Preparation method of a highly elastic biological polyurethane foam

Abstract

The present invention discloses a preparation method of a super-elastic bio-based polyurethane foam. A eutectic solvent is used to prepare a lignin solution by mixing lignin and dimethyl sulfoxide in a certain mass ratio, and then the mixture is uniformly mixed by water bath ultrasonic treatment; polyethylene glycol 200 and polyethylene glycol 400 are mixed in a certain volume ratio to prepare a mixed polyethylene glycol solution; the lignin solution, the mixed polyethylene glycol solution, deionized water, dibutyltin dilaurate, triethylenediamine and a foam stabilizer are mixed to prepare a component A solution; the component A solution and hexamethylene diisocyanate are mixed, and a high-elastic bio-based foam is obtained by a one-step preparation process. The bio-based polyurethane foam of the present invention has high elasticity and a high bio-replacement amount, and is applied to packaging cushioning materials, obtaining a green, environmentally friendly, safe, non-toxic and green biodegradable polyurethane foam material.

Description

Technical Field

[0001] The invention relates to a method for preparing biomass polyurethane foam by using lignin, in particular to a method for preparing high-elastic bio-polyurethane foam. Background Art

[0002] Polyurethane foam has excellent mechanical properties, wear resistance, acoustic properties, electrical properties and anti-aging properties. Its good chemical and physical properties make it widely used in cushioning materials, energy storage materials, packaging materials and medical materials, and it is of great significance in national construction materials. However, with the consumption of petrochemical energy and the serious problem of environmental pollution, green and degradable polyurethane foam has gradually become a research hotspot. Lignin is widely present in the cells of woody plants, herbaceous plants and all vascular plants, and plays a role in strengthening plant tissues. At the same time, lignin, as the third largest organic resource in nature, is widely used in the papermaking industry and burned as energy, but has not been fully utilized. Lignin is also a green, environmentally friendly, renewable, abundant, low-priced and low-content natural polymer compound. If it is used, it can greatly reduce the cost of polyurethane foam and the damage to the environment. Lignin contains many functional groups, such as phenolic hydroxyl, alcohol oxygen, methoxy and other active groups. Lignin is used as a biological reaction raw material to replace petroleum-based resources as part of the raw material of polyurethane foam, and reacts with isocyanate to prepare bio-polyurethane foam.

[0003] At present, most of the lignin raw materials in bio-polyurethane foams are commercial dealkalized lignin and organic modified lignin, which have low reactivity, complex lignin modification procedures, poor environmental performance and low mechanical properties of polyurethane foam. For example, Chinese patent CN201510026963.3 is a method of mixing methanol organic solvent type lignin with diethanolamine or diethylenetriamine under alkaline solution conditions, slowly adding formaldehyde aqueous solution, reacting to obtain lignin amino polyol or lignin amine, and then using catechol as a catalyst and epichlorohydrin to graft glycerol to prepare lignin amino polyol-glycerol or lignin amine-glycerol; mixing lignin amino polyol-glycerol or lignin amine-glycerol with organic solvent polyol, and then using polyurethane foam foaming process to prepare thermal insulation bio-based polyurethane foam. As described in Chinese patent CN202011465445.9, the bio-polyurethane foam is prepared by mixing component A and component B in a mass ratio of 1:1.0-1.5; in terms of mass percentage, component A is composed of the following raw materials: 30-60% lignin, 20-30% polycaprolactone, 10-20% polyether polyol, 3-5% cross-linking agent, 1-2% foaming agent A, 1-2% foaming agent B, 0.5-10% water, 0.3-1.5% catalyst, and 0-20% filler; component B is isophorone diisocyanate, and a bio-polyurethane foam is prepared. For example, in patent CN201510624881.9, lignin, a liquefaction agent, a catalyst and a surfactant are evenly mixed, reacted at 130-180°C with stirring for 30-120 minutes, and after the reaction is completed, naturally cooled to obtain lignin liquefied polyol; the obtained lignin liquefied polyol is mixed with a polyether polyol, and then a bio-based polyurethane foam is prepared according to the foaming process of polyurethane foam.

[0004] Lignin has a higher phenolic hydroxyl content and higher activity. At the same time, its relatively small molecular weight can better replace petroleum-based resources to participate in the reaction of polyurethane foam. The mixed ratio of polyethylene glycol with different molecular weights makes the polyurethane foam have better mechanical properties, taking into account the flexibility of high molecules and the rigidity of low molecules, and has better compatibility with lignin, so as to prepare super elastic, green, biodegradable, chemically and thermally stable bio-polyurethane foam. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the present invention provides a method for preparing super-elastic bio-polyurethane foam. The preparation method using low eutectic solvent lignin as raw material and double molecular weight polyethylene glycol overcomes the current problems of low activity of bio-based raw materials, insufficient participation in the reaction, poor strength of the prepared bio-polyurethane foam, and poor compatibility.

[0006] The bio-polyurethane foam obtained by the invention has high elasticity and high bioreplacement amount, is applied to packaging cushioning materials, and is a green, environmentally friendly, safe, non-toxic, green and degradable polyurethane foam material.

[0007] The technical solution adopted by the present invention is:

[0008] 1) preparing a lignin dissolving system: mixing lignin prepared by a low eutectic solvent and dimethyl sulfoxide in a certain mass ratio, and then mixing them uniformly by water bath ultrasonication to prepare a lignin dissolving solution;

[0009] 2) preparing a mixed system of polyethylene glycols with different molecular weights: mixing polyethylene glycol 200 and polyethylene glycol 400 in a certain volume ratio to prepare a mixed polyethylene glycol solution;

[0010] 3) preparing a component A system: mixing the lignin solution of step 1), the mixed polyethylene glycol solution of step 2), deionized water, dibutyltin dilaurate, triethylenediamine and a foam stabilizer to prepare a component A solution;

[0011] 4) Preparation process of polyurethane foam: The component A solution in step (3) is mixed with hexamethylene diisocyanate, and a high-elasticity bio-based foam is obtained by a one-step preparation process.

[0012] In the step 1), the mass ratio of the lignin prepared by the low eutectic solvent to dimethyl sulfoxide is 1:1.0-3.0.

[0013] In step 1) of the present invention, the low eutectic solvent is used to prepare lignin by subjecting the lignin raw material and the low eutectic solvent to ultrasonic-assisted separation, filtration and purification.

[0014] In the step 1), the deep eutectic solvent is used to prepare lignin by the following method:

[0015] 1.1) First, a hydrogen bond acceptor and a hydrogen bond donor are stirred and heated at a temperature of 80-120° C. for 2 h in a mass ratio of 1:1.0-1.4 to form a low eutectic solvent, which is a green and environmentally friendly raw material;

[0016] 1.2) Then, the lignin raw material is added according to the mass ratio of the lignin raw material to the low eutectic solvent of 1:20-40, and the mixture is heated in an oil bath for 0.5-1.0h to obtain a pre-depolymerization solution;

[0017] 1.3) Then, the pre-depolymerization solution is placed under an ultrasonic stripper for water bath ultrasonication to obtain a depolymerization solution, which can enhance the activity;

[0018] 1.4) Finally, the low eutectic solvent is obtained by filtering, washing and drying in sequence to prepare lignin.

[0019] The hydrogen bond donor is at least one of oxalic acid, malic acid, citric acid, succinic acid, lactic acid, formic acid, and succinic acid, among which oxalic acid, lactic acid, and succinic acid have the best effects;

[0020] The hydrogen bond acceptor is at least one of choline chloride, proline, glycine, betaine, and carboxytrimethylammonium chloride, among which choline chloride and glycine have the best effects;

[0021] The lignin raw material is at least one of bamboo powder, wood powder, wheat bran, cocoa, strawberry, soybean, zucchini, sugarcane, hardwood and masson pine. The lignin raw material is preferably bamboo powder or wood powder.

[0022] In the step 1.4), the operations of suction filtration, washing and drying are specifically as follows:

[0023] 1.4.1) Add ethanol to the prepared depolymerization solution and vortex to obtain a preliminary depolymerized lignin solution;

[0024] 1.4.2) Put the preliminary depolymerized lignin solution into a Buchner funnel with a diameter range of 2-9 mm for coarse filtration. The filtration time is about 1 hour to obtain a preliminary coarse filtration solution;

[0025] 1.4.3) Add 400 ml of pure water to the preliminary coarse filtered solution, place it in a 1L beaker and let it stand for 6 hours;

[0026] 1.4.4) Take the preliminary coarse filtration solution after standing, pour it into a sand core funnel with a pore size of 100-200um for re-filtration, remove the upper precipitate, repeatedly wash and dry with ethanol aqueous solution to obtain a low eutectic solvent for preparing lignin.

[0027] In the step 1.4.1), the mass ratio of ethanol to the depolymerization solution is 42:79.

[0028] The volume ratio V of the ethanol in step 1.4.1) to the pure water in step 1.4.3) is about 1:4.

[0029] The drying methods include forced air oven drying, vacuum oven drying and freeze drying.

[0030] The ultrasonic power of the water bath ultrasound is 50-95w (40kHz), the ultrasonic time is 0.5h-6h, and the ultrasonic temperature is 60℃-100℃.

[0031] In the step 2), polyethylene glycol 200 and polyethylene glycol 400 are mixed in a volume ratio of 1:1.0-4.0 to prepare polyethylene glycol compound solutions with different molecular weights as mixed polyethylene glycol solutions.

[0032] In the step 3), 0.1-4 parts by weight of lignin solution, 15-50 parts by weight of mixed polyethylene glycol solution, 0.1-2 parts by weight of deionized water, 0.1-1 parts by weight of dibutyltin diosilicate, 0.5-1 parts by weight of foam stabilizer and 0.1-1 parts by weight of triethylenediamine are mixed.

[0033] The foam stabilizer is a silicone oil foam stabilizer.

[0034] In the step 4), the component A solution and hexamethylene diisocyanate are mixed at a mass ratio of 1:1.0-1.4 by high-speed stirring for 30s-60s, poured into a preheated mold, and then the mold is placed in an oven at the same temperature for curing and molding.

[0035] In the specific implementation, the overall process ratio of polyurethane foaming is: 0.1-4 parts by mass of lignin, 1-2 parts by mass of dimethyl sulfoxide, 10-25 parts by mass of polyethylene glycol 200, 5-25 parts by mass of polyethylene glycol 400, 0.1-2 parts by mass of deionized water, 0.1-1 parts by mass of dibutyltin diosilicate, 0.5-1 parts by mass of foam stabilizer, and 0.1-1 parts by mass of triethylenediamine.

[0036] The present invention controls the amount ratio of the low eutectic solvent, the power of the ultrasonic assistance and the time of the ultrasonic assistance to obtain the low eutectic solvent to prepare lignin, thereby improving the activity of the lignin and enabling the biomass material to better participate in the reaction of the polyurethane foam. At the same time, by adjusting the ratio of the composite solution of polyethylene glycol solutions with different molecular weights and the replacement amount of lignin, the superelasticity, green environmental protection and degradability of the biomass polyurethane foam are enhanced.

[0037] The beneficial effects of the present invention are as follows:

[0038] The method of the present invention realizes the preparation of super-elastic biomass polyurethane foam and has the following outstanding beneficial effects:

[0039] (1) Using natural bamboo powder, wood powder and other non-food biomass resources as raw materials, which have the advantages of low price, wide source, and environmental protection and renewable, and at the same time obtain lignin with high phenolic hydroxyl activity;

[0040] (2) Lignin is used as the raw material for biomass reaction. The raw material has a high phenolic hydroxyl content, a small relative molecular weight, and a high reaction activity. At the same time, a compounded polyethylene glycol solution is used to participate in the reaction to achieve solution viscosity control, so that the reaction time of biomass polyurethane foam can be controlled, and the mechanical strength of the polyurethane foam is better, etc.;

[0041] (3) It improves the problems of low reaction activity of traditional commercial dealkalized lignin, low replacement amount of polyurethane foam, and poor reaction compatibility.

[0042] The process of organically modified lignin is relatively complicated and the cost is relatively high. The present invention uses a low eutectic solvent as a reaction solvent carrier and extracts lignin under ultrasonic-assisted process conditions, which greatly increases the phenolic hydroxyl content of lignin and improves the relative purity of its extraction at a low cost. By adjusting the ratio of the polyethylene glycol solution system, the viscosity change of the system is adjusted, and the elasticity of the bio-polyurethane foam is greatly improved compared with the traditional single polyol system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a physical picture of lignin polyurethane foam;

[0044] Figure 2 This is the microstructure diagram of biomass polyurethane foam;

[0045] Figure 3 The mechanical properties diagram of polyurethane foam with different lignin contents;

[0046] Figure 4 This is the stress-strain curve of lignin polyurethane foam after 1000 cycles;

[0047] Figure 5 The Young's modulus and maximum stress curve of lignin polyurethane foam after 1000 cycles;

[0048] Figure 6 The elastic modulus diagram of bio-polyurethane foam prepared at different times;

[0049] Figure 7 The elastic modulus diagram of bio-polyurethane foam prepared at different powers;

[0050] Figure 8 The stress-strain curves of lignin under different ultrasonic times. DETAILED DESCRIPTION

[0051] The present invention is described in more detail by the following examples, but the examples are not intended to limit the present invention.

[0052] The material prepared by the invention is used for extracting lignin, and the mechanical property and microstructure of the bio-based polyurethane foam are two important parameters for evaluating the performance of the material.

[0053] Embodiments of the present invention are as follows:

[0054] Embodiment 1:

[0055] 1) mixing choline chloride and oxalic acid dihydrate in a molar ratio of (1:1) to obtain a composite pretreatment solution;

[0056] 2) adding 2 g of bamboo powder to 40 g of the prepared low co-solvent solution, and then stirring at 100° C. for 0.5 h to obtain a preliminary pre-depolymerization solution;

[0057] 3) Ultrasonic depolymerization system: The pre-depolymerization solution was placed in an ultrasonic water bath device, ultrasonicated for 0.5 h, the ultrasonic temperature was 70°C, and the ultrasonic power was 80 W (40 kHz) to obtain a completely depolymerized solution;

[0058] 4) Add 100 ml of alcohol to the completely depolymerized solution, stir it with a vortex, then pour it into a Buchner funnel with 9 mm filter paper for suction filtration, and remove the lower layer of filtrate;

[0059] 5) Add 400 ml of deionized water to the lower filtrate in step 4) and leave it for 6 hours to allow lignin to precipitate better.

[0060] 6) The solution in step 5) is poured into a star funnel with a 200 um filter paper for suction filtration, and then the precipitate on the filter paper is taken and then fully rinsed with an ethanol / deionized water mixed solution (v:v, 1:4), and dried to obtain the extracted lignin.

[0061] 7) 0.1 g of lignin and 1 ml of dimethyl sulfoxide were mixed, and ultrasonicated in a water bath for 5 min to obtain a dissolved low eutectic solvent lignin with a relative molecular weight of (632-1120) g / mol;

[0062] 8) Mix polyethylene glycol 200 and polyethylene glycol 400 in a mass ratio of 2:1.

[0063] 9) 1 ml of dissolved lignin in step 6); 20 ml of polyethylene glycol and 10 ml of polyethylene glycol 400 in step 8); 1 ml of deionized water; 1 ml of silicone oil foam stabilizer; 0.3 ml of dibutyltin dilaurate; 0.3 g of triethylenediamine were stirred at 800 rpm / min for 10 min to prepare a component A solution.

[0064] 10) The component A solution of step 9) and 30 ml of hexamethylene diisocyanate were mixed and stirred at 2000 rpm / min for 30 seconds and then poured into a preheated mold at 60° C., and then molded and cured in an oven at 60° C. Figure 1 The prepared lignin polyurethane foam is Figure 2 This is the microstructure diagram of the prepared lignin polyurethane foam.

[0065] Example 2-4: The lignin content in Example 1 was changed to 0g, 0.1g, 0.2g, and 0.3g, and the other conditions were the same as in Example 1. Figure 3As shown in the figure, with the increase of lignin, the mechanical properties of bio-polyurethane foam showed a trend of first strengthening and then weakening. When the content of low eutectic solvent lignin was 0.2g, the rebound performance of the sample reached the best, which could reach 30kPa. Figure 4 This is the mechanical cycle curve of 0.2g lignin after 1000 cycles. After 1000 cycles, lignin still maintains good mechanical properties. Figure 5 It is the change of maximum stress and elastic modulus after 1000 cycles. After 1000 cycles, the maximum stress of lignin still maintains 84% ​​of the initial stress, showing excellent resilience.

[0066] The effects of the ultrasonic-assisted process conditions of the embodiment on the phenolic hydroxyl content and purity of the low eutectic solvent lignin are shown in Table 1 below.

[0067] Table 1 Effect of ultrasonic-assisted process conditions on phenolic hydroxyl content and purity of lignin in deep eutectic solvent

[0068]

[0069] Embodiment 5-10:

[0070] The ultrasonic time conditions in Example 1 were changed to 0 min, 30 min, 60 min, 90 min and 120 min, and the other conditions were the same as those in Example 1. Figure 7 The ultrasonic time affects the phenolic hydroxyl content and extraction rate of lignin. When the ultrasonic time is 30 minutes, the elastic modulus of the bio-polyurethane foam is the best, reaching 174.75 kPa under a strain of 70%. As the ultrasonic time increases, the elastic modulus of the bio-foam shows a trend of first increasing and then decreasing.

[0071] Embodiment 11-15:

[0072] The ultrasonic power in Example 1 was changed to 60, 70, 80 and 90 W (40 kHz), and the other conditions were the same as those in Example 1. Figure 6 With the increase of ultrasonic power, the elastic modulus of bio-polyurethane foam increases first and then decreases. When the ultrasonic power is 80W, the elastic modulus of bio-polyurethane foam is the largest, reaching 165.74KPa under the condition of 80% strain.

[0073] Embodiment 16-18:

[0074] The mass ratio of polyethylene glycol in Example 1 was changed to 3:4 and 1:3, and the other conditions were the same as in Example 1. Figure 8As shown, as the ratio of the polyethylene glycol compound solution changes, the relative mass of polyethylene glycol 400 increases, and the mechanical strength of the foam increases; when the mass ratio of polyethylene glycol in the bio-polyurethane foam is 1:3, the strength of the bio-polyurethane foam is the best, reaching 198KPa at a strain strength of 70%.

[0075] As can be seen from the above implementation, the preparation method of the present invention is simple to operate, green and environmentally friendly, and the depolymerization of lignin and cellulose is accelerated by combining a heating process and an ultrasonic process in a low eutectic solvent system, thereby achieving the preparation of highly reactive and high-purity lignin, which is beneficial to the replacement of petroleum-based polyols by lignin, and enhances biocompatibility and mechanical properties. In addition, the compounding of different types of polyethylene glycol not only improves the processing performance of the biopolyurethane foam, but also improves the mechanical properties of the biopolyurethane foam, achieving superelasticity.

Claims

1. A method for preparing a super-elastic bio-polyurethane foam, characterized in that the method comprises the following steps: 1) Prepare a lignin dissolution system: Mix lignin prepared from a eutectic solvent and dimethyl sulfoxide in a certain mass ratio, and then mix them evenly by water bath ultrasonic to prepare a lignin solution; In the step 1), the lignin prepared from the eutectic solvent is prepared by the following method: 1.1) First, stir and heat a hydrogen bond acceptor and a hydrogen bond donor at a mass ratio of 1:1.0 - 1.4 at a temperature of 80 - 120 °C for 2 h to form a eutectic solvent; 1.2) Then, add a lignin raw material in a mass ratio of the lignin raw material to the eutectic solvent of 1:20 - 40 and mix them, and heat to obtain a pre-depolymerization solution under an oil bath condition; 1.3) Then, place the pre-depolymerization solution under an ultrasonic stripper for water bath ultrasonic to obtain a depolymerization solution; For the water bath ultrasonic, the ultrasonic power is 70 w, the ultrasonic time is 0.5 h, and the ultrasonic temperature is 80 °C; 1.4) Finally, obtain the lignin prepared from the eutectic solvent through the operations of suction filtration, washing, and drying; In the step 1.4), the operations of suction filtration, washing, and drying are specifically as follows: 1.4.1) Add the prepared depolymerization solution to ethanol and perform vortex oscillation to obtain a preliminary depolymerized lignin solution; 1.4.2) Place the preliminary depolymerized lignin solution in a Buchner funnel with a diameter ranging from 2 - 9 mm for rough filtration to obtain a preliminary rough filtrate solution; 1.4.3) Add pure water to the preliminary rough filtrate solution and then let it stand for 6 h; 1.4.4) Take the preliminary rough filtrate solution after standing, pour it into a sintered glass funnel with a pore size of 100 - 200 μm for re - filtration, take the upper precipitate, and repeatedly wash and dry it with an ethanol - water solution to obtain deep eutectic solvent - prepared lignin; 2) Prepare a mixed system of polyethylene glycols with different molecular weights: Mix polyethylene glycol 200 and polyethylene glycol 400 according to a volume ratio of 1:1.0 - 4.0 to prepare a mixed polyethylene glycol solution; 3) Prepare component A system: Mix the lignin solution in step 1), the mixed polyethylene glycol solution in step 2), deionized water, dibutyltin dilaurate, triethylenediamine, and a foam stabilizer to prepare component A solution; 4) Preparation process of polyurethane foam: Mix the component A solution in step (3) and hexamethylene diisocyanate, and adopt a one - step preparation process to obtain a highly elastic bio - based foam.

2. A method for preparing a super - elastic bio - polyurethane foam according to claim 1, wherein: In step 1), the mass ratio of the deep eutectic solvent - prepared lignin to dimethyl sulfoxide is 1:1.0 - 3.

0.

3. A method for preparing a super - elastic bio - polyurethane foam according to claim 1, wherein: The hydrogen - bond donor is at least one of oxalic acid, malic acid, citric acid, succinic acid, lactic acid, and formic acid; The hydrogen - bond acceptor is at least one of choline chloride, proline, glycine, and betaine; The lignin raw material is at least one of bamboo powder, wood powder, wheat bran, sugarcane, broad - leaved wood, and masson pine.

4. A method for preparing a super - elastic bio - polyurethane foam according to claim 1, wherein: In step 3), 0.1 - 4 parts by mass of the lignin solution, 15 - 50 parts by mass of the mixed polyethylene glycol solution, 0.1 - 2 parts by mass of deionized water, 0.1 - 1 part by mass of dibutyltin dilaurate, 0.5 - 1 part by mass of the foam stabilizer, and 0.1 - 1 part by mass of triethylenediamine are mixed.

5. A method for preparing a super - elastic bio - polyurethane foam according to claim 1, wherein: In step 4), the component A solution and hexamethylene diisocyanate are mixed at a mass ratio of 1:1.0 - 1.4 with high - speed stirring for 30 s - 60 s, poured into a pre - heated mold in advance, and then the mold is placed in an oven at the same temperature for curing and forming.

6. A super - elastic bio - polyurethane foam, wherein, It is prepared by the preparation method according to any one of claims 1 - 5.

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