CN113201112A - Waterborne polyurethane with lignin as chain extender and preparation method and application thereof - Google Patents
Waterborne polyurethane with lignin as chain extender and preparation method and application thereof Download PDFInfo
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- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
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- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/64—Macromolecular compounds not provided for by groups C08G18/42 - C08G18/63
- C08G18/6492—Lignin containing materials; Wood resins; Wood tars; Derivatives thereof
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- C08G18/00—Polymeric products of isocyanates or isothiocyanates
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- C08G18/40—High-molecular-weight compounds
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
- C09D175/04—Polyurethanes
Abstract
The invention discloses waterborne polyurethane taking lignin as a chain extender, a preparation method and application thereof, wherein the preparation method comprises the following steps: dissolving 4-20 parts of lignin in a solvent, and slowly dropwise adding 6-30 parts of polyurethane prepolymer under the protection of nitrogen and stirring at 40-80 ℃; after the dropwise addition is finished, reacting for 2-4 hours at 40-80 ℃; then cooling to below 30 ℃, adding a neutralizing agent, and reacting for 10-30 minutes at below 30 ℃; and finally, adding deionized water, and performing high-speed shearing emulsification to obtain the waterborne polyurethane emulsion. The lignin used in the preparation method provided by the invention can directly participate in the reaction to synthesize the waterborne polyurethane without chemical modification, so that the synthesis process is simplified and the cost is reduced. According to the preparation method disclosed by the invention, lignin is used as the hydrophilic chain extender, and other hydrophilic chain extenders are not required to be added, so that the prepared waterborne polyurethane emulsion is good in stability and excellent in performance.
Description
Technical Field
The invention belongs to the field of modified lignin, and particularly relates to waterborne polyurethane taking lignin as a chain extender, and a preparation method and application thereof.
Background
The waterborne polyurethane has the advantages of good wear resistance, glossiness, strong adhesive force and the like, and is widely applied to the fields of wood coatings, automobile coatings, paper coating agents and the like. However, the molecular chain of the traditional waterborne polyurethane is a simple linear molecular structure and does not have strong chemical crosslinking effect, so that the traditional waterborne polyurethane has the problems of poor heat resistance and ultraviolet aging resistance, and is easy to decompose and lose efficacy in severe environments of high temperature and strong ultraviolet. Therefore, the preparation of the waterborne polyurethane coating with excellent heat resistance or ultraviolet aging resistance through modification is a research hotspot in the field.
In recent years, researches on lignin modified waterborne polyurethane have more reports, and modification methods can be mainly divided into two types, namely blending modification and copolymerization modification.
The blending modification is to physically compound the lignin and the polyurethane emulsion, and has the advantage of simple modification method. In order to improve the compatibility of lignin and aqueous polyurethane, researchers try to add the lignin to the aqueous polyurethane after the lignin is physically or chemically modified.
The copolymerization modification is to use modified lignin to replace partial polyol as a main reactant to prepare the modified waterborne polyurethane.
In the above studies on lignin-modified aqueous polyurethane, the following problems exist in both blending modification and copolymerization modification: (1) the lignin can be used as a raw material for modifying the waterborne polyurethane after being physically or chemically modified, the pre-modification of the lignin obviously improves the production cost of the waterborne polyurethane, and the utilization rate of the lignin is also reduced. (2) The addition amount of lignin is generally lower than 15%, and in fact, due to the limitation of the effective content of lignin and the reaction efficiency, the lignin content in the prepared lignin modified waterborne polyurethane is lower. (3) In the research of copolymerization modification, lignin only replaces part of polyol, and a hydrophilic chain extender needs to be additionally added, so that no report that lignin is used as the hydrophilic chain extender for preparing the waterborne polyurethane is provided.
Disclosure of Invention
The invention aims to provide waterborne polyurethane and a preparation method and application thereof.
