Method for preserving natural latex in acidic environment

Abstract

The invention provides a method for preserving natural latex in an acid environment, and belongs to the technical field of natural latex preservation. The method provided by the invention comprises the following steps: adding a surfactant into natural latex, adjusting the pH value, and then adding lysozyme; the surface active agent is an anionic surface active agent or a nonionic surface active agent; the pH value is 5 to 7. The invention provides a method for preserving fresh natural latex in a weakly acidic and even neutral environment (the pH value is 5.0-7.0), which is opposite to a natural latex strong alkali environment (the pH value is 8-11) preservation technology in the current industry. Compared with the traditional alkali preservation latex, the shelf life of the fresh field latex is prolonged from several hours to 30 days or even longer, the fresh field latex is not solidified or rotten or stink, and a brand new thought is provided for long-time stable preservation of the fresh latex.

Description

Technical Field

[0001] The invention relates to the technical field of natural latex preservation, in particular to a method for preserving natural latex in an acidic environment. Background Art

[0002] Natural latex is a white viscous milky water dispersion of rubber particles in a near-neutral medium. If it is not preserved and treated in time, the infection of bacteria, enzymes and microorganisms will cause the proteins and sugars in the latex to metabolize and multiply, resulting in fermentation and hydrolysis, which will reduce the pH value of the fresh latex to the weak acid range. The stability of the latex will gradually decrease, and it may produce odor and coagulate naturally in 2-12 hours, which is called premature coagulation. It makes further handling of the latex, such as collection, transportation, storage and further processing, more difficult or almost impossible.

[0003] In the current latex industrial production, ammonia is usually used as the most ideal anticoagulant for the early storage (collection, transportation, centrifugation) and long-term storage (stable storage after centrifugation until the production of latex products) of latex. It has low cost and significant effect. Alkaline bactericidal or antibacterial additives are added to fresh latex or nearly neutral natural latex to inhibit the corruption process caused by bacterial growth, while increasing the pH value of the latex to keep it away from the isoelectric point of protein (usually pH 4-5), increase the thickness of the double electric layer of rubber particles, and thus enhance the stability of the latex. The higher the alkalinity, the better its stability. For the preservation of fresh field latex, ammonia water is usually added at 0.3-0.8% of the weight of the latex according to the length of time required for storage, the condition of the latex and other factors. When used in combination with other bactericides (such as tetramethylthiourea / zinc oxide TMTD / ZnO, etc.), the amount of ammonia added is reduced to 0.2-0.5% by weight. In recent years, scholars and practitioners at home and abroad have developed composite preservatives based on ammonia and combined with various fungicides and enzyme reagents to improve the stability of latex. However, ammonia has a strong pungent smell, which has adverse effects on the surrounding environmental pollution and the health of practitioners. In addition, alkaline substances are formed in the latex preserved by ammonia, which promotes the hydrolysis of phospholipids related to rubber particles into long-chain fatty acid soaps and glycerol and then enters the whey, making the protein in the protective layer account for the majority, affecting the branching structure of natural rubber and thus affecting its mechanical properties, such as tensile strength and wear resistance. Due to the large-scale harvesting of high-yield asexual rubber trees and the use of ethephon to stimulate production in recent years, the sugar and invertase content of latex is relatively high, resulting in the rapid formation of volatile fatty acids after latex is infected by bacteria. Using ammonia alone as a preservative can no longer meet the requirements. The amount of ammonia added has reached 0.5% or even 1%, and it cannot make the fresh latex effective for several days. The volatile fatty acid value of the concentrated natural latex produced often exceeds the specified quality index, which brings great trouble and loss to production.

[0004] Therefore, a method for long-term preservation and stabilization of fresh latex is needed without or with less use of ammonia, an alkaline basic preservation material. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preserving natural latex in an acidic environment. The method provided by the present invention achieves long-term preservation and stabilization of fresh natural latex without containing ammonia, TMTD, ZnO or other harmful chemicals.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preserving natural latex in an acidic environment, comprising adding a surfactant to the natural latex, adjusting the pH value, and then adding lysozyme;

[0008] The surfactant is an anionic surfactant or a nonionic surfactant;

[0009] The pH value is 5-7.

[0010] In some embodiments of the present invention, the preferred pH value is 5-6.

