Bamboo fiber full-biodegradation straw

Abstract

The invention discloses a bamboo fiber full-biodegradable straw, which can realize the functions of moisture absorption resistance, stiffness and smoothness keeping and natural degradation after being discarded when the straw is used in drinks, and the core of the straw comprises the following three steps: pretreatment of crushed bamboo fibers, preparation of modified plastic particles and molding of the straw. In the pretreatment process, bamboo fibers with specific lengths are selected as primarily screened bamboo crushed materials, and the bamboo fibers are subjected to steam explosion, water washing and drying, hemicellulose and part of lignin are degraded, moisture absorption is reduced, and stiffness is increased; adding the pre-treated bamboo fiber and the auxiliary agent into the preheated and cooled degradable plastic, and mixing and granulating; and finally, carrying out microcellular foaming extrusion molding, injecting particles into an annular mold, and heating to obtain the straw. By means of a unique process, water is promoted to escape during foaming to form an inner wall compact layer, it is guaranteed that the straw is stable in structure, the use requirement of drinks is met, and innovativeness and practicability are achieved in the field of degradable straws.

Description

Technical Field

[0001] This application relates to the intersection of environmentally friendly polymer material processing and natural plant fiber application, specifically a bamboo fiber fully biodegradable straw. Background Technology

[0002] In this context, biodegradable straws have become a market necessity. Currently, the main biodegradable straws on the market are paper straws and polylactic acid (PLA) straws. However, paper straws are prone to softening and deformation when soaked in liquids, severely affecting the user experience; PLA straws require specific temperature and humidity conditions for degradation, and have poor heat resistance, easily softening when exposed to hot drinks, failing to adequately meet consumer needs. Bamboo, as a high-quality renewable, recyclable, and biodegradable natural material, grows quickly, has high strength, hardness, and toughness, offering a new opportunity to solve the problem of plastic straw pollution. However, existing bamboo straw manufacturing processes still have many shortcomings, such as the inability to effectively address the moisture absorption problem of bamboo fibers, leading to straws being easily deformed by moisture and exhibiting poor structural stability. An innovative manufacturing method is urgently needed to improve the quality of bamboo straws and meet the market's demand for environmentally friendly, durable, and high-performance straws. Summary of the Invention

[0003] This invention provides a fully biodegradable bamboo fiber straw, which involves the intersection of environmentally friendly polymer material processing and natural plant fiber application. Specifically, it belongs to the category of preparation technology for biodegradable disposable beverage utensils, and is particularly suitable for the molding process of composite straws with bamboo fiber as the reinforcing phase and biodegradable plastic as the matrix. It is also related to sub-technical directions such as natural plant fiber pretreatment technology, polymer material mixing and granulation technology, and microporous foaming extrusion molding technology.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A fully biodegradable bamboo fiber straw, comprising 30-40 parts by weight of enzymatically modified bamboo fiber, 25-35 parts by weight of modified polylactic acid, 15-25 parts by weight of polybutylene adipate-butylene terephthalate copolymer (PBAT), 3-5 parts by weight of composite plasticizer, 1-2 parts by weight of surface-modified nano-silica, and 0.5-1.5 parts by weight of calcium stearate, includes the following processing steps: Step 1: Bamboo fiber pretreatment. Select bamboo fibers with a length of 1-3 mm and soak them in a 3%-5% sodium hydroxide solution at a constant temperature of 60-70℃ for 2-3 hours, stirring at 60-80 rpm every 30 minutes. After soaking, rinse repeatedly with deionized water at 20-25℃ until the pH value reaches 6.8-7.2. Then, transfer them to a forced-air drying oven and dry them continuously at 80-90℃ for 4-5 hours, controlling the moisture content to 8%-10%, to obtain pretreated bamboo fibers. Enzymatic modification of the pretreated bamboo fibers. Place them in a 0.5%-1.0% cellulase solution at a constant temperature of 45-50℃ and stir at 40-60 rpm for 1.5-2 hours. After the reaction, rinse with deionized water until neutral and dry at 75-85℃ for 3-4 hours to obtain enzymatically modified bamboo fibers. Step 2: Raw material mixing and co-extrusion. Weigh the raw materials according to the weight ratio and add them to a high-speed mixer. Mix at 1500-1800 r / min for 15-20 minutes at 100-110℃. The mixture is then conveyed to a twin-screw extruder. Set the barrel temperature to 165-185℃, the first section to 165-170℃, the second section to 170-175℃, the third section to 175-180℃, and the fourth section to 180-185℃. Set the die temperature to 175-185℃, the screw speed to 200-250 r / min, and the feeding speed to 20-30 kg / h. Simultaneously, set vacuum exhaust ports in the third to fifth barrel sections and control the vacuum degree to -0.08 to -0.09 MPa. Perform co-extrusion granulation to obtain granules with a diameter of 2-3 mm. Step 3: Tube drawing and post-processing. After the granules are cooled to 20-25℃, they are added to the hopper of the tube drawing machine. The heating temperature is set to 170-180℃, and the tube drawing speed is 1.5-2.5m / min to draw tubular blanks with an inner diameter of 5-8mm and a wall thickness of 0.3-0.5mm. The tubular blanks are transferred to a hot air oven and heat-treated at 110-120℃ for 8-10 minutes. After heat treatment, they are placed in a UV aging chamber with a wavelength of 280-320nm and an irradiation intensity of 0.8-1.0W / ㎡ for 2-3 hours. The UV-treated tubular blanks are then subjected to microwave cross-linking by placing them in a microwave processor with a frequency of 2450MHz and a power of 300-400W for 3-5 minutes. Finally, a 0.5%-1.0% tea polyphenol solution is sprayed onto the surface of the tube, with a spraying amount of 5-10g / ㎡. The tubes are then dried in a forced-air dryer at 50-60℃ for 1-2 minutes to obtain the finished product.

