A method for repairing the stability of multi-batch cyclic processing of recycled polypropylene

Abstract

The application discloses a recycled polypropylene multi-batch circulation processing stability repair method, and relates to the technical field of waste plastic recycling and reprocessing. The method comprises the following steps: pre-treating a plurality of recycled polypropylene batches and grouping them according to initial melt flow rates, performing a thermal residence induction test on a to-be-repaired group, detecting melt flow rates and oxidation induction times before and after thermal residence, calculating delay flow transition rates, stable reserve attenuation rates and batch instability characterization values, identifying thermal residence triggered low stable reserve batches, determining repair intensity grades according to instability degrees, adding a stability repair component, and then performing melting mixing, extrusion, cooling and granulation, and finally performing thermal residence review to determine repair eligibility. The method is beneficial to reducing the flow performance drift and discharge fluctuation risk in the continuous processing of recycled polypropylene.

Description

Technical Field

[0001] This invention relates to the field of waste plastic recycling and reprocessing technology, and in particular to a method for restoring the stability of multi-batch cyclic processing of recycled polypropylene. Background Technology

[0002] Polypropylene (PP) is widely used in packaging containers, turnover boxes, household appliance parts, automotive interior parts, daily necessities, woven products, and industrial parts due to its low density, good chemical resistance, excellent processing and molding performance, and low cost. With the increasing use of PP products, the recycling and reprocessing of waste PP has become an important way to recycle plastic resources. Existing recycled PP waste plastics typically undergo processes such as sorting, crushing, washing, drying, melt extrusion, filtration, cooling, and granulation to be remade into recycled PP granules for subsequent injection molding, extrusion, sheet production, fiber drawing, or modified granulation. In actual production, to determine whether different batches of recycled PP are suitable for the same processing system, their initial melt flow rate, appearance, ash content, tensile strength, or impact strength are usually tested, and grading, blending, or feeding are based on these indicators.

[0003] However, the sources of recycled polypropylene waste plastics are complex, and different batches of materials may vary in their original grade, service time, thermal history, shear history, photo-oxidative aging degree, residual antioxidant capacity, contaminant residue, and degree of hidden chain breakage. Even if multiple batches of recycled polypropylene have similar initial melt flow rates before feeding, this does not mean that they have the same thermal and oxygen stability reserves and molecular chain retention capacity during subsequent melt reprocessing. Some low-stability reserve batches may exhibit normal plasticization and stable discharge in the early stages of processing, but after experiencing the same melting temperature, thermal residence time, and shearing action, they are prone to delayed melt flow rate jumps, leading to problems such as sudden drops in melt viscosity, extrusion pressure fluctuations, unstable strip traction, decreased pellet uniformity, and product performance dispersion in the later stages of continuous processing. Existing methods mostly rely on static detection results before feeding, making it difficult to identify recycled polypropylene batches with similar initial melt flow rates but different subsequent thermal residence stability in a timely manner. Furthermore, there is a lack of a processing mechanism for graded repair and verification feedback for such low-stability reserve batches, making it difficult to meet the requirements for stable recycling of multi-source, multi-batch recycled polypropylene waste plastics. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies where, when recycling and reprocessing multiple batches of recycled polypropylene, it is difficult to identify low-stability reserve batches based solely on the initial melt flow rate, leading to drift in flow properties, fluctuations in output, and dispersion in product performance during subsequent melt processing. Therefore, this invention proposes a method for restoring the stability of recycled polypropylene in multiple batches of cyclic processing.

[0005] In view of this, the present invention provides a method for restoring the stability of recycled polypropylene through multiple batch cyclic processing, comprising the following steps: S1. Pre-treat multiple batches of recycled polypropylene separately, and detect the initial melt flow rate of each batch of recycled polypropylene. and the initial melt flow rate Multiple batches of recycled polypropylene within the same defined range are grouped into the same repair group; S2. Perform a heat retention induction test on each batch of recycled polypropylene in the group to be repaired, and detect the initial melt flow rate before heat retention. and initial oxidation induction time And detect the melt flow rate after heat hold. Oxidation induction time after heat retention ; S3, based on the initial melt flow rate and the melt flow rate after the heat residence Calculate the delayed flow transition rate According to the initial oxidation induction time and the oxidation induction time after heat residence Calculate the rate of decline of stable reserves And according to the said delayed flow transition rate and the stable reserve decay rate Determine batch instability characterization values ; S4. Based on the batch instability characterization values With setting an instability threshold Based on the comparison results, the corresponding recycled polypropylene batches are determined to be either heat-stable batches or heat-stable triggered low-stability reserve batches, and the batch instability characterization values ​​are used as a basis for classification. Determine the repair intensity level of the aforementioned heat-induced low-stability reserve batch; S5. According to the repair strength level, add the stability repair component to the heat-induced low-stability reserve batch, and perform melt mixing, extrusion, cooling and granulation to obtain repaired recycled polypropylene granules. S6. Perform a heat retention verification test on the repaired recycled polypropylene particles and calculate the instability characterization value after repair. And based on the instability characterization values ​​after repair Determine whether the corresponding batch of recycled polypropylene has been repaired and is qualified.

[0006] Preferably, in step S1, the pretreatment includes crushing, washing, drying, and preliminary homogenization of the recycled polypropylene waste plastic.

