A method for improving the anti-swelling performance and mechanical properties of seaweed-based degradable straws

Abstract

The present invention discloses a method for improving the anti-swelling performance and mechanical properties of seaweed-based degradable straws, and belongs to the technical field of in-situ bionic mineralization. The present invention adopts the following method to improve the physical properties of seaweed-based straws: the seaweed-based straws are first soaked in a calcium chloride solution, and then soaked in a sodium carbonate solution, so that a layer of calcium carbonate armor is generated on the surface of the seaweed-based straws to improve the physical properties of the seaweed-based straws. The present invention successfully adds CaCO3 armor to the surface of the straw by in-situ mineralization, further enhancing the mechanical properties and water resistance of the seaweed-based straws. In addition, the present invention also expands the potential use of such straw waste as heavy metal adsorbents, indicating that seaweed-based straws are not only the most promising alternative to plastic straws, but also have extremely high economic feasibility.

Description

Technical Field

[0001] The invention belongs to the technical field of in-situ bionic mineralization, and specifically relates to a method for improving the anti-swelling property and mechanical property of a seaweed-based degradable straw. Background Art

[0002] In order to cope with the harm caused by petroleum-based plastic straws to the human body and the environment, degradable straws such as paper straws and PLA straws have been developed as alternatives to plastic straws and have been used to a certain extent. However, during the application and commercialization process, these alternatives have exposed a series of problems, including that paper straws are not water-resistant, easily disintegrate in hot water, and have a poor consumer experience, giving people a feeling of eating paper. Polylactic acid (PLA) is a compost-degradable polymer that does not degrade naturally in the natural environment. Its degradation requires strict conditions such as specific temperature, humidity, pH environment, and specific microorganisms, which greatly increases the degradation cost. Therefore, it cannot be regarded as a degradable polymer. In addition, polylactic acid is currently mainly prepared from starch as raw material, which may cause a food crisis to a certain extent.

[0003] The prior art (CN 114311721 A) focuses on non-food polymers such as seaweed, and develops a new method for preparing straws, preparing a seaweed-based straw. The seaweed-based straw can be quickly degraded under natural conditions, does not require composting, and has excellent water stability. However, due to the inherent water resistance of alginate polymers, the anti-swelling performance and mechanical properties of seaweed-based straws are poor. Therefore, further improvements are needed to improve the physical properties of seaweed-based straws to meet new market demands. Summary of the invention

[0004] The present invention provides a method for improving the physical properties of seaweed-based straws, comprising the following steps:

[0005] The seaweed-based straws are first soaked in a calcium chloride solution and then in a sodium carbonate solution to form a layer of calcium carbonate armor on the surface of the seaweed-based straws to improve the physical properties of the seaweed-based straws.

[0006] In the above method, the concentration of the calcium chloride solution is selected from 5 to 40% wt, preferably 10% wt; the concentration of the sodium carbonate solution is selected from 1 to 40% wt, preferably 5% wt.

[0007] In the above method, the soaking time of the seaweed-based straws in the calcium chloride solution is selected from 10 minutes to 3 hours, preferably 1 hour; the soaking time of the seaweed-based straws in the sodium carbonate solution is selected from 1 to 10 minutes, preferably 1 minute.

[0008] In the above method, the physical property is selected from anti-swelling property and / or mechanical property.

[0009] In the above method, the seaweed-based straw is prepared by the following method:

[0010] (1) Preparation of gel mold

[0011] Dissolving agar powder and calcium chloride powder in water, stirring and heating; then, pouring the agar solution into a tube mold; solidifying to form a sol-gel transition, and obtaining a gel mold;

[0012] (2) Cross-linking and demolding

[0013] Dissolve sodium alginate powder in water to form a sodium alginate solution; then, immerse the gel mold in the sodium alginate solution for directional diffusion cross-linking; after the cross-linking is completed, take out the gel mold to obtain a hollow tube; immerse the hollow tube in a calcium chloride solution; then, immerse the hollow tube in water to remove excess calcium chloride to obtain a cross-linked and strengthened hollow tube; dry the hollow tube to obtain a seaweed-based straw.

[0014] In the above-mentioned method for preparing seaweed-based straws, in the step (1), the mass ratio of agar powder, calcium chloride powder and water is selected from 0.5 to 10:1 to 30:100; preferably 3:8:100.

[0015] In the method for preparing the seaweed-based straws, in step (1), the temperature is heated to 85-100°C, preferably 95°C.

[0016] In the above-mentioned method for preparing seaweed-based straws, in the step (1), the curing conditions are selected from: curing at 0 to 50° C. for 5 to 100 min; preferably: curing at room temperature for 30 min.

[0017] In the above-mentioned method for preparing seaweed-based straws, in the step (2), the concentration of the sodium alginate solution is 0.5-15%wt; preferably 2%wt.

[0018] In the above-mentioned method for preparing seaweed-based straws, in the step (2), the immersion time in the sodium alginate solution is 10 to 120 minutes, preferably 30 minutes.

[0019] In the above-mentioned method for preparing seaweed-based straws, in the step (2), the concentration of the calcium chloride solution is selected from 0.1 to 1.5M, preferably 0.25M.

[0020] In the method for preparing the seaweed-based straws, in step (2), the time in the calcium chloride solution is 5 to 120 minutes, preferably 15 minutes.

