CN112778540A - Lignin-based polyol for synthesizing polyurethane and preparation method thereof - Google Patents
Lignin-based polyol for synthesizing polyurethane and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of polyurethane synthesis, and discloses lignin-based polyol for synthesizing polyurethane and a preparation method thereof. The method comprises the following steps: carrying out hydrothermal degradation on lignin acetate under the catalysis of metal oxides, and precipitating degradation products by using dilute acid; and carrying out hydroxylation modification on the degraded lignin to obtain polyhydroxy lignin polyol. The method provided by the invention solves the problems of low lignin reaction activity, low reaction participation degree, poor compatibility between lignin and polyurethane matrix and the like. The needed lignin raw material has wide sources, is environment-friendly and degradable, and realizes high-value utilization of lignin. In the preparation method provided by the invention, the adopted raw material of the lignin acetate has good solubility in an organic solvent, less inorganic substance-containing ash and less structural change, and is beneficial to subsequent structural modification and application.
Description
Technical Field
The invention belongs to the technical field of lignin modification, and particularly relates to lignin-based polyol for synthesizing polyurethane and a preparation method thereof.
Background
Polyurethanes are generally polymers having repeating structural units of urethane segments made by reacting di-or poly-organic isocyanates with polyol compounds. At present, the raw materials for producing the polyurethane mainly come from petrochemical products. As petroleum resources are gradually depleted, raw materials from petroleum are also in short supply. The use of petrochemical resources in large quantities also raises serious environmental concerns. The traditional polyurethane is difficult to degrade and recycle, and causes certain pollution to the environment. Currently, attempts are being made to replace petrochemical products with renewable biomass feedstocks in the production of polyol components for the production of polyurethanes.
Lignin is the second largest biomass resource in nature that is second only to cellulose. Lignin is a complex, rigid, aromatic natural polymer with a three-dimensional network structure. Industrial lignin is mainly a by-product from the pulp and paper industry and other biorefinery industries. The worldwide pulp and paper industry produces over 5000 million tons of industrial lignin per year, but most of them are not utilized to a high value due to the complexity of the lignin structure and heterogeneity of properties. Therefore, the efficient utilization of the industrial lignin has great economic, environmental and social significance.
Lignin is a renewable, biodegradable and biocompatible polymer, and contains various functional groups such as phenolic hydroxyl, alcoholic hydroxyl, methoxyl and carbonyl in the molecule, so that various chemical reactions can occur. Lignin can replace fossil raw materials for the production of various chemicals and materials. Hydroxyl in lignin molecules can react with isocyanate to synthesize polyurethane materials. However, lignin exhibits poor compatibility with other components and low reactivity during polyurethane synthesis due to the low content of hydroxyl groups available to react in the industrial lignin molecule and the poor compatibility of lignin with other components of the synthetic polyurethane. Thus, there is a need for modifying lignin to overcome the above disadvantages. This can be achieved by increasing the number of available reactive functional groups (e.g., hydroxyl groups) in the lignin, or by introducing other reactive functional groups into the lignin to produce a lignin-based polyol having a higher reactivity. These modification methods mainly include amination, methylation, hydroxymethylation, phenolation, oxidation, liquefaction, and the like.
At present, polyether polyols used for the synthesis of polyurethanes are mainly classified into two types: (1) polyether polyol with high functionality (3.0-8.0), low relative molecular mass (150-1000) and high hydroxyl value (250-1000 mg KOH/g), which is mainly used for producing rigid foam, rigid coating and elastic plastic; (2) polyether polyols of low functionality (2.0-3.0), high relative molecular mass (1000-6500) and low hydroxyl value (28-160 mg KOH/g) are mainly used for the production of flexible foams and elastomers.
In the chinese patent application 201911297985.8, li chongqing et al, lignin and ethylene oxide (or propylene oxide, etc.) gaseous epoxy compound are reacted under pressure and in the presence of a catalyst (mainly organic phosphorus nitrile salt) and an inert gas under a gradually increasing temperature condition to attach hydrophilic side chains to the lignin to produce a liquid lignin-based polyether polyol. The method can liquefy lignin without solvent, and the prepared lignin polyether polyol has good reaction activity and can be used for preparing polyurethane rigid foam. The disadvantages of this method are: during the reaction process, lignin may be accompanied by side reactions such as cross-linking, and the compatibility of lignin and other components of the synthetic polyurethane is affected.