[0011] The present invention first adds a surfactant to keep the fresh latex stable and not coagulate, and then adjusts the pH value of the latex to be compatible with the most suitable pH value of lysozyme. The acidic environment can inhibit the growth of bacteria and the lysozyme can efficiently destroy the peptidoglycan of the bacterial cell wall. The two work together to protect the natural latex from bacterial invasion, thereby achieving long-term preservation and stabilization of the fresh natural latex.

[0012] In some embodiments of the present invention, the natural latex is fresh latex collected from rubber trees (i.e., fresh latex 3 hours after collection, with a total solid content of 20-35%) or neutral natural latex concentrated by conventional techniques (such as high-speed centrifugation) but not subjected to preservation treatment.

[0013] In some embodiments of the present invention, the anionic surfactant is a sulfonate surfactant, an alkyl sulfate surfactant, an alkyl phosphate surfactant, a polyoxyalkyl alkyl sulfate surfactant or a polyoxyalkyl alkyl phosphate surfactant; the nonionic surfactant is an ester ethylene oxide adduct, an alkyl ether ethylene oxide adduct, an amine ethylene oxide adduct, an amide ethylene oxide adduct or a thiol ether ethylene oxide adduct.

[0014] In the same surfactant concentration range, anionic surfactants can make the Zeta potential amplitude better than nonionic surfactants, and their preservation effect is better, so anionic surfactants are preferred to stabilize natural rubber latex. Further, according to the properties of the surfactant in water and the possible interaction with lysozyme, sulfonate surfactants or alkyl sulfate surfactants are preferred.

[0015] In some embodiments of the present invention, the sulfonate surfactant is alkylbenzene sulfonate, alkyl sulfonate, alkylnaphthalene sulfonate, naphthalene sulfonate or diphenyl ether sulfonate; preferably sodium dodecylbenzene sulfonate; and the alkyl sulfate surfactant is preferably sodium dodecyl sulfate.

[0016] In some embodiments of the present invention, the amount of the surfactant is 0.5-5% by weight of the natural rubber latex.

[0017] In some embodiments of the present invention, the amount of the surfactant is 0.5-3% by weight of the natural rubber latex.

[0018] When adding the surfactant, the surfactant is first prepared into a solution and then added into the natural latex, and stirred at the same time to promote the diffusion of the surfactant. The next step can be performed after stirring for 5-60 minutes.

[0019] After the surfactant is mixed with the natural latex, a defoamer accounting for 0.01-0.3% of the weight of the natural latex can be added to defoam. The present invention does not specifically limit the selection of the defoamer, and the defoamer commonly used by those skilled in the art can be selected, such as lanolin, methyl silicone oil or organosiloxane.

[0020] In some embodiments of the present invention, the reagent used to adjust the pH is hydrochloric acid, sulfuric acid, formic acid or acetic acid. When adjusting the pH value of the present invention, it is preferably a dilute solution of formic acid or acetic acid, for example: the concentration is 2-10% (v / v). In the present invention, the acid solution is slowly dripped into the stabilized latex and stirred evenly until the pH value of the latex reaches 5.0-7.0, and the stirring is continued for 5-30 minutes.

[0021] In some embodiments of the present invention, the amount of lysozyme used is 0.01-1.0% by weight of the natural rubber latex.

[0022] In some embodiments of the present invention, the amount of lysozyme used is 0.4-0.7% by weight of the natural rubber latex.

[0023] When adding lysozyme, the lysozyme is prepared into a bacterial solution and then added. In order to maintain the activity of the lysozyme, 2-hydroxypropyl-β-cyclodextrin is also added. The present invention does not make special requirements on the amount of 2-hydroxypropyl-β-cyclodextrin, which can meet the activity of the lysozyme, for example: 0.1-1 times the mass of the lysozyme.

[0024] In some embodiments of the present invention, after adding lysozyme, a stirring step is further included to evenly disperse the lysozyme.

[0025] The present invention uses enzyme reagents to preserve fresh natural latex or freshly centrifuged neutral latex in a weakly acidic or even neutral environment (pH = 5.5-7.0), and eliminates harmful bacteria by exerting the sterilization mechanism of lysozyme to destroy the cell wall of microorganisms under the optimal pH environment, thereby reducing the erosion and hydrolysis of rubber particles by microorganisms including bacteria, so that the rubber particles remain stable for a long time. This is very different from the current technology in the industry that adds strong alkaline substances to keep the pH value of latex between 8 and 11 to achieve stable storage of latex.

