Preparation method of rod-like porous polyvinyl alcohol xerogel

Abstract

The invention relates to a preparation method of rodlike porous polyvinyl alcohol xerogel. The xerogel is prepared from the following raw materials: polyvinyl alcohol, deionized water and a pore-forming agent in a mass ratio of (0.6-1.8) g: (9.4-8.2) g: (0.1-0.3) g. According to the rodlike porous polyvinyl alcohol xerogel, polyvinyl alcohol serves as a matrix, a porous structure is constructed in the mode that calcium carbonate reacts with hydrochloric acid to generate gas to form pores, the formed pore structure is uniform, a rodlike structure is obtained through solution extrusion molding, meanwhile, the gel structure is stable through physical and chemical cross-linking, and the gel has good biocompatibility. After ethanol treatment, freeze drying is performed, so that a pore structure can be well reserved. The rodlike xerogel is simple and convenient in preparation process, high in water absorption swelling rate and uniform in pore structure, has hydrophilicity and environment-friendly characteristics of PVA, is beneficial to physical adsorption due to the rodlike porous structure, and is a candidate material with application potential in the field of water body detection.

Description

Technical Field

[0001] The invention relates to the field of hydrogel materials, and in particular to a method for preparing rod-shaped porous polyvinyl alcohol xerogel. Background Art

[0002] Polyvinyl alcohol (PVA) hydrogel has important application value in medical dressings, tissue engineering, and environmental water testing due to its excellent biocompatibility, strong hydrophilicity, and adjustable physical properties. Porous materials are widely used in the field of detection, and their unique structural characteristics (high specific surface area, adjustable pore size distribution, surface functionalization capabilities, etc.) provide a material basis for highly sensitive and highly selective detection. Porous polyvinyl alcohol gel has the advantages of both porous materials and polyvinyl alcohol hydrogels. Its uniform pore structure, large specific surface area, and good hydrophilicity will show strong advantages in loading recognition molecules, enriching detection molecules, and adsorption rate, making it suitable for the field of water testing.

[0003] Traditional polyvinyl alcohol gels are typically cross-linked using freeze-thaw, chemical cross-linking, or UV light. These gels typically form sheets or blocks, with large cross-sectional curvatures that can easily lead to structural collapse. Conventional methods for preparing porous gels are prone to uneven pore size distribution, toxic reagent residues, and large pore sizes. Gel drying also faces challenges such as pore collapse caused by atmospheric pressure drying, loss of pore wall continuity during freeze-drying, and the high cost of supercritical drying equipment.

[0004] To address the above problems, the present invention uses calcium carbonate as a pore-forming agent and utilizes the reaction of calcium carbonate with hydrochloric acid to generate gas pores to construct a porous structure. The formed pore structure is relatively uniform, and a rod-shaped structure is obtained by solution extrusion molding. At the same time, boric acid cross-linking and freeze-thaw cycle processing are used to stabilize the gel structure. After ethanol treatment and freeze-drying, the pore structure can be well retained, thereby preparing a rod-shaped porous polyvinyl alcohol dry gel material that can be used for efficient water body detection. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a method for preparing rod-shaped porous polyvinyl alcohol xerogel.

[0006] The technical solution of the present invention is as follows: a polyvinyl alcohol aqueous solution of appropriate concentration, containing a pore-forming agent, is obtained by heating and stirring. A rod-shaped gel is obtained by solution extrusion and cross-linking with boric acid in a cross-linking agent solution. Simultaneously, the pore-forming agent reacts with the hydrochloric acid in the cross-linking agent to release gas, resulting in a uniform pore structure. During the cyclic freezing and thawing process, polyvinyl alcohol crystals are generated as physical cross-linking points, and the physical cross-linking structure further stabilizes the rod-shaped gel. Finally, the gel is soaked in ethanol to displace water molecules, allowing for a rapid freeze-drying process while preserving the pore structure without collapse.

[0007] The heating and stirring were as follows: sealed at 95°C and stirred at 1000 rpm for 3 h; The suitable concentrations of the polyvinyl alcohol aqueous solution are: 6wt%, 10wt%, 12wt%, 15wt% and 18wt%; The pore-forming agent and its content are: calcium carbonate and 1-3wt%; The crosslinking agent solution is a mixed solution of 1 wt% hydrochloric acid, 4 wt% boric acid and 3 wt% calcium chloride; The curing time is: 24 h; The freezing and thawing cycle was as follows: freezing at -20°C for 10 h and thawing at room temperature for 2 h, repeated three times; The ethanol soaking is: 12 h; The freeze drying step is as follows: freeze drying at -40°C for 4 h.

