A low odor bio-based liquid natural rubber and a method of making the same

Abstract

The application provides a high-performance low-cost bio-based liquid natural rubber and a preparation method thereof. Natural rubber is added into a banbury mixer for banburying, is transported into a first double-screw extruder through a continuous closed feeding device, the molecular chain of the natural rubber is broken at low temperature by using the good heat transfer capacity of a barrel wall and a screw shaft and the high shearing action of a screw, is transported into a second double-screw extruder through a conveying device, and the cooling and conveying process of the natural rubber is completed by using the good heat transfer effect of the same-direction double-screw equipment, so that the liquid natural rubber with a number average molecular weight Mn of 6000-18000, a molecular weight distribution of 2-6 and low odor is obtained. The odor of the liquid natural rubber is minimized by using bio-based natural rubber as a raw material, adjusting a formula, designing equipment and optimizing a process, the whole preparation process is completed under a closed oxygen isolation condition, the obtained liquid natural rubber has excellent performance, and has the advantages of operation safety, simplicity, continuity and energy saving.

Description

Technical Field

[0001] This invention relates to the field of chemical materials, and more particularly to a low-odor bio-based liquid natural rubber and its preparation method. Background Technology

[0002] Liquid natural rubber is a transparent, viscous liquid with a certain degree of fluidity at room temperature. It has a relatively low molecular weight, making it relatively easy to process and mold. It has a wide range of applications in industrial production, such as being used as a plasticizer for rubber, a toughening agent for resin, and a modifier for asphalt.

[0003] Liquid natural rubber is a medium molecular weight polymer, with a molecular weight between that of small molecule monomers and solid rubber macromolecules. Therefore, there are currently two main types of preparation methods: small molecule monomer polymerization and solid macromolecule rubber degradation.

[0004] Small molecule monomer polymerization is a method that transforms small molecules into long-chain polymers through anionic polymerization, coordination polymerization, and free radical polymerization. Liao Shuangquan et al. (CN 101942042B Method for Preparing Liquid Natural Rubber) proposed a method for preparing liquid natural rubber by adding appropriate amounts of free radical initiators and carbonyl compounds to purified latex and reacting it in a water bath at 50–80°C for 20–26 hours. This method is simple and produces little pollution, but it requires subsequent coagulation with acetone, soaking the product in water for 24 hours and washing it, followed by drying in a vacuum at room temperature. The process is cumbersome, time-consuming, and costly for industrial production.

[0005] Currently, methods for preparing liquid natural rubber using solid macromolecular rubber degradation are employed. Xu Jiming et al. (CN109822776 A Low-molecular-weight liquid rubber preparation device) proposed a device for preparing low-molecular-weight liquid rubber. This method involves first crushing the rubber into small particles, then softening them in a heating chamber using an extrusion screw. The particles are then extruded and heated to the degradation temperature at the degradation shaft section, where they are degraded into low-molecular-weight liquid rubber. This method is suitable for continuous industrial production, but it has certain problems. When the temperature in the degradation section is too high (above 350℃), the proteins in the natural rubber easily decompose, producing amine derivatives, fatty acids, and other substances that cannot be discharged in time. Furthermore, the small molecules produced by the decomposition of natural rubber at excessively high temperatures combine with oxygen to produce unpleasant substances, resulting in a high impurity content and an unpleasant odor in the final liquid rubber, affecting the user experience. Summary of the Invention

[0006] This invention provides a low-odor bio-based liquid natural rubber and its preparation method to solve or at least alleviate at least one problem existing in the prior art.

[0007] This invention provides a method for preparing low-odor bio-based liquid natural rubber, the method comprising:

[0008] Natural rubber is added to a mixer for plasticizing. The plasticized natural rubber is then transferred to a first screw extruder. The temperature of the first screw extruder is controlled to break the molecular chains of the plasticized natural rubber and degas it. The rubber is then transferred to a second screw extruder, where it is cooled and degassed before being extruded to obtain liquid natural rubber.

[0009] In a preferred embodiment of the present invention, the rotor speed of the internal mixer is 50-90 r / min, the filling coefficient is 0.4-0.8, and the mixing time is 180-420 s.