[0021] In the above-mentioned method for preparing seaweed-based straws, in step (2), the time in water is 5 to 60 minutes, preferably 10 minutes.

[0022] The present invention provides a seaweed-based straw with a calcium carbonate armor prepared under the above method conditions.

[0023] The present invention provides the use of the seaweed-based straw with calcium carbonate armor in heavy metal adsorption.

[0024] The beneficial effects of the present invention are:

[0025] The present invention successfully adds CaCO3 armor to the surface of the straw through in-situ mineralization, further enhancing the mechanical properties and water resistance of the seaweed-based straw. Compared with commercial paper straws and PLA straws, the comprehensive performance of seaweed-based straws is significantly better than both, and it is a very promising alternative to plastic straws. Compared with the previous mineralization of calcium carbonate in the alginate network based on the sacrifice of the egg box structure, the present invention uses exogenous free calcium to shield the reaction between calcium carbonate and bound calcium, and utilizes the -COO on the alginate G block to form a protective film. - The -COO groups on the M and GM / MG blocks establish a strong cross-linking network. - The groups attract free Ca through electrostatic forces 2+ , thereby promoting CaCO3 nucleation. This effectively prevents -COOH hydration, reduces swelling, and inlays nano- to micron-sized CaCO3 particles on the straw surface, strengthening the structure without affecting the cross-linked network.

[0026] Compared with unmineralized seaweed-based straws, the performance of seaweed-based straws equipped with calcium carbonate armor is significantly improved, including a 102% increase in water contact angle (contact with distilled water at room temperature for 1 minute), a 35% reduction in swelling (immersion in distilled water at room temperature for 30 minutes), and an increase in ultimate bending stress and tensile stress of 35.5% and 37.5%, respectively; the application results of seaweed-based straws in different beverage systems show that seaweed-based straws can maintain good performance in various acid-base beverage systems without obvious dissolution of substances; compared with paper straws and PLA straws, the seaweed-based straws of the present invention have excellent comprehensive performance and broad commercial prospects. Degradation experiments show that the seaweed-based straws of the present invention can be rapidly degraded in 180 days and will not accumulate in the environment. In addition, the present invention also expands the potential use of such straw waste as heavy metal adsorbents, indicating that seaweed-based straws are not only the most promising alternative to plastic straws, but also have extremely high economic feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the directed diffusion combination and in-situ mineralization method;

[0028] Figure 2 Bending (a) and tensile strain-stress (b) curves of the seaweed-based straw prepared in Scheme S;

[0029] Figure 3 The swelling degree of the seaweed-based straw prepared in Scheme S;

[0030] Figure 4 is the solubility of each pipette;

[0031] Figure 5 The calcium ion content of the seaweed-based straw prepared in Scheme S;

[0032] Figure 6 The contact angle of the seaweed-based straw prepared in Scheme S;

[0033] Figure 7 Water vapor transmission rates of straws prepared for Scheme S, Scheme N, and Scheme B;

[0034] Figure 8 XRD spectrum of the seaweed-based straw prepared in Scheme S;

[0035] Fig. 9 SEM images of different straw samples;

[0036] Fig.10 Swelling degree (a), solubility (b), digital photo (c) and contact angle (d) of each pipette in Scheme W;

[0037] Fig.11 Swelling degree and contact angle of the seaweed-based straw prepared in Scheme N;

[0038] Fig.12 Water contact angle and swelling degree of the seaweed-based straws prepared in Schemes B and P;

[0039] Fig.13 The swelling degree (a), bending stress (b), tensile stress (c), weight loss rate (d) and comprehensive performance comparison (e) of each straw;

[0040] Fig.14 The swelling degree, bending stress and solubility of seaweed-based straws in beverage systems with different pH values ​​and water at different temperatures;

[0041] Fig.15 Cu 2+ Schematic diagram of adsorption (a); Cu 2+ Adsorption kinetics curve (b); adsorption of Cu by straw waste 2+ Energy spectrum after adsorption (c); Cu 2+ FTIR analysis of post-straw and straw waste (d). DETAILED DESCRIPTION

[0042] The raw materials used in the present invention are as follows:

[0043] Calcium carbonate (AR, ≥99%) was purchased from Sigma-Aldrich, USA. Agar (ash content ≤1.5%, high gel strength ≈1000-1200 g / cm 2 ) and PVA (alcoholysis degree ≈ 98–99% mol / mol) were purchased from Shanghai MacLean Biochemical Technology Co., Ltd. (Shanghai, China).

[0044] In the present invention, the seaweed-based straw is prepared by the following method:

[0045] (1) Preparation of gel mold

[0046] Dissolve 3g agar powder and 8g anhydrous calcium chloride powder in 100g distilled water and heat to 95°C while stirring. Then, immediately pour the agar solution into a tube mold with an inner diameter of 8mm. Curing at room temperature for 30min forms a sol-gel transition and obtains a gel mold (solid).

