WO2020087952A1

WO2020087952A1 - Method for flocculating fresh latex

Info

Publication number: WO2020087952A1
Application number: PCT/CN2019/093192
Authority: WO
Inventors: 汪传生; 谢苗; 江瑞
Original assignee: 青岛科技大学
Priority date: 2018-10-29
Filing date: 2019-06-27
Publication date: 2020-05-07
Also published as: CN109485753A; CN109485753B

Abstract

Disclosed is a method for flocculating fresh latex, comprising firstly, slowly adding fresh latex into a seawater-like flocculant under stirring and continuing stirring for 20-40 minutes after complete addition of the fresh latex, reacting the fresh latex and the seawater-like flocculant at 40-60ºC for 1-3 hours, and then allowing the reaction to cool naturally to 15-35ºC to obtain a latex clot; and subsequently, rinsing the latex clot with 300 mL of deionized water, and then placing the latex clot in an open mill and a drying machine successively to conduct dehydration and drying, thus obtaining natural rubber. The method has the following advantages: firstly, the seawater-like flocculant is inexpensive, readily available, and environmentally friendly; secondly, the requirement for equipment is low and conventional equipment will suffice, and the reaction conditions are mild and do not cause corrosion of equipment; thirdly, no irritating smell is generated during the production process, reducing the impact on operators, and being friendly to the environment; and fourthly, the impact of weather, fresh latex quality and a non-tapping period, amongst other factors, on the continuous production of natural rubber can be overcome.

Description

Fresh rubber latex flocculation method

Technical field:

The invention belongs to the technical field of natural rubber production, and relates to a method for flocculating fresh rubber latex. The seawater-like flocculant is used to rapidly flocculate the fresh rubber latex to prepare natural rubber with excellent performance.

Background technique:

Fresh latex, also known as field latex, is unprocessed latex flowing from gum-producing plants. It is a colloidal water dispersion system in which the continuous phase is composed of water and water-soluble substances, and the dispersed phase is composed of various water-insoluble particles. In order to avoid the early natural coagulation caused by bacteria and other effects, preservatives are often added, which is the basic raw material for manufacturing natural rubber and latex products. Natural rubber (NR) is a natural polymer compound with cis-1,4-polyisoprene as the main component, and 91% to 94% of its components are rubber hydrocarbons (cis-1,4-polyisoprene) Diene), and the rest are non-rubber substances such as protein, fatty acids, ash, and sugars. Natural rubber is the most widely used general-purpose rubber. Natural rubber has excellent properties such as resilience, insulation, water barrier and plasticity, and after proper treatment, it also has precious properties such as oil resistance, acid resistance, alkali resistance, heat resistance, cold resistance, pressure resistance, and wear resistance. Widely used. For example, rain boots, warm water bags, elastic bands used in daily life; surgeon gloves, blood transfusion tubes, condoms used in the medical and health industry; various tires used in transportation; conveyor belts, transport belts used in industry, acid and resistance Alkaline gloves; irrigation and drainage hoses and ammonia bags used in agriculture; air exploration balloons for meteorological measurements; sealing and shockproof equipment for scientific tests; aircraft, tanks, artillery, gas masks used in national defense; even rockets and artificial earth satellites Natural rubber is inseparable from high-end and sophisticated scientific and technological products such as spacecraft. As natural rubber is widely used in transportation, military industry and aerospace, natural rubber, coal, steel, and petroleum are also called the four major industrial raw materials. Natural rubber is prepared by natural rubber latex through the steps of collection, coagulation, cleaning and drying. The coagulation process is an important step in the formation of natural rubber. At present, the natural latex coagulation methods mainly include natural flocculation, microbial flocculation, acid flocculation, inorganic salt flocculation and biological flocculation. Flocculation refers to the accumulation of suspended particles in water or liquid to become larger or form flocs, thereby accelerating the particle sedimentation -For the purpose of liquid separation, this phenomenon or operation is called flocculation. The flocculation is usually carried out by adding appropriate flocculants, the role is to adsorb the particles, "bridge" between the particles, thereby promoting aggregation. In the natural latex industry, flocculation is the first stage of latex coagulation and is an irreversible aggregation. The flocculant is usually an electrolyte such as ammonium salt or a colloidal chemical with adsorption. The flocculation effect depends on the characteristics of the particles and the fluid mixing conditions. Adding a coagulant to the water containing small particles will cause the particles to destabilize and start flocculation. The flocculation rate of fine particles is related to the diffusion rate between particles. For small particles (particle size less than 0.1 μm), the main mechanism of aggregation is Brownian motion or micro-flocculation. Micro-flocculation is also called anisotropic flocculation. When small particles aggregate, larger particles are formed. After a short time (several seconds), microflocs of 1-100 μm are formed; for particles larger than 1 μm, the main mechanism of flocculation is the slow mixing of water, often using mechanical agitators. The velocity gradient caused by the stirring causes the collision between suspended particles is called macro-flocculation or co-flocculation. However, in the mixing process of macro-flocculation, the floc particles will be subjected to shear forces, which will lead to the disintegration, breakage or breakage of some floc aggregates. After mixing for a period of time, flocs with a stable size distribution are formed. The formation and breakage of floc particles are almost balanced, and the stability of suspended particles to form flocs can be ensured by controlling the hydraulic conditions of the solution and the use of chemical flocculants. The sedimentation of particles at different rates will cause the aggregation and growth of flocs. During the precipitation process, the different sedimentation particles formed in the heterogeneous suspension (different particle size) provide an additional mechanism for promoting flocculation. For a large range of suspensions, differential settlement is an important flocculation mechanism. The flocculation caused by the differential settlement will not affect the direct filtration, dissolved air flotation and high-speed precipitation processes. Among them, acid flocculation usually uses acids such as formic acid, acetic acid or sulfuric acid as the flocculant. The mechanism of acid flocculant coagulation of natural latex is to increase the amount of hydrogen ions in natural latex, reduce the pH of natural latex, and compress the double surface of natural latex particles. The electric layer makes the hydration film thinner. When the isoelectric point of the protein is reached, the electrokinetic potential is zero. There is no repulsion between the natural rubber particles and then they aggregate with each other and solidify into a block. Different coagulation methods directly affect the quality of natural rubber. When acidic flocculants are added to natural latex, dense coagulum will form at the coagulation point, preventing the flocculant from being evenly distributed in the latex, and it is difficult to form a uniform structure of coagulum, which affects Natural latex particles form macromolecular chains. Traditional strong acid flocculation has unavoidable defects, which will not only affect the health of operators, corrode containers and equipment, the drying period after flocculation is long, it is easy to produce acid gas and affect the environment, if the strong acid is not cleaned, it will also affect the subsequent Vulcanization time. Vulcanization in an acidic environment will lead to lag in vulcanization time, limiting the industrialization of natural rubber. Therefore, seeking to design a natural rubber flocculation process can make the natural rubber production process green and environmentally friendly and easy to industrialize, and the product quality is stable, which becomes an urgent matter.