In the chinese patent application 201811334958.9 by duderarmy, lignin-based polyols are prepared by mixing lignin with a catalyst antimony trioxide, a glycol (e.g., ethylene glycol or propylene glycol), a polyol (e.g., glycerol), and an alkali modifier (e.g., sodium hydroxide) in proportions and heating and pressurizing under conditions. The essence of the method is to introduce hydroxyl into lignin, thereby solving the problems of insolubility and insolubility of lignin to a certain extent.
The two patent documents mentioned above do not relate to lignin relative molecular mass and functional group content data, and it can be concluded that there is no control over lignin relative molecular mass and functional group content.
Guo Seattu et al in Chinese patent application 202010102186.7 provide a method for preparing lignin-based polyols. Firstly, mixing lignin, a sodium hydroxide solution, ethanol and an allyl compound, and carrying out allylation reaction to obtain allylation modified lignin; and then mixing the allylation modified lignin, the organic solvent and the mercapto compound to perform mercapto-alkene click reaction to obtain the lignin-based polyol. The inventors believe that this method modifies the low-reactive phenolic hydroxyl groups in the lignin molecule into primary alcoholic hydroxyl groups having high reactivity and high degree of crosslinking. However, the modification method uses expensive chemical agents, the total hydroxyl content of the lignin is reduced to 4.69mmol/g from 8.51mmol/g before reaction, and the weight average relative molecular mass of the lignin after modification is increased to 5047 from 3393, so that the requirements of reducing the relative molecular mass and improving the content of reactive functional groups are not met.
The qiu scholan et al, in chinese patent application 201811189140.2, disclose a preparation method of partially decomposed lignin for synthesizing polyurethane elastomer. The method comprises dissolving lignin in alkaline solution, and depolymerizing lignin under heating and pressurizing conditions (155 deg.C, 0.6 MPa). Then, the depolymerized lignin is reacted with the prepolymer to prepare a polyurethane elastomer. The method can effectively reduce the relative molecular mass of the lignin and improve the reaction activity of the lignin; meanwhile, the prepared polyurethane elastomer can be recycled. However, as the alkali consumption in the lignin depolymerization process is large, the sodium hydroxide consumption is as high as 80% of the lignin quality according to example 1, and the degradation reaction time is as long as 8 hours; in addition, the hydroxyl content of the lignin after depolymerization was only increased by about 0.4mmol/g compared to before reaction.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide lignin-based polyol for synthesizing polyurethane and a preparation method thereof.
The preparation method provided by the invention can moderately reduce the relative molecular mass of lignin and improve the hydroxyl content of lignin, so as to obtain lignin-based polyol with lower relative molecular mass and higher hydroxyl content. The purpose is realized by two steps of hydrothermal degradation and hydroxylation modification. The lignin-based polyol provided by the invention can replace part of polymeric polyol to be used for preparing modified lignin-based polyurethane materials, and the prepared lignin-based polyurethane materials have good mechanical properties and excellent thermal stability.
The purpose of the invention is realized by at least one of the following technical solutions.
The preparation method of the lignin-based polyol for synthesizing polyurethane provided by the invention comprises the following steps:
(1) hydrothermal degradation of lignin: dissolving lignin acetate in an alkaline solution to obtain a mixed solution, adding metal oxide, uniformly mixing, heating, stirring for reaction to obtain a reaction solution, filtering to obtain a filtrate (filtering to remove insoluble substances in the reaction solution), adjusting the pH of the filtrate to be acidic to separate out a precipitate, repeatedly washing with water, and drying to obtain degraded lignin;
(2) hydroxylation modification of degraded lignin: dissolving the degraded lignin obtained in the step (1) in a sodium hydroxide solution, uniformly mixing, adding a hydrogen peroxide solution and potassium permanganate, uniformly mixing, heating to carry out condensation reflux reaction, filtering to remove unreacted potassium permanganate after the reaction is finished, taking filtrate, adjusting the pH of the filtrate to be acidic to separate out a precipitate, washing, and drying to obtain the lignin-based polyol for synthesizing polyurethane.
Further, the alkaline solution in the step (1) is a sodium hydroxide solution, and the concentration of the alkaline solution is 0.25-0.5 mol/L; the mass-volume ratio of the acetic acid lignin to the alkaline solution is 1:10-1:50 g/mL. The acetic acid lignin is lignin separated from plant fiber raw materials by taking acetic acid as a treatment agent.
