Water-soluble degradable fiber and preparation method thereof

Abstract

The invention relates to the technical field of degradable materials, and discloses a water-soluble degradable fiber and a preparation method thereof. The water-soluble degradable fiber disclosed by the invention is prepared by taking polylactic acid as a main matrix, adding modified sodium lignin sulfonate, polyvinyl alcohol and polyethylene wax, blending, carrying out melt extrusion, and carrying out melt spinning. The fiber has water solubility, degradability, sand carrying performance and salt resistance, and has a good application prospect in a fracturing fluid used in a well drilling fracturing process based on the advantages of water solubility, degradability, sand carrying performance and salt resistance.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials technology, specifically to a water-soluble biodegradable fiber and its preparation method. Background Technology

[0002] In the development of unconventional oil and gas resources (such as shale gas and tight oil), horizontal well drilling and multi-stage hydraulic fracturing are core technologies. In this process, the performance of drilling fluid and fracturing fluid is crucial, as they need to perform multiple tasks such as carrying cuttings, stabilizing the wellbore, cooling the drill bit, creating fractures, and carrying proppant. However, traditional technologies face the following severe challenges: (1) Low proppant carrying efficiency. If the proppant carrying capacity is insufficient, the proppant will settle rapidly, leading to sand blockage in the near-wellbore zone, or only forming a sand dam at the bottom of the fracture, which cannot effectively support the entire fracture height and seriously affects the fracturing effect; (2) Reservoir damage. Polymers (such as guar gum) and chemical additives in traditional fracturing fluids may remain in the formation, blocking the micropores of oil and gas flow, leading to a decrease in reservoir permeability and affecting the final recovery rate.

[0003] Polylactic acid (PLA), as a green polymer material with renewable sources and ultimate biodegradability into carbon dioxide and water, has long been introduced into the field of oilfield chemistry. However, traditional PLA fibers face several key technical bottlenecks: (1) hydrophobicity and insolubility in water limit the degradation efficiency of the fibers; (2) the degradation rate is controlled by formation temperature and pH; and (3) the application environment is limited, and its solubility and dispersion performance are easily affected in highly saline formation water or brine. To overcome these technical bottlenecks, researchers have turned their attention to functional fiber materials. Water-soluble biodegradable fibers, as a new type of smart responsive material, have been introduced into drilling fracturing fluids, providing an innovative solution to traditional problems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a water-soluble biodegradable fiber and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions: A water-soluble biodegradable fiber comprising the following raw materials in parts by weight: 50-60 parts polylactic acid, 25-35 parts modified sodium lignosulfonate, 8-12 parts polyvinyl alcohol, and 1.5-3.5 parts polyethylene wax. The modified sodium lignin sulfonate is prepared by the following steps: Step A1: Dissolve sodium lignosulfonate and sodium hydroxide in water by stirring. Add diethylenetriamine and stir for 10 minutes. Heat to 85°C and slowly add 36wt% formaldehyde aqueous solution. Stir for 4-6 hours under reflux. Cool to room temperature and add 1mol / L hydrochloric acid dropwise until no brown precipitate forms. Filter, wash, dry, grind, wash twice, and dry twice to obtain amino-modified sodium lignosulfonate. Further, the washing in step A1 is to wash three times each with isopropanol and petroleum ether, and the second washing is to wash three times with deionized water. Furthermore, in step A1, the ratio of sodium lignosulfonate, sodium hydroxide, water, diethylenetriamine, and formaldehyde aqueous solution is 20g:0.8-1.2g:50mL:5-7g:8-10mL; Step A2: After stirring the amino-modified sodium lignosulfonate and triethylamine in dichloromethane, transfer the mixture to an ice-water bath, add dimethyl chlorophosphate, maintain the temperature and stir for 1 hour, then raise the temperature to room temperature and stir for 12 hours. Filter, wash and dry to obtain phosphate-modified sodium lignosulfonate. Furthermore, in step A2, the ratio of sodium amino-modified lignin sulfonate, triethylamine, dichloromethane, and dimethyl chlorophosphate is 10g:0.1-0.3mol:100mL:0.1-0.3mol; Step A3: Stir the nanofiller in a mixture of ethanol and water until homogeneous, then add 3-chloropropyltrimethoxysilane and reflux for 5-7 hours. Rotary evaporate and dry to obtain the modified nanofiller. Furthermore, in step A3, the ratio of nanofiller, ethanol, water, and 3-chloropropyltrimethoxysilane is 2g:30mL:10mL:0.1-0.3mL; Furthermore, the nanofiller mentioned in step A3 is one of nano-silica, nano-zinc oxide, or nano-calcium carbonate; Step A4: Under nitrogen atmosphere, stir the modified nanofiller, N,N-dimethylformamide and triethylamine evenly, then add phosphate-modified sodium lignosulfonate, and heat to 85℃ and reflux for 4-6 hours. After rotary evaporation, washing and drying, the modified sodium lignosulfonate is obtained. Furthermore, in step A4, the ratio of modified nanofiller, N,N-dimethylformamide, triethylamine, and phosphate-modified sodium lignosulfonate is 1-2g:100mL:1.5-2.5mL:10g.