The purpose of the invention is realized by the following technical scheme:
a preparation method of waterborne polyurethane comprises the following steps:
dissolving 4-20 parts of lignin in a solvent, and slowly dropwise adding 6-30 parts of polyurethane prepolymer under the protection of nitrogen and stirring at 40-80 ℃; after the dropwise addition is finished, reacting for 2-4 hours at 40-80 ℃; then cooling to below 30 ℃, adding a neutralizing agent, and reacting for 10-30 minutes at below 30 ℃; finally, adding deionized water for high-speed shearing emulsification to obtain a waterborne polyurethane emulsion;
preferably, the using amount of the lignin is 10.4-13.2 parts, and the using amount of the polyurethane prepolymer is 26.7 parts; under the dosage proportion, the lignin content of the obtained waterborne polyurethane emulsion is 19.88-24.68%, the emulsion has good stability (small particle size) and excellent mechanical property, and the prepared varnish has high pencil hardness.
The dosage of the neutralizer is 0.4-2 parts;
the polyurethane prepolymer is prepared by the following steps:
under the protection of nitrogen, mixing 4-20 parts of polyol with 2-10 parts of isocyanate, dropwise adding a catalyst, and stirring and reacting at 60-80 ℃ for 1-4 hours to obtain a polyurethane prepolymer;
the parts are parts by mass.
Preferably, the lignin is one of alkali lignin, enzymatic hydrolysis lignin, high-boiling alcohol lignin or lignosulfonate;
preferably, the solvent is one of acetone, N-dimethylformamide or N, N-dimethylacetamide;
preferably, the neutralizing agent is triethylamine;
preferably, the polyhydric alcohol is one of polypropylene glycol, polytetrahydrofuran ether glycol or polyethylene glycol;
the number average molecular weight of the polypropylene glycol is 600-5000;
the number average molecular weight of the polytetrahydrofuran ether glycol is 600-5000;
the number average molecular weight of the polyethylene glycol is 600-5000;
preferably, the isocyanate is one of isophorone diisocyanate, toluene diisocyanate or diphenylmethane diisocyanate;
preferably, the catalyst is dibutyltin dilaurate.
The waterborne polyurethane emulsion prepared by the method can be used for preparing woodware varnish;
specifically, the waterborne polyurethane emulsion is prepared into emulsion with solid content of 10 wt%, and the emulsion is coated on woodware, dried, coated with a layer of emulsion and dried.
Compared with the prior art, the invention has the following advantages and effects:
1. the lignin used in the preparation method provided by the invention can directly participate in the reaction to synthesize the waterborne polyurethane without chemical modification, so that the synthesis process is simplified and the cost is reduced.
2. According to the preparation method disclosed by the invention, lignin is used as the hydrophilic chain extender, and other hydrophilic chain extenders are not required to be added, so that the prepared waterborne polyurethane emulsion is good in stability and excellent in performance.
3. The highest content of lignin in the lignin-based waterborne polyurethane prepared by the invention can reach 24.68%. The high lignin content can reduce the consumption of fossil raw materials, reduce the synthesis cost and improve the environmental protection and economy.
4. The lignin-based waterborne polyurethane prepared by the invention can be applied to wood varnish, and the application field of the lignin-based waterborne polyurethane is widened.
Drawings
FIG. 1 is an infrared spectrum of the aqueous polyurethane emulsion obtained in example 1.
FIG. 2 is a graph showing the average particle diameter of the aqueous polyurethane emulsion obtained in examples 1 to 4.
FIG. 3 is an appearance diagram of the aqueous polyurethane film obtained in example 4.
FIG. 4 is a scanning electron micrograph of a cross section of the aqueous polyurethane film obtained in example 4.
FIG. 5 is a stress-strain diagram of the waterborne polyurethane films obtained in examples 1 to 4 and a commercial Waterborne Polyurethane (WPU) film.
FIG. 6 is a thermogravimetric analysis of the waterborne polyurethane films and the commercial WPU films obtained in examples 1-4.