[0047] (2) Cross-linking and demolding

[0048] Sodium alginate powder was dissolved in deionized water to form a 2% wt sodium alginate solution. The solution was heated at 55°C and stirred vigorously until completely dissolved, then centrifuged for degassing (4000 r min -1 , 10min) to obtain a uniform and bubble-free sodium alginate solution. Then, immerse the prepared gel mold in the sodium alginate solution for directional diffusion cross-linking, and the immersion time is 30min. After the cross-linking is completed, take out the gel mold to obtain a hollow tube. The hollow tube is re-immersed in a 0.25M calcium chloride solution to maximize the cross-linking, and the immersion time is 15min. Subsequently, it is immersed in deionized water for 10min to remove excess CaCl2 to obtain a cross-linked and strengthened hollow tube. The hollow tube is fixed (sheathed) on a glass rod with a diameter of 8mm for drying, and the drying conditions are 60°C and 80% relative humidity (adjustable). After drying is complete, demoulding is performed. There are many ways to demold the product. For example, a demolding agent can be applied to the glass rod, or the straw and the glass rod can be directly immersed in water for demolding. The taken out tube blank is put on a new glass rod (the diameter of the support column here is smaller than the diameter of the support column in the previous step, because the tube blank has a certain hardness at this time, and the support column does not need to fit tightly to the inner wall of the tube blank), and then continue drying (drying conditions 60°C, 55% relative humidity) to obtain seaweed-based straws.

[0049] Using the directed diffusion assembly method (DDA method), we can successfully produce biodegradable seaweed-based straws using alginate as a model material. However, the inherent hydrophilicity of alginate still significantly affects the overall performance of the straw, including key properties such as anti-swelling and surface hydrophobicity. Inspired by the excellent mechanical strength and anti-swelling properties of materials such as bones and mussels, the present invention embeds CaCO3 armor into the surface of the alginate network through in situ mineralization. The operation process is as follows Figure 1 shown.

[0050] As we all know, there are M blocks and G blocks in alginate polymers, and the carboxyl groups on the G blocks can cross-link with calcium ions to form an egg-box structure. Therefore, previous calcium carbonate mineralization often utilizes the cross-linked calcium in the egg-box structure, which will damage the network structure.

[0051] In the present invention, we speculate that the carboxyl groups on the alginate M block have the ability to attract calcium ions, thereby inducing and stabilizing the in situ mineralization process of calcium carbonate. Thus, the destruction of the egg-box structure by mineralization can be shielded by free calcium, and this process can embed a waterproof and strong CaCO3 armor on the surface of the alginate network.

[0052] Specifically, free Ca 2+ The straw is immersed in Na2CO3 solution, CO3 2- It reacts rapidly with free calcium, promoting the continuous nucleation of CaCO3 crystals within the calcium alginate network. The color of the straw gradually changes from transparent to white, indicating that the CaCO3 crystals are successfully embedded in the surface network. This method can be used to prepare an algae-based straw with an organic-inorganic hybrid structure, which significantly enhances the anti-swelling and mechanical properties of the straw.

[0053] Since carbonate has a stronger complexing ability for calcium ions than alginate, CO3 2- The addition of can destroy the egg-box structure of alginate, leading to network disintegration. Mineralizing CaCO3 without destroying the calcium alginate network is a challenge. The present invention selectively functionalizes carboxyl groups in different blocks to maximize the degree of crosslinking while inducing the nucleation growth of CaCO3. This consumes the M blocks that cannot react with CaCO3. 2+ The method gives the straw higher mechanical strength and anti-swelling properties.

[0054] Other materials used in the present invention, if not otherwise stated, can be obtained through commercial channels. Other terms used in the present invention, unless otherwise specified, generally have the meanings commonly understood by those of ordinary skill in the art. The present invention is further described in detail below in conjunction with specific examples and with reference to data. The following examples are only for illustrating the present invention, and are not intended to limit the scope of the present invention in any way.

[0055] Example

[0056] The present invention improves the seaweed-based straw prepared by the directed diffusion assembly method (as a control group) and provides the following solutions:

[0057] Plan S:

[0058] The seaweed-based straws were soaked in a calcium chloride solution (concentration of 10%wt) for 1 hour, then soaked in sodium carbonate solutions (Na2CO3) with concentrations of 1.25%, 2.5%, 5%, 7.5%, 10%, and 12.5%wt for 1 minute, and then thoroughly rinsed with distilled water at least 3 times to obtain seaweed-based straws with calcium carbonate armor. The obtained seaweed-based straw samples were named S1.25%, S2.5%, S5%, S7.5%, S10%, and S12.5%, respectively.

[0059] Plan W:

[0060] The seaweed-based straws were directly immersed in Na2CO3 solution, and the immersion time and concentration were consistent with those in Scheme S, without providing free calcium. The obtained seaweed-based straw samples were named W1.25%, W2.5%, W5%, and W10%.

[0061] Option B:

[0062] Add CaCO3 powder to sodium alginate solution (2%wt), stir vigorously at 55°C to prepare a mixed slurry of sodium alginate and CaCO3. Soak the gel mold in the above control group step (1) in the SA / CaCO3 blend system for 30 minutes, then remove the gel mold to obtain a seaweed-based straw (hollow tube), and the subsequent drying and demolding process are consistent with the control group. In this scheme, the CaCO3 content in the straw is kept consistent with the CaCO3 content generated in situ in scheme S, and the prepared seaweed-based straw samples are named B1.25% (the calcium carbonate content in the straw is consistent with S1.25%, and so on), B2.5%, B5% and B10%. The CaCO3 content is determined by ICP-OES.

[0063] Scheme N:

[0064] The seaweed-based straws were directly immersed in four NaOH solutions with the same pH value as the Na2CO3 solutions with concentrations of 1.25%, 2.5%, 5%, and 10%, and then rinsed to obtain the N straws. The obtained seaweed-based straw samples were named N1.25%, N2.5%, N5%, and N10%, respectively.

