Method for one-step in-situ preparation of reprocessable thermosetting straw plastic
The preparation of reprocessable thermoset straw plastics through eutectic solvents and mechanochemical methods solves the problem of difficult separation and high-value utilization of straws, and realizes efficient conversion of straws into reprocessable plastics, improves plastic performance and reduces environmental pollution.
Patent Information
- Application Number
- CN202510413571.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-03
- Publication Date
- 2025-07-04
AI Technical Summary
The prior art is difficult to effectively separate and use the three components of cellulose, lignin and hemicellulose in crop straws at high value, making it difficult to directly thermoform the straw, and the production of petroleum-based plastics faces resource shortage and environmental pollution problems.
Reprocessable thermosetting straw plastics are prepared by using eutectic solvents (DES) to react with straw and terephthaldehyde in a dense mixer, and the hydrogen bond network of straw is destroyed by mechanical force, and acetal-like dynamic covalent bond crosslinking network is formed.
The efficient and environmentally friendly transformation of straw into reprocessable thermosetting plastics is achieved, which improves the flexibility, solvent resistance and mechanical properties of the plastics, and reduces dependence on petroleum resources.
Smart Images
Figure CN120248643A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of the preparation of bio-based thermosetting plastics, and relates to a method for in-situ preparation of reprocessable thermosetting straw plastics in one step. Background Art
[0002] Many common plastic varieties, such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), etc., are mostly petroleum-based plastics. With the gradual depletion of petroleum resources, the production of petroleum-based plastics will face the problem of tight raw material supply, and at the same time, its production is also greatly affected by the fluctuation of petroleum prices. These plastics are very difficult to degrade in the natural environment and will exist in the environment such as soil and water bodies for a long time, causing soil compaction, affecting the growth of crops, and may also be eaten by animals, threatening the life and health of animals. In order to reduce plastic pollution, one of the most promising solutions is to develop new processable plastics using renewable, degradable and cheap raw materials.
[0003] There are a wide variety of crop straws in large quantities, which is a very rich and renewable biomass resource. The main crop straws include wheat straw, rice straw, corn straw, sorghum straw, etc. China produced more than 800 million tons of crop straws in 2023. In the past few decades, the utilization ways of straws have mainly been for fertilization, animal feeding and fuel, and even many straws have been directly burned in the farmland, causing relatively serious environmental pollution problems. In recent years, with the improvement of environmental protection awareness and the introduction of relevant policies, straw burning has been strictly restricted. Coupled with the development of large-scale breeding and the improvement of the specialization and refinement degree of feeds, the share of straws in the feed market has gradually declined. These factors have made straw treatment a burden on farmers. With the increasingly severe ecological problems and the continuous attention of people to sustainable biomass materials, an effective method for converting waste crop straws into clean and value-added products has become a research issue of great interest to the academic and industrial circles. From a chemical structure perspective, the internal components of straws are relatively complex, containing not only a large amount of cellulose, but also hemicellulose and lignin. [1] Achieving the effective separation of lignin, hemicellulose and cellulose in straws, that is, deconstructing the plant cell wall to make full use of the three major components, is a hot strategy for enhancing the value of straw resources. [2] Zhang et al. [3] A novel solvent containing ionic liquid and polyol was used to achieve the selective fractionation of lignin in corn straws, and the extraction rate of lignin could reach up to 88.2%. The lignin extracted from corn straws has excellent room temperature phosphorescence performance, antioxidant performance and long-term light stability due to the presence of a large amount of syringyl and phenolic hydroxyl groups. Flexible films, fibers, aerogels and coatings with a room temperature phosphorescence lifetime of 0.654 s were prepared after combining the extracted lignin with polyvinyl alcohol.