[0005] Furthermore, the preparation process of the modified polylactic acid is as follows: Step 1: Polylactic acid grafting modification. Weigh 100 parts of polylactic acid, 5-8 parts of maleic anhydride, and 0.8-1.2 parts of dicumyl peroxide according to the weight ratio. Add them to a high-speed mixer and mix at 800-1000 r / min for 15-20 minutes at 80-90℃. Feed the mixture into a twin-screw extruder and set the barrel temperature to 170-190℃, the first stage to 170-175℃, the second stage to 175-180℃, the third stage to 180-185℃, and the fourth stage to 185-190℃. Set the die temperature to 180-190℃ and the screw speed to 180-200 r / min. Extrude and granulate to obtain polylactic acid granules grafted with maleic anhydride. Step 2: Chitosan blending modification. Weigh 90-95 parts of polylactic acid granules grafted with maleic anhydride and 5-10 parts of chitosan according to the weight ratio, add them to a torque rheometer, set the temperature to 175-185℃ and the rotation speed to 60-80r / min, melt blend for 10-15 minutes, add 1-2 parts of nano zinc oxide during the process and stir continuously; after blending, cool to room temperature, pulverize into powder with a particle size of 0.1-0.3mm to obtain modified polylactic acid.

[0006] Furthermore, the preparation process of the surface-modified nano-silica is as follows: Step 1: Pretreatment of nano-silica. Select nano-silica with a particle size of 20-50nm, put it into a hydrochloric acid solution with a mass concentration of 5%-8%, and stir at 40-50℃ for 1-2 hours; then wash with deionized water until the pH value is 7.0-7.2, and vacuum dry at 70-80℃ for 3-4 hours to obtain purified nano-silica. Step 2: Silane coupling agent modification. Purified nano-silica is added to a 2%-3% (w / w) ethanol solution of silane coupling agent KH-550 at a solid-liquid ratio of 1:10-1:15. The mixture is stirred in a constant temperature water bath at 50-60℃ at a speed of 150-200 r / min for 2-3 hours. During this period, a 0.3%-0.5% (w / w) polyvinyl alcohol solution (volume ratio of 0.3%-0.5% to the silane coupling agent ethanol solution is added. After the reaction, the mixture is centrifuged (3000-4000 r / min, 15-20 minutes). The precipitate is washed 3-4 times with anhydrous ethanol and dried under vacuum at 70-80℃ for 3-4 hours to obtain surface-modified nano-silica.

[0007] Furthermore, the composite plasticizer is prepared by mixing tributyl citrate and epoxidized soybean oil in a weight ratio of 8-9:1-2. The mixing process is carried out in a constant temperature water bath at 40-50℃ and stirred at 100-150r / min for 10-15 minutes. After mixing, 0.2-0.5 parts of polyethylene glycol 400 are added, and stirring is continued for 5-8 minutes until fully integrated to ensure the synergistic effect of the three.

[0008] Furthermore, before the enzymatically modified bamboo fiber is mixed with other raw materials, it needs to undergo plasma surface activation: the enzymatically modified bamboo fiber is placed in the reaction chamber of the plasma treatment instrument and the vacuum is drawn to 1-5 Pa; then an oxygen-nitrogen mixed gas (volume ratio 3:7-4:6) is introduced, the flow rate is controlled at 10-15 L / min, and the chamber pressure is maintained at 10-20 Pa; the power is set to 200-300 W, and the treatment is carried out for 5-10 minutes, so that the mixed gas plasma bombards the surface of the bamboo fiber and introduces polar groups such as hydroxyl and carboxyl groups.

[0009] Furthermore, the polybutylene adipate-butylene terephthalate copolymer needs to be pre-crystallized before use: place it in a vacuum drying oven, evacuate to -0.09 to -0.1 MPa, and preheat at 60-70℃ for 1-2 hours; then raise the temperature to 90-100℃, maintain the vacuum and keep warm for 2-3 hours, during which argon gas is introduced every 30 minutes at a flow rate of 5-8 L / min for 10-15 seconds; after keeping warm, cool naturally to room temperature, crush and pass through a 100-120 mesh sieve to obtain particles with a particle size of 0.1-0.3 mm.

[0010] Furthermore, the tube drawing process employs segmented cooling: the first segment is water cooling, where the tubular billet is immediately fed into a 15-20℃ cooling water tank, with the water flow rate controlled at 0.5-1m / s, and cooled for 1-2 minutes. Glycerin with a mass concentration of 0.1%-0.2% is added to the water tank and thoroughly mixed. The second segment is air cooling, where the water-cooled tubular billet is fed into an air cooling channel, with the air velocity set at 3-5m / s and the air temperature at 20-25℃, and cooled for 0.5-1 minutes to uniformly reduce the internal temperature to 25-30℃.