[0065] Plan P:

[0066] Preparation of PVA in-situ mineralized film:

[0067] PVA powder was dissolved in deionized water and stirred vigorously at 90°C to obtain a 2%wt PVA solution. Then, it was poured into a petri dish and dried to obtain a PVA film. This PVA film was used to replace the seaweed-based straws in Scheme S. The PVA film was soaked in a calcium chloride solution (concentration of 10%wt) for 1h, and then soaked in a sodium carbonate solution (Na2CO3) with concentrations of 1.25%, 2.5%, 5%, and 10%wt for 1min, respectively, and then rinsed thoroughly with distilled water at least 3 times to obtain a PVA film with calcium carbonate armor. The obtained PVA film samples were named PVA-S1.25%, PVA-S2.5%, PVA-S5%, and PVA-S10%, respectively.

[0068] Preparation of PVA blend films:

[0069] Add CaCO3 powder to PVA solution (2%wt), stir vigorously at 55°C to prepare a mixed slurry of PVA and CaCO3, and obtain a PVA / CaCO3 blended film after drying. In this scheme, the CaCO3 content in the blended film is kept consistent with the CaCO3 content generated in situ in the PVA in-situ mineralized film. The prepared PVA film samples are named PVA-B1.25% (the calcium carbonate content in the blended film is consistent with PVA-S1.25%, and so on), PVA-B2.5%, PVA-B5% and PVA-B10%. The CaCO3 content is determined by ICP-OES

[0070] The above scheme is shown in Table 1:

[0071] Table 1

[0072]

[0073] The following test determinations of the present invention were repeated three times, and the results were expressed as mean ± standard deviation. SPSS 20.0 (SPSS Inc., Chicago, USA) was used for statistical analysis, and the significance was determined by one-way analysis of variance (ANOVA) and Duncan's test. The significance test was performed at the P < 0.05 level. The pictures were drawn using Origin software.

[0074] 1. Mechanical properties of straws

[0075] This test measured the mechanical properties of the straws prepared in Scheme S and the control group (SA).

[0076] Bending test:

[0077] The bending resistance of seaweed-based straws was characterized using a texture meter equipped with a three-point bending probe. During the three-point bending test, the straws were placed on two roller supports and kept at a fixed distance of 50 mm. The sample was placed on two roller supports and subjected to a concentrated load at the center of the sample at a constant test speed of 3 mm / min at room temperature. The bending strength of the hollow tube can be derived from the following formula:

[0078]

[0079] In formula (1), M is the maximum bending moment, γ is the maximum distance from the center of the tube (equal to d / 2), L is the distance between the two points below the specimen, F is the applied force, d is the outer diameter of the straw, and d is the inner diameter of the straw.

[0080] Tensile test:

[0081] Tensile tests were performed in air at room temperature (25°C) using a universal material testing machine. In the tensile test, the straw was cut into 2 mm wide slices, then clamped at both ends and stretched at a constant speed of 10 mm / min along the length of the sample, with the distance between the clamps fixed at 40 mm. All experiments were performed at least three times.

[0082] The test results are as follows Figure 2 As shown:

[0083] In the process of optimizing material properties, the improvement of one property is often accompanied by the decline of another property, which ultimately results in the overall performance of the material not being improved much or even declining. Figure 2 It can be seen that compared with the control group, Scheme S of the present invention can effectively improve the mechanical properties of seaweed-based straws. Among them, the bending resistance of S5% seaweed-based straws is improved by 33.4%, and the tensile resistance is improved by 44.5%. Combined with the SEM image, it shows that the inorganic phase reinforces the organic network and optimizes the overall mechanical properties of the seaweed-based straws.

[0084] 2. Water resistance of straws

[0085] 1. Anti-swelling performance

[0086] The seaweed-based straws prepared in Scheme S and the seaweed-based straws of the control group were cut into squares (2×2 cm), dried at 105°C for 24 h, and their initial dry weight (W1) was determined. Subsequently, the dried samples were immersed in 50 mL of solutions of different pH values, gently stirred at different temperatures, and the pH values ​​(2.88-8.38) were adjusted with acetic acid solution (pH≈2.88), H2CO3 solution (pH≈4.38 and 5.38), distilled water (pH≈6.8) and NaHCO3 solution (pH≈8.38) to simulate commercial beverages. The film samples were then taken out, blotted dry with filter paper, and weighed (W2). Each sample was tested three times under the same conditions. The swelling degree (SD) (%) value of the membrane was calculated as follows:

[0087]

[0088] The test results are as follows Figure 3 As shown:

[0089] When the sodium carbonate concentration is ≤5%, the swelling resistance of the seaweed-based straws prepared by Scheme S increases with the increase in the concentration of the Na2CO3 solution. Compared with the control group, the swelling degree of the S5% straws (seaweed-based straws induced by 5% Na2CO3 solution) was significantly reduced from 34% to 21% (swelling in distilled water for 30 minutes), indicating that the swelling resistance of the straws was significantly improved. However, when the Na2CO3 concentration reached 10%, the swelling degree of the straws (S10%) significantly increased to 37%, even exceeding that of the control group without mineralization treatment. These results indicate that the organic network of the S10% straws may be destroyed due to the high proportion of the inorganic phase (CaCO3), resulting in network swelling.