[0008] Beneficial effects of the present invention: The present invention achieves a rod-like structure through solution extrusion molding, while simultaneously stabilizing the gel structure through boric acid crosslinking and freeze-thaw cycles. Calcium carbonate, a pore-forming agent, is introduced into the gel matrix, and pores are formed by chemically reacting with hydrochloric acid to produce carbon dioxide gas. The gas escapes, leaving evenly distributed pores within the gel matrix, creating a porous framework with a high specific surface area and a suitable pore size distribution. After ethanol treatment and freeze-drying, the pore structure is well preserved.

[0009] The preparation method is simple to operate, has low production cost, does not use toxic cross-linking agents, is highly safe, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a photograph of the rod-shaped porous polyvinyl alcohol xerogel prepared in Example 5.

[0011] Figure 2 This is an SEM photograph of the rod-shaped porous polyvinyl alcohol xerogel prepared in Example 5. After the cross section of the rod-shaped gel is magnified 2000 times, the pore structure is uniform and the matrix structure is continuous and stable.

[0012] Figure 3 This is a time-swelling rate diagram of the rod-shaped porous polyvinyl alcohol xerogel prepared in Example 5. The swelling rate of the porous structure gel increases rapidly, reaching 167.5% at 10 minutes, while that of the non-porous structure gel is only 64.3%. The porous gel reaches swelling equilibrium at 120 minutes, with a swelling rate of 533.5%. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further illustrated and described below through specific implementation methods.

[0014] The swelling ratio (SR) detection method in the embodiment is as follows: The swelling rate of the dry gel was determined by weighing method. A certain mass (W0) of dry gel was immersed in deionized water. The surface water was absorbed with filter paper at different soaking times T (min). The mass (W t ), calculate the swelling rate at each time according to the formula: SR=(W t -W0) / W0·100%.

[0015] Example 1 (1) Weigh 0.6 g, 1.0 g, 1.2 g, 1.5 g, and 1.8 g of PVA, add 9.4 mL, 9.0 mL, 8.8 mL, 8.5 mL, and 8.2 mL of deionized water, respectively. Seal the solution and stir at 1000 rpm at 95 °C for 3 h to prepare PVA solutions with concentrations of 6 wt%, 10 wt%, 12 wt%, 15 wt%, and 18 wt%. (2) After the solution is cooled, the PVA solution is squeezed into a pre-prepared mixed cross-linking solution of boric acid (4 wt%) and calcium chloride (3 wt%) using a syringe in the form of a rod. After reacting for 24 h, the rods are rinsed with deionized water. By observing the morphology of rod-shaped gels of solutions with different concentrations, it was found that 6wt% and 10wt% PVA solutions were difficult to form, floated on the surface of the solution, and had irregular shapes. The PVA solution with a concentration of 18wt% had a high viscosity, was difficult to draw with the syringe, and would cause the syringe to clog, and the stirring process was difficult. PVA solutions with concentrations of 12wt% and 15wt% could form rod-shaped gels in the mixed cross-linking solution, but the PVA with a concentration of 12wt% partially melted after rinsing and had an unstable shape, while the PVA with a concentration of 15wt% had a stable shape, was easy to distinguish, was not melted, and had good elasticity. Therefore, a PVA solution with a concentration of 15wt% was selected for the subsequent experimental operations.

[0016] Example 2 (1) Weigh 1.5 g of PVA and 8.5 mL of deionized water, then add 0.1 g, 0.3 g, and 0.5 g of pore formers, respectively. Seal the container and stir at 1000 rpm at 95 °C for 3 h to prepare a 15 wt% PVA solution with 1 wt%, 3 wt%, and 5 wt% pore former concentrations. (2) After the solution is cooled, the PVA solution is squeezed into a pre-prepared mixed cross-linking solution of hydrochloric acid (1 wt%), boric acid (4 wt%), and calcium chloride (3 wt%) using a syringe in the form of a rod. After reacting for 24 h, the rod is rinsed with deionized water. The pore-forming agent used in the example is calcium carbonate. The morphology of the rod-shaped porous gel is observed with different concentrations of the pore-forming agent. It is found that at 3wt%, the pore structure is uniform and stable, while at 5wt%, there are many pores and the gel shape is unstable. Therefore, a PVA solution with a pore-forming agent concentration of 3wt% is selected for the subsequent experimental operation.

