Green hydrophobic lightweight bio-based composite materials with wood-like structures and methods of making the same

Abstract

The application discloses a kind of green hydrophobic light-weight bio-based composite material of wood structure imitation and preparation method thereof, comprising the following steps: plant fiber is treated by low-alkali cooking pretreatment, standby;Starch is mixed with water, then 75-95 ℃ is added with ultrasonic vibration stirring 1-2h, then adding mesophilic alpha amylase is carried out enzymolysis, after enzymolysis is completed, oxidation treatment is carried out, then urea is added to starch, stirring reaction 1-2h, finally foaming agent is added, uniformly stirred, and the foaming hot melt modified starch is prepared;Wood pulp fiber, lignin, pretreated plant fiber and foaming hot melt modified starch are mixed according to proportion, and mixed slurry is obtained;The mixed slurry is injected in injection molding machine, and the intermediate bubble layer is prepared;A layer of waterproof film containing lignin nanocellulose slurry and polylactic acid mixed solution is sprayed on the surface of the intermediate bubble layer, and the dense waterproof layer is prepared, that is, obtained.

Description

Technical Field

[0001] This invention belongs to the field of novel green and environmentally friendly application materials, specifically relating to a green, hydrophobic, lightweight bio-based composite material with a wood-like structure and its preparation method. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Plastics are highly attractive materials due to their ease of molding, excellent performance, and low cost. They are used to make products widely used in daily life, such as furniture, toys, and packaging. However, due to their lack of biodegradability, waste plastics can cause serious harm to the environment. Tiny plastics have entered the food chain, threatening ecosystems and human health. Therefore, developing alternative biodegradable materials with similar properties to address the environmental problems caused by waste plastics is of great significance. Natural polymers, including cellulose, lignin, starch, and chitosan, are biodegradable under natural conditions. They have the advantages of abundant production, low price, easy access, and renewability. However, natural polymers are difficult to mold, resulting in low production efficiency. In addition, natural polymers are prone to absorbing water, leading to a decline in mechanical properties in humid environments. Difficult processing, high hydrophilicity, and poor mechanical properties limit the industrial application of natural polymers.

[0004] Trees produce a large number of natural polymers (cellulose, hemicellulose, and lignin, etc.) through photosynthesis, and these polymers constitute wood. Wood has excellent mechanical properties, is lightweight, and inexpensive. However, unlike plastics, wood is difficult to injection molded; it can only be cut into complex shapes, which places certain requirements on the size of the trees and severely limits its industrial applications. Most synthetic wood panels are made by adding large amounts of adhesives to existing wood boards or wood particles, without changing the fundamental problem of wood's inability to be injection molded. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a green, hydrophobic, lightweight bio-based composite material with a wood-like structure and its preparation method.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a green, hydrophobic, lightweight bio-based composite material with a wood-like structure, comprising the following steps:

[0008] Plant fibers are pretreated by low-alkali cooking and then set aside.

[0009] After mixing starch with water, stir at 75-95℃ with ultrasonic vibration for 1-2 hours, then add medium-temperature α-amylase for enzymatic hydrolysis. After enzymatic hydrolysis, perform oxidation treatment, then add urea to the starch and stir for 1-2 hours. Finally, add foaming agent and stir evenly to obtain foamable hot melt modified starch.

[0010] Wood pulp fiber, lignin, pretreated plant fiber and foamable hot melt modified starch are mixed in proportion to obtain a mixed pulp, which is then granulated.

[0011] The mixed slurry is injection molded in an injection molding machine to obtain an intermediate cell layer;

[0012] A dense waterproof layer is obtained by spraying a layer of lignin nanocellulose slurry and polylactic acid mixture onto the surface of the intermediate pore layer.

[0013] Among them, the role of lignin-containing nanocellulose is to enhance the strength of the polylactic acid surface layer, and also to increase the bonding strength between the polylactic acid surface layer and the intermediate layer.

[0014] The role of polylactic acid: to prepare waterproof and biodegradable surface layers.

