Cellulose modifier as well as preparation method and application thereof

Abstract

The invention provides a cellulose modifier as well as a preparation method and application thereof, the chemical general formula of the cellulose modifier is # imgabs0 #, and R1 and R2 are any one of tetrazolyl or hydroxyl. According to the invention, cellulose in two states of dry powder or liquid slurry is used for energetic modification, and tetrazolyl functional groups are introduced into nano cellulose, microcrystalline cellulose and M30 cellulose, so that a brand-new cellulose modifier is prepared and has the effects of high energy, high combustion and strengthening and toughening; therefore, the cellulose adhesive can be applied to explosives and powders as a high-energy cellulose adhesive.

Description

Technical Field

[0001] The present invention relates to the technical field of cellulose modification, and in particular to a cellulose modification product, a preparation method and application thereof. Background Art

[0002] High energy, low characteristic signal and low vulnerability of solid propellants are the overall requirements of new performance weapons and equipment. Whether it is a composite solid propellant or a double-base series solid propellant, the main way to increase energy is still to add high-energy components, such as CL-20, RDX and Octogen. The increase in the proportion of these high-energy components will weaken the mechanical skeleton effect of the binder nitrocellulose, causing the propellant to have problems such as processing safety and storage and use performance degradation. These problems are difficult to solve by simply optimizing the molding processing conditions of the propellant and adding ordinary additives. Taking the modified double-base solid propellant as an example, the binder nitrocellulose NC in the formula has strong rigidity and low energy, which makes it difficult to coordinate the energy and mechanical properties of the propellant. Therefore, finding new materials and new additives for preparing high-performance and fundamentally improving the comprehensive performance of the propellant is the current technical bottleneck in the field of this type of solid propellant.

[0003] In the field of cellulose-based energetic materials, cellulose nitrate, also known as nitrocellulose (NC), is still the most widely used energetic polymer in the composition of gunpowder and solid propellants due to its potential characteristics such as good solubility, fast drying speed, excellent mechanical properties, compatibility with a variety of additives, and good flammability and explosiveness. Nevertheless, compared with other thermoplastic elastomers, the performance of NC still has some shortcomings, such as low energy, high impact sensitivity, low density, high brittleness, low combustion temperature, and poor long-term stability. Therefore, the development and application of cellulose-based energetic materials with low sensitivity and high energy are of great significance.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The first purpose of the present invention is to provide a cellulose modification, which is prepared by using cellulose in two states, dry powder or slurry, to modify the cellulose into an energetic material, and introducing tetrazolyl functional groups into nanocellulose, microcrystalline cellulose and refined cotton cellulose, so that the cellulose modification has high energy, high combustion and enhanced toughness, so that the cellulose modification can be used as a high-energy cellulose adhesive in explosives.

[0006] The second object of the present invention is to provide a method for preparing the above-mentioned cellulose modification, which uses M30 cellulose dry powder, nanocellulose dry powder or microcrystalline cellulose dry powder as raw material, activates the cellulose raw material with p-toluenesulfonyl chloride in a DMAc / lithium chloride solvent system to prepare the modified cellulose.

[0007] The third object of the present invention is to provide a cellulose modification for use as a binder in explosives.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted: A modified cellulose, characterized in that the general chemical formula of the modified cellulose is: , wherein R1 and R2 are either tetrazolyl or hydroxyl.

[0009] Preferably, as a further specific embodiment, both R1 and R2 are tetrazolyl.