[0010] In a preferred embodiment of the present invention, controlling the temperature of the first screw extruder to break down the molecular chains of the plasticized natural rubber compound and degas it before transferring it to the second screw extruder includes:

[0011] The temperature of the first screw extruder is controlled at 180-270°C. After 2-6 minutes of molecular chain breakage and degassing, the material is transferred to the second screw extruder.

[0012] In a preferred embodiment of the present invention, the conveying section temperature of the first screw extruder is 180-220°C, the shearing section temperature is 220-270°C, and the cooling section temperature is 180-200°C.

[0013] In a preferred embodiment of the present invention, the cooling section of the first screw extruder is provided with a high-temperature resistant rubber deodorizer, the deodorizer being composed of inorganic silicate; the mass ratio of the natural rubber compound to the deodorizer is 100:(0.2-0.5).

[0014] As a preferred embodiment of the present invention, the process of extruding liquid natural rubber after temperature control, cooling and venting includes: controlling the temperature of the barrel and mandrel of the second screw extruder at 10-50°C, cooling for 1-5 minutes to remove gas, and then extruding liquid natural rubber.

[0015] In a preferred embodiment of the present invention, the first screw extruder is a co-rotating twin-screw extruder, wherein the length-to-diameter ratio of the screw is (42-60):1, and the screw speed is 120-270 r / min.

[0016] In a preferred embodiment of the present invention, the second screw extruder is a co-rotating or counter-rotating twin-screw extruder, wherein the length-to-diameter ratio of the screw is (36-54):1, and the screw speed is 40-80 r / min.

[0017] In a preferred embodiment of the present invention, both the first screw extruder and the second screw extruder are provided with exhaust ports on the side of their barrels.

[0018] This invention provides a low-odor bio-based liquid natural rubber, which is prepared by the preparation method of the low-odor bio-based liquid natural rubber provided by this invention.

[0019] The method for preparing low-odor bio-based liquid natural rubber provided by this invention can obtain liquid natural rubber with a temperature below 50°C, a number-average molecular weight Mn of 6000-18000, and a molecular weight distribution of 2-6.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] During the preparation process, the addition of additives can generate volatile substances, resulting in unpleasant odors. Therefore, this process uses pure natural rubber as the raw material, reducing the introduction of additives with high odor levels. This not only reduces odor generation but also simplifies the formulation and lowers production costs. Natural rubber has poor thermal conductivity and excellent elasticity, making direct processing difficult. Therefore, it is first plasticized in a mixer to reduce its Mooney viscosity, facilitating feeding and shearing in the subsequent screw extruder. During mixing, the rubber temperature rises, and the movement of its internal molecular chains becomes more active, which is beneficial for thermal shearing in the subsequent twin-screw extruder. The material enters the first screw extruder, where a reverse screw element is added to the feeding section to isolate oxygen. By rationally controlling the temperature of each section of the screw, the material shearing efficiency is effectively improved. Setting a lower degradation temperature avoids excessive decomposition of the rubber at excessively high temperatures, which would produce a large amount of low-molecular-weight products and result in a strong odor. It also effectively breaks down the rubber molecular chains, reducing the material's viscosity. Vacuum venting allows for the timely removal of small molecules from the extruder. Adding a certain amount of inorganic silicate as a deodorizing agent to the cooling section of the screw extruder, with its porous structure, effectively adsorbs small molecular impurities trapped within the rubber compound. In the second screw extruder, the high-temperature material continues its molecular chain breaking reaction under weak shear. Properly setting the cooling temperature and venting outlet further removes small molecular products while simultaneously cooling the material, ensuring stable extrusion.