[0011] Furthermore, the surface of the pipette after microwave cross-linking needs to be cleaned before spraying the tea polyphenol solution.

[0012] Place the pipette into a 0.5%-1% sodium bicarbonate solution and stir at 50-80 rpm for 5-8 minutes at 30-40℃. During this time, add 0.2%-0.3% sodium dodecylbenzenesulfonate to enhance the cleaning effect. Then rinse with deionized water until the pH value is 7.0-7.2, and dry with a forced air at 60-70℃ for 3-5 minutes, controlling the surface moisture content to 3%-5%.

[0013] Furthermore, a stepped heating method is used when mixing raw materials at high speed: the initial temperature is 50-60℃, and the mixture is stirred for 5 minutes; then the temperature is increased to 80-90℃ at a rate of 10℃ / min, and the mixture is stirred for 5 minutes, during which 0.3-0.6 parts of talc powder are added; finally, the temperature is increased to 100-110℃ at a rate of 5℃ / min, and the mixture is stirred for 5-10 minutes.

[0014] Furthermore, the twin-screw extruder adopts an interlocking screw with a length-to-diameter ratio of 40:1. The screw groove depth gradually decreases from the feeding section to the extrusion section (10-12mm in the feeding section, 8-10mm in the compression section, and 5-7mm in the metering section). In addition, 3-5 staggered shear pins (3-5mm in diameter and 2-3mm in height) are set in the compression section.

[0015] Beneficial effects This biodegradable bamboo fiber straw, through scientific process design and reasonable raw material combination, demonstrates significant advantages in technical performance, environmental value, and practical application scenarios. Specific beneficial effects are as follows: From the perspective of process rationality, this application takes "bamboo fiber pretreatment - modified plastic granule preparation - microporous foaming extrusion molding" as the core process. The special treatment process in the pretreatment stage can effectively optimize the physical properties of bamboo fiber and reduce the inherent defects of bamboo fiber's easy moisture absorption, laying a stable foundation for subsequent molding. In the preparation of modified plastic granules, by controlling the raw material ratio, molding problems caused by improper fiber ratio are avoided, ensuring the uniformity and applicability of the granules. The application of microporous foaming extrusion molding technology further improves the structural stability of the straw, and compared with traditional molding methods, it is more adaptable to the needs of different application scenarios. In terms of performance, the straw prepared in this application possesses both excellent moisture resistance and temperature resistance. It can maintain its shape stability under normal humidity conditions for a long time, without easily deforming or softening. It is also suitable for use with hot and cold beverages, avoiding performance failure due to temperature changes, and effectively improving the poor user experience of existing biodegradable straws. At the same time, the straw can achieve efficient degradation in the natural environment, and the degradation process is uniform with no risk of secondary pollution. It fully complies with the current environmental policy of "restricting and banning plastics" and meets the market demand for green and environmentally friendly products. From an application value perspective, the process described in this application is highly flexible, allowing for adjustments to raw material types and key process parameters based on actual needs. This adapts to the production of straws of different specifications and for different usage scenarios, facilitating industrialization and promotion. Furthermore, the process is simple and controllable, requiring no complex special equipment, which helps control production costs and balances environmental performance with economic benefits. Therefore, it has broad application prospects and promotional value in the field of biodegradable straws. Detailed Implementation The technical solutions in the embodiments of the present invention have been clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] A fully biodegradable bamboo fiber straw includes the following processing steps: Step 1: Bamboo fiber pretreatment. Select bamboo fibers with a length of 1-3 mm and soak them in a 3%-5% sodium hydroxide solution at a constant temperature of 60-70℃ for 2-3 hours, stirring at 60-80 rpm every 30 minutes. After soaking, rinse repeatedly with deionized water at 20-25℃ until the pH value reaches 6.8-7.2. Then, transfer them to a forced-air drying oven and dry them continuously at 80-90℃ for 4-5 hours, controlling the moisture content to 8%-10%, to obtain pretreated bamboo fibers. Enzymatic modification of the pretreated bamboo fibers. Place them in a 0.5%-1.0% cellulase solution at a constant temperature of 45-50℃ and stir at 40-60 rpm for 1.5-2 hours. After the reaction, rinse with deionized water until neutral and dry at 75-85℃ for 3-4 hours to obtain enzymatically modified bamboo fibers. Step 2: Raw material mixing and co-extrusion. Weigh out 30-40 parts by weight of enzymatically modified bamboo fiber, 25-35 parts by weight of modified polylactic acid, 15-25 parts by weight of polybutylene adipate-butyl terephthalate copolymer, 3-5 parts by weight of composite plasticizer, 1-2 parts by weight of surface-modified nano silica, and 0.5-1.5 parts by weight of calcium stearate. Add these to a high-speed mixer and mix at 100-110℃ and 1500-1800 r / min for 15-20 minutes. The mixture is then conveyed to a twin-screw extruder. The material is discharged from the machine with the barrel temperature set at 165-185℃, the first section at 165-170℃, the second section at 170-175℃, the third section at 175-180℃, and the fourth section at 180-185℃. The die head temperature is 175-185℃, the screw speed is 200-250 r / min, and the feeding speed is 20-30 kg / h. At the same time, vacuum exhaust ports are set in the third to fifth sections of the barrel to control the vacuum degree to -0.08 to -0.09 MPa. The material is then blended, extruded, and granulated to obtain granules with a diameter of 2-3 mm. Step 3: Tube drawing and post-processing. After the granules are cooled to 20-25℃, they are added to the hopper of the tube drawing machine. The heating temperature is set to 170-180℃, and the tube drawing speed is 1.5-2.5m / min to draw tubular blanks with an inner diameter of 5-8mm and a wall thickness of 0.3-0.5mm. The tubular blanks are transferred to a hot air oven and heat-treated at 110-120℃ for 8-10 minutes. After heat treatment, they are placed in a UV aging chamber with a wavelength of 280-320nm and an irradiation intensity of 0.8-1.0W / ㎡ for 2-3 hours. The UV-treated tubular blanks are then subjected to microwave cross-linking by placing them in a microwave processor with a frequency of 2450MHz and a power of 300-400W for 3-5 minutes. Finally, a 0.5%-1.0% tea polyphenol solution is sprayed onto the surface of the tube, with a spraying amount of 5-10g / ㎡. The tubes are then dried in a forced-air dryer at 50-60℃ for 1-2 minutes to obtain the finished product. This method enhances the reactivity of bamboo fiber through enzymatic modification and strengthens intermolecular bonds through microwave crosslinking, thereby synergistically improving the mechanical properties, degradation performance, and stability of the straw.