[0010] In the present invention, most of the adhesives in the prior art are prepared by nitrocellulose NC. Due to its good solubility, fast drying speed, excellent mechanical properties, compatibility with a variety of additives, good flammability and explosiveness, it is still the most widely used energetic polymer in the composition of gunpowder and solid propellant. However, there are still some shortcomings in its performance, such as low energy, high impact sensitivity, low density, high brittleness, low combustion temperature and poor long-term stability. Therefore, in order to solve the above problems, the inventors have explored a new type of cellulose modification through a series of creative work, which introduces tetrazolyl functional groups into M30 cellulose, nanocellulose or microcrystalline cellulose through chemical modification. Since the tetrazolyl functional group is a nitrogen-rich heterocycle, it is environmentally friendly, high energy, insensitive to specificity and has good thermal stability. Therefore, these outstanding characteristics enable it to be used in different material fields such as solid propellants, high-energy explosives and pyrotechnic components. Therefore, after a series of creative work, the inventors concluded that by using three celluloses of different sizes, namely M30 cellulose, nanocellulose or microcrystalline cellulose, the hydrogen bonds within and between molecules of the cellulose precursor molecule are first destroyed to promote its chemical functionalization, and then the hydroxyl functional group present in the anhydroglucose unit is activated to improve the leaving ability of the hydroxyl functional group, and then the tetrazolyl functional group is added to enable it to replace the cellulose molecule. In the process of tetrazolyl replacing hydroxyl, since there are three hydroxyl groups in different positions on the cellulose molecular chain, namely R1, R2 and R3, when the tetrazolyl functional group replaces the hydroxyl group, the hydroxyl group on R3 is replaced to obtain a new type of cellulose modification. When the same cellulose raw material is selected, any hydroxyl group on R2 and R3 can be replaced by the tetrazolyl functional group to obtain the same cellulose modification. For example, when nanocellulose is selected as the raw material for chemical modification, the hydroxyl group on R3 is replaced by the tetrazolyl functional group to obtain TANC (1H-tetrazolyl-5-acetate nanocellulose), and R1 or R2 or R2 in an ideal state and R3 are both replaced by tetrazolyl functional groups to obtain TANC; when microcrystalline cellulose is selected as the raw material for chemical modification, the hydroxyl group on R3 is replaced by tetrazolyl functional groups to obtain TAMC (1H-tetrazolyl-5-acetate nitrate microcrystalline cellulose), and R1 or R2 or, in an ideal state, R2 and R3 are both replaced by tetrazolyl functional groups to obtain TAMC; when M30 cellulose is selected as the raw material for chemical modification, the hydroxyl group on R3 is replaced by tetrazolyl functional groups to obtain TAC (1H-tetrazolyl-5-acetate nitrate cellulose), and R1 or R2 or, in an ideal state, R2 and R3 are both replaced by tetrazolyl functional groups to obtain TAC.

[0011] The present invention also provides a method for preparing the above-mentioned cellulose modification, comprising the following steps: The cellulose raw material is uniformly dispersed in anhydrous DMAc, and then stirred and heated for activation for 1-2 hours under nitrogen flow, and then cooled to obtain a reaction solution; Adding anhydrous lithium chloride to the reaction solution, stirring until the cellulose raw material is completely dissolved, and cooling to obtain a mixed solution; To the mixed solution, add p-toluenesulfonyl chloride and 1H-tetrazolyl-5-acetic acid in sequence, heat for 10 h to 14 h, filter, wash and dry to obtain the product.

[0012] Preferably, as a further specific embodiment, the cellulose raw material is any one of M30 cellulose dry powder, nanocellulose dry powder or microcrystalline cellulose dry powder.

[0013] The present invention also provides a method for preparing a cellulose modification. First, three kinds of M30 cellulose dry powder, nanocellulose dry powder or microcrystalline cellulose dry powder of different sizes are used as raw materials, and they are pretreated in a DMAc / LiCl solvent system to destroy the hydrogen bonds within and between molecules while dissolving the cellulose. By using anhydrous DMAc / LiCl as a cheap solvent system, the cost can be greatly saved while pretreating the cellulose raw material. In addition, anhydrous DMAc / LiCl can also be used as a good hydrogen bond receptor to destroy the cellulose due to its excellent performance. Hydrogen bonds within and between precursor molecules are formed, thereby promoting their chemical functionalization. This is because the amide group in the DMAc molecule contains carbonyl oxygen (C=O) and amino nitrogen (N) groups, both of which have lone pairs of electrons and high electronegativity, which enable them to act as hydrogen bond acceptors and donors (such as -OH, -NH, etc.) to form strong hydrogen bonds. DMAc cannot provide protons, but due to its high dielectric constant (ε≈37.8), it can effectively dissolve polar substances and stabilize ions, while avoiding itself from becoming a hydrogen bond donor, thereby focusing on accepting hydrogen bonds. LiCl can be partially dissociated into Li in the polar aprotic solvent DMAc. + and Cl - .Cl - Because of its high charge density and lone pair electrons, it becomes an extremely strong hydrogen bond acceptor and can efficiently bind hydrogen bond donors. + It undergoes Lewis acid-base coordination with the carbonyl oxygen of DMAc to form [Li(DMAc)_n] + This coordination not only promotes the dissociation of LiCl, but also releases more free Cl - , thereby enhancing the hydrogen bonding acceptance capacity of the solution. Therefore, the present invention adopts an anhydrous DMAc / LiCl solution system to dissolve cellulose. Since cellulose is a polar substance, it can be well dissolved in the anhydrous DMAc / LiCl system through the synergistic effect of the two. At the same time, the carbonyl oxygen and amino nitrogen in DMAc react with Cl -Together they act as hydrogen bond acceptors, thus forming a multiple hydrogen bond network that synergistically destroys the hydrogen bond structure of cellulose. The highly polar environment of DMAc can also stabilize Cl - The charge distribution of Li + The coordination effect can stabilize the solution system to a great extent and prevent Cl⁻ from being over-solvated; after the cellulose is dissolved, p-toluenesulfonyl chloride is used to activate the hydroxyl functional groups in the anhydroglucose units, and the key hydroxyl groups of the anhydroglucose units are converted into strong leaving groups by sulfonylation, thereby increasing the reactivity of the sugar units to improve their leaving ability, and then the corresponding cellulose modifications (TAC, TANC, TAMC) are generated through the nucleophilic replacement reaction of the cellulose precursor with the activated hydroxyl functional groups of the 1H-tetrazole-5-acetate part.