Further, the metal oxide in the step (1) is more than one of manganese dioxide, ferric oxide, ferroferric oxide, titanium dioxide, vanadium oxide, zinc oxide, cobalt oxide and nickel oxide; the mass of the metal oxide is 5-15% of that of the lignin. The metal oxide is an oxide of titanium, vanadium, manganese, iron, cobalt, nickel, copper and zinc.
Further, the temperature of the stirring reaction in the step (1) is 150 ℃ and 250 ℃, and the time of the stirring reaction is 0.5-2 h.
Further, in the step (1), the pH value of the reaction solution is adjusted to 2.0-3.0.
Further, the concentration of the sodium hydroxide solution in the step (2) is 0.25-0.5 mol/L; the mass-volume ratio of the degraded lignin to the sodium hydroxide solution is 1:10-1:100 g/mL.
Further, the mass ratio of the hydrogen peroxide solution in the step (2) to the degraded lignin is 0.4:1-1.4: 1; the mass percentage concentration of the hydrogen peroxide solution is 30 wt%.
Further, the mass of the potassium permanganate in the step (2) is 1% -10% of the mass of the lignin.
Further, the temperature of the condensation reflux reaction in the step (2) is 50-90 ℃, and the time of the condensation reflux reaction is 30-90 min.
The invention provides lignin-based polyol for synthesizing polyurethane, which is prepared by the preparation method.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) in the preparation method provided by the invention, the adopted raw material of the lignin acetate has good solubility in an organic solvent, less inorganic substance-containing ash and less structural change, and is beneficial to subsequent structural modification and application.
(2) In the preparation method provided by the invention, the adopted raw material of the lignin acetate is subjected to hydrothermal degradation and hydroxylation modification, so that the relative molecular mass is obviously reduced, the distribution range of the relative molecular mass is narrowed, the number of the reactive functional groups of the lignin is increased, the reaction activity is improved, the compatibility with isocyanate is better, and the lignin can be directly used as polyol to synthesize the polyurethane material.
Drawings
FIG. 1 is a graph showing the relative molecular mass distribution of lignin acetate before and after modification in example 1;
FIG. 2 is an infrared spectrum of lignin acetate before and after modification in example 1;
FIG. 3 shows the results of lignin acetate before and after modification in example 11H-NMR spectrum;
FIG. 4 is a graph showing the relative molecular mass distribution of lignin acetate before and after modification in example 11;
FIG. 5 is an infrared spectrum of lignin acetate before and after modification in example 11;
FIG. 6 shows the results of lignin acetate before and after modification in example 111H-NMR spectrum;
FIG. 7 is a graph showing the relative molecular mass distribution of lignin acetate before and after modification in example 21;
FIG. 8 is an infrared spectrum of lignin acetate before and after modification in example 21;
FIG. 9 shows the results of lignin acetate before and after modification in example 211H-NMR spectrum.
Detailed Description
The following examples are presented to further illustrate the practice of the invention, but the practice and protection of the invention is not limited thereto. It is noted that the processes described below, if not specifically described in detail, are all realizable or understandable by those skilled in the art with reference to the prior art. The reagents or apparatus used are not indicated to the manufacturer, and are considered to be conventional products available by commercial purchase.
Example 1
(1) Hydrothermal degradation of lignin: dissolving 10g of acetic acid lignin in 500mL of sodium hydroxide aqueous solution (the concentration is 0.5mol/L) to obtain a mixed solution, simultaneously adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, and heating to 200 ℃ for reaction for 60 min; after the reaction is finished and cooled to room temperature, filtering the mixture by using a Buchner funnel to remove insoluble substances to obtain filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using a dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin was 2052 and the hydroxyl group content was 7.06mmol/g as determined by gel chromatography.
(2) Hydroxylation modification of degraded lignin: weighing 10g of degraded lignin, dissolving the degraded lignin in 100mL of a sodium hydroxide aqueous solution (the concentration is 0.25mol/L), fully stirring until the lignin is completely dissolved, pouring the lignin solution into a three-neck flask, adding 0.1g of potassium permanganate and 10g of a 30 wt% hydrogen peroxide solution, carrying out condensation reflux reaction at 60 ℃ for 1h, cooling to room temperature after the reaction is finished, filtering to remove potassium permanganate precipitate by using a sand core funnel to obtain a filtrate, adjusting the pH of the filtrate to be acidic by using dilute hydrochloric acid to separate out the precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate obtained by the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the hydroxylated modified Lignin-based polyol (the Lignin-based polyol used to synthesize the Polyurethane) was 1405 and the hydroxyl group content was 8.29mmol/g (the number average relative molecular mass and the hydroxyl group content of the Lignin-based polyol used to synthesize the Polyurethane were determined by reference to the method described in "High-Performance lipid-Containing-purifying Polyurethane Elastomers with Dynamic solvent polymers Networks", the same applies hereinafter).