[0006] A method for preparing a water-soluble biodegradable fiber includes the following steps: Weigh the raw materials according to the weight parts, add polylactic acid, modified sodium lignosulfonate, polyvinyl alcohol and polyethylene wax into a mixer and stir evenly, then transfer to a twin-screw extruder for extrusion at a temperature of 180-200℃, cool to room temperature, and then melt spin to obtain water-soluble biodegradable fiber. Furthermore, during the melt spinning process, the aspect ratio of the spinneret is controlled at 2.30-2.50, and the spinning speed is 800-1000 m / min.

[0007] The beneficial effects of this invention are: The water-soluble biodegradable fiber of this invention is prepared by melt extrusion of polylactic acid as the main matrix, followed by the addition of modified sodium lignosulfonate, polyvinyl alcohol and polyethylene wax, and then melt spinning. This fiber has water solubility, biodegradability, sand carrying capacity and salt resistance. Based on these advantages, it has good application prospects in fracturing fluids used in drilling and fracturing processes.

[0008] When the water-soluble biodegradable fibers of this invention are dispersed in fracturing fluid, they interweave and overlap to form a weakened "three-dimensional fiber network structure" that runs through the entire liquid. This fiber network is like an extremely fine net that can effectively support proppant particles and greatly hinder their sedimentation. Even if the viscosity of the liquid itself is not high, the fiber network can prevent the proppant from sinking rapidly through physical action, thereby improving the static suspension capacity.

[0009] The introduction of modified sodium lignosulfonate not only improves the biodegradability, water solubility, and salt resistance of the fiber, but also enhances its sand-carrying capacity during fracturing. Specifically, the introduction of hydrophilic groups (ether bonds, sulfonic acid groups) on modified sodium lignosulfonate increases the overall hydrophilicity of the PLA fiber, accelerating the penetration and diffusion of water molecules into the fiber interior. This speeds up the hydrolysis reaction. Under the influence of formation water and temperature, the ester bonds of PLA undergo hydrolysis, breaking long molecular chains into short-chain lactic acid oligomers, ultimately generating lactic acid. As the molecular chains break down, the mechanical strength of the fiber rapidly decreases, disintegrating from a complete fiber structure into tiny fragments until it completely dissolves in water, preventing permanent blockage of the formation. The phosphate ester groups introduced into modified sodium lignosulfonate also enhance the hydrophilicity of divalent cations (such as Ca²⁺, Ca²⁺, and Ca²⁺). 2+ Mg 2+It possesses excellent complexing ability. In highly mineralized brine, phosphate groups preferentially complex with divalent cations and other ions that easily cause precipitation or destabilize the fiber, forming soluble complexes. This "shields" the negative impact of these ions on the hydrolysis process and fiber network structure of PLA fibers. By complexing away interfering ions, it provides PLA fibers with a relatively more stable and controllable hydrolysis environment, ensuring that its performance can be maintained and degraded as expected in brine. Furthermore, sodium lignosulfonate itself is a natural high-molecular surfactant and dispersant. In melt spinning, it helps the raw materials to mix more evenly, thereby enabling the modified fibers to be better dispersed into individual fibers in fracturing fluid, preventing fiber agglomeration, and forming a more uniform and stable three-dimensional network structure, which greatly improves sand carrying efficiency. In addition, the nanofillers introduced into the modified sodium lignosulfonate also improve the surface roughness of the fiber. The rough surface can increase the contact area between the proppant and the fiber, forming a more stable mechanical lock, reducing the risk of proppant detachment, and at the same time slowing down the settling speed of the proppant in the fracturing fluid, thus improving the proppant carrying efficiency. Detailed Implementation