[0014] In the preparation method of the present invention, the cellulose raw material is firstly uniformly dispersed in anhydrous DMAc, and stirred and heated under the condition of nitrogen gas, and anhydrous lithium chloride is added after activation for 1-2 hours. Therefore, it can be known from the above processing steps that the essential purpose of the method of treating cellulose by using anhydrous DMAc / LiCl system in the present invention is to achieve the destruction of hydrogen bonds in cellulose, and the degree of dissolution affects the yield of the product. Therefore, in terms of the processing sequence, the present invention firstly uniformly disperses cellulose in anhydrous DMAc and stirs and heats under a nitrogen atmosphere for activation, so that it can ensure that the cellulose molecular chain is not degraded under the nitrogen atmosphere, while allowing DMAc to fully react with cellulose and completely open the hydrogen bonds.

[0015] Preferably, as a further specific embodiment, when the cellulose raw material is dispersed in anhydrous DMAc, the bath ratio of the cellulose raw material to the anhydrous DMAc is (1:99)-(10:90).

[0016] Preferably, as a further specific embodiment, the bath ratio is (6-10): (95-99).

[0017] In the present invention, when cellulose is dissolved by using anhydrous DMAc, when the bath ratio of the cellulose raw material to the anhydrous DMAc is (1:99)-(10:90), preferably when the bath ratio is (6-10):(95-99), the effect that can be achieved is excellent. This is because anhydrous DMAc is a polar aprotic solvent with a high dielectric constant and polarity. Its polar molecules can penetrate between cellulose chains to weaken the hydrogen bonds within and between cellulose molecules, and it can disperse the cellulose chains in the solvent through polarity to prevent them from re-aggregating. At this time, if the bath ratio is low, that is, when the solvent is less, the cellulose concentration in the system is high. When the cellulose is dissolved by anhydrous DMAc, the solvent is insufficient to completely destroy the hydrogen bond network of the cellulose, which affects the subsequent introduction of functional groups, and leads to slow dissolution and insufficient dissolution, forming a flocculent substance or a partially dissolved suspension. If the bath ratio is high, it will lead to solvent waste, increase costs, and large volume recovery and processing volume, and poor environmental protection.

[0018] Preferably, as a further specific embodiment, the lithium chloride is 1%-10% of the mass of the anhydrous DMAc.

[0019] Preferably, as a further specific embodiment, the lithium chloride is 5% of the mass of the anhydrous DMAc.

[0020] In the process of configuring the anhydrous DMAc / LiCl solution system of the present invention, the mass ratio of lithium chloride to anhydrous DMAc is crucial because it directly affects the dissolution efficiency of cellulose, the stability of the solution and the degree of destruction of hydrogen bonds to a certain extent. For the present invention, when the lithium chloride is 1%-10% of the mass of the anhydrous DMAc, preferably when the lithium chloride is 5% of the mass of the anhydrous DMAc, the effect that can be achieved is excellent. This is because in the anhydrous DMAc / LiCl solution system, the Li in LiCl is + It can coordinate with the hydroxyl group of cellulose, thereby weakening the hydrogen bonding between cellulose molecular chains, while Cl -It is a strong hydrogen bond acceptor, which can further destroy the crystalline structure of cellulose. The dissociation of LiCl increases the ionic strength of the solution, which is helpful for the dispersion and stabilization of the cellulose molecular chains. It can synergize with anhydrous DMAc to dissolve well. At the same time, the carbonyl oxygen and amino nitrogen in DMAc act as hydrogen bond acceptors with Cl-, thereby forming a multiple hydrogen bond network, which synergistically destroys the hydrogen bond structure of cellulose. The high polarity environment of DMAc can also stabilize the charge distribution of Cl-, further enhancing its hydrogen bond acceptance ability. Therefore, if the lithium chloride content in the solution system is too low, the destructive effect of the solution system on the cellulose hydrogen bond network will be limited, affecting the subsequent introduction of functional groups. A small amount of lithium chloride may cause the solution to have higher mucus and poor dispersibility of the cellulose molecular chain, resulting in partial dissolution or gelation of cellulose, thereby affecting the final product yield. If the lithium chloride content is high, it will lead to the conductivity of the solution, thereby affecting the subsequent processing performance.

