A full-bio-based light-weight high-strength flame-retardant green plate

Abstract

This invention relates to the field of board technology, specifically to a fully bio-based lightweight, high-strength, flame-retardant green board. The board is prepared from polylactic acid resin, crop straw powder, acicular wollastonite, phytate triazine oligolactic acid grafted lignin, sodium bicarbonate, and anhydrous citric acid. The phytate triazine oligolactic acid grafted lignin is a modified lignin obtained by sequentially phosphorylating basic lignin, constructing a phytate composite structure, triazinizing, and grafting oligolactic acid segments. By introducing phosphorus-, nitrogen-, and calcium-containing phytate structures and oligolactic acid compatible segments onto the lignin skeleton, and preferentially distributing them at the straw powder / acicular wollastonite interface, this invention improves the interfacial bonding, wet heat strength retention, and flame-retardant properties of the composite material while reducing the board density. It is suitable for green building, decorative boards, and lightweight flame-retardant composite materials.

Description

Technical Field

[0001] This invention relates to the field of sheet technology, and in particular to a fully bio-based lightweight, high-strength, flame-retardant green sheet. Background Technology

[0002] Polylactic acid (PLA), a fully biodegradable aliphatic polyester, has become an important green material to replace petrochemical-based plastics due to its renewable source and excellent mechanical properties, and is widely used in packaging, building materials, and other fields. To reduce costs and improve rigidity, industrial manufacturers often add biomass or inorganic fillers such as wheat straw powder, lignin, and wollastonite to PLA, while also improving its properties by incorporating phytates, phosphorus / nitrogen-containing flame retardants, and petrochemical-based compatibilizers.

[0003] However, existing composite boards mostly adopt a simple blending approach of "filler + flame retardant + compatibilizer". The components are only bound by physical forces. Polylactic acid has poor interfacial compatibility with high polarity straw powder and inorganic fillers. Under humid and hot conditions, the strength drops sharply due to interfacial debonding. Flame retardants are mostly physically dispersed, which are easy to migrate and precipitate, resulting in low flame retardant efficiency. Moreover, the use of petrochemical-based compatibilizers violates the green original intention of all-bio-based materials.

[0004] If a foaming system is further introduced to achieve lightweighting, the presence of a porous structure will further weaken the interfacial bonding, leading to problems such as "low density equals low strength" and "loss of balance between flame retardancy and mechanical properties" in the boards. Existing products cannot simultaneously meet the multiple requirements of lightweight, high strength, high-efficiency flame retardancy, and resistance to damp heat, thus limiting their application in the field of high-end green buildings. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a fully bio-based lightweight, high-strength, flame-retardant green board, so that the polylactic acid / straw composite board can still have high strength, moisture and heat resistance and high flame retardant properties after foaming and lightweighting without the need for petrochemical compatibilizers.

[0006] To achieve the above objectives, this invention provides a fully bio-based lightweight, high-strength, flame-retardant, and green board material, wherein the board material is a polylactic acid-based foamed composite board material; based on the mass parts of the raw materials used to prepare the board material, the board material is prepared from the following raw materials: 560-740 parts polylactic acid resin, 360-480 parts crop straw powder, 80-160 parts acicular wollastonite, 70-130 parts phytate triazine oligolactic acid grafted lignin, 16-30 parts sodium bicarbonate, and 12-24 parts anhydrous citric acid; The phosphate-phytate triazine oligolactic acid grafted lignin is a modified lignin obtained by sequentially phosphorylating, constructing phytate microdomains, triazinizing and grafting oligolactic acid onto alkaline lignin, and the number-average degree of polymerization of the oligolactic acid is 5-20. The wheat straw powder, the needle-shaped wollastonite, and the phosphate phytate triazine oligolactic acid grafted lignin are pre-coated at the interface to form an interface pre-treated powder, which is then mixed with the polylactic acid resin, the sodium bicarbonate, and the anhydrous citric acid and melt-molded into the board.

[0007] Preferably, the thickness of the plate is 3-10mm.

[0008] Preferably, the crop straw powder is wheat straw powder that has been crushed and passed through an 80-mesh sieve; the acicular wollastonite has an aspect ratio of 10-20 and a moisture content of ≤1%.

[0009] Preferably, the phosphorylation is performed by mixing 200 parts by weight of dry alkaline lignin, 55-85 parts by weight of ammonium dihydrogen phosphate, and 75-110 parts by weight of urea, and reacting at 138-152°C for 100-150 min under nitrogen protection to obtain phosphorylated lignin; the phytate microdomain construction is performed by sequentially treating 150 parts by weight of phosphorylated lignin, 18-32 parts by weight of 50% phytic acid solution, 5-10 parts by weight of calcium lactate, 2-5 parts by weight of nano-hydroxyapatite, and 4-8 parts by weight of ammonium bicarbonate to obtain phosphorylated lignin containing calcium-crosslinked phytate microcores and an ammonium-modified phytate outer layer; Triazinization is performed by reacting 120 parts by weight of phosphorylated lignin containing calcium-crosslinked phytate microcores and ammonium-modified phytate outer layers, 22-34 parts by weight of melamine, 14-23 parts by weight of paraformaldehyde, and 7-13 parts by weight of sodium carbonate at 82-90℃ for 4-6 hours to obtain phosphate-modified phytate triazinized lignin; the oligolactic acid grafting is performed by adding 45-75 parts by weight of L-(-)-lactide and 0.3-0.7 parts by weight of stannous octoate to every 100 parts by weight of phosphate-modified phytate triazinized lignin, and reacting at 120-130℃ for 3-5 hours under nitrogen protection to obtain phosphate-modified phytate triazin oligolactic acid grafted lignin.

[0010] Preferably, the particle size of the nano-hydroxyapatite is <100nm.

[0011] Preferably, by mass parts, the interface pre-coating treatment is as follows: 360-480 parts of wheat straw powder, 80-160 parts of needle-shaped wollastonite and 70-130 parts of phytate triazine oligolactic acid grafted lignin are added to a high-speed mixer and mixed at 800 r / min for 20 min at 90°C to obtain the interface pre-treated powder.

[0012] Preferably, by mass, 510-770 parts of interface pretreated powder, 560-740 parts of polylactic acid resin, 16-30 parts of sodium bicarbonate and 12-24 parts of anhydrous citric acid are mixed at 80°C and 500 r / min for 10 min to obtain the extrusion mixture.

[0013] Preferably, the melt molding process includes adding the extrusion mixture to a co-rotating twin-screw extruder, extruding it through a flat die, then feeding it into a three-roll calender to achieve a fixed thickness, followed by cooling and cutting by cooling rollers; the temperatures of zones one to seven of the co-rotating twin-screw extruder are 135°C, 150°C, 160°C, 170°C, 170°C, 165°C, and 155°C respectively, the screw speed is 80 r / min, the material residence time in the extruder is 3 min, the flat die temperature is 150°C, and the die gap is 5 mm; the temperature of the three-roll calender is 60°C, and the temperature of the cooling rollers is 25°C.