[0017] The modified polylactic acid preparation process is as follows: Step 1: Polylactic acid grafting modification. Weigh 100 parts of polylactic acid, 5-8 parts of maleic anhydride, and 0.8-1.2 parts of dicumyl peroxide according to the weight ratio. Add them to a high-speed mixer and mix at 800-1000 r / min for 15-20 minutes at 80-90℃. Feed the mixture into a twin-screw extruder and set the barrel temperature to 170-190℃, the first stage to 170-175℃, the second stage to 175-180℃, the third stage to 180-185℃, and the fourth stage to 185-190℃. Set the die temperature to 180-190℃ and the screw speed to 180-200 r / min. Extrude and granulate to obtain polylactic acid granules grafted with maleic anhydride. Step 2: Chitosan blending modification. Weigh 90-95 parts by weight of polylactic acid particles grafted with maleic anhydride and 5-10 parts by weight of chitosan, add them to a torque rheometer, set the temperature to 175-185℃ and the rotation speed to 60-80 r / min, and melt-blend for 10-15 minutes. During this time, add 1-2 parts by weight of nano-zinc oxide and continue stirring. After blending, cool to room temperature and pulverize into powder with a particle size of 0.1-0.3 mm to obtain modified polylactic acid. Through the three-step method of "grafting + blending + nanoparticle doping", polar groups are introduced into the polylactic acid molecular chain and combined with chitosan. At the same time, nano-zinc oxide is used to enhance the antibacterial properties, making the straw achieve an antibacterial rate of over 90% against Escherichia coli, while taking into account both hydrophilicity and antibacterial properties.

[0018] The preparation process of the surface-modified nano-silica: Step 1: Pretreatment of nano-silica. Select nano-silica with a particle size of 20-50nm, put it into a hydrochloric acid solution with a mass concentration of 5%-8%, and stir at 40-50℃ for 1-2 hours; then wash with deionized water until the pH value is 7.0-7.2, and vacuum dry at 70-80℃ for 3-4 hours to obtain purified nano-silica. The silane coupling agent modification involves adding purified nano-silica to a 2%-3% (w / w) ethanol solution of silane coupling agent KH-550 at a solid-liquid ratio of 1:10-1:15. The mixture is stirred in a constant-temperature water bath at 50-60℃ at 150-200 rpm for 2-3 hours, during which a 0.3%-0.5% (w / w) polyvinyl alcohol solution (volume ratio to silane coupling agent ethanol solution 1:5-1:8) is added. After the reaction, the mixture is centrifuged (3000-4000 rpm for 15-20 minutes), and the precipitate is washed 3-4 times with anhydrous ethanol and vacuum dried at 70-80℃ for 3-4 hours to obtain surface-modified nano-silica. Polyvinyl alcohol-assisted modification further enhances the compatibility of nano-silica with polymer materials, prevents agglomeration, and strengthens the flexibility of the straw, resulting in an additional 5%-8% increase in elongation at break.

[0019] The composite plasticizer is prepared by mixing tributyl citrate and epoxidized soybean oil in a weight ratio of 8-9:1-2. The mixing process is carried out in a constant temperature water bath at 40-50℃ and stirred at 100-150 rpm for 10-15 minutes. After mixing, 0.2-0.5 parts of polyethylene glycol 400 are added, and stirring is continued for 5-8 minutes until fully integrated to ensure the synergistic effect of the three components. This composite plasticizer maintains the plasticizing efficiency of tributyl citrate, enhances thermal stability through epoxidized soybean oil, and strengthens the interfacial bonding with bamboo fiber with polyethylene glycol, thereby increasing the heat distortion temperature of the straw by 10-15℃. At the same time, the plasticizer migration is controlled below 0.5%, extending the service life.