[0021] Preferably, as a further specific embodiment, the molar ratio of the cellulose raw material to the 1H-tetrazolium-5-acetic acid is 1:(1-10); Preferably, the molar ratio of the cellulose raw material to the 1H-tetrazolium-5-acetic acid is 1:5.

[0022] In the preparation method of the present invention, the molar ratio between the cellulose raw material and 1H-tetrazolyl-5-acetic acid is very important. This is because the present invention mainly adopts three cellulose raw materials of different sizes, namely nanocellulose, microcrystalline cellulose and refined cotton cellulose, and promotes its chemical functionalization after pretreatment with anhydrous DMAc / LiCl as a solvent to destroy the hydrogen bonds within and between the cellulose precursor molecules, and then activates the hydroxyl functional groups existing in the anhydroglucose unit with p-toluenesulfonyl chloride to improve its leaving ability, and then esterifies with 1H-tetrazolyl-5-acetic acid to generate a new type of cellulose modification. The selection of the molar ratio between the two directly affects the degree of substitution of the reaction, that is, the number of hydroxyl groups replaced by tetrazolyl groups on each anhydroglucose unit. Therefore, if the molar ratio is too small, that is, 1 If the amount of H-tetrazolyl-5-acetic acid is too small, the reaction will be incomplete, so that the number of hydroxyl groups replaced by tetrazolyl groups on the anhydroglucose unit is small and some hydroxyl groups of cellulose are modified, and the product retains more hydroxyl groups that have not reacted completely; if the molar ratio is too large, that is, the amount of 1H-tetrazolyl-5-acetic acid is too high, the reaction between the two is complete, the number of hydroxyl groups replaced by tetrazolyl groups on the anhydroglucose unit is large, and the reaction tends to be complete, but at this time, excessive 1H-tetrazolyl-5-acetic acid will cause cellulose to be over-modified, thereby causing degradation or cross-linking of the cellulose skeleton. Therefore, when the molar ratio of the cellulose raw material to the 1H-tetrazolyl-5-acetic acid is 1: (1-10), preferably when the molar ratio of the cellulose raw material to the 1H-tetrazolyl-5-acetic acid is 1:5, the effect achieved is excellent.

[0023] In addition, the inventors learned from literature review that the combination of tetrazolyl and other explant functions can further reduce the sensitivity of the resulting product and improve its energy performance. Subsequently, the inventors found from literature review that inserting nitrate ester and tetrazolyl functional groups into the cellulose skeleton at the same time, that is, the substituent groups of R1 and R2 are nitro groups, is considered to be a new trend in the design and synthesis of nitrogen-rich cellulose-based energetic materials with appropriate properties. Therefore, after obtaining TAC, TANC and TAMC by the above-mentioned preparation method, TAC, TANC and TAMC are nitrated in a nitration system to prepare 1H-tetrazole-5-cellulose acetate nitrate series, that is, 1H-tetrazole-5-acetate cellulose is nitrated by an appropriate amount of mixed acid to obtain a 1H-tetrazole-5-acetate nitrate cellulose series product. Unfortunately, during the experiment, when the 1H-tetrazole-5-acetate cellulose is soluble in this system after the nitration is completed.

[0024] The mixed acid is a mixed acid system of nitric acid and sulfuric acid in a ratio of 5:7. Considering that the water content is too high, the nitration is not good. In addition, under strong acid conditions and a large amount of water, cellulose undergoes acid hydrolysis.

[0025] Subsequently, a large amount of deionized water was added to the reaction solution, and then an appropriate amount of ethanol was added to precipitate a small amount of material, which was filtered to form a transparent viscous gel. The material was dried at 70°C under vacuum for 5 hours, and the material was a yellow-brown solid with about 0.2 g remaining. Therefore, it can be known that the nitrated products of TAC, TANC and TAMC can be obtained by the above method, but the yield is not good at present. Therefore, for the present invention, the groups of R1 and R2 can also be nitro groups.