FIG. 7 is an appearance of the aqueous polyurethane varnish obtained in examples 1 to 4.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
The lignin related by the invention comprises alkali lignin, enzymolysis lignin, high-boiling alcohol lignin and lignosulfonate, and the sources are as follows:
the alkali lignin is purchased from Taiwan auxiliary agent factories of Shaoxing city in Shaoxing province of Zhejiang, and is obtained by acid-washing and purifying by-products of alkaline pulping;
the enzymatic hydrolysis lignin is purchased from Shandong Longli biological science and technology Co., Ltd, corncobs are used as raw materials, and byproducts after enzymatic hydrolysis by cellulase are adopted;
the high-boiling alcohol lignin is purchased from Songmang fine chemical auxiliary agent Co., Ltd, Nanping, Fujian province, and is extracted from wood by a high-boiling alcohol (1, 4-butanediol) solvent method;
lignosulfonate, purchased from the Square chemical assistant factory, Turkey, Jilin province, is a by-product of acid pulping of pine pulp.
Example 1
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 20g of polypropylene glycol (with the number average molecular weight of 1000) and 6.7g of isophorone diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.01g of dibutyltin dilaurate, and stirring at 80 ℃ for reacting for 2 hours to obtain a polyurethane prepolymer;
(2) dissolving 8.9g of alkali lignin in 40g N, N-dimethylformamide, adding the dissolved alkali lignin into a three-neck flask protected by nitrogen after complete dissolution, and slowly dropping the alkali lignin into the polyurethane prepolymer while stirring at the temperature of 80 ℃; after the dropwise addition, reacting for 2 hours at 80 ℃; then cooling to 30 ℃, adding 0.9g of triethylamine, and reacting for 30 minutes at 30 ℃; and finally, adding 80g of deionized water, shearing at a high speed and emulsifying for 30 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based aqueous polyurethane emulsion (LWPU) prepared in example 1 was named LWPU1. LWPU in this example1The lignin content of (A) was 16.77%, and the average particle size of the emulsion was 233 nm. LWPU (light-weight polyurethane) by using dilute hydrochloric acid1Adjusting the pH value of the emulsion to 2-3, washing the obtained precipitate with deionized water for multiple times until the precipitate is neutral, and drying the precipitate in a vacuum oven at 50 ℃ for 8 hours to obtain a purified product.
Example 2
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 20g of polypropylene glycol (with the number average molecular weight of 1000) and 6.7g of isophorone diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.01g of dibutyltin dilaurate, and stirring at 80 ℃ for reacting for 2 hours to obtain a polyurethane prepolymer;
(2) dissolving 10.4g of alkali lignin in 40g N, N-dimethylformamide, adding the dissolved alkali lignin into a three-neck flask protected by nitrogen after complete dissolution, and slowly dropping polyurethane prepolymer while stirring at 80 ℃; after the dropwise addition, reacting for 2 hours at 80 ℃; then cooling to 30 ℃, adding 1g of triethylamine, and reacting for 30 minutes at 30 ℃; and finally, adding 80g of deionized water, shearing at a high speed and emulsifying for 30 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based aqueous polyurethane emulsion prepared in example 2 was named LWPU2. LWPU in this example2The lignin content of (A) was 19.88%, and the average particle size of the emulsion was 198 nm.
Example 3
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 20g of polypropylene glycol (with the number average molecular weight of 1000) and 6.7g of isophorone diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.01g of dibutyltin dilaurate, and stirring at 80 ℃ for reacting for 2 hours to obtain a polyurethane prepolymer;
(2) dissolving 11.4g of alkali lignin in 40g N, N-dimethylformamide, adding the dissolved alkali lignin into a three-neck flask protected by nitrogen after complete dissolution, and slowly dropping polyurethane prepolymer while stirring at 80 ℃; after the dropwise addition, reacting for 2 hours at 80 ℃; then cooling to 30 ℃, adding 1.1g of triethylamine, and reacting for 30 minutes at 30 ℃; and finally, adding 80g of deionized water, shearing at a high speed and emulsifying for 30 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based aqueous polyurethane emulsion prepared in example 3 was named LWPU3. LWPU in this example3The lignin content of (A) was 21.47%, and the average particle size of the emulsion was 188 nm.
