All-bamboo-based thermosetting bioplastic as well as preparation method and application thereof

Abstract

The invention provides all-bamboo-based thermosetting bioplastic as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out ball milling on bamboo powder and an alkali solution under a mixing condition; diluting the ball-milled slurry, adjusting the pH value to be less than or equal to 7 by using an acid solution, and centrifuging; and adjusting the solid content of the centrifugal slurry, forming a film, and carrying out hot press molding to obtain the all-bamboo-based thermosetting bioplastic. The technical problem to be solved is how to effectively utilize bamboo wood to prepare the all-bamboo-based thermosetting bioplastic, so that all components of the bamboo wood can be utilized, the preparation process is simple, the reaction condition is mild, the efficiency is high, and the prepared all-bamboo-based thermosetting bioplastic is excellent in comprehensive performance, good in flexibility and excellent in solvent resistance, has the tensile strength larger than or equal to 50 MPa and can be widely applied to the field of bioplastics. Therefore, the device is more practical.

Description

Technical Field

[0001] The invention belongs to the technical field of bamboo material processing and utilization, and particularly relates to a full-bamboo-based thermosetting bioplastic and a preparation method and application thereof. Background Art

[0002] Plastic is a cheap, lightweight, and durable material that is widely used in various fields. Due to the extremely slow biodegradation rate of plastics, their accumulation in the environment leads to soil and water pollution, and they are also accidentally eaten by animals. Therefore, it is of great practical significance to develop bio-based degradable plastic products to replace non-renewable petroleum-based plastics.

[0003] Bamboo is one of the most famous fast-growing plants in the world, with its fast growth and high yield. Its high strength and good processability make it an ideal choice for manufacturing various bio-based materials. In the process of seeking sustainable alternatives, bamboo and bamboo products are considered as potential substitutes for plastics due to their renewable and biodegradable properties, which can help reduce dependence on traditional plastics.

[0004] There are generally two methods for preparing bio-based plastics using wood or agricultural and forestry residues as raw materials: First, the raw materials are usually deconstructed, that is, lignin and hemicellulose are removed to obtain the cellulose part, and then the cellulose part is subjected to mechanical methods (such as high-pressure homogenization, microfluidization, mechanical ball milling or high-intensity ultrasonic treatment) or / and chemical modification methods (such as TEMPO oxidation, sodium periodate oxidation, esterification, carboxymethylation, etherification, etc.) to prepare nanocellulose, and then obtain cellulose-based plastics. Second, a high-concentration salt solution (such as 72wt% ZnCl 2 、80wt%ZnCl 2 / AlCl 3 、70wt%ZnCl 2 / CaCl 2 ), ionic liquids, low eutectic solvents, quaternary ammonium salt / quaternary phosphonium salt aqueous solutions, alkali / urea and NaOH / thiourea systems, etc., first dissolve cellulose, then precipitate it in a specific solution to obtain regenerated cellulose, which is then further prepared into cellulose-based plastics. However, the above two modification or preparation methods are cumbersome and often involve the use of toxic and harmful volatile organic compounds, solvents, catalysts, etc., and the cost is also high, so it is difficult to have actual production and use value.

[0005] Although bamboo is also mainly composed of three components: cellulose, hemicellulose, and lignin, its own organizational structure characteristics determine that its cell strength is usually greater than that of wood and agricultural straw, so the permeability of chemicals to bamboo is poor; in addition, the wall of bamboo parenchyma cells is thin and easy to depolymerize, and bamboo contains a large amount of fat and inorganic substances. Therefore, there are currently few systematic solutions for the efficient and green activation of bamboo components and the preparation of high-strength bamboo-based plastics. Most of the existing technologies for the modification of bamboo are: first separate the bamboo into three components, and then prepare bamboo-based bioplastics through chemical modification. The preparation process is cumbersome and inefficient, and it cannot realize the full utilization of bamboo raw materials; at the same time, the prepared bio-based plastics often have problems with poor flexibility and poor water resistance. Summary of the invention

[0006] The main purpose of the present invention is to provide a bamboo-based thermosetting bioplastic and a preparation method and application thereof. The technical problem to be solved is how to effectively use bamboo to prepare a bamboo-based thermosetting bioplastic so that the bamboo can be fully utilized. The preparation process is simple, the reaction conditions are mild, and the efficiency is high. The prepared bamboo-based thermosetting bioplastic has excellent comprehensive performance, a tensile strength of ≥50MPa, good flexibility, and excellent solvent resistance, so that it is more suitable for practical use.

[0007] The purpose of the present invention and the technical problem to be solved are achieved by adopting the following technical solutions. According to a method for preparing a bamboo-based thermosetting bioplastic proposed by the present invention, the method comprises the following steps:

[0008] S1 ball-milling bamboo powder and alkaline solution under mixing conditions;

[0009] S2 dilutes the ball mill slurry, adjusts its pH value to ≤7 with an acid solution, and centrifuges;

[0010] S3 adjusts the solid content of the centrifugal slurry, forms a film, and performs hot pressing to obtain a fully bamboo-based thermosetting bioplastic.