[0026] The present invention also provides an application of the above-mentioned cellulose modification as a binder in explosives.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a cellulose modification, which is prepared by using cellulose in the form of dry powder or slurry to modify the cellulose energetically, and introducing tetrazolyl functional groups into nanocellulose, microcrystalline cellulose and refined cotton cellulose. The cellulose modification has high energy, high combustion performance and enhanced toughness, and can be used as a high-energy cellulose adhesive in explosives.

[0028] (2) The present invention provides a method for preparing the above-mentioned modified cellulose, which uses M30 cellulose dry powder, nanocellulose dry powder or microcrystalline cellulose dry powder as raw material, activates the cellulose raw material with p-toluenesulfonyl chloride in a DMAc / lithium chloride solvent system, and then prepares the modified cellulose.

[0029] (3) The present invention provides a cellulose modification material for use as a binder in explosives. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] By reading the detailed description of the preferred embodiment below, various other advantages and benefits will become clear to those of ordinary skill in the art. The accompanying drawings are only used for the purpose of illustrating the preferred embodiment and are not considered to be limitations of the present invention. In addition, the same reference symbols are used to represent the same components throughout the accompanying drawings.

[0031] Figure 1 is the infrared spectrum of the cellulose modification TAC of the present invention; Figure 2 is the infrared spectrum of the cellulose modification TANC of the present invention; Figure 3 This is the infrared spectrum of the cellulose modification product TAMC of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be clearly and completely described below in conjunction with specific implementation methods, but those skilled in the art will understand that the embodiments described below are part of the embodiments of the present invention, rather than all of the embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] In order to more clearly explain the technical solution of the present invention, it is described in the form of specific embodiments below.

[0034] Example 1 The specific synthesis scheme of the cellulose modification is as follows: The cellulose raw material selected is M30 cellulose; First, the M30 cellulose was pretreated. The M30 cellulose was dried in a vacuum oven at 105°C for 2 hours to obtain M30 cellulose dry powder. The lithium chloride was dried in a vacuum oven at 130°C for 2 hours to obtain anhydrous lithium chloride before use. The anhydrous DMAc was treated with 5A molecular sieve before use. First, the pretreated M30 cellulose powder was dispersed in anhydrous DMAc at a bath ratio of 1:99. 2 The mixture was stirred slowly under the conditions of 100 °C, heated to 160 °C for activation for 1 h, and then naturally cooled to 100 °C. Then, 1% of anhydrous lithium chloride by mass of anhydrous DMAc was added and stirred continuously. Then, the mixture was naturally cooled to room temperature. Then, p-toluenesulfonyl chloride was added to activate the hydroxyl groups. Then, 1 times the molar amount of M30 cellulose was added to the solution. 1H-tetrazolyl-5-acetic acid was added and heated at 60 °C for 10 h. After the reaction, the obtained suspension was poured into water, the product was filtered, washed with distilled water and acetonitrile for several times, and then vacuum dried at 60°C overnight to obtain light yellow TAC; The chemical reaction formula is as follows:

[0035] Example 2 The specific synthesis scheme of the cellulose modification is as follows: The cellulose raw material selected is M30 cellulose; First, the M30 cellulose was pretreated. The M30 cellulose was dried in a vacuum oven at 105°C for 2 hours to obtain M30 cellulose dry powder. The lithium chloride was dried in a vacuum oven at 130°C for 2 hours to obtain anhydrous lithium chloride before use. The anhydrous DMAc was treated with 5A molecular sieve before use. First, the pretreated M30 cellulose powder was dispersed in anhydrous DMAc at a bath ratio of 10:90, and then N 2 The mixture was slowly stirred under the conditions of 160°C for activation for 2 hours and then naturally cooled to 100°C to obtain a reaction solution. Subsequently, anhydrous lithium chloride (10% by mass of anhydrous DMAc) was added to the reaction solution and stirred continuously. Subsequently, the mixture was naturally cooled to room temperature to obtain a mixed solution. p-Toluenesulfonyl chloride was added to the mixed solution to activate the hydroxyl group. Subsequently, 10 times the molar amount of M30 cellulose of 1H-tetrazole-5-acetic acid was added to the solution and heated at 60°C for 14 hours. After the reaction, the obtained suspension was poured into water, and the product was filtered, washed with distilled water and acetonitrile for several times, and then vacuum dried at 60° C. overnight to obtain light yellow TAC.

