Preparation method of polyvinyl alcohol / lignin blend

Abstract

The invention discloses a preparation method of a polyvinyl alcohol / lignin blend. The method is characterized in that after polyvinyl alcohol and lignin are blended, epichlorohydrin is added as a cross-linking agent to improve the quality of the blend. The blend is prepared from the following raw material components in parts by mass: 65 to 95 parts of polyvinyl alcohol; 4 to 30 parts of lignin; and 1 to 5 parts of epoxy chloropropane. The invention provides a new method for preparing a polyvinyl alcohol / lignin blend, and the method can enhance the thermal stability and mechanical strength of the polyvinyl alcohol / lignin blend, thereby providing more applications for the new materials.

Description

Technical Field

[0001] The invention provides a method for preparing a polyvinyl alcohol / lignin blend, belonging to the field of polymer chemical industry. Background Art

[0002] Polyvinyl alcohol (PVA), as a water-soluble polymer, is widely used in many fields due to its excellent tensile strength, oxygen barrier properties, biodegradability and biocompatibility. However, the large number of hydroxyl groups in its molecular main chain makes the melting temperature very close to the decomposition temperature, which poses a challenge to the melt processing process. Although its melting point can be lowered by chemical modification or blending modification, these methods often lead to a significant decrease in its mechanical properties. In addition, PVA also has the problems of insufficient water resistance and single function, which greatly hinders its wider application. In order to improve the performance of PVA and enrich its functions, adding modifiers to it has become an effective strategy, which not only helps to improve its performance, but also further expands its scope of application.

[0003] Lignin, an alkyl-aromatic polymer commonly found in plant cell walls, accounts for 15% to 30% of the total dry weight of plants and plays a key role in strengthening cell wall structure and resisting pathogen attacks. Due to its abundant sources and wide range of functions, lignin has become a preferred raw material for the development of functional composite materials. Industrial-grade lignin is not only diverse in sources and cost-effective, but also green, environmentally friendly, and biodegradable. It also has multiple properties such as antioxidant and UV protection. The application of lignin in the modification of PVA to manufacture fully biodegradable composite materials has important economic and environmental significance. However, the strong hydrogen bonding effect of lignin itself makes it easy to aggregate in the PVA matrix, resulting in weak interfacial forces, which makes the mechanical properties of lignin / PVA composites poor. In view of the above problems, polyvinyl alcohol is used as raw material, lignin and waterborne polyurethane are used as fillers, lignin is liquefied to prepare lignin liquefied material, and a lignin-based waterborne polyvinyl alcohol blended film is successfully prepared by solution casting method, and the mechanical properties and water resistance of the blended film are improved (Preparation and Performance of Lignin-based Waterborne Polyurethane / Polyvinyl Alcohol Blended Film, Transactions of the Chinese Society of Agricultural Engineering, 2024). However, the thermal stability of the blended film still needs to be improved. In view of this, the inventor proposes to add epichlorohydrin as a cross-linking agent after the blending of polyvinyl alcohol and lignin to prepare the final blend, and combine it with two ultrasonic vibration methods to increase the thermal stability and mechanical strength of the blend. Summary of the invention

[0004] Objective: To overcome the defects of the prior art, the present invention provides a method for preparing a polyvinyl alcohol / lignin blend, which can enhance the thermal stability and mechanical strength of the polyvinyl alcohol / lignin blend, thereby enabling such new materials to be applied in more fields.

[0005] A method for preparing a polyvinyl alcohol / lignin blend, wherein the raw material components of the blend and the mass parts of each component are as follows:

[0006] Polyvinyl alcohol: 65 to 95 parts;

[0007] Lignin: 4 to 30 parts;

[0008] Epichlorohydrin: 1 to 5 parts.