(3) Analyzing the structures of the degraded lignin of the step (1) and the lignin-based polyol for synthesizing polyurethane respectively. Using gel chromatography, infrared spectroscopy and1H-NMR spectra characterize their relative molecular masses and chemical structures. The results are shown in FIGS. 1, 2 and 3. As can be seen from FIG. 1, the degradation and modification of the lignin acetate by the above method can effectively reduce the relative molecular mass of the lignin, and the distribution of the relative molecular mass is narrowed.As can be seen from fig. 2 and 3, the hydroxyl content of the lignin-based polyol obtained by degradation and modification is significantly increased while still retaining the basic unit structure of lignin. The relative molecular mass and hydroxyl content of lignin before and after modification are shown in table 1.
TABLE 1 relative molecular mass and hydroxyl content of lignin acetate before and after modification
Example 2
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 100mL of sodium hydroxide aqueous solution (0.4mol/L) to obtain a mixed solution, adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 150 ℃ for reaction for 30min, cooling to room temperature after the reaction is finished, filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 3056, and the hydroxyl content is 5.21 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1988, and the hydroxyl content is 6.15 mmol/g.
Example 3
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 500mL of sodium hydroxide aqueous solution (0.4mol/L) to obtain a mixed solution, adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 150 ℃ for reaction for 30min, cooling to room temperature after the reaction is finished, filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin. The number average molecular mass of the degraded lignin was 2905, and the hydroxyl content was 5.41 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1866, and the hydroxyl content is 6.34 mmol/g.
Example 4
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 1000mL of sodium hydroxide aqueous solution (0.4mol/L) to obtain a mixed solution, adjusting to obtain the mixed solution, adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 150 ℃, reacting for 30min, cooling to room temperature after the reaction is finished, filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate, and adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 2859, and the hydroxyl content is 5.50 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1840, and the hydroxyl content is 6.41 mmol/g.
Example 5
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 500mL of sodium hydroxide aqueous solution (0.4mol/L) to obtain a mixed solution, adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 200 ℃ for reaction for 30min, cooling to room temperature after the reaction is finished, and filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate. Then adjusting the pH value of the filtrate to 2.0-3.0 by using a dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin, wherein the number average molecular mass of the degraded lignin is 2798, and the hydroxyl content is 5.60 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1798, and the hydroxyl content is 6.56 mmol/g.
Example 6
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 500mL of sodium hydroxide aqueous solution (0.4mol/L) to obtain a mixed solution, adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 250 ℃ for reaction for 30min, cooling to room temperature after the reaction is finished, and filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate. Then adjusting the pH value of the filtrate to 2.0-3.0 by using a dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 2736, and the hydroxyl content is 5.67 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1768, and the hydroxyl content is 6.61 mmol/g.
Example 7
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 500mL of sodium hydroxide aqueous solution (0.4mol/L) to obtain a mixed solution, adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 200 ℃ for reaction for 60min, cooling to room temperature after the reaction is finished, and filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate. Then adjusting the pH value of the filtrate to 2.0-3.0 by using a dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally placing the precipitate in a vacuum drying oven at 50 ℃ for 24 hours, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 2543, and the hydroxyl content is 5.95 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1650, and the hydroxyl content is 7.01 mmol/g.
Example 8
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 500mL of sodium hydroxide aqueous solution (0.4mol/L) to obtain a mixed solution, adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 200 ℃ for reaction for 120min, cooling to room temperature after the reaction is finished, filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally placing the precipitate in a vacuum drying oven at 50 ℃ for 24 hours, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 2410, and the hydroxyl content is 6.03 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1556, and the hydroxyl content is 7.02 mmol/g.
Example 9
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 500mL of sodium hydroxide aqueous solution (0.25mol/L) to obtain a mixed solution, adding 0.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 200 ℃ for reaction for 60min, cooling to room temperature after the reaction is finished, filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin was 2808 and the hydroxyl group content was 5.51 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1819, and the hydroxyl group content is 6.44 mmol/g.