[0007] Preferably, in step S1, batches of recycled polypropylene that satisfy the following formula are grouped into the same group to be repaired:

[0008] in, The target melt flow rate, To allow for the initial melt flow rate deviation, The initial melt flow rate is given.

[0009] Preferably, in step S2, the melting temperature, the hot residence time, and the equipment rotation speed or shear rate used to characterize the shearing action in the heat residence induction test are determined according to the target melt reprocessing conditions of the corresponding recycled polypropylene batch.

[0010] Preferably, in step S3, the delayed flow transition rate Calculate according to the following formula:

[0011] The stable reserve decay rate Calculate according to the following formula:

[0012] The batch instability characterization value Calculate according to the following formula:

[0013] in, To delay the flow transition rate, This represents the melt flow rate after thermal residence. The initial melt flow rate; To stabilize the reserve decay rate, The initial oxidation induction time. This refers to the oxidation induction time after heat retention; This represents the batch instability characterization value.

[0014] Preferably, in step S4, when the batch instability characterization value Greater than the set instability threshold When the corresponding recycled polypropylene batch is identified as a heat-induced low-stability reserve batch, and the batch's instability characterization value is... Not greater than the set instability threshold At that time, the corresponding recycled polypropylene batch will be classified as a heat-stable batch.

[0015] Preferably, in step S4, the repair strength level includes light repair batches, moderate repair batches, and severe repair batches; when Greater than And not greater than the first repair threshold When this occurs, the corresponding recycled polypropylene batch will be classified as a slightly repaired batch; when Greater than And not greater than the second repair threshold When the corresponding recycled polypropylene batch is identified as a moderately repaired batch; when Greater than At that time, the corresponding recycled polypropylene batch will be identified as a heavily rehabilitated batch; among which, .

[0016] Preferably, in step S5, the stability repair component includes an antioxidant stabilizing component and a chain stabilizing component, and the total amount of the stability repair component added is 0.1% to 2.5% of the mass of the recycled polypropylene.

[0017] Preferably, the amount of stabilizing component added for the mild, moderate, and severe repair batches increases sequentially; the amount of antioxidant stabilizing component added is based on the stabilization reserve decay rate. It is determined that the amount of the chain-stabilizing component added is based on the delayed flow transition rate. Sure.

[0018] Preferably, in step S6, the hot residence verification test includes detecting the initial melt flow rate after repair. Melt flow rate after repair and heat retention Initial oxidation induction time after repair and the oxidation induction time after heat retention following repair and according to , , and Calculate the instability characterization value after repair ; When the instability characterization value after repair Not greater than the set instability threshold And satisfy At that time, the corresponding batch of recycled polypropylene was deemed to have passed the repair test. When the instability characterization value after repair Greater than the set instability threshold If the corresponding recycled polypropylene batch is not identified as a severely repaired batch, the repair strength level of the corresponding recycled polypropylene batch shall be increased and stability repair shall be carried out again. When the instability characterization value after repair Greater than the set instability threshold When the corresponding recycled polypropylene batch has been identified as a heavily repaired batch, the amount of stability repair component added is adjusted within the range of 0.1% to 2.5% of the total amount of stability repair component added, and stability repair is carried out again.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention groups multiple batches of recycled polypropylene with initial melt flow rates within the same set range into the same repair group and conducts heat residence induction tests on each batch. This allows for further identification of the degree of melt flow rate jump and oxidation induction time decay in different batches after heat residence, even when the initial melt flow rates are similar before feeding. By comprehensively judging batch stability through delayed flow transition rate, stable reserve decay rate, and batch instability characterization value, heat residence-triggered low-stability reserve batches that are not easily exposed in the early stages of processing can be identified in advance. This avoids the situation where low-stability reserve batches enter the continuous processing process due to feeding classification based solely on the initial melt flow rate, thereby helping to reduce the risks of sudden viscosity drops, extrusion pressure fluctuations, unstable strip traction, and decreased pellet uniformity during subsequent melt reprocessing.

[0020] 2. This invention determines the repair strength level based on batch instability characterization values, and determines the amount of antioxidant stabilizing component to be added based on the stability reserve decay rate and the amount of chain stabilizing component to be added based on the delayed flow transition rate. This ensures that the addition of stability repair components corresponds to the degree of thermal and oxygen stability reserve loss and melt flow transition degree of each batch. By conducting a heat residence verification test on the repaired recycled polypropylene granules again, and using whether the instability characterization value and the melt flow rate after heat residence meet the target allowable range as the criteria for qualification, a closed-loop processing process of batch grouping, heat residence induction, instability identification, graded repair, and verification feedback is formed. This improves the batch stability and processing adaptability in the recycling and reprocessing of multi-source, multi-cycle recycled polypropylene waste plastics, which helps reduce the risk of product performance dispersion and enhances the recycling value of recycled polypropylene granules. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a flowchart of the method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to the present invention. Figure 2 A schematic diagram of the thermal dwell-triggered melt flow transition for low-stability reserve batches with equal melt index; Figure 3 A schematic diagram showing the correspondence between batch instability characterization values ​​and repair strength levels; Figure 4 A schematic diagram of the closed loop for stability repair and verification of low-stability reserve batches. Detailed Implementation

[0022] The following describes a method for restoring the stability of recycled polypropylene through multiple batch recycling processes, with specific embodiments. It should be understood that the following embodiments are for illustrating the technical solution of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the technical concept of the present invention, those skilled in the art can adaptively adjust the melting temperature, hot residence time, equipment speed, threshold, and the amount of stability restoration components added, based on the source of the recycled polypropylene waste plastic, the intended use of the target product, and the actual melting and reprocessing conditions.