[0090] 2. Solubility

[0091] The straws prepared in Scheme S, Scheme B and Scheme N were cut into squares (2×2 cm), dried at 105°C for 24 h, and their initial dry weight (W1) was determined. Subsequently, the dried samples were immersed in 50 mL of distilled water solution, gently stirred, and then dried at 105°C for 24 h, and their initial dry weight (W3) was determined. Each sample was tested three times under the same conditions. The solubility (%) value of the film was calculated as follows:

[0092]

[0093] The test results are as follows Figure 4 As shown:

[0094] like Figure 4As shown, all the straws prepared by Scheme N and Scheme B and the straws before S5% in Scheme S will not dissolve in water, while S7.5%, S10% and S12.5% ​​will dissolve significantly, and the solubility increases with the increase of sodium carbonate concentration, which further confirms that sodium carbonate can destroy the alginate egg box structure and chelate the calcium therein to form calcium carbonate crystals, while the addition of free calcium can shield the destruction of the egg box structure by sodium carbonate, prompting sodium carbonate to react with free calcium first. When the sodium carbonate concentration is 5% and the immersion time is 1min, sodium carbonate and free calcium react completely; when the sodium carbonate concentration exceeds 5%, sodium carbonate and free calcium react completely and there is a residue, which continues to react with calcium in the egg box structure, thereby destroying the network structure and affecting the performance of the straw. Therefore, 5% sodium carbonate is selected as the optimal concentration for forming calcium carbonate armor on the surface of the straw.

[0095] 3. Calcium ion content

[0096] After the straws were completely dried, a certain amount of straws were immersed in a mixed digestion solution of nitric acid, hydrochloric acid, perchloric acid, and hydrofluoric acid, and heated at 180°C until the solution was completely volatilized / evaporated. The sample was fixed to a fixed volume, and the components to be tested were fully shaken to determine their calcium ion content using ICP-OES (PerkinElmer OPTMA8000DV, USA).

[0097] The test results are as follows Figure 5 As shown:

[0098] like Figure 5 As shown, with the increase of sodium carbonate concentration in mineralization, the calcium ion content in the straw also increased accordingly, which indicates that calcium carbonate crystals were successfully embedded in the straw surface, but exceeding the sodium carbonate concentration of more than 5% would destroy the egg-box network structure formed on the straw surface.

[0099] 4. Surface hydrophobicity

[0100] The water contact angle test of the pipette was performed using a contact angle system equipped with an automated charge coupled device and a video capture system. 2 μL of deionized water was deposited on the surface of the pipette and the contact angle was measured.

[0101] The test results are as follows Figure 6 As shown:

[0102] The surface contact angle of the seaweed-based straws prepared by Scheme S increases with the increase in the concentration of the Na2CO3 solution. Compared with the control group (SA) without mineralization treatment, the water contact angle of the S5% straw increased from 36° to 73° (contact with DI water for 1 min), indicating that the surface hydrophobicity of the straw was improved. In addition, although S10% has a higher surface contact angle than S5% (91.2°, contact with DI water for 1 min), its anti-swelling degree is significantly reduced. Therefore, it can be inferred that the construction of the organic-inorganic structure can significantly increase the surface hydrophobicity, and the surface contact angle increases with the increase in the proportion of the inorganic phase, thereby blocking the invasion of water. With the formation of the inorganic phase (exceeding S5%), although the surface hydrophobicity is higher, the organic network may be destroyed, which leads to a decrease in the anti-swelling performance of the network and network swelling.

[0103] 5. Water vapor transmission rate

[0104] This test measures the water vapor transmission rate of the straws prepared in Scheme S, Scheme N and Scheme B.

[0105] Water vapor transmission rate (WVP) test: WVP was measured gravimetrically using a water vapor transmission rate tester (TSY-TIH, China). The film cut from the straw was placed at 23±2℃ and 50±5% RH for 72h and then attached to the top of the sample rack. The sample was placed in the constant temperature and humidity chamber of the instrument. The equilibrium time was 180min and the test temperature was 30℃. Each test was performed three times in parallel.

[0106] The test results are as follows Figure 7 As shown:

[0107] The water vapor permeability of the S10% sample is significantly higher than that of the other samples. In addition, the calcium ion content of S10% is also significantly higher than that of S5%, which indicates that the proportion of the inorganic phase has increased, further indicating that more calcium ions are used to generate the inorganic phase. Therefore, it can be speculated that in the egg-box structure of S10%, because the free calcium has completely reacted, the carbonate reacts with the bound calcium, which eventually leads to the dissociation of the alginate network.

[0108] 3. Structural analysis and structure-activity relationship of straws

[0109] 1. XRD pattern

[0110] This experiment measured the XRD patterns of the straws prepared by Scheme S (S2.5%, S5%, S10%) and the straws of the control group.

[0111] The XRD patterns of the straws were analyzed using a D / max-2200 diffractometer (Rigaku, Japan) under Cu-Kα radiation with a voltage of 40 kV and a current of 30 mA. The 2θ scanning range was 10-80° and the scanning rate was 5° / min.

