Preparation process and method of reclaimed rubber powder capable of regulating and controlling different molecular chain lengths

Abstract

The invention discloses a preparation process of reclaimed rubber powder capable of regulating and controlling different molecular chain lengths, which comprises the following steps: raw material pretreatment and grading, preliminary chain scission by mechanical shearing, deep chain scission by chemical regulation and control, activation and stabilization treatment, separation and grading, and drying and packaging. Compared with the prior art, the preparation process and the preparation method of the reclaimed rubber powder capable of regulating and controlling the different molecular chain lengths have the advantages that the proportion of long chains to short chains can be controlled, so that the molecular chains in the reclaimed rubber powder are uniformly distributed, and the application range of the reclaimed rubber powder is widened; the required performance can be achieved without repeated processing and screening, the production efficiency and the product quality are greatly improved, the molecular chain length fluctuation is relatively small, the process stability is relatively high, the generated wastes and byproducts are relatively few, and the pollution to the environment is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of polymer material recycling technology, specifically relating to a preparation process and method for regenerated rubber powder with adjustable molecular chain lengths. Background Technology

[0002] Reclaimed rubber powder, as an important recycled rubber resource, has wide applications in the rubber industry, building materials, and other fields. Reclaimed rubber powder with different molecular chain lengths has different properties; for example, reclaimed rubber powder with shorter molecular chains has better processing flowability, while reclaimed rubber powder with longer molecular chains has advantages in mechanical properties.

[0003] Currently, the preparation process and methods for reclaimed rubber powder cannot control the different molecular chain lengths, and the ratio of long chains to short chains is uncontrollable, resulting in uneven distribution of molecular chains in the reclaimed rubber powder. This affects the physical properties of reclaimed rubber, such as tensile strength, abrasion resistance, and elasticity, leading to unstable product performance and difficulty in meeting the needs of specific application scenarios.

[0004] Different applications have specific requirements for the molecular chain length of reclaimed rubber powder. For example, tire manufacturing requires longer molecular chains to provide sufficient strength and abrasion resistance, while rubber flooring may prioritize the flexibility provided by shorter chains. Uncontrollable processes cannot produce reclaimed rubber powder that meets specific requirements, thus limiting its application range.

[0005] If the process cannot effectively control the molecular chain length, multiple processing or screening steps may be required to achieve the desired performance, which not only increases production costs but also reduces production efficiency. Furthermore, uneven molecular chain distribution can lead to uneven flow and inconsistent vulcanization of reclaimed rubber during processing, further impacting production efficiency and product quality.

[0006] Processes with uncontrollable molecular chain lengths are often sensitive to raw material quality and processing conditions; even minor changes can lead to significant fluctuations in molecular chain length. This instability makes it difficult to achieve large-scale, continuous production, increasing the difficulty and cost of production management.

[0007] Uncontrollable processes may generate more waste or byproducts, such as residues of underutilized short-chain molecules or excessively long-chain molecules. Improper handling of these wastes can pollute the environment, increasing the environmental burden and remediation costs for businesses.

[0008] Therefore, in order to address the above-mentioned technical problems, it is necessary to provide a preparation process and method for regenerated rubber powder with adjustable molecular chain lengths.

[0009] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0010] The purpose of this invention is to provide a preparation process and method for regenerated rubber powder with adjustable molecular chain lengths, which can solve the problems mentioned in the background art.

[0011] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution: a preparation process and method for regenerated rubber powder with adjustable molecular chain lengths, comprising the following steps: the process includes raw material pretreatment and classification, mechanical shearing for preliminary chain breaking, chemical regulation for deep chain breaking, activation and stabilization treatment, separation and classification, and drying and packaging. By synergistically regulating mechanical shearing parameters and chemical chain breaking conditions, the directional control of the molecular chain length of the regenerated rubber powder is achieved.

[0012] In one or more embodiments of the present invention, the preliminary chain breaking step of mechanical shearing is carried out using a twin-screw extruder at 80-120°C. The screw speed is controlled at 100-300 rpm and the shearing time is 5-15 min. The shearing parameters are adjusted in real time by monitoring and feedback from an online viscometer.

[0013] In one or more embodiments of the present invention, in the chemically regulated deep chain scission step, the chain scission agent used is an organic peroxide or an amine compound, the amount of which is added is 0.5-5 wt% of the mass of the rubber powder, the reaction temperature is controlled at 120-180℃, and the reaction time is 30-120 min.

[0014] In one or more embodiments of the present invention, the separation and grading step employs gradient centrifugation technology combined with online gel permeation chromatography to separate the regenerated rubber powder into long-chain components (molecular weight > 500,000), medium-chain components (molecular weight 200,000-500,000), and short-chain components (molecular weight < 200,000).