[0014] Furthermore, the present invention also provides a method for preparing a fully bio-based lightweight, high-strength, flame-retardant, and green board, characterized by comprising the following steps: S1. Phosphorylation of basic lignin yields phosphorylated lignin; S2. Phytate microdomains are constructed on the phosphorylated lignin to obtain phosphorylated lignin containing calcium-crosslinked phytate micronuclei and an ammonium-modified phytate outer layer. S3. Triazine the phosphorylated lignin containing calcium-crosslinked phytate micronucleus and ammonium-modified phytate outer layer to obtain phosphorylated phytate triazine lignin. S4. Graft the phosphate-phytate triazine lignin onto oligolactic acid to obtain phosphate-phytate triazine oligolactic acid grafted lignin. S5. The wheat straw powder, needle-shaped wollastonite and the phosphate phytate triazine oligolactic acid grafted lignin are subjected to interface pre-coating treatment to obtain interface pre-treated powder. S6. The interface pretreated powder is mixed with polylactic acid resin, sodium bicarbonate and anhydrous citric acid to obtain a mixture for extrusion. S7. The extrusion mixture is melt-extruded, formed by a flat die, calendered to a certain thickness by three-roll calendering, cooled and cut to obtain the all-bio-based lightweight high-strength flame-retardant green board.

[0015] In this invention, "interface pre-coating treatment" refers to the process of pre-contaminating crop straw powder, acicular wollastonite, and phytate triazine oligolactic acid grafted lignin under heating and high-speed shearing conditions before adding polylactic acid resin. This allows the modified lignin to be at least partially distributed on the surface of the straw powder and acicular wollastonite through hydrogen bonding, polar interactions, Ca / P coordination, and the compatibility of oligolactic acid segments, forming an interface pre-treated powder. This interface pre-coating treatment differs from the one-time ordinary mixing of components with polylactic acid resin; its function is to preferentially locate the phosphorus-, nitrogen-, and calcium-containing flame-retardant structures at the interface between the hydrophilic straw powder and the inorganic acicular filler, thereby improving interfacial bonding and increasing the utilization efficiency of the flame-retardant components during subsequent melt extrusion and foaming processes.

[0016] The beneficial effects of this invention are: (1) The phosphate phytate triazine oligolactic acid grafted lignin prepared by the present invention fixes the phosphorus source, phytate calcium phosphorus microregion, nitrogen-containing triazine structure and oligolactic acid compatible chain segment on the same lignin skeleton, and can achieve the interfacial polarity transition and wet heat resistance of polylactic acid, wheat straw powder and needle wollastonite without petrochemical compatibilizer.

[0017] (2) By pre-coating the interface of crop straw powder, needle-shaped wollastonite and modified lignin, the spatial distribution of functional components can be precisely controlled, and the efficiency of interface interaction can be greatly improved.

[0018] (3) Combining the sodium bicarbonate / anhydrous citric acid foaming system with the char-forming barrier effect of modified lignin, the board achieves lightweight while ensuring flame retardant performance, solving the industry problem of "lightweight materials are necessarily weak and flame retardant materials are necessarily heavy". Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0020] Raw material sources and types: The polylactic acid resin used is REVODE110 polylactic acid resin from Zhejiang Hisun Biomaterials Co., Ltd.; the alkaline lignin used is L330880 lignin (alkaline) from Shanghai Aladdin Biochemical Technology Co., Ltd.; the wheat straw powder used is Solarbio straw powder (fermentation specific) from Beijing Solarbio Technology Co., Ltd., product number FA0350, which is crushed and sieved through an 80-mesh sieve before use; the needle-shaped wollastonite used is F-series wollastonite needle powder from Xinyu Southern Wollastonite Co., Ltd., with a length of... The particle size distribution is 10-20, and the water content is ≤1%. The phytic acid solution used is P108518 phytic acid solution from Shanghai Aladdin Biochemical Technology Co., Ltd., with a mass fraction of 50%. The nano-hydroxyapatite used is H106378 nano-hydroxyapatite from Shanghai Aladdin Biochemical Technology Co., Ltd., with a particle size <100nm. The paraformaldehyde used is C104190 paraformaldehyde from Shanghai Aladdin Biochemical Technology Co., Ltd., and the L-(-)-lactide used is S161079 L-(-)-lactide from Shanghai Aladdin Biochemical Technology Co., Ltd. Example

[0021] Step 1: Weigh 300g of alkaline lignin and place it in a vacuum drying oven. Dry it for 8 hours at 80℃ and a vacuum degree ≤-90kPa. Weigh 600g of wheat straw powder, pulverize it, pass it through an 80-mesh sieve, and dry it at 105℃ for 6 hours. Weigh 200g of needle-shaped wollastonite and dry it at 110℃ for 4 hours. Weigh 900g of polylactic acid resin and dry it for 8 hours at 60℃ and a vacuum degree ≤-90kPa. Step 2: Weigh 200g of the dried alkaline lignin obtained in Step 1, 70g of ammonium dihydrogen phosphate, and 90g of urea and add them to a high-speed mixer. Mix at 600r / min for 15min at 25℃ to obtain a solid mixture. Place the solid mixture in a reaction vessel with a nitrogen inlet, purge with nitrogen at 100mL / min for 30min, then raise the temperature to 145℃ and react at 145℃ for 120min. After the reaction is complete, cool to 50℃, add 2000g of deionized water, stir at 300r / min for 30min at 50℃, filter, wash the filter cake three times with 1000g of deionized water, and then wash twice with 600g of anhydrous ethanol. Dry the washed filter cake at 70℃ and a vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin. Step 3: Weigh 150g of phosphorylated lignin obtained in Step 2, 600g of deionized water, and 600g of anhydrous ethanol and add them to the reaction vessel. Disperse at 400r / min for 30min at 60℃. Add 24g of 50% phytic acid solution and continue stirring at 60℃ for 20min. Then add 7g of calcium lactate and stir at 60℃ for 30min. Add 3g of nano-hydroxyapatite and stir at 60℃ for 60min. Cool the system to 35℃. Dissolve 6g of ammonium bicarbonate in 100g of deionized water and add it to the reaction vessel. Stir at 300r / min for 30min at 35℃. Filter the mixture. Wash the filter cake twice with 800g of deionized water and once with 500g of anhydrous ethanol. Dry the mixture at 70℃ and vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin containing calcium cross-linked phytate microcores and ammonium-modified phytate outer layer. Step 4: Weigh 120g of phosphorylated lignin containing calcium-crosslinked phytate microcores and ammonium-modified phytate outer layers obtained in Step 3, 900g of dimethyl sulfoxide, and 300g of deionized water and add them to the reaction vessel. Disperse the lignin at 70℃ and 400r / min for 40min. Add 28g of melamine, 18g of paraformaldehyde, and 10g of sodium carbonate to the reaction vessel. Raise the reaction temperature to 85℃ and react at 300r / min for 5h. After the reaction is complete, cool to 40℃, add 1800g of deionized water to precipitate the solid, filter, and wash the filter cake successively with 1000g of deionized water, 600g of anhydrous ethanol, and 600g of deionized water. Dry the filter cake at 70℃ and vacuum degree ≤-90kPa for 12h to obtain phosphate-modified phytate triazine lignin. Step 5: Add 100g of phytate triazine lignin obtained in Step 4, 60g of L-(-)-lactide, and 500mg of stannous octoate to a dry reaction vessel. Purge with nitrogen at 100mL / min for 30min, then raise the temperature to 125℃ and react at 200r / min for 4h. After the reaction is complete, cool to 70℃, add 800g of ethyl acetate, and stir at 70℃ for 30min to dissolve the ungrafted oligomers and free L-(-)-lactide. Filter, and wash the filter cake twice with 800g of anhydrous ethanol. Dry the filter cake at 60℃ and under vacuum ≤-90kPa for 12h to obtain phytate triazine oligolactic acid grafted lignin. The number-average degree of polymerization of the obtained oligolactic acid short chain is 12. Step Six: Weigh 420g of the dried wheat straw powder obtained in Step One, 120g of the dried needle-shaped wollastonite obtained in Step One, and 100g of the phytate triazine oligolactic acid grafted lignin obtained in Step Five and add them to a high-speed mixer. Mix at 800r / min for 20min at 90℃ to obtain the interface pretreated powder. Then add 650g of the dried polylactic acid resin obtained in Step One, 24g of sodium bicarbonate, and 18g of anhydrous citric acid to the high-speed mixer and mix at 500r / min for 10min at 80℃ to obtain the extrusion mixture. Step 7: Add the extrusion mixture obtained in Step 6 to a co-rotating twin-screw extruder. Set the temperatures of zones 1 to 7 of the extruder to 135℃, 150℃, 160℃, 170℃, 170℃, 165℃ and 155℃ respectively. Set the screw speed to 80 r / min. Control the material residence time in the extruder to 3 min. Set the die temperature to 150℃ and the die gap to 5 mm. After the melt is extruded through the die, it enters a 60℃ three-roll calender to determine the thickness, and then is cooled by a 25℃ cooling roller. Cut the calender to obtain a 5 mm thick all-bio-based lightweight, high-strength, flame-retardant green sheet. Example

