Medical micro-ammonia concentrated natural latex and preparation method thereof

Abstract

The invention belongs to the technical field of natural latex, and particularly relates to medical micro-ammonia concentrated natural latex and a preparation method thereof.The preparation method comprises the steps that fresh latex is filtered to remove impurities and clots, then the fresh latex is added into an HY preservation system, centrifugal concentration is conducted, and latex and whey are obtained; reacting an N-methyl piperazinyl silane coupling agent with a vinyl silane coupling agent, then adding sodium alginate as an end-capping reagent, and reacting to obtain a modified antibacterial agent; adding the modified antibacterial agent into the whey to carry out free radical polymerization reaction, then standing for 10-20 hours, taking an upper latex layer, and carrying out centrifugal concentration to obtain modified whey; and mixing the latex and the modified whey, then supplementing ammonia until the mass fraction is 0.05-0.1%, and then supplementing the HY preservation system to obtain the medical micro-ammonia concentrated natural latex. By modifying the N-methyl piperazinyl silane coupling agent, whey grafting is achieved, the antibacterial effect is achieved, the ammonia consumption is remarkably reduced, and meanwhile the stability of latex can be improved through negative charges of grafted sodium alginate.

Description

Technical Field

[0001] This invention belongs to the field of natural latex technology, specifically relating to a medical-grade microammonia-concentrated natural latex and its preparation method. Background Technology

[0002] Natural latex, as an important industrial raw material, is widely used in many fields such as medicine, food, and daily necessities. However, traditional natural latex has many problems in preservation and processing, especially the use of ammonia, which has spurred research and development on natural latex concentrated with trace amounts of ammonia.

[0003] Natural latex is the sap collected from rubber trees, primarily composed of rubber hydrocarbon particles, water, proteins, sugars, and esters, forming a complex colloidal system. Non-rubber substances such as proteins and lipids form a protective film around the rubber particles, giving them a negative charge and maintaining the relative stability of the colloid. However, fresh natural latex collected from rubber trees has poor stability. Under the action of enzymes and bacteria, especially in oxygen and light environments, the proteins, sugars, and esters in the latex rapidly decompose, generating organic acids or putrefactive substances. These decomposition products neutralize the charge on the rubber particles, disrupting the stability of the colloid and causing the latex to coagulate. Furthermore, the presence of metal salts, particularly magnesium ions, reacts with the protective layer in the latex and promotes the activation of enzymes and bacteria, further accelerating coagulation. Typically, latex may coagulate naturally 6-12 hours after tapping. If latex coagulates, the aging resistance of the subsequently produced rubber will be significantly reduced because the proteins and their decomposition products are damaged or removed.

[0004] To address the coagulation problem of natural latex, ammonia has long been added as a bactericide and preservative during latex storage. Ammonia plays multiple roles in natural latex: First, as a bactericide, it inhibits bacterial growth and enzyme activity, effectively reducing bacterial spoilage. Second, due to its alkalinity, it neutralizes acids produced by bacterial action in the latex and increases the negative charge on the surface of rubber particles, thereby improving latex stability. Third, it reacts chemically with phosphate and magnesium ions in the latex to form magnesium phosphate ammonium, which has a very low degree of dissociation, acting as a metal ion separator. Fourth, it reacts with higher fatty acids produced by lipid hydrolysis to form ammonium soaps, which adsorb onto the surface of rubber particles, increasing the negative charge and hydration of the particles and further stabilizing the colloid. Fifth, it forms aldehyde-amine or ketone-amine complexes with sugars, inhibiting the decomposition and utilization of sugars by bacteria and reducing the rate of volatile fatty acid formation.