[0015] In one or more embodiments of the present invention, in the raw material pretreatment and grading step, the waste rubber is divided into three grades: high, medium and low, according to the degree of crosslinking, and different subsequent treatment parameters are adopted for each grade.

[0016] In one or more embodiments of the present invention, in the activation and stabilization treatment step, zinc oxide and stearic acid are added as activators, with the addition amounts being 1-3 wt% and 0.5-2 wt% of the mass of the adhesive powder, respectively, and 0.1-1 wt% of an antioxidant is added simultaneously.

[0017] In one or more embodiments of the present invention, the molecular chain length is controlled by adjusting the concentration of the chain scissor and the reaction time: when preparing long-chain components, 0.5-2 wt% chain scissor and 30-60 min reaction time are used; when preparing short-chain components, 2-5 wt% chain scissor and 60-120 min reaction time are used.

[0018] In one or more embodiments of the present invention, the speed range of the gradient centrifugation separation technology is 500-3000 rpm, and the separation of components with different molecular weights is achieved through 3-5 grade gradient speeds.

[0019] In one or more embodiments of the present invention, the synergistic regulation of mechanical shearing and chemical chain breaking is achieved through an intelligent control system that automatically matches the optimal process parameters based on the type of raw materials and the target product.

[0020] In one or more embodiments of the present invention, the ratio of long chains to short chains in the reclaimed rubber powder produced by the process can be controlled within the range of 1:9 to 9:1 to meet the performance requirements of different application scenarios.

[0021] Compared with the prior art, the preparation process and method of regenerated rubber powder with adjustable molecular chain length of the present invention can control the ratio of long chain to short chain, so that the molecular chain in the regenerated rubber powder is evenly distributed, which increases the application range of the regenerated rubber powder. It can achieve the required performance without multiple processing and screening, which greatly improves production efficiency and product quality. The molecular chain length fluctuation is small, the process stability is high, and less waste and by-products are generated, which greatly reduces the pollution to the environment. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a process flow diagram of the preparation of regenerated rubber powder with adjustable molecular chain length in one embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0025] This process achieves controllable molecular chain length of reclaimed rubber powder through a "stepwise chain breaking - precise control - graded separation" technical route. By leveraging the synergistic effect of mechanical shearing and chemical depolymerization, combined with precise control of reaction conditions, the degree of molecular chain breakage can be directionally controlled, ultimately obtaining reclaimed rubber powder with a specific chain length distribution through graded separation.

[0026] In industrial production, the recycling of waste rubber is an important environmental protection measure and a manifestation of resource recycling. The following details the waste rubber recycling process, which includes six main steps:

[0027] First, the raw materials undergo pretreatment and grading. Waste rubber raw materials, such as discarded tires and rubber products, first need to be crushed to reduce their volume for easier subsequent processing. Then, iron impurities are removed using magnetic separation equipment, and other impurities, such as mud and sand, are removed through a washing step. The washed rubber particles are further pulverized until their particle size reaches 5-10 mm. Based on the degree of cross-linking, the rubber raw materials are classified into three grades: high cross-linking, medium cross-linking, and low cross-linking, to facilitate subsequent processing.

[0028] Next, preliminary chain breaking is performed using mechanical shearing. This step involves mechanically shearing the rubber granules using a twin-screw extruder at low temperatures (80-120℃). The initial chain breaking of the rubber molecules is achieved by controlling the screw speed (100-300 rpm) and the shearing time (5-15 minutes). To ensure the efficiency of the shearing process, an online viscometer is used to monitor the melt viscosity in real time, and the shearing parameters are adjusted based on the monitoring results to achieve the best chain breaking effect.

[0029] The third step is chemically regulated deep chain scission. The rubber powder, after initial chain scission, is fed into a reactor, and a customized chain-scission agent, such as organic peroxides or amine compounds, is added. By controlling the reaction temperature (120-180℃), reaction time (30-120 minutes), and chain-scission agent concentration (0.5-5 wt%), deep chain scission of the rubber molecules is achieved. The concentration of the chain-scission agent and the reaction time are adjusted according to the desired product chain length. If the goal is to produce a long-chain product, a low concentration of chain-scission agent (0.5-2 wt%) and a short reaction time (30-60 minutes) are used; if the goal is to produce a short-chain product, a high concentration of chain-scission agent (2-5 wt%) and a long reaction time (60-120 minutes) are used.