[0022] Through extensive experiments and theoretical calculations, this invention leverages the flexible and varied geometric arrangement of the screw extruder's threaded elements, creating multiple variations in material flow direction and velocity. This results in highly efficient shearing action on the material and oxygen isolation, reducing rubber oxidation. Furthermore, based on finite element analysis and calculations of the material-metal dynamic friction coefficient, this invention organically integrates various stages to ensure effective degradation of natural rubber while lowering the degradation temperature and significantly reducing energy consumption. It effectively minimizes high-temperature degradation and oxidation during the degradation process. The rational vacuum exhaust structure and the addition of deodorizing agents also minimize odor. Due to the significant degradation of the main chain, the prepared liquid natural rubber allows for easier dispersion of additives in downstream applications, thus offering broader application prospects. Detailed Implementation

[0023] Exemplary embodiments of the present invention will now be described in more detail. While exemplary embodiments are provided, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey its scope to those skilled in the art. Unless otherwise specified, the reagents, methods, and apparatus used in this invention are conventional reagents, methods, and apparatus in this art.

[0024] Example 1

[0025] 100 parts of natural rubber were added to a mixer for plasticizing at a rotor speed of 50 r / min, a filling factor of 0.4, and a mixing time of 420 s, resulting in a material with a temperature of 60℃ and a Mooney viscosity of 65. This material was then fed into the first twin-screw extruder via a continuous closed feeding device. The screw length-to-diameter ratio was 52:1, and the screw speed was 230 r / min. The extruder's conveying section temperature was controlled at 220℃, the shearing section temperature at 270℃, and the cooling section temperature at 180℃. In the cooling section, 0.4 parts of inorganic silicate were added, and the molecular chains were broken and vented within 4 minutes. The material then passed through a conveying device into the second twin-screw extruder with a screw length-to-diameter ratio of 40:1 and a screw speed of 45 r / min. The barrel and mandrel temperatures were controlled at 40℃. After cooling for 3 minutes and degassing, liquid natural rubber with a temperature below 50℃, a number-average molecular weight (Mn) of 6378, and a molecular weight distribution of 2.2 was obtained.

[0026] Example 2

[0027] 100 parts of natural rubber were added to a mixer for plasticizing at a rotor speed of 70 r / min, a filling factor of 0.7, and a mixing time of 260 s, resulting in a material with a temperature of 88℃ and a Mooney viscosity of 58. This material was then fed into the first twin-screw extruder via a continuous closed feeding device. The screw length-to-diameter ratio was 48:1, and the screw speed was 180 r / min. The extruder's conveying section temperature was controlled at 200℃, the shearing section temperature at 260℃, and the cooling section temperature at 190℃. In the cooling section, 0.3 parts of inorganic silicate were added, and the molecular chains were broken and vented within 6 minutes. The material then passed through a conveying device into the second twin-screw extruder with a screw length-to-diameter ratio of 45:1 and a screw speed of 55 r / min. The barrel and mandrel temperatures were controlled at 35℃. After cooling for 2 minutes and degassing, liquid natural rubber with a temperature below 50℃, a number-average molecular weight (Mn) of 9634, and a molecular weight distribution of 4.5 was obtained.

[0028] Example 3

[0029] 100 parts of natural rubber were added to a mixer for plasticizing. The rotor speed was 80 r / min, the filling factor was 0.6, and the mixing time was 180 s, resulting in a material with a temperature of 106℃ and a Mooney viscosity of 30. The material is then fed into the first twin-screw extruder via a continuous closed feeding device. The screw has a length-to-diameter ratio of 60:1 and a screw speed of 270 r / min. The temperature of the screw extruder's conveying section is controlled at 205℃, the shearing section at 245℃, and the cooling section at 190℃. In the cooling section, 0.2 parts of inorganic silicate are added. The molecular chains are broken and the gas is vented within 5 minutes. The material then enters the second twin-screw extruder via a conveying device. The screw has a length-to-diameter ratio of 54:1 and a screw speed of 80 r / min. The temperature of the barrel and mandrel of the screw extruder is controlled at 50℃. After cooling for 5 minutes, the gas is removed, and liquid natural rubber with a temperature below 50℃, a number-average molecular weight (Mn) of 11977, and a molecular weight distribution of 3.1 is obtained.

