Flame-retardant cellulose ester thin film and preparation method therefor

Abstract

The present application relates to the field of the manufacturing of flame-retardant thin films, in particular to a method for preparing a flame-retardant cellulose ester thin film. Dimethyl phosphite, which acts as a flame-retardant monomer, is subjected to transesterification using 1,8-diazabicycloundec-7-ene as a catalyst in a 1-butyl-3-methylimidazolium chloride / dimethyl sulfoxide cosolvent system to synthesize a phosphite cellulose ester, and then, a phosphite cellulose ester thin film is prepared in dimethyl sulfoxide by means of solvent evaporation. The residual carbon rate of the prepared phosphite cellulose ester thin film is 30.4-33.7%. The operation process is simple, the cellulose solvent used is green and environmentally-friendly, the prepared cellulose ester can be applied to flame-retardant coatings, and the cellulose ester thin film can be applied to packaging materials, so that the problems of flammability, etc. of existing cellulose-based products are solved.

Description

Flame-retardant cellulose ester film and preparation method thereof Technical Field

[0001] The invention relates to the field of flame retardant film manufacturing, and in particular to a method for preparing a flame retardant cellulose ester film. Background Art

[0002] With growing environmental awareness, cellulose has become a popular choice for manufacturing various materials due to its renewable, biodegradable, and biocompatible properties. Driven by the demand for environmentally friendly products, cellulose-based products hold enormous potential in a variety of applications, including packaging, biomedical composites, electrodes and capacitors, and adsorption separations. However, untreated microcrystalline cellulose has a residual carbon content of only 0.37%, making it highly flammable, significantly limiting its use in applications requiring flame retardancy.

[0003] In fact, cellulose modification is widely considered a key method for achieving cellulose functionalization applications. Generally, chemical reactions involving anhydroglucose units within the cellulose molecular chain or cellulose surface groups (such as -OH, -CHO, and -COOH) are the most common methods for functionalizing and modifying cellulose's molecular structure. Correspondingly, esterification, acylation, silanization, and polymer grafting are also important avenues for functionalizing cellulose. Therefore, molecular structure modification can improve the flame retardancy of cellulose-based products, promoting the functionalization and high-value utilization of cellulose.

[0004] Molecular structure modification methods to improve the flame retardancy of cellulose primarily include phosphorylation, silanization, cross-linking, and covalent functionalization. Indeed, when designing the molecular structure of cellulose, it is crucial to swell or dissolve the cellulose to expose more hydrogen bonds. Homogeneous chemical modification is, to a certain extent, an effective technique for converting cellulose into highly homogenized derivatives. This process alters the physical and chemical properties of cellulose, thereby promoting its utilization. Generally, homogeneous systems used for cellulose esterification modification include dimethyl sulfoxide / tetrabutylammonium fluoride, lithium chloride / N,N-dimethylacetamide, and ionic liquids. Among these homogeneous systems, ionic liquids are most promising for preparing cellulose derivatives with specific structures. Homogeneous dissolution of cellulose is a critical step before molecular structure modification. After cellulose is dissolved in the homogeneous system, the hydroxyl groups are replaced by phosphite groups through an ester exchange reaction. The flame retardancy of cellulose is achieved through the inherent flame retardancy of these phosphite groups. Summary of the Invention

[0005] The present invention aims to provide a method for preparing flame-retardant cellulose ester and a film thereof.

[0006] The present invention dissolves a certain amount of cellulose in an ionic liquid co-solvent system to form a homogeneous cellulose solution. During the modification process, the numerous exposed hydroxyl groups in the cellulose increase the number of reactive sites for transesterification, allowing more flame-retardant monomers to be grafted onto the cellulose, thereby improving the flame retardancy of the cellulose ester. This method offers the advantages of a simple operation process and the environmentally friendly cellulose solvent used. The prepared cellulose ester can be used in flame-retardant coatings, and cellulose ester films can be used in packaging materials, addressing the flammability issues currently associated with cellulose-based products.

[0007] To achieve the above object of the invention, the present invention provides a method for preparing a flame retardant cellulose ester film, comprising the following steps:

[0008] Step (1), adding cellulose to an ionic liquid co-solvent system to prepare a homogeneous cellulose solution;

[0009] Step (2), adding dimethyl phosphite and a catalyst to the homogeneous cellulose solution obtained in step (1), performing an ester exchange reaction, and reacting to obtain a cellulose phosphite ester solution;

[0010] Step (3) precipitating the cellulose phosphite solution in step (2) with a regenerated solvent, washing, centrifuging and drying to obtain cellulose phosphite powder;

[0011] Step (4): dissolving the cellulose phosphite powder prepared in step (3) in dimethyl sulfoxide and then evaporating the solvent to prepare a flame-retardant cellulose ester film.