[0026] The present invention discloses the following technical effects:

[0027] The present invention provides a method for preserving fresh natural latex in a weakly acidic or even neutral environment (pH = 5.0-7.0), which is contrary to the current industry's natural latex preservation technology in a strong alkaline environment (pH = 8-11). Compared with traditional alkali-preserved latex, the shelf life of fresh field latex is increased from a few hours to 30 days or even longer, and it neither coagulates nor becomes rancid and smelly.

[0028] Since lysozyme can be used as a food preservative and fresh-keeping additive and a harmless medicine to the human body, ammonia and other alkaline reagents are no longer used in the latex preservation process, thus avoiding the volatilization of pungent odors in the natural rubber production process. At the same time, water treatment facilities are no longer needed to remove ammonia and its derivatives, thus reducing the intensity of rubber wastewater treatment and making it safer and more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 The state diagram of Example 2-7 after storage at room temperature for 0 days (A) and 30 days (B). DETAILED DESCRIPTION

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] The isoelectric point of natural latex is about pH=4.5 (derived from the isoelectric point of latex protein, which is mostly between pH 4 and 5), the isoelectric point of lecithin is pH=6.7, and the pH value of fresh latex collected from rubber trees is generally 6.8. When the pH value of fresh latex reaches the isoelectric point of protein, it will slowly thicken, and after a period of time, it will form a uniform clot with a network structure. The natural coagulation of natural latex is generally believed to be caused by one or more mechanisms, namely: (1) the growth of microorganisms (including bacteria) interacts with the non-rubber components of latex, causing sugars and proteins to ferment and hydrolyze to produce various water-soluble low-level fatty acids, especially volatile fatty acids, which reduce the stability of the colloidal system and cause coagulation; and / or (2) microbial growth and / or enzymes present in the latex itself cause the hydrolysis of non-rubber substances in the latex, and fatty acid anions are released. These anions are adsorbed on the surface of the colloidal rubber particles, or may replace the proteins adsorbed on the surface of the particles. The reduction in latex pH caused by the generated acidic compounds reduces the number of carboxyl anions on the surface of the rubber particles, which in turn reduces the electrostatic repulsion of the colloidal particles, thereby reducing the stability of the latex; and / or (3) the rubber particles with fatty acid anion groups adsorbed on the surface interact with the calcium ions and magnesium ions present in the latex, resulting in a reduction in the number of carboxyl anions, thereby reducing the stability of the colloidal dispersion and ultimately causing the coagulation of the rubber particles. The stability of the latex can be improved by inhibiting the coagulation mechanism.

[0037] Lysozyme is an alkaline globulin, which contains alkaline amino acids, amide residues and aromatic amino acids in its molecules. The high proportion of these components makes lysozyme show high activity under specific pH conditions. The bactericidal mechanism of lysozyme mainly depends on its ability to hydrolyze bacterial cell walls. By destroying the β-1,4 glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine in the cell wall, the insoluble mucopolysaccharide in the cell wall is decomposed into soluble glycopeptides, causing the cell wall to rupture and the contents to escape, thereby dissolving the bacteria. Lysozyme is widely present in the tissues of the human body, animals and plants. It is a natural preservative with high safety and bactericidal effect. Therefore, it is an ideal preservative for the preservation and stabilization of natural latex.

[0038] Lysozyme can effectively decompose the peptidoglycan in the bacterial cell wall and cause the chemical bonds to break, thus damaging the bacterial cell wall. Peptidoglycan is the main component of the bacterial cell wall. It is a multi-layered network macromolecular structure composed of disaccharide units, tetrapeptide tails and peptide bridges, and is not a component of the cell membrane. Natural latex contains sugars, but they are mainly simple sugars, such as glucose, fructose, etc., which are not polysaccharides. Therefore, lysozyme will only kill bacteria, but will not degrade the natural rubber particle structure with a cell membrane-like structure. The effect of lysozyme on bacteria is achieved through its antibacterial properties, and will not change the spatial conformation of proteins in the natural latex particle structure, so it does not involve protein denaturation. In addition, there is a relatively complex interaction between lysozyme and phospholipids, and its possible mechanisms of action are: 1) Electrostatic interaction: Lysozyme is positively charged under near-neutral conditions, and electrostatically interacts with the negatively charged phospholipid membrane, resulting in the adsorption and structural changes of lysozyme on the phospholipid membrane; 2) Structural changes: Lysozyme regulates its own structure during the unfolding process, inducing phospholipids to undergo lateral displacement and ultimately enrichment and phase separation; 3) Membrane fusion mechanism: Lysozyme penetration into the lipid layer may lead to structural reorganization, thereby affecting the stability of the membrane. Therefore, in the process of preservation and stabilization of natural latex, lysozyme mainly plays a role in killing bacteria, and at the same time promotes the hydrolysis of phospholipids in the protective layer of natural latex particles, but does not cause strong damage to the basic structure of natural rubber.

[0039] However, the sterilization process of lysozyme will be hindered under alkaline conditions. Alkali will inhibit the activity of lysozyme, affecting its destruction and killing effect on bacteria. Lysozyme contains more alkaline amino acid residues, so its isoelectric point is as high as about 10.7 (between 10.5-11.5, different literatures), and the most suitable pH value is 6.5-6.6. Lysozyme is stable in an acidic environment. Under the conditions of high temperature of 96°C and pH value of 3, its activity can still be maintained at 87% after 15 minutes, but it is easily inactivated in an alkaline environment. Therefore, it is not easy to play a sterilizing role in natural latex stored in an alkaline environment.

[0040] There are many mechanisms for the production of volatile fatty acids, which are indicators of the deterioration and quality of natural latex, but the combined action of bacteria and enzymes plays a decisive role. Therefore, killing or inhibiting the activity of bacteria can inhibit the production of volatile fatty acids or reduce the rate of production of volatile fatty acids, thereby achieving the purpose of preserving natural latex. Generally speaking, bacteria are more likely to survive in a neutral or weakly alkaline environment (usually between pH 7.2 and 7.6). In contrast, an acidic environment has a certain inhibitory effect on the growth of bacteria, and most bacteria cannot survive in an acidic environment. An acidic environment can destroy the DNA and RNA of bacteria, preventing their cell division and proliferation; an acidic environment can cause changes in the charge of the cell membrane, affecting the absorption of nutrients by bacteria, and at the same time inhibiting the activity of certain enzymes and hindering the normal metabolism of bacteria. Therefore, storing latex in a weakly acidic environment is conducive to inhibiting the growth of bacteria, which is consistent with the most suitable pH value for lysozyme to exert its bactericidal properties, so as to better exert the antibacterial and bactericidal effects of the two and avoid the production of low-level fatty acids.

[0041] Therefore, in the method for preserving natural latex in an acidic environment provided by the present invention, the long-term preservation of latex is achieved by maintaining the colloidal stability through two pathways: 1) the surfactant adsorbs its hydrophobic tail and embeds it into the rubber particles, and directs its hydrophilic head toward the aqueous serum, thereby strengthening the protective layer of the protein-phospholipid layer of the rubber particles; 2) the combined action of the acidic environment and lysozyme inhibits and kills bacteria, so that the natural latex does not contain volatile fatty acids.

[0042] This method of preserving latex in an acidic environment goes against common sense for anyone in the latex industry, because natural latex in an emulsion state is usually stabilized by ammonia in an alkaline environment, and contact with acids (such as sulfuric acid or formic acid) will quickly cause acid-base neutralization and cause the latex to coagulate. This is a common solid raw rubber production process in the traditional rubber industry.

[0043] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels, and corresponding effects can be achieved.

[0044] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0045] Example 1

[0046] Take 3 portions of 1 kg fresh latex (solid content of 32.1%), add 30 ml of 5% (v / v) acetic acid, 5 grams of lysozyme and 10 grams of alkaline protease to treat natural rubber, stir evenly and let stand, after the natural latex solidifies into a clot, use a crepe machine to press the clot to dehydrate, soak it in water for 10 hours and wash away the residual substances, finally hang the film and dry it in an oven at 100°C to obtain solid natural rubber. Then use a Kjeldahl nitrogen analyzer to measure its protein content, and the results are 3.1%, 3.6% and 2.1% respectively. The nitrogen content of lysozyme coagulated rubber is slightly higher than that of acetic acid coagulated rubber but much higher than that of enzyme coagulated rubber. This is because lysozyme itself is a protein that will be adsorbed on the outside of rubber particles, resulting in its protein determination result being greater than that of ordinary natural rubber. The results fully show that lysozyme has little damage to the protein in latex and will not have a strong effect on the degree of protein hydrolysis. The rubber protein is basically preserved, which is exactly the opposite of the strong effect of protease on rubber protein. It also shows that when no surfactant is added to the latex, only adding lysozyme will cause the latex to become unstable and coagulate, indicating that surfactant is crucial to the stability of latex.