Example 10
(1) Hydrothermal degradation of lignin: dissolving 10g of acetic acid lignin in 500mL of sodium hydroxide aqueous solution (0.5mol/L) to obtain a mixed solution, adding 0.5g of ferric oxide serving as a catalyst, uniformly mixing, heating to 200 ℃ for reaction for 60min, cooling to room temperature after the reaction is finished, filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 2205, and the hydroxyl content is 6.90 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1440, and the hydroxyl content is 8.02 mmol/g.
Example 11
(1) Hydrothermal degradation of lignin: dissolving 10g of acetic acid lignin in 500mL of sodium hydroxide aqueous solution (0.5mol/L) to obtain a mixed solution, adding 0.5g of zinc oxide as a catalyst, uniformly mixing, heating to 200 ℃ for reaction for 60min, cooling to room temperature after the reaction is finished, filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 2163, and the hydroxyl content is 6.95 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1412, and the hydroxyl content is 8.09 mmol/g.
Example 12
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 500mL of sodium hydroxide aqueous solution (0.5mol/L) to obtain a mixed solution, adding 1g of manganese dioxide as a catalyst, uniformly mixing, heating to 200 ℃ for reaction for 60min, cooling to room temperature after the reaction is finished, filtering insoluble substances by using a Buchner funnel to obtain a filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; repeatedly filtering and washing the precipitate with deionized water until the pH of the filtrate of the last washing is close to neutral, finally placing the precipitate in a vacuum drying oven at 50 ℃ for 24 hours, and grinding to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 2202, and the hydroxyl content is 6.55 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1489, and the hydroxyl content is 7.69 mmol/g.
Example 13
(1) Hydrothermal degradation of lignin: dissolving 10g of lignin acetate in 500mL of sodium hydroxide aqueous solution (0.5mol/L) to obtain a mixed solution, adding 1.5g of manganese dioxide as a catalyst, uniformly mixing, heating to 200 ℃ for reaction for 60min, cooling to room temperature after the reaction is finished, filtering to remove insoluble substances by using a Buchner funnel to obtain a filtrate, and then adjusting the pH value of the filtrate to 2.0-3.0 by using dilute HCl solution to separate out a precipitate; the precipitate was washed with deionized water repeatedly until the pH of the filtrate from the last wash was near neutral. And finally, putting the lignin into a vacuum drying oven at 50 ℃ for 24 hours, and grinding the lignin to obtain the degraded lignin. The number average relative molecular mass of the degraded lignin is 2248, and the hydroxyl content is 6.53 mmol/g.
(2) Hydroxylation modification of degraded lignin: the method is the same as example 1, and the lignin-based polyol for synthesizing polyurethane is obtained. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1456, and the hydroxyl group content is 7.64 mmol/g.
(3) Analyzing the structures of the degraded lignin in the step (1) and the lignin-based polyol for synthesizing polyurethane in the step (2) respectively. Using gel chromatography, infrared spectroscopy and1H-NMR spectra characterize their relative molecular masses and chemical structures. The results are shown in fig. 4, 5 and 6. As can be seen from FIG. 4, the degradation and modification of the lignin acetate by the above method can effectively reduce the relative molecular mass of the lignin, and the distribution of the relative molecular mass is narrowed. As can be seen from fig. 5 and 6, the hydroxyl content of the lignin-based polyol obtained by degradation and modification is significantly increased while still maintaining the basic unit structure of lignin.
Example 14
(1) Hydrothermal degradation of lignin: the process was the same as in example 1 to obtain a degraded lignin. The number average relative molecular mass of the degraded lignin is 2052, and the hydroxyl content is 7.06 mmol/g.
(2) Hydroxylation modification of degraded lignin: 10g of degraded lignin was weighed out and dissolved in 100mL of an aqueous solution of sodium hydroxide (concentration: 0.25mol/L), and the solution was sufficiently stirred until the lignin was completely dissolved. Then the lignin solution was poured into a three-necked flask, 0.1g of potassium permanganate and 10g of a 30% hydrogen peroxide solution were added, and the mixture was subjected to condensation reflux reaction at 90 ℃ for 1 hour. After the reaction is finished, cooling to room temperature, filtering by using a sand core funnel to remove potassium permanganate precipitate to obtain filtrate, adjusting the pH of the filtrate to be acidic by using a dilute hydrochloric acid solution to separate out precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate obtained by the last washing is close to neutrality, finally putting the filtrate into a vacuum drying oven at 50 ℃ for 24 hours, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the hydroxylated modified lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) is 1353, and the hydroxyl content is 8.22 mmol/g.