[0112] The test results are as follows Figure 8 As shown:

[0113] Contains free Ca 2+ The straw is immersed in Na2CO3 solution, CO3 2- The rapid reaction with free calcium resulted in the continuous nucleation of CaCO3 crystals within the calcium alginate network. The color of the straw gradually changed from transparent to white, indicating that the CaCO3 crystals were successfully embedded in the surface network. Figure 8 The XRD spectrum shown confirms that CaCO3 crystals are formed in the alginate network, and the crystal form of the crystals is calcite. And as the concentration of the Na2CO3 solution increases, the peak intensity of the XRD spectrum gradually increases, indicating that the proportion of the inorganic phase (CaCO3) increases.

[0114] 2. SEM image

[0115] This test measured the SEM images of the straws prepared by Scheme S (S2.5%, S5%, S10%) and the straws prepared by Scheme W (W5%).

[0116] In order to characterize the morphology of the straws, the straws were treated with liquid nitrogen for 3 min and then freeze-dried in a vacuum freeze dryer for 48 h. A layer of palladium gold was sprayed on the cross section of the freeze-dried sample, and the morphology of the sample was observed using a scanning electron microscope at a voltage of 5 kV.

[0117] The test results are as follows Fig. 9 As shown:

[0118] Compared with Scheme S, Scheme W does not provide free calcium ions. The formation of calcium carbonate crystals in W5% straws is based on sacrificing the alginate egg-box structure, which proves that carbonate ions will destroy the alginate egg-box structure. It can be seen that the use of free calcium can shield carbonate ions from damaging the egg-box structure. As the concentration of Na2CO3 increases, the number and size of crystals continue to increase. The formation of these large crystal structures requires more calcium ions, which is inevitably accompanied by the dissociation of the egg-box structure and the release of calcium ions, which in turn destroys the organic network of the straw, resulting in reduced water resistance of the straw. Mechanistically, due to the free Ca 2+ The supply is limited, and excess CO3 2- It consumes the bound calcium in the egg-box structure, leading to network disruption.

[0119] 3. Formation dynamics of calcium carbonate armor

[0120] To further explore the CO32- The competition mechanism between sodium alginate and sodium alginate is designed in the present invention to provide no free Ca 2+ The straws prepared by Scheme W turned white, similar to Scheme S, and had corrosion holes on the surface, indicating that the formation of calcium carbonate crystals was at the expense of the egg box network. SEM images of the seaweed-based straws prepared by Scheme S ( Fig. 9 ) and digital photos ( Fig.10 c) further confirmed that the organic network was partially destroyed. Therefore, it can be concluded that CO3 2- It can dissociate calcium ions in the egg-box structure, causing the network to disintegrate.

[0121] In addition, the swelling degree of the straws prepared using Scheme W ( Fig.10 a) and solubility ( Fig.10 b) are significantly higher than S5%, and similar to S10%. However, the contact angle is still higher than that of the control group SA ( Fig.10 d), which is similar to S5% and S10%. From the above results, it can be seen that the destruction of the network inevitably leads to the swelling of the straw, while the increase of the surface contact angle is mainly affected by the in-situ mineralization of calcium carbonate crystals.

[0122] In addition, in order to eliminate the interference of the alkaline environment of the Na2CO3 solution on the experiment, the present invention soaks the straw in a NaOH solution with the same pH as the 1.25%, 2.5%, 5% and 10% Na2CO3 solution (Scheme N). Fig.11 As shown, the swelling degree of the straw prepared by Scheme N ( Fig.11 a) and contact angle ( Fig.11 b) There was no significant difference compared with the control group, indicating that pH had no significant effect on the performance of the straw. Therefore, it can be considered that the increase in surface hydrophobicity is due to the formation of CaCO3 crystals rather than the change in pH.

[0123] From the comparison of the three schemes S, W, and N, it is obvious that the mineralization with 5% Na2CO3 is the critical point for the complete consumption of free calcium, and the bound calcium in the egg box structure begins to react. Specifically, when the Na2CO3 concentration is lower than 5%, CO3 2- Only with free Ca 2+ reaction, while the Ca in the egg-box structure 2+ Does not participate in the reaction. When it exceeds 5%, both free calcium and bound calcium react with CO3 2- The reaction formed armor, but the original alginate network was destroyed. Therefore, S5% showed the best performance.

[0124] 4. Study on structure-activity mechanism

[0125] The above experiments have proved that the addition of CaCO3 armor significantly improved the water resistance of the straws compared with the control group. The swelling degree of the blended straws (Scheme B) decreased compared with the control group, but was still higher than S5%. In addition, the contact angle of the blended straws began to decrease from 0 within 60s, which was significantly lower than S5%, and even lower than the control group. The inorganic phase ratio of the blended straws was the same as that of the straws prepared by Scheme S, but its surface hydrophilicity was significantly higher than that of the Scheme S sample, even higher than the control, but the swelling degree was lower than the control group. This shows that both in-situ mineralization and blended CaCO3 crystals can limit the swelling of the straws, and there may be no necessary correlation between the degree of swelling and the surface hydrophilicity. The strengthening effect of in-situ mineralization on the swelling degree and surface hydrophobicity is significantly better than blending. Therefore, it can be concluded that in-situ mineralization of CaCO3 crystals in the alginate network can significantly improve the anti-swelling properties of the straws. Different ways of introducing CaCO3 crystals can adjust the hydrophilicity of the straw surface.

[0126] In order to study the effect of carboxyl groups in the alginate network on the nucleation and growth of CaCO3, sodium alginate was replaced by PVA containing only hydroxyl groups, and PVA / CaCO3 membranes were prepared by both in situ mineralization and blending methods (Scheme P).