[0022] Step 1: Weigh 300g of alkaline lignin and place it in a vacuum drying oven. Dry it for 8 hours at 80℃ and a vacuum degree ≤-90kPa. Weigh 600g of wheat straw powder, pulverize it, pass it through an 80-mesh sieve, and dry it at 105℃ for 6 hours. Weigh 200g of needle-shaped wollastonite and dry it at 110℃ for 4 hours. Weigh 900g of polylactic acid resin and dry it for 8 hours at 60℃ and a vacuum degree ≤-90kPa. Step 2: Weigh 200g of the dried alkaline lignin obtained in Step 1, 55g of ammonium dihydrogen phosphate, and 75g of urea and add them to a high-speed mixer. Mix at 600r / min for 15min at 25℃ to obtain a solid mixture. Place the solid mixture in a reaction vessel with a nitrogen inlet, purge with nitrogen at 100mL / min for 30min, then raise the temperature to 138℃ and react at 138℃ for 100min. After the reaction, cool to 50℃, add 2000g of deionized water, stir at 300r / min for 30min at 50℃, filter, wash the filter cake three times with 1000g of deionized water, and then wash twice with 600g of anhydrous ethanol. Dry the washed filter cake at 70℃ and a vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin. Step 3: Weigh 150g of phosphorylated lignin obtained in Step 2, 600g of deionized water, and 600g of anhydrous ethanol and add them to the reaction vessel. Disperse at 400r / min for 30min at 60℃. Add 18g of 50% phytic acid solution and continue stirring at 60℃ for 20min. Then add 5g of calcium lactate and stir at 60℃ for 30min. Add 2g of nano-hydroxyapatite and stir at 60℃ for 60min. Cool the system to 35℃. Dissolve 4g of ammonium bicarbonate in 100g of deionized water and add it to the reaction vessel. Stir at 300r / min for 30min at 35℃. Filter the mixture. Wash the filter cake twice with 800g of deionized water and once with 500g of anhydrous ethanol. Dry the mixture at 70℃ and vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin containing calcium cross-linked phytate microcores and ammonium-modified phytate outer layer. Step 4: Weigh 120g of phosphorylated lignin containing calcium-crosslinked phytate microcores and ammonium-modified phytate outer layers obtained in Step 3, 900g of dimethyl sulfoxide, and 300g of deionized water and add them to the reaction vessel. Disperse the lignin at 70℃ and 400r / min for 40min. Add 22g of melamine, 14g of paraformaldehyde, and 7g of sodium carbonate to the reaction vessel. Raise the reaction temperature to 82℃ and react at 300r / min for 4h. After the reaction is complete, cool to 40℃, add 1800g of deionized water to precipitate the solid, filter, and wash the filter cake successively with 1000g of deionized water, 600g of anhydrous ethanol, and 600g of deionized water. Dry the filter cake at 70℃ and vacuum degree ≤-90kPa for 12h to obtain phosphate-modified phytate triazine lignin. Step 5: Add 100g of phytate triazine lignin obtained in Step 4, 45g of L-(-)-lactide, and 300mg of stannous octoate to a dry reaction vessel. Purge with nitrogen at 100mL / min for 30min, then raise the temperature to 120℃ and react at 200r / min for 3h. After the reaction is complete, cool to 70℃, add 800g of ethyl acetate, and stir at 70℃ for 30min to dissolve the ungrafted oligomers and free L-(-)-lactide. Filter, and wash the filter cake twice with 800g of anhydrous ethanol. Dry the filter cake at 60℃ and vacuum degree ≤-90kPa for 12h to obtain phytate triazine oligolactic acid grafted lignin. The number-average degree of polymerization of the obtained oligolactic acid short chain is 6. Step Six: Weigh 360g of the dried wheat straw powder obtained in Step One, 80g of the dried needle-shaped wollastonite obtained in Step One, and 70g of the phosphate phytate triazine oligolactic acid grafted lignin obtained in Step Five and add them to a high-speed mixer. Mix at 800 r / min for 20 min at 90℃ to obtain the interface pretreated powder. Then add 740g of the dried polylactic acid resin obtained in Step One, 16g of sodium bicarbonate, and 12g of anhydrous citric acid to the high-speed mixer and mix at 500 r / min for 10 min at 80℃ to obtain the extrusion mixture. Step 7: Add the extrusion mixture obtained in Step 6 to a co-rotating twin-screw extruder. Set the temperatures of zones 1 to 7 of the extruder to 135℃, 150℃, 160℃, 170℃, 170℃, 165℃ and 155℃ respectively. Set the screw speed to 80 r / min. Control the material residence time in the extruder to 3 min. Set the die temperature to 150℃ and the die gap to 5 mm. After the melt is extruded through the die, it enters a 60℃ three-roll calender to determine the thickness, and then is cooled by a 25℃ cooling roller. Cut the calender to obtain a 5 mm thick all-bio-based lightweight, high-strength, flame-retardant green sheet. Example