[0030] Example 4

[0031] 100 parts of natural rubber were added to a mixer for plasticizing. The rotor speed was 90 r / min, the filling factor was 0.8, and the mixing time was 300 s, resulting in a material with a temperature of 160℃ and a Mooney viscosity of 58. The material is then fed into the first twin-screw extruder via a continuous closed feeding device. The screw has a length-to-diameter ratio of 42:1 and a screw speed of 120 r / min. The temperature of the screw extruder's conveying section is controlled at 180℃, the shearing section at 220℃, and the cooling section at 200℃. 0.5 parts of inorganic silicate are added in the cooling section. The molecular chains are broken and the gas is vented within 3 minutes. The material then enters the second twin-screw extruder via a conveying device. The screw has a length-to-diameter ratio of 36:1 and a screw speed of 40 r / min. The temperature of the barrel and mandrel of the screw extruder is controlled at 10℃. After cooling for 1 minute, the gas is removed, and liquid natural rubber with a temperature below 50℃, a number-average molecular weight (Mn) of 17634, and a molecular weight distribution of 5.5 is obtained.

[0032] This invention involves adding natural rubber to a mixer for plasticizing, then conveying it to a first twin-screw extruder via a continuous, closed feeding device. Utilizing the excellent heat transfer capabilities of the barrel wall and screw mandrel, as well as the high shear force of the screw, the natural rubber molecular chains are broken at low temperatures. The rubber then enters a second twin-screw extruder via a conveying device, where the excellent heat transfer of the co-rotating twin-screw extruder completes the cooling and conveying process, resulting in a low-odor liquid natural rubber with a number-average molecular weight (Mn) of 6000–18000 and a molecular weight distribution of 2–6. Using bio-based natural rubber as raw material, and through adjustments to the formulation, equipment design, and process optimization, the odor of the liquid natural rubber is minimized. The entire preparation process is completed under closed, oxygen-free conditions, resulting in a liquid natural rubber with excellent performance and advantages such as safe, simple, continuous, and energy-efficient operation.

[0033] It should be understood that, in order to simplify the invention and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment or description thereof in the above description of exemplary embodiments of the invention. However, this approach should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the following claims, inventive aspects lie in fewer than all features of a single embodiment of the foregoing invention. Therefore, the claims following the detailed description are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0034] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features but not others included in other embodiments, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments can be used in any combination.

[0035] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that any improvements and additions made by those skilled in the art without departing from the method of the present invention should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art using the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a low-odor bio-based liquid natural rubber, characterized in that, The method includes: adding natural rubber into a mixer for plasticizing, transferring the plasticized natural rubber to a first screw extruder, controlling the temperature of the first screw extruder to break the molecular chains of the plasticized natural rubber and degas it, then transferring it to a second screw extruder, controlling the temperature to cool and degas it, and extruding it to obtain liquid natural rubber. The internal mixer has a rotor speed of 50–90 r / min, a filling coefficient of 0.4–0.8, and a mixing time of 180–420 s; Controlling the temperature of the first screw extruder to break the molecular chains and degas the plasticized natural rubber compound before transferring it to the second screw extruder includes: controlling the temperature of the first screw extruder at 180–270°C, and transferring it to the second screw extruder after 2–6 minutes of molecular chain breaking and degassing; the conveying section temperature of the first screw extruder is 180–220°C, the shearing section temperature is 220–270°C, and the cooling section temperature is 180–200°C. The cooling section of the first screw extruder is equipped with a high-temperature resistant rubber deodorizer, the deodorizer being composed of inorganic silicates; the mass ratio of the natural rubber compound to the deodorizer is 100:(0.2-0.5); The process of extruding liquid natural rubber after temperature control, cooling and venting includes: controlling the temperature of the barrel and mandrel of the second screw extruder at 10-50°C, cooling for 1-5 minutes to remove gas, and then extruding to obtain liquid natural rubber. The first screw extruder is a co-rotating twin-screw extruder, wherein the length-to-diameter ratio of the screw is (42-60):1, and the screw speed is 120-270 r / min; the second screw extruder is a co-rotating twin-screw extruder, wherein the length-to-diameter ratio of the screw is (36-54):1, and the screw speed is 40-80 r / min; Both the first screw extruder and the second screw extruder have vents on the side of their barrels.

2. A low-odor bio-based liquid natural rubber, characterized in that, The low-odor bio-based liquid natural rubber is prepared by the method for preparing low-odor bio-based liquid natural rubber according to claim 1.