[0010] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0011] Example 1: Modified sodium lignosulfonate was prepared by the following steps: Step A1: Dissolve 20g sodium lignosulfonate and 0.8g sodium hydroxide in 50mL of water. Add 5g diethylenetriamine and stir for 10min. Heat to 85℃ and slowly add 8mL of 36wt% formaldehyde aqueous solution. Stir for 4h under reflux. Cool to room temperature and add 1mol / L hydrochloric acid until no brown precipitate forms. Filter, wash three times each with isopropanol and petroleum ether, dry, grind, wash three times with deionized water, and dry twice to obtain amino-modified sodium lignosulfonate. Step A2: After stirring 10g of amino-modified sodium lignosulfonate and 0.1mol of triethylamine in 100mL of dichloromethane, transfer the mixture to an ice-water bath, add 0.1mol of dimethyl chlorophosphate, maintain the temperature and stir for 1h, then raise the temperature to room temperature and stir for 12h. Filter, wash and dry to obtain phosphate-modified sodium lignosulfonate. Step A3: Stir 2g of nano-calcium carbonate in a mixture of 30mL ethanol and 10mL water until homogeneous, then add 0.1mL of 3-chloropropyltrimethoxysilane and reflux for 5h. Rotary evaporate and dry to obtain the modified nanofiller. Step A4: Under nitrogen atmosphere, stir 1g of modified nanofiller, 100mL of N,N-dimethylformamide and 1.5mL of triethylamine evenly, then add 10g of phosphate-modified sodium lignosulfonate, and heat to 85℃ and reflux for 4h. After rotary evaporation, washing and drying, the modified sodium lignosulfonate is obtained.

[0012] Example 2: Modified sodium lignosulfonate was prepared by the following steps: Step A1: Dissolve 20g sodium lignosulfonate and 1g sodium hydroxide in 50mL of water. Add 6g diethylenetriamine and stir for 10min. Heat to 85℃ and slowly add 9mL of 36wt% formaldehyde aqueous solution. Stir for 5h under reflux. Cool to room temperature and add 1mol / L hydrochloric acid until no brown precipitate forms. Filter, wash three times each with isopropanol and petroleum ether, dry, grind, wash three times with deionized water, and dry twice to obtain amino-modified sodium lignosulfonate. Step A2: After stirring 10g of amino-modified sodium lignosulfonate and 0.2mol of triethylamine in 100mL of dichloromethane, transfer the mixture to an ice-water bath, add 0.2mol of dimethyl chlorophosphate, maintain the temperature and stir for 1h, then raise the temperature to room temperature and stir for 12h. Filter, wash and dry to obtain phosphate-modified sodium lignosulfonate. Step A3: Stir 2g of nano zinc oxide in a mixture of 30mL ethanol and 10mL water until homogeneous, then add 0.2mL of 3-chloropropyltrimethoxysilane and reflux for 6h. Rotary evaporate and dry to obtain the modified nanofiller. Step A4: Under nitrogen atmosphere, stir 1.5g of modified nanofiller, 100mL of N,N-dimethylformamide and 2mL of triethylamine evenly, then add 10g of phosphate-modified sodium lignosulfonate, and heat to 85℃ and reflux for 5h. After rotary evaporation, washing and drying, the modified sodium lignosulfonate is obtained.

[0013] Example 3: Modified sodium lignosulfonate was prepared by the following steps: Step A1: Dissolve 20g sodium lignosulfonate and 1.2g sodium hydroxide in 50mL of water. Add 7g diethylenetriamine and stir for 10min. Heat to 85℃ and slowly add 10mL of 36wt% formaldehyde aqueous solution. Stir for 6h under reflux. Cool to room temperature and add 1mol / L hydrochloric acid until no brown precipitate forms. Filter, wash three times each with isopropanol and petroleum ether, dry, grind, wash three times with deionized water, and dry twice to obtain amino-modified sodium lignosulfonate. Step A2: After stirring 10g of amino-modified sodium lignosulfonate and 0.3mol of triethylamine in 100mL of dichloromethane, transfer the mixture to an ice-water bath, add 0.3mol of dimethyl chlorophosphate, maintain the temperature and stir for 1h, then raise the temperature to room temperature and stir for 12h. Filter, wash and dry to obtain phosphate-modified sodium lignosulfonate. Step A3: Stir 2g of nano-silica in a mixture of 30mL ethanol and 10mL water until homogeneous, then add 0.3mL of 3-chloropropyltrimethoxysilane and reflux for 7h. Rotary evaporate and dry to obtain the modified nanofiller. Step A4: Under nitrogen atmosphere, stir 2g of modified nanofiller, 100mL of N,N-dimethylformamide and 2.5mL of triethylamine evenly, then add 10g of phosphate-modified sodium lignosulfonate, and heat to 85℃ and reflux for 6h. After rotary evaporation, washing and drying, the modified sodium lignosulfonate is obtained.