[0023] In this embodiment, the recycled polypropylene batch refers to batches of recycled polypropylene materials formed separately after recycling, whether from the same or different sources. The recycled polypropylene waste plastics can originate from waste turnover boxes, waste packaging containers, waste daily necessities, waste polypropylene parts from household appliances, waste polypropylene parts from automotive interiors, or industrial production scraps. Although each batch of recycled polypropylene waste plastics is a polypropylene material, their original grade, service life, thermal history, shear history, photo-oxidative aging degree, residual antioxidant capacity, and degree of hidden chain breakage may differ.

[0024] In this embodiment, melt flow rate is used to characterize the melt flow state of recycled polypropylene during testing; oxidation induction time is used to characterize the thermo-oxygen stability reserve of recycled polypropylene. Melt flow rate can be tested according to GB / T 3682.1 or an equivalent test method, and the test conditions can be the commonly used conditions for polypropylene, i.e., a temperature of 230 degrees Celsius and a load of 2.16 kg. Oxidation induction time can be tested according to GB / T 19466.6 or an equivalent test method, using differential scanning calorimetry. At a set temperature, the atmosphere is switched from inert to oxygen, and the time corresponding to the appearance of the exothermic oxidation inflection point is recorded.

[0025] In this embodiment, the stability-restoring components include an antioxidant stabilizing component and a chain stabilizing component. The antioxidant stabilizing component is used to compensate for the loss of thermo-oxidative stability reserves in recycled polypropylene after multiple melt processing; the chain stabilizing component is used to reduce the tendency of recycled polypropylene to continue to experience a surge in melt flow rate during subsequent hot residence processes. The antioxidant stabilizing component can be selected from one or more of hindered phenolic antioxidants, phosphite antioxidants, and thioester antioxidants; the chain stabilizing component can be selected from one or more of polymer chain stabilizers containing epoxy functional groups, epoxy chain extenders, and maleic anhydride-grafted polypropylene. The above-mentioned stability-restoring components are only used to restore the cyclic processing stability of recycled polypropylene and are not intended to change the basic category of the recycled polypropylene material.

[0026] As a specific approach, the antioxidant stabilizing component consists of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a 1:1 mass ratio; the chain stabilizing component consists of maleic anhydride-grafted polypropylene and an epoxy chain extender in a 2:1 mass ratio. The hindered phenolic antioxidant 1010 is used to capture free radicals formed during thermo-oxidative degradation, the phosphite antioxidant 168 is used to decompose hydroperoxides, the maleic anhydride-grafted polypropylene is used to improve the interfacial compatibility between aged segments, low-molecular-weight components, and residual polar impurities in the recycled polypropylene system, and the epoxy chain extender is used to reduce the tendency for the melt flow rate of recycled polypropylene to continue to increase after heat holding. When the calculated amount of antioxidant stabilizing component added... Subsequently, the hindered phenolic antioxidant 1010 and phosphite antioxidant 168 were respectively processed according to... 50% is added; when the amount of chain-stabilizing component added is calculated. Subsequently, maleic anhydride grafted polypropylene was processed according to... Add 2 / 3 of the amount, and the epoxy chain extender is added according to... Add 1 / 3.

[0027] When determining the amount of stabilizing repair components to be added, first determine the total amount of stabilizing repair components to be added based on the repair strength level. When the corresponding recycled polypropylene batch is a slightly repaired batch, It is 0.3% to 0.8% of the mass of recycled polypropylene; when the corresponding recycled polypropylene batch is a moderately rehabilitated batch, It is 0.8% to 1.6% of the mass of recycled polypropylene; when the corresponding recycled polypropylene batch is a heavily reprocessed batch, The amount of antioxidant stabilizing component added is 1.6% to 2.5% of the mass of recycled polypropylene. Addition amount of chain stabilizing component Determined according to the following formula:

[0028]

[0029] in, , This refers to the amount of antioxidant stabilizing component added. This refers to the amount of chain-stabilizing component added. This refers to the total amount of stability-restoring components added. To stabilize the reserve decay rate, This represents the delayed flow transition rate. When If it is determined that the corresponding batch does not pose a risk of low stability due to heat retention, no targeted addition of stability repair components will be carried out.

[0030] In actual production, an instability threshold is set. First repair threshold Second repair threshold This can be determined based on historical batch data. Specifically, recycled polypropylene batches that did not experience abnormal fluctuations in extrusion pressure, abnormal strip traction, or uneven pelletizing during continuous melt reprocessing, whose subsequent products' tensile strength, flexural strength, or impact strength met the internal control requirements for the corresponding recycled polypropylene products, and whose melt flow rate after heat holding met the target allowable range, are considered historical qualified batches. The batch instability characterization values ​​of these historical qualified batches are then statistically analyzed. maximum value ,Will Add a safety margin as the setting instability threshold Low-stability reserve batches that can meet the repair qualification conditions after minor repairs The upper limit of the value is used as the first repair threshold. Low-stability reserve batches that can meet the repair qualification conditions after moderate repair. Value upper limit as the second repair threshold The safety margin can be determined based on testing errors, production batch fluctuations, and the quality requirements of the target product.

