Antibacterial transparent bast fiber composite materials, their preparation methods and applications

Abstract

This application provides an antibacterial transparent bast fiber composite material, its preparation method, and its application, belonging to the field of bast cellulose fibers. The preparation method of the antibacterial transparent bast fiber composite material includes the following steps: pretreating bast fibers sequentially with an alkali / salt mixed solution, followed by treatment with an alcohol / water / alkali / salt system until the bast fibers turn white, obtaining micro / nano-structured lignin fibers; reacting the micro / nano-structured lignin fibers with metal bromides under acidic conditions to obtain phenolic modified fibers; immersing the phenolic modified fibers in alcohol for a preset time, arranging them in parallel into a preset shape, placing them in a mold, adding resin to the mold, vacuuming, and curing to obtain the antibacterial transparent bast fiber composite material. This application is advantageous in retaining the aesthetics, texture, most of the grain, high mechanical strength, and non-deformation advantages of bast fibers, while endowing the composite material with antibacterial properties and transparency, resulting in a composite material with high transparency, low haze, and high antibacterial activity.

Description

Technical Field

[0001] This invention relates to the field of novel bast cellulose fiber technology, specifically to an antibacterial transparent bast fiber composite material, its preparation method, and its application. Background Technology

[0002] With the increasing prominence of resource shortages and energy crises, people have deeply realized the importance and urgent need for environmental protection and the rational use of resources to achieve sustainable social and economic development. Therefore, utilizing renewable biological resources to manufacture new materials has become a research hotspot. Compared to relatively scarce timber resources, flax, sisal, kenaf, and other hemp resources with shorter growth cycles, as well as widely available agricultural and forestry residues such as straw, have become new research directions.

[0003] Flax, sisal, kenaf, and other hemp fibers are not only easily biodegradable and recyclable, but also possess unique advantages such as high temperature resistance, acid and alkali resistance, rapid heat dissipation, and no static electricity. Furthermore, they exhibit high specific strength and specific modulus. Studies have shown that composite materials made from natural plant fibers other than wood, especially hemp fibers, have mechanical properties comparable to those made from glass fibers. Developing transparent composite materials using these hemp fibers to replace traditional glass and transparent plastics has scientific significance and research value. However, there are few reports on the preparation of transparent bast fibers with antibacterial properties, and currently, there is no effective method for preparing transparent bast fibers with antibacterial properties. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides an antibacterial transparent bast fiber composite material, its preparation method and application, aiming to solve the technical problem of the inability to effectively prepare antibacterial transparent bast fibers.

[0005] In a first aspect, embodiments of this application provide a method for preparing an antibacterial transparent bast fiber composite material, comprising the following steps:

[0006] S1. Bast fibers are pretreated with an alkali / salt mixed solution to obtain pretreated fibers;

[0007] S2. The pretreated fibers are treated with an alcohol / water / alkali / salt system until the bast fibers turn white to obtain micro-nano structured lignin fibers.

[0008] S3. The micro-nano structured lignin fiber is reacted with metal bromide under acidic conditions to obtain phenolic modified fiber;

[0009] S4. After soaking the phenolic modified fibers in alcohol for a preset time, arrange them in parallel into a preset shape and place them in a mold. Then, add resin glue to the mold, vacuum and cure to obtain an antibacterial transparent bast fiber composite material.

[0010] In the technical solution of this application embodiment, the bast fibers are first pretreated with an alkali / salt mixed solution to efficiently remove impurities and some lignin from the surface of the bast fibers; then, an alcohol / water / alkali / salt system is used to further break down the lignin molecular chains, and the structure, distribution, and content of residual lignin on the surface of the pretreated fibers are controlled in situ using micro-nano techniques, while also controlling the color of the bast fibers; next, a phenolic modification treatment is performed to improve the antibacterial properties of the fibers; finally, a resin adhesive is used to composite the fibers, which improves the transparency of the composite material without weakening the antibacterial properties, resulting in an antibacterial transparent bast fiber composite material.

[0011] In some embodiments, in step S2, the alcohol / water / alkali / salt system is prepared by mixing an alcohol / water mixed solution with the alkali / salt mixed solution used in step S1 at a volume ratio of 1:(1-3); the volume ratio of alcohol to water in the alcohol / water mixed solution is 10%-50%:50%-90%.

[0012] In this embodiment, by rationally controlling the changes in the ratio of alcohol, water, alkali, and salt in the alcohol / water / alkali / salt system, the degree of breakage of the remaining lignin molecular chains on the surface of the pretreated fiber is efficiently controlled, thereby in-situ regulating the structure, content, and distribution of micro-nano lignin. This not only provides favorable conditions for subsequent phenolic modification treatment, but also regulates the color of the fiber, providing conditions for the preparation of transparent composite materials.

[0013] In some embodiments, in step S1, the mass percentage of alkali and salt in the alkali / salt mixed solution is 5%-20%, and the molar mass ratio of alkali to salt is 1:(1-5).

[0014] In this embodiment, by rationally controlling the content and ratio of alkali and salt in the alkali / salt mixed solution, the lignin on the surface of bast fibers is efficiently and rapidly destroyed and removed, providing a guarantee for subsequent in-situ micro-nano-scale regulation of lignin.

[0015] In some embodiments, step S3 specifically involves: immersing the micro / nano structured lignin fibers in a metal bromide solution with a mass concentration of 40%-60% and a pH of 3-6 at a bath ratio of 1:(20-100), reacting at a reaction temperature of 100-120°C for a reaction time of 60-120 min; the metal bromide includes one or more of lithium bromide, sodium bromide, and potassium bromide.