[0015] The role of plant fibers: as a skeletal structure for the intermediate pore structure;

[0016] The role of expandable, hot-melt modified starch: as a binder for intermediate cell structure materials, it bonds the skeletal structure of the cell structure together;

[0017] The role of wood pulp fiber: as a filler to improve the flexibility of the intermediate layer material;

[0018] The role of lignin: to improve the water resistance of the intermediate layer.

[0019] In some embodiments, the plant fiber low-alkali cooking pretreatment involves a cooking temperature of 95-100°C, a cooking time of 30-50 min, and a NaOH concentration of 0.3-0.8 wt% in the cooking liquid.

[0020] The plant fiber is a 2-4mm plant fiber that has been mechanically crushed. If the length is too long, it will not be conducive to the rheological properties of the slurry and will affect the material molding. If the length is too short, it will not play a reinforcing or skeletal role. Therefore, the length should be moderate.

[0021] The purpose of low-alkali cooking treatment of plant fibers is to remove impurities such as ash, pectin, and wax from the surface of the plant fibers.

[0022] Preferably, the cooked plant fiber is washed 2-4 times and dried at 80-90℃ for 10-14 hours.

[0023] In some embodiments, the starch is dried, ball-milled, and then mixed with water;

[0024] The mass ratio of α-amylase to starch at medium temperature is 1:500-3000;

[0025] The mass ratio of urea to starch is 1:5-20.

[0026] Preferably, when oxidizing starch, the mass ratio of potassium permanganate to starch is 1:10-40; the mass ratio of hydrogen peroxide to starch is 1:10-40.

[0027] In some embodiments, the mass ratio of wood pulp fiber, lignin, pretreated plant fiber, and foamable hot-melt modified starch is 250-400:20-40:20-40:40-60.

[0028] The wood pulp fiber is poplar wood pulp, pine wood pulp, etc.;

[0029] The plant fibers are sisal fibers, jute fibers, etc.;

[0030] The starch mentioned is cassava starch, corn starch, wheat starch, etc.

[0031] The starch mentioned is cassava starch, corn starch, wheat starch, etc.

[0032] The foaming agent is azodicarbonamide or sodium bicarbonate.

[0033] In some embodiments, when the mixed slurry is injected into an injection molding machine, the injection pressure is 100-150 MPa, the holding pressure is 40-60 MPa, the barrel temperature is 180℃-200℃, the upper mold temperature is 150-170℃, the lower mold temperature is 155-175℃, and the injection time of the injection molding machine is 3-6 seconds.

[0034] Preferably, after the mixed slurry is injected, cooling water is quickly circulated into the injection molding machine to rapidly cool the lower mold to 140-160°C, and high-pressure gas is blown in to achieve demolding.

[0035] In some embodiments, the lignin-containing nanocellulose slurry and polylactic acid mixture contains 3-8% by mass of lignin-containing nanocellulose.

[0036] In some embodiments, the raw material containing lignin nanocellulose is derived from tree bark. The bark is treated with a low-alkali high-temperature cooking process, with the concentration of alkali solution being 0.3-0.6 wt%, the cooking temperature being 90-110°C, and the cooking time being 30-50 min.

[0037] After steaming and boiling, wash the bark and soak it in warm water at a temperature of 50-80℃.

[0038] The soaked bark is mixed with water at a mass ratio of 1:400-600 and then milled 10-20 times, with the milling gaps gradually decreasing, to obtain a lignin-containing nanocellulose slurry.

[0039] Preferably, the grinding gaps are set from largest to smallest as follows: 2mm, 1.5mm, 1mm, 0.5mm, 0.4mm, 0.3mm, 0.2mm, 0.1mm, 0.05mm, and 0mm.

[0040] Preferably, polylactic acid is dissolved in a mixed solvent of methyl acetate and glacial acetic acid to obtain a polylactic acid solution;

[0041] The lignin-containing nanocellulose was replaced with a methyl acetate solution of lignin-containing nanocellulose using a solvent displacement method.

[0042] A methyl acetate solution of lignin-containing nanocellulose is mixed with a polylactic acid solution to obtain a lignin-containing nanocellulose slurry and a polylactic acid mixture.