[0031] The conditions for the heat residence induction test are used to reproduce the heat residence and shear effects in the target melt reprocessing, and it is not required that the rotational speed of the experimental equipment be exactly the same as the screw speed of the production equipment. When a torque rheometer is used for the heat residence induction test, the rotor speed represents the shear effect; when a small extruder is used, the screw speed represents the shear effect; when a capillary rheometer is used, the shear rate represents the shear effect. The heat residence induction test conditions can be calibrated by corresponding the changes in melt flow rate of a stable batch before and after heat residence with the discharge fluctuations of a stable batch in the target melt reprocessing.

[0032] Example 1

[0033] This embodiment provides a method for restoring the stability of recycled polypropylene through multiple batch cyclic processing, including the following steps.

[0034] like Figure 1As shown, this invention first pre-treats multiple batches of recycled polypropylene and establishes a group to be repaired based on the initial melt flow rate. Then, a heat residence induction test is performed on the group to be repaired to detect the melt flow rate and oxidation induction time before and after heat residence, and to calculate the delayed flow transition rate, stable reserve decay rate, and batch instability characterization value. When the batch instability characterization value is not greater than the set instability threshold, the corresponding batch is output as a heat residence stable batch. When the batch instability characterization value is greater than the set instability threshold, the corresponding batch is identified as a heat residence triggered low stability reserve batch, and a stability repair component is added according to the repair strength level. After melt mixing, extrusion, cooling, and granulation, a heat residence verification is performed. If the verification is qualified, a qualified repair batch is output. If the verification is unqualified, the repair strength level or the amount of stability repair component added is adjusted and the repair is repeated, thus forming a closed-loop processing flow of batch identification, graded repair, and verification feedback.

[0035] S1. Establish a group of multiple batches of recycled polypropylene to be repaired with similar initial melt flow rates; Four batches of recycled polypropylene waste plastic from different sources were selected and labeled as batch A, batch B, batch C, and batch D. All four batches are recycled polypropylene waste plastic, but their sources are different. Batch A comes from waste turnover boxes, batch B comes from waste packaging containers, batch C comes from industrial polypropylene scraps, and batch D comes from mixed daily consumer goods polypropylene waste.

[0036] Batch A, batch B, batch C, and batch D were subjected to crushing, washing, drying, and preliminary homogenization. Crushing yielded flaky or granular recycled polypropylene material; washing was used to remove surface dust, oil, and washable impurities; drying was used to reduce the impact of moisture on subsequent melt testing and melt mixing; preliminary homogenization was used to reduce local variations within the same batch.

[0037] After drying, the initial melt flow rate of each batch of recycled polypropylene was tested. In this embodiment, a target melt flow rate is set. The allowable initial melt flow rate deviation is 10.0 g / 10 min. The concentration is 1.0 g / 10 min. When a batch meets the following formula, it is classified into the same group to be repaired:

[0038] The initial melt flow rate of batch A was detected. The initial melt flow rate of batch B was 9.7 g / 10 min. The initial melt flow rate of batch C was 10.2 g / 10 min. The initial melt flow rate of batch D was 9.9 g / 10 min. The value is 10.5g / 10min.

[0039] Batch A, batch B, batch C, and batch D all meet the requirements. Therefore, the four batches were grouped into the same remediation group. This step ensures that subsequent processing focuses on recycled polypropylene batches with similar initial melt flow rates, avoiding the direct mixing of batches with significant initial flow differences into the same remediation assessment process.

[0040] S2. Conduct a heat retention induction test on the repair group; Samples were taken from batches A, B, C, and D, and a heat retention induction test was performed on each batch. The heat retention induction test was used to simulate the heat retention and shear forces experienced by recycled polypropylene during the target melt reprocessing.

[0041] In this embodiment, the target melt reprocessing is a twin-screw extrusion granulation process, with an actual processing temperature range of 180°C to 210°C and a screw speed of 180 r / min. To simulate this process equivalently under laboratory conditions, a torque rheometer was used for a thermal residence induction test, with the melt temperature set at 210°C, the rotor speed at 60 r / min, and the thermal residence time at 20 min. The rotor speed was used to characterize the shear effect. When using a small extruder for the thermal residence induction test, the screw speed can also be used to characterize the shear effect; when using a capillary rheometer for the thermal residence induction test, the shear rate can also be used to characterize the shear effect.

[0042] In this embodiment, the process for determining the heat residence induction test conditions is as follows: First, a batch of recycled polypropylene with stable output in historical processing is selected as a stable calibration batch. Processing or heat residence tests are then conducted under both the target twin-screw extrusion granulation conditions and torque rheometer conditions. When the change in melt flow rate after heat residence of the stable calibration batch under torque rheometer conditions is within the same fluctuation range as that of the stable calibration batch under the target twin-screw extrusion granulation conditions, the torque rheometer conditions are used as the heat residence induction test conditions. Therefore, the melt temperature, rotor speed, and heat residence time for this embodiment are determined to be 210 degrees Celsius, 60 r / min, and 20 min, respectively.

[0043] Before the heat retention induction test, the initial melt flow rate of each batch was measured. and initial oxidation induction time After the heat retention induction test, the melt flow rate of each batch after heat retention was measured. Oxidation induction time after heat retention .