[0016] In this embodiment, the micro-nano structured lignin fibers are first fully swollen by controlling the bath ratio within a suitable range; then, the concentration, acidity, temperature, and time of the metal bromide solution are reasonably controlled to efficiently convert the aryl methoxy group of lignin into phenolic hydroxyl groups, thereby achieving phenolic modification of lignin, improving the antibacterial properties of the fibers, and obtaining phenolic modified fibers.

[0017] In some embodiments, in step S4, the mass ratio of the resin adhesive to the phenolic modified fiber is 1:(1-3).

[0018] In this embodiment, by rationally controlling the ratio of resin adhesive to phenolic modified fiber, favorable conditions are provided for vacuuming and curing, thereby improving the transparency of the final prepared composite material; at the same time, the resin adhesive is better combined with the phenolic modified fiber, thereby improving the strength of the composite material.

[0019] In some embodiments, the vacuuming temperature is 20-30℃ and the time is 1-2 hours; the vacuuming is performed by multiple vacuum-atmospheric pressure cycles; the curing temperature is 20-30℃ and the time is 18-24 hours.

[0020] In this embodiment, by reasonably controlling the temperature, time, and method of vacuuming, the gas in the phenolic modified fiber is extracted to the maximum extent; by reasonably controlling the curing temperature and time, the composite material is formed quickly and efficiently, improving the bonding tightness between the resin and the phenolic modified fiber, and obtaining an antibacterial transparent bast fiber composite material.

[0021] In some embodiments, step S1 specifically involves reacting the bast fibers in the alkali / salt mixed solution at a bath ratio of 1:(30-100), at a reaction temperature of 80-100°C, and for a reaction time of 1-5 hours; step S2 specifically involves reacting the pretreated fibers in the alcohol / water / alkali / salt system at a bath ratio of 1:(30-100), at a reaction temperature of 80-100°C, and taking them out for observation at intervals during the reaction until the pretreated fibers turn white.

[0022] In this embodiment, by reasonably controlling the bath ratio, reaction temperature and reaction time of steps S1 and S2, the pretreatment and micro-nano-scale regulation of bast fibers can be carried out smoothly, thereby gradually regulating the structure, quantity and distribution of residual lignin on the surface of bast fibers, providing favorable conditions for the antibacterial properties and transparency of the composite material.

[0023] In some embodiments, the bast fiber includes one or more of ramie fiber, flax fiber, jute fiber, hemp fiber, and Apocynum venetum fiber.

[0024] In this embodiment, by rationally selecting the type of bast fiber, pretreatment, in-situ micro-nano control, phenolic modification, and composite with resin adhesive can be carried out smoothly, resulting in a bast fiber composite material with high transparency, low haze, and high antibacterial properties.

[0025] Secondly, embodiments of this application provide an antibacterial transparent bast fiber composite material, which is prepared using the preparation method of the antibacterial transparent bast fiber composite material provided in the first aspect of this application.

[0026] In the technical solution of this application embodiment, an antibacterial transparent bast fiber composite material is prepared by adopting the specific method of this application, which retains the aesthetics, texture, most of the texture, high mechanical strength and non-deformation of the bast fiber, and obtains a composite material with high transparency, low haze and high antibacterial properties.

[0027] Thirdly, embodiments of this application provide an application of an antibacterial transparent bast fiber composite material in the green textile, furniture, and construction industries.

[0028] In the technical solutions of this application embodiment, composite materials with high transparency, low haze, and high antibacterial properties are applied to the green textile, furniture, and construction industries to improve the functionality of textiles, furniture, and building materials.

[0029] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0031] Figure 1 This is a flowchart illustrating the preparation method of the antibacterial transparent bast fiber composite material in the embodiments of this application.

[0032] Figure 2 This is a comparison chart of the transmittance of the antibacterial transparent bast fiber composite materials prepared in Examples 1, 10, and 9 of this application. Detailed Implementation

[0033] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] Developing transparent composite materials using hemp fibers has scientific significance and research value. However, there are few reports on the preparation of transparent bast fibers with antibacterial properties, and there is currently no effective method for preparing transparent bast fibers with antibacterial properties.

[0037] To address the technical problem of effectively preparing antibacterial transparent bast fibers, this application provides an antibacterial transparent bast fiber composite material, its preparation method, and its application. The antibacterial properties of the fiber are improved by controlling the morphology, distribution, and quantity of lignin originally present on the surface of the bast fiber. Except for color, the morphology and molecular structure of the bast fiber are essentially unchanged, thus preserving the aesthetic appeal, texture, most of the grain, high mechanical strength, and non-deformation advantages of the bast fiber, thereby endowing it with antibacterial properties. Furthermore, by combining the antibacterial fiber with a resin adhesive, the bast fiber can be made transparent without weakening its antibacterial properties, resulting in a composite material that combines high transparency, low haze, and high antibacterial properties.

[0038] Please refer to Figure 1 In a first aspect, embodiments of this application provide a method for preparing an antibacterial transparent bast fiber composite material, comprising the following steps:

[0039] S1. Bast fibers are pretreated with an alkali / salt mixed solution to obtain pretreated fibers;

[0040] S2. The pretreated fibers are treated with an alcohol / water / alkali / salt system until the bast fibers turn white to obtain micro-nano structured lignin fibers.

[0041] S3. Micro-nano structured lignin fibers are reacted with metal bromides under acidic conditions to obtain phenolic modified fibers.