Example 4
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 20g of polypropylene glycol (with the number average molecular weight of 1000) and 6.7g of isophorone diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.01g of dibutyltin dilaurate, and stirring at 80 ℃ for reacting for 2 hours to obtain a polyurethane prepolymer;
(2) dissolving 13.2g of alkali lignin in 40g N, N-dimethylformamide, adding the dissolved alkali lignin into a three-neck flask protected by nitrogen after complete dissolution, and slowly dropping the alkali lignin into the polyurethane prepolymer while stirring at the temperature of 80 ℃; after the dropwise addition, reacting for 2 hours at 80 ℃; then cooling to 30 ℃, adding 1.3g of triethylamine, and reacting for 30 minutes at 30 ℃; and finally, adding 80g of deionized water, shearing at a high speed and emulsifying for 30 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based aqueous polyurethane emulsion prepared in example 4 was named LWPU4. LWPU in this example3The lignin content of (A) was 24.68%, and the average particle size of the emulsion was 127 nm.
Example 5
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 4g of polypropylene glycol (with the number average molecular weight of 600) and 2g of isophorone diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.01g of dibutyltin dilaurate, and stirring at 80 ℃ for reacting for 2 hours to obtain a polyurethane prepolymer;
(2) dissolving 4g of alkali lignin in 20g N, N-dimethylformamide, adding the dissolved alkali lignin into a three-neck flask protected by nitrogen after complete dissolution, and slowly dripping the alkali lignin into the polyurethane prepolymer while stirring at the temperature of 80 ℃; after the dropwise addition, reacting for 2 hours at 80 ℃; then cooling to 30 ℃, adding 0.4g of triethylamine, and reacting for 10 minutes at 30 ℃; and finally, adding 40g of deionized water, shearing at a high speed and emulsifying for 10 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based aqueous polyurethane prepared in this example had a lignin content of 21.33% and an emulsion average particle size of 195 nm.
Example 6
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 20g of polypropylene glycol (with the number average molecular weight of 5000) and 3g of diphenylmethane diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.1g of dibutyltin dilaurate, and stirring at 60 ℃ for reaction for 1 hour to obtain a polyurethane prepolymer;
(2) dissolving 10g of alkali lignin in 30g N, N-dimethylacetamide, adding the alkali lignin into a three-neck flask protected by nitrogen after the alkali lignin is completely dissolved, and slowly dripping the alkali lignin into the polyurethane prepolymer while stirring at the temperature of 40 ℃; after the dropwise addition, reacting for 2 hours at 40 ℃; then cooling to 30 ℃, adding 1g of triethylamine, and reacting for 30 minutes at 30 ℃; and finally, adding 70g of deionized water, shearing at a high speed and emulsifying for 30 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based waterborne polyurethane prepared in the example had a lignin content of 18.72% and an emulsion average particle size of 216 nm.
Example 7
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 20g of polyethylene glycol (with the number average molecular weight of 600) and 10g of toluene diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.01g of dibutyltin dilaurate, and stirring at 60 ℃ for reacting for 4 hours to obtain a polyurethane prepolymer;
(2) dissolving 20g of enzymatic hydrolysis lignin in 40g of acetone, adding the dissolved enzymatic hydrolysis lignin into a three-neck flask protected by nitrogen after complete dissolution, and slowly dripping the polyurethane prepolymer while stirring at the temperature of 60 ℃; after the dropwise addition, reacting for 4 hours at 60 ℃; then cooling to 30 ℃, adding 2g of triethylamine, and reacting for 30 minutes at 30 ℃; and finally, adding 80g of deionized water, shearing at a high speed and emulsifying for 30 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based waterborne polyurethane prepared in the example had a lignin content of 23.45% and an emulsion average particle size of 151 nm.