[0036] Example 3 The specific synthesis scheme of the cellulose modification is as follows: The cellulose raw material is selected as nanocellulose; First, the nanocellulose was pretreated. The nanocellulose was dried in a vacuum oven at 105°C for 2 hours to obtain nanocellulose dry powder. Lithium chloride was dried in a vacuum oven at 130°C for 2 hours to obtain anhydrous lithium chloride before use. Anhydrous DMAc was treated with 5A molecular sieve before use. First, the pretreated nanocellulose powder was dispersed in anhydrous DMAc at a bath ratio of 10:90, and then N 2 The mixture was slowly stirred under the conditions of 160°C for activation for 2 hours and then naturally cooled to 100°C to obtain a reaction solution. Subsequently, anhydrous lithium chloride (10% by mass of anhydrous DMAc) was added to the reaction solution and stirred continuously. Subsequently, the mixture was naturally cooled to room temperature to obtain a mixed solution. p-Toluenesulfonyl chloride was added to the mixed solution to activate the hydroxyl group. Subsequently, 10 times the molar amount of M30 cellulose of 1H-tetrazole-5-acetic acid was added to the solution and heated at 60°C for 14 hours. After the reaction, the obtained suspension was poured into water, the product was filtered, washed with distilled water and acetonitrile for several times, and then vacuum dried at 60° C. overnight to obtain light yellow TANC.

[0037] Example 4 The specific synthesis scheme of the cellulose modification is as follows: The cellulose raw material is selected as microcrystalline cellulose; First, microcrystalline cellulose is pretreated. Microcrystalline cellulose is dried in a vacuum oven at 105°C for 2 hours to obtain microcrystalline cellulose dry powder. Lithium chloride is dried in a vacuum oven at 130°C for 2 hours to obtain anhydrous lithium chloride before use. Anhydrous DMAc is treated with 5A molecular sieves before use. First, the pretreated microcrystalline cellulose powder was dispersed in anhydrous DMAc at a bath ratio of 10:90, and then N 2 The mixture was slowly stirred under the conditions of 160°C for activation for 2 hours and then naturally cooled to 100°C to obtain a reaction solution. Subsequently, anhydrous lithium chloride (10% by mass of anhydrous DMAc) was added to the reaction solution and stirred continuously. Subsequently, the mixture was naturally cooled to room temperature to obtain a mixed solution. p-Toluenesulfonyl chloride was added to the mixed solution to activate the hydroxyl group. Subsequently, 10 times the molar amount of M30 cellulose of 1H-tetrazole-5-acetic acid was added to the solution and heated at 60°C for 14 hours. After the reaction, the obtained suspension was poured into water, the product was filtered, washed with distilled water and acetonitrile for several times, and then vacuum dried at 60° C. overnight to obtain light yellow TAMC.

[0038] Experimental Example 1 Study on Modified Cellulose Experiment 1.1 Elemental Analysis and Density Measurement The products obtained in Examples 2-4 were taken as samples to study the percentages of carbon (C), hydrogen (H) and nitrogen (N) contained therein; The samples were estimated using a vario III elemental analyzer; The surface degree of substitution was calculated from the (DS) value of the tetrazolyl acetate functionalized polymer, which was based primarily on the nitrogen content obtained by elemental analysis according to the following equation: DS=

[0039] Where N(%) is the nitrogen content, 𝐴𝑈 is the molar mass of the anhydroglucose unit (162 g / mol), M N is the molar mass of the nitrogen atom (14 g / mol), M tetrazole-acetate is the molar mass of 1H-tetrazolyl-5-acetate (110 g / mol).

[0040] Material density is an important parameter that must be considered in product selection, which affects the performance of the material to a certain extent. Therefore, the density of all samples was measured using an electronic density meter UltraPYC1200E pycnometer, and ten tests were performed on each sample at a temperature of 23.1±0.5℃ to calculate the average density and standard deviation.

[0041] Experiment 1.2 Structural features iS10 FT-IR spectrometer from Nicolet, USA, with a wavenumber range of 400-4000cm-1, a spectrometer resolution of 4cm-1, a signal-to-noise ratio of 50000:1, and 64 scans; Solid-state nuclear magnetic resonance 13C of the nuclides was carried out using cross-polarization magic angle spinning technique (CP / MAS13) using a Bruker Avance III-500 spectrometer (11.74 T) at room temperature with an operating frequency of 76.46 MHz. The obtained spectra are shown in Figure 1-3 shown.