[0042] S4. After soaking the phenolic modified fibers in alcohol for a preset time, arrange them in parallel into a preset shape and place them in a mold. Then add resin glue to the mold, vacuum and cure to obtain an antibacterial transparent bast fiber composite material.

[0043] In the technical solution of this application embodiment, the bast fiber is first pretreated with an alkali / salt mixed solution to efficiently remove impurities and some lignin from the surface of the bast fiber, leaving an appropriate amount of blocky residual lignin on the surface of the bast fiber, resulting in pretreated fiber with blocky lignin uniformly adhered to the surface; then, the pretreated fiber after preliminary lignin removal is treated with an alcohol / water / alkali / salt system, further breaking down the molecular chains of the blocky lignin on the surface of the pretreated fiber. With the further breakage of the lignin molecular chains, the structure, distribution, and content of the residual lignin on the surface of the pretreated fiber are controlled in situ micro-nano-scale, so that the blocky lignin on the surface of the pretreated fiber becomes micro-nano-structured lignin and is uniformly adhered to the surface of the bast fiber. At the same time, the color of the bast fiber is controlled to obtain white micro-nano-structured lignin fiber with multiple active sites on the surface, providing a basis for the antibacterial properties and transparency of the composite material; then, the micro-nano-structured lignin fiber is reacted with a metal bromide under acidic conditions, with the metal bromide acting as a bimolecular nucleophile. The nucleophilic reagent of the substitution reaction breaks the CO bond of the methoxy group in the lignin molecule and forms a hydroxyl group, thereby achieving phenolic modification of lignin and increasing the number of phenolic hydroxyl groups in the lignin molecule, resulting in phenolic modified fibers with highly efficient antibacterial properties. The phenolic modified fibers are then treated in alcohol for a predetermined time to allow them to fully swell, increasing the porosity of the surface and interior of the phenolic modified fibers, providing a prerequisite for resin entry. Next, the phenolic modified fibers are arranged in a predetermined shape in a mold, and resin is added, allowing the resin to uniformly fill the pores of the phenolic modified fibers and bond with the active bonds in the fiber molecule. While the gas in the fiber pores is removed by vacuum, the resin penetrates evenly and fully into the micropores of the phenolic modified fibers under negative pressure to improve the transparency of the composite material and further enhance the bonding strength between the resin and the fiber, thus improving the strength of the composite material. Finally, a curing process is performed to shape the resin and phenolic modified fibers, further strengthening their bond and yielding an antibacterial transparent bast fiber composite material. This application enhances the antibacterial properties of bast fibers by regulating the morphology, distribution, and quantity of lignin originally present on the surface of bast fibers. Aside from color, the morphology and molecular structure of the bast fibers remain largely unchanged, thus preserving their aesthetic appeal, texture, most of their grain, high mechanical strength, and non-deformation properties. This process imparts antibacterial properties and alters the fiber's color, providing favorable conditions for the preparation of transparent composite materials. Furthermore, by combining the antibacterial fibers with a resin adhesive, the bast fibers achieve light transmission and transparency without weakening the antibacterial properties, resulting in a composite material with high transparency, low haze, and high antibacterial activity. The entire preparation process is short, simple, uses few chemicals, and meets the requirements for large-scale production. The resulting composite material has the potential to become a new material for home decoration and furniture design.

[0044] Further, in some embodiments, in step S2, the alcohol / water / alkali / salt system is prepared by mixing an alcohol / water mixture with the alkali / salt mixture used in step S1 at a volume ratio of 1:(1-3); the volume ratio of alcohol to water in the alcohol / water mixture is 10%-50%:50%-90%. Specifically, the alcohol includes one or more of ethanol, ethylene glycol, 1,2-propanediol, glycerol, and 1,4-butanediol, preferably ethanol.

[0045] In the technical solution of this application embodiment, by reasonably controlling the changes in the proportions of alcohol, water, alkali, and salt in the alcohol / water / alkali / salt system, suitable conditions are provided for the further removal of residual blocky lignin on the surface of pretreated fibers. The degree of lignin molecular chain breakage on the surface of pretreated fibers is efficiently controlled, ensuring that the lignin molecular chain breakage proceeds smoothly while avoiding excessive or insufficient breakage. This allows for in-situ regulation of the structure, content, and distribution of micro-nano-structured lignin, enabling a suitable amount of micro-nano-structured lignin to uniformly adhere to the fiber surface, resulting in micro-nano-structured lignin fibers with excellent structure. This not only provides favorable conditions for subsequent phenolic modification treatment but also regulates the color of the fibers, providing conditions for the preparation of transparent composite materials.

[0046] Further, in some embodiments, in step S1, the mass percentage of alkali and salt in the alkali / salt mixed solution is 5%-20% (i.e., the mass percentage of the alkali and salt mixture), and the molar mass ratio of alkali to salt is 1:(1-5). Specifically, the alkali includes one or more of sodium hydroxide and potassium hydroxide; the salt includes one or more of sulfate and carbonate.

[0047] In the technical solution of this application embodiment, by reasonably controlling the content and ratio of alkali and salt in the alkali / salt mixed solution, the lignin on the surface of bast fibers is efficiently and rapidly destroyed and removed, and an appropriate amount of blocky lignin is uniformly retained on the surface of the pretreated fibers, providing a guarantee for subsequent in-situ micro-nano-scale regulation of lignin. Compared with simple alkali solution pretreatment, the alkali / salt mixed solution has a shorter reaction time and higher efficiency for the pretreatment of bast fibers, while also being green, environmentally friendly, economical, and energy-saving.