[0011] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0012] Preferably, in the aforementioned preparation method, the alkaline solution is selected from KOH, NaOH, LiOH, Ba(OH) 2 , at least one of aqueous ammonia and ethanolamine.

[0013] Preferably, in the aforementioned preparation method, the concentration of the alkaline solution is 0.1 to 3 mol / L.

[0014] Preferably, in the aforementioned preparation method, the particle size of the bamboo powder is 10 to 100 meshes.

[0015] Preferably, in the aforementioned preparation method, the mass ratio of the bamboo powder to the alkaline solution is 1:8-20.

[0016] Preferably, in the aforementioned preparation method, the acid solution is selected from at least one of hydrochloric acid, sulfuric acid, formic acid and acetic acid.

[0017] Preferably, in the aforementioned preparation method, the process parameters of the hot pressing are as follows: the hot pressing temperature is from room temperature to 180° C., the hot pressing pressure is 5 to 20 MPa, and the hot pressing time is 10 to 120 min.

[0018] The purpose of the present invention and the technical problem solved by the present invention are also achieved by the following technical solutions: A bamboo-based thermosetting bioplastic proposed by the present invention comprises, by mass percentage, lignin ≥ 30%, cellulose ≥ 47%, and hemicellulose ≤ 15%.

[0019] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0020] Preferably, the aforementioned all-bamboo-based thermosetting bioplastic has a tensile strength of ≥50 MPa and is solvent-resistant.

[0021] The purpose of the present invention and the technical problems solved therein are also achieved by adopting the following technical solutions: The present invention proposes an application of the aforementioned all-bamboo-based thermosetting bioplastic in the field of bamboo material processing and plastic manufacturing.

[0022] By means of the above technical solution, the all-bamboo-based thermosetting bioplastic and its preparation method and application proposed by the present invention have at least the following advantages:

[0023] The all-bamboo-based thermosetting bioplastic and its preparation method and application proposed in the present invention do not need to pre-treat the bamboo material to remove lignin in advance, but directly use bamboo powder as raw material. It only needs to mix the bamboo powder with an alkaline solution and then ball-mill. The hydroxyl groups on the cellulose molecular chain combine with the hydroxide ions to destroy the hydrogen bonds between the fibers, and the fibers swell, making the internal structure of the bamboo fibers loose, which provides convenience for ball milling. The alkaline solution cooperates with the ball milling, so that the grinding balls strongly impact, rub and crush the materials, thereby realizing the refinement and fibrillation of the bamboo materials. At the same time, the alkaline solution dissolves and removes part of the lignin and hemicellulose in the bamboo material. The method comprises the steps of: dissolving the lignin in the solution; and then adjusting the pH value to ≤7 by an acid solution to precipitate the lignin. On the one hand, the lignin can be attached to the surface of the fiber. In the subsequent film-forming hot pressing process, the lignin can be used as a binder to further strengthen the connection between the bamboo fibers. The prepared bioplastic has excellent performance through the combined effect of chemical bonding and physical bonding, and its tensile strength is ≥50MPa. On the other hand, acid precipitation can make the lignin released during the ball milling process of the alkaline solution precipitate again, thereby reducing the raw material loss with the centrifugal liquid during water washing, which is beneficial to the utilization of all components of the bamboo powder raw material, and the utilization rate of the bamboo powder raw material is as high as more than 90%.

[0024] In the technical solution of the present invention, since part of the hemicellulose is removed, its solvent resistance is enhanced. After the prepared bioplastic is immersed in different solvents for 30 days, the bioplastic remains intact and only slightly changes color in 1% NaOH solution, indicating that it is slightly soluble. Since part of the lignin is removed, its flexibility is enhanced, and the toughness of the prepared bioplastic is ≥9MJ / m 3 .

[0025] The technical solution of the present invention prepares bioplastics by ball milling under mixed conditions of alkaline solution and bamboo powder, followed by acid precipitation and film-forming hot pressing. No toxic or harmful solvents need to be used in the entire process, which is green and environmentally friendly. The ball milling efficiency of bamboo powder is improved by the combined process of alkaline solution and ball milling. At the same time, no pretreatment is required, and bamboo powder can be directly used to prepare all-bamboo-based bioplastics, which have excellent mechanical properties and good biodegradability.