[0014] Example 4: A method for preparing a water-soluble biodegradable fiber includes the following steps: 50 parts of polylactic acid, 25 parts of modified sodium lignosulfonate prepared in Example 1, 8 parts of polyvinyl alcohol, and 1.5 parts of polyethylene wax. The raw materials were weighed according to the weight proportions. Polylactic acid, modified sodium lignosulfonate prepared in Example 1, polyvinyl alcohol and polyethylene wax were added to a mixer and stirred evenly. The mixture was then transferred to a twin-screw extruder for extrusion at a temperature of 180°C. After cooling to room temperature, the mixture was melt-spun to obtain water-soluble biodegradable fiber. During the melt spinning process, the spinneret length-to-diameter ratio was controlled at 2.30 and the spinning speed was 800 m / min.

[0015] Example 5: A method for preparing a water-soluble biodegradable fiber includes the following steps: 55 parts of polylactic acid, 30 parts of modified sodium lignosulfonate prepared in Example 2, 10 parts of polyvinyl alcohol, and 2.5 parts of polyethylene wax; The raw materials were weighed according to the weight proportions. Polylactic acid, modified sodium lignosulfonate prepared in Example 2, polyvinyl alcohol and polyethylene wax were added to a mixer and stirred evenly. The mixture was then transferred to a twin-screw extruder for extrusion at a temperature of 190°C. After cooling to room temperature, the mixture was melt-spun to obtain water-soluble biodegradable fiber. During the melt spinning process, the spinneret length-to-diameter ratio was controlled at 2.40 and the spinning speed was 900 m / min.

[0016] Example 6: A method for preparing a water-soluble biodegradable fiber includes the following steps: 60 parts of polylactic acid, 35 parts of modified sodium lignosulfonate prepared in Example 3, 12 parts of polyvinyl alcohol, and 3.5 parts of polyethylene wax; The raw materials were weighed according to the weight proportions. Polylactic acid, modified sodium lignosulfonate prepared in Example 3, polyvinyl alcohol and polyethylene wax were added to a mixer and stirred evenly. The mixture was then transferred to a twin-screw extruder for extrusion at a temperature of 200°C. After cooling to room temperature, the mixture was melt-spun to obtain water-soluble biodegradable fiber. During the melt spinning process, the spinneret length-to-diameter ratio was controlled at 2.50 and the spinning speed was 1000 m / min.

[0017] Comparative Example 1: This comparative example is a biodegradable polylactic acid fiber.

[0018] Comparative Example 2: This comparative example is a biodegradable fiber. The difference between this example and Example 6 is that the modified sodium lignin sulfonate prepared in Example 3 was not added. All other aspects are the same.

[0019] Comparative Example 3: This comparative example is a biodegradable fiber. The difference between this example and Example 6 is that sodium lignosulfonate is used instead of the modified sodium lignosulfonate prepared in Example 3. All other aspects are the same.

[0020] The biodegradable fibers prepared in Examples 4-6 and Comparative Examples 1-3 were subjected to performance tests: Water solubility test: 50g of the biodegradable fibers prepared in Examples 4-6 and Comparative Examples 1-3 were respectively put into water at 80°C, kept at the temperature for 24h, filtered to remove the undissolved part, dried at 80°C for 2h, and then weighed to calculate the water solubility (%). Water solubility (%) = (weight before dissolution - weight remaining after dissolution) / weight before dissolution * 100%. Sand-carrying performance test: In accordance with the requirements of Q / SH10202676-2018 "Technical Requirements for Fibers for Fracturing", the reduction rate of static settling velocity of ceramsite was tested; Salt resistance test: The tensile strength of the fiber monofilament before and after being tested in a simulated high-salt environment was determined according to the test standard ISO11566. The high-salt solution consisted of 5 wt% sodium chloride solution, 3 wt% magnesium chloride solution, 2 wt% calcium chloride solution and the balance water. The fiber was soaked for 24 hours at room temperature. The test results are shown in Table 1: Table 1: Performance Test Results As can be seen from Table 1, the water-soluble biodegradable fiber prepared by this invention not only maintains high water solubility but also has excellent sand-carrying capacity and salt resistance, thus making it a promising candidate for application in drilling fracturing fluids.