[0048] Further, in some embodiments, step S3 specifically involves: immersing micro / nano-structured lignin fibers in a metal bromide solution with a mass concentration of 40%-60% and a pH of 3-6 at a bath ratio of 1:(20-100), reacting at a reaction temperature of 100-120°C for 60-120 minutes; the metal bromide includes one or more of lithium bromide, sodium bromide, and potassium bromide. Specifically, acid is added to the metal bromide solution to adjust the pH value to the desired level, wherein the acid is one or more of hydrobromic acid and hydrochloric acid.

[0049] In the technical solution of this application embodiment, firstly, by controlling the bath ratio within a suitable range, the micro / nano-structured lignin fibers are uniformly and fully immersed in a metal bromide solution, allowing the micro / nano-structured lignin fibers to swell sufficiently, ensuring that the lignin on their surface is in full contact with the metal bromide. Then, by rationally controlling the concentration, acidity, and temperature and time of the metal bromide solution, acidic hydrogen halide acts as the proton source for the reaction, and the metal bromide acts as the nucleophile for the bimolecular nucleophilic substitution reaction, causing the CO bonds of the methoxy groups in the lignin molecular structure to fully break and form hydroxyl groups. This efficiently converts the aryl methoxy groups of lignin into phenolic hydroxyl groups, achieving phenolic modification of the lignin, improving the antibacterial properties of the fiber, and obtaining phenolic modified fiber. The bath ratio, also known as the liquid ratio, refers to the mass ratio of the fiber to the soaking solution during the soaking process. This process uses a relatively large bath ratio (i.e., a larger amount of soaking solution is used). Compared to a small bath ratio, this allows for sufficient and uniform phenolic modification of the methoxy groups in the micro / nano-structured lignin at different positions on the surface of the micro / nano-structured lignin fibers, thereby improving the antibacterial properties of the fiber.

[0050] Furthermore, in some embodiments, in step S4, the mass ratio of the resin adhesive to the phenolic modified fiber is 1:(1-3). Specifically, the resin adhesive is a mixture of resin and curing agent, and the mass ratio of resin to curing agent is 1:(1-5), preferably 1:3.

[0051] In the technical solution of this application embodiment, by reasonably controlling the type, composition, and ratio of the resin adhesive, as well as the ratio of the resin adhesive to the phenolic modified fiber, it can not only smoothly and uniformly penetrate into the interior of the phenolic modified fiber, providing favorable conditions for vacuuming and curing, thereby improving the transparency of the final prepared composite material; but also enable the resin adhesive to better combine with the phenolic modified fiber, thereby improving the strength of the composite material.

[0052] Furthermore, in some embodiments, the vacuuming temperature is 20-30°C, and the time is 1-2 hours; the vacuuming involves multiple vacuum-atmospheric pressure cycles; the curing temperature is 20-30°C, and the time is 18-24 hours. Specifically, the vacuuming is performed in a vacuum drying oven.

[0053] In the technical solution of this application embodiment, by reasonably controlling the temperature and time of vacuuming, the vacuuming process is carried out smoothly, and the gas in the phenolic modified fiber is extracted to the maximum extent. This allows the resin to uniformly and almost completely fill the pores of the fiber and firmly bond with it, thereby improving the transparency and strength of the composite material. The vacuuming is set to multiple vacuum-atmospheric pressure cycles, gradually removing the gas from the pores of the phenolic modified fiber, resulting in a higher gas removal rate and higher transparency of the resulting composite material. By reasonably controlling the curing temperature and time, the composite material is rapidly and efficiently molded, further improving the bonding tightness between the resin and the phenolic modified fiber, resulting in an antibacterial transparent bast fiber composite material.

[0054] Further, in some embodiments, step S1 specifically involves: selecting bundled bast fibers, drying them at 90-100°C, reacting the bast fibers in an alkali / salt mixed solution at a bath ratio of 1:(30-100) at a reaction temperature of 80-100°C for 1-5 hours, cooling the reaction solution after the reaction, removing the fibers, thoroughly washing, removing impurities, and drying to obtain pretreated fibers; step S2 specifically involves: reacting the pretreated fibers in an alcohol / water / alkali / salt system at a bath ratio of 1:(30-100) at a reaction temperature of 80-100°C, taking them out for observation at intervals during the reaction until the pretreated fibers turn white, cooling the reaction solution after the reaction, removing the fibers, thoroughly washing, and drying to obtain micro-nano structured lignin fibers.

[0055] In the technical solution of this application embodiment, in step S1, suitable bast fibers are first selected and dried to remove moisture, providing conditions for subsequent pretreatment. Then, by controlling the bath ratio within a suitable range, the bast fibers are uniformly and fully immersed in a suitable concentration of alkali / salt mixed solution to fully swell. Next, the reaction temperature and time are reasonably controlled to thoroughly remove impurities and selectively remove an appropriate amount of lignin, ensuring that an appropriate amount of blocky lignin remains attached to the surface of the bast fibers, providing favorable conditions for subsequent in-situ micro / nano-scale control. In step S2, by controlling the bath ratio within a suitable range, the pretreated fibers are uniformly and fully immersed in a suitable concentration of alcohol / water / alkali / salt system to fully swell. Then, the reaction temperature is reasonably controlled, and the color of the pretreated fibers is observed continuously. This allows for efficient in-situ micro / nano-scale control of the structure, distribution, and content of residual lignin in the pretreated fibers, while simultaneously controlling the fiber color, resulting in micro / nano-structured lignin fibers with excellent structure. In addition, both steps S1 and S2 use a relatively large liquor ratio, which, compared to a small liquor ratio, enables uniform control of the lignin structure, quantity, and distribution on the surface of the bast fibers.