[0127] The results showed that the addition of CaCO3 armor to the PVA network (via in-situ mineralization and blending) slightly improved the anti-swelling properties and hydrophobicity. However, this enhancement was not significant compared to the seaweed-based straws.

[0128] like Fig.12 As shown in the figure, in the PVA model system, the swelling degree of the film was reduced by 7.3% (in situ) and 13.1% (blended), and the contact angle was increased by 12.5% ​​(in situ) and 21% (blended). In contrast, the swelling degree of S5% was reduced by 35% and the water contact angle increased by 102%. This indicates that the interaction between carboxyl groups and CaCO3 mineralization can consume the proportion of carboxyl groups in the network, thereby limiting swelling.

[0129] Mechanistically, the interaction between the hydrophilic groups and water molecules causes the gel to absorb water, which is the main reason for network swelling. The crosslinking density and the number of hydrophilic groups are two factors that determine the swelling of the polymer network. In the present invention, reducing the number of hydrophilic groups is the main reason for the anti-swelling of S5%. Specifically, the carboxyl groups on the G blocks in the alginate network have been replaced by Ca 2+ Completely cross-linked, while the carboxyl groups on the M block are consumed by calcium carbonate mineralization.

[0130] However, the organic-inorganic hybrid system constructed with PVA (without carboxyl groups) had weaker anti-swelling and surface properties. This suggests that the reaction between carboxyl groups and CaCO3 plays an important role in enhancing the water resistance of the straw compared to the alginate network. Specifically, in the calcium alginate network, the residual carboxyl groups in the M region do not react with CaCO3. 2+ Cross-linking guides the aggregation of free calcium ions through electrostatic attraction and acts as a nucleus to initiate the nucleation and growth of CaCO3 crystals. This limits the degree of interaction between carboxyl groups and water molecules, ultimately reducing water absorption by the straw.

[0131] In terms of the source of carboxyl groups, the carboxyl groups on the G block of sodium alginate have been 2+ The egg-box structure is fully cross-linked. However, the carboxyl groups on the M block are not cross-linked. Therefore, CaCO3 nucleates and grows around the carboxyl groups of the M block, limiting the water absorption of the straw network.

[0132] In addition, the anti-swelling performance of the blended straw (suppression of hydrophilic group water by random attachment of CaCO3 crystals to the network) is not satisfactory compared with Scheme S.

[0133] In summary, the selective functionalization of carboxyl groups on different blocks plays a vital role in constructing a strong network structure with waterproof armor reinforcement. Reducing the proportion of hydrophilic groups by consuming carboxyl groups in the M block can significantly improve the water resistance of the straw.

[0134] 4. Performance comparison with other commercial straws

[0135] In order to evaluate the comprehensive performance of seaweed-based straws, the present invention conducted a comprehensive comparison of seaweed-based straws (S5%), paper straws and PLA straws, including key factors such as anti-swelling, mechanical properties, biodegradability and cost-effectiveness. Among them, paper straws and polylactic acid straws were purchased from RT-Mart Supermarket.

[0136] The specific operation of the biodegradation test is as follows:

[0137] The straws were buried in soil samples from the Qingdao Agricultural University campus at a temperature of 20 ± 2 °C and a depth of 10 cm. The straws were periodically extracted and cleaned, and degradation parameters were evaluated.

[0138] The molecular weight of the pipette was determined as follows: the pipette was dissolved in 0.1 mol / L EDTA-2Na solution, and the resulting solution was filtered through a dialysis bag with a molecular weight cutoff of 14 000. The dialyzed solution was then concentrated by rotary evaporation at 58°C and further freeze-dried. The molecular weight was determined by high performance liquid chromatography. The mobile phase was 0.2 mol / L NaCl at a flow rate of 0.5 mol / L. Chromatographic separation was performed using a TSK-gel GM PWxl column, maintained at 40°C, and an injection volume of 20uL.

[0139] The results are as follows Fig.13 As shown:

[0140] In terms of swelling resistance, seaweed-based straws are better than paper straws and are not much different from PLA straws. In terms of mechanical properties, seaweed-based straws exhibit superior bending stress and tensile stress, and show higher mechanical strength compared to paper straws and PLA straws. The results of the biodegradation experiment showed that the weight loss rate of seaweed-based straws and paper straws reached 98% within 180 days, while PLA straws hardly degraded, indicating that the biodegradability of seaweed-based straws is significantly better than that of PLA straws.

[0141] In addition, according to the analysis of existing literature, paper straw base paper has been proven to be the most cost-effective option, followed by sodium alginate, while polylactic acid has been confirmed as the most expensive option, approximately four times the cost of base paper and sodium alginate (Bressanin et al., 2022; Nesic et al., 2023).

[0142] To sum up, compared with paper straws and PLA straws, seaweed straws have excellent performance in all aspects and are the most promising alternative.

[0143] 5. Application of seaweed-based straws in different beverage systems

[0144] Developing biodegradable straws that can adapt to consumers' needs for drinking a variety of beverages at different temperatures is a rarely explored and challenging task. Temperature and pH are considered important factors affecting straw performance. For example, at high temperatures, polylactic acid (PLA) straws soften, while paper straws absorb water and disintegrate. Therefore, it is crucial to study the applicability of seaweed straws in different beverage environments.