[0020] Before mixing the enzymatically modified bamboo fiber with other raw materials, it needs to undergo plasma surface activation: the enzymatically modified bamboo fiber is placed in the reaction chamber of a plasma treatment instrument, and a vacuum is drawn to 1-5 Pa; then, an oxygen-nitrogen mixed gas (volume ratio 3:7-4:6) is introduced, with a flow rate controlled at 10-15 L / min, maintaining a chamber pressure of 10-20 Pa; the power is set to 200-300 W, and the treatment lasts for 5-10 minutes, allowing the mixed gas plasma to bombard the surface of the bamboo fiber, introducing polar groups such as hydroxyl and carboxyl groups. After activation, the contact angle of the bamboo fiber surface decreases from 70°-80° to 30°-40°, the hydrophilicity is significantly improved, and the interfacial bonding force with modified polylactic acid and polybutylene adipate-butyl terephthalate copolymer is enhanced by more than 30%, effectively reducing delamination during use.

[0021] The polybutylene adipate-butyl terephthalate copolymer requires pre-crystallization before use: It is placed in a vacuum drying oven, evacuated to -0.09 to -0.1 MPa, and preheated at 60-70°C for 1-2 hours; then heated to 90-100°C, maintaining the vacuum for 2-3 hours, during which argon gas is introduced every 30 minutes at a flow rate of 5-8 L / min for 10-15 seconds; after holding at this temperature, it is naturally cooled to room temperature, pulverized, and passed through a 100-120 mesh sieve to obtain particles with a diameter of 0.1-0.3 mm. Pre-crystallization, combined with inert gas assistance, increases the copolymer's crystallinity from 30%-35% to 45%-50% and ensures uniform crystallization, improving its compatibility with bamboo fiber and modified polylactic acid, and reducing the fluctuation range of the straw's tensile strength to ±2 MPa.

[0022] The tube drawing employs segmented cooling: the first segment is water cooling, where the tubular blank is immediately placed into a 15-20℃ cooling water bath with a controlled water flow rate of 0.5-1m / s for 1-2 minutes. Glycerin with a mass concentration of 0.1%-0.2% is added to the water bath and thoroughly mixed. The second segment is air cooling, where the water-cooled tubular blank is placed into an air-cooling channel with a wind speed of 3-5m / s and a wind temperature of 20-25℃ for 0.5-1 minutes, allowing the internal temperature to uniformly drop to 25-30℃. This method avoids excessive temperature differences between the inside and outside of the tube, preventing internal stress, deformation, and improving surface smoothness, reducing straightness error to 0.1-0.2mm / m.

[0023] Before spraying the tea polyphenol solution, the surface of the microwave-crosslinked pipette needs to be cleaned.

[0024] Place the straw in a 0.5%-1% sodium bicarbonate solution and stir at 50-80 rpm for 5-8 minutes at 30-40℃, adding 0.2%-0.3% sodium dodecylbenzenesulfonate during this time to enhance the cleaning effect. Then rinse with deionized water until the pH reaches 7.0-7.2, and dry in a forced-air dryer at 60-70℃ for 3-5 minutes, controlling the surface moisture content to 3%-5%. This cleaning treatment ensures uniform adhesion of the tea polyphenol solution, forming a continuous and complete protective film, preventing voids, and improving the straw's oil resistance by more than 20%, with no significant swelling within 24 hours of contact with edible oil.

[0025] The high-speed mixing of raw materials employs a stepped heating method: an initial temperature of 50-60℃, stirred for 5 minutes; then, heating at a rate of 10℃ / min to 80-90℃, stirred for 5 minutes, during which 0.3-0.6 parts of talc powder are added; finally, heating at a rate of 5℃ / min to 100-110℃, stirred for 5-10 minutes. This method avoids localized overheating and degradation of the raw materials due to rapid heating, allowing raw materials with different melting points to gradually soften and mix evenly. Simultaneously, the use of talc powder improves material flowability, increasing mixing uniformity by more than 15%, and reducing the maximum difference in elongation at break across different parts of the straw to 1%-2%.

[0026] The twin-screw extruder employs an intermeshing screw with a length-to-diameter ratio of 40:1. The screw groove depth gradually decreases from the feeding section to the extrusion section (10-12 mm in the feeding section, 8-10 mm in the compression section, and 5-7 mm in the metering section). Furthermore, 3-5 staggered shear pins (3-5 mm in diameter and 2-3 mm in height) are installed in the compression section. The intermeshing screw, specific length-to-diameter ratio, and shear pins synergistically enhance shear mixing, resulting in more complete melting and more uniform dispersion of the raw material. Melting time is shortened by 10%-15%, and the fluctuation range of the extruded particle melt flow rate is reduced to ±0.2 g / 10 min, providing a stable quality raw material for the tube drawing process.

[0027] Embodiments of the present invention Example 1 Pretreatment of bamboo chips: Select bamboo chips for initial screening to screen out bamboo fibers with a length of 1-2 mm; place the bamboo fibers in a steam explosion device and treat them at a pressure of 0.8 MPa and a temperature of 180℃ for 5 minutes. Then wash them with water to remove impurities and put them into a drying device to dry them at 80℃ until the moisture content is ≤8%, thus completing the pretreatment.

[0028] Preparation of modified plastic granules: Polybutylene adipate-butylene terephthalate (PBAT) was used as a biodegradable plastic. It was preheated at 60℃ for 30 min, cooled to room temperature, and then mixed with pretreated bamboo fiber at a mass ratio of 9:1. Antioxidant 1010 was added at 0.5% of the total mass of the mixture. The mixture was then placed in a twin-screw extruder and granulated at 160℃ to obtain modified plastic granules.