[0056] Furthermore, in some embodiments, the bast fiber includes one or more of ramie fiber, flax fiber, jute fiber, hemp fiber, and Apocynum venetum fiber.

[0057] In the technical solution of this application embodiment, by reasonably selecting the type of bast fiber, the pretreatment, in-situ micro-nano control and phenolic modification can be carried out smoothly on the fiber surface, while the fiber and resin can be efficiently bonded, resulting in a bast fiber composite material with high transparency, low haze and high antibacterial properties.

[0058] Secondly, embodiments of this application provide an antibacterial transparent bast fiber composite material, which is prepared using the preparation method of the antibacterial transparent bast fiber composite material provided in the first aspect of this application.

[0059] In the technical solution of this application embodiment, an antibacterial transparent bast fiber composite material is prepared by a specific method of this application. This method retains the aesthetics, texture, most of the grain, high mechanical strength, and non-deformation advantages of bast fibers, resulting in a composite material with high transparency, low haze, and high antibacterial properties. This antibacterial transparent bast fiber composite material shows great potential in packaging, electronics, optoelectronics, and other fields, especially excelling in products such as membrane switches, panels, and flexible display substrates. It opens a new chapter in the application of bast fibers, with a vast and promising market prospect.

[0060] Thirdly, embodiments of this application provide an application of an antibacterial transparent bast fiber composite material in the green textile, furniture, and construction industries.

[0061] In the technical solutions of this application embodiment, composite materials with high transparency, low haze, and high antibacterial properties are applied to the green textile, furniture, and construction industries to improve the functionality of textiles, furniture, and building materials.

[0062] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0063] Example 1

[0064] A method for preparing an antibacterial transparent bast fiber composite material includes the following steps:

[0065] S1. Select bundled hemp bast fibers and dry them at 95℃ for later use.

[0066] Prepare a mixed solution of sodium hydroxide and anhydrous sodium sulfate. The mass percentage of alkali and salt in the alkali / salt mixed solution is 10%, and the molar mass ratio of alkali to salt is 1:3.

[0067] Bast fibers were reacted in an alkali / salt mixed solution at a bath ratio of 1:60 at a reaction temperature of 100°C using a water bath for 3 hours. After the reaction was completed, the reaction solution was cooled, and the fibers were removed, thoroughly washed, impurities removed, and dried to obtain pretreated fibers.

[0068] S2. The pretreated fibers are reacted in an alcohol / water / alkali / salt system at a bath ratio of 1:80 and the reaction temperature is 90℃. During the reaction, the fibers are taken out and observed every 20 minutes until all the pretreated fibers turn white. After the reaction is completed, the reaction solution is cooled and the fibers are taken out, washed thoroughly and dried to obtain micro-nano structured lignin fibers.

[0069] The alcohol / water / alkali / salt system is prepared by mixing an alcohol / water mixture with an alkali / salt mixture used in step S1 at a volume ratio of 1:2; the volume ratio of ethanol to water in the alcohol / water mixture is 30%:70%.

[0070] S3. Add hydrobromic acid to the lithium bromide solution to adjust the pH to 4. Immerse the micro / nano-structured lignin fibers in a 50% (w / w) acidic lithium bromide solution at a bath ratio of 1:50. The reaction temperature is 110℃, and the reaction time is 90 min. After the reaction, cool the fiber-solution mixture in ice water, filter it through a glass funnel, collect the fibers, wash them several times with deionized water, and dry them in a 40℃ constant temperature drying oven to constant weight to obtain phenolic modified fibers.

[0071] S4. Soak the phenolic modified fiber in anhydrous ethanol overnight for later use.

[0072] Phenolic modified fibers soaked in ethanol were arranged in parallel into sheets of a certain size and placed in a mold of the same size. The prepared resin was poured into the mold, and the mold was placed in a vacuum drying oven. Excess gas inside the phenolic modified fibers was extracted through multiple vacuum-atmospheric pressure cycles. The resin was an alicyclic epoxy resin and a curing agent compounded at a mass ratio of 1:3, with the mass ratio of the alicyclic epoxy resin to the phenolic modified fibers being 1:1. The vacuuming temperature was 25℃, and the time was 1.5 hours.

[0073] Next, the fiber mixture combined with the alicyclic epoxy resin is placed at room temperature for curing for 20 hours. After curing, an antibacterial transparent bast fiber composite material can be obtained.

[0074] Examples 2-3 and Comparative Examples 1-2

[0075] A method for preparing an antibacterial transparent bast fiber composite material differs from Example 1 in that the mass percentage content (concentration) of alkali and salt in the alkali / salt mixed solution in step S1 is different. Otherwise, it is roughly the same as Example 1 and will not be repeated here.

[0076] The antibacterial transparent bast fiber composites prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests, and the results are shown in Table 1.

[0077] The antibacterial rate test was conducted according to the absorption method of GB / T20994.2-2007, and the antibacterial rate against Staphylococcus aureus (hereinafter referred to as Staphylococcus aureus) and Escherichia coli was detected. The antibacterial rate of untreated raw hemp bast fiber against Staphylococcus aureus and Escherichia coli was 0.

[0078] Transmittance testing shall be performed in accordance with GB / T 2410-2008, using a spectrophotometer or haze meter; the transmittance of untreated raw hemp bast fibers shall be less than 10%.