[0021] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. A water-soluble biodegradable fiber, characterized in that, The raw materials include the following parts by weight: 50-60 parts of polylactic acid, 25-35 parts of modified sodium lignosulfonate, 8-12 parts of polyvinyl alcohol, and 1.5-3.5 parts of polyethylene wax. The modified sodium lignin sulfonate is prepared by the following steps: Step A1: Dissolve sodium lignosulfonate and sodium hydroxide in water by stirring. Add diethylenetriamine and stir for 10 minutes. Heat to 85°C and slowly add 36wt% formaldehyde aqueous solution. Stir for 4-6 hours under reflux. Cool to room temperature and add 1mol / L hydrochloric acid dropwise until no brown precipitate forms. Filter, wash, dry, grind, wash twice, and dry twice to obtain amino-modified sodium lignosulfonate. Step A2: After stirring the amino-modified sodium lignosulfonate and triethylamine in dichloromethane, transfer the mixture to an ice-water bath, add dimethyl chlorophosphate, maintain the temperature and stir for 1 hour, then raise the temperature to room temperature and stir for 12 hours. Filter, wash and dry to obtain phosphate-modified sodium lignosulfonate. Step A3: Stir the nanofiller in a mixture of ethanol and water until homogeneous, then add 3-chloropropyltrimethoxysilane and reflux for 5-7 hours. Rotary evaporate and dry to obtain the modified nanofiller. Step A4: Under nitrogen atmosphere, stir the modified nanofiller, N,N-dimethylformamide and triethylamine evenly, then add phosphate-modified sodium lignosulfonate, and reflux at 85°C for 4-6 hours. After rotary evaporation, washing and drying, the modified sodium lignosulfonate is obtained.

2. The water-soluble biodegradable fiber according to claim 1, characterized in that, The washing in step A1 consists of washing three times each with isopropanol and petroleum ether, and the second washing consists of washing three times with deionized water.

3. The water-soluble biodegradable fiber according to claim 1, characterized in that, In step A1, the ratio of sodium lignosulfonate, sodium hydroxide, water, diethylenetriamine, and formaldehyde aqueous solution is 20g:0.8-1.2g:50mL:5-7g:8-10mL.

4. The water-soluble biodegradable fiber according to claim 1, characterized in that, In step A2, the ratio of sodium aminated lignin sulfonate, triethylamine, dichloromethane, and dimethyl chlorophosphate is 10g:0.1-0.3mol:100mL:0.1-0.3mol.

5. The water-soluble biodegradable fiber according to claim 1, characterized in that, In step A3, the ratio of nanofiller, ethanol, water and 3-chloropropyltrimethoxysilane is 2g:30mL:10mL:0.1-0.3mL.

6. The water-soluble biodegradable fiber according to claim 1, characterized in that, The nanofiller mentioned in step A3 is one of nano-silica, nano-zinc oxide, or nano-calcium carbonate.

7. The water-soluble biodegradable fiber according to claim 1, characterized in that, In step A4, the ratio of modified nanofiller, N,N-dimethylformamide, triethylamine and phosphate-modified sodium lignosulfonate is 1-2g:100mL:1.5-2.5mL:10g.

8. A method for preparing the water-soluble biodegradable fiber according to any one of claims 1-7, characterized in that, Includes the following steps: Weigh the raw materials according to the weight proportions, add polylactic acid, modified sodium lignosulfonate, polyvinyl alcohol and polyethylene wax into a mixer and stir evenly, then transfer to a twin-screw extruder for extrusion at a temperature of 180-200℃, cool to room temperature, and then melt spin to obtain water-soluble biodegradable fiber.

9. The method for preparing a water-soluble biodegradable fiber according to claim 8, characterized in that, During the melt spinning process, the aspect ratio of the spinneret is controlled at 2.30-2.50, and the spinning speed is 800-1000 m / min.

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