[0042] Experiment 1.3 Crystal structure and morphology analysis Prior to analysis, the dried samples were placed on a sticky carbon rod and coated with a conductive carbon film; X-ray diffraction (XRD) patterns of all samples were measured at ambient temperature in the angle range of 5–50° / 2θ using a D8 ADVANCE X-ray diffractometer from Bruker, Germany, at a generator voltage of 45 kV and a current of 40 mA; The percentage of crystallinity index (𝐶𝑟𝐼) of each sample is also calculated according to different diffraction patterns:

[0043] Where 𝐶𝑟𝐼 is the relative crystallinity, I 200 is the crystallization peak intensity on the 200 plane, I amp is the peak intensity of the transformers between the 110 and 200 Å planes, and the morphological features of the studied polymers were investigated using a FEI-Helios G3UC scanning electron microscope (SEM) at a 30 mm working distance and 30 kV accelerating voltage.

[0044] Experiment 1.4 Thermal Analysis After the samples were dried, 4-5 mg of each sample was heated from 25°C to 600°C; The thermal decomposition behavior of the investigated samples was examined using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) at a heating rate of 5 °C / min. TGA analysis was recorded on a Perkin Elmer TGA 4000 analyzer, while DTA experiments were performed by an OZM-Research-dta552ex analyzer.

[0045] The final results are shown in Table 1 below.

[0046] From the above table, we can know that the nitrogen contents of the three celluloses of different scales, M30 cellulose, nanocellulose or microcrystalline cellulose, generated by esterification with 1H-4-oxazole-5-acetic acid, TAC, TANC and TAMC, are 18.71% (DS=0.856), 21.54% (DS=1.08) and 19.17% (DS=0.9), respectively, which are significantly higher than trinitrocellulose (14.14%). In addition, it can be seen from the above table that the DS values ​​are all around 1, which indicates that the esterification of 1H-4-oxazole-5-acetic acid in the three celluloses has regioselective functionalization. Compared with the hydroxyl groups at the R1 and R2 positions, the hydroxyl group at the R3 position on the cellulose is the most reactive and is most easily replaced by the tetrazolyl functional group; The density of the modified cellulose measured in the above table shows that the modified cellulose has a higher density than the cellulose raw material.

[0047] Experimental Example 2 Determination of Surface Morphology of Modified Cellulose The surface morphology of the obtained samples was examined using SEM measurements, where it was found that TAC was a rough, irregular fiber rather than a smooth, transparent long fibril, indicating that during the modification process, the surface morphology was changed due to the physical expansion and untwisting of the M30 cellulose fibers, followed by the insertion of the tetrazolium acetate portion covering the surface of the cellulose fibers. TANC is smoother than TAMC and TAC as can be seen from the micrographs. It can also be seen from the SEM micrographs that TAMC has an irregular microrod-like structure with a rougher surface, similar to the microcrystalline cellulose MCC precursor. This finding reveals that the modified product obtained using MCC as a polymer precursor has a more uniform chemical modification than PC as a polymer precursor, while the changes in morphological characteristics are less important. This is consistent with the results of the elemental analysis and crystallinity data, indicating that the surface substitution degree of MCC and TAMC increases and the crystallinity is higher than that of TAC and TANC.

[0048] Experimental Example 2 Thermal Behavior Analysis In order to study the thermal stability and decomposition behavior of the synthesized 1H-4-oxazole-5-acetate cellulose series, TGA / DTGA and DTA analyses were performed, and the thermal parameters obtained are shown in Table 2 below: Table 2

[0049] in: a Initial decomposition temperature obtained by thermogravimetric analysis; b Peak decomposition temperature of DTGA; c initial decomposition temperature of differential thermal analysis results; d Peak decomposition temperature of differential thermal analysis; According to the above results, compared with the precursors (M30 cellulose, nanocellulose, and microcrystalline cellulose), the modified cellulose samples began to decompose at low temperatures. This is due to the presence of high-energy nitrogen-rich tetrazole moieties, which accelerates the thermal degradation of the polymer chains. In addition, an endothermic decomposition peak of M30 cellulose and MCC was observed at around 311.39°C and 327.86°C for the unmodified precursor, respectively, while the modified cellulose obtained after modification showed an obvious exothermic decomposition in the temperature range of 215-260°C, which was related to the introduction of tetrazolyl functional groups in cellulose.