[0004] Multiple complex components in straw are tightly connected by hydrogen bonds and chemical bonds to form a complex and intertwined structure. Among them, cellulose molecules are intertwined into bundles and dispersed in hemicellulose and lignin components, forming a structure similar to "reinforced concrete". This structure plays a role in support and protection during plant growth, but at the same time brings great challenges to the effective separation of the three components. Although partial separation of lignin, hemicellulose, and cellulose components can be achieved through chemical treatment methods such as acids, alkalis, and organic solvents, usually only one or two of these components can be utilized, and it is difficult to achieve the high-value utilization of all three components simultaneously. [4] During the separation process of the three components of straw, it is easy to cause lignin condensation and hemicellulose structure damage. There are also problems in the separation process such as long reaction processes, easy environmental pollution, and high separation costs. These problems greatly limit the high-value conversion of straw resources. Therefore, it will be very attractive to directly utilize straw in a high-value manner through a strategy of not separating cellulose, lignin, and hemicellulose, especially in the field of biomass plastics. However, due to the rich hydrogen bonds and crystalline structures in the internal structure of typical crop straws, their theoretical melting temperature is much higher than the thermal decomposition temperature, that is, the straw undergoes thermal degradation before melting during the heating and processing process, making it difficult for straw to be directly thermoformed. Therefore, there is an urgent need to develop new technologies to prepare straw plastics through simple, efficient, and environmentally friendly means, which can not only achieve the high-value utilization of straw but also alleviate the dependence of the plastics industry on petroleum resources. Summary of the Invention
[0005] In order to solve technical problems such as the difficulty of separating the three components of crop straw and its high-value utilization, the present invention first proposes a method for in-situ preparation of reprocessable thermosetting straw plastics from straw in one step. First, a deep eutectic solvent (DES) is prepared by mixing a hydrogen bond donor (such as amides, carboxylic acids, and polyols and other compounds) and a hydrogen bond acceptor (such as quaternary ammonium salts) in a certain proportion. Subsequently, DES, straw, and terephthalaldehyde are used as raw materials and added to a mixer to react to prepare straw plastics. The present invention mainly includes three design concepts, namely: 1) DES deconstructs and activates straw, breaks the chemical bonds between lignin and cellulose, and weakens the original intermolecular and intramolecular hydrogen bond networks of straw; 2) The mixer provides strong mechanical force for the materials through the mutual extrusion of two rotors, breaks the regular structure of straw, and promotes the reaction; 3) Terephthalaldehyde is used as a cross-linking agent for straw, and a cross-linking network with acetal-based dynamic covalent bonds as cross-linking sites is formed through the condensation reaction of aldehyde groups and hydroxyl groups, which not only ensures the reprocessability of straw plastics but also improves the solvent resistance and mechanical properties of the plastics.
[0006] The technical solution of the present invention:
[0007] A method for in-situ preparation of reprocessable thermosetting straw plastics in one step, the steps are as follows:
[0008] Step 1: Mix the hydrogen bond donor and the hydrogen bond acceptor, and heat and stir until it becomes a clear solution, thus preparing the deep eutectic solvent DES.
[0009] The hydrogen bond donor is one or more mixtures of polyols, carboxylic acids, amides, etc.; the polyols are ethylene glycol, glycerol, etc., the carboxylic acids are citric acid, lactic acid, oxalic acid, etc., and the amides are such as urea, etc.
[0010] The hydrogen bond acceptor is one or more mixtures of quaternary ammonium salts, tertiary amines, metal halides, phosphorus-containing compounds, etc.; the quaternary ammonium salts are choline chloride (ChCl), etc.; the tertiary amines are triethylamine (TEA), etc.; the metal halides are zinc chloride (ZnCl2), iron(III) chloride (FeCl3), etc.; the phosphorus-containing compounds are trimethyl phosphate (TMP), etc.
[0011] The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:1 to 6:1.
[0012] The heating temperature range is: 40°C to 100°C.
[0013] Step 2: Add DES, straw, and terephthalaldehyde to a mixer, take it out after the reaction, and hot press it using a flat hot press to obtain straw plastic.
[0014] The straw includes: straw of wheat, rice, corn, potatoes, rapeseed, cotton, sugarcane, and other crops.
[0015] The mass ratio range of the DES to the straw is 0.75 - 2.