Example 8
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 20g of polyethylene glycol (with the number average molecular weight of 5000) and 3g of diphenylmethane diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.1g of dibutyltin dilaurate, and stirring at 60 ℃ for reaction for 1 hour to obtain a polyurethane prepolymer;
(2) dissolving 5.8g of high-boiling alcohol lignin in 25g of acetone, adding the dissolved high-boiling alcohol lignin into a three-neck flask protected by nitrogen after complete dissolution, and slowly dripping the polyurethane prepolymer while stirring at the temperature of 40 ℃; after the dropwise addition, reacting for 2 hours at 40 ℃; then cooling to 20 ℃, adding 0.6g of triethylamine, and reacting for 30 minutes at 20 ℃; and finally, adding 50g of deionized water, shearing at a high speed and emulsifying for 30 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based waterborne polyurethane prepared in the example had a lignin content of 8.38% and an emulsion average particle size of 240 nm.
Example 9
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 4g of polytetrahydrofuran ether glycol (the number average molecular weight is 600) and 2g of isophorone diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.1g of dibutyltin dilaurate, and stirring at 60 ℃ to react for 1 hour to obtain a polyurethane prepolymer;
(2) dissolving 4g of lignosulfonate in 20g N, N-dimethylformamide, adding the dissolved lignosulfonate into a nitrogen-protected three-neck flask, and slowly dripping the dissolved lignosulfonate into a polyurethane prepolymer at 40 ℃ while stirring; after the dropwise addition, reacting for 2 hours at 40 ℃; then cooling to 20 ℃, adding 0.4g of triethylamine, and reacting for 10 minutes at 20 ℃; and finally, adding 40g of deionized water, shearing at a high speed and emulsifying for 10 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based waterborne polyurethane prepared in the example had a lignin content of 22.38% and an emulsion average particle size of 149 nm.
Example 10
A preparation method of waterborne polyurethane comprises the following steps:
(1) adding 20g of polytetrahydrofuran ether glycol (with the number average molecular weight of 5000) and 3g of diphenylmethane diisocyanate into a nitrogen-protected three-neck flask, dropwise adding 0.1g of dibutyltin dilaurate, and stirring at 60 ℃ for reaction for 1 hour to obtain a polyurethane prepolymer;
(2) dissolving 12.4g of alkali lignin in 30g N, N-dimethylacetamide, adding the solution into a nitrogen-protected three-neck flask after the alkali lignin is completely dissolved, and slowly dripping polyurethane prepolymer while stirring at the temperature of 40 ℃; after the dropwise addition, reacting for 2 hours at 60 ℃; then cooling to 30 ℃, adding 1.2g of triethylamine, and reacting for 30 minutes at 30 ℃; and finally, adding 70g of deionized water, shearing at a high speed and emulsifying for 30 minutes to obtain the waterborne polyurethane emulsion.
The lignin-based aqueous polyurethane prepared in this example had a lignin content of 20.91% and an emulsion average particle size of 166 nm.
Description of the effects of the embodiments
Example 1 is reversedThe purified product LWPU which is to be obtained1Infrared spectroscopy was performed with Alkali Lignin (AL) as a control, and the results are shown in FIG. 1. As can be seen from the figure, the depth is 1710cm-1LWPU at wavelength1A new absorption peak appears, which is not present in the alkali lignin raw material and is attributed to the stretching vibration of C ═ O in the characteristic group-NHCOO-. Preliminary explanation suggests the formation of urethane bonds. 1100cm-1The stronger absorption peak is the stretching vibration peak of-C-O-C-, which also proves the existence of the urethane bond. 2270cm-1The stretching vibration peak of the-NCO is absent, and the fact that no residual-NCO groups exist in the system is indicated.
Measured LWPU1、LWPU2、LWPU3And LWPU4The average particle size of the emulsion is shown in FIG. 2. As can be seen from FIG. 2, the particle size of the LWPU emulsion is in the range of 120-240 nm, wherein LWPU emulsion has a particle size of LWPU4The particle size of (A) is the smallest and reaches 127nm, which shows that the LWPU emulsion prepared by the invention has good stability.