Summary of the invention:

The purpose of the present invention is to overcome the shortcomings of the wet mixing process in the prior art, to develop and design a fresh latex flocculation method to avoid the problem of deterioration of the rubber compound performance by adding acidic components to flocculate the mixing rubber.

In order to achieve the above object, the process of the fresh latex flocculation method involved in the present invention is as follows: First, slowly add 50 phr of solid latex with a mass content of 25% to the seawater-like flocculant, and add 10-5% while adding fresh latex. Stir the seawater-like flocculant at a speed of 300r / min. After the fresh latex is added, continue to stir for 20-40min. The fresh latex and the seawater-like flocculant are placed under the temperature condition of 40-60 ℃ for 1-3 hours. Then, naturally Cool to 15-35 ° C to obtain a gel block; then, use 300ml of deionized water to clean the gel block; finally, place the gel block in an open mixer and a dryer for dehydration and drying, respectively. natural rubber.

The ratio of fresh latex to seawater-like flocculant involved in the present invention is a volume ratio of 1: 1-3.

The seawater-like flocculant involved in the present invention is a polymer of inorganic salts and trace metal ions, including the following parts by weight: 10-20 parts sodium chloride, 30-50 parts deionized water, 5-10 parts magnesium chloride hexahydrate, 20-35 parts of water-soluble starch, 2-5 parts of sodium hydroxide and 30-50 parts of sea water; the preferred parts by weight are 15 parts of sodium chloride, 30 parts of deionized water, 6 parts of magnesium chloride hexahydrate, 25 parts of water-soluble Starch, 3 parts sodium hydroxide and 45 parts sea water; its components have a wide range of sources and low cost. It can neutralize the charge on the surface of colloidal particles and suspended solids, better adapt to the sedimentation of charged colloidal particles. In this case, the sedimentation speed of colloidal particles is significantly increased, the turbidity of the supernatant is reduced, and a better flocculation effect is achieved.

The stability of the natural rubber prepared by the present invention is achieved by the structure of a hydrated layer formed by the negatively charged latex particles and the surrounding counter ions forming a double charge, and the hydrophilic protein and water molecules adsorbed on the surface of the colloidal particles.

The principle of the fresh latex flocculation method involved in the present invention is: the multivalent traces added in the fresh latex neutralize the charge of the colloidal particles, destroy the surface protective layer of the colloidal particles, and destabilize the fresh latex to form a gel block; according to the uncle mining -Hardy's valence rules, the higher the valence of metal cations, the greater the settling capacity, the gelation efficiency of monovalent metal salts is low, when in contact with the colloidal particles, the metal cations cannot damage the protective layer on the surface of the colloidal particles, fresh The latex cannot flocculate; the trivalent metal salt has a strong gelling ability. When contacting with the colloidal particles, the colloidal particles quickly destabilize, the protective layer on the surface of the colloidal particles is lost, the molecular chain is destroyed, and the fresh latex forms a dense gel block , Reduces the molecular weight of natural rubber; the metal cation of the divalent metal salt can make the fresh latex particles flocculate into a uniform and firm gel block with a network structure, forming a complete molecular chain. The resulting gel block dehydrates, shrinks and After drying, it is easy to form natural rubber with complete structure, stable quality and high molecular weight.