[0044] The test results are as follows: Batch A It is 9.7g / 10min. 10.5g / 10min It is 18.0 min. It takes 15.2 minutes; Batch B It is 10.2g / 10min. It is 16.8g / 10min. It is 9.5 minutes. It is 4.1 min; Batch C It is 9.9g / 10min. It is 11.1g / 10min. It lasted 16.8 minutes. It took 13.7 minutes; Batch D 10.5g / 10min It is 18.2g / 10min. It takes 8.2 minutes. It takes 3.0 minutes.

[0045] The data above shows that the initial melt flow rates of batches A, B, C, and D before feeding were in a similar range. However, after the same heat residence induction test, the melt flow rates of batches B and D increased significantly after heat residence, and the oxidation induction time decreased significantly. This indicates that batches B and D have low stability reserves and the risk of heat residence-triggered melt flow transition.

[0046] like Figure 2 As shown, in the initial stage of hot residence, the hot residence stable batch and the hot residence triggered low-stability reserve batch have similar initial melt flow rates, both within the allowable range of the target melt flow rate. With prolonged hot residence time, the melt flow rate of the hot residence stable batch changes little, while the hot residence triggered low-stability reserve batch, due to insufficient thermo-oxygen stability reserves and the accumulation of hidden chain breakage, exhibits a rapid increase in melt flow rate within the delayed flow transition region, thus deviating from the allowable range of the target melt flow rate. This figure illustrates how the present invention identifies recycled polypropylene batches with similar initial melt flow rates but different subsequent processing stability through a hot residence-induced test.

[0047] S3. Calculate the batch instability characterization value; Calculate the delayed flow transition rate for each batch based on the melt flow rate before and after the heat residence. Delayed flow transition rate Calculate according to the following formula:

[0048] The stable stock decay rate for each batch was calculated based on the oxidation induction time before and after heat treatment. Stable reserve decay rate Calculate according to the following formula:

[0049] Based on delayed flow transition rate and stable reserve decay rate Calculate the batch instability characterization value for each batch. Batch instability characterization values Calculate according to the following formula:

[0050] The calculation yielded: Batch A It is 0.082. It is 0.156. It is 0.095; Batch B It is 0.647. It is 0.568. It is 1.015; Batch C It is 0.121. It is 0.185. It is 0.144; Batch D It is 0.733. It is 0.634. It is 1.198.

[0051] In this embodiment, if the detection error leads to or If the problem persists after retesting, the corresponding sample will be retested. If the problem still occurs after retesting, the corresponding difference will be treated as zero to avoid the instability caused by the detection error being amplified in reverse.

[0052] S4. Identify the low-stability reserve batches triggered by heat retention and determine the repair intensity level; In this embodiment, an instability threshold is set. The first repair threshold is 0.25. The second repair threshold is 0.75. It is 1.10 and satisfies .

[0053] The set instability threshold This was determined through historical qualified batch statistics. Specifically, for multiple groups of known products that did not experience significant fluctuations in output during continuous extrusion granulation, and whose subsequent products met the internal control requirements for the corresponding recycled polypropylene products in terms of tensile strength, flexural strength, or impact strength, and also met the requirements... The recycled polypropylene batches were subjected to heat retention induction tests to obtain its Value distribution. Historical qualified batches. The values ​​are all no greater than 0.22, and 0.03 is taken as a safety margin, therefore, it is set to... The value is 0.25. This is the first repair threshold. Second repair threshold According to low-stability reserve batches The value distribution, the allowable deviation of the target melt flow rate, and the pass rate after repair were determined. In this embodiment, the low-stability reserve batch that can meet the repair qualification conditions after slight repair is included. The upper limit of the value is determined as follows Low-stability reserve batches that can meet the repair qualification conditions after moderate repair The upper limit of the value is determined as follows .

[0054] when Not greater than When the corresponding recycled polypropylene batch is determined to be a heat-stable batch, then... Greater than At that time, the corresponding recycled polypropylene batch will be classified as a heat-induced low-stability reserve batch.

[0055] According to the above judgment rules, batch A... The value is 0.095, for batch C. The value is 0.144, and none of them are greater than 0.144. Therefore, batches A and C are classified as heat-stable batches. Batch B... The value is 1.015, for batch D. The values ​​are all greater than 1.198. Therefore, batches B and D were classified as heat-induced low-stability reserve batches. Furthermore, when Greater than and not greater than When this occurs, the corresponding recycled polypropylene batch will be classified as a slightly repaired batch; when Greater than and not greater than When the corresponding recycled polypropylene batch is identified as a moderately repaired batch; when Greater than At that time, the corresponding recycled polypropylene batch will be identified as a heavily repaired batch.

[0056] Batch B The value is 1.015, which satisfies the condition of being greater than 1.015. and not greater than Therefore, batch B was designated as a moderately repaired batch. Batch D... It is 1.198, which is greater than Therefore, batch D was identified as a batch requiring severe repair.

[0057] like Figure 3 As shown, batch instability characterization values Increasing laterally, and by setting an instability threshold. First repair threshold Second repair threshold Divided into different processing intervals; when Not greater than When the corresponding batch is determined to be a heat-stable batch, Greater than and not greater than At that time, the corresponding batch was determined to be a batch requiring minor repair. Greater than and not greater than At that time, the corresponding batch was determined to be a moderately repaired batch. Greater than At that time, the corresponding batch is determined to be a severely repaired batch. This figure is used to illustrate the determination relationship of graded repair based on the degree of batch instability in this invention.