[0030] The fourth step is activation and stabilization. In this step, activators such as zinc oxide, stearic acid, and antioxidants are added to the reactor to terminate the chain-splitting reaction and stabilize the molecular chain structure. By controlling the activation temperature (100-140℃) and time (15-30 minutes), the complete termination of the reaction and the stabilization of the molecular chain are ensured.

[0031] The fifth step is separation and classification. Gradient centrifugation is used to classify the rubber powder according to its molecular chain length. Combined with gel permeation chromatography (GPC) online detection technology, rubber powder within specific chain length ranges is precisely collected. Based on molecular weight, the rubber powder is divided into long-chain components (molecular weight > 500,000), medium-chain components (molecular weight 200,000-500,000), and short-chain components (molecular weight < 200,000). These components with different chain lengths will be used in different application areas. For example, long-chain components are suitable for high-strength applications such as tires, medium-chain components are suitable for general applications such as conveyor belts, and short-chain components are suitable for applications with special flexibility requirements such as rubber flooring.

[0032] The final step is drying and packaging. The rubber powder is dried to a moisture content of less than 1% using vacuum drying (60-80℃, vacuum degree -0.08MPa) to ensure product stability and shelf life. The dried rubber powder is then packaged according to chain length and stored for later use.

[0033] Example 1: High-strength long-chain recycled rubber powder for tires (weight average molecular weight 500,000-800,000)

[0034] I. Raw Material Selection and Pretreatment

[0035] First, 90% of waste heavy-duty tire tread rubber (with high cross-linking properties) and 10% natural rubber scraps are carefully selected and mixed according to the specified weight ratio. The mixed raw materials are then crushed using a jaw crusher to achieve a particle size of 8mm. Next, a three-stage magnetic separator (magnetic field strength controlled within the range of 1200-1500 Gs) is used to remove metallic impurities. To further purify the raw materials, they are circulated and washed with 60℃ hot water, with 0.5wt% baking soda added to the washing water, for a duration of 15 minutes. Finally, a vacuum dehydration process (vacuum degree of -0.07MPa, temperature of 80℃) is used to reduce the moisture content of the raw materials to less than 3%.

[0036] II. Gradient Mechanical Shearing

[0037] A temperature-controlled twin-screw extruder (L / D ratio of 40) was used, with three temperature zones: 80℃ in the feeding zone, 110℃ in the shearing zone, and 90℃ in the discharge zone. The screw speed was controlled using a gradient mode: 120 rpm for the first stage, increasing to 180 rpm for the second stage, and then 150 rpm for the third stage, for the fourth stage. The melt viscosity was monitored in real-time using an online rotational viscometer (1 Hz) to ensure it remained stable within 900 ± 50 Pa·s. A feedback adjustment system was used to control the screw speed fluctuation to no more than ± 10 rpm.

[0038] III. Precise Chemical Regulation

[0039] The sheared rubber powder was fed into a reactor equipped with a stirrer (stirring speed 60 rpm), and di-tert-butyl peroxide (pre-dissolved in 10 wt% toluene solution) was added at 1.2 wt% of the rubber powder mass. Under a nitrogen atmosphere (nitrogen flow rate 0.5 L / min), the reactor temperature was raised to 145 °C and maintained for 50 minutes. The reaction was monitored at 1600 cm⁻¹ using online Fourier transform infrared spectroscopy (FTIR). -1 Changes in the characteristic peaks of double bonds at the site ensure that the degree of chain scission reaction is strictly controlled between 30-35%.

[0040] IV. Synergistic Activation and Stabilization

[0041] After the reaction was completed, the temperature was lowered to 120℃, and 2.0 wt% of nano-sized zinc oxide (50 nm particle size), 1.0 wt% of stearic acid, 0.3 wt% of antioxidant RD, and 0.2 wt% of antioxidant 4020 were added to form a composite activation system, which was then stirred continuously for 20 minutes. Differential scanning calorimetry (DSC) was used to verify that the oxidation induction period of the activated system was not less than 120 minutes.

[0042] V. Multi-stage separation and purification

[0043] A combined centrifugation + membrane separation process was used for separation and purification: First, centrifugation was performed at 1200 rpm for 15 minutes to remove coarse impurities; then, cross-flow filtration was performed through a 300-mesh ultrafiltration membrane (molecular weight cutoff of 500,000) at 800 rpm, and the components on the membrane were collected; finally, gel permeation chromatography (GPC) was used for detection, and components with a weight average molecular weight in the range of 500,000-800,000 were collected (detection conditions: mobile phase: tetrahydrofuran, flow rate: 1.0 mL / min, column temperature: 35℃).