[0043] More preferably, in the mixture of lignin-containing nanocellulose slurry and polylactic acid, the concentration of lignin-containing nanocellulose is 5-15 g / L and the concentration of polylactic acid is 50-150 g / L.

[0044] Secondly, the present invention provides a green, hydrophobic, lightweight bio-based composite material with a wood-like structure, prepared by the aforementioned preparation method.

[0045] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0046] This invention mimics the structural principles of trees, using wood pulp fiber as the main raw material. A porous intermediate layer is prepared through a special foaming process. Then, lignin-containing nanocellulose pulp is prepared using tree bark as the raw material. Finally, a dense, waterproof surface layer is prepared using a spraying process. Ultimately, a green, hydrophobic, lightweight, bio-based composite material with a lightweight porous structure in the middle and a dense, waterproof membrane covering the surface is produced, mimicking a wood structure.

[0047] This invention uses all fully biodegradable raw materials to achieve the goal of making the prepared material fully biodegradable; secondly, all reagents are non-toxic and green, ensuring the safety and environmental friendliness of the product; the product is easy to mold and can be made into products with various complex structures; this tree-like structure material has the characteristics of good water resistance and lightweight.

[0048] This invention provides a biodegradable hydrophobic biocomposite material with a sandwich structure, which can be injection molded into various complex shapes similar to plastics. The fully biodegradable biocomposite is prepared using natural polymers including sisal fiber, wood pulp fiber, and hot-melt starch. The hydrophobicity of the biocomposite is achieved by using lignin-containing nanofibers and a polylactic acid composite film as the surface layer.

[0049] The raw materials are natural polymers, which are low in cost. There is no chemical polymerization reaction and no non-degradable polymer materials are added. The products can be biodegraded in a short time under natural conditions.

[0050] By performing hot-melt modification on starch, hot-melt processing of starch combined with wood pulp fiber and plant fiber was achieved, which greatly improved the molding efficiency of the above biomass composite materials.

[0051] The injection molding process using a high-pressure jet combined with a negative pressure cavity rapid injection nozzle enables the rapid delivery of bio-based slurries with low water content.

[0052] The material surface is covered with a dense polylactic acid layer containing lignin cellulose, which ensures that the material is both biodegradable and waterproof. The middle layer has a large number of pore structures, which is conducive to the material's lightweight nature, reduces the amount of raw materials used, and lowers the material cost. At the same time, the pore structure is beneficial for good barrier properties such as heat insulation and sound insulation. Attached Figure Description

[0053] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0054] Figure 1 These are internal structural diagrams of a green, hydrophobic, lightweight bio-based composite material with a wood-like structure. (a) is a schematic diagram of the internal structure of a tree, and (b) is a schematic diagram of the internal structure of the biomass composite material with a tree-like structure and a structural diagram of the dense waterproof surface layer. Detailed Implementation

[0055] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0056] The present invention will be further described below with reference to the embodiments.

[0057] Example 1

[0058] Step (1): Select 50g of sisal fiber and perform low-alkali high-temperature steaming treatment. The high temperature is 100℃, and 1L of 0.5wt% NaOH solution is used. The steaming time is 30 minutes. After steaming, the plant fiber is washed with clean water 3 times and dried at 85℃ for 12 hours. The above plant fiber is mechanically crushed to obtain 3-4mm fiber.

[0059] Step (2): Select 50g of corn starch, dry the starch at 140℃ for 6h, then put the starch into a ball mill and grind it for 2.5h; then put the dried and ground starch into 150g of water and stir it thoroughly, stirring at 85℃ with ultrasonic vibration for 2h; then add 0.025g of medium-temperature α-amylase; stir at high speed for 20min; then heat the above slurry to 140℃ for enzyme inactivation treatment for 20min; at this time, add 2.5g of potassium permanganate for oxidation treatment, and stir evenly for 25min; then add urea and stir rapidly for 1.5h; finally, add 2.5g of foaming agent and stir evenly for 50min; cool to room temperature to obtain foamable hot melt modified starch.