Compared with the prior art, the present invention flocculates fresh rubber latex with seawater-like flocculant to obtain a gel block. The gel block is dehydrated, shrunk and dried to form a natural rubber with complete structure, stable quality and high molecular weight, which has the following advantages: First, the seawater flocculant is cheap, easy to obtain, and environmentally friendly, which greatly reduces the production cost of natural rubber. Second, the equipment requirements are low, all are conventional equipment, the reaction conditions are mild, the equipment is not corroded, and the third is the process is non-irritating Sexual odor is emitted, which has little impact on the operator and is friendly to the environment; Fourth, it overcomes the effects of weather, fresh rubber latex quality and glue stop period on the continuous production of natural rubber; its simple process and convenient operation improve the fresh rubber latex The flocculation speed of the obtained natural rubber is stable in quality and superior in performance. It is suitable for the continuous industrial production of tread rubber and engineering rubber, and has good promotion value.

detailed description:

The present invention will be further illustrated by the following examples.

Example 1:

The process of the fresh latex flocculation method involved in this embodiment is as follows: First, 1 part by volume of 50 phr of solid content and 25% by weight of fresh latex is slowly added to 2 parts by volume of seawater flocculant. Stir the seawater-like flocculant at a speed of 10-300r / min. After the fresh latex is added, continue to stir for 20-40min. Put the fresh latex and seawater-like flocculant under the temperature condition of 40-60 ℃ for 1-3 hours, then , Naturally cooled to 15-35 ℃, to obtain a gel block; then, use 300ml of deionized water to clean the gel block; finally, the gel block is placed in an open mixer and dryer in order to dehydrate and dry, respectively, Made of natural rubber.

The seawater-like flocculant involved in this embodiment includes the following parts by weight: 15 parts sodium chloride, 30 parts deionized water, 6 parts magnesium chloride hexahydrate, 25 parts water-soluble starch, 3 parts sodium hydroxide, and 45 parts seawater.

Example 2:

This example relates to the comprehensive performance test of vulcanized rubber. First, natural rubber was prepared by conventional acid flocculation method and Example 1 flocculation method, and then 100 phr of natural rubber (calculated as 100 g of dry rubber), 5 phr of zinc oxide, and 2 phr of Stearic acid, 0.7 phr of NS / TBBS and 30 phr of N330 carbon black are used as formulas to prepare masterbatch. Finally, the masterbatch is placed in a kneading machine to adjust the roll cover roll, and zinc oxide and stearin are added in sequence according to the set quality. Acid, NS and N330 carbon blacks, triangulated 6 times, compressed to a set thickness, and after 8 hours of parking, the experimental samples were obtained. 30g of the experimental samples were vulcanized with a flat vulcanizing machine, and the experimental samples after vulcanization were taken for mechanical Performance test, the results are as follows:

It is known that the vulcanization time T90 of the natural rubber experimental sample prepared by the flocculation method in Example 1 is shorter than the vulcanization time T90 of the natural rubber experimental sample prepared by the conventional flocculation method. Under high deformation conditions, the vulcanization method prepared in Example 1 is obtained The strength of the natural rubber experimental sample is high, and the 300% constant tensile stress of the natural rubber experimental sample prepared by the flocculation method in Example 1 is high, reflecting a high filler network structure and strong filler-filler interaction.

Claims

A method for flocculation of fresh latex, characterized in that first, fresh latex with 50 phr solid content and mass fraction of 25% is slowly added to the seawater-like flocculant, and seawater-like seawater is stirred at a speed of 10-300 r / min while the fresh latex is added After adding the flocculant and fresh latex, continue to stir for 20-40min, put the fresh latex and seawater-like flocculant under the temperature condition of 40-60 ℃ for 1-3 hours, and then, naturally cool to 15-35 ℃ to obtain The gel block; then, use 300ml of deionized water to clean the gel block; finally, the gel block is placed in a kneader and dryer in order to dehydrate and dry, respectively, to obtain natural rubber.
The fresh latex flocculation method according to claim 1, wherein the ratio of fresh latex to seawater-like flocculant is a volume ratio of 1: 1-3.
The fresh latex flocculation method according to claim 1, characterized in that the seawater-like flocculant is a polymer of inorganic salts and trace metal ions, including the following parts by weight: 10-20 parts sodium chloride, 30-50 parts Ionized water, 5-10 parts of magnesium chloride hexahydrate, 20-35 parts of water-soluble starch, 2-5 parts of sodium hydroxide and 30-50 parts of sea water; the preferred parts by weight are 15 parts of sodium chloride and 30 parts of deionized water , 6 parts magnesium chloride hexahydrate, 25 parts water-soluble starch, 3 parts sodium hydroxide and 45 parts seawater.
The method for flocculating fresh rubber latex according to claim 1, characterized in that the stability of the prepared natural rubber is composed of negatively charged latex particles and surrounding counter ions to form a double charge, and hydrophilic proteins and water molecules adsorbed on the surface of the colloidal particles The structure of the hydration layer is realized.