[0029] Straw Forming: Modified plastic granules are injected into a ring mold using a microporous foaming extrusion molding machine. The mold is then directionally heated at 170℃, with the extrusion speed controlled at 1m / min. After cooling, the straws are cut into 20cm long straws, yielding biodegradable bamboo fiber straws. These straws show no moisture absorption or deformation after being placed in an environment of 25℃ and 60% relative humidity for 72 hours. They maintain good firmness after holding 80℃ hot drinks for 30 minutes and naturally degrade within 6 months of disposal.

[0030] Example 2 Bamboo chip fiber pretreatment: The bamboo chips are initially screened to select bamboo fibers with a length of 2-3 mm; steam explosion treatment is carried out at 1.0 MPa pressure and 190℃ for 6 min, followed by water washing and drying at 85℃ until the moisture content is ≤8%.

[0031] Preparation of modified plastic granules: Polylactic acid (PLA) was selected as the biodegradable plastic. It was preheated at 70℃ for 40 minutes, cooled, and then mixed with pretreated bamboo fiber at a mass ratio of 8:2. Toughening agent ACR was added at a mass ratio of 0.8% of the total mass of the mixture, and then granulated at 170℃.

[0032] Straw forming: The granules are injected into a ring mold, directionally heated at 180℃, extruded at a speed of 0.8m / min, and cut into 22cm straws. The straws do not soften after holding 4℃ cold drinks for 24 hours, do not absorb moisture or deform after being placed in an environment of 25℃ and 70% relative humidity for 96 hours, and naturally degrade within 8 months after disposal.

[0033] Example 3 Bamboo fiber pretreatment: bamboo fibers with a length of 0.5-1mm are screened, steam-exploded at 0.9MPa pressure and 185℃ for 4 minutes, washed with water and dried at 82℃ until the moisture content is ≤8%.

[0034] Preparation of modified plastic granules: A composite biodegradable plastic was prepared by mixing PBAT and PLA at a mass ratio of 1:1, preheating at 65℃ for 35 minutes, cooling, and then mixing the composite plastic with pretreated bamboo fiber at a mass ratio of 8.5:1.5. Antioxidant 1076 was added at a mass ratio of 0.6% of the total mass of the mixture, and then granulated at 165℃.

[0035] Straw forming: The ring mold is directionally heated to 175℃, the extrusion speed is 0.9m / min, and it is cut into 18cm straws. The straw holds its shape after holding a 60℃ beverage for 1 hour, does not absorb moisture after being placed in an environment of 25℃ and 65% relative humidity for 84 hours, and degrades naturally within 7 months after disposal.

[0036] Comparative Example 1, without steam explosion pretreatment: Bamboo chip fiber processing: Select bamboo chips through a primary sieve to screen out bamboo fibers with a length of 1-2mm. After directly washing to remove impurities, dry at 80℃ until the moisture content is ≤8%. No steam explosion treatment is performed.

[0037] Preparation of modified plastic granules: Same as in Example 1, PBAT was used as the biodegradable plastic, preheated at 60°C for 30 min, cooled and mixed at a mass ratio of PBAT to bamboo fiber of 9:1, 0.5% antioxidant 1010 was added, and the mixture was granulated at 160°C.

[0038] Straw forming: Same as in Example 1, directional heating at 170℃ and extrusion speed of 1m / min to obtain a 20cm straw.

[0039] Performance results: After being placed in an environment of 25℃ and 60% relative humidity for 48 hours, obvious moisture absorption and deformation occurred; after holding 80℃ hot drinks for 15 minutes, the stiffness decreased and the tube wall showed slight softening; after disposal, the degradation period was extended to 9 months, and the degradation was uneven.

[0040] Comparative Example 2: The proportion of bamboo fiber added was too high. Bamboo fiber pretreatment: Same as in Example 2, 2-3 mm bamboo fibers were screened, steamed at 1.0 MPa and 190℃ for 6 min, and dried at 85℃ until the moisture content was ≤8%.

[0041] Preparation of modified plastic granules: PLA was selected as a biodegradable plastic, preheated at 70°C for 40 min, and after cooling, it was mixed with bamboo fiber at a mass ratio of 6:4 (the proportion of bamboo fiber was higher than 20% in Example 2), and 0.8% toughening agent ACR was added. The mixture was then granulated at 170°C.

[0042] Straw forming: Same as in Example 2, directional heating at 180°C and extrusion speed of 0.8 m / min were used to obtain a 22 cm straw.

[0043] Performance results: Fiber agglomeration occurred during the granule mixing process, and obvious air bubbles and impurities were present on the straw wall after molding; after holding 4°C cold drinks for 12 hours, the straw became brittle; after being placed in an environment of 25°C and 70% relative humidity for 72 hours, the moisture absorption deformation reached 15%, which far exceeded the stable state of Example 2.

[0044] Comparative Example 3, without microporous foam extrusion molding: Bamboo fiber pretreatment: Same as in Example 3, 0.5-1mm bamboo fiber was screened, steamed at 0.9MPa and 185℃ for 4 minutes, and dried at 82℃ until the moisture content was ≤8%.

[0045] Preparation of modified plastic granules: Same as in Example 3, using PBAT and PLA 1:1 composite plastic, preheated at 65℃ for 35 min, bamboo fiber mixed in a ratio of 8.5:1.5, 0.6% antioxidant 1076 added, and mixed and granulated at 165℃.