[0060] Step (3): Weigh 300g of wood pulp fiber, 25g of lignin, 25g of sisal fiber and 50g of modified starch, add them to a twin-screw extruder and mix thoroughly, then granulate. This step needs to be carried out at room temperature.

[0061] Step (4): Place the mixed slurry from step (3) into the JM980-Ai injection molding machine, equipped with a high-pressure jet combined with a negative pressure cavity fast injection nozzle, set the injection pressure to 120MPa, the holding pressure to 50MPa, the barrel temperature to 180℃, the upper mold temperature to 160℃, the lower mold temperature to 165℃, and the injection time of the injection molding machine to 5s.

[0062] Step (5): After injection, cooling water is quickly circulated, the lower mold is rapidly cooled to 145°C, and high-pressure gas is blown in to achieve demolding, thus obtaining a foamed material with a certain shape and structure, which imitates the internal structure of trees and serves as the intermediate foam layer.

[0063] Step (6) involves spraying a waterproof membrane composed of lignin-based nanocellulose slurry and polylactic acid onto the surface of the foamed material obtained in step (5), mimicking tree bark, as a surface waterproof layer. This results in a bio-based, fully degradable material with a dense waterproof surface and a lightweight, wood-like structure consisting of a porous plant fiber reinforcement, wood pulp fiber filling, and hot-melt starch bonding in the middle. The material exhibits a water contact angle of 96° and an apparent density as low as 0.1 g / cm³. 3 The tensile strength and compressive strength are as high as 6.7 MPa and 6.9 MPa, respectively.

[0064] The raw material for the lignin-containing nanofiber tree in step (6) comes from the bark of pine trees. Weigh 20g of pine bark and treat it using a low-alkali high-temperature cooking process. The alkali used is 1L of 0.5wt% NaOH solution, the high temperature is 100℃, and the cooking time is 45min. After cooking, the bark is washed three times with clean water. The bark after high-temperature cooking is soaked in warm water for 24h at a temperature of 60℃. Then, the above bark and water mixture (mass ratio of 1:500) is put into a SuperMasscolloider for grinding. The grinding gaps are set from large to small as 2mm, 1.5mm, 1mm, 0.5mm, 0.4mm, 0.3mm, 0.2mm, 0.1mm, 0.05mm, and 0mm, respectively. Grind 20 times to obtain a lignin-containing nanocellulose slurry.

[0065] Polylactic acid is dissolved in a mixed solvent of methyl acetate and glacial acetic acid to obtain a polylactic acid solution.

[0066] The obtained lignin-containing nanocellulose was replaced with methyl acetate solvent using a solvent displacement method and mixed with polylactic acid solution. The mixed liquid was placed in a spray gun and sprayed onto the foam layer using a spraying method.

[0067] Example 2

[0068] Step (1): Select 50g of jute fiber and use low-alkali high-temperature steaming treatment. The high temperature is 100℃, and 1L of 0.5wt% NaOH solution is used. The steaming time is 20 minutes. After steaming, the plant fiber is washed with clean water 3 times and dried at 85℃ for 12 hours. The above plant fiber is mechanically crushed to obtain 3-4mm fiber.

[0069] Step (2): Select 50g of wheat starch, dry the starch at 140℃ for 6h, then put the starch into a ball mill and grind it for 2.5h; then put the dried and ground starch into 150g of water and stir it thoroughly, stirring at 85℃ with ultrasonic vibration for 2h; then add 0.025g of medium-temperature α-amylase; stir at high speed for 20min; then heat the above slurry to 140℃ for enzyme inactivation treatment for 20min; at this time, add 2.5g of hydrogen peroxide for oxidation treatment, and stir evenly for 25min; then add urea and stir rapidly for 1.5h; finally, add 2.5g of foaming agent and stir evenly for 50min; cool to room temperature to obtain foamable hot melt modified starch.

[0070] Step (3): Weigh 400g of wood pulp fiber, 30g of lignin, 30g of jute fiber and 50g of modified starch, add them to a twin-screw extruder and mix thoroughly, then granulate. This step needs to be carried out at room temperature.