[0005] However, the use of ammonia also brings a series of serious problems. From a health perspective, ammonia has a strong, pungent odor. Contact with or inhalation of volatile ammonia gas is not only unbearable but can also cause skin allergies, respiratory irritation, and other health problems. From a production perspective, the presence of ammonia interferes with the vulcanization process of natural latex, a crucial step in chemical cross-linking. Ammonia can cause harmful side reactions during vulcanization, leading to difficulties in vulcanization, prolonged vulcanization time, increased production costs, and affecting product quality and performance. Moreover, in some high-end applications, such as medical latex products (surgical gloves, medical catheters, etc.) and food contact materials (rubber gaskets, food conveyor belts, etc.), the risk of ammonia residue limits the application of traditional ammonia-containing natural latex.

[0006] Therefore, developing efficient and economical ammonia-free or low-ammonia natural latex production processes has become an inevitable trend in the development of the natural rubber industry. Currently, extensive research has been conducted both domestically and internationally on reducing the ammonia content in natural latex, resulting in the emergence of medium-ammonia and low-ammonia latexes, but many shortcomings remain. Some technologies partially replace the role of ammonia by adding other chemical substances, such as antibacterial agents, pH adjusters, and colloidal stabilizers, but these methods often fail to achieve the same stability as traditional high-ammonia preservation systems. Regarding mechanical stability, some low-ammonia or ammonia-free latexes are prone to thickening, flocculation, and even coagulation during storage, transportation, and processing. For example, in some natural latexes preserved with low ammonia, although the ammonia content is reduced, the mechanical stability cannot meet the national standard's minimum limit of 650 seconds, severely affecting subsequent processing and applications.

[0007] Therefore, it is necessary to provide an improved medical-grade microammonia-concentrated natural latex to solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a medical-grade microammonia-concentrated natural latex and its preparation method. By modifying the N-methylpiperazinylsilane coupling agent, whey grafting is achieved, which exerts antibacterial effects and significantly reduces the amount of ammonia used. At the same time, the negative charge of the grafted sodium alginate can improve the stability of the latex.

[0009] To achieve the above objectives, the present invention provides a method for preparing medical-grade microammonia-concentrated natural latex, comprising the following steps: S1, filter the fresh latex to remove impurities and clumps, then add it to the HY preservation system, centrifuge and concentrate to obtain latex and whey; S2, react N-methylpiperazinylsilane coupling agent and vinylsilane coupling agent, then add sodium alginate as a capping agent to react and obtain a modified antibacterial agent; S3, the modified antibacterial agent is added to the whey to carry out a free radical polymerization reaction, and then the mixture is allowed to stand for 10-20 hours. The upper latex layer is then taken and centrifuged to concentrate the mixture, thus obtaining the modified whey. S4. Mix the latex obtained in step S1 and the modified whey obtained in step S3, and then add ammonia to a mass fraction of 0.05~0.1% to obtain medical-grade micro-ammonia concentrated natural latex.

[0010] Furthermore, the molar ratio of the N-methylpiperazinylsilane coupling agent, the vinylsilane coupling agent, and the sodium alginate is (2-4):(0.5-1):1.

[0011] Furthermore, the N-methylpiperazinylpropylmethyldimethoxysilane has the following structural formula, and the vinyl silane coupling agent is vinylmethyldimethoxysilane.

[0012]

[0013] Further, step S2 specifically includes: adding N-methylpiperazinylsilane coupling agent and vinylsilane coupling agent to a mixed solvent of ethanol and water, heating to 50-65℃, adding an acid catalyst, adding sodium alginate aqueous solution dropwise during the reaction, and reacting for 1-2 hours after the addition is complete to obtain the modified antibacterial agent.

[0014] Furthermore, in step S3, the amount of the modified antibacterial agent added is 5%-10% of the dry gum mass in the whey.

[0015] Furthermore, in step S1, the dry gel content of the whey is 4% to 6%.

[0016] Furthermore, the HY preservation system consists of 1,3,5-trimethylhexahydrotriazine, sodium dodecyl sulfonate, and KOH in a mass ratio of 3:2:1.

[0017] Furthermore, in step S1, the amount of 1,3,5-trimethylhexahydrotriazine added is 0.15% to 0.25% of the mass of fresh latex.