[0012] The ionic liquid co-solvent system in step (1) is specifically a mixture of 1-butyl-3-methylimidazolium chloride and dimethyl sulfoxide, with a mass ratio of 2:1.

[0013] Through the above technical solution, the addition of a certain amount of dimethyl sulfoxide can increase the dissolution rate of cellulose and also help to reduce the viscosity of the ionic liquid.

[0014] In the step (1), the mass ratio of cellulose to the ionic liquid co-solvent system is 1:30, the cellulose is microcrystalline cellulose with a degree of polymerization of 280, the dissolution temperature of the cellulose in the ionic liquid co-solvent system is 110° C., and the reaction time is 1 h.

[0015] In order to obtain more homogeneous cellulose solution through the above technical solution, more cellulose should be dissolved. If too much cellulose is added, the viscosity of the ionic liquid will increase and the cellulose will not be fully dissolved, and the obtained cellulose solution will contain undissolved cellulose.

[0016] In step (2), the molar ratio of the anhydroglucose unit of the cellulose to dimethyl phosphite is 1:(7-9), the reaction temperature is 110°C, and the reaction time is 3 hours. In step (2), the catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene, and the molar ratio of 1,8-diazabicyclo[5.4.0]undec-7-ene to dimethyl phosphite is 1:4.

[0017] Through the above technical solution, the anhydroglucose unit contains a reducing hydroxyl group, and the dimethyl phosphite contains an ester group. The two will undergo an ester exchange reaction under the action of an alkaline catalyst, thereby grafting the phosphorus-containing group onto the cellulose molecular chain, and the flame retardancy of the cellulose is improved through the phosphorus element group.

[0018] The regeneration solvent in step (3) is ethanol. The mass ratio of cellulose phosphite powder to dimethyl sulfoxide in step (4) is 3:100.

[0019] Through the above technical solution, cellulose phosphite can be dissolved in dimethyl sulfoxide, and then the cellulose phosphite film can be prepared by evaporating the solvent.

[0020] The flame-retardant cellulose ester film has a residual carbon rate of 30.4-33.7%, and does not generate toxic and corrosive gases when thermally decomposed. The film can be applied to the fields of flame-retardant coatings, chemicals, packaging films, and agricultural mulch films.

[0021] The beneficial effects of the present invention are:

[0022] The present invention prepares cellulose phosphite by dissolving cellulose first and then modifying the cellulose.

[0023] The invention uses ionic liquid as solvent and prepares flame-retardant cellulose ester film by molecular structure design method, which has the advantages of being green and environmentally friendly, simple to operate, recyclable ionic liquid, easy to industrialize, etc.

[0024] The cellulose phosphite prepared in the present invention is formed by linking cellulose and phosphite groups via chemical bonds.

[0025] The present invention can regulate the esterification degree of cellulose phosphite by adjusting the molar ratio of reactants, thereby controlling the flame retardancy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0027] Figure 1 is a schematic diagram of the preparation of cellulose phosphite film.

[0028] FIG2 is an infrared spectra of microcrystalline cellulose and Example 1.

[0029] FIG3 is a nuclear magnetic resonance phosphorus spectrum of Example 1.

[0030] FIG4 is a thermogravimetric diagram of microcrystalline cellulose and Example 1.

[0031] FIG5 is a surface scanning electron microscope image of Example 1. DETAILED DESCRIPTION

[0032] In order to further understand the present invention, the embodiments of the present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto. Example 1

[0033] A method for preparing a flame-retardant cellulose ester film comprises the following steps:

[0034] Step (1) Weigh 0.5 g of microcrystalline cellulose and disperse it in 5 g of dimethyl sulfoxide by ultrasonication. Add the dispersed cellulose dispersion to 10 g of 1-butyl-3-methylimidazolium chloride solution and react at 110°C for 1 h to obtain a homogeneous cellulose solution.

[0035] Step (2) Add 2.55 mL of dimethyl phosphite and 1.06 mL of 1,8-diazabicyclo[5.4.0]undec-7-ene to the homogeneous cellulose solution, and react at 110° C. for 3 h to obtain a cellulose phosphite solution.

[0036] Step (3) adding 30 mL of ethanol to the cellulose phosphite solution to obtain a cellulose phosphite mixture, centrifuging the mixture to obtain a cellulose phosphite precipitate, repeating this washing and centrifugation step 5 times, and then drying the precipitate to obtain a cellulose phosphite powder.

[0037] As shown in Figure 2, cellulose phosphite has a -1 There is a peak of P=O at 843 cm -1 Peaks of PH bonds appear at these locations, which are characteristic peaks of phosphite groups.