[0071] Step (4): Place the mixed slurry from step (3) into the JM980-Ai injection molding machine, equipped with a high-pressure jet combined with a negative pressure cavity fast injection nozzle, set the injection pressure to 120MPa, the holding pressure to 50MPa, the barrel temperature to 180℃, the upper mold temperature to 160℃, the lower mold temperature to 165℃, and the injection time of the injection molding machine to 3s.

[0072] Step (5): After injection, cooling water is quickly circulated, the lower mold is quickly cooled to 140°C, and high-pressure gas is blown in to achieve demolding, thus obtaining a foamed material with a certain shape and structure, which imitates the internal structure of trees and serves as the intermediate foam layer.

[0073] Step (6) involves spraying a waterproof membrane composed of lignin-nanocellulose slurry and polylactic acid onto the surface of the foamed material obtained in step (5), mimicking tree bark, as a surface waterproof layer. This results in a bio-based, fully degradable material with a dense waterproof surface and a lightweight, wood-like structure consisting of a porous plant fiber reinforcement, wood pulp fiber filling, and hot-melt starch bonding in the middle. The material exhibits a water contact angle of 95° and an apparent density as low as 0.1 g / cm³. 3 The tensile strength and compressive strength are as high as 6.3 MPa and 6.5 MPa, respectively.

[0074] The raw material for the lignin-containing nanofiber tree in step (6) comes from the bark of poplar trees. Weigh 20g of poplar bark and treat it using a low-alkali high-temperature cooking process. The alkali used is 1L of 0.5wt% NaOH solution, the high temperature is 100℃, and the cooking time is 45min. After cooking, the bark is washed three times with clean water. The bark after high-temperature cooking is soaked in warm water for 24h at a temperature of 50℃. Then, the above bark and water mixture (mass ratio of 1:500) is put into a SuperMasscolloider for grinding. The grinding gaps are set from large to small as follows: 2mm, 1.5mm, 1mm, 0.5mm, 0.4mm, 0.3mm, 0.2mm, 0.1mm, 0.05mm, 0mm. Grind 15 times to obtain lignin-containing nanocellulose slurry.

[0075] Polylactic acid is dissolved in a mixed solvent of methyl acetate and glacial acetic acid to obtain a polylactic acid solution.

[0076] Lignin-containing nanocellulose is replaced with methyl acetate solvent using a solvent displacement method and mixed with polylactic acid solution. The mixed liquid is then placed in a spray gun and sprayed onto the foam layer using a spraying method.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A green, hydrophobic, lightweight bio-based composite material with a wood-like structure, characterized in that: The green, hydrophobic, lightweight, bio-based composite material with a wood-like structure is prepared by the following method: Plant fibers are pretreated by low-alkali cooking and then set aside. After mixing starch with water, stir at 75-95℃ with ultrasonic vibration for 1-2 hours, then add medium-temperature α-amylase for enzymatic hydrolysis. After enzymatic hydrolysis, perform oxidation treatment, then add urea to the starch and stir for 1-2 hours. Finally, add foaming agent and stir evenly to obtain foamable hot melt modified starch. Wood pulp fiber, lignin, pretreated plant fiber and foamable hot melt modified starch are mixed in proportion to obtain a mixed pulp, which is then granulated. The mass ratio of wood pulp fiber, lignin, pretreated plant fiber, and foamable hot-melt modified starch is 250-400:20-40:20-40:40-60. The mixed slurry is injected into an injection molding machine to obtain the intermediate cell layer; A dense waterproof layer is obtained by spraying a layer of lignin nanocellulose slurry and polylactic acid mixture onto the surface of the intermediate pore layer. The plant fiber is a 2-4 mm plant fiber that has been mechanically crushed; In the mixture of lignin-containing nanocellulose slurry and polylactic acid, the mass percentage of lignin-containing nanocellulose is 3-8%.