[0018] Furthermore, in step S4, the modified whey content in the medical microammonia concentrated natural latex is 15%~20%.

[0019] Furthermore, the dry gel content of the fresh latex is 24-28%; the dry gel content of the medical micro-ammonia concentrated natural latex is 60%-68%; and the dry gel content of the modified whey is 30%-35%.

[0020] The present invention also provides a medical-grade microammonia concentrated natural latex, which is prepared by any of the preparation methods described above.

[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. The preparation method of medical-grade micro-ammonia concentrated natural latex provided by this invention utilizes an N-methylpiperazinylsilane coupling agent, which has certain antibacterial properties. This agent achieves chemical grafting between vinyl groups and rubber particles in whey, and the negative charge of the terminal sodium alginate enhances the stability of the rubber particles while simultaneously helping to repel the adhesion of positively charged bacteria. Using the modified antibacterial agent of this invention significantly reduces the amount of ammonia used, and also reduces the amount of HY (hygroscopic hydrochloride) used in the preservation system, thereby reducing the amount of KOH used and thus minimizing the negative impact of strong alkali on the latex. 2. This invention optimizes the principle, ratio, and preparation process of the modified antibacterial agent to obtain an antibacterial agent with a better structure, thereby significantly improving its mechanical stability. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation method of the medical-grade microammonia concentrated natural latex of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] This invention provides a method for preparing medical-grade microammonia-concentrated natural latex, comprising the following steps: S1, filter the fresh latex to remove impurities and clumps, then add it to the HY preservation system, centrifuge and concentrate to obtain latex and whey; S2, react N-methylpiperazinylsilane coupling agent and vinylsilane coupling agent, then add sodium alginate as a capping agent to react and obtain a modified antibacterial agent; S3, the modified antibacterial agent is added to the whey to carry out a free radical polymerization reaction, and then the mixture is allowed to stand for 10-20 hours. The upper latex layer is then taken and centrifuged to concentrate the mixture, thus obtaining the modified whey. S4. Mix the latex obtained in step S1 and the modified whey obtained in step S3, and then add ammonia to a mass fraction of 0.05~0.1% to obtain medical-grade micro-ammonia concentrated natural latex.

[0025] The N-methylpiperazinylsilane coupling agent used has certain antibacterial properties. It achieves chemical grafting between vinyl groups and rubber particles in whey, and the negative charge of the terminal sodium alginate enhances the stability of the rubber particles while simultaneously helping to repel the adhesion of positively charged bacteria. Using the modified antibacterial agent of this invention significantly reduces the amount of ammonia used, and also reduces the amount used in the HY preservation system, thereby reducing the amount of KOH used and minimizing the negative impact of strong alkali on the latex.

[0026] Furthermore, the molar ratio of the N-methylpiperazinylsilane coupling agent, the vinylsilane coupling agent, and sodium alginate is (2-4):(0.5-1):1. By controlling the content of the three components, the modified antibacterial agent can be regulated to achieve both chemical grafting and excessive cross-linking, while possessing excellent antibacterial properties and stability. Sodium alginate helps to improve its water solubility, facilitating subsequent grafting reactions.

[0027] Furthermore, the N-methylpiperazinylpropylmethyldimethoxysilane and the vinylsilane coupling agent are vinylmethyldimethoxysilane. The modified antibacterial agent has the following structural formula, but the degree of polymerization is not given.

[0028]

[0029] R1 represents sodium alginate, and R2 represents N-methylpiperazinylpropyl.