[0038] As shown in FIG3 , a signal appeared at around 0.5 ppm in cellulose phosphite, indicating that its molecule contained a phosphite group.

[0039] Step (4) Weigh 0.3 g of cellulose phosphite powder and add it to 10 g of dimethyl sulfoxide, and dissolve it by ultrasonication at 50°C for 30 min to prepare a cellulose phosphite-dimethyl sulfoxide solution. Pour the prepared solution into a polytetrafluoroethylene culture dish with a diameter of 8 cm, and dry it in a vacuum drying oven at 80°C for 48 h to prepare a cellulose phosphite film.

[0040] The test results show that the thickness of the prepared cellulose phosphite film is 30~40 μm, the residual carbon rate is 33.7%, the tensile strength is 10.6 MPa, and the elongation at break is 20.3%.

[0041] The specific performance test is:

[0042] (1) Thickness measurement: According to GB / T 6672-2001, the thickness of the film is measured by an electronic thickness gauge. The sample size is a circle with a diameter of 8 cm. Five points of the sample are taken for each test.

[0043] (2) Determination of residual carbon rate: According to the test method of weight loss and residual amount by thermogravimetric analyzer GB / T 27761-2011, a TGA550 thermogravimetric analyzer was used. The test temperature range was between 30-600 °C, and the heating rate was controlled at 10 °C min -1 The test gas was nitrogen with a flow rate of 30 mL min -1 The greater the residual carbon rate, the better the flame retardant performance.

[0044] (3) Determination of tensile properties: According to the test method for tensile properties of plastics and films GB / T 13022-1991, an EJA Vantage 10 24″ tensile testing machine was used. The rectangular specimen size was 30 mm × 10 mm, and the thickness was determined by the performance test (1). The test process was carried out at 25 °C with a speed of 2 mm min. -1 The test was carried out at a tensile rate of 500 nm. Each group of samples was tested five times and the average value was calculated. The greater the tensile strength, the better the mechanical properties of the film, and the greater the elongation at break, the better the ductility of the film. Example 2

[0045] A method for preparing a flame-retardant cellulose ester film comprises the following steps:

[0046] Step (1) Weigh 0.5 g of microcrystalline cellulose and disperse it in 5 g of dimethyl sulfoxide by ultrasonication. Add the dispersed cellulose dispersion to 10 g of 1-butyl-3-methylimidazolium chloride solution and react at 110°C for 1 h to obtain a homogeneous cellulose solution.

[0047] Step (2) Add 2.264 mL of dimethyl phosphite and 0.94 mL of 1,8-diazabicyclo[5.4.0]undec-7-ene to the homogeneous cellulose solution, and react at 110° C. for 2 h to obtain a cellulose phosphite solution.

[0048] Step (3) adding 30 mL of ethanol to the cellulose phosphite solution to obtain a cellulose phosphite mixture, centrifuging the mixture to obtain a cellulose phosphite precipitate, repeating this washing and centrifugation step 5 times, and then drying the precipitate to obtain a cellulose phosphite powder.

[0049] Step (4) Weigh 0.3 g of cellulose phosphite powder and add it to 10 g of dimethyl sulfoxide, and dissolve it by ultrasonication at 50°C for 30 min to prepare a cellulose phosphite-dimethyl sulfoxide solution. Pour the prepared solution into a polytetrafluoroethylene culture dish with a diameter of 8 cm, and dry it in a vacuum drying oven at 80°C for 48 h to prepare a cellulose phosphite film.

[0050] The test results show that the thickness of the prepared cellulose phosphite film is 30~40 μm, the residual carbon rate is 31.9%, the tensile strength is 10.6 MPa, and the elongation at break is 18.8%. Example 3

[0051] A method for preparing a flame-retardant cellulose ester film comprises the following steps:

[0052] Step (1) Weigh 0.5 g of microcrystalline cellulose and disperse it in 5 g of dimethyl sulfoxide by ultrasonication. Add the dispersed cellulose dispersion to 10 g of 1-butyl-3-methylimidazolium chloride solution and react at 110°C for 1 h to obtain a homogeneous cellulose solution.

[0053] Step (2) 1.981 mL of dimethyl phosphite and 0.82 mL of 1,8-diazabicyclo[5.4.0]undec-7-ene were added to the homogeneous cellulose solution, and the mixture was reacted at 110° C. for 2 h to obtain a cellulose phosphite solution.

[0054] Step (3) adding 30 mL of ethanol to the cellulose phosphite solution to obtain a cellulose phosphite mixture, centrifuging the mixture to obtain a cellulose phosphite precipitate, repeating this washing and centrifugation step 5 times, and then drying the precipitate to obtain a cellulose phosphite powder.