[0016] The mass ratio range of the terephthalaldehyde to the straw is 0.25 - 0.4.
[0017] The reaction temperature range of the mixer is 80°C - 120°C.
[0018] The reaction time of the mixer is 0.5 h - 3 h.
[0019] The hot pressing temperature range of the hot press is 80°C - 120°C.
[0020] The hot pressing time range of the hot press is 0.5 h - 2 h.
[0021] Advantages of the present invention:
[0022] The preparation strategy of the present invention has many advantages, such as cheap and easily available raw materials, short reaction process, no need for pretreatment of raw materials, no need for separation and purification of products, no need for catalysts, no need for organic solvents, etc., which highly meets the current requirements for green and efficient preparation of sustainable new materials. The present invention uses a mixer as the reaction vessel, and applies shear and extrusion forces to the materials by the relative rotation of two rotors, which not only minimizes the use of organic solvents to the greatest extent, but also can promote the progress of chemical reactions through the additionally applied mechanical energy; the present invention uses DES to assist in the one-step plasticization of straw. DES can not only break the hydrogen bonds and some chemical bonds of straw to play a role in deconstruction and activation, but also can be used as a plasticizer for straw plastics to further improve the flexibility, plasticity and processing performance of plastics; a small amount of terephthalaldehyde is added during the preparation of straw plastics in the present invention, which is beneficial to the formation of a cross-linked network based on acetal-based dynamic covalent bonds, and improves the mechanical properties, thermal stability and solvent resistance of straw plastics.
[0023] Compared with the prior art, the beneficial effects of the present invention are reflected in:
[0024] 1. The raw material crop straw used in the present invention has a wide source, a large output, a low price or even free, and is biodegradable. The reaction process of the present invention is short, and there is no need to pretreat the straw, which has higher economic value.
[0025] 2. The present invention uses a mixer as the reaction vessel, which not only applies mechanical forces to promote the reaction, but also can destroy the regular structure inside the straw through mechanical extrusion, weaken the intermolecular forces, and improve the flexibility and plasticity of the straw.
[0026] 3. The present invention uses DES with low vapor pressure, non-flammable, chemically adjustable and wide dissolution ability, avoiding the use of traditional toxic organic solvents, and is more green and environmentally friendly.
[0027] 4. The straw thermosetting plastic prepared by the present invention replaces part of the hydrogen bond network with acetal-based dynamic covalent bonds. The dynamic covalent bond cross-linking strategy enables the material to have excellent thermal and mechanical properties at room temperature while taking into account the reprocessability under high temperature conditions. Description of the Drawings
[0028] Figure 1 is the scanning electron microscope image of the straw plastic in Example 1;
[0029] Figure 2 is the infrared spectrum of the straw plastic in Example 1;
[0030] Figure 3 is the XRD spectrum of the straw plastic in Example 1;
[0031] Figure 4 is the DMA curve of the straw plastic in Example 1;
[0032] Figure 5 It is the tensile curve of the straw plastic in Example 1. Specific embodiments
[0033] The following further illustrates the specific embodiments of the present invention in conjunction with the accompanying drawings and technical solutions.
[0034] Example 1:
[0035] Oxalic acid (hydrogen bond donor) and choline chloride (hydrogen bond acceptor) were mixed in a molar ratio of 1:1, and then continuously stirred under a constant temperature condition of 50 °C until the mixture turned into a transparent and clear solution. When the solution was naturally cooled to room temperature, it could still maintain a clear and transparent state, and at this time, the oxalic acid-choline chloride DES was successfully prepared.
[0036] Corn straw, DES, and terephthalaldehyde were added to a mixer in a mass ratio of 1:1:0.25 and reacted at 110 °C for 1 hour. After the reaction, the product was taken out. Since the product taken out from the mixer was in the form of irregular lumps, it was crushed and then hot-pressed in a flat vulcanizer at 110 °C for 30 minutes. After the hot pressing was completed and cooled to room temperature, straw plastic with a thickness of about 1 mm could be obtained.