[0145] To verify the wide applicability of seaweed-based straws (S5%), we evaluated their anti-swelling and wet strength in carbonated beverages, juices, milk, and soda (Table 2). These beverages were selected based on their common consumption varieties and different pH values.

[0146] Table 2 Beverages tested and their corresponding pH

[0147]

[0148] The test results are as follows Fig.14 As shown:

[0149] Whether it is acidic beverages (such as carbonated beverages or juices) or alkaline beverages (such as soda water), seaweed-based straws show excellent anti-swelling properties and wet strength in various pH environments. Test results on straw performance at various drinking temperatures show that seaweed-based straws show excellent anti-swelling and mechanical properties in both cold and hot water.

[0150] In addition, compared with the control group without CaCO3 armor, the seaweed straws equipped with CaCO3 armor showed stronger anti-swelling properties and smaller performance fluctuations in various beverage environments. This can be attributed to the presence of CaCO3 armor, which protects the alginate network inside the straw and reduces the damage to the gel network caused by temperature and acidic and alkaline beverages. In contrast, the control group without armor may have suffered damage to the alginate complex structure due to the various acidic substances (such as carbonic acid, phosphoric acid, and citric acid) present in carbonated beverages. Similarly, alkaline substances in soda water may also cause damage to the network structure. Therefore, the CaCO3 armor effectively protects the straw from the influence of the external environment, further proving the positive role of the armor in improving the performance of the straw.

[0151] 6. Heavy metal adsorption experiment

[0152] In order to verify the adsorption capacity of seaweed-based straws, the present invention uses Cu 2+ As a representative of heavy metal ions.

[0153] 0.5 g of seaweed-based straws (S5%, 6 mm in diameter, 50 mm in length) were immersed in 0.5 L of CuSO4 solution (concentration 200 mg / L) to measure the adsorption capacity of the straws for heavy metals. The adsorption process was carried out at a temperature of 25°C for 24 hours.

[0154] The test results are as follows Fig.15 As shown:

[0155] Soak the pipette in Cu 2+ In the solution, the color of the pipette turned into a distinct blue, indicating that the pipette successfully adsorbed Cu 2+ , and the EDS spectrum confirmed this result ( Fig.15 c) Adsorption kinetics curves showing the adsorption of straw waste to Cu 2+ The ions were captured efficiently, and the maximum adsorption capacity of 28.4 mg / g was achieved within 24 h. Fig.15 b). Its adsorption mechanism ( Fig.15 a) shows that the carboxyl group is the adsorption site, Cu 2+ The Ca in the egg-box structure may have been replaced by an ion exchange process. 2+ FT-IR spectrum band from 3250cm -1 Slightly moved to 3230cm -1 , from 1411cm-1 Slightly moved to 1403cm -1 ( Fig.15 d), indicating that the adsorbent and Cu 2+ There is a potential interaction between them.

[0156] After the adsorption is completed, EDTA can be used to desorb the adsorbed heavy metal ions, and then the desorbed straw waste can be reused for further adsorption or degradation.

[0157] In summary, after use, the waste of seaweed-based straws can be used as an excellent adsorbent to achieve the adsorption of heavy metal ions.

[0158] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for improving the physical properties of seaweed-based straws, characterized in that: The steps include: The seaweed-based straws are first soaked in a calcium chloride solution with a concentration of 5 to 40%wt, and then soaked in a sodium carbonate solution with a concentration of 1 to 40%wt, so that a layer of calcium carbonate armor is formed on the surface of the seaweed-based straws to improve the physical properties of the seaweed-based straws; The seaweed-based straw is prepared by the following method: (1) Preparation of gel mold Dissolving agar powder and calcium chloride powder in water, stirring and heating; then, pouring the agar solution into a tube mold; solidifying to form a sol-gel transition, and obtaining a gel mold; (2) Cross-linking and demolding Dissolving sodium alginate powder in water to form a sodium alginate solution; then, immersing the gel mold in the sodium alginate solution to perform directional diffusion cross-linking; After the cross-linking is completed, the gel mold is taken out to obtain a hollow tube; the hollow tube is immersed in a calcium chloride solution with a concentration of 0.1 to 1.5 M; then, the hollow tube is immersed in water to remove excess calcium chloride to obtain a cross-linked and strengthened hollow tube; The hollow tubes are dried to obtain seaweed-based straws.

2. The method according to claim 1, characterized in that The soaking time of the seaweed-based straw in the calcium chloride solution is selected from 10 minutes to 3 hours, and the soaking time of the seaweed-based straw in the sodium carbonate solution is selected from 1 to 10 minutes.

3. The method according to claim 1, characterized in that In the step (1), the mass ratio of agar powder, calcium chloride powder and water is selected from 0.5-10:1-30:100; the temperature is heated to 85-100° C.; and the curing conditions are selected from: curing at 0-50° C. for 5-100 min.

4. The method according to claim 1, characterized in that: In the step (2), the concentration of the sodium alginate solution is 0.5 to 15% wt.

5. The method according to claim 1, characterized in that The immersion time in the sodium alginate solution is 10 to 120 minutes; the time in the calcium chloride solution is 5 to 120 minutes; and the time in water is 5 to 60 minutes.

6. Seaweed-based straws with calcium carbonate armor prepared under the conditions of any one of claims 1 to 5.

7. Use of the seaweed-based straw with calcium carbonate armor as claimed in claim 6 in heavy metal adsorption.

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