[0047] Therefore, when lysozyme is used to treat fresh natural latex, lysozyme only acts on the microorganisms in the latex and the phospholipids in the latex particles, that is, it sterilizes by destroying the cell walls of the microorganisms, and interacts with the phospholipids of the latex particles to cause certain changes in the protein and phospholipid layers adsorbed by the latex protective layer, but it will not damage the basic structure of natural rubber and will not affect its macroscopic properties.

[0048] Example 2

[0049] In 1 kilogram of fresh latex (solid content is 32.1%, pH is 7.4) newly collected, add 300 grams of sodium dodecylbenzene sulfonate solution (sodium dodecylbenzene sulfonate accounts for 3% of fresh latex weight) of 10wt%, stir 30min, then use 5% (v / v) acetic acid to adopt the mode of dropwise adding to adjust pH value to 5.5, leave to preserve. Its shelf life can reach 7 days without corruption, and there is no obvious thickening. Continue to adjust the latex pH value to 4.0, latex still does not produce clots, good fluidity and do not have coagulation stinking phenomenon. Therefore, under acidic environment, even if the pH value of latex is reduced to 4.0, after adding enough surfactant, fresh latex still can maintain stable and does not coagulate.

[0050] Example 3

[0051] 200 g of 10 wt% sodium dodecylbenzene sulfonate solution (sodium dodecylbenzene sulfonate accounts for 2% of the weight of the latex) was added to 1 kg of fresh latex (solid content of 32.1%, pH of 7.4) and stirred for 30 min. Then, 5% (v / v) acetic acid was added dropwise to adjust the pH value to 6.0. Stirring was continued for 20 min. Then, 100 g of 5% lysozyme solution (lysozyme accounts for 0.5% of the weight of the latex) was added and stirred for 30 min. The mixture was left to stand for storage. The smell, coagulum (filtered with a 40-mesh screen) and viscosity were observed on the 5th, 10th, 15th, 20th and 30th days. The results showed that no odor or large coagulum appeared for up to 30 days, and the viscosity was basically maintained at 10-12 mPa.s -1 The fluidity is good, there is no obvious thickening phenomenon, and no mold spots appear in the later stage.

[0052] Example 4

[0053] 200 g of 10 wt% sodium dodecyl sulfate solution (sodium dodecyl sulfate accounts for 2% of the weight of the latex) was added to 1 kg of fresh latex (solid content of 32.1%, pH of 7.4) and stirred for 30 min. Then, 5% (v / v) acetic acid was added dropwise to adjust the pH value to 6.0. Stirring was continued for 20 min. Then, 100 g of 5% lysozyme solution (lysozyme accounts for 0.5% of the weight of the latex) and 5 g of 2-hydroxypropyl-β-cyclodextrin were added and stirred for 30 min. The mixture was left to stand for storage. The smell, agglomerates (filtered with a 40-mesh screen) and viscosity were observed on the 5th, 10th, 20th and 30th days. No odor or large agglomerates appeared for 30 days, and the viscosity was basically maintained at 12-15 mPa.s. -1 The fluidity was good, there was no obvious thickening phenomenon, and no mildew stains appeared in the later stage. (Compared with Example 3, the difference is that sodium dodecylbenzene sulfonate was replaced by sodium dodecyl sulfate)