[0026] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the morphological change of bamboo fiber before and after ball milling in alkaline solution - optical microscope image;

[0028] Figure 2 This is the optical microscopy image of the fiber morphology changes after ball milling assisted by different concentrations of alkali and then acid precipitation;

[0029] Figure 3 It is the difference between the surface and cross-section SEM images of bioplastics pressed at room temperature and hot pressed;

[0030] Figure 4 is a graph showing the color change of the bioplastic in a specific embodiment of the present invention at different hot pressing temperatures;

[0031] Figure 5 is a graph showing changes in mechanical properties of bioplastics in a specific embodiment of the present invention at different hot pressing temperatures;

[0032] Figure 6 is a photographic comparison of a bioplastic according to a specific embodiment of the present invention immersed in different solvents from 0 day to 30 days;

[0033] Figure 7 are stress-strain curves of Example 1 and Comparative Example 1;

[0034] Figure 8 are the test results of Young's modulus and toughness of Example 1 and Comparative Example 1;

[0035] Fig. 9 The following are pictures of products of different thicknesses processed from the bioplastic of Example 1. DETAILED DESCRIPTION

[0036] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description of a bamboo-based thermosetting bioplastic and its preparation method and application proposed by the present invention, its specific implementation method, structure, characteristics and effects, in combination with the accompanying drawings and preferred embodiments.

[0037] The present invention provides a method for preparing a bamboo-based thermosetting bioplastic, which comprises the following steps:

[0038] First, the bamboo powder and the alkaline solution are ball-milled under mixed conditions.

[0039] Bamboo mainly contains cellulose, lignin and hemicellulose. In this step, the alkaline solution has two main effects. On the one hand, the alkaline solution can swell the cellulose in the bamboo. The hydroxyl groups on the cellulose molecular chain combine with the hydroxide ions to destroy the hydrogen bonds between the cellulose chains, causing the fibers to swell and loosen the internal structure of the bamboo fibers, facilitating the ball milling process. On the other hand, the alkaline solution can also dissolve and remove part of the lignin and hemicellulose in the bamboo, preventing the lignin in the bamboo from affecting the flexibility and processability of subsequent materials, and preventing the strong hydrophilicity of the hemicellulose in the bamboo from adversely affecting the water resistance and stability of bioplastics. In addition, the detached lignin migrates to the fiber surface and acts as an "adhesive" in the subsequent hot pressing process.

[0040] In the above steps, the ball milling is carried out under the condition that the alkaline solution and the bamboo powder are mixed, that is, the ball milling process runs through each stage of the mixing of the alkaline solution and the bamboo powder. In the present invention, through the mechanical action of the ball milling, the collision and grinding of the grinding balls generate a strong mechanical force on the bamboo powder during the ball milling process, and this mechanical force acts on the swollen bamboo fibers to break up the fiber bundles, thereby gradually splitting the large fiber bundles into finer fibers.

[0041] In the above steps, the synergistic effect of the alkaline solution and the mechanical ball milling leads to the fibrillation and brooming of the bamboo fibers, that is, under the synergistic effect of the alkali solution swelling and the mechanical force of the ball milling, the lignin and hemicellulose in the cell wall of the bamboo fibers are partially removed or modified, the connection between the cellulose microfibrils is weakened, and the microfibrils are separated and broomed to form finer, more fluffy bamboo fibers with fibrillation and brooming characteristics; the morphology of the bamboo raw material before the synergistic ball milling of the bamboo fibers and the alkaline solution, and the morphology of the fibrillation and brooming after the synergistic ball milling of the bamboo fibers and the alkaline solution are shown in the attached figure Figure 1 As shown by Figure 1 It can be seen that after ball milling with alkaline solution, the bamboo fiber showed obvious fibrillation phenomenon.

[0042] The above-mentioned fibrillated bamboo fibers can improve the performance of the fibers. The finer bamboo fiber diameter and the fibrillated structure can increase the specific surface area of ​​the bamboo fibers, making them more closely integrated with the matrix material in applications such as composite materials, and can effectively improve the mechanical properties of the composite materials. In addition, the fibrillated bamboo fibers have enhanced flexibility, making the bioplastics more moldable and improving the strength and other properties of the plastics. The fibrillated structure can allow adjacent fibers to form a entangled structure with each other, increasing the connectivity between the fibers, thereby making the prepared bioplastics have higher strength.

[0043] In the above steps, the fiber diameter and fiber structure of the bamboo fibers after coordinated ball milling vary due to different process parameters, but they can all achieve the technical effects of the present invention; the specific process parameter design can be adjusted and optimized according to the actual situation in actual applications.