[0009] The specific steps are as follows:

[0010] a) preparing a lignin solution;

[0011] b) preparing a polyvinyl alcohol solution;

[0012] c) mixing the lignin solution and the polyvinyl alcohol solution, placing them in an ultrasonic vibration device, heating them to 80 degrees Celsius, and stirring them at a rate of 300-600 rpm for 2 hours;

[0013] d) preparing an epichlorohydrin solution;

[0014] e) adding the epichlorohydrin solution to the mixed solution of lignin and polyvinyl alcohol, placing it in an ultrasonic vibration device again, heating it to 80 degrees Celsius, and stirring it at a rate of 300-600 rpm for 1 hour;

[0015] f) taking the blended liquid out of the ultrasonic vibration device, cooling and drying it to obtain the desired blend.

[0016] Preferably, the method for preparing the above lignin solution is to dissolve lignin in an alkaline solution, wherein the concentration of the alkaline solution is 3%-5%.

[0017] Preferably, the method for preparing the polyvinyl alcohol solution is to dissolve polyvinyl alcohol in water, and the mass percentage of polyvinyl alcohol is 80%-95%.

[0018] Preferably, the method for preparing the epichlorohydrin solution is to dissolve epichlorohydrin in water, and the mass percentage of epichlorohydrin is 1%-2%.

[0019] Preferably, the above-mentioned lignin is one or a combination of papermaking lignin, alkali lignin, lignin sulfonate, organic solvent lignin, enzymatic lignin and lignin modified from the above-mentioned lignin.

[0020] Beneficial effects: The method of the present invention can enhance the thermal stability and mechanical strength of the polyvinyl alcohol / lignin blend, so that such new materials can be applied to more occasions, such as chemical industry, electronics, sensing, packaging, environmental protection and other fields. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0022] Embodiment 1:

[0023] A new method for preparing a polyvinyl alcohol / lignin blend, wherein the raw material components of the blend and the mass parts of each component are as follows:

[0024] Polyvinyl alcohol: 79 parts;

[0025] Lignin: 20 parts;

[0026] Epichlorohydrin: 1 part.

[0027] A new method for preparing a polyvinyl alcohol / lignin blend, the specific steps are as follows:

[0028] a) dissolving lignin in 4% sodium hydroxide solution;

[0029] b) dissolving polyvinyl alcohol in deionized water to obtain a 90 wt % polyvinyl alcohol solution;

[0030] c) mixing the lignin solution and the polyvinyl alcohol solution, placing them in an ultrasonic vibration device, heating them to 80 degrees Celsius, and stirring them at a speed of 450 rpm for 2 hours;

[0031] d) dissolving epichlorohydrin in deionized water to obtain a 1 wt % epichlorohydrin solution;

[0032] e) adding the epichlorohydrin solution to the mixed solution of lignin and polyvinyl alcohol, placing it in an ultrasonic vibration device again, heating it to 80 degrees Celsius, and stirring it at a speed of 400 rpm for 1 hour;

[0033] f) taking the blended liquid out of the ultrasonic vibration device, cooling and drying it to obtain the desired blend.

[0034] Embodiment 2:

[0035] A new method for preparing a polyvinyl alcohol / lignin blend, wherein the raw material components of the blend and the mass parts of each component are as follows:

[0036] Polyvinyl alcohol: 83 parts;

[0037] Lignin: 15 parts;

[0038] Epichlorohydrin: 2 parts.

[0039] A new method for preparing a polyvinyl alcohol / lignin blend, the specific steps are as follows:

[0040] a) dissolving lignin in 3% sodium hydroxide solution;

[0041] b) dissolving polyvinyl alcohol in water to obtain an 85 wt % polyvinyl alcohol solution;

[0042] c) mixing the lignin solution and the polyvinyl alcohol solution, placing them in an ultrasonic vibration device, heating them to 80 degrees Celsius, and stirring them at a speed of 400 rpm for 2 hours;

[0043] d) dissolving epichlorohydrin in water to obtain a 1 wt % epichlorohydrin solution;

[0044] e) adding the epichlorohydrin solution to the mixed solution of lignin and polyvinyl alcohol, placing it in an ultrasonic vibration device again, heating it to 80 degrees Celsius, and stirring it at a speed of 400 rpm for 1 hour;

[0045] f) taking the blended liquid out of the ultrasonic vibration device, cooling and drying it to obtain the desired blend.