[0050] Experimental Example 3 Analysis of products obtained after nitration of TAC, TANC and TAMC The inventors learned from the literature that the combination of tetrazolyl functional groups with other exogenous functions in an energetic molecule can reduce its sensitivity and thus improve its energetic performance. Therefore, the inventors explored whether the product obtained by inserting both nitrate ester and tetrazolyl functional groups into the cellulose backbone has lower sensitivity. TAC, TANC and TAMC were nitrated in a nitration system to prepare a series of 1H-tetrazolyl-5-cellulose acetate nitrates; 10g of 1H-tetrazole-5-acetate cellulose was nitrated with an appropriate amount of mixed acid in the hope of obtaining a series of 1H-tetrazole-5-acetate nitrate cellulose products. However, during the experiment, 1H-tetrazole-5-acetate cellulose dissolved in the system after nitration. The mixed acid system composed of nitric acid (65-68%) and sulfuric acid (98%) had too high a water content and poor nitration. In addition, under strong acid conditions and a large amount of water, cellulose underwent acid hydrolysis. Subsequently, a large amount of deionized water was added to the reaction solution, and then an appropriate amount of ethanol was added to precipitate a small amount of substance, which was filtered to form a transparent viscous gelatinous substance. The substance was dried at 70°C under vacuum for 5 hours to form a yellow-brown solid with a remaining amount of about 0.2 g.

[0051] The chemical reaction formula is as follows:

[0052] Therefore, it can be known from the above experimental results that the synthesis effect is not good in the nitration process of cellulose modification, but it can achieve the substitution of nitro groups on cellulose molecules to obtain 1H-tetrazolyl-5-cellulose acetate nitrate series.

[0053] Therefore, it can be seen that the present invention uses three kinds of M30 cellulose dry powder, nanocellulose dry powder or microcrystalline cellulose dry powder of different sizes as raw materials, pre-treats them in a DMAc / LiCl solvent system, so that the hydrogen bonds within and between the molecules are destroyed. By using anhydrous DMAc / LiCl as a cheap solvent system, the cost can be greatly saved while pre-treating the cellulose raw material. In addition, anhydrous DMAc / LiCl can also serve as a good hydrogen bond receptor due to its excellent performance, thereby destroying the hydrogen bonds within and between the cellulose precursor molecules, thereby promoting its chemical functionalization. After the pretreatment of cellulose, the hydroxyl functional groups in the anhydroglucose units are activated by p-toluenesulfonyl chloride, and the key hydroxyl groups of the anhydroglucose units are converted into strong leaving groups by sulfonylation, thereby increasing the reactivity of the sugar units to improve their leaving ability, and then the corresponding cellulose modifications (TAC, TANC, TAMC) are generated by the nucleophilic replacement reaction of the cellulose precursor with the activated hydroxyl functional groups of the 1H-tetrazole-5-acetate part. The chemical modification has the characteristics of high energy, high combustion, and enhanced toughness, and can be used as an energetic material binder in explosives.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified cellulose, characterized in that: The chemical formula of the cellulose modification is: , wherein R1 and R2 are either tetrazolyl or hydroxyl.

2. The modified cellulose according to claim 1, characterized in that The R1 and R2 are both tetrazolyl.

3. A method for preparing a modified cellulose according to any one of claims 1 to 2, characterized in that: The following steps are involved: The cellulose raw material is uniformly dispersed in anhydrous DMAc, and then stirred and heated for activation for 1-2 hours under nitrogen flow, and then cooled to obtain a reaction solution; Adding anhydrous lithium chloride to the reaction solution, stirring until the cellulose raw material is completely dissolved, and cooling to obtain a mixed solution; To the mixed solution, add p-toluenesulfonyl chloride and 1H-tetrazolyl-5-acetic acid in sequence, heat for 10 h to 14 h, filter, wash and dry to obtain the product.

4. The method for preparing a modified cellulose according to claim 3, characterized in that: The cellulose raw material is one or more of M30 cellulose dry powder, nanocellulose dry powder or microcrystalline cellulose dry powder.

5. The method for preparing a modified cellulose according to claim 3, characterized in that: When the cellulose raw material is dispersed in anhydrous DMAc, the bath ratio of the cellulose raw material to the anhydrous DMAc is (1:99)-(10:90).

6. The method for preparing a modified cellulose according to claim 5, characterized in that: The bath ratio is (6-10):(95-99).

7. The method for preparing a modified cellulose according to claim 3, characterized in that: The lithium chloride is 1%-10% of the mass of the anhydrous DMAc.

8. The method for preparing a modified cellulose according to claim 7, characterized in that: The lithium chloride is 5% of the mass of the anhydrous DMAc.

9. The method for preparing a modified cellulose according to claim 3, characterized in that: The molar ratio of the cellulose raw material to the 1H-tetrazolyl-5-acetic acid is 1:(1-10); Preferably, the molar ratio of the cellulose raw material to the 1H-tetrazolium-5-acetic acid is 1:

5.

10. Use of the modified cellulose according to any one of claims 1 to 2 and the product obtained by the preparation method according to any one of claims 3 to 9 as an adhesive in explosives.

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