Example 15
(1) Hydrothermal degradation of lignin: the process was the same as in example 1 to obtain a degraded lignin. The number average relative molecular mass of the degraded lignin is 2052, and the hydroxyl content is 7.06 mmol/g.
(2) Hydroxylation modification of degraded lignin: 10g of degraded lignin was weighed out and dissolved in 100mL of an aqueous solution of sodium hydroxide (concentration: 0.25mol/L), and the solution was sufficiently stirred until the lignin was completely dissolved. Then the lignin solution was poured into a three-necked flask, and 0.1g of potassium permanganate and 10g of a 30% hydrogen peroxide solution were added thereto, followed by condensation reflux reaction at 50 ℃ for 60 min. After the reaction is finished, cooling to room temperature, filtering by using a sand core funnel to remove potassium permanganate precipitate to obtain filtrate, adjusting the pH of the filtrate to be acidic by using dilute hydrochloric acid to separate out precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate obtained by the last washing is close to neutrality, finally putting the filtrate into a vacuum drying oven at 50 ℃ for 24 hours, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1496, and the hydroxyl content is 8.04 mmol/g.
Example 16
(1) Hydrothermal degradation of lignin: the process was the same as in example 1 to obtain a degraded lignin. The number average relative molecular mass of the degraded lignin is 2052, and the hydroxyl content is 7.06 mmol/g.
(2) Hydroxylation modification of degraded lignin: 10g of degraded lignin was weighed out and dissolved in 100mL of an aqueous solution of sodium hydroxide (concentration: 0.25mol/L), and the solution was sufficiently stirred until the lignin was completely dissolved. Then the lignin solution was poured into a three-necked flask, 0.1g of potassium permanganate and 10g of a 30% hydrogen peroxide solution were added, and the mixture was subjected to a condensation reflux reaction at 60 ℃ for 30 min. After the reaction is finished, cooling to room temperature, filtering by using a sand core funnel to remove potassium permanganate precipitate to obtain filtrate, adjusting the pH of the filtrate to be acidic by using dilute hydrochloric acid to separate out precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate obtained by the last washing is close to neutrality, finally drying in a vacuum drying oven at 50 ℃ for 24 hours, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1565, and the hydroxyl content is 7.89 mmol/g.
Example 17
(1) Hydrothermal degradation of lignin: the process was the same as in example 1 to obtain a degraded lignin. The number average relative molecular mass of the degraded lignin is 2052, and the hydroxyl content is 7.06 mmol/g.
(2) Hydroxylation modification of degraded lignin: 10g of degraded lignin was weighed out and dissolved in 100mL of an aqueous solution of sodium hydroxide (concentration: 0.25mol/L), and the solution was sufficiently stirred until the lignin was completely dissolved. And then pouring the lignin solution into a three-neck flask, adding 0.1g of potassium permanganate and 10g of 30% hydrogen peroxide solution, carrying out condensation reflux reaction at 60 ℃ for 90min, cooling to room temperature after the reaction is finished, filtering by using a sand core funnel to remove potassium permanganate precipitate to obtain a filtrate, adjusting the pH of the filtrate to be acidic by using dilute hydrochloric acid to separate out a precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate subjected to the last washing is close to neutrality, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1374, and the hydroxyl content is 8.01 mmol/g.
Example 18
(1) Hydrothermal degradation of lignin: the process was the same as in example 1 to obtain a degraded lignin. The number average relative molecular mass of the degraded lignin is 2052, and the hydroxyl content is 7.06 mmol/g.
(2) Hydroxylation modification of degraded lignin: 10g of degraded lignin was weighed out and dissolved in 100mL of an aqueous solution of sodium hydroxide (concentration: 0.25mol/L), and the solution was sufficiently stirred until the lignin was completely dissolved. And then pouring the lignin solution into a three-neck flask, adding 0.1g of potassium permanganate and 4g of 30% hydrogen peroxide solution, carrying out condensation reflux reaction at 60 ℃ for 60min, cooling to room temperature after the reaction is finished, filtering by using a sand core funnel to remove potassium permanganate precipitate to obtain a filtrate, adjusting the pH of the filtrate to be acidic by using dilute hydrochloric acid to separate out a precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate subjected to the last washing is close to neutrality, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1932, and the hydroxyl content is 7.40 mmol/g.