[0058] S5. Perform stability repair and reprocessing on heat-induced low-stability reserve batches; Batch B and Batch D, which were identified as low-stability reserve batches triggered by heat retention, underwent stability repair and reprocessing.

[0059] In this embodiment, the stability repair component includes an antioxidant stabilizing component and a chain stabilizing component. The antioxidant stabilizing component consists of hindered phenolic antioxidant 1010 and phosphite antioxidant 168, with a mass ratio of 1:1; the chain stabilizing component consists of maleic anhydride-grafted polypropylene and an epoxy chain extender, with a mass ratio of 2:1. The antioxidant stabilizing component is used to compensate for the thermo-oxidative stability reserve of the recycled polypropylene, reducing the oxidation-induced time decay during the hot residence process; the chain stabilizing component is used to inhibit the continued jump in melt flow rate of the recycled polypropylene during subsequent hot residence processes. When the calculated amount of antioxidant stabilizing component added... Subsequently, the hindered phenolic antioxidant 1010 and phosphite antioxidant 168 were respectively processed according to... 50% is added; when the amount of chain-stabilizing component added is calculated. Subsequently, maleic anhydride grafted polypropylene was processed according to... Add 2 / 3 of the amount, and the epoxy chain extender is added according to... Add 1 / 3.

[0060] In this embodiment, the total amount of stabilizing repair components added for the lightly repaired, moderately repaired, and heavily repaired batches increases sequentially, and the total amount of stabilizing repair components added is controlled within the range of 0.1% to 2.5% of the mass of recycled polypropylene. Specifically, the total amount of stabilizing repair components added for the lightly repaired batch is 0.3% to 0.8% of the mass of recycled polypropylene; the total amount added for the moderately repaired batch is 0.8% to 1.6% of the mass of recycled polypropylene; and the total amount added for the heavily repaired batch is 1.6% to 2.5% of the mass of recycled polypropylene.

[0061] For batch B, since it was identified as a moderately remediated batch, the total amount of stability remediation components added was... The selected value is 1.2% of the mass of recycled polypropylene from batch B. Based on batch B... and The amount of antioxidant stabilizing component added is calculated according to the following formula. Addition amount of chain stabilizing component :

[0062]

[0063] The calculated amount of antioxidant stabilizing component added in batch B was... The amount of chain stabilizing component added is 0.561% of the mass of recycled polypropylene in batch B. The amount of recycled polypropylene in batch B is 0.639% of the total mass. Specifically, the amount of hindered phenolic antioxidant 1010 is 0.2805% of the total mass of recycled polypropylene in batch B, the amount of phosphite antioxidant 168 is 0.2805% of the total mass of recycled polypropylene in batch B, the amount of maleic anhydride-grafted polypropylene is 0.426% of the total mass of recycled polypropylene in batch B, and the amount of epoxy chain extender is 0.213% of the total mass of recycled polypropylene in batch B.

[0064] For batch D, since it was identified as a heavily remediated batch, the total amount of stability remediation components added was... The selected value is 2.0% of the mass of recycled polypropylene in batch D. Based on batch D... and The amount of antioxidant stabilizing component added in batch D was calculated according to the above formula. The amount of chain stabilizing component added is 0.928% of the mass of recycled polypropylene in batch D. The amount added is 1.072% of the mass of recycled polypropylene in batch D. Specifically, the amount of hindered phenolic antioxidant 1010 added is 0.464% of the mass of recycled polypropylene in batch D, the amount of phosphite antioxidant 168 added is 0.464% of the mass of recycled polypropylene in batch D, the amount of maleic anhydride-grafted polypropylene added is 0.715% of the mass of recycled polypropylene in batch D, and the amount of epoxy chain extender added is 0.357% of the mass of recycled polypropylene in batch D.

[0065] When adding the stability-restoring component, the recycled polypropylene granules from the heat-induced low-stability reserve batch are first mixed with the stability-restoring component in a high-speed mixer to initially disperse the stability-restoring component on the surface of the recycled polypropylene granules. The mixed material is then fed into a twin-screw extruder for melt mixing, extrusion, cooling, and granulation.

[0066] In this embodiment, the twin-screw extruder is equipped with multiple temperature zones along the material conveying direction, with the temperatures of each zone set sequentially to 170°C, 185°C, 195°C, 205°C, 205°C, and 200°C; the screw speed is 180 r / min; the extruded material is water-cooled and then pelletized to obtain repaired recycled polypropylene granules. The above temperature and speed correspond to the target melt reprocessing conditions simulated in the heat residence induction test in S2, ensuring consistency between the repair process and the heat residence induction test.

[0067] Batch A and batch C were determined to be heat-stable batches, and no directional addition of stability-restoring components was carried out, or only conventional granulation was performed according to actual production needs.

[0068] S6. Conduct a post-repair heat retention verification test; Hot residence verification tests were conducted on the repaired batches B and D. The hot residence verification tests used the same melting temperature, hot residence time, and equipment rotation speed to characterize the shearing action as S2, namely, melting temperature of 210 degrees Celsius, rotor speed of 60 r / min, and hot residence time of 20 min.

[0069] Detect the initial melt flow rate after repair Melt flow rate after repair and heat retention Initial oxidation induction time after repair and the oxidation induction time after heat retention following repair Calculate the delayed flow transition rate after repair, following the calculation method in S3. , Stable reserve decay rate after repair and the instability characterization value after repair .