[0054] Example 5

[0055] The concentrated latex (solid content of 65.1%, pH of 8.1) just after centrifugation and not yet preserved by adding ammonia is diluted with water to a concentration of 32% (m / v, g / mL), 200 g of a 10wt% sodium dodecylbenzene sulfonate solution (sodium dodecylbenzene sulfonate accounts for 2% of the weight of 1 kg of the diluted latex) is added to 1 kg of the diluted latex and stirred for 30 min, then the pH value is adjusted to 6.0 by dropwise addition of 5% (v / v) acetic acid, stirring is continued for 40 min, and then 100 g of a 5% lysozyme solution (lysozyme accounts for 0.5% of the weight of the latex) and 5 g of 2-hydroxypropyl-β-cyclodextrin are added, stirred for 30 min, and allowed to stand for storage. The changes in odor, agglomerates (filtered with a 40-mesh screen) and viscosity were observed on the 5th, 10th, 20th and 30th days. No odor or large agglomerates appeared for 30 days, and the viscosity was basically maintained at 20-23mPa.s. -1 The fluidity is good, there is no obvious thickening phenomenon, and no mold spots appear in the later stage.

[0056] Example 6

[0057] Same as Example 3, except that lysozyme accounts for 0.7% of the weight of the latex.

[0058] Example 7

[0059] Same as Example 3, except that the amount of surfactant used is 0.3% of the weight of the latex, and the amount of lysozyme used is 0.7% of the weight of the latex. (This example is a comparative example in which the amount of surfactant used is less than 0.5% of the weight of the natural latex)

[0060] The changes in odor, coagulum (filtered with a 40-mesh screen) and viscosity of the natural latex under the storage conditions of Examples 5 and 6 were observed on the 5th, 10th, 20th and 30th days respectively. No odor or large coagulum appeared for up to 30 days, the fluidity was good, there was no obvious thickening phenomenon, and no mold spots appeared in the later period. However, in Example 7, more coagulum was observed on the second day, accompanied by a slight corrupt odor. Coagulum of different sizes appeared after the fourth day, and the gas in the container increased. Comparing Example 6 with Example 7, when the amount of lysozyme added was the same, the natural latex was prone to instability when the amount of surfactant used was less than 0.5% of the weight of the latex.

[0061] The state diagram of the natural latex of Example 2-7 stored at room temperature for 0 days and 30 days is as follows Figure 1 As shown (in the figure, the numbers 1-6 on the bottles correspond to Examples 2-7 respectively, and Example 7 has solidified).

[0062] The present invention also verifies that when other non-ionic surfactant Triton-100 (i.e., polyethylene glycol monooctylphenyl ether) is selected, an experiment of preserving natural latex is carried out under the same conditions as in Example 3. The results show that after a storage time of up to 30 days, within this time range, no odor or large agglomerates appear, the fluidity is good, there is no obvious thickening phenomenon, and no mold spots appear in the later period.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preserving natural rubber latex in an acidic environment, characterized in that: After adding surfactant to natural rubber latex, the pH value is adjusted and then lysozyme is added; The surfactant is an anionic surfactant or a nonionic surfactant; The pH value is 5-7.

2. The method for preserving natural rubber latex in an acidic environment according to claim 1, characterized in that: The natural latex is fresh latex collected from rubber trees or neutral natural latex concentrated by conventional technology but not subjected to preservation treatment.

3. The method for preserving natural rubber latex in an acidic environment according to claim 1, characterized in that: The anionic surfactant is a sulfonate surfactant, an alkyl sulfate surfactant, an alkyl phosphate surfactant, a polyoxyalkyl alkyl sulfate surfactant or a polyoxyalkyl alkyl phosphate surfactant; the nonionic surfactant is an ester ethylene oxide adduct, an alkyl ether ethylene oxide adduct, an amine ethylene oxide adduct, an amide ethylene oxide adduct or a thiol ether ethylene oxide adduct.

4. The method for preserving natural rubber latex in an acidic environment according to claim 3, characterized in that: The sulfonate surfactant is alkylbenzene sulfonate, alkyl sulfonate, alkylnaphthalene sulfonate, naphthalene sulfonate or diphenyl ether sulfonate; the alkyl sulfate surfactant is sodium dodecyl sulfate.

5. The method for preserving natural latex in an acidic environment according to claim 1, characterized in that: The amount of the surfactant used is 0.5-5% by weight of the natural rubber latex.

6. The method for preserving natural rubber latex in an acidic environment according to claim 1, characterized in that: The reagents used to adjust pH are hydrochloric acid, sulfuric acid, formic acid or acetic acid.

7. The method for preserving natural latex in an acidic environment according to claim 1, characterized in that: The amount of lysozyme used is 0.01-1.0% by weight of the natural rubber latex.

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