Example 19
(1) Hydrothermal degradation of lignin: the process was the same as in example 1 to obtain a degraded lignin. The number average relative molecular mass of the degraded lignin is 2052, and the hydroxyl content is 7.06 mmol/g.
(2) Hydroxylation modification of degraded lignin: 10g of degraded lignin was weighed out and dissolved in 100mL of an aqueous solution of sodium hydroxide (concentration: 0.25mol/L), and the solution was sufficiently stirred until the lignin was completely dissolved. Then the lignin solution was poured into a three-necked flask, 0.1g of potassium permanganate and 14g of a 30% hydrogen peroxide solution were added, and the mixture was subjected to a condensation reflux reaction at 60 ℃ for 60 min. After the reaction is finished, cooling to room temperature, filtering by using a sand core funnel to remove potassium permanganate precipitate to obtain filtrate, adjusting the pH of the filtrate to be acidic by using dilute hydrochloric acid to separate out precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate obtained by the last washing is close to neutrality, finally drying in a vacuum drying oven at 50 ℃ for 24 hours, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1312, and the hydroxyl content is 8.30 mmol/g.
Example 20
(1) Hydrothermal degradation of lignin: the process was the same as in example 1 to obtain a degraded lignin. The number average relative molecular mass of the degraded lignin is 2052, and the hydroxyl content is 7.06 mmol/g.
(2) Hydroxylation modification of degraded lignin: 10g of degraded lignin was weighed out and dissolved in 100mL of an aqueous solution of sodium hydroxide (concentration: 0.25mol/L), and the solution was sufficiently stirred until the lignin was completely dissolved. And then pouring the lignin solution into a three-neck flask, adding 0.5g of potassium permanganate and 10g of 30% hydrogen peroxide solution, carrying out condensation reflux reaction at 60 ℃ for 60min, cooling to room temperature after the reaction is finished, filtering by using a sand core funnel to remove potassium permanganate precipitate to obtain a filtrate, adjusting the pH of the filtrate to be acidic by using a dilute hydrochloric acid solution to separate out a precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate subjected to the last washing is close to neutrality, finally drying in a vacuum drying oven at 50 ℃ for 24h, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1341, and the hydroxyl content is 8.28 mmol/g.
Example 21
(1) Hydrothermal degradation of lignin: the process was the same as in example 1 to obtain a degraded lignin. The number average relative molecular mass of the degraded lignin is 2052, and the hydroxyl content is 7.06 mmol/g.
(2) Hydroxylation modification of degraded lignin: 10g of degraded lignin was weighed out and dissolved in 100mL of an aqueous solution of sodium hydroxide (concentration: 0.25mol/L), and the solution was sufficiently stirred until the lignin was completely dissolved. And then pouring the lignin solution into a three-neck flask, adding 1g of potassium permanganate and 10g of 30% hydrogen peroxide solution, carrying out condensation reflux reaction at 60 ℃ for 60min, cooling to room temperature after the reaction is finished, filtering by using a sand core funnel to remove potassium permanganate precipitate to obtain filtrate, adjusting the pH of the filtrate to be acidic by using dilute hydrochloric acid to separate out precipitate, taking the precipitate, repeatedly filtering and washing by using deionized water until the pH of the filtrate subjected to the last washing is close to neutrality, finally drying in a 50 ℃ vacuum drying oven for 24h, and grinding into powder to obtain the lignin-based polyol for synthesizing polyurethane. The number average relative molecular mass of the lignin-based polyol (the lignin-based polyol for synthesizing polyurethane) after the hydroxylation modification is 1365, and the hydroxyl content is 8.27 mmol/g.
(3) Analyzing the structures of the degraded lignin in the step (1) and the lignin-based polyol for synthesizing polyurethane in the step (2) respectively. Using gel chromatography, infrared spectroscopy and1H-NMR spectra characterize their relative molecular masses and chemical structures. The results are shown in fig. 7, 8 and 9. As can be seen from fig. 7By adopting the method for degrading and modifying the lignin acetate, the relative molecular mass of the lignin can be effectively reduced, and the distribution of the relative molecular mass is narrowed. As can be seen from fig. 8 and 9, the hydroxyl content of the lignin-based polyol obtained by degradation and modification is significantly increased while still retaining the basic unit structure of lignin.