[0046] Straw forming: Using ordinary extrusion molding equipment (without microporous foaming technology), heating at 175℃ and extrusion speed of 0.9m / min, 18cm straws were produced.

[0047] Performance results: The straw wall density is too high, and the weight increases by 20% compared with Example 3. It feels hard when used. After holding a 60°C beverage for 30 minutes, the straw wall shrinks slightly, while the straw in Example 3 does not show obvious changes. The degradation period after disposal is 8.5 months, which is longer than the 7 months of Example 3.

[0048] Explanation of Embodiments and Comparative Examples of the Invention and Table of Detection Results Example and Comparative Example Design Description Examples 1-3 are based on the core process of this invention, namely "pretreatment of bamboo fiber chips (including steam explosion) - preparation of modified plastic granules (reasonable fiber ratio) - microporous foaming extrusion molding". Different bamboo fiber lengths, types of biodegradable plastics and additives were selected to verify the flexibility and stability of the process. Comparative Examples 1-3, through the design of single variables such as "omitting steam explosion pretreatment", "increasing the proportion of bamboo fiber added" and "replacing with ordinary extrusion molding", specifically verified the key impact of the core process of this invention on the performance of straws, highlighting the necessity of the technical solution of this invention.

[0049] II. Key Parameters and Test Results Table Note: "-" indicates that Comparative Example 2 did not complete the full degradation cycle test due to severe brittleness; heat resistance / cold resistance tests were all based on the target usage scenarios of the corresponding examples / comparative examples.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fully biodegradable bamboo fiber straw, characterized in that, It is composed of 30-40 parts by weight of enzymatically modified bamboo fiber, 25-35 parts of modified polylactic acid, 15-25 parts of polybutylene adipate-butyl terephthalate copolymer (PBAT), 3-5 parts of composite plasticizer, 1-2 parts of surface-modified nano silica, and 0.5-1.5 parts of calcium stearate. The process includes the following steps: Step 1: Bamboo fiber pretreatment. Select bamboo fibers with a length of 1-3 mm and immerse them in a 3%-5% sodium hydroxide solution. Soak them in a constant temperature water bath at 60-70℃ for 2-3 hours, stirring at 60-80 r / min every 30 minutes. After soaking, rinse repeatedly with deionized water at 20-25℃ until the pH value reaches 6.8-7.

2. Then transfer them to a forced-air drying oven and dry them continuously at 80-90℃ for 4-5 hours, controlling the moisture content to 8%-10%, to obtain pretreated bamboo fibers. Enzymatic modification of pretreated bamboo fiber was carried out by placing it in a 0.5%-1.0% (w / w) cellulase solution and stirring it at 40-60 r / min for 1.5-2 hours in a constant temperature water bath at 45-50℃. After the reaction, it was rinsed with deionized water until neutral and dried at 75-85℃ for 3-4 hours to obtain enzymatically modified bamboo fiber. Step 2: Raw material mixing and co-extrusion. Add the raw materials to a high-speed mixer according to the weight ratio and mix at 1500-1800 r / min for 15-20 minutes at 100-110℃. The mixture is then conveyed to a twin-screw extruder. The barrel temperature is set at 165-185℃, the first section at 165-170℃, the second section at 170-175℃, the third section at 175-180℃, and the fourth section at 180-185℃. The die temperature is set at 175-185℃, the screw speed is 200-250 r / min, and the feeding speed is 20-30 kg / h. At the same time, vacuum exhaust ports are set in the third to fifth barrel sections to control the vacuum degree to -0.08 to -0.09 MPa. Co-extrusion granulation is performed to obtain granules with a diameter of 2-3 mm. Step 3: Tube drawing and post-processing. After the granules are cooled to 20-25℃, they are added to the hopper of the tube drawing machine. The heating temperature is set to 170-180℃, and the tube drawing speed is 1.5-2.5m / min to draw tubular blanks with an inner diameter of 5-8mm and a wall thickness of 0.3-0.5mm. The tubular blanks are transferred to a hot air oven and heat-treated at 110-120℃ for 8-10 minutes. After heat treatment, they are placed in a UV aging chamber with a wavelength of 280-320nm and an irradiation intensity of 0.8-1.0W / ㎡ for 2-3 hours. The UV-treated tubular blanks are then subjected to microwave cross-linking by placing them in a microwave processor with a frequency of 2450MHz and a power of 300-400W for 3-5 minutes. Finally, a 0.5%-1.0% tea polyphenol solution is sprayed onto the surface of the tube, with a spraying amount of 5-10g / ㎡. The tubes are then dried in a forced-air dryer at 50-60℃ for 1-2 minutes to obtain the finished product.

2. The bamboo fiber fully biodegradable straw according to claim 1, characterized in that, The modified polylactic acid preparation process is as follows: Step 1: Polylactic acid grafting modification. Weigh 100 parts of polylactic acid, 5-8 parts of maleic anhydride, and 0.8-1.2 parts of dicumyl peroxide according to the weight ratio. Add them to a high-speed mixer and mix at 800-1000 r / min for 15-20 minutes at 80-90℃. Feed the mixture into a twin-screw extruder and set the barrel temperature to 170-190℃, the first stage to 170-175℃, the second stage to 175-180℃, the third stage to 180-185℃, and the fourth stage to 185-190℃. Set the die temperature to 180-190℃ and the screw speed to 180-200 r / min. Extrude and granulate to obtain polylactic acid granules grafted with maleic anhydride. Step 2: Chitosan blending modification. Weigh 90-95 parts of polylactic acid granules grafted with maleic anhydride and 5-10 parts of chitosan according to the weight ratio, add them to a torque rheometer, set the temperature to 175-185℃ and the rotation speed to 60-80r / min, melt blend for 10-15 minutes, add 1-2 parts of nano zinc oxide during the process and stir continuously; after blending, cool to room temperature, pulverize into powder with a particle size of 0.1-0.3mm to obtain modified polylactic acid.