[0044] VI. Low-temperature vacuum drying

[0045] The adhesive powder was dried under a vacuum of -0.09 MPa and at 75°C for 3 hours until the moisture content stabilized at 0.5 ± 0.1%. The particle size of the finished product was controlled within the range of 80-100 mesh. Before packaging, a laser particle size analyzer was used for random sampling to ensure that the particle size distribution range did not exceed 1.2.

[0046] Performance indicators: tensile strength 20.5±0.8MPa, 300% constant elongation stress 8.2±0.5MPa, elongation at break 480±30%, Akron abrasion ≤0.15cm. 3 / 1.61km, fully meeting the requirements for first-class recycled rubber for tires in GB / T13460-2016.

[0047] Example 2: Short-chain recycled rubber powder for flexible rubber flooring (weight average molecular weight 100,000-200,000)

[0048] I. Raw material preparation and pretreatment

[0049] 70% waste styrene-butadiene rubber (with medium cross-linking properties) and 30% waste ethylene propylene diene monomer (EPDM) rubber were mixed and crushed to a particle size of 5 mm. After two-stage magnetic separation (magnetic field strength of 1000 Gs), the mixture was ultrasonically cleaned with deionized water at 50°C (cleaning power of 300 W) for 10 minutes. Subsequently, the moisture content was reduced to less than 4% by centrifugation (speed of 1500 rpm for 5 minutes).

[0050] II. Enhanced Mechanical Shearing

[0051] The twin-screw extruder is configured as follows: feeding section temperature 90℃, shearing section temperature 130℃, and discharge section temperature 110℃. The screw speed adopts a stepped increase mode: initial speed 200 rpm for 4 minutes; intermediate speed increased to 280 rpm for 6 minutes; and final speed adjusted to 250 rpm for 3 minutes. The melt viscosity is controlled within 400±30 Pa·s using an online viscosity monitoring system, and feedback adjustment via a torque sensor ensures a stable shear energy input of 80±5 kJ / kg.

[0052] III. Deep chemical chain scission

[0053] The gel powder was fed into a reaction vessel, and 3.0 wt% benzoyl peroxide (pre-dissolved in 15 wt% ethyl acetate solution) was added. The stirring speed was 80 rpm. Under air atmosphere, the temperature was raised to 165 °C and maintained for 95 minutes. The reaction was terminated when the weight-average molecular weight dropped to approximately 150,000, as monitored online by gel permeation chromatography (sampled every 10 minutes).

[0054] IV. Mild Activation Treatment

[0055] After the reaction was complete, the temperature was lowered to 130°C, and 1.5 wt% of micron-sized zinc oxide (2 μm particle size), 0.8 wt% of stearic acid, and 0.4 wt% of antioxidant 264 were added, followed by continuous stirring for 25 minutes. Thermogravimetric analysis (TGA) was used to verify that the weight loss below 200°C was less than 2%.

[0056] VI. Refined grading and screening

[0057] A three-stage centrifugation process was employed: first, centrifugation at 2000 rpm for 10 minutes removed large particulate impurities; then, centrifugation at 2500 rpm for 15 minutes collected intermediate components; and finally, centrifugation at 3000 rpm for 20 minutes separated short-chain components. After filtration through a 1 million molecular weight cutoff membrane, gel permeation chromatography (GPC) was used to collect components with a weight-average molecular weight in the range of 100,000 to 200,000.

[0058] VII. Low-temperature airflow drying

[0059] The product is dried using a pulsed airflow dryer with an inlet temperature of 70℃ and an outlet temperature of 45℃ for 30 seconds, until the moisture content reaches 0.6±0.1%. The finished product particle size is controlled within the range of 120-150 mesh, and is measured using a laser particle size analyzer to ensure that the particle size distribution span does not exceed 1.0.

[0060] Performance indicators: Shore A hardness is 60±3 degrees, elongation at break is 650±40%, and compression set (after 22 hours at 70℃) is ≤25%, which fully meets the requirements for elastic materials for rubber flooring in GB / T4085-2015.

[0061] Example 3: Medium-chain recycled rubber powder for general conveyor belts (weight average molecular weight 300,000-500,000)

[0062] Raw material processing: Mix 50% of tire sidewall rubber with 50% nitrile rubber waste, crush to 6mm particle size, and perform routine cleaning to remove impurities.

[0063] Shear parameters: A twin-screw extruder was used, with the temperature set at 100℃, the speed at 200 rpm, the shearing time at 8 minutes, and the melt viscosity controlled within the range of 650±50 Pa·s.

[0064] Chain breaking conditions: Add 2.0 wt% di-tert-amyl peroxide and react at 150 °C for 70 minutes.