Example 22
(1) Hydrothermal degradation of lignin: the procedure is as in example 1.
(2) Hydroxylation modification of degraded lignin: the procedure is as in example 1.
(3) Preparation of lignin-based polyurethane elastomer: weighing 0.5g of lignin polyol obtained in example 1, dissolving the lignin polyol in 15mL of N, N-dimethylformamide, adding 4.5g of anhydrous polytetramethylene ether glycol 2000 after the lignin polyol is completely dissolved, uniformly mixing, adding 1.19g of hexamethyldiisocyanate, uniformly stirring, adding 2-3 drops of butyltin dilaurate, reacting at room temperature for 10 hours to obtain a reaction solution after the reaction is finished, pouring the reaction solution into a 10cm × 10cm glass mold, gradually heating to 80 ℃ to volatilize the solvent for 12 hours, transferring the reaction solution into a 105 ℃ oven, drying for 2 hours to obtain a film with the thickness of 0.4-0.5 mm, and cooling the sample to obtain the lignin-based polyurethane elastomer. The elongation at break was 1190% and the tensile strength was 40.4MPa as measured by tensile test (refer to GB/T1040.2-2006 for tensile testing of lignin-based polyurethane elastomers).
The above examples are only preferred embodiments of the present invention, which are intended to be illustrative and not limiting, and those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention.
Claims (10)
1. A preparation method of lignin-based polyol for synthesizing polyurethane is characterized by comprising the following steps:
(1) dissolving lignin acetate in an alkaline solution to obtain a mixed solution, adding metal oxide, uniformly mixing, heating, stirring for reaction to obtain a reaction solution, filtering to obtain a filtrate, adjusting the pH of the filtrate to be acidic to separate out a precipitate, washing, and drying to obtain degraded lignin;
(2) dissolving the degraded lignin obtained in the step (1) in a sodium hydroxide solution, uniformly mixing, adding a hydrogen peroxide solution and potassium permanganate, uniformly mixing, heating to carry out condensation reflux reaction, filtering to remove unreacted potassium permanganate after the reaction is finished, taking filtrate, adjusting the pH of the filtrate to be acidic to separate out a precipitate, washing, and drying to obtain the lignin-based polyol for synthesizing polyurethane.
2. The method for preparing lignin-based polyol for polyurethane synthesis according to claim 1, wherein the alkaline solution of step (1) is sodium hydroxide solution, and the concentration of the alkaline solution is 0.25mol/L to 0.5 mol/L; the mass-volume ratio of the acetic acid lignin to the alkaline solution is 1:10-1:50 g/mL.
3. The method for preparing the lignin-based polyol used for synthesizing polyurethane according to claim 1, wherein the metal oxide in step (1) is one or more of manganese dioxide, ferric oxide, ferroferric oxide, titanium dioxide, vanadium oxide, zinc oxide, cobalt oxide, and nickel oxide; the mass of the metal oxide is 5-15% of that of the lignin.
4. The method as claimed in claim 1, wherein the temperature of the stirring reaction in step (1) is 150 ℃ to 250 ℃ and the stirring reaction time is 0.5-2 h.
5. The method of claim 1, wherein in step (1), the pH of the reaction solution is adjusted to a range of 2.0 to 3.0.
6. The method of preparing lignin-based polyol for polyurethane synthesis according to claim 1, wherein the concentration of the sodium hydroxide solution of step (2) is 0.25mol/L to 0.5 mol/L; the mass-volume ratio of the degraded lignin to the sodium hydroxide solution is 1:10-1:100 g/mL.
7. The method for preparing the lignin-based polyol for polyurethane synthesis according to claim 1, wherein the mass ratio of the hydrogen peroxide solution to the degraded lignin in step (2) is 0.4:1 to 1.4: 1; the mass percentage concentration of the hydrogen peroxide solution is 30 wt%.
8. The method for preparing the lignin-based polyol for polyurethane synthesis according to claim 1, wherein the potassium permanganate in the step (2) has a mass of 1-10% of the mass of lignin.
9. The method for preparing the lignin-based polyol for polyurethane synthesis according to claim 1, wherein the temperature of the condensation reflux reaction in the step (2) is 50-90 ℃ and the time of the condensation reflux reaction is 30-90 min.
10. A lignin-based polyol for polyurethane synthesis prepared by the preparation method of any one of claims 1 to 9.
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