Mixing LWPU1、LWPU2、LWPU3And LWPU4Drying the emulsion to form a film to obtain the LWPU film, wherein the LWPU film4The appearance of the film is shown in figure 3. LWPU prepared in example 44After the thin film was brittle with liquid nitrogen, the cross section of the film was observed and analyzed by a scanning electron microscope, and the results are shown in FIG. 4. As can be seen from FIGS. 3 and 4, LWPU4The appearance of the film is flat and smooth, and the cross section of the film has no agglomerated lignin particles, which shows that the lignin/polyurethane film obtained by the invention is a homogeneous system, and a phase interface does not exist between the lignin and the polyurethane, so that the homogeneous structure is favorable for improving the mechanical property of the composite resin.
Mixing LWPU1、LWPU2、LWPU3And LWPU4The films were subjected to elemental analysis with Alkali Lignin (AL) and commercial WPU as controls. The lignin content in the LWPU was calculated from the difference in the sulfur (S) element content, and the results are shown in table 1.
TABLE 1 elemental analysis of AL, WPU and LWPU
From the data in table 1, it can be seen that the commercial WPU contains no elemental sulfur, and the elemental sulfur content of AL is 1.81%. By calculation, LWPU1、LWPU2、LWPU3And LWPU4The Al contents in the solution are 16.77%, 19.88%, 21.47% and 24.68%, respectively.
For the prepared LWPU1、LWPU2、LWPU3And LWPU4The films were subjected to mechanical property testing with a commercial WPU as a control, and the results are shown in fig. 5 and table 2.
TABLE 2 mechanical Properties of LWPU and WPU films
As can be seen from fig. 5 and table 2, the tensile strength of the LWPU film increased and then decreased as the lignin content increased, and the tensile strength of the LWPU film was higher than that of the commercial WPU film when the lignin content was more than 19.88%, wherein the LWPU film was used in the present invention3The tensile strength of the film was 20.99MPa maximum, which is 1.31 times the tensile strength of commercial WPU films. When the lignin content in the LWPU exceeds 21.47%, the tensile strength of the LWPU film decreases. Experimental results show that the prepared LWPU film has excellent mechanical properties.
For the prepared LWPU1、LWPU2、LWPU3And LWPU4The films were subjected to thermogravimetric analysis with a commercial WPU as a control and the results are shown in figure 6. As can be seen from the thermogravimetric analysis chart of fig. 6, the LWPU films had higher temperatures at 20% mass loss than the commercial WPU films, and the thermal decomposition temperature of the films increased with increasing lignin content. In addition, the residual carbon content of the commercial WPU film at 400 ℃ was only 0.08%, whereas the residual carbon content of the LWPU film at 400 ℃ was higher than 20%. The experimental results show that the thermal stability of the prepared LWPU film is better than that of the commercial WPU film.
The invention expands the application of the lignin-based waterborne polyurethane emulsion in the field of wood varnish. Mixing LWPU1、LWPU2、LWPU3And LWPU4The emulsion is prepared into the emulsion with the solid content of 10 wt%. Then accurately weighing 2g of emulsion sample, uniformly coating the emulsion sample on a round pine board with the diameter D of 30mm, and naturally drying the coated paint film for 24 hours in a ventilation environment; then, a sample was applied to the dried paint film, and the paint film was naturally dried in a ventilated environment, and the appearance of the paint film was recorded by photographing, as shown in FIG. 7. A commercial WPU emulsion was also used as a control.
The varnish prepared was subjected to pencil hardness and adhesion tests while using a commercial WPU as a control, and the results are shown in table 3.
TABLE 3 Pencil hardness and adhesion of WPU and LWPU varnishes
Remarking: the pencil hardness is represented by 17 grades, i.e., 6B, 5B, 4B, 3B, 2B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H. The pencil hardness of 6B was the lowest and the pencil hardness of 9H was the highest. The adhesion is represented by 6 levels, namely 0, 1, 2, 3, 4, 5. The 0 th order indicates the best adhesion of the coating film, and the 5 th order indicates the worst adhesion.