[0030] Specifically, N-methylpiperazinylsilane coupling agent and vinylsilane coupling agent are added to a solvent of ethanol and water in a volume ratio of 60:40, the temperature is raised to 60°C, an acid catalyst is added, and sodium alginate aqueous solution is added dropwise during the reaction. After the addition is complete, the reaction is carried out for 1-2 hours to obtain the modified antibacterial agent. By controlling the reaction time and the dropping rate of sodium alginate, the degree of polymerization of the modified antibacterial agent can be controlled to prevent its molecular weight from being too large and affecting the latex properties. The preferred dropping rate of sodium alginate aqueous solution is 3-6 ml / min, and the mass fraction of sodium alginate aqueous solution is 1%-5%.

[0031] Furthermore, in step S3, the amount of the modified antibacterial agent added is 5%-10% of the dry gum mass in the whey.

[0032] Furthermore, in step S1, the dry gel content of the whey is 4% to 6%.

[0033] Furthermore, the HY preservation system consists of 1,3,5-trimethylhexahydrotriazine, sodium dodecyl sulfonate, and KOH in a mass ratio of 3:2:1.

[0034] Furthermore, in step S1, the amount of 1,3,5-trimethylhexahydrotriazine added is 0.15% to 0.25% of the mass of fresh latex.

[0035] Furthermore, in step S4, the modified whey content in the medical microammonia concentrated natural latex is 15%~20%.

[0036] Furthermore, the dry gel content of the fresh latex is 24-28%; the dry gel content of the medical micro-ammonia concentrated natural latex is 60%-68%; and the dry gel content of the modified whey is 30%-35%.

[0037] Example 1 A method for preparing medical-grade microammonia-concentrated natural latex includes the following steps: S1, Fresh latex (dry latex content 26%) is filtered to remove impurities and clumps, then added to the HY preservation system, centrifuged and concentrated to obtain latex and whey; wherein, the HY preservation system is composed of 1,3,5-trimethylhexahydrotriazine, sodium dodecyl sulfonate and KOH, and the addition amounts are 0.2%, 0.2% and 0.1% of the mass of fresh latex, respectively.

[0038] S2, N-methylpiperazinylpropylmethyldimethoxysilane and vinylmethyldimethoxysilane were added to a solvent of ethanol and water in a volume ratio of 60:40, the temperature was raised to 60℃, an acid catalyst was added, and sodium alginate aqueous solution (mass fraction of 2%) was added dropwise at a rate of 4 ml / min during the reaction. After the addition was completed, the reaction was carried out for 1 h to obtain a modified antibacterial agent; wherein, the molar ratio of N-methylpiperazinylpropylmethyldimethoxysilane, vinylmethyldimethoxysilane and sodium alginate was 3:0.5:1; S3, add the modified antibacterial agent to the whey (the amount of modified antibacterial agent added is 8% of the dry glue mass of the whey), add a free radical initiator, carry out a free radical polymerization reaction at 100°C, then let it stand for 15 hours, take the upper latex layer, centrifuge and concentrate to obtain modified whey (dry glue mass content 32%). S4. Mix the latex obtained in step S1 and the modified whey obtained in step S3, and then add ammonia to a mass fraction of 0.06% to obtain medical micro-ammonia concentrated natural latex (modified whey mass content is 16%).

[0039] Example 2 A method for preparing medical microammonia concentrated natural latex differs from Example 1 in that the amount of modified antibacterial agent added is 5% of the dry gel mass in the whey.

[0040] Example 3 A method for preparing medical-grade microammonia concentrated natural latex differs from Example 1 in that the amount of modified antibacterial agent added is 2% of the dry gel mass in the whey.

[0041] Example 4 The method for preparing medical microammonia concentrated natural latex differs from Example 1 in that the molar ratio of N-methylpiperazinylpropylmethyldimethoxysilane, vinylmethyldimethoxysilane, and sodium alginate is 3:1:1.

[0042] Example 5 The method for preparing medical microammonia concentrated natural latex differs from Example 1 in that the molar ratio of N-methylpiperazinylpropylmethyldimethoxysilane, vinylmethyldimethoxysilane, and sodium alginate is 2:0.5:1.