[0046] Embodiment three:

[0047] A new method for preparing a polyvinyl alcohol / lignin blend, wherein the raw material components of the blend and the mass parts of each component are as follows:

[0048] Polyvinyl alcohol: 75 parts;

[0049] Lignin: 22 parts;

[0050] Epichlorohydrin: 3 parts.

[0051] A new method for preparing a polyvinyl alcohol / lignin blend, the specific steps are as follows:

[0052] a) dissolving lignin in 5% sodium hydroxide solution;

[0053] b) dissolving polyvinyl alcohol in water to obtain a 92 wt % polyvinyl alcohol solution;

[0054] c) mixing the lignin solution and the polyvinyl alcohol solution, placing them in an ultrasonic vibration device, heating them to 80 degrees Celsius, and stirring them at a speed of 430 rpm for 2 hours;

[0055] d) dissolving epichlorohydrin in water to obtain a 2 wt % epichlorohydrin solution;

[0056] e) adding the epichlorohydrin solution to the mixed solution of lignin and polyvinyl alcohol, placing it in an ultrasonic vibration device again, heating it to 80 degrees Celsius, and stirring it at a rate of 500 rpm for 1 hour;

[0057] f) taking the blended liquid out of the ultrasonic vibration device, cooling and drying it to obtain the desired blend.

[0058] The performance of the three embodiments and the control group using only polyvinyl alcohol / lignin blend without epichlorohydrin were characterized by measuring the residual weight rate at 450°C using thermogravimetric analysis and measuring the tensile strength using a tensile test. The specific data are shown in the following table, indicating that the thermal stability and mechanical strength of the blends prepared by the invention are greatly improved.

[0059] Performance Indicators Residual weight rate at 450℃(%) Tensile strength(MPa) Embodiment 1 8.6 23.2 Embodiment 2 9.5 24.7 Embodiment 3 10.3 25.6 Control group 7.7 21.5

[0060] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Two modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a polyvinyl alcohol / lignin blend, characterized in that: After polyvinyl alcohol and lignin are blended, epichlorohydrin is added as a cross-linking agent to prepare the final blend.

2. The method for preparing a polyvinyl alcohol / lignin blend according to claim 1, characterized in that: The raw material components of the blend and the mass parts of each component are as follows: Polyvinyl alcohol: 65 to 95 parts; Lignin: 4 to 30 parts; Epichlorohydrin: 1 to 5 parts.

3. The method for preparing a polyvinyl alcohol / lignin blend according to claim 1 or 2, characterized in that: The specific steps are as follows: a) preparing a lignin solution; b) preparing a polyvinyl alcohol solution; c) mixing the lignin solution and the polyvinyl alcohol solution, placing them in an ultrasonic vibration device, heating them to 80 degrees Celsius, and stirring them at a rate of 300-600 rpm for 2 hours; d) preparing an epichlorohydrin solution; e) adding the epichlorohydrin solution to the mixed solution of lignin and polyvinyl alcohol, placing it in an ultrasonic vibration device again, heating it to 80 degrees Celsius, and stirring it at a rate of 300-600 rpm for 1 hour; f) taking the blended liquid out of the ultrasonic vibration device, cooling and drying it to obtain the desired blend.

4. The method for preparing a polyvinyl alcohol / lignin blend according to claim 3, characterized in that: The method for preparing the lignin solution is to dissolve the lignin in an alkaline solution, wherein the concentration of the alkaline solution is 3%-5%.

5. The method for preparing a polyvinyl alcohol / lignin blend according to claim 3, characterized in that: The method for preparing the polyvinyl alcohol solution is to dissolve polyvinyl alcohol in water, wherein the mass percentage of the polyvinyl alcohol is 80%-95%.

6. The method for preparing a polyvinyl alcohol / lignin blend according to claim 3, characterized in that: The preparation method of the epichlorohydrin solution is to dissolve epichlorohydrin in water, and the mass percentage of epichlorohydrin is 1%-2%.

7. The method for preparing a polyvinyl alcohol / lignin blend according to claim 1, characterized in that: The lignin is one or a combination of papermaking lignin, alkali lignin, lignin sulfonate, organic solvent lignin, enzymatic lignin, and lignin modified from the above lignins.