[0044] When bamboo powder is mixed with alkaline solution for ball milling, the type of alkali needs to be selected based on multiple factors. First, the alkalinity strength should be considered. Generally, strong alkalis are preferred, such as sodium hydroxide (NaOH) and potassium hydroxide (KOH). Because of their strong alkalinity, they can quickly and effectively destroy the chemical bonds between lignin, hemicellulose and cellulose in bamboo powder, so that cellulose can be better separated and the fiber separation effect can be improved. However, in some cases where the degree of fiber damage is low and a mild reaction is desired, weak alkalis such as sodium carbonate (Na2CO3) are also selected. 2 CO 3 ), sodium bicarbonate (NaHCO 3), but usually need to cooperate with other treatment methods or extend the treatment time. Second, solubility and reactivity should be considered. Since the present invention uses water as the solvent for environmental protection, the alkali is required to have good solubility in water so that it can fully contact and react with bamboo powder; sodium hydroxide, potassium hydroxide, etc. have high solubility in water, can be quickly and evenly dispersed in the system, and fully react with various parts of bamboo powder. Third, its reactivity with bamboo powder should be moderate. Too high reactivity may cause excessive degradation of bamboo fiber and affect product performance; while too low reactivity may cause incomplete reaction; sodium hydroxide and the like have a more appropriate reactivity with bamboo powder, which can achieve better delignification and silk brooming effects under certain time and temperature conditions. Fourth, based on cost and safety considerations, cost is an important consideration in industrial production. Sodium hydroxide is relatively low in price and widely available, and is a common choice. Some special alkalis, such as lithium hydroxide (LiOH), have unique properties, but high costs, which limit large-scale applications. Sodium hydroxide, potassium hydroxide, etc. are highly corrosive and strict protective measures need to be taken when used, but because of their superior performance, they are still widely used under standardized operations. Some alkalis with weak alkalinity and low corrosiveness, such as sodium carbonate, are highly safe, but the treatment effect is relatively weak. Taking various influencing factors into consideration, the present invention preferably uses the alkali solution selected from KOH, NaOH, LiOH, Ba(OH) 2 The preferred alkaline solution type can not only make the bamboo fiber have a better fiber diameter and fiber structure, meet the performance requirements of the subsequent preparation of bioplastics, but also the raw materials are easy to obtain, and the solubility, reactivity and safety are all at a more suitable level.

[0045] There are many factors that affect the effect of synergistic ball milling of bamboo fibers, among which the concentration of the alkaline solution is a more critical control factor. A large number of experimental studies have shown that when the concentration of the alkaline solution is 0.5-3 mol / L, the final prepared bioplastic has better performance; the reason may be that: the higher the concentration of the alkaline solution, the stronger its dissolution effect on lignin and hemicellulose in the bamboo fiber, and the easier it is to promote the fibrillation of the bamboo fiber, but when the concentration of the alkaline solution is too high, the bamboo fiber itself will be damaged. The preferred concentration of the alkaline solution of the present invention is 0.1-3 mol / L, and the tensile strength of the bioplastic can reach more than 50 MPa under this concentration adjustment; the concentration of the alkaline solution is further preferably 0.5-1.3 mol / L, and the tensile strength of the bioplastic can reach more than 80 MPa under this concentration adjustment; the concentration of the alkaline solution is further preferably 0.9-1.1 mol / L, and the tensile strength of the bioplastic can reach more than 120 MPa under this concentration adjustment.

[0046] The temperature of the alkaline solution also has a certain influence on the effect of the synergistic ball milling treatment of bamboo fibers. Increasing the temperature can accelerate the reaction rate of the alkaline solution and the bamboo fibers, enhance the swelling effect, and facilitate the fibrillation; however, too high a temperature will degrade the bamboo fibers. The present invention preferably performs the synergistic ball milling treatment at room temperature, which can not only ensure the performance requirements of the subsequent bioplastics, but also save energy consumption.

[0047] The time of the coordinated ball milling treatment of bamboo fiber also has a certain influence on its fibrillation and brooming effect. Prolonging the alkali treatment time may increase the degree of interaction between the alkali solution and the bamboo fiber, making the fibrillation and brooming more complete, and the longer the ball milling time, the higher the degree of fibrillation and brooming; however, if the alkali solution treatment time is too long, the bamboo fiber will be excessively damaged, and if the ball milling time is too long, the fiber will be overly refined and the performance will be reduced. The preferred alkali solution coordinated ball milling treatment time of the present invention is 20 to 200 minutes. The treatment within this coordinated treatment time range can make the performance of the bioplastic prepared from bamboo fiber at a better level.

[0048] The ball milling speed also has a certain influence on the effect of the synergistic ball milling treatment of bamboo fiber, because the speed will affect the collision energy and frequency of the grinding balls. When the speed is high, the mechanical force is strong and the fiber separation is fast, but when the speed is too high, the fiber will be seriously broken. The preferred ball milling speed of the present invention is 300-500rpm, and the specific range may vary slightly due to different ball mill specifications, and the present invention does not make specific restrictions on this.

[0049] The type of bamboo also has a certain influence on the effect of the synergistic ball milling treatment of bamboo fiber. The cellulose, hemicellulose and lignin content and structure of different types of bamboo are different, which will also affect the degree of filamentation. In practical applications, suitable bamboo species can be selected according to the required degree of filamentation. The present invention does not make specific restrictions on this. In the subsequent specific embodiments, the bamboo powder used in the present invention is composed as follows: in terms of mass percentage, the lignin content is 23.50%, the cellulose content is 44.79%, the hemicellulose content is 18.00%, and the other components are 13.71%. This composition is all illustrative and is not intended to limit the scope of the present invention.