2. A method for preparing a green, hydrophobic, lightweight bio-based composite material with a wood-like structure as described in claim 1, characterized in that: Includes the following steps: Plant fibers are pretreated by low-alkali cooking and then set aside. After mixing starch with water, stir at 75-95℃ with ultrasonic vibration for 1-2 hours, then add medium-temperature α-amylase for enzymatic hydrolysis. After enzymatic hydrolysis, perform oxidation treatment, then add urea to the starch and stir for 1-2 hours. Finally, add foaming agent and stir evenly to obtain foamable hot melt modified starch. Wood pulp fiber, lignin, pretreated plant fiber and foamable hot melt modified starch are mixed in proportion to obtain a mixed pulp, which is then granulated. The mass ratio of wood pulp fiber, lignin, pretreated plant fiber, and foamable hot-melt modified starch is 250-400:20-40:20-40:40-60. The mixed slurry is injection molded in an injection molding machine to obtain an intermediate cell layer; A dense waterproof layer is obtained by spraying a layer of lignin nanocellulose slurry and polylactic acid mixture onto the surface of the intermediate pore layer. The plant fiber is a 2-4 mm plant fiber that has been mechanically crushed; In the mixture of lignin-containing nanocellulose slurry and polylactic acid, the mass percentage of lignin-containing nanocellulose is 3-8%.

3. The method for preparing the green, hydrophobic, lightweight bio-based composite material with a wood-like structure according to claim 2, characterized in that: The temperature of the low-alkali cooking pretreatment of the plant fiber is 95-100℃, the cooking time is 30-50 min, and the concentration of NaOH in the cooking liquid is 0.3-0.8 wt%.

4. The method for preparing the green, hydrophobic, lightweight bio-based composite material with a wood-like structure according to claim 3, characterized in that: Wash the cooked plant fibers 2-4 times and dry them at 80-90℃ for 10-14 hours.

5. The method for preparing the green, hydrophobic, lightweight bio-based composite material with a wood-like structure according to claim 2, characterized in that: The starch is dried, ball-milled, and then mixed with water; The mass ratio of α-amylase to starch at medium temperature is 1:500-3000; The mass ratio of urea to starch is 1:5-20.

6. The method for preparing the green, hydrophobic, lightweight bio-based composite material with a wood-like structure according to claim 2, characterized in that: When oxidizing starch, the mass ratio of potassium permanganate to starch is 1:10-40; the mass ratio of hydrogen peroxide to starch is 1:10-40.

7. The method for preparing the green, hydrophobic, lightweight bio-based composite material with a wood-like structure according to claim 2, characterized in that: When the mixed slurry is injected into the injection molding machine, the injection pressure is 100-150MPa, the holding pressure is 40-60MPa, the barrel temperature is 180℃-200℃, the upper mold temperature is 150-170℃, the lower mold temperature is 155-175℃, and the injection time of the injection molding machine is 3-6s.

8. The method for preparing the green, hydrophobic, lightweight bio-based composite material with a wood-like structure according to claim 2, characterized in that: The raw material for lignin-containing nanocellulose comes from tree bark. The bark is treated with a low-alkali, high-temperature cooking process. The concentration of the alkali solution is 0.3-0.6 wt%, the cooking temperature is 90-110℃, and the cooking time is 30-50 min. After steaming and boiling, wash the bark and soak it in warm water at a temperature of 50-80℃. The soaked bark is mixed with water at a mass ratio of 1:400-600 and then milled 10-20 times, with the milling gaps gradually decreasing, to obtain a lignin-containing nanocellulose slurry.

9. The method for preparing the green, hydrophobic, lightweight bio-based composite material with a wood-like structure according to claim 8, characterized in that: Polylactic acid is dissolved in a mixed solvent of methyl acetate and glacial acetic acid to obtain a polylactic acid solution. The lignin-containing nanocellulose slurry was replaced with a methyl acetate solution of lignin-containing nanocellulose using a solvent replacement method. A methyl acetate solution of lignin-containing nanocellulose is mixed with a polylactic acid solution to obtain a lignin-containing nanocellulose slurry and a polylactic acid mixture.

10. The method for preparing the green, hydrophobic, lightweight bio-based composite material with a wood-like structure according to claim 9, characterized in that: In the mixture of lignin-containing nanocellulose slurry and polylactic acid, the concentration of lignin-containing nanocellulose is 5-15 g / L, and the concentration of polylactic acid is 50-150 g / L.

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