[0079] Haze detection should be performed according to GB / T 2410-2008, using a spectrophotometer or haze meter; the haze of untreated raw hemp bast fibers should be higher than 98%.

[0080] Strength testing was conducted according to GB / T 1447-2005, using a universal testing machine to test tensile mechanical properties; the tensile strength of untreated raw hemp bast fibers was less than 5 MPa.

[0081] Table 1. Performance of antibacterial transparent bast fiber composites in Examples 1-3 and Comparative Examples 1-2

[0082]

[0083] As shown in Table 1, with the increase of alkali and salt concentrations in the alkali / salt mixed solution, the antibacterial rate, transmittance, and strength first increased and then decreased; the haze fluctuated within a certain range. This may be because the changes in alkali and salt concentrations in the alkali / salt mixed solution affect the lignin removal process during the pretreatment of bast fibers, thereby affecting the microstructure of the subsequently obtained micro / nano-structured lignin fibers, influencing the phenolic modification and the curing process of the fiber and resin adhesive, and ultimately affecting the structure and properties of the obtained antibacterial transparent bast fiber composite material. The antibacterial transparent bast fiber composite materials obtained in Examples 1-3 have an antibacterial rate higher than 90%, a transmittance higher than 87%, a haze generally lower than 11, and a strength higher than 27 MPa, exhibiting good overall performance.

[0084] Examples 4-5 and Comparative Examples 3-4

[0085] The preparation method of an antibacterial transparent bast fiber composite material differs from that of Example 1 in that the volume ratio of ethanol to water in the alcohol / water mixed solution used in the alcohol / water / alkali / salt system in step S2 is different (hereinafter referred to as the alcohol / water ratio). The rest is roughly the same as that of Example 1 and will not be repeated here.

[0086] The antibacterial transparent bast fiber composites prepared in Examples 4-5 and Comparative Examples 3-4 were subjected to performance tests, and the results are shown in Table 2.

[0087] Table 2. Performance of the antibacterial transparent bast fiber composites in Examples 4-5 and Comparative Examples 3-4

[0088]

[0089] Table 2 shows that by changing the volume ratio of ethanol to water in the alcohol / water mixture within a certain range, the antibacterial rate, transmittance, haze, and strength of the resulting antibacterial transparent bast fiber composite material fluctuated within a certain range, and the overall performance was good. When the amount of ethanol was too small or too large, the antibacterial rate and transmittance of the resulting antibacterial transparent bast fiber composite material decreased significantly, and the haze and strength were also affected. This may be because the volume ratio of ethanol to water affects the micro-nano-scale regulation of the remaining lignin on the surface of the pretreated fiber by the alcohol / water / alkali / salt system, which changes the size and distribution of lignin on the surface of the resulting micro-nano-structured lignin fiber, thereby affecting the subsequent phenolation modification and molding process, and ultimately affecting the structure and properties of the antibacterial transparent bast fiber composite material.

[0090] Examples 6-7 and Comparative Examples 5-6

[0091] A method for preparing an antibacterial transparent bast fiber composite material differs from Example 1 in that the concentration of lithium bromide solution in step S3 is different, while the rest is roughly the same as in Example 1, and will not be repeated here.

[0092] The antibacterial transparent bast fiber composites prepared in Examples 6-7 and Comparative Examples 5-6 were subjected to performance tests, and the results are shown in Table 3.

[0093] Table 3. Performance of the antibacterial transparent bast fiber composites of Examples 6-7 and Comparative Examples 5-6

[0094]

[0095]

[0096] Table 3 shows that as the concentration of lithium bromide solution increases, the antibacterial rate and transmittance of the obtained antibacterial transparent bast fiber composite material first increase and then decrease. When the concentration of lithium bromide solution is 50%, both the antibacterial rate and transmittance reach their highest values, while the haze is the lowest, the strength is high, and the overall performance is optimal. This may be because when the concentration of lithium bromide solution is too low, the phenolic modification reaction is not sufficient, while when the concentration of lithium bromide solution is too high, the high concentration makes the phenolic modification reaction too violent, thus affecting the distribution of hydroxyl groups on the surface of the phenolic modified fiber, and also affecting the subsequent structural interaction between the phenolic modified fiber and the resin adhesive, ultimately affecting the performance of the composite material.

[0097] Examples 8-9 and Comparative Examples 7-8

[0098] A method for preparing an antibacterial transparent bast fiber composite material differs from Example 1 in that the mass ratio of alicyclic epoxy resin to phenolic modified fiber is different in step S4. The other steps are largely the same as in Example 1 and will not be repeated here.

[0099] The antibacterial transparent bast fiber composites prepared in Examples 8-9 and Comparative Examples 7-8 were subjected to performance tests, and the results are shown in Table 4.

[0100] Table 4. Properties of the antibacterial transparent bast fiber composites of Examples 8-9 and Comparative Examples 7-8

[0101]

[0102] Table 4 shows that with the increase of phenolic modified fiber content, the antibacterial rate, transmittance, and strength of the resulting antibacterial transparent bast fiber composite material generally show a decreasing trend, while the haze increases. This may be because the change in the amount of phenolic modified fiber affects the bonding between the phenolic modified fiber and the resin adhesive, thus affecting the structure and properties of the resulting antibacterial transparent bast fiber composite material. When the amount of resin adhesive is too high, the antibacterial rate of the composite material decreases significantly; therefore, a mass ratio of 1:1 is the optimal ratio.