[0037] Explanation in conjunction with the accompanying drawings: Straw plastic was prepared in situ in one step by using mechanochemistry, DES, and dynamic crosslinking strategies. Among them, mechanochemistry played the role of mixing materials and promoting reactions, DES played the role of deconstructing and activating straw, and terephthalaldehyde crosslinked straw to prepare a crosslinked network based on acetal dynamic covalent bonds, which improved mechanical properties, solvent resistance, and thermal stability without losing the reprocessing performance. Figure 1 It is the SEM image of the straw plastic, and the surface of the plastic is smooth and dense. As Figure 2 shown, the FT-IR spectrum of corn straw shows the characteristic absorption signals of cellulose and lignin structures. Among them, lignin was confirmed by the absorption signal at 1730 cm -1 This signal corresponds to the C=O vibration of lignin. The C=O stretching vibration signal in the aldehyde group of terephthalaldehyde is located at 1700 cm -1 , which may be due to the formation of a conjugated system between the aldehyde group and the benzene ring, causing the C=O vibration frequency to shift towards the low wavenumber direction. The FT-IR spectrum of the straw plastic basically retains the characteristic absorption signals of the original straw, indicating that the structures of the components in the straw are mostly retained during the reaction, and no obvious aldehyde group signals from terephthalaldehyde were detected in the straw plastic, which may be due to the condensation reaction between the aldehyde group and the hydroxyl group of the straw to form a crosslinked network, consuming the aldehyde group. From the XRD results ([ Figure 3), the XRD diffraction peak intensity of straw plastic is significantly lower than that of its raw material straw, which is attributed to two factors: 1) the chloride ions of DES form competitive hydrogen bonds with the hydroxyl groups of straw, weakening the hydrogen bonds widely present between and within the original molecules of straw; 2) the extrusion and shearing action of mechanochemistry on the straw destroys some crystalline areas of the straw. The destruction of hydrogen bonds and crystalline areas of straw promotes the movement of molecular chain segments, enhances the reactivity of functional groups, and helps promote the crosslinking and plasticization of straw. Figure 4 The storage modulus and Tan Delta curves of straw plastics with temperature are shown. The Tan Delta curve of straw plastics has only one peak, indicating that DES and straw have good compatibility and no phase separation occurs during mechanochemical reactions or hot pressing. The temperature corresponding to the peak of the Tan Delta curve is Tg, and the Tg of straw plastics is 57.7°C. When the flat straw plastic at room temperature is heated to Tg, it can be fixed into a curved shape by applying external force, which proves the excellent plasticity of straw plastics. Figure 5 The tensile stress-strain curve of straw plastic is shown. From the curve, it can be seen that the maximum tensile strength of straw plastic is 2658kPa and the elongation at break is 33.2%. Straw plastic contains acetal bonds that can undergo dynamic exchange reactions. This property enables it to be repeatedly recycled and reprocessed like traditional thermoplastics. Straw plastic particles can be restored to a dense film after hot pressing at 80℃ for 15 minutes, indicating that straw plastic has excellent reprocessability.
[0038] Embodiment 2:
[0039] Glycerol (hydrogen bond donor) and choline chloride (hydrogen bond acceptor) are mixed in a molar ratio of 6:1, and then stirred continuously at a constant temperature of 100°C until the mixture turns into a transparent solution. When the solution is naturally cooled to room temperature, it can still remain clear and transparent, and glycerol-choline chloride DES is successfully prepared.
[0040] Wheat straw, DES and terephthalaldehyde were added to an internal mixer in a mass ratio of 1:2:0.4, and reacted at 120°C for 0.5 hours. The product was taken out after the reaction. Since the product taken out from the internal mixer was in irregular blocks, it was crushed and then placed in a flat vulcanizer at 120°C for hot pressing for 60 minutes. After the hot pressing was completed, it was cooled to room temperature, and a straw plastic with a thickness of about 1 mm was obtained.
[0041] The glass transition temperature of straw plastic is 76.4℃, the maximum tensile strength is 4598kPa, and the elongation at break is 23.8%. The straw plastic particles can be restored to a dense film after being hot-pressed at 100℃ for 30 minutes, indicating that straw plastic has excellent reprocessability.
[0042] Example 3:
[0043] Citric acid (hydrogen bond donor) and choline chloride (hydrogen bond acceptor) were mixed at a molar ratio of 3:1, and then continuously stirred under constant temperature conditions of 40 °C until the mixture turned into a transparent and clear solution. When the solution was naturally cooled to room temperature, it still remained clear and transparent, and at this time, the citric acid-choline chloride DES was successfully prepared.
[0044] Rice straw, DES, and terephthalaldehyde were added to a mixer at a mass ratio of 1:0.75:0.3 and reacted at 80 °C for 3 hours. After the reaction, the product was taken out. Since the product taken out from the mixer was in the form of irregular lumps, it was crushed and then hot-pressed in a flat vulcanizer at 80 °C for 2 h. After the hot pressing was completed and cooled to room temperature, straw plastic with a thickness of about 1 mm could be obtained at this time.
[0045] The glass transition temperature of the straw plastic was 49.8 °C, the maximum tensile strength was 7652 kPa, and the elongation at break was 35.9%. The straw plastic particles could be restored to a dense film after hot pressing at 80 °C for 15 minutes, indicating that the straw plastic had excellent reprocessability.
[0046] From the above examples, it can be seen that using the method of the present invention, straw plastic can be prepared by a green, environmentally friendly and efficient method, providing a new strategy for solving the problem of white pollution and the high-value utilization of straw.
Claims
1. A method for one-step in-situ preparation of reprocessable thermosetting straw plastics, characterized in that, The steps are as follows: Step 1: Mix the hydrogen bond donor and the hydrogen bond acceptor, and heat and stir until it becomes a clear solution, that is, a deep eutectic solvent DES is prepared; The hydrogen bond donor is one or more mixtures of polyols, carboxylic acids, amides; The hydrogen bond acceptor is one or more mixtures of quaternary ammonium salts, tertiary amines, metal halides, phosphorus-containing compounds; The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:1 to 6:1; Step 2: Add DES, straw and terephthalaldehyde to a mixer, take it out after the reaction, and hot press it with a flat hot press to obtain straw plastic; The mass ratio range of the DES to the straw is 0.75 - 2; The mass ratio range of the terephthalaldehyde to the straw is 0.25 - 0.
4.
2. The method for one-step in-situ preparation of reprocessable thermosetting straw plastics according to claim 1, characterized in that The polyols are one or two mixtures of ethylene glycol and glycerol, the carboxylic acids are one or more mixtures of citric acid, lactic acid, oxalic acid, and the amides are such as urea.
3. The method for one-step in-situ preparation of reprocessable thermosetting straw plastics according to claim 1, characterized in that, The quaternary ammonium salts are choline chloride; the tertiary amines are triethylamine; the metal halides are one or two mixtures of zinc chloride and iron chloride; the phosphorus-containing compounds are trimethyl phosphate.
4. The method for one-step in-situ preparation of reprocessable thermosetting straw plastics according to claim 1, characterized in that, The heating temperature range in Step 1 is: 40°C to 100°C.
5. The method for one-step in-situ preparation of reprocessable thermosetting straw plastics according to claim 1, characterized in that, The straw is one or more mixtures of wheat, rice, corn, potatoes, rapeseed, cotton, sugarcane and other crop straws.
6. The method for one-step in-situ preparation of reprocessable thermosetting straw plastics according to claim 1, characterized in that, In Step 2, the reaction temperature range of the mixer is 80°C - 120°C, and the reaction time of the mixer is 0.5 h - 3 h.
7. The method for one-step in-situ preparation of reprocessable thermosetting straw plastics according to claim 1, characterized in that In Step 2, the hot pressing temperature range of the hot press is 80°C - 120°C, and the hot pressing time range of the hot press is 0.5 h - 2 h.