[0070] The following results were obtained after batch B was repaired: It is 10.4g / 10min. It is 11.0g / 10min. It is 18.5 minutes. It is 15.8 minutes. The calculated result is... It is 0.058. It is 0.146. It is 0.066.

[0071] The following results were obtained after the repair of batch D: It is 10.6g / 10min. It is 10.8g / 10min. It was 19.2 minutes. It is 16.0 min. The calculation yields... It is 0.019. It is 0.167. It is 0.022.

[0072] Due to the repairs of batches B and D All are not greater than the set instability threshold. And batch B meets the requirements. Batch D meets the requirements. Therefore, batches B and D were deemed to have passed the repair test.

[0073] Through the above-mentioned repair, although batches B and D had similar initial melt flow rates to batches A and C before feeding, they were targeted for repair due to their low thermal oxygen stability reserves and the risk of heat residence-triggered melt flow jumps. This resulted in a reduced increase in melt flow rate of the regenerated polypropylene under the same heat residence conditions and an improved ability to maintain oxidation induction time, thereby reducing the risk of sudden viscosity drops, discharge fluctuations, and product performance dispersion in the later stages of continuous processing.

[0074] like Figure 4 As shown, for recycled polypropylene batches identified as heat-induced unstable reserve batches, the repair strength level is first determined based on the batch instability characterization value. Then, stability repair components, including antioxidant and chain stabilizing components, are added. The resulting recycled polypropylene granules are obtained through melt mixing, extrusion, cooling, and granulation. Next, a heat-induced stability verification test is conducted on the repaired recycled polypropylene granules, and the repair strength is determined based on the instability characterization value. The system determines whether the repair is qualified by checking whether the melt flow rate after heat retention meets the target range. If qualified, the batch is output as qualified. If unqualified, the repair strength level or the amount of stability repair component added is adjusted, and the process is returned to the stability repair step for reprocessing, thus forming a closed loop of stability repair and verification feedback for low-stability reserve batches.

[0075] Example 2

[0076] This embodiment provides a method for re-repairing a heavily repaired batch that fails to meet standards after the initial repair. This embodiment applies to situations where the corresponding recycled polypropylene batch has been identified as a heavily repaired batch, and the amount of stability repair component added is adjusted within the total amount of stability repair component added, and stability repair is performed again.

[0077] Batch E of recycled polypropylene waste plastic was selected. After crushing, washing, drying, and preliminary homogenization, the initial melt flow rate of batch E was tested. The value is 10.3g / 10min. This embodiment still sets... 10.0g / 10min The concentration is 1.0 g / 10 min, therefore batch E meets the requirements. It was classified as a group awaiting repair.

[0078] A heat retention induction test was conducted on batch E under the same conditions as in Example 1. The results for batch E were... It is 10.3g / 10min. It is 19.6g / 10min. It lasted 7.6 minutes. It is 2.4 minutes. Calculated... It is 0.903. It is 0.684. It is 1.520. Because... Greater than Batch E was identified as a batch requiring severe repair.

[0079] During the initial remediation, the total amount of stabilization remediation components added... The selected value is 2.0% of the mass of recycled polypropylene in batch E. Based on batch E... and The amount of antioxidant stabilizing component added was calculated. The amount of chain stabilizing component added is 0.862% of the mass of recycled polypropylene in batch E. The content of recycled polypropylene in batch E was 1.138% of the total mass. Specifically, hindered phenolic antioxidant 1010 accounted for 0.431% of the total mass of recycled polypropylene in batch E, phosphite antioxidant 168 accounted for 0.431% of the total mass, maleic anhydride-grafted polypropylene accounted for 0.759% of the total mass, and epoxy chain extender accounted for 0.379% of the total mass. After melt mixing, extrusion, cooling, and granulation, a heat retention verification test was conducted on batch E.

[0080] Detected after the first repair It is 10.7g / 10min. It is 12.1g / 10min. It is 16.0 min. It is 11.8 minutes. The calculated result is... It is 0.131. It is 0.263. It is 0.165.

[0081] Although the first repair after batch E Not greater than However, due to greater than Therefore, batch E does not meet the remediation qualification conditions. At this time, provided that the total amount of stability remediation components is still within the range of 0.1% to 2.5%, the amount of stability remediation components and the ratio of antioxidant stabilizing components and chain stabilizing components should be adjusted.

[0082] During the subsequent repair, the total amount of stability-restoring components was adjusted to 2.4% of the mass of recycled polypropylene from batch E. Specifically, the amount of antioxidant stabilizers was adjusted to 1.0% of the mass of recycled polypropylene from batch E, and the amount of chain stabilizers was adjusted to 1.4% of the mass of recycled polypropylene from batch E. In the antioxidant stabilizers, hindered phenolic antioxidant 1010 and phosphite antioxidant 168 were each added at 0.5%. In the chain stabilizers, maleic anhydride-grafted polypropylene was added at 0.933%, and epoxy chain extenders were added at 0.467%. This adjustment was based on the fact that the melt flow rate of batch E after heat treatment still exceeded the allowable range for the target melt flow rate. Therefore, the proportion of chain stabilizers was increased within the total addition range to suppress further increases in melt flow rate after heat treatment.

[0083] After remelting, mixing, extrusion, cooling, and granulation, batch E underwent another heat retention verification test. The results showed... 10.5g / 10min It is 10.9g / 10min. It was 17.4 minutes. It is 13.9 minutes. The calculated result is... It is 0.038. It is 0.201. It is 0.046. Because... Not greater than And satisfy Therefore, batch E was deemed to have passed the repair test.