[0055] Step (4) Weigh 0.3 g of cellulose phosphite powder and add it to 10 g of dimethyl sulfoxide, and dissolve it by ultrasonication at 50°C for 30 min to prepare a cellulose phosphite-dimethyl sulfoxide solution. Pour the prepared solution into a polytetrafluoroethylene culture dish with a diameter of 8 cm, and dry it in a vacuum drying oven at 80°C for 48 h to prepare a cellulose phosphite film.

[0056] The test results show that the thickness of the prepared cellulose phosphite film is 30~40 μm, the residual carbon rate is 30.4%, the tensile strength is 7.4 MPa, and the elongation at break is 18.1%.

[0057] The following is a further description of the accompanying drawings:

[0058] Figure 4 shows the thermogravimetric diagrams of microcrystalline cellulose and Example 1. As can be seen from Figure 4, there are significant differences between microcrystalline cellulose and Example 1 during thermal decomposition: the successful grafting of phosphorus-containing groups significantly increases the carbon residue rate of the cellulose phosphite film. That is, under thermal conditions, a relatively large carbon residue layer can prevent further combustion of the flame, thereby imparting a certain degree of flame retardancy.

[0059] Figure 5 is a surface scanning electron microscope image of Example 1. As can be seen from Figure 5, the surface of the cellulose phosphite film is smooth and flat.

[0060] In summary, the present invention uses dimethyl phosphite as a flame retardant monomer and 1,8-diazabicyclo[5.4.0]undec-7-ene as a catalyst in a green and environmentally friendly 1-butyl-3-methylimidazolium chloride / dimethyl sulfoxide co-solvent system to synthesize cellulose phosphite through an ester exchange reaction, and then prepares a cellulose phosphite film by evaporating the solvent in dimethyl sulfoxide. The preparation process is mild, environmentally friendly, and easy to operate.

Claims

1. A method for preparing a flame retardant cellulose ester film, characterized in that: The following steps are involved: Step (1), adding cellulose to an ionic liquid co-solvent system to prepare a homogeneous cellulose solution; Step (2), adding dimethyl phosphite and a catalyst to the homogeneous cellulose solution obtained in step (1), performing an ester exchange reaction, and reacting to obtain a cellulose phosphite ester solution; Step (3), subjecting the cellulose phosphite solution obtained in step (2) to precipitation with a regenerated solvent, washing, centrifugation and drying to obtain cellulose phosphite powder; Step (4): dissolving the cellulose phosphite powder prepared in step (3) in dimethyl sulfoxide and then evaporating the solvent to prepare a flame-retardant cellulose ester film.

2. The preparation method according to claim 1, characterized in that The ionic liquid co-solvent system in step (1) is specifically a mixture of 1-butyl-3-methylimidazolium chloride and dimethyl sulfoxide, with a mass ratio of 2:

1.

3. The preparation method according to claim 1 or 2, characterized in that In step (1), the mass ratio of cellulose to the ionic liquid co-solvent system is 1:30, the cellulose is microcrystalline cellulose powder with a degree of polymerization of 280, the dissolution temperature of the cellulose in the ionic liquid co-solvent system is 110° C., and the reaction time is 1 h.

4. The preparation method according to claim 1, characterized in that In step (2), the molar ratio of anhydroglucose units to dimethyl phosphite in the homogeneous cellulose solution is 1:(7-9), the reaction temperature is 110°C, and the reaction time is 3 h.

5. The preparation method according to claim 1, characterized in that In step (2), the catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene, and the molar ratio of 1,8-diazabicyclo[5.4.0]undec-7-ene to dimethyl phosphite is 1:

4.

6. The preparation method according to claim 1, characterized in that Step (3) specifically comprises: adding ethanol to the cellulose phosphite solution to obtain a cellulose phosphite precipitate, wherein the mass ratio of ethanol to the ionic liquid co-solvent system is 2:1; repeating this washing and centrifugation step 5 times, and then drying the precipitate to obtain cellulose phosphite powder.

7. The preparation method according to claim 1, characterized in that Step (4) specifically comprises: weighing cellulose phosphite powder and adding it to a dimethyl sulfoxide solution to dissolve it to obtain a cellulose phosphite-dimethyl sulfoxide solution, wherein the mass ratio of the cellulose phosphite powder to the dimethyl sulfoxide is 3:100; drying the obtained solution in a vacuum drying oven at 80° C. for 48 h to obtain a cellulose phosphite film.

8. The flame-retardant cellulose ester film prepared by the preparation method according to claim 7, characterized in that: The residual carbon rate of flame retardant cellulose ester film is 30.4~33.7%.

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