[0103] Example 10 and Comparative Example 9

[0104] A method for preparing an antibacterial transparent bast fiber composite material differs from Example 1 in that the type of adhesive used in step S4 is different; otherwise, it is largely the same as Example 1 and will not be repeated here. Specifically, the adhesive used in Example 10 is epoxy resin 6800AB adhesive, and the adhesive used in Comparative Example 9 is PU adhesive.

[0105] The antibacterial transparent bast fiber composite materials prepared in Example 10 and Comparative Example 9 were subjected to performance tests, and the results are shown in Table 5.

[0106] Table 5. Performance of the antibacterial transparent bast fiber composite materials of Example 10 and Comparative Example 9

[0107]

[0108] From Table 5 and Figure 2 It is known that the type of adhesive used to fill the voids inside the fibers affects the antibacterial properties, transparency, and strength of the composite material. Epoxy resin 6800AB and alicyclic epoxy resin adhesives have better effects. PU adhesives result in composite materials with higher strength but are unstable, and their other properties are also poor.

[0109] Comparative Example 10

[0110] A method for preparing an antibacterial transparent bast fiber composite material differs from Example 1 in that step S2 is omitted, i.e., the alcohol / water / alkali / salt system treatment is omitted, and the treatment time of step S1 is extended to whiten the fiber while retaining some lignin. The rest is roughly the same as in Example 1 and will not be described in detail here.

[0111] Comparative Example 11

[0112] The preparation method of an antibacterial transparent bast fiber composite material differs from that of Example 1 in that step S3 is not performed, i.e., the phenolic modification reaction is not performed. The rest is roughly the same as that of Example 1, and will not be described again here.

[0113] Comparative Example 12

[0114] A method for preparing an antibacterial transparent bast fiber composite material includes the following steps:

[0115] S1. Select bundled hemp bast fibers and dry them at 95℃ for later use.

[0116] Prepare a mixed solution of sodium hydroxide and anhydrous sodium sulfate. The mass percentage of alkali and salt in the alkali / salt mixed solution is 10%, and the molar mass ratio of alkali to salt is 1:3.

[0117] Bast fibers were reacted in an alkali / salt mixed solution at a bath ratio of 1:60 at a reaction temperature of 100°C using a water bath for 5 hours to completely remove lignin from the surface of the antibacterial bast fibers (while the fibers turned white). After the reaction was completed, the reaction solution was cooled and the fibers were removed, thoroughly washed, impurities removed, and dried to obtain pretreated fibers.

[0118] S2. After dissolving lignin in deionized water, the pH is adjusted to 2 with hydrochloric acid for acid precipitation. After washing until the pH is 3-4, the lignin is added to an organic solvent or mixed solvent and stirred at room temperature. After filtration and drying, graded lignin is obtained. Subsequently, the lignin is dissolved in an organic solvent system and subjected to anti-solvent precipitation (dilution water is added dropwise to the solution at a uniform rate or the reverse operation is performed). Finally, the lignin with micro-nano structures with a size between 200-300 nm is obtained by rotary evaporation and drying.

[0119] The prepared micro / nano-structured lignin with a size between 200-300 nm was dispersed in an alcohol / water / alkali / salt system to obtain a lignin ethanol solution with a lignin mass concentration of 25 mg / mL (the mass concentration of lignin in the micro / nano-structured lignin fiber in Example 1 was 25 mg / mL). The volume ratio of ethanol to water in the alcohol / water / alkali / salt ethanol / water system was 30%:70%.

[0120] S3. Weigh 2.0g of the pretreated fiber prepared in step S1 and add it to 160mL of lignin ethanol solution at a bath ratio of 1:80 to obtain a lignin nanoparticle / fiber blend suspension. Slowly add 58mL of 1g / L gelatinized cationic starch solution to the blend suspension while stirring. At this time, the lignin nanoparticles will bind to the fiber in situ with the cationic gelatinized starch as a medium and precipitate. Filter the product to obtain lignin-based hemp bast fiber.

[0121] S4. Add hydrobromic acid to the lithium bromide solution to adjust the pH to 4. Immerse the lignin-based hemp bast fibers in a 50% (w / w) acidic lithium bromide solution at a bath ratio of 1:50. React at 110℃ for 90 min. After the reaction, cool the fiber-solution mixture in ice water and filter it through a glass funnel. Collect the fibers, wash them several times with deionized water, and dry them in a 40℃ constant temperature drying oven to constant weight to obtain phenolic modified fibers.

[0122] S5. Soak the phenolic modified fiber in anhydrous ethanol overnight for later use.

[0123] Phenolic modified fibers soaked in ethanol were arranged in parallel into sheets of a certain size and placed in a mold of the same size. The prepared resin was poured into the mold, and the mold was placed in a vacuum drying oven. Excess gas inside the phenolic modified fibers was extracted through multiple vacuum-atmospheric pressure cycles. The resin was an alicyclic epoxy resin and a curing agent compounded at a mass ratio of 1:3, with the mass ratio of the alicyclic epoxy resin to the phenolic modified fibers being 1:1. The vacuuming temperature was 25℃, and the time was 1.5 hours.

[0124] Comparative Example 13

[0125] A method for preparing a transparent bast fiber composite material includes the following steps:

[0126] S1. Select bundled hemp bast fibers and dry them at 95℃ for later use.

[0127] S2. Thoroughly mix the dried sample, pure water, biological enzyme (synthesized laccase / xylanase system, enzyme dosage of 10 IU / g) and glacial acetic acid (adjust pH to 3.5), add a trace amount of hydrogen peroxide, react at 45℃ for 1 hour, and then rinse with deionized water; the mass ratio of sample to water is 1:30, and the added hydrogen peroxide is 4% of the sample mass.