[0065] Separation requirements: Separate at a centrifugation speed of 1500 rpm and collect components with molecular weights in the range of 3 million to 5 million.

[0066] Performance indicators: tensile strength is 16.2MPa, elongation at break is 520%, which fully meets the standard requirements for recycled rubber for conveyor belts in HG / T2196-2018.

[0067] Verification of process advantages:

[0068] By comparing the product performance of the traditional process and the process of this invention (sample size: 5), the results show that the molecular weight distribution index (PDI) of the product of this process is controlled within the range of 2.5-3.5 (4.5-6.0 of the traditional process), the tensile strength fluctuation between batches does not exceed 5% (15%-20% of the traditional process), the raw material utilization rate is increased to 92% (75% of the traditional process), and the energy consumption per ton of product is reduced by 18%.

[0069] This process achieves directional control of the molecular chain length of recycled rubber powder by precisely adjusting the mechanical shearing and chemical chain breaking parameters. It effectively solves the problems of unstable product performance, limited application range, and low production efficiency of traditional processes, while reducing waste generation and lowering environmental pressure.

[0070] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0071] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A preparation process for regenerated rubber powder with adjustable molecular chain lengths, characterized in that, Includes the following steps: The process includes raw material pretreatment and grading, preliminary chain breaking by mechanical shearing, deep chain breaking by chemical regulation, activation and stabilization treatment, separation, grading and drying packaging. By synergistically regulating mechanical shearing parameters and chemical chain breaking conditions, the molecular chain length of regenerated rubber powder can be controlled in a directional manner.

2. The preparation process of regenerated rubber powder with adjustable molecular chain length according to claim 1, characterized in that, The preliminary chain-breaking step of mechanical shearing is carried out using a twin-screw extruder at 80-120℃. The screw speed is controlled at 100-300 rpm and the shearing time is 5-15 min. The shearing parameters are adjusted in real time by monitoring and feedback from an online viscometer.

3. The preparation process of regenerated rubber powder with adjustable molecular chain length according to claim 1, characterized in that, In the chemically regulated deep chain scission step, the chain scission agent used is an organic peroxide or amine compound, and its addition amount is 0.5-5 wt% of the rubber powder mass. The reaction temperature is controlled at 120-180℃ and the reaction time is 30-120 min.

4. The preparation process of regenerated rubber powder with adjustable molecular chain length according to claim 1, characterized in that, The separation and grading step employs gradient centrifugation technology combined with online gel permeation chromatography to separate the regenerated rubber powder into long-chain components (molecular weight > 500,000), medium-chain components (molecular weight 200,000-500,000), and short-chain components (molecular weight < 200,000).

5. The preparation process of regenerated rubber powder with adjustable molecular chain length according to claim 1, characterized in that, In the raw material pretreatment and grading steps, the waste rubber is divided into three grades: high, medium, and low, according to the degree of cross-linking, and different subsequent treatment parameters are adopted for each grade.

6. The preparation process of regenerated rubber powder with adjustable molecular chain length according to claim 1, characterized in that, In the activation and stabilization step, zinc oxide and stearic acid are added as activators, with addition amounts of 1-3 wt% and 0.5-2 wt% of the rubber powder mass, respectively, and 0.1-1 wt% of antioxidant is added at the same time.

7. A method for preparing reclaimed rubber powder with adjustable molecular chain lengths, comprising the preparation process of reclaimed rubber powder with adjustable molecular chain lengths according to claims 1-6, characterized in that, include: The molecular chain length can be controlled by adjusting the concentration of the chain scissor and the reaction time: when preparing long-chain components, use 0.5-2 wt% chain scissor and 30-60 min reaction time; when preparing short-chain components, use 2-5 wt% chain scissor and 60-120 min reaction time.

8. The method for preparing regenerated rubber powder with adjustable molecular chain length according to claim 7, characterized in that, The gradient centrifugation technology operates at speeds ranging from 500 to 3000 rpm, achieving the separation of components with different molecular weights through 3-5 graded speed gradients.

9. The method for preparing regenerated rubber powder with adjustable molecular chain length according to claim 7, characterized in that, The coordinated control of mechanical shearing and chemical chain breaking is achieved through an intelligent control system that automatically matches the optimal process parameters based on the type of raw materials and the target product.

10. The method for preparing regenerated rubber powder with adjustable molecular chain length according to claim 7, characterized in that, The ratio of long-chain to short-chain rubber powder produced by the process can be controlled within the range of 1:9 to 9:1 to meet the performance requirements of different application scenarios.

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