform transparent liquid is formed, wherein the hydrogen bond donor is urea, and the hydrogen bond acceptor is urea phosphate, or urea phosphate and betaine hydrochloride, or guanidine phosphate and betaine hydrochloride, wherein urea phosphate and guanidine phosphate are phosphorus-nitrogen phosphorylating reagents, to obtain two deep eutectic solvents containing phosphorus-nitrogen phosphorylating reagents;

[0015] (2) Modification pretreatment of cellulose: The cellulose raw material is added to a low eutectic solvent containing a phosphorus-nitrogen phosphorylation reagent and reacted at 80-170°C. After the reaction is completed, it is washed with deionized water and dried to obtain a phosphorylated cellulose material.

[0016] The preparation method of the low eutectic solvent containing the phosphorus-nitrogen phosphorylation reagent in step (1) is: guanidine phosphate or urea phosphate, betaine hydrochloride and urea are stirred at 50-130°C until a uniform transparent liquid is formed, preferably 60°C; or urea phosphate and urea are stirred at 90-130°C until a uniform transparent liquid is formed, preferably 90°C.

[0017] Preferably, the molar ratio of guanidine phosphate or urea phosphate, betaine hydrochloride and urea in the deep eutectic solvent in step (1) is 0.1-5:1:0.5-9; the molar ratio of urea phosphate and urea in the deep eutectic solvent in step (1) is 1:0.2-1:10, preferably 1:2.

[0018] Preferably, in step (2), the mass ratio of cellulose to the deep eutectic solvent is 1% to 10%, 1% to 5%, or 5% to 10%; the reaction temperature of cellulose is 80 to 170°C, 80 to 150°C, 150 to 170°C, 130 to 150°C, preferably 150°C, and the reaction time is 1 to 6 hours, or 2 to 6 hours.

[0019] After the reaction in step (2) is completed, the mixture is washed several times with deionized water until the conductivity of the filtrate is below 50 μs / cm to remove unreacted reagents.

[0020] The cellulose raw material may be derived from one or more of wood, cotton, wheat straw, rice straw, reed, hemp, mulberry bark, sugarcane bagasse and bacterial cellulose.

[0021] The phosphorylated cellulose is used as a flame retardant material in the fields of textiles (such as flame retardant fibers), papermaking (such as flame retardant paper), and flame retardant building materials (such as flame retardant wood).

[0022] The beneficial effects of the present invention are:

[0023] (1) The cellulose raw material swells in a low eutectic solvent containing a phosphorus-nitrogen phosphatizing agent. During the reaction, the phosphorus-nitrogen phosphatizing agent combines with the cellulose raw material to prepare a modified cellulose material containing both N and P elements and having an excellent flame retardant effect.

[0024] (2) Compared with the existing cellulose materials modified with low eutectic solvents containing phosphorous acid (publication number CN118165129A), the cellulose materials modified with guanidine phosphate and urea phosphate of the present invention have better flame retardant properties. For example, the limiting oxygen index of cellulose phosphorylated by the phosphorous acid system at 150°C is 47%, the limiting oxygen index of cellulose phosphorylated by the guanidine phosphate system at 150°C can reach 57.5%, and the limiting oxygen index of cellulose phosphorylated by the urea phosphate system at 150°C can reach 89.5%.

[0025] (3) The method of the present invention is simple to operate, has low energy loss, low cost, little environmental pollution, and greatly reduces water consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are photos of the ternary guanidine phosphate-based deep eutectic solvent (A) prepared in Example 1 and the dibasic urea phosphate-based deep eutectic solvent (B) prepared in Example 5.

[0027] Figure 2 This is an infrared image of bleached softwood pulp and modified flame-retardant cellulose. 2A is guanidine phosphate modified flame-retardant cellulose. Figure 2 B is urea phosphate modified flame retardant cellulose.

[0028] Figure 3 The microcalorimetric combustion performance diagram of bleached softwood pulp and modified flame-retardant cellulose prepared, wherein 3A is guanidine phosphate modified flame-retardant cellulose, Figure 3 B is urea phosphate modified flame retardant cellulose.

[0029] Figure 4 These are the infrared spectra and micro-calorimetric combustion performance diagrams of cotton fabric and flame-retardant cotton fabric.

[0030] Figure 5 Microcalorimetric combustion performance diagram of wood chips and flame-retardant wood chips. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be further described in detail below in conjunction with specific implementation methods, but this does not constitute any limitation to the present invention.

[0032] Compared to traditional aqueous systems, DES can swell and even dissolve cellulose, enabling a reaction between the phosphorylating agent in the DES and cellulose, completing the phosphorylation modification of cellulose. The phosphorylation modification process involves two key points: first, preparing a DES containing a phosphorylating agent, and second, ensuring that the phosphorylating agent reacts with cellulose within the DES system. However, experiments have shown that, given the same hydrogen bond acceptor (or hydrogen bond donor), changing the phosphorylating agent as the hydrogen bond donor (or hydrogen bond acceptor) makes it difficult to form a uniform and stable DES (e.g., guanyl urea phosphate, betaine hydrochloride, and urea are difficult to form a stable DES, while guanidine phosphate and urea are difficult to form a uniform and stable DES). Even if a DES is formed, the phosphorylating agent in the DES is difficult to react with cellulose (e.g., a DES formed from guanidine phosphate, choline chloride, and urea is difficult to phosphorylate cellulose). Therefore, the selection of phosphorylating agents is not always straightforward.

[0033] Example 1

[0034] The present embodiment relates to a method for preparing flame-retardant cellulose containing a phosphorus-nitrogen deep eutectic solvent system, comprising the following steps:

[0035] (1) 0.0102 mol of guanidine phosphate, 0.0376 mol of betaine hydrochloride, and 0.0567 mol of urea were heated at 60°C while magnetically stirring for 60 min at a speed of 500 r / min to form a transparent and uniform ternary deep eutectic solvent, such as Figure 1 As shown in A.

[0036] (2) Bleached coniferous pulp was added to the ternary low eutectic solvent, and the mass ratio of the bleached coniferous pulp to the ternary low eutectic solvent was 5%. The ternary low eutectic solvent system was heated to 150° C. and reacted for 3 h. After the reaction, the modified cellulose was taken out from the glass bottle, and repeatedly filtered and washed with deionized water until the conductivity of the filtrate dropped below 50 μs / cm. After filtration and washing, the guanidine phosphate modified flame retardant cellulose was obtained by drying.

[0037] The reaction equation of step (2) is:

[0038]

[0039] Figure 2 A is the infrared image of bleached coniferous pulp and the prepared guanidine phosphate modified flame retardant cellulose, which shows that the cellulose modification is successful.

[0040] Figure 3 A is a micro-calorimetric combustion performance diagram of bleached softwood pulp and the prepared guanidine phosphate modified flame retardant cellulose, from which it can be seen that guanidine phosphate modified flame retardant cellulose has good flame retardancy.

[0041] Examples 2 to 4

[0042] Examples 2 to 4 are the same as Example 1 except that the reaction temperatures of the ternary deep eutectic solvent system in step (2) are 110° C., 130° C., and 170° C., respectively.

[0043] Comparative Example 1

[0044] This comparative example is the same as Example 1, except that betaine hydrochloride is replaced with choline chloride in the ternary deep eutectic solvent. The ternary deep eutectic solvent is prepared by heating 0.0102 mol of guanidine phosphate, 0.0376 mol of choline chloride, and 0.0567 mol of urea at 60°C while magnetically stirring for 60 minutes at a speed of 500 rpm to form a transparent and uniform ternary deep eutectic solvent. However, this ternary deep eutectic solvent is mixed with bleached softwood pulp and reacts at a temperature between 110 and 170°C, failing to effectively phosphorylate cellulose.

[0045] Example 5

[0046] This embodiment relates to a method for preparing flame-retardant cellulose based on a phosphate-based deep eutectic solvent, comprising the following steps:

[0047] (1) 0.0361 mol of urea phosphate and 0.0717 mol of urea were heated at 90°C with magnetic stirring for 60 min at a speed of 500 r / min to form a transparent and uniform binary deep eutectic solvent, such as Figure 1 As shown in B.

[0048] (2) Bleached coniferous pulp was added to the binary low eutectic solvent, and the mass ratio of the bleached coniferous pulp to the binary low eutectic solvent was 5%. The binary low eutectic solvent system was heated to 150°C and reacted for 2 hours. After the reaction, the modified cellulose was taken out from the glass bottle, and repeatedly filtered and washed with deionized water until the conductivity of the filtrate dropped below 50 μs / cm. The cellulose was then filtered and washed, and then dried to obtain urea phosphate modified flame retardant cellulose.

[0049] The reaction equation of step (2) is:

[0050]

[0051] Figure 2 B is the infrared image of bleached coniferous pulp and the prepared urea phosphate modified flame retardant cellulose, which shows that the cellulose modification is successful.

[0052] Figure 3 B is a micro-calorimetric combustion performance diagram of bleached softwood pulp and the prepared urea phosphate modified flame retardant cellulose, from which it can be seen that urea phosphate modified flame retardant cellulose has good flame retardancy.

[0053] Examples 6 to 8

[0054] Examples 6 to 8 are the same as Example 5 except that the reaction temperatures of the binary deep eutectic solvent system in step (2) are 110° C., 130° C., and 170° C., respectively.

[0055] The phosphorus content of the modified cellulose prepared in Examples 1-8 was calculated by inductively coupled plasma atomic emission spectroscopy. The results are shown in the following table. The higher the phosphorus content, the higher the amount of grafted phosphate groups, and theoretically the better the flame retardancy.

[0056] Table 1 Phosphorus content of bleached wood pulp after eutectic system treatment under different embodiments

[0057]

[0058] Application Example 1

[0059] Guanidine phosphate, urea, and betaine hydrochloride were mixed in a molar ratio of 1:1.5:2. A total of 300g (66g of guanidine phosphate, 102g of urea, and 132g of betaine hydrochloride) was dissolved in a thermostatic oil bath at 90°C. The solution was poured into a glass tray at a rotor speed of 340 rpm. A cotton fabric (20cm x 30cm) that had been previously washed with deionized water and dried was added. The fabric was smoothed and thoroughly soaked. The fabric was then placed in an oven heated to 150°C for 2 hours. The remaining solution was removed by scrubbing with running water, then rinsed three to four times with deionized water and dried in an oven at 37°C to obtain a flame-retardant cotton fabric. Figure 4 These are the infrared spectra and micro-calorimetric combustion performance diagrams of cotton fabric and flame-retardant cotton fabric.

[0060] Application Example 2

[0061] Weigh 88g of betaine hydrochloride, 68g of urea, and 44g of guanidine phosphate into a 1000mL reaction flask. The molar ratio of betaine hydrochloride, urea, and guanidine phosphate is 1:2:1. Heat and dissolve in a thermostatic oil bath at 90°C to form a uniform solution. Pour the dissolved solution into a glass tray, add 2mm thick wood chips (3cm x 10cm), raise the temperature to 130°C, and react for 3 hours. Remove the reacted solution and filter it until the conductivity is below 50µs / m to obtain a modified flame-retardant wood board. Figure 5 Microcalorimetric combustion performance diagram of wood chips and flame-retardant wood chips.

[0062] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although this specification has described the present invention in detail with reference to the above embodiments, it should be understood by those skilled in the art that the present invention may still be modified or replaced by equivalents. All technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A flame-retardant cellulose based on a phosphorus-nitrogen deep eutectic solvent system, characterized in that: Its molecular formula is: Wherein, n is the degree of polymerization, 50≤n<15000.

2. A method for preparing flame-retardant cellulose containing a phosphorus-nitrogen deep eutectic solvent system, characterized in that: The following steps are involved: (1) Synthesis of a deep eutectic solvent: A hydrogen bond donor and a hydrogen bond acceptor are stirred until a uniform transparent liquid is formed, wherein the hydrogen bond donor is urea, and the hydrogen bond acceptor is urea phosphate, or urea phosphate and betaine hydrochloride, or guanidine phosphate and betaine hydrochloride, wherein urea phosphate and guanidine phosphate are phosphorus-nitrogen phosphorylating reagents, to obtain two deep eutectic solvents containing phosphorus-nitrogen phosphorylating reagents; (2) Modification pretreatment of cellulose: The cellulose raw material is added to a low eutectic solvent containing a phosphorus-nitrogen phosphorylation reagent and reacted at 80-170°C. After the reaction is completed, it is washed with deionized water and dried to obtain a phosphorylated cellulose material.

3. The method for preparing flame-retardant cellulose containing a phosphorus-nitrogen deep eutectic solvent system according to claim 1, characterized in that: The preparation method of the low eutectic solvent containing the phosphorus-nitrogen phosphorylation reagent in step (1) is: guanidine phosphate or urea phosphate, betaine hydrochloride and urea are stirred at 50-130° C. until a uniform transparent liquid is formed; or urea phosphate and urea are stirred at 90-130° C. until a uniform transparent liquid is formed.

4. The method for preparing flame-retardant cellulose containing a phosphorus-nitrogen deep eutectic solvent system according to claim 1, characterized in that: The molar ratio of guanidine phosphate or urea phosphate, betaine hydrochloride and urea in the low eutectic solvent in step (1) is 0.1-5:1:0.5-9; the molar ratio of urea phosphate and urea in the low eutectic solvent in step (1) is 1:0.2-1:

10.

5. The method for preparing flame-retardant cellulose containing a phosphorus-nitrogen deep eutectic solvent system according to claim 1, characterized in that: In step (2), the mass ratio of cellulose to the deep eutectic solvent is 1% to 10%.

6. The method for preparing flame-retardant cellulose containing a phosphorus-nitrogen deep eutectic solvent system according to claim 1, characterized in that: The cellulose raw material is derived from one or more of wood, cotton, wheat straw, rice straw, reed, hemp, mulberry bark, sugarcane bagasse and bacterial cellulose.

7. Use of the flame-retardant cellulose according to claim 1 or the flame-retardant cellulose prepared by the method according to any one of claims 2 to 6 as a flame-retardant material.

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