A kind of medical ammonia-free concentrated natural latex and preparation method thereof

Abstract

The invention belongs to the technical field of natural latex, specifically a kind of medical ammonia-free concentrated natural latex and preparation method thereof, fresh latex is filtered to remove impurities and clots, then HY preservation system is added, centrifuged and concentrated to obtain latex and whey; oleic acid and acidic catalyst are added to an esterification reactor, stirred at 80-90°C for 1-3h, then 16-hydroxypalmitic acid is added, esterification reaction is carried out at 130-150°C for 2-6h to obtain oleate; oleate is used to modify the rubber hydrocarbon particles in the whey by free radical polymerization, then a creaming agent is added to cream the modified whey, then centrifuged and concentrated to obtain creamed modified whey; the latex obtained in step S1 and the creamed modified whey obtained in step S2 are mixed, and then KOH is added to obtain medical ammonia-free concentrated natural latex. The present invention can improve the mechanical stability of natural latex and improve the utilization rate of raw materials.

Description

Technical Field

[0001] The invention belongs to the technical field of natural latex, and in particular relates to medical ammonia-free concentrated natural latex and a preparation method thereof. Background Art

[0002] Concentrated natural rubber latex (CNRL) mainly includes water, rubber hydrocarbon particles, proteins, lipids, sugars, inorganic salts, bacteria, etc. Among them, bacteria can easily decompose and utilize non-rubber components such as sugars and proteins to reproduce and grow in latex, causing it to rot and deteriorate. The corruption products include fatty acids, which can destroy the protective layer on the surface of particles in the latex, and then cause particle agglomeration. The apparent phenomenon is the coagulation and deterioration of latex. Therefore, it is necessary to add latex protective agents to inhibit the corruption and deterioration process.

[0003] Ammonia substances are the most common natural latex protective agents, which can inhibit the activity of enzymes and bacteria. However, ammonia substances themselves are highly volatile, and when used in large quantities, they will produce pungent odors due to the volatilized ammonia. It has an adverse effect on the health of workshop workers and the surrounding environment. Therefore, ammonia-free preservatives have emerged, such as sodium pentachlorophenol, zinc sulfate, tea extract, triazine, etc. However, the current ammonia-free preservatives are mainly designed to reduce the content of volatile fatty acids in latex, and most of them cannot take into account the improvement of the physical and mechanical properties of latex. Under normal circumstances, after natural latex leaves the rubber tree and is concentrated by centrifugation, its mechanical stability should be between 100-200s. Concentrated latex usually needs to be matured for more than 6 months during production and application, so the stability requirements of the preservative are relatively high. Low mechanical stability will cause natural latex to be prone to thickening, flocculation and other phenomena during transportation, storage, and processing, and even completely coagulate in severe cases. Therefore, it is necessary to provide an improved medical ammonia-free concentrated natural latex and a preparation method thereof to improve its mechanical stability. Summary of the invention

[0004] The object of the present invention is to provide a medical ammonia-free concentrated natural latex and a preparation method thereof, which can simultaneously improve the stability of latex and whey through oleic acid ester grafting modification, thereby improving the utilization rate of raw materials.

[0005] To achieve the above object, the present invention provides a method for preparing medical ammonia-free concentrated natural latex, comprising the following steps:

[0006] S1, filtering the fresh latex to remove impurities and clots, then adding HY preservation system, centrifuging and concentrating to obtain latex and whey;

[0007] S2, adding oleic acid and an acid catalyst into an esterification reaction kettle, stirring at 80-90° C. for 1-3 hours, then adding 16-hydroxypalmitic acid, and carrying out esterification reaction at 130-150° C. for 2-6 hours to obtain oleic acid ester;

[0008] S3, using the oleate to modify the rubber hydrocarbon particles in the whey through free radical polymerization, then adding a creaming agent to cream the modified whey, and then centrifugally concentrating it to obtain creamed modified whey;

[0009] S4. Mix the latex obtained in step S1 and the creamed modified whey obtained in step S2, then add KOH, and then supplement the HY preservation system to obtain medical ammonia-free concentrated natural latex; the added amount of KOH is 0.1-0.3% of the total mass of the latex and the creamed modified whey.

[0010] Furthermore, the mass content of the creamed modified whey in the medical ammonia-free concentrated natural latex is 5-25%.

[0011] Furthermore, the molar ratio of oleic acid to 16-hydroxypalmitic acid is 1:(1.2-2).

[0012] Furthermore, the acidic catalyst is hydrochloric acid, sulfuric acid or methanesulfonic acid.

[0013] Furthermore, the dry gum content of the whey is 4-6% by mass, and the added amount of the oleic acid ester is 5-15% by mass of the dry gum in the whey.

[0014] Furthermore, the creaming agent comprises sodium alginate and carboxymethyl cellulose in a mass ratio of (2-3):1; the added amount of the creaming agent is 0.05-0.2% of the mass of the whey.

[0015] Furthermore, the free radical polymerization is carried out under the catalysis of azobisisobutyronitrile, the reaction temperature is 90-100° C., and the time is 2-8 hours.

[0016] Furthermore, the dry glue mass content of the fresh latex is 24-28%; the dry glue mass content of the medical ammonia-free concentrated natural latex is 60-68%; and the dry glue mass content of the creamed modified whey is 30-35%.

[0017] Furthermore, the HY preservation system consists of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecyl sulfonate and KOH in a mass ratio of 3:2:1.

[0018] The present invention also provides a medical ammonia-free concentrated natural latex, which is obtained by any of the above preparation methods.

[0019] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0020] The preparation method of the medical ammonia-free concentrated natural latex provided by the present invention comprises an ester group and a carboxyl group in the oleic acid ester, and under alkaline conditions, the ester group is gradually hydrolyzed to generate oleate and 6-hydroxypalmitate, and the oleate is grafted on the surface of rubber hydrocarbon particles, which helps to improve the stability of this part of rubber hydrocarbon particles, and the 6-hydroxypalmitate is adsorbed on the surface of other rubber hydrocarbon particles, thereby achieving an improvement in overall stability. At the same time, the utilization rate of raw materials is also improved. Therefore, the present invention has a better comprehensive effect and good economic value. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] The present invention provides a method for preparing medical ammonia-free concentrated natural latex, comprising the following steps:

[0023] S1, filtering the fresh latex to remove impurities and clots, then adding HY preservation system, centrifuging and concentrating to obtain latex and whey;

[0024] S2, adding oleic acid and an acid catalyst into an esterification reaction kettle, stirring at 80-90° C. for 1-3 hours, then adding 16-hydroxypalmitic acid, and carrying out esterification reaction at 130-150° C. for 2-6 hours to obtain oleic acid ester;

[0025] S3, using the oleate to modify the rubber hydrocarbon particles in the whey through free radical polymerization, then adding a creaming agent to cream the modified whey, and then centrifugally concentrating it to obtain creamed modified whey;

[0026] S4. Mix the latex obtained in step S1 and the creamed modified whey obtained in step S2, then add KOH, and then supplement the HY preservation system to obtain medical ammonia-free concentrated natural latex; the added amount of KOH is 0.1-0.3% of the total mass of the latex and the creamed modified whey.

[0027] Whey contains a small amount of unused rubber hydrocarbon particles. The double bonds in oleic acid esters can be grafted with rubber hydrocarbon particles through free radical polymerization, which improves their stability and is conducive to creaming and aggregation. The obtained oleic acid ester contains ester groups and carboxyl groups. Under alkaline conditions, the ester groups gradually hydrolyze to generate oleate and 6-hydroxypalmitate. Oleate is grafted on the surface of rubber hydrocarbon particles, which helps to improve the stability of this part of rubber hydrocarbon particles. 6-hydroxypalmitate is adsorbed on the surface of other rubber hydrocarbon particles, thereby improving the overall stability. At the same time, the utilization rate of raw materials is also improved.

[0028] Furthermore, the mass content of the creamed modified whey in the medical ammonia-free concentrated natural latex is 5-25%.

[0029] Furthermore, the molar ratio of oleic acid to 16-hydroxypalmitic acid is 1:(1.2-2).

[0030] Furthermore, the acidic catalyst is hydrochloric acid, sulfuric acid or methanesulfonic acid.

[0031] Furthermore, the dry gum content of the whey is 4-6% by mass, and the added amount of the oleic acid ester is 5-15% by mass of the dry gum in the whey.

[0032] Furthermore, the creaming agent comprises sodium alginate and carboxymethyl cellulose in a mass ratio of (2-3):1; the added amount of the creaming agent is 0.05-0.2% of the mass of the whey.

[0033] Furthermore, the free radical polymerization is carried out under the catalysis of azobisisobutyronitrile, the reaction temperature is 90-100° C., and the time is 2-8 hours.

[0034] Furthermore, the dry glue mass content of the fresh latex is 24-28%; the dry glue mass content of the medical ammonia-free concentrated natural latex is 60-68%; and the dry glue mass content of the creamed modified whey is 30-35%.

[0035] The HY preservation system is composed of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecylsulfonate and KOH in a mass ratio of 3:2:1. In step S1, the amount of 1,3,5-trimethylhexahydro-s-triazine added is 0.25-35% of the mass of fresh latex; in step S4, the amount of 1,3,5-trimethylhexahydro-s-triazine added is 0.02-0.05% of the mass of medical ammonia-free concentrated natural latex.

[0036] Example 1

[0037] A method for preparing medical ammonia-free concentrated natural latex comprises the following steps:

[0038] S1. Filter the fresh latex (dry latex content is 26%) to remove impurities and clots, then add HY preservation system, centrifuge and concentrate to obtain latex and whey (dry latex content is 5%); wherein the HY preservation system is composed of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecyl sulfonate and KOH, and the added amounts are 0.3%, 0.2% and 0.1% of the fresh latex mass, respectively.

[0039] S2. Add oleic acid and methanesulfonic acid into an esterification reaction kettle, stir at 90° C. for 2 h, then add 16-hydroxypalmitic acid, and carry out esterification reaction at 140° C. for 5 h under nitrogen protection to obtain oleic acid ester; wherein the amount of methanesulfonic acid added is 0.2% of the mass of oleic acid, and the molar ratio of oleic acid to 16-hydroxypalmitic acid is 1:1.2.

[0040] S3, the oleate and the whey are mixed (the amount of oleate added is 10% of the mass of the dry glue in the whey), then azobisisobutyronitrile is added, and the mixture is reacted at 100° C. under nitrogen protection for 5 hours, and then sodium alginate and carboxymethyl cellulose are added in a mass ratio of 3:1 (the amount of sodium alginate added is 0.1% of the mass of the whey), the modified whey is creamed and aggregated, and then centrifuged and concentrated to obtain creamed modified whey (the mass content of dry glue is 32.5%);

[0041] S4. Mix the latex obtained in step S1 and the creamed modified whey obtained in step S3, then add KOH, and then supplement the HY preservation system to obtain medical ammonia-free concentrated natural latex; the amount of KOH added is 0.2% of the total mass of the latex and the creamed modified whey. The amounts of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecylsulfonate and KOH added in the HY preservation system are 0.03%, 0.02% and 0.01% of the mass of the medical ammonia-free concentrated natural latex, respectively. The mass content of the creamed modified whey in the medical ammonia-free concentrated natural latex is 15%.

[0042] Example 2

[0043] A method for preparing medical ammonia-free concentrated natural latex, which is different from Example 1 in that the added amount of oleic acid ester is 5% of the mass of dry latex in whey.

[0044] Example 3

[0045] A method for preparing medical ammonia-free concentrated natural latex, which is different from Example 1 in that the amount of oleic acid ester added is 15% of the mass of dry latex in whey.

[0046] Comparative Example 1

[0047] A method for preparing a medical ammonia-free concentrated natural latex, which is different from Example 1 in that the mass content of the creamed modified whey in the medical ammonia-free concentrated natural latex is 1%.

[0048] Comparative Example 2

[0049] A method for preparing medical ammonia-free concentrated natural latex comprises the following steps:

[0050] S1. Filter the fresh latex (dry latex content is 26%) to remove impurities and clots, then add HY preservation system, centrifuge and concentrate to obtain latex and whey (dry latex content is 5%); wherein the HY preservation system is composed of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecyl sulfonate and KOH, and the added amounts are 0.3%, 0.2% and 0.1% of the fresh latex mass, respectively.

[0051] S2, adding sodium alginate and carboxymethyl cellulose in a mass ratio of 3:1 to the whey (the amount of sodium alginate added is 0.1% of the mass of the whey), so that the whey is creamed and aggregated, and then centrifuged and concentrated to obtain creamed whey (the mass content of dry gelatin is 32.1%);

[0052] S3. Mix the latex obtained in step S1 and the creamed whey obtained in step S2, then add KOH, and then supplement the HY preservation system to obtain medical ammonia-free concentrated natural latex; the amount of KOH added is 0.2% of the total mass of the latex and the creamed modified whey. The amounts of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecylsulfonate and KOH added in the HY preservation system are 0.03%, 0.02% and 0.01% of the mass of the medical ammonia-free concentrated natural latex, respectively. The mass content of creamed whey in the medical ammonia-free concentrated natural latex is 15%.

[0053] Comparative Example 3

[0054] A method for preparing medical ammonia-free concentrated natural latex comprises the following steps:

[0055] S1. Filter the fresh latex (dry latex content is 26%) to remove impurities and clots, then add HY preservation system, centrifuge and concentrate to obtain latex and whey (dry latex content is 5%); wherein the HY preservation system is composed of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecyl sulfonate and KOH, and the added amounts are 0.3%, 0.2% and 0.1% of the fresh latex mass, respectively.

[0056] S2. Add oleic acid and methanesulfonic acid into an esterification reaction kettle, stir at 90° C. for 2 h, then add 16-hydroxypalmitic acid, and carry out esterification reaction at 140° C. for 5 h under nitrogen protection to obtain oleic acid ester; wherein the amount of methanesulfonic acid added is 0.2% of the mass of oleic acid, and the molar ratio of oleic acid to 16-hydroxypalmitic acid is 1:1.2.

[0057] S3, adding sodium alginate and carboxymethyl cellulose in a mass ratio of 3:1 to the whey (the amount of sodium alginate added is 0.1% of the mass of the whey), so that the whey is creamed and aggregated, and then centrifuged and concentrated to obtain creamed whey (the mass content of dry gelatin is 32.1%);

[0058] S4. Mix the latex obtained in step S1, the creamed whey obtained in step S3, and the oleic acid ester, then add KOH, and then supplement the HY preservation system to obtain a medical ammonia-free concentrated natural latex; the amount of KOH added is 0.2% of the total mass of the latex and the creamed modified whey. The amounts of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecylsulfonate, and KOH added in the HY preservation system are 0.03%, 0.02%, and 0.01% of the mass of the medical ammonia-free concentrated natural latex, respectively. The mass content of the creamed modified whey in the medical ammonia-free concentrated natural latex is 15%, and the amount of oleic acid ester added is 10% of the mass of the creamed whey.

[0059] The standard for determination of dry glue content is GB / T8292-2008. The test standard for volatile fatty acids is GB / T8299-2008. The test standard for 10-day and 30-day mechanical stability is GB / T8301-2008.

[0060] Table 1 Test results of examples and comparative examples

[0061] Sample Dry content (%) Volatile fatty acids (%) 10-day mechanical stability (%) 30-day mechanical stability (%) Example 1 61.58 0.012 820 1145 Example 2 61.01 0.011 768 1050 Example 3 60.80 0.013 835 1160 Comparative Example 1 61.11 0.013 455 725 Comparative Example 2 61.05 0.014 360 546 Comparative Example 3 60.51 0.016 510 810

[0062] As can be seen from Table 1, the mechanical stability is improved faster by the preparation method of the present invention. When the amount of creamed modified whey is small, the mechanical stability decreases, because the oleate content decreases and the fatty acid soap produced by hydrolysis decreases. When oleate modification is not used, the mechanical stability decreases more significantly, indicating that whey alone is not conducive to the improvement of mechanical stability. When oleate is not used to graft the whey, the mechanical stability is also reduced, indicating that after the grafted oleate is hydrolyzed, it is convenient for oleic acid soap to directly adsorb on the surface of rubber particles, thereby improving stability.

[0063] It will be easily understood by those skilled in the art that the above description is only 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 in the protection scope of the present invention.

Claims

1. A method for preparing a medical ammonia-free concentrated natural latex, characterized in that: The following steps are involved: S1, filtering the fresh latex to remove impurities and clots, then adding HY preservation system, centrifuging and concentrating to obtain latex and whey; S2, adding oleic acid and an acid catalyst into an esterification reaction kettle, stirring at 80-90° C. for 1-3 hours, then adding 16-hydroxypalmitic acid, and carrying out esterification reaction at 130-150° C. for 2-6 hours to obtain oleic acid ester; S3, using the oleate to modify the rubber hydrocarbon particles in the whey through free radical polymerization, then adding a creaming agent to cream the modified whey, and then centrifugally concentrating it to obtain creamed modified whey; S4. Mix the latex obtained in step S1 and the creamed modified whey obtained in step S3, then add KOH, and then supplement the HY preservation system to obtain medical ammonia-free concentrated natural latex; the amount of KOH added is 0.1-0.3% of the total mass of the latex and the creamed modified whey; the mass content of the creamed modified whey in the medical ammonia-free concentrated natural latex is 5-25%.

2. The method for preparing the medical ammonia-free concentrated natural latex according to claim 1, characterized in that: The molar ratio of oleic acid to 16-hydroxypalmitic acid is 1:(1.2-2).

3. The method for preparing the medical ammonia-free concentrated natural latex according to claim 1, characterized in that: The acid catalyst is hydrochloric acid, sulfuric acid or methanesulfonic acid.

4. The method for preparing the medical ammonia-free concentrated natural latex according to claim 1, characterized in that: The dry rubber content of the whey is 4-6% by mass, and the added amount of the oleic acid ester is 5-15% by mass of the dry rubber in the whey.

5. The method for preparing the medical ammonia-free concentrated natural latex according to claim 1, characterized in that: The creaming agent comprises sodium alginate and carboxymethyl cellulose in a mass ratio of (2-3):1; the added amount of the creaming agent is 0.05-0.2% of the mass of the whey.

6. The method for preparing the medical ammonia-free concentrated natural latex according to claim 1, characterized in that: The free radical polymerization is carried out under the catalysis of azobisisobutyronitrile, the reaction temperature is 90-100° C., and the reaction time is 2-8 hours.

7. The method for preparing the medical ammonia-free concentrated natural latex according to claim 1, characterized in that: The dry glue mass content of the fresh latex is 24-28%; the dry glue mass content of the medical ammonia-free concentrated natural latex is 60-68%; and the dry glue mass content of the creamed modified whey is 30-35%.

8. The method for preparing the medical ammonia-free concentrated natural latex according to claim 1, characterized in that: The HY preservation system consists of 1,3,5-trimethylhexahydro-s-triazine, sodium dodecyl sulfonate and KOH in a mass ratio of 3:2:

1.

9. A medical ammonia-free concentrated natural latex, characterized in that: Obtained by the preparation method according to any one of claims 1 to 8.