[0017] Example 3 (1) Weigh 1.5 g of PVA and 8.5 mL of deionized water, add 0.3 g of calcium carbonate, seal the container, and stir at 1000 rpm at 95°C for 3 h to prepare a 15 wt% PVA solution with a pore-forming agent concentration of 3 wt%. (2) After the solution is cooled, the PVA solution is squeezed into a pre-prepared mixed cross-linking solution of hydrochloric acid (1 wt%), boric acid (4 wt%), and calcium chloride (3 wt%) using a syringe in the shape of a rod and allowed to set for 10 minutes; (3) The rod-shaped porous gel was placed in a mixed cross-linking solution of boric acid (4 wt%) and calcium chloride (3 wt%) for 24 h and then rinsed with deionized water.

[0018] Example 4 (1) Weigh 1.5 g of PVA and 8.5 mL of deionized water, add 0.3 g of calcium carbonate, seal the mixture, and stir at 1000 rpm at 95°C for 3 h to prepare a 15 wt% PVA solution with a pore-forming agent concentration of 3 wt%. (2) After the solution is cooled, the PVA solution is squeezed into a pre-prepared mixed cross-linking solution of hydrochloric acid (1 wt%), boric acid (4 wt%), and calcium chloride (3 wt%) using a syringe in the shape of a rod and allowed to set for 10 minutes; (3) The rod-shaped porous gel was placed in a mixed crosslinking solution of boric acid (4 wt %) and calcium chloride (3 wt %) and reacted for 24 h, and then rinsed with deionized water; (4) The rod-shaped porous gel was subjected to a freeze-thaw cycle, i.e., frozen at -20°C for 10 h and thawed at room temperature for 2 h, repeated three times; (5) The rod-shaped porous gel was freeze-dried at -40°C for 10 h.

[0019] After freeze-drying, the cross-section of the rod-shaped gel was observed using a scanning electron microscope, and it was found that the pore structure collapsed and the gel dried very slowly.

[0020] Example 5 (1) Weigh 1.5 g of PVA and 8.5 mL of deionized water, add 0.3 g of calcium carbonate, seal the mixture, and stir at 1000 rpm at 95°C for 3 h to prepare a 15 wt% PVA solution with a pore-forming agent concentration of 3 wt%. (2) After the solution is cooled, the PVA solution is squeezed into a pre-prepared mixed cross-linking solution of hydrochloric acid (1 wt%), boric acid (4 wt%), and calcium chloride (3 wt%) using a syringe in the shape of a rod and allowed to set for 10 minutes; (3) The rod-shaped porous gel was placed in a mixed crosslinking solution of boric acid (4 wt%) and calcium chloride (3 wt%) for 24 h and then rinsed with deionized water; (4) The rod-shaped porous gel was subjected to a freeze-thaw cycle, i.e., frozen at -20°C for 10 h and thawed at room temperature for 2 h, repeated three times; (5) The rod-shaped porous gel was soaked in anhydrous ethanol for 12 h and then freeze-dried at -40°C for 4 h.

[0021] The cross-section of the rod-shaped porous xerogel was observed by scanning electron microscopy, and the swelling ratio was tested.

[0022] The above description is only the best embodiment of the present invention, and therefore cannot limit the scope of implementation of the present invention. That is, equivalent changes and modifications made to the patent scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a rod-shaped porous polyvinyl alcohol xerogel, comprising the following steps: (1) Weigh 1.5 g of polyvinyl alcohol and 8.5 mL of deionized water, add 0.3 g of calcium carbonate, seal the container, and stir at 1000 rpm at 95°C for 3 h to prepare a 15 wt% polyvinyl alcohol solution with a pore-forming agent concentration of 3 wt%. (2) After the solution is cooled, the polyvinyl alcohol solution is squeezed into a pre-prepared mixed cross-linking solution of 1 wt% hydrochloric acid, 4 wt% boric acid, and 3 wt% calcium chloride in the form of a rod using a syringe and allowed to set for 10 minutes; (3) The rod-shaped porous gel was placed in a mixed cross-linking solution of 4 wt% boric acid and 3 wt% calcium chloride for 24 h, and then rinsed with deionized water; (4) The rod-shaped porous gel was subjected to a freeze-thaw cycle, i.e., frozen at -20°C for 10 h and thawed at room temperature for 2 h, repeated three times; (5) The rod-shaped porous gel was soaked in anhydrous ethanol for 12 h and then freeze-dried at -40°C for 4 h.

Images