[0023] Step 1: Weigh 300g of alkaline lignin and place it in a vacuum drying oven. Dry it for 8 hours at 80℃ and a vacuum degree ≤-90kPa. Weigh 600g of wheat straw powder, pulverize it, pass it through an 80-mesh sieve, and dry it at 105℃ for 6 hours. Weigh 200g of needle-shaped wollastonite and dry it at 110℃ for 4 hours. Weigh 900g of polylactic acid resin and dry it for 8 hours at 60℃ and a vacuum degree ≤-90kPa. Step 2: Weigh 200g of the dried alkaline lignin obtained in Step 1, 85g of ammonium dihydrogen phosphate, and 110g of urea and add them to a high-speed mixer. Mix at 600r / min for 15min at 25℃ to obtain a solid mixture. Place the solid mixture in a reaction vessel with a nitrogen inlet, purge with nitrogen at 100mL / min for 30min, then raise the temperature to 152℃ and react at 152℃ for 150min. After the reaction is complete, cool to 50℃, add 2000g of deionized water, stir at 300r / min for 30min at 50℃, filter, wash the filter cake three times with 1000g of deionized water, and then wash twice with 600g of anhydrous ethanol. Dry the washed filter cake at 70℃ and a vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin. Step 3: Weigh 150g of phosphorylated lignin obtained in Step 2, 600g of deionized water and 600g of anhydrous ethanol and add them to the reaction vessel. Disperse at 400r / min for 30min at 60℃. Add 32g of 50% phytic acid solution and continue stirring at 60℃ for 20min. Then add 10g of calcium lactate and stir at 60℃ for 30min. Add 5g of nano-hydroxyapatite and stir at 60℃ for 60min. Cool the system to 35℃. Dissolve 8g of ammonium bicarbonate in 100g of deionized water and add it to the reaction vessel. Stir at 300r / min for 30min at 35℃. Filter the mixture. Wash the filter cake twice with 800g of deionized water and once with 500g of anhydrous ethanol. Dry the mixture at 70℃ and vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin containing calcium cross-linked phytate microcores and ammonium-modified phytate outer layer. Step 4: Weigh 120g of phosphorylated lignin containing calcium-crosslinked phytate microcores and ammonium-modified phytate outer layers obtained in Step 3, 900g of dimethyl sulfoxide, and 300g of deionized water and add them to the reaction vessel. Disperse the lignin at 70℃ and 400r / min for 40min. Add 34g of melamine, 23g of paraformaldehyde, and 13g of sodium carbonate to the reaction vessel. Raise the reaction temperature to 90℃ and react at 300r / min for 6h. After the reaction is complete, cool to 40℃, add 1800g of deionized water to precipitate the solid, filter, and wash the filter cake successively with 1000g of deionized water, 600g of anhydrous ethanol, and 600g of deionized water. Dry the filter cake at 70℃ and vacuum degree ≤-90kPa for 12h to obtain phosphorylated phytate triazine lignin. Step 5: Add 100g of phytate triazine lignin obtained in Step 4, 75g of L-(-)-lactide, and 700mg of stannous octoate to a dry reaction vessel. Purge with nitrogen at 100mL / min for 30min, then raise the temperature to 130℃ and react at 200r / min for 5h. After the reaction, cool to 70℃, add 800g of ethyl acetate, and stir at 70℃ for 30min to dissolve the ungrafted oligomers and free L-(-)-lactide. Filter, and wash the filter cake twice with 800g of anhydrous ethanol. Dry the filter cake at 60℃ and under vacuum ≤-90kPa for 12h to obtain phytate triazine oligolactic acid grafted lignin. The number-average degree of polymerization of the obtained oligolactic acid short chain is 19. Step Six: Weigh 480g of the dried wheat straw powder obtained in Step One, 160g of the dried needle-shaped wollastonite obtained in Step One, and 130g of the phosphate phytate triazine oligolactic acid grafted lignin obtained in Step Five and add them to a high-speed mixer. Mix at 800r / min for 20min at 90℃ to obtain the interface pretreated powder. Then add 560g of the dried polylactic acid resin obtained in Step One, 30g of sodium bicarbonate, and 24g of anhydrous citric acid to the high-speed mixer and mix at 500r / min for 10min at 80℃ to obtain the extrusion mixture. Step 7: Add the extrusion mixture obtained in Step 6 to a co-rotating twin-screw extruder. Set the temperatures of zones 1 to 7 of the extruder to 135℃, 150℃, 160℃, 170℃, 170℃, 165℃ and 155℃ respectively. Set the screw speed to 80 r / min. Control the material residence time in the extruder to 3 min. Set the die temperature to 150℃ and the die gap to 5 mm. After the melt is extruded through the die, it enters a 60℃ three-roll calender to determine the thickness, and then is cooled by a 25℃ cooling roller. Cut the calender to obtain a 5 mm thick all-bio-based lightweight, high-strength, flame-retardant green sheet. Example