[0084] This embodiment illustrates that for recycled polypropylene that has been identified as a heavily repaired batch, if the re-verification conditions are still not met after the first repair, the amount and composition ratio of the stability repair components can be adjusted within the total amount of stability repair components added, and stability repair can be carried out again so that the repaired recycled polypropylene meets the heat retention stability requirements.

[0085] Example 3

[0086] This embodiment provides a method for restoring the stability of recycled polypropylene under different target melt flow rates in multi-batch cyclic processing.

[0087] Batch F, batch G, and batch H of recycled polypropylene waste plastic were selected. These three batches were used to prepare extrusion-grade recycled polypropylene granules with a target melt flow rate of low value; therefore, a target melt flow rate was set. The allowable initial melt flow rate deviation is 6.0 g / 10 min. The value is 0.8g / 10min.

[0088] After crushing, washing, drying, and preliminary homogenization, batches F, G, and H were respectively tested for their initial melt flow rates. The initial melt flow rate of batch F was determined to be... The concentration was 5.7g / 10min, in batch G. The concentration was 6.2g / 10min, for batch H. The concentration was 6.6g / 10min. All three batches met the requirements. Therefore, batches F, G, and H were grouped into the same repair group.

[0089] Since the target application of this type of recycled polypropylene is extruded products, its target melt reprocessing temperature range is 175°C to 200°C, and the screw speed is 150 r / min. In this embodiment, the heat residence induction test is conducted using a torque rheometer, with the melt temperature set at 200°C, the rotor speed at 50 r / min, and the heat residence time at 25 min.

[0090] After the heat retention induction test, the test was performed according to the method described in Example 1. , , and and calculate , and .set up It is 0.22. It is 0.65. The value is 1.00. If a certain batch... Not greater than If a certain batch is heat-stable, then the batch is determined to be a heat-stable batch; if a certain batch Greater than If so, the batch is determined to be a heat-triggered low-stability reserve batch, and based on... The repair intensity level is determined by the location of the area.

[0091] For recycled polypropylene batches identified as heat-induced low-stability reserve batches, the total amount of stability-restoring components added is determined according to the restoration strength level. and according to and Determine the amount of antioxidant stabilizing component to be added respectively Addition amount of chain stabilizing component The process involves melt mixing, extrusion, cooling, and granulation. A heat retention verification test is then performed after repair. The instability characterization value after repair is then... Not greater than And satisfy At that time, the corresponding batch was deemed to have passed the repair test.

[0092] This embodiment illustrates that the method of the present invention is not limited to recycled polypropylene batches with a target melt flow rate of 10.0 g / 10 min, but is also applicable to the stability repair of multiple batches of recycled polypropylene under different target melt flow rates, different subsequent processing uses, and different target melt reprocessing conditions.

[0093] Comparative Example 1 This comparative example uses conventional recycled polypropylene processing methods to process batches A, B, C, and D in Example 1.

[0094] In this comparative example, only the initial melt flow rate before feeding is considered. The batches were grouped. Because batches A, B, C, and D... All four batches were within the range of 9.0 g / 10 min to 11.0 g / 10 min, therefore all four batches were deemed suitable for extrusion granulation under the same process conditions. This method does not perform a heat retention induction test, nor does it detect the melt flow rate after heat retention. Oxidation induction time after heat retention The delayed flow transition rate is not calculated. Stable reserve depletion rate and batch instability characterization values Batch A, batch B, batch C, and batch D were granulated under the same twin-screw extrusion conditions as in Example 1. Due to the significant increase in melt flow rate under hot residence conditions, batches B and D exhibited decreased extrusion pressure, fluctuating strip traction, and reduced pellet uniformity in the later stages of continuous processing. In contrast, batches A and C did not show significant discharge fluctuations.

[0095] Under the same extrusion conditions, the extrusion pressure fluctuation range of batch A was 0.4 MPa, and that of batch C was 0.5 MPa; the extrusion pressure fluctuation range of batch B was 1.8 MPa, and that of batch D was 2.1 MPa. The diameter fluctuation range of the pellets in batches A and C was no greater than 0.15 mm, while the diameter fluctuation ranges for batches B and D were 0.42 mm and 0.48 mm, respectively. The pellet length deviation of batches A and C was no greater than 0.3 mm, while the pellet length deviations for batches B and D were 0.9 mm and 1.1 mm, respectively.

[0096] Post-heat hold testing was performed on batches B and D that had not undergone stability repair. The melt flow rate of batch B after the heat hold was measured. The melt flow rate of batch D after heat residence is 16.8 g / 10 min. The melt flow rate was 18.2 g / 10 min; while in Example 1, after stability repair, the melt flow rate of batch B after heat retention was 18.2 g / 10 min. The melt flow rate after heat retention in batch D was 11.0 g / 10 min. The value was 10.8 g / 10 min. This demonstrates that, after repair using the method of this invention, the increase in melt flow rate after hot residence in low-stability reserve batches was significantly reduced.

[0097] This comparative example illustrates that judging the processability of recycled polypropylene batches solely based on initial melt flow rates makes it difficult to identify low-stability batches with similar initial melt flow rates but different thermal and oxygen stability reserves. This can easily lead to sudden drops in viscