Lignin-based waterborne polyurethane reinforced fiber composite foam material and preparation method thereof

Abstract

The invention relates to the field of waste lignocellulose biomass, and relates to a lignin-based waterborne polyurethane reinforced fiber composite foam material and a preparation method of the lignin-based waterborne polyurethane reinforced fiber composite foam material. According to the method, fruit tree pruned waste is used as a raw material, and fruit tree sulfate lignin and pruned fibers are obtained through synergistic treatment of a sulfate method and a mechanical disc mill. The fruit tree sulfate lignin is used as a chain extender and is directly used for synthesizing lignin-based waterborne polyurethane (LWPU), and the LWPU is used for enhancing pruning fiber foam, so that all-component high-value utilization of pruning waste is realized. The fiber foam material synthesized by the method has high strength, high heat resistance, high thermal insulation, excellent water stability and biodegradability. The preparation method is simple, green, clean and efficient, and has a wide practical application prospect.

Description

Technical Field

[0001] The invention belongs to the field of high-value comprehensive utilization of agricultural and forestry wastes, and specifically relates to a lignin-based waterborne polyurethane reinforced fiber composite foam material and a preparation method thereof. Background Art

[0002] my country has a long history of fruit tree cultivation, and the area of ​​orchards has increased year by year from 1.657 million hectares (1978) to 13.031 million hectares (2019). In order to improve fruit quality and facilitate pest control, most fruit trees need to be pruned every year, with a pruning weight of 4500 kg / hm2. 2 It is calculated that the annual amount of fruit tree pruning is as high as 58.641 million tons. Due to the lack of high value-added applications, a large amount of pruned wood is used for direct combustion, biomass gasification and fermentation composting, causing environmental problems such as air pollution and solid waste accumulation.

[0003] Fruit wood contains abundant cellulose and lignin, among which lignin is relatively high. For example, the lignin content of lychee wood is 43.01%, which is much higher than other plant fiber raw materials. However, lignin, which is widely distributed in plant cells, often exists as a by-product of papermaking and is only used for low-value fuel functions, polluting the environment and causing great waste of resources.

[0004] Polyurethane is a multifunctional polymer, known as the "fifth plastic". It has the characteristics of high strength, high toughness, high hardness, wear resistance and impact resistance. It is widely used in fibers, coatings, adhesives, insulation, construction, furniture and medical equipment. It is one of the most widely used products in polymers. Traditional PU usually uses a large amount of organic solvents in the preparation process, and then volatile organic compounds (VOCs) are released into the atmosphere, causing air pollution and having considerable adverse effects on human health. In order to solve these problems, researchers began to study waterborne polyurethane (WPU) in the mid-1960s. WPU is a new type of polyurethane system that partially or completely replaces organic solvents with water as a dispersion medium. Hydrophilic groups (carboxylates, sulfonates, quaternary ammonium salts or hydrophilic segments) are introduced into the polyurethane molecular chain to make it hydrophilic, and then dispersed in a continuous aqueous medium. Therefore, during the application and drying process, WPU releases water instead of organic solvents. WPU combines the excellent mechanical properties of PU with the excellent stability of colloids / emulsions, and has the advantages of excellent material properties, processability and sustainability.

[0005] Foam materials are widely used in many fields such as automotive industry, building insulation, and electronic products due to their low density, high strength, heat insulation, and sound absorption. In 2018, the global foam material market value reached US$109.7 billion, and it is expected to continue to expand at an annual growth rate of 4% between 2019 and 2025. Currently, the widely used foam materials are mainly polystyrene foam and polyurethane foam, etc. The raw materials for their production mainly come from non-renewable petrochemical resources, and plastic foams are basically non-biodegradable. Therefore, the development of bio-based degradable foam materials is particularly important. Therefore, exploring the high-value application of all components of fruit tree prunings and developing lignin-based waterborne polyurethane reinforced fiber composite foam materials and preparation methods thereof have become technical problems that technicians in this field need to solve urgently. Summary of the invention

[0006] In view of the background technology, the present invention proposes a lignin-based waterborne polyurethane reinforced fiber composite foam material and a preparation method thereof. The present invention proposes to use fruit tree prunings as raw materials, and adopt a sulfate method to obtain sulfate lignin and pruning fibers. Lignin is directly used as a chain extender for the synthesis of lignin-based waterborne polyurethane (LWPU), and LWPU is used to enhance the foam of fruit tree pruning fibers, thereby comprehensively improving the performance of pruning fiber foams, while retaining good biodegradability, and realizing the high-value utilization of all components of fruit tree pruning waste. The preparation method of the present invention is simple, green, clean and efficient, and has broad practical application prospects. The specific technical scheme is as follows:

[0007] In the technical solution of the present invention, a lignin-based waterborne polyurethane reinforced fiber composite foam material and a preparation method thereof are provided, the method comprising the following steps:

[0008] (1) Fruit pruning waste is used as raw material, peeled and sliced, and the wood chips after moisture content is measured are treated by the sulfate method. The sulfate cooking process conditions are: liquid ratio of 1:4, alkali amount of 8-20%, sulfidation degree of 14%, heating time of 45min, insulation time of 90min; the temperature range during the treatment process is 80-160℃. The black liquor after treatment is collected and acid precipitated to obtain fruit kraft lignin, and the solid residue is mechanically disc-milled with a disc gap of 0.6mm, and then sieved with a 0.15mm flat screen to obtain fruit pruning fiber.

[0009] (2) PTMEG and IPDI were added to a three-necked flask, and 0.05 wt% of the catalyst DBTDL was added. The mixture was stirred in an oil bath at 80°C for 1 hour under a nitrogen atmosphere. 6 wt% of DMBA was dissolved in an appropriate amount of DMF and added dropwise to the three-necked flask. The mixture was stirred in an oil bath at 80°C for 1 hour to obtain a prepolymer. The oil bath temperature was adjusted to 70°C, and the kraft lignin from fruit wood prunings was dissolved in DMF and added dropwise to the three-necked flask containing the prepolymer. The reaction was continued for 3 hours. The oil bath temperature was lowered to 35°C, and TEA was added for neutralization reaction for 30 minutes. Finally, the reaction product was added dropwise to deionized water under high-speed stirring to obtain a LWPU emulsion. During the reaction, an appropriate amount of acetone was added to adjust the viscosity, and -NCO / -OH in the reaction system was controlled to be 1.5, where -OH is the total amount of -OH in the polyether polyol and lignin.

[0010] (3) The prepared LWPU and pruning fiber were mixed to obtain a fiber suspension, and the fiber content in the suspension was adjusted to 2wt%. 0.08wt% sodium dodecyl sulfate (SDS) was added to the fiber suspension, and then a deflaker was used to stir at a speed of 3000rpm for 10min to obtain a wet foam. The obtained wet foam was poured into a homemade mold (with a nylon mesh at the bottom), and the water was filtered until no liquid dripped, and then placed in a 60℃ oven to dry for 6h, and then transferred to a 120℃ oven for curing and cross-linking for 1h to obtain LWPU-reinforced fruit wood pruning fiber foam.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] 1. The present invention uses fruit pruning waste as raw materials, adopts the sulfate process to obtain fruit pruning sulfate lignin and fiber, and directly uses lignin as a chain extender for the synthesis of LWPU. At the same time, LWPU is used to enhance the pruning fiber foam material. The high-value utilization of all components of fruit pruning waste is achieved, providing a new idea for the high-value-added utilization of agricultural and forestry pruning wastes.

[0013] 2. The lignin-based waterborne polyurethane reinforced fiber composite foam material of the present invention has the excellent properties of light weight, high porosity, high mechanical strength, high heat resistance, high thermal insulation, high water stability, recyclability and biodegradability; the preparation method has convenient and renewable raw material sources, a simple preparation process, low cost, and a green and environmentally friendly preparation process.

[0014] 3. The preparation process of the technical solution of the present invention realizes the high-value utilization of fruit tree pruning waste. The fruit tree pruning fiber foam material improves the mechanical strength and stability of the foam by adding lignin-based water-based polyurethane. The drying process adopts normal pressure oven drying to reduce energy consumption. The raw material source of this method is abundant and renewable, the process is simple and efficient, and it has the potential for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram of the fruit wood pruning fiber composite foam reinforced with lignin-based waterborne polyurethane of the present invention.

[0016] Figure 2 These are cross-sectional SEM images of the fruit wood fiber composite foams with lignin-based waterborne polyurethane loadings of 0%, 30%, 40%, 50%, 60% and 90% respectively.

[0017] Figure 3 This is a mechanical property diagram of the fruit wood fiber composite foam with lignin-based waterborne polyurethane loadings of 0%, 30%, 40%, 50% and 60% respectively. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0019] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on this patent; in order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0020] Example 1: Lignin-based waterborne polyurethane reinforced fiber composite foam material, including the following components by weight: 64 parts of fruit wood fiber, 2.29 parts of lignin, 23 parts of polyether polyol, 12.29 parts of isocyanate, 0.11 parts of catalyst, 2.4 parts of hydrophilic chain extender, 1.65 parts of triethylamine, and 0.3 parts of foaming agent.

[0021] Example 2: Lignin-based waterborne polyurethane reinforced fiber composite foam material, comprising the following components by weight: 56 parts of fruit wood fiber, 6.58 parts of lignin, 22 parts of polyether polyol, 12.75 parts of isocyanate, 0.11 parts of catalyst, 2.6 parts of hydrophilic chain extender, 1.79 parts of triethylamine, and 0.4 parts of foaming agent.

[0022] Example 3: Lignin-based waterborne polyurethane reinforced fiber composite foam material, comprising the following components by weight: 49 parts of fruit wood fiber, 11 parts of lignin, 22 parts of polyether polyol, 13.87 parts of isocyanate, 0.11 parts of catalyst, 3.0 parts of hydrophilic chain extender, 2.05 parts of triethylamine, and 0.5 parts of foaming agent.

[0023] Example 4: Lignin-based waterborne polyurethane reinforced fiber composite foam material, including the following components by weight: 44 parts of fruit wood fiber, 13 parts of lignin, 26 parts of polyether polyol, 16.64 parts of isocyanate, 0.13 parts of catalyst, 3.6 parts of hydrophilic chain extender, 2.46 parts of triethylamine, and 0.5 parts of foaming agent.

[0024] Example 5: A litchi pruning fiber composite foam reinforced with litchi pruning lignin-based waterborne polyurethane and a preparation method thereof, the method comprising the following steps:

[0025] (1) The litchi pruning waste was used as raw material, peeled and sliced, and the wood chips after the moisture content was measured were treated by the sulfate method. The sulfate cooking process conditions were: liquid ratio of 1:4, alkali amount of 16%, sulfidation degree of 14%, heating time of 45min, insulation time of 90min; the temperature during the treatment process was 100℃. The black liquor after treatment was collected and acid precipitated to obtain litchi kraft lignin, and the solid residue was mechanically disc-milled with a disc gap of 0.6mm, and then sieved with a 0.15mm flat screen to obtain litchi pruning fiber.

[0026] (2) PTMEG and IPDI are added to a three-necked flask, and 0.05 wt% of the catalyst DBTDL is added. The mixture is stirred in an oil bath at 80°C for 1 hour under a nitrogen atmosphere. 6 wt% of DMBA is dissolved in an appropriate amount of DMF and added dropwise to the three-necked flask. The mixture is stirred in an oil bath at 80°C for 1 hour to obtain a prepolymer. The oil bath temperature is adjusted to 70°C, and the lychee pruning kraft lignin is dissolved in DMF, and added dropwise to the three-necked flask containing the prepolymer. The reaction is continued for 3 hours. The oil bath temperature is lowered to 35°C, and TEA is added to neutralize the reaction for 30 minutes. Finally, the reaction product is added dropwise to deionized water under high-speed stirring to obtain an LWPU emulsion. During the reaction, an appropriate amount of acetone is added to adjust the viscosity, and the -NCO / -OH in the reaction system is controlled to be 1.5, where -OH is the total amount of -OH in the polyether polyol and lignin. The sample LWPU with a lignin content of 21.19 wt% prepared by the method of this example is selected. 21.19 Used for comparison of effect verification.

[0027] (3) The prepared LWPU and litchi wood pruning fiber were mixed to obtain a fiber suspension, and the fiber content in the suspension was adjusted to 2wt%. 0.08wt% sodium dodecyl sulfate (SDS) was added to the fiber suspension, and then a deflaking machine was used to stir at a speed of 3000rpm for 10min to obtain a wet foam. The obtained wet foam was poured into a homemade mold (with a nylon mesh at the bottom), and the water was filtered until no liquid dripped. It was placed in a 60°C oven to dry for 6h, and then transferred to a 120°C oven for curing and crosslinking for 1h to obtain LWPU-reinforced litchi wood pruning fiber foam. The LWPU prepared by the method of this example with a lignin content of 21.19wt%, a solid content of 10%, and a LWPU loading of 60% was selected to strengthen the sample FPL-60% for comparison of effect verification.

[0028] Example 6: The method is the same as that of Example 5, except that LWPU is not added in the synthesis of litchi wood pruning fiber foam, and only pruning fiber is used as raw material. The foam sample prepared by the method of this example is named FPL-0%.

[0029] Effect verification:

[0030] Table 1 shows the performance indicators of a litchi wood pruning lignin-based waterborne polyurethane film. 21.19 The tensile stress and elastic modulus of the film are 4.02 and 490.80 times that of commercial WPU, respectively. 21.19 The Shore hardness of the film is increased by 70A compared with commercial WPU, indicating that the addition of litchi wood pruning lignin can greatly improve the performance of waterborne polyurethane.

[0031] Table 1 Performance indexes of a waterborne polyurethane film based on lignin from litchi wood prunings

[0032]

[0033]

[0034] Table 2 shows the performance indicators of litchi wood pruning fiber composite foam reinforced with waterborne polyurethane based on litchi wood pruning lignin. It can be seen that the compressive stress and compression modulus of FPL-60% are 16.98 times and 16.91 times of those of sample FPL-0%, respectively, indicating that the addition of lignin can greatly improve the ability of waterborne polyurethane to strengthen the performance of litchi wood pruning fiber foam material.

[0035] Table 2 Performance indexes of litchi wood pruning fiber composite foam reinforced with litchi wood pruning lignin-based waterborne polyurethane

[0036] sample Compression stress(kPa) Compression modulus (kPa) FPL-60% (Example 5) 191.16(±2.86) 782.49(±5.95) F-0% (Example 6) 11.26(±0.06) 46.27(±0.08)

[0037] The soil landfill test was conducted on FPL-60% (Example 5). The results showed that after 120 days of soil landfill, about 83.12 wt% of the structure of FPL-60% was degraded, indicating that LWPU retained good biodegradability while strengthening the performance of litchi wood pruning fiber foam material.

[0038] It should be noted that the above specific implementations are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art should understand that various modifications, equivalent substitutions, changes, etc. can be made to the present invention. However, as long as these changes do not deviate from the spirit of the present invention, they should be within the scope of protection of the present invention. In addition, some terms used in the specification and claims of this application are not restrictive, but are only for the convenience of description.

Claims

1. A lignin-based waterborne polyurethane reinforced fiber composite foam material, characterized in that: The composition includes the following components in parts by weight: 40-60 parts of fruit wood fiber, 6-13 parts of lignin, 23-26 parts of polyether polyol, 12-17 parts of isocyanate, 0.11-0.13 parts of catalyst, 2.4-3.6 parts of hydrophilic chain extender, 1.6-2.5 parts of triethylamine and 0.3-0.5 parts of foaming agent.

2. The lignin-based waterborne polyurethane reinforced fiber composite foam material according to claim 1, characterized in that: The foaming agent is sodium dodecyl sulfate (SDS).

3. A method for preparing a lignin-based waterborne polyurethane reinforced fiber composite foam material, characterized in that: The steps include: (1) Using fruit tree pruning waste as raw material, peeling it and slicing it for later use; (2) After slicing and measuring the moisture content of the pruning waste, the pruning waste is subjected to a sulfate cooking process, and the black liquor after the treatment is collected and acid precipitated to obtain fruit wood sulfate lignin. The solid residue is mechanically disc-milled and sieved to obtain fruit wood pruning fiber; (3) Dehydrated fruit wood kraft lignin was directly used as a chain extender in the synthesis of LWPU, and the performance of LWPU was regulated by adjusting the amount of lignin added; (4) LWPU was mixed with pruning fibers as a dispersant, stirred for 10 min under gravity and mechanical shearing to obtain wet foam, introduced into a mold and allowed to stand and drain until no liquid dripped, and dried to obtain LWPU composite pruning fiber foam.

4. The method according to claim 3, characterized in that In step (1), the size of the sliced ​​fruit wood pruning chips is between 3-5 mm.

5. The method according to claim 3, characterized in that In step (2), the kraft cooking process conditions are: NaOH dosage is 8-20wt%, Na2S·9H2O dosage is 14wt%, the liquid ratio of wood chip mass to water is 1:4, the heating time is 45min, the heat preservation time is 90min, and the temperature range during the cooking process is 80-160°C.

6. The method according to claim 3, characterized in that In step (2), the mechanical disc grinding gap is 0.6 mm, and then a 0.15 mm flat screen is used to screen to obtain fruit wood pruning fibers.

7. The method according to claim 3, characterized in that In step (3), PTMEG and IPDI are added to a three-necked flask, and 0.05 wt% of the catalyst DBTDL is added, and the mixture is stirred in an oil bath at 80° C. for 1 h under a nitrogen atmosphere, 6 wt% of DMBA is dissolved in an appropriate amount of DMF and added dropwise to the three-necked flask, and the mixture is further stirred in an oil bath at 80° C. for 1 h to obtain a prepolymer; the oil bath temperature is adjusted to 70° C., litchi wood pruning kraft lignin is dissolved in DMF, and the mixture is added dropwise to the three-necked flask containing the prepolymer, and the reaction is continued for 3 h, the oil bath temperature is lowered to 35° C., TEA is added for neutralization reaction for 30 min, and the reaction product is finally added dropwise to deionized water under high-speed stirring to obtain a LWPU emulsion, and an appropriate amount of acetone is added during the reaction to adjust the viscosity, and the -NCO / -OH in the reaction system is controlled to be 1.5, wherein -OH is the total amount of -OH in the polyether polyol and lignin.

8. The method according to claim 3, characterized in that In step (4), LWPU and pruning fibers are mixed to obtain a fiber suspension having a fiber concentration of 2 wt %. 0.08 wt % of SDS is added to the fiber suspension, and then a deflaker is used to stir at a rotation speed of 3000 rpm for 10 min to obtain wet foam.

9. The method according to claim 3, characterized in that In step (4), the obtained wet foam is poured into a mold with a nylon mesh at the bottom, allowed to stand and drain until no liquid drips, placed in a 60°C oven to dry for 6 hours, and then transferred to a 120°C oven for curing and cross-linking for 1 hour to obtain LWPU-reinforced fruit wood pruning fiber foam.

10. Application of LWPU reinforced fruit wood pruning fiber foam prepared by the method according to any one of claims 3 to 9, characterized in that: It is made from various agricultural and forestry wastes and has good biodegradability.

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