[0043] Example 6 A method for preparing medical microammonia concentrated natural latex differs from Example 1 in that step S2 is as follows: N-methylpiperazinylpropylmethyldimethoxysilane and vinylmethyldimethoxysilane are added to a solvent with a volume ratio of ethanol to water of 60:40, the temperature is raised to 60°C, an acid catalyst is added, and the reaction is carried out for the same time as in Example 1. Then, an aqueous solution of sodium alginate (mass fraction of 2%) is added, and the reaction is continued for 1 hour. The molar ratio of N-methylpiperazinylpropylmethyldimethoxysilane, vinylmethyldimethoxysilane, and sodium alginate is 3:0.5:1.

[0044] Comparative Example 1 A method for preparing medical-grade microammonia-concentrated natural latex differs from Example 1 in that the modified whey content in the medical-grade microammonia-concentrated natural latex is 5%.

[0045] Comparative Example 2 A method for preparing medical-grade microammonia-concentrated natural latex includes the following steps: S1, Fresh latex (dry latex content 26%) is filtered to remove impurities and clumps, then added to the HY preservation system, centrifuged and concentrated to obtain latex and whey; wherein, the HY preservation system is composed of 1,3,5-trimethylhexahydrotriazine, sodium dodecyl sulfonate and KOH, and the addition amounts are 0.2%, 0.2% and 0.1% of the mass of fresh latex, respectively.

[0046] S2, N-methylpiperazinylpropylmethyldimethoxysilane is added to a solvent of ethanol and water in a volume ratio of 60:40, the temperature is raised to 60°C, an acid catalyst is added, and the reaction is carried out for 1 hour to obtain an antibacterial agent; S3, add the antibacterial agent to the whey (the amount of antibacterial agent added is 8% of the dry glue mass of the whey), add a free radical initiator, carry out a free radical polymerization reaction at 100°C, then let it stand for 15 hours, take the upper latex layer, centrifuge and concentrate to obtain modified whey (dry glue mass content 32%). S4. Mix the latex obtained in step S1 and the modified whey obtained in step S3, and then add ammonia to a mass fraction of 0.06% to obtain medical micro-ammonia concentrated natural latex (modified whey mass content is 16%).

[0047] Comparative Example 3 A method for preparing medical-grade microammonia-concentrated natural latex includes the following steps: S1, Fresh latex (dry latex content 26%) is filtered to remove impurities and clumps, then added to the HY preservation system, centrifuged and concentrated to obtain latex and whey; wherein, the HY preservation system is composed of 1,3,5-trimethylhexahydrotriazine, sodium dodecyl sulfonate and KOH, and the addition amounts are 0.2%, 0.2% and 0.1% of the mass of fresh latex, respectively.

[0048] S2, N-methylpiperazinylpropylmethyldimethoxysilane and vinylmethyldimethoxysilane are added to a solvent of ethanol and water in a volume ratio of 60:40, the temperature is raised to 60℃, an acid catalyst is added, and the reaction is carried out for 1 hour to obtain a modified antibacterial agent; wherein, the molar ratio of N-methylpiperazinylpropylmethyldimethoxysilane and vinylmethyldimethoxysilane is 3:0.5; S3, add the modified antibacterial agent (the amount of modified antibacterial agent added is 6.2% of the dry gum mass of the whey) and sodium alginate (the amount of added is 1.8% of the dry gum mass of the whey) to the whey, add a free radical initiator, carry out a free radical polymerization reaction at 100°C, then let it stand for 15 hours, take the upper latex layer, centrifuge and concentrate to obtain modified whey (dry gum mass content 32%). S4. Mix the latex obtained in step S1 and the modified whey obtained in step S3, and then add ammonia to a mass fraction of 0.06% to obtain medical micro-ammonia concentrated natural latex (modified whey mass content is 16%).

[0049] The standard for determining dry gum content is GB / T8292-2008. The standard for testing volatile fatty acids is GB / T8299-2008. The standard for testing mechanical stability after 30 days is GB / T8301-2008.

[0050] Table 1. Performance test results of the examples and comparative examples.

[0051] As shown in Table 1, the modified antibacterial agent of this invention exhibits high mechanical stability. When the amount of modified antibacterial agent added is too small (Example 3), the mechanical stability decreases significantly. The mechanical stability also decreases when the vinyl content increases, possibly due to excessive cross-linking leading to aggregation. The mechanical stability also decreases when sodium alginate is added asynchronously, indicating that the reaction between N-methylpiperazinylpropylmethyldimethoxysilane and vinylmethyldimethoxysilane may involve excessive condensation, and a large molecular weight is detrimental to stability. Insufficient modified whey is also unfavorable. When vinyl and sodium alginate grafting is not performed, the mechanical stability decreases significantly. Adding sodium alginate alone, without condensation grafting to the antibacterial agent, also yields poor results.

[0052] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing medical-grade microammonia-concentrated natural latex, characterized in that, Includes the following steps: S1, filter the fresh latex to remove impurities and clumps, then add it to the HY preservation system, centrifuge and concentrate to obtain latex and whey; S2, react N-methylpiperazinylsilane coupling agent and vinylsilane coupling agent, then add sodium alginate as a capping agent to react and obtain a modified antibacterial agent; S3, the modified antibacterial agent is added to the whey to carry out a free radical polymerization reaction, and then the mixture is allowed to stand for 10-20 hours. The upper latex layer is then taken and centrifuged to concentrate the mixture, thus obtaining the modified whey. S4. Mix the latex obtained in step S1 and the modified whey obtained in step S3, and then add ammonia to a mass fraction of 0.05~0.1% to obtain medical-grade micro-ammonia concentrated natural latex.

2. The method for preparing medical-grade microammonia-concentrated natural latex according to claim 1, characterized in that, The molar ratio of the N-methylpiperazinylsilane coupling agent, the vinylsilane coupling agent, and the sodium alginate is (2-4):(0.5-1):

1.

3. The method for preparing medical-grade microammonia-concentrated natural latex according to claim 1 or 2, characterized in that, The N-methylpiperazinylpropylmethyldimethoxysilane is used as the vinyl silane coupling agent.

4. The method for preparing medical-grade microammonia-concentrated natural latex according to claim 3, characterized in that, Step S2 specifically includes: adding N-methylpiperazinylsilane coupling agent and vinylsilane coupling agent to a mixed solvent of ethanol and water, heating to 50-65℃, adding an acid catalyst, adding sodium alginate aqueous solution dropwise during the reaction, and reacting for 1-2 hours after the addition is complete to obtain the modified antibacterial agent.

5. The method for preparing medical-grade microammonia-concentrated natural latex according to claim 1, characterized in that, In step S1, the amount of modified antibacterial agent added is 5%-10% of the dry gum mass of the whey, and the dry gum mass content of the whey is 4%-6%.

6. The method for preparing medical-grade microammonia-concentrated natural latex according to claim 1, characterized in that, The HY preservation system consists of 1,3,5-trimethylhexahydrotriazine, sodium dodecyl sulfonate, and KOH in a mass ratio of 3:2:

1.

7. The method for preparing medical-grade microammonia-concentrated natural latex according to claim 6, characterized in that, In step S1, the amount of 1,3,5-trimethylhexahydrotriazine added is 0.15% to 0.25% of the mass of fresh latex.

8. The method for preparing medical-grade microammonia-concentrated natural latex according to claim 1, characterized in that, In step S4, the modified whey content in the medical microammonia concentrated natural latex is 15%~20%.

9. The method for preparing medical-grade microammonia-concentrated natural latex according to claim 1, characterized in that, The fresh latex has a dry gel content of 24-28%; the medical-grade microammonia concentrated natural latex has a dry gel content of 60%-68%; and the modified whey has a dry gel content of 30%-35%.

10. A medical-grade micro-ammonia concentrated natural latex, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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