As can be seen from the data in Table 3, the adhesion of both the LWPU varnish and the commercial WPU varnish is 0 grade, indicating that both varnishes have good adhesion to the pine board and the adhesion of the varnishes is excellent. Furthermore, the pencil hardness of LWPU varnishes increases with increasing AL content in the polyurethane structure, where LWPU4The pencil hardness of the varnish was 2H maximum, higher than that of the commercial WPU varnish.
And testing the ultraviolet aging resistance of the prepared varnish. The LWPU varnish and the commercial WPU varnish were placed in a UV-aging oven (parameters: 50W, 310nm, 60 ℃) for 360 hours, and the results are shown in Table 4.
TABLE 4 change in properties of WPU and LWPU varnishes before and after UV irradiation for 360 hours
Remarking: the "/" in the table indicates that the paint film failed the performance test after uv aging.
As can be seen from the test results in table 4, the commercial WPU varnish undergoes significant softening decomposition after 360 hours of uv irradiation, resulting in failure to perform the performance test after uv aging; the LWPU varnish series has no change in appearance before and after 360 hours of ultraviolet radiation, the varnish film is flat and smooth, and the pencil hardness and the adhesive force of the LWPU varnish are kept unchanged before and after the ultraviolet test. The experimental result shows that the LWPU series varnish has excellent ultraviolet aging resistance.
The lignin-based waterborne polyurethane emulsion has excellent stability, and the particle size range of the emulsion is 120-240 nm; compared with a commercial WPU film, the mechanical property and the thermal stability of the lignin-based waterborne polyurethane film are remarkably improved. The prepared lignin-based waterborne polyurethane is applied to the wood varnish, and the obtained varnish is level and smooth in appearance, has excellent pencil hardness, adhesive force and ultraviolet aging resistance, shows that the varnish is excellent in comprehensive application performance and has wide application prospects.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. A preparation method of waterborne polyurethane is characterized by comprising the following steps:
dissolving 4-20 parts of lignin in a solvent, and slowly dropwise adding 6-30 parts of polyurethane prepolymer under the protection of nitrogen and stirring at 40-80 ℃; after the dropwise addition is finished, reacting for 2-4 hours at 40-80 ℃; then cooling to below 30 ℃, adding a neutralizing agent, and reacting for 10-30 minutes at below 30 ℃; and finally, adding deionized water, and performing high-speed shearing emulsification to obtain the waterborne polyurethane emulsion.
2. The method of claim 1, wherein: the dosage of the lignin is 10.4-13.2 parts, and the polyurethane prepolymer is 26.7 parts.
3. The method of claim 1, wherein: the polyurethane prepolymer is prepared by the following steps:
under the protection of nitrogen, 4-20 parts of polyol and 2-10 parts of isocyanate are mixed, a catalyst is dripped, and the mixture is stirred and reacts for 1-4 hours at the temperature of 60-80 ℃ to obtain the polyurethane prepolymer.
4. The method of claim 1, wherein: the lignin is one of alkali lignin, enzymolysis lignin, high-boiling alcohol lignin or lignosulfonate.
5. The production method according to claim 3, characterized in that: the polyalcohol is one of polypropylene glycol, polytetrahydrofuran ether glycol or polyethylene glycol.
6. The method of claim 5, wherein:
the number average molecular weight of the polypropylene glycol is 600-5000;
the number average molecular weight of the polytetrahydrofuran ether glycol is 600-5000;
the number average molecular weight of the polyethylene glycol is 600-5000.
7. The production method according to claim 3, characterized in that: the isocyanate is one of isophorone diisocyanate, toluene diisocyanate or diphenylmethane diisocyanate.
8. The method of claim 1, wherein:
the dosage of the neutralizer is 0.4-2 parts;
the neutralizing agent is triethylamine.
9. An aqueous polyurethane prepared by the method of any one of claims 1 to 8.
10. The use of the aqueous polyurethane emulsion of claim 9 in the preparation of wood varnish.
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