[0128] S3. Then extract the sample with 30% hydrogen peroxide and 25% ammonia at a volume ratio of 15:1.

[0129] S4. After extraction, the sample is rinsed with deionized water, and then ultrasonically extracted and dehydrated in sequence with pure ethanol, a mixture of ethanol and acetone, and pure acetone. Each ultrasonic extraction and dehydration step is repeated three times, for 3 minutes each time. The volume ratio of the ethanol and acetone mixture is 0.5:1; the volume ratio of pure ethanol, the mixture of ethanol and acetone, and pure acetone is 1:1:1.

[0130] S5. Injecting the polymer to impregnate the cavity of the delignified template and the nanofiber network on the cell wall, specifically including:

[0131] 1) Mix pure MMA monomer (methyl methacrylate) and AIBN (0.2 g / mL) initiator, stir evenly, and prepolymerize at 80℃ for 15 min;

[0132] 2) Terminate the reaction by cooling to room temperature in an ice-water bath;

[0133] 3) The obtained prepolymerized MMA was impregnated with the delignified template three times under vacuum for 30 min each time;

[0134] 4) Heat the material in an oven at 75°C for 4 hours to obtain a transparent bast fiber composite material.

[0135] The antibacterial transparent bast fiber composites prepared in Comparative Examples 10-13 were subjected to performance tests, and the results are shown in Table 6.

[0136] Table 6. Properties of antibacterial transparent bast fiber composites in Comparative Examples 10-13

[0137]

[0138] As shown in Table 6, the antibacterial transparent bast fiber composite material prepared in Comparative Example 10 had poor overall performance because it was not treated with an alcohol / water / alkali / salt system, i.e., the lignin on the fiber surface was not micro-nano-regulated.

[0139] The data from Comparative Example 11 and Example 1 further illustrate that the phenolic modification treatment increases the number of phenolic hydroxyl groups in the lignin molecular structure, thereby improving the antibacterial properties. At the same time, the data from Comparative Example 11 show that the phenolic modification process also affects the transparency of the composite material.

[0140] The antibacterial rate, transparency, and strength of the antibacterial transparent bast fiber composite material prepared in Comparative Example 12 were significantly reduced. It can be seen that the artificial attachment of micro-nano structured lignin to the fiber surface and the phenolic modification treatment seriously affected the antibacterial properties, strength, and mutual bonding between the fiber and the resin glue, thereby affecting the performance of the resulting composite material.

[0141] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing an antibacterial transparent bast fiber composite material, characterized in that, Includes the following steps: S1. Bast fibers are pretreated with an alkali / salt mixed solution to obtain pretreated fibers; S2. The pretreated fibers are treated with an alcohol / water / alkali / salt system until the bast fibers turn white to obtain micro-nano structured lignin fibers. S3. The micro-nano structured lignin fiber is reacted with metal bromide under acidic conditions to obtain phenolic modified fiber; S4. After soaking the phenolic modified fiber in alcohol for a preset time, arrange it in parallel into a preset shape and place it in a mold. Then add resin glue into the mold, vacuum and cure to obtain an antibacterial transparent bast fiber composite material. In step S2, the alcohol / water / alkali / salt system is prepared by mixing an alcohol / water mixed solution with the alkali / salt mixed solution used in step S1 at a volume ratio of 1:(1-3); the volume ratio of alcohol to water in the alcohol / water mixed solution is 10%-50%:50%-90%. In step S1, the mass percentage of alkali and salt in the alkali / salt mixed solution is 2%-20%, and the molar mass ratio of alkali to salt is 1:(1-5). Step S3 specifically involves: immersing the micro / nano structured lignin fibers in a metal bromide solution with a mass concentration of 40%-60% and a pH of 3-6 at a bath ratio of 1:(20-100), reacting at a temperature of 100-120°C for 60-120 minutes; the metal bromide includes one or more of lithium bromide, sodium bromide, and potassium bromide. In step S4, the mass ratio of the resin adhesive to the phenolic modified fiber is 1:(1-3).

2. The method for preparing the antibacterial transparent bast fiber composite material according to claim 1, characterized in that, The vacuuming temperature is 20-30°C and the time is 1-2 hours; the vacuuming is performed by multiple vacuum-atmospheric pressure cycles; the curing temperature is 20-30°C and the time is 18-24 hours.

3. The method for preparing the antibacterial transparent bast fiber composite material according to claim 1, characterized in that, Step S1 specifically involves reacting the bast fibers in the alkali / salt mixed solution at a bath ratio of 1:(30-100), at a reaction temperature of 80-100°C, and for a reaction time of 1-5 hours. Step S2 specifically involves reacting the pretreated fibers in the alcohol / water / alkali / salt system at a bath ratio of 1:(30-100), at a reaction temperature of 80-100°C, taking them out for observation at intervals during the reaction until the pretreated fibers turn white.

4. The method for preparing the antibacterial transparent bast fiber composite material according to claim 1, characterized in that, The bast fibers include one or more of ramie fiber, flax fiber, jute fiber, hemp fiber, and Apocynum venetum fiber.

5. An antibacterial transparent bast fiber composite material, characterized in that, The antibacterial transparent bast fiber composite material was prepared using the preparation method described in any one of claims 1-4.

6. The antibacterial transparent bast fiber composite material prepared by the preparation method of any one of claims 1-4, or the antibacterial transparent bast fiber composite material of claim 5, in the green textile, furniture, and construction industries.

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