3. The bamboo fiber fully biodegradable straw according to claim 1, characterized in that, The preparation process of the surface-modified nano-silica: Step 1: Pretreatment of nano-silica. Select nano-silica with a particle size of 20-50nm, put it into a hydrochloric acid solution with a mass concentration of 5%-8%, and stir at 40-50℃ for 1-2 hours; then wash with deionized water until the pH value is 7.0-7.2, and vacuum dry at 70-80℃ for 3-4 hours to obtain purified nano-silica. Step 2: Silane coupling agent modification. Purified nano-silica is added to a 2%-3% (w / w) ethanol solution of silane coupling agent KH-550 at a solid-liquid ratio of 1:10-1:

15. The mixture is stirred in a constant temperature water bath at 50-60℃ at a speed of 150-200 r / min for 2-3 hours. During this time, a 0.3%-0.5% (w / w) polyvinyl alcohol solution is added, with a volume ratio of 1:5-1:8 between the polyvinyl alcohol solution and the silane coupling agent ethanol solution. After the reaction, the mixture is centrifuged at 3000-4000 r / min for 15-20 minutes. The precipitate is washed 3-4 times with anhydrous ethanol and then vacuum dried at 70-80℃ for 3-4 hours to obtain surface-modified nano-silica.

4. The bamboo fiber fully biodegradable straw according to claim 1, characterized in that, The composite plasticizer is prepared by mixing tributyl citrate and epoxidized soybean oil in a weight ratio of 8-9:1-2. The mixing process is carried out in a constant temperature water bath at 40-50℃ and stirred at 100-150r / min for 10-15 minutes. After mixing, 0.2-0.5 parts of polyethylene glycol 400 are added, and stirring is continued for 5-8 minutes until completely integrated to ensure the synergistic effect of the three.

5. A bamboo fiber fully biodegradable straw according to claim 1, characterized in that, Before mixing enzymatically modified bamboo fiber with other raw materials, plasma surface activation is required: place the enzymatically modified bamboo fiber into the reaction chamber of the plasma treatment instrument and evacuate to 1-5 Pa; then introduce a mixed oxygen and nitrogen gas, control the flow rate to 10-15 L / min, and maintain the chamber pressure at 10-20 Pa; set the power to 200-300 W and treat for 5-10 minutes, so that the mixed gas plasma bombards the surface of the bamboo fiber and introduces polar groups such as hydroxyl and carboxyl groups.

6. The bamboo fiber fully biodegradable straw according to claim 1, characterized in that, Polybutylene adipate-butylene terephthalate copolymer needs to be pre-crystallized before use: place it in a vacuum drying oven, evacuate to -0.09 to -0.1 MPa, and preheat at 60-70℃ for 1-2 hours; then raise the temperature to 90-100℃, maintain the vacuum and keep it at that temperature for 2-3 hours, during which argon gas is introduced every 30 minutes at a flow rate of 5-8 L / min for 10-15 seconds; after keeping it at that temperature, let it cool naturally to room temperature, crush it and pass it through a 100-120 mesh sieve to obtain particles with a particle size of 0.1-0.3 mm.

7. A bamboo fiber fully biodegradable straw according to claim 1, characterized in that, The tube drawing process employs segmented cooling: the first segment is water cooling, where the tubular billet is immediately placed into a 15-20℃ cooling water bath, with the water flow rate controlled at 0.5-1m / s, and cooled for 1-2 minutes. Glycerin with a mass concentration of 0.1%-0.2% is added to the water bath and thoroughly mixed. The second segment is air cooling, where the water-cooled tubular billet is placed into an air cooling channel, with the air velocity set at 3-5m / s and the air temperature at 20-25℃, and cooled for 0.5-1 minutes to uniformly reduce the internal temperature to 25-30℃.

8. A bamboo fiber fully biodegradable straw according to claim 1, characterized in that, Before spraying the tea polyphenol solution, the surface of the pipette after microwave cross-linking needs to be cleaned.

9. A bamboo fiber fully biodegradable straw according to claim 1, characterized in that, When mixing raw materials at high speed, a step-wise heating method is used: the initial temperature is 50-60℃, and the mixture is stirred for 5 minutes; then the temperature is increased to 80-90℃ at a rate of 10℃ / min, and the mixture is stirred for 5 minutes, during which 0.3-0.6 parts of talc powder are added; finally, the temperature is increased to 100-110℃ at a rate of 5℃ / min, and the mixture is stirred for 5-10 minutes.

10. A bamboo fiber fully biodegradable straw according to claim 1, characterized in that, The twin-screw extruder uses an interlocking screw with a length-to-diameter ratio of 40:

1. The screw groove depth gradually decreases from the feeding section to the extrusion section, and 3-5 staggered shear pins are set in the compression section.

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