[0024] Step 1: Weigh 300g of alkaline lignin and place it in a vacuum drying oven. Dry it for 8 hours at 80℃ and a vacuum degree ≤-90kPa. Weigh 600g of wheat straw powder, pulverize it, pass it through an 80-mesh sieve, and dry it at 105℃ for 6 hours. Weigh 200g of needle-shaped wollastonite and dry it at 110℃ for 4 hours. Weigh 900g of polylactic acid resin and dry it for 8 hours at 60℃ and a vacuum degree ≤-90kPa. Step 2: Weigh 200g of the dried alkaline lignin obtained in Step 1, 78g of ammonium dihydrogen phosphate, and 100g of urea and add them to a high-speed mixer. Mix at 600r / min for 15min at 25℃ to obtain a solid mixture. Place the solid mixture in a reaction vessel with a nitrogen inlet, purge with nitrogen at 100mL / min for 30min, then raise the temperature to 148℃ and react at 148℃ for 135min. After the reaction is complete, cool to 50℃, add 2000g of deionized water, stir at 300r / min for 30min at 50℃, filter, wash the filter cake three times with 1000g of deionized water, and then wash twice with 600g of anhydrous ethanol. Dry the washed filter cake at 70℃ and a vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin. Step 3: Weigh 150g of phosphorylated lignin obtained in Step 2, 600g of deionized water and 600g of anhydrous ethanol and add them to the reaction vessel. Disperse at 400r / min for 30min at 60℃. Add 30g of 50% phytic acid solution and continue stirring at 60℃ for 20min. Then add 9g of calcium lactate and stir at 60℃ for 30min. Add 4g of nano-hydroxyapatite and stir at 60℃ for 60min. Cool the system to 35℃. Dissolve 7g of ammonium bicarbonate in 100g of deionized water and add it to the reaction vessel. Stir at 300r / min for 30min at 35℃. Filter the mixture. Wash the filter cake twice with 800g of deionized water and once with 500g of anhydrous ethanol. Dry the mixture at 70℃ and vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin containing calcium cross-linked phytate microcores and ammonium-modified phytate outer layer. Step 4: Weigh 120g of phosphorylated lignin containing calcium-crosslinked phytate microcores and ammonium-modified phytate outer layers obtained in Step 3, 900g of dimethyl sulfoxide, and 300g of deionized water and add them to the reaction vessel. Disperse the lignin at 70℃ and 400r / min for 40min. Add 31g of melamine, 21g of paraformaldehyde, and 12g of sodium carbonate to the reaction vessel. Raise the reaction temperature to 88℃ and react at 300r / min for 5.5h. After the reaction is complete, cool to 40℃, add 1800g of deionized water to precipitate the solid, filter, and wash the filter cake successively with 1000g of deionized water, 600g of anhydrous ethanol, and 600g of deionized water. Dry the filter cake at 70℃ and vacuum degree ≤-90kPa for 12h to obtain phosphate-modified phytate triazine lignin. Step 5: Add 100g of phytate triazine lignin obtained in Step 4, 68g of L-(-)-lactide, and 600mg of stannous octoate to a dry reaction vessel. Purge with nitrogen at 100mL / min for 30min, then raise the temperature to 128℃ and react at 200r / min for 4.5h. After the reaction is complete, cool to 70℃, add 800g of ethyl acetate, and stir at 70℃ for 30min to dissolve the ungrafted oligomers and free L-(-)-lactide. Filter, and wash the filter cake twice with 800g of anhydrous ethanol. Dry the filter cake at 60℃ and vacuum degree ≤-90kPa for 12h to obtain phytate triazine oligolactic acid grafted lignin. The number-average degree of polymerization of the obtained oligolactic acid short chain is 15. Step Six: Weigh 450g of the dried wheat straw powder obtained in Step One, 140g of the dried needle-shaped wollastonite obtained in Step One, and 120g of the phosphate phytate triazine oligolactic acid grafted lignin obtained in Step Five and add them to a high-speed mixer. Mix at 800r / min for 20min at 90℃ to obtain the interface pretreated powder. Then add 600g of the dried polylactic acid resin obtained in Step One, 28g of sodium bicarbonate, and 22g of anhydrous citric acid to the high-speed mixer and mix at 500r / min for 10min at 80℃ to obtain the extrusion mixture. Step 7: Add the extrusion mixture obtained in Step 6 to a co-rotating twin-screw extruder. Set the temperatures of zones 1 to 7 of the extruder to 135℃, 150℃, 160℃, 170℃, 170℃, 165℃ and 155℃ respectively. Set the screw speed to 80 r / min. Control the material residence time in the extruder to 3 min. Set the die temperature to 150℃ and the die gap to 5 mm. After the melt is extruded through the die, it enters a 60℃ three-roll calender to determine the thickness, and then is cooled by a 25℃ cooling roller. Cut the calender to obtain a 5 mm thick all-bio-based lightweight, high-strength, flame-retardant green sheet. Example

[0025] Step 1: Weigh 300g of alkaline lignin and place it in a vacuum drying oven. Dry it for 8 hours at 80℃ and a vacuum degree ≤-90kPa. Weigh 600g of wheat straw powder, pulverize it, pass it through an 80-mesh sieve, and dry it at 105℃ for 6 hours. Weigh 200g of needle-shaped wollastonite and dry it at 110℃ for 4 hours. Weigh 900g of polylactic acid resin and dry it for 8 hours at 60℃ and a vacuum degree ≤-90kPa. Step 2: Weigh 200g of the dried alkaline lignin obtained in Step 1, 62g of ammonium dihydrogen phosphate, and 82g of urea and add them to a high-speed mixer. Mix at 600r / min for 15min at 25℃ to obtain a solid mixture. Place the solid mixture in a reaction vessel with a nitrogen inlet, purge with nitrogen at 100mL / min for 30min, then raise the temperature to 142℃ and react at 142℃ for 110min. After the reaction, cool to 50℃, add 2000g of deionized water, stir at 300r / min for 30min at 50℃, filter, wash the filter cake three times with 1000g of deionized water, and then wash twice with 600g of anhydrous ethanol. Dry the washed filter cake at 70℃ and a vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin. Step 3: Weigh 150g of phosphorylated lignin obtained in Step 2, 600g of deionized water, and 600g of anhydrous ethanol and add them to the reaction vessel. Disperse at 400r / min for 30min at 60℃. Add 21g of 50% phytic acid solution and continue stirring at 60℃ for 20min. Then add 6g of calcium lactate and stir at 60℃ for 30min. Add 2.5g of nano-hydroxyapatite and stir at 60℃ for 60min. Cool the system to 35℃. Dissolve 5g of ammonium bicarbonate in 100g of deionized water and add it to the reaction vessel. Stir at 300r / min for 30min at 35℃. Filter the mixture. Wash the filter cake twice with 800g of deionized water and once with 500g of anhydrous ethanol. Dry the mixture at 70℃ and vacuum degree ≤-90kPa for 10h to obtain phosphorylated lignin containing calcium cross-linked phytate microcores and ammonium-modified phytate outer layer. Step 4: Weigh 120g of phosphorylated lignin containing calcium-crosslinked phytate microcores and ammonium-modified phytate outer layers obtained in Step 3, 900g of dimethyl sulfoxide, and 300g of deionized water and add them to the reaction vessel. Disperse the lignin at 70℃ and 400r / min for 40min. Add 25g of melamine, 16g of paraformaldehyde, and 8g of sodium carbonate to the reaction vessel. Raise the reaction temperature to 84℃ and react at 300r / min for 4.5h. After the reaction is complete, cool to 40℃, add 1800g of deionized water to precipitate the solid, filter, and wash the filter cake successively with 1000g of deionized water, 600g of anhydrous ethanol, and 600g of deionized water. Dry the filter cake at 70℃ and vacuum degree ≤-90kPa for 12h to obtain phosphorylated phytate triazine lignin. Step 5: Add 100g of phytate triazine lignin obtained in Step 4, 52g of L-(-)-lactide, and 400mg of stannous octoate to a dry reaction vessel. Purge with nitrogen at 100mL / min for 30min, then heat to 123℃ and react at 200r / min for 3.5h. After the reaction, cool to 70℃, add 800g of ethyl acetate, and stir at 70℃ for 30min to dissolve the ungrafted oligomers and free L-(-)-lactide. Filter, and wash the filter cake twice with 800g of anhydrous ethanol. Dry the filter cake at 60℃ and vacuum degree ≤-90kPa for 12h to obtain phytate triazine oligolactic acid grafted lignin. The number-average degree of polymerization of the obtained oligolactic acid short chain is 9. Step Six: Weigh 400g of the dried wheat straw powder obtained in Step One, 100g of the dried needle-shaped wollastonite obtained in Step One, and 90g of the phosphate phytate triazine oligolactic acid grafted lignin obtained in Step Five and add them to a high-speed mixer. Mix at 800r / min for 20min at 90℃ to obtain the interface pretreated powder. Then add 700g of the dried polylactic acid resin obtained in Step One, 20g of sodium bicarbonate, and 15g of anhydrous citric acid to the high-speed mixer and mix at 500r / min for 10min at 80℃ to obtain the extrusion mixture. Step 7: Add the extrusion mixture obtained in Step 6 to a co-rotating twin-screw extruder. Set the temperatures of zones 1 to 7 of the extruder to 135℃, 150℃, 160℃, 170℃, 170℃, 165℃ and 155℃ respectively. Set the screw speed to 80 r / min. Control the material residence time in the extruder to 3 min. Set the die temperature to 150℃ and the die gap to 5 mm. After the melt is extruded through the die, it enters a 60℃ three-roll calender to determine the thickness, and then is cooled by a 25℃ cooling roller. Cut the calender to obtain a 5 mm thick all-bio-based lightweight, high-strength, flame-retardant green sheet.