[0050] The particle size of bamboo powder also has a certain influence on the effect of bamboo fiber synergistic ball milling. The smaller the particle size of bamboo powder, the larger its specific surface area, which makes the alkaline solution and ball milling more sufficient, thereby making it easier to separate and broom. The particle size of bamboo powder can be controlled by screening and other methods. The preferred particle size of bamboo powder in the present invention is 10-100 mesh, which can make it easier to separate and broom and improve efficiency, and at the same time avoid the fiber being too fine and damaged, which affects the strength and other properties of bioplastics.

[0051] The mass ratio of bamboo powder to alkaline solution also has a certain influence on the synergistic ball milling treatment effect of bamboo fiber. If the mass ratio of bamboo powder to alkaline solution is too low, the ball milling material is thinner, and the force of the grinding ball on the bamboo powder is weaker; while if the mass ratio of bamboo powder to alkaline solution is too high, the ball milling material is thicker, and the grinding ball will float on the surface of the ball milling material, resulting in the grinding ball being unable to act on the bamboo powder. The preferred mass ratio of bamboo powder to alkaline solution of the present invention is 1:8-20 to ensure the ball milling effect of bamboo powder.

[0052] After the bamboo powder is ball-milled with an alkaline solution, the ball-milled slurry is diluted, adjusted to a pH value of ≤7 with an acid solution, and centrifuged.

[0053] In the above steps, the ball mill slurry is diluted by adding water thereto and stirring it evenly; the amount of water added can be adjusted according to actual conditions, for example, adding twice the volume of water to the ball mill slurry; at this time, the removed lignin and hemicellulose are dissolved in the aqueous solution.

[0054] In the above steps, pH adjustment is performed by adding an acid solution to the diluent. The technical purpose of adjusting pH is to allow the lignin in the solution to precipitate and adhere to the fiber surface, so that the bamboo fiber presents a form in which the lignin migrates to the fiber surface; the acid precipitation step, on the one hand, can allow the lignin to adhere to the fiber surface, so that in the subsequent film-forming hot pressing process, the lignin can be used as a binder to further strengthen the connection between the bamboo fibers, thereby ensuring its tensile strength; on the other hand, the acid precipitation step can allow the lignin that has been removed during the ball milling process of the alkaline solution to precipitate again, thereby reducing the loss of raw materials with the centrifugal liquid during water washing, which is beneficial to the utilization of all components of the bamboo powder raw materials, and the utilization rate of the bamboo powder raw materials can be as high as 90% or more. As shown in the attached Figure 2 The fiber morphology after ball milling and acid precipitation under different alkali concentration conditions is shown, where the alkali concentration is the molar concentration, the unit is mol / L, and is marked in the upper left corner of each figure; Figure 2 As shown, under different concentrations of alkali-assisted ball milling, the thickness and length of the fiber are significantly different, and with the increase of alkali concentration, the fiber shows a trend of increasing length and decreasing diameter; and, with the increase of alkali concentration, the lignin migrating to the fiber surface increases significantly, indicating that the content of lignin released into the solution under alkali-assisted ball milling conditions increases with the increase of alkali concentration, and this part of lignin will precipitate again during the pH adjustment process of the acid solution and adhere to the surface of the fiber. The lignin attached to the fiber surface will act as a binder in the subsequent hot pressing process, which is beneficial to enhance the tensile strength of the bioplastic prepared by the present invention. The type of acid used to adjust the pH value can be any type as long as it can achieve the precipitation of lignin and adhesion to the surface of the fiber through pH adjustment without affecting the fiber performance. The preferred acid solution of the present invention is at least one acid selected from hydrochloric acid, sulfuric acid, formic acid and acetic acid.

[0055] The next step is to adjust the solid content of the centrifugal slurry to form a film.

[0056] In the above steps, the solid content of the centrifugal slurry is adjusted by adding water thereto; the specific solid content level can be selected and determined according to different film-forming processes, and the present invention does not specifically limit this. The film-forming process can be tape casting, vacuum filtration molding, or smearing molding, etc., and the present invention does not specifically limit this.

[0057] Finally, the film is heat-pressed to make it cross-linked and cured to obtain a full bamboo-based thermosetting bioplastic.

[0058] As attached Figure 3 The figure shows the difference in morphology of bioplastics after hot pressing and room temperature pressing. Figure 3 It can be seen that after pressing at room temperature (25°C, 20MPa for 20min), the surface of the membrane is rough and the inside is loose; after hot pressing under hot pressing conditions (140°C, 20MPa for 20min), the surface of the membrane is fine and the inside is dense; this may be because lignin can melt, flow and cross-link under the action of heat and pressure, thereby achieving a certain bonding effect on adjacent fibers while filling the fiber gaps.

[0059] In the above steps, the process parameters of the hot pressing molding can be determined according to the type of bamboo powder and the target product performance.

[0060] When the hot pressing temperature is too low, the lignin may not melt, resulting in poor mechanical properties of bioplastics, such as low tensile strength and Young's modulus; when the hot pressing temperature is too high, it may cause thermal degradation of the active ingredients, resulting in a decrease in the mechanical properties of bioplastics, making them brittle and fragile. Figure 4 The color change diagram of the bioplastic in a specific embodiment at different hot pressing temperatures is shown in the attached figure. Figure 5 The figure shows the change of mechanical properties of bioplastics at different hot pressing temperatures in a specific embodiment; Figure 4 and Figure 5 It can be seen that when hot-pressed at a temperature higher than 160°C, the color of the bioplastic becomes darker, which may be due to the carbonization of the plastic; accordingly, its corresponding mechanical strength also becomes poor; and when the hot-pressing temperature is lower, since the lignin has not yet softened and cross-linked, its corresponding mechanical strength is also poor. The preferred hot-pressing temperature of the present invention is room temperature to 180°C; the more preferred hot-pressing temperature is 110-160°C; and the more preferred hot-pressing temperature is 130-150°C.

[0061] When the hot pressing pressure is too low, the materials may not be tightly combined, resulting in gaps inside the bioplastic, which leads to poor mechanical properties such as tensile strength and hardness; when the hot pressing pressure is too high, the structure of the bamboo powder may be destroyed, causing stress concentration inside the bioplastic, resulting in reduced toughness and easy breakage when stressed; on the other hand, appropriate pressure can make the bioplastic more dense and improve its waterproofness, barrier properties, etc. The preferred hot pressing pressure of the present invention is 5 to 20 MPa.

[0062] The hot pressing time will affect the mechanical properties and energy consumption of bioplastics. The selection of the hot pressing time of the present invention is mainly determined by the thickness of the bioplastic; for thicker bioplastics, if the hot pressing time is too short, the cross-linking and curing reaction of the bamboo fiber may be insufficient, so that the plastic inside cannot be well cross-linked and cured, and the mechanical properties of the bioplastic cannot reach the best. For thinner bioplastics, if the hot pressing time is too long, it may cause energy waste. The preferred hot pressing time of the present invention is 10 to 120 minutes.

[0063] The present invention also provides a full bamboo-based thermosetting bioplastic, which comprises, by weight percentage, lignin ≥ 30%, cellulose ≥ 47%, and hemicellulose ≤ 15%.

[0064] The compositions of the bioplastics prepared in some specific examples are shown in Table 1 below, wherein the component analyses are all determined using the National Renewable Energy Laboratory (NREL) method.

[0065] Table 1

[0066]

[0067] The contents of lignin, cellulose and hemicellulose in Table 1 are all in mass percentage; the raw material utilization rate in Table 1 is measured by weight and calculated according to the following formula 1).

[0068]

[0069] It can be seen from the above measurement data that when no alkaline solution is added during the ball milling of bamboo powder, the content of lignin in the prepared plastic is basically equivalent to the content of lignin in the bamboo powder; when the alkaline solution is co-milled but no subsequent acid precipitation is performed, the content of lignin in the prepared plastic is lower than the content of lignin in the bamboo powder. This may be because the lignin in the bamboo powder is partially removed into the solution during the ball milling with the alkaline solution, and then lost with the centrifuge in the subsequent centrifugation process; in the technical scheme of the present invention, after the alkaline solution is co-milled, an acid solution is subsequently added for acid precipitation, and the content of lignin in the prepared plastic is higher than the content of lignin in the bamboo powder. This may be because the lignin and hemicellulose are partially removed into the solution during the ball milling with the alkaline solution, and then most of the lignin is precipitated and attached to the surface of the fiber in the subsequent acid precipitation process, while the hemicellulose is lost with the centrifuge in the subsequent centrifugation process. Through the technical scheme of the present invention, on the one hand, lignin can be attached to the surface of the fiber, so that in the subsequent film-forming hot pressing process, lignin can be used as a binder to further strengthen the connection between the bamboo fibers, thereby ensuring its tensile strength; on the other hand, acid precipitation can make the lignin released during the ball milling process of the alkaline solution precipitate again, thereby reducing the raw material loss with the centrifugal liquid during water washing, which is beneficial to the utilization of all components of the bamboo powder raw material and makes the utilization rate of the bamboo powder raw material as high as more than 90%.

[0070] The bamboo-based thermosetting bioplastic prepared by the method of the present invention has a tensile strength of ≥50MPa and has good solvent resistance. Figure 6 The following is a comparison of photos of a bioplastic of a specific embodiment immersed in different solvents from 0 day to 30 days. Figure 6 It can be seen that after the bioplastic prepared by the present invention is immersed in different solvents for 30 days, the bioplastic remains intact, and only slightly changes color and becomes slightly soluble in 1% NaOH solution, indicating that the bioplastic prepared by the present invention has better solvent resistance.

[0071] By adjusting the process parameters of alkaline solution ball milling, acid precipitation and hot pressing, the tensile strength of the all-bamboo-based thermosetting bioplastic prepared by the method of the present invention is ≥80MPa; further, by adjusting the process parameters of alkaline solution ball milling, acid precipitation and hot pressing, the tensile strength of the all-bamboo-based thermosetting bioplastic prepared by the method of the present invention is ≥120MPa, and its Young's modulus is ≥3GPa, and its toughness is ≥9MJ / m 3 .

[0072] The present invention also proposes an application of the aforementioned all-bamboo-based thermosetting bioplastic in the fields of bamboo material processing and utilization and plastic manufacturing.

[0073] The present invention will be further described below in conjunction with specific embodiments, but this should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by technicians in this field based on the above-mentioned contents of the present invention still fall within the scope of protection of the present invention.

[0074] Unless otherwise specified, the materials, reagents, etc. involved below are all commercially available products well known to those skilled in the art; unless otherwise specified, the methods described are all methods well known in the art. Unless otherwise defined, the technical terms or scientific terms used should have the common meanings understood by ordinary technicians in the field to which the present invention belongs.

[0075] Embodiment 1:

[0076] The bamboo material is crushed into bamboo powder of 10-100 mesh for later use. The composition of the bamboo powder used in this embodiment is as follows: in terms of mass percentage, the lignin content is 23.50%, the cellulose content is 44.79%, and the hemicellulose content is 18.00%.

[0077] The bamboo powder was mixed with 1 mol / L NaOH solution in a mass ratio of 1:10 and added into a ball mill, and the mixture was ball milled at a speed of 500 rpm for 120 min to obtain a ball mill slurry; the ball mill slurry was taken out, and two times the volume of water was added to dilute it, and an appropriate amount of acetic acid was added to adjust the pH value to ≤7; the solution after pH adjustment was centrifuged, and the slurry was retained; some water was added to the slurry to make it dilute and have a consistency suitable for tape casting; tape casting was performed to form a film; and the film was transferred to a hot press and hot pressed at 140°C and 20 MPa for 20 min to fully cross-link and solidify the bamboo units in the film.

[0078] The cured film was cut into 50×10 mm strips and subjected to tensile strength test using a universal tensile machine at a rate of 50 mm / min according to GB / T 1040.3-2006. The tensile stress-strain curve is shown in the attached figure. Figure 7 As shown, its tensile strength reaches 124.27±1.83MPa.

[0079] The toughness is obtained by calculating the closed area of ​​the stress-strain curve, and the result is 10MJ / m 3 ; The Young's modulus was obtained by fitting the slope of the stress-strain curve, and the result was 3 GPa, as shown in the attached Figure 8 As shown, the ordinate on the right is toughness, and the gray column is toughness; the ordinate on the left is Young's modulus, and the black column is Young's modulus.

[0080] The bioplastics of this example were processed into products of different thicknesses. The results are shown in the attached figure. Fig. 9 shown.

[0081] Example 2

[0082] Same as Example 1, except that the hot pressing temperature is 180°C, and the tensile strength is 54.44±0.93 MPa.

[0083] Example 3

[0084] The same as Example 1, except that the alkaline solution is 1 mol / L ammonia water, and the tensile strength is 110.32±2.16 MPa.

[0085] Example 4

[0086] The same as Example 1, except that the alkaline solution is an ethanolamine solution with a concentration of 1 mol / L, and the tensile strength is 122.40±5.73 MPa.

[0087] Example 5

[0088] Same as Example 1, except that the concentration of the alkaline solution is 0.1 mol / L, and the tensile strength is 51.25±2.05 MPa.

[0089] Example 6

[0090] Same as Example 1, except that the concentration of the alkaline solution is 0.5 mol / L, and the tensile strength is 89.17±2.16 MPa.

[0091] Example 7

[0092] Same as Example 1, except that the concentration of the alkaline solution is 3.0 mol / L, and the tensile strength is 55.38±7.03 MPa.

[0093] Example 8

[0094] Same as Example 1, except that the concentration of the alkaline solution is 2.0 mol / L, and the tensile strength is 51.53±6.31 MPa.

[0095] Example 9

[0096] Same as Example 1, except that the concentration of the alkaline solution is 1.5 mol / L, and the tensile strength is 50.54±5.73 MPa.

[0097] Example 10

[0098] Same as Example 1, except that the concentration of the alkaline solution is 2.5 mol / L, and the tensile strength is 53.61±4.79 MPa.

[0099] Embodiment 11

[0100] The same as Example 1, except that the mass ratio of bamboo powder to NaOH solution is 1:8, and the tensile strength is 122.76±3.59 MPa.

[0101] Example 12

[0102] The same as Example 1, except that the mass ratio of bamboo powder to NaOH solution is 1:20, and the tensile strength is 119.98±6.38 MPa.

[0103] Embodiment 13

[0104] Same as Example 1, except that the acid solution for adjusting pH is hydrochloric acid, and the tensile strength is 121.63±1.56 MPa.

[0105] Embodiment 14

[0106] Same as Example 1, except that the hot pressing temperature is room temperature, and the tensile strength is 85.43±3.33 MPa.

[0107] Embodiment 15

[0108] Same as Example 1, except that the hot pressing temperature is 100°C, and the tensile strength is 87.19±3.23 MPa.

[0109] Example 16

[0110] Same as Example 1, except that the hot pressing temperature is 110°C, and the tensile strength is 93.19±5.45 MPa.

[0111] Embodiment 17

[0112] Same as Example 1, except that the hot pressing temperature is 120°C, and the tensile strength is 105.57±1.63 MPa.

[0113] Embodiment 18

[0114] Same as Example 1, except that the hot pressing temperature is 140°C, and the tensile strength is 124.44±1.61 MPa.

[0115] Embodiment 19

[0116] Same as Example 1, except that the hot pressing temperature is 160°C, and the tensile strength is 103.73±3.56MPa.

[0117] Embodiment 20

[0118] Same as Example 1, except that the film forming process is vacuum filtration, and the tensile strength is 124.44±1.61 MPa.

[0119] Embodiment 21

[0120] Same as Example 1, except that the concentration of the alkaline solution is 1.3 mol / L, and the tensile strength is 82.64±1.89 MPa.

[0121] Embodiment 22

[0122] Same as Example 1, except that the concentration of the alkaline solution is 1.1 mol / L, and the tensile strength is 119.87±2.76 MPa.

[0123] Embodiment 23

[0124] Same as Example 1, except that the concentration of the alkaline solution is 0.9 mol / L, and the tensile strength is 120.95±4.22 MPa.

[0125] Comparative Example 1

[0126] The same as Example 1, except that no alkaline solution was added during ball milling, but water and bamboo powder were added to the ball mill according to the proportion and ball milled, and no acid was added to adjust the pH value. The tensile strength was 32.86±1.38MPa.

[0127] Comparative Example 2

[0128] The same as Example 1, except that an alkaline solution was added during ball milling to assist the ball milling, and no acid solution was added to adjust the pH value. The tensile strength was 90.93±1.61 MPa; based on mass, the utilization rate of bamboo powder raw materials was less than 80%.

[0129] The technical features in the claims and / or the specification of the present invention may be combined, and the combination is not limited to the combination obtained by reference in the claims. The technical solution obtained by combining the technical features in the claims and / or the specification is also within the protection scope of the present invention.

[0130] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a bamboo-based thermosetting bioplastic, characterized in that: It includes the following steps: S1 ball-milling bamboo powder and alkaline solution under mixing conditions; S2 dilutes the ball mill slurry, adjusts its pH value to ≤7 with an acid solution, and centrifuges; S3 adjusts the solid content of the centrifugal slurry, forms a film, and performs hot pressing to obtain a fully bamboo-based thermosetting bioplastic.

2. The preparation method according to claim 1, characterized in that: The alkaline solution is selected from at least one of KOH, NaOH, LiOH, Ba(OH)2, ammonia and ethanolamine.

3. The preparation method according to claim 1, characterized in that: The concentration of the alkaline solution is 0.1-3 mol / L.

4. The preparation method according to claim 1, characterized in that: The particle size of the bamboo powder is 10 to 100 meshes.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the bamboo powder to the alkaline solution is 1:8-20.

6. The preparation method according to claim 1, characterized in that: The acid solution is selected from at least one of hydrochloric acid, sulfuric acid, formic acid and acetic acid.

7. The preparation method according to claim 1, characterized in that: The process parameters of the hot pressing are as follows: the hot pressing temperature is from room temperature to 180° C., the hot pressing pressure is 5 to 20 MPa, and the hot pressing time is 10 to 120 min.

8. A bamboo-based thermosetting bioplastic, characterized in that: Calculated by mass percentage, it includes: lignin ≥ 30%, cellulose ≥ 47%, and hemicellulose ≤ 15%.

9. The all-bamboo-based thermosetting bioplastic according to claim 8, characterized in that: Its tensile strength is ≥50MPa and it is solvent resistant.

10. Use of the all-bamboo-based thermosetting bioplastic according to claim 8 or 9 in the fields of bamboo material processing and utilization and plastic manufacturing.

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