[0026] Comparative Example 1: The difference from Example 1 is that in step six, 100g of phytate triazine oligolactic acid grafted lignin obtained in step five is replaced with 100g of dry alkaline lignin obtained in step one, and the other conditions are the same as in Example 1.

[0027] Comparative Example 2: The difference from Example 1 is that: in step two, 70g of ammonium dihydrogen phosphate and 90g of urea are not added, and the reaction at 145°C is not carried out. Instead, 200g of the dried alkaline lignin obtained in step one is directly treated with 2000g of deionized water and 600g of anhydrous ethanol according to the washing and drying conditions of step two in Example 1 to obtain the product obtained in step two. The other conditions are the same as in Example 1.

[0028] Comparative Example 3: The difference from Example 1 is that: in step three, 24g of 50% phytic acid solution, 7g of calcium lactate, 3g of nano-hydroxyapatite and 6g of ammonium bicarbonate are not added. The phosphorylated lignin obtained in step two is treated with the dispersion, filtration, washing and drying conditions of step three in Example 1 as the product obtained in step three. The other conditions are the same as in Example 1.

[0029] Comparative Example 4: The difference from Example 1 is that 28g of melamine, 18g of paraformaldehyde and 10g of sodium carbonate are not added in step four. The phosphorylated lignin containing calcium cross-linked phytate micronuclei and ammonium phytate outer layer obtained in step three is treated with the dispersion, precipitation, filtration, washing and drying conditions of step four in Example 1 as the product obtained in step four. The other conditions are the same as in Example 1.

[0030] Comparative Example 5: The difference from Example 1 is that 60g of L-(-)-lactide and 500mg of stannous octoate are not added in step five. The phosphate phytate triazine lignin obtained in step four is treated with nitrogen replacement, heating, ethyl acetate treatment, filtration, anhydrous ethanol washing and drying conditions as in step five of Example 1, and is used as the product obtained in step five. The other conditions are the same as in Example 1.

[0031] Comparative Example 6: The difference from Example 1 is that in step five, 60g of L-(-)-lactide was replaced with 25g of L-(-)-lactide, and the number-average degree of polymerization of the resulting short-chain oligolactic acid was 3. The other conditions were the same as in Example 1.

[0032] Comparative Example 7: The difference from Example 1 is that in step five, 60g of L-(-)-lactide was replaced with 95g of L-(-)-lactide, and the number-average degree of polymerization of the resulting short oligolactic acid chain was 25. The other conditions were the same as in Example 1.

[0033] Comparative Example 8: The difference from Example 1 is that in step six, instead of subjecting 420g of the dried wheat straw powder obtained in step one, 120g of the dried acicular wollastonite obtained in step one, and 100g of the phosphate-modified triazine oligolactic acid grafted lignin obtained in step five to a 20-minute interface pretreatment at 90°C and 800 rpm, 420g of the dried wheat straw powder obtained in step one, 120g of the dried acicular wollastonite obtained in step one, 100g of the phosphate-modified triazine oligolactic acid grafted lignin obtained in step five, 650g of the dried polylactic acid resin obtained in step one, 24g of sodium bicarbonate, and 18g of anhydrous citric acid are simultaneously added to a high-speed mixer and mixed at 80°C and 500 rpm for 10 minutes to obtain the extrusion mixture. The remaining conditions are the same as in Example 1.

[0034] Comparative Example 9: The difference from Example 1 is that in step six, 120g of the dried needle-shaped wollastonite obtained in step one is replaced with 120g of the dried wheat straw powder obtained in step one to make up the total amount of filler. The other conditions are the same as in Example 1.

[0035] Comparative Example 10: The difference from Example 1 is that 24g of sodium bicarbonate and 18g of anhydrous citric acid are not added in step six. At the same time, the 650g of dried polylactic acid resin obtained in step one is adjusted to 692g of dried polylactic acid resin obtained in step one to make up the total amount of materials. The other conditions are the same as in Example 1.

[0036] Performance testing: The 5mm thick, fully bio-based lightweight, high-strength, flame-retardant green boards prepared in Examples 1 to 5 and Comparative Examples 1 to 10 were used as test samples. Samples were taken from the center of each board, at least 20mm from the edge, and cut using a precision panel cutter. After cutting, the burrs were lightly smoothed with 800-grit sandpaper, without edge sealing. All samples were conditioned for 48 hours in a standard environment of 23°C and 50% relative humidity before testing. For each test item, at least five parallel samples were tested for each specimen, and the results were taken as the arithmetic mean.

[0037] Apparent density test: Apparent density was tested according to GB / T 6343-2009 "Determination of Apparent Density of Foamed Plastics and Rubber". The boards from Examples 1 to 5 and Comparative Examples 1 to 10 were cut into 50mm × 50mm × 5mm specimens, with 5 specimens tested in each group. Length, width, and thickness were measured using a vernier caliper with an accuracy of 0.01mm, and mass was measured using an electronic balance with an accuracy of 0.001g. Apparent density was calculated by dividing mass by apparent volume.

[0038] Static bending strength and flexural modulus of elasticity were tested according to the three-point bending method for determining static bending strength and modulus of elasticity in GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The boards from Examples 1 to 5 and Comparative Examples 1 to 10 were cut into 150mm × 50mm × 5mm specimens, with 6 specimens tested per group. The support span was set to 100mm, the loading head was located at the center of the span, and the loading speed was set to 5mm / min. The maximum load and load-deflection curves were recorded, and the static bending strength and flexural modulus of elasticity were calculated.

[0039] Test for retention rate of static bending strength after damp heat treatment: The plates from Examples 1 to 5 and Comparative Examples 1 to 10 were cut into 150mm × 50mm × 5mm specimens, with 6 specimens tested in each group. First, the static bending strength of the untreated specimen was measured according to Test Item 5. Then, another specimen of the same specification was placed in a constant temperature and humidity chamber at 70℃ and 95% relative humidity for 168 hours. After removal, it was placed in an environment at 23℃ and 50% relative humidity for 2 hours. The static bending strength after damp heat treatment was then measured according to Test Item 5 with the same span and loading speed. The retention rate of static bending strength after damp heat treatment was calculated by dividing the static bending strength after damp heat treatment by the static bending strength of the untreated specimen and then multiplying by 100%.

[0040] 24-hour water absorption thickness swelling rate test: The test was conducted according to the method for determining the water absorption thickness swelling rate in GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The boards from Examples 1 to 5 and Comparative Examples 1 to 10 were cut into 50mm × 50mm × 5mm specimens, with 5 specimens tested in each group. Before testing, the initial thickness was measured at the center point of the specimen. The specimen was then vertically immersed in 20℃ deionized water, with the upper surface 25mm below the water surface. After 24 hours of immersion, the specimen was removed, surface moisture was absorbed with filter paper, and the thickness after immersion was measured at the same center point. The 24-hour water absorption thickness swelling rate was calculated by dividing the increase in thickness after immersion by the initial thickness and then multiplying by 100%.

[0041] Limiting oxygen index test: The test was conducted according to GB / T 2406.2-2009 "Determination of flammability by oxygen index method for plastics - Part 2: Room temperature test". The sheets from Examples 1 to 5 and Comparative Examples 1 to 10 were cut into 100mm × 10mm × 5mm specimens, with at least 5 specimens per test group. After conditioning the specimens to an environment of 23℃ and 50% relative humidity for 48 hours, they were vertically clamped in the combustion chamber of the oxygen index tester. The specimens were ignited using a top-ignition method. The oxygen volume fraction in the oxygen and nitrogen mixture was adjusted, and the minimum oxygen volume fraction required for the sample to maintain the specified combustion state was determined.

[0042] Vertical burning test: The vertical burning test was conducted according to GB / T 2408-2021 "Determination of flammability of plastics - Horizontal and Vertical Methods". The sheets from Examples 1 to 5 and Comparative Examples 1 to 10 were cut into 125mm × 13mm × 5mm specimens, with 5 specimens per group. After conditioning the specimens to an environment of 23℃ and 50% relative humidity for 48 hours, two 10-second flame tests were conducted under a 50W flame, and the vertical burning rating was recorded.

[0043] Table 1 Performance Test Results Example 1 708 49.6 3570 89.2 0.8 33.2 V-0 Example 2 784 40.7 2810 83.6 1.0 30.4 V-0 Example 3 646 47.8 4015 86.9 0.9 35.4 V-0 Example 4 672 52.4 3890 92.1 0.6 34.3 V-0 Example 5 748 45.2 3185 87.5 0.9 31.6 V-0 Comparative Example 1 726 31.4 2470 70.6 3.2 24.5 V-2 Comparative Example 2 718 42.1 3225 84.0 1.2 29.1 V-1 Comparative Example 3 712 43.4 3305 84.7 1.1 28.4 V-1 Comparative Example 4 716 42.6 3150 85.1 1.1 30.3 V-1 Comparative Example 5 735 38.5 2895 76.4 2.0 31.4 V-1 Comparative Example 6 721 44.0 3280 85.5 1.2 32.1 V-0 Comparative Example 7 714 45.1 3410 86.3 1.0 30.9 V-1 Comparative Example 8 742 39.3 3030 78.8 2.2 29.7 V-1 Comparative Example 9 688 36.6 2545 76.8 2.5 31.0 V-1 Comparative Example 10 1048 56.2 4070 90.0 0.7 31.5 V-0 As shown in Table 1, in Comparative Example 1, after replacing the phytate triazine oligolactic acid grafted lignin with ordinary alkaline lignin, the static bending strength of the board was only 31.4 MPa, the static bending strength retention rate after wet heat treatment was 70.6%, the thickness expansion rate after 24 hours of water absorption reached 3.2%, the limiting oxygen index was only 24.5%, and the vertical burning rating was V-2. This indicates that although ordinary lignin has a certain tendency to form char, it is difficult to simultaneously undertake the functions of flame retardancy, interfacial compatibility, and wet heat stability.

[0044] Compared with Comparative Example 1, the static bending strength of Example 1 increased to 49.6 MPa, the static bending strength retention rate after wet heat treatment increased to 89.2%, the thickness expansion rate after 24h water absorption decreased to 0.8%, the limiting oxygen index increased to 33.2%, and the vertical combustion reached V-0 level. This indicates that lignin after phosphorylation, phytate micro-zone construction, triazine structure fixation, and short-linked oligolactic acid can more effectively improve the interfacial interaction between polylactic acid, wheat straw powder, and acicular wollastonite, and improve the char formation and barrier ability during combustion.

[0045] After omitting phosphorylation, phytate microregions, or triazine structures in Comparative Examples 2 to 4, although some flame-retardant or compatible structures were still retained, their limiting oxygen index, vertical burning rating, and wet heat stability were all lower than those in Example 1. This indicates that the phosphorus source, phytate calcium phosphorus microregions, and nitrogen-containing triazine structures are not simply superimposed, but rather work together on the same lignin skeleton, which is more conducive to forming a continuous and effective flame-retardant interface layer.

[0046] Comparative Example 5, which was not grafted with polylactic acid, still had a limiting oxygen index of 31.4%, but its static bending strength decreased to 38.5 MPa. After wet heat treatment, the static bending strength retention rate decreased to 76.4%, and the thickness expansion rate after 24 hours of water absorption increased to 2.0%. This indicates that without polylactic acid compatible segments, the highly polar phosphorus-nitrogen-calcium-phosphorus structure is difficult to fully balance flame retardancy and interfacial reinforcement.

[0047] Comparative Examples 6 and 7 adjusted the number-average degree of polymerization of short-chain oligolactic acid to 3 and 25, respectively. Their overall performance was lower than that of Example 1, indicating that when the oligolactic acid chain segments are too short, the interfacial transition effect is insufficient, and when the chain segments are too long, the effective exposure of the flame-retardant micro-region and the interfacial positioning effect may be weakened. Controlling the number-average degree of polymerization in the range of 5 to 20 is more conducive to taking into account mechanical properties, hygrothermal stability and flame-retardant properties.

[0048] In Comparative Example 8, after the interface pretreatment before the addition of polylactic acid resin was removed, the static bending strength decreased to 39.3 MPa, the static bending strength retention rate after wet heat treatment decreased to 78.8%, and the limiting oxygen index decreased to 29.7%, all under the same composition. This indicates that the premixing of wheat straw powder, acicular wollastonite, and modified lignin is beneficial to improving the interfacial interaction and the utilization efficiency of flame retardant components.

[0049] In Comparative Example 9, after removing the acicular wollastonite, the density of the slab decreased to 688 kg·m³. -3 However, the static bending strength and flexural modulus decreased to 36.6 MPa and 2545 MPa, respectively, and the static bending strength retention rate after hygrothermal treatment decreased to 76.8%, indicating that acicular wollastonite not only enhances the bending load at room temperature, but also helps maintain the structural stability under hygrothermal and combustion conditions.

[0050] Comparative Example 10, without the addition of a foaming system, showed an increased static bending strength of 56.2 MPa, but an apparent density of 1048 kg·m³. -3 It clearly loses its lightweight advantage; in contrast, Examples 1 to 5 have a weight of 646 kg·m³. -3 Up to 784 kg·m -3 It maintains a static bending strength of 40.7 MPa to 52.4 MPa, a flexural modulus of elasticity of 2810 MPa to 4015 MPa, a limiting oxygen index of 30.4% to 35.4%, and a V-0 vertical flammability rating at a lower density.

[0051] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A fully bio-based lightweight, high-strength, flame-retardant, and green building material, characterized in that, The board is a polylactic acid-based foamed composite board; based on the mass parts of the raw materials used to prepare the board, the board is prepared from the following raw materials: 560-740 parts polylactic acid resin, 360-480 parts crop straw powder, 80-160 parts acicular wollastonite, 70-130 parts phytate triazine oligolactic acid grafted lignin, 16-30 parts sodium bicarbonate and 12-24 parts anhydrous citric acid; The phosphate-phytate triazine oligolactic acid grafted lignin is a modified lignin obtained by sequentially phosphorylating, constructing phytate microdomains, triazinizing and grafting oligolactic acid onto alkaline lignin, and the number-average degree of polymerization of the oligolactic acid is 5-20. The wheat straw powder, the needle-shaped wollastonite, and the phosphate phytate triazine oligolactic acid grafted lignin are pre-coated at the interface to form an interface pre-treated powder, which is then mixed with the polylactic acid resin, the sodium bicarbonate, and the anhydrous citric acid and melt-molded into the board.

2. The all-bio-based lightweight, high-strength, flame-retardant green board according to claim 1, characterized in that, The thickness of the plate is 3-10mm.

3. The all-bio-based lightweight, high-strength, flame-retardant green board according to claim 1, characterized in that, The crop straw powder is wheat straw powder that has been crushed and passed through an 80-mesh sieve; the acicular wollastonite has an aspect ratio of 10-20 and a moisture content of ≤1%.

4. The all-bio-based lightweight, high-strength, flame-retardant green board according to claim 1, characterized in that, The phosphorylation is performed by mixing 200 parts by weight of dry alkaline lignin, 55-85 parts by weight of ammonium dihydrogen phosphate, and 75-110 parts by weight of urea, and reacting at 138-152℃ for 100-150 min under nitrogen protection to obtain phosphorylated lignin; the phytate microdomain construction is performed by sequentially treating 150 parts by weight of phosphorylated lignin, 18-32 parts by weight of 50% phytic acid solution, 5-10 parts by weight of calcium lactate, 2-5 parts by weight of nano-hydroxyapatite, and 4-8 parts by weight of ammonium bicarbonate to obtain phosphorylated lignin containing calcium-crosslinked phytate microcores and an ammonium-modified phytate outer layer; the triazine The process involves reacting 120 parts by weight of phosphorylated lignin containing calcium-crosslinked phytate microcores and ammonium-modified phytate outer layers, 22-34 parts of melamine, 14-23 parts of paraformaldehyde, and 7-13 parts of sodium carbonate at 82-90℃ for 4-6 hours to obtain phosphate-modified phytate triazine lignin; the oligolactic acid grafting process involves adding 45-75 parts by weight of L-(-)-lactide and 0.3-0.7 parts by weight of phosphate-modified phytate triazine lignin per 100 parts by weight, and reacting at 120-130℃ for 3-5 hours under nitrogen protection to obtain phosphate-modified phytate triazine oligolactic acid grafted lignin.

5. The all-bio-based lightweight, high-strength, flame-retardant green board according to claim 4, characterized in that, The particle size of the nano-hydroxyapatite is <100nm.

6. The all-bio-based lightweight, high-strength, flame-retardant green board according to claim 1, characterized in that, The interface pre-coating treatment, by mass parts, is as follows: 360-480 parts of wheat straw powder, 80-160 parts of needle-shaped wollastonite and 70-130 parts of phytate triazine oligolactic acid grafted lignin are added to a high-speed mixer and mixed at 800 r / min for 20 min at 90°C to obtain the interface pre-treated powder.

7. The all-bio-based lightweight, high-strength, flame-retardant green board according to claim 1, characterized in that, By mass, 510-770 parts of interface pretreated powder, 560-740 parts of polylactic acid resin, 16-30 parts of sodium bicarbonate and 12-24 parts of anhydrous citric acid are mixed at 80°C and 500 r / min for 10 min to obtain a mixture for extrusion.

8. The all-bio-based lightweight, high-strength, flame-retardant green board according to claim 7, characterized in that, The melt molding process includes adding the extrusion mixture to a co-rotating twin-screw extruder, extruding it through a flat die, then feeding it into a three-roll calender to achieve a fixed thickness, followed by cooling and cutting by cooling rollers. The temperatures of zones one through seven of the co-rotating twin-screw extruder are 135°C, 150°C, 160°C, 170°C, 170°C, 165°C, and 155°C, respectively. The screw speed is 80 r / min, the material residence time in the extruder is 3 min, the flat die temperature is 150°C, and the die gap is 5 mm. The temperature of the three-roll calender is 60°C, and the temperature of the cooling rollers is 25°C.

9. A method for preparing a fully bio-based lightweight, high-strength, flame-retardant green board according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Phosphorylation of basic lignin yields phosphorylated lignin; S2. Phytate microdomains are constructed on the phosphorylated lignin to obtain phosphorylated lignin containing calcium-crosslinked phytate micronuclei and an ammonium-modified phytate outer layer. S3. Triazine the phosphorylated lignin containing calcium-crosslinked phytate micronucleus and ammonium-modified phytate outer layer to obtain phosphorylated phytate triazine lignin. S4. Graft the phosphate-phytate triazine lignin onto oligolactic acid to obtain phosphate-phytate triazine oligolactic acid grafted lignin. S5. The wheat straw powder, needle-shaped wollastonite and the phosphate phytate triazine oligolactic acid grafted lignin are subjected to interface pre-coating treatment to obtain interface pre-treated powder. S6. The interface pretreated powder is mixed with polylactic acid resin, sodium bicarbonate and anhydrous citric acid to obtain a mixture for extrusion. S7. The extrusion mixture is melt-extruded, formed by a flat die, calendered to a certain thickness by three-roll calendering, cooled and cut to obtain the all-bio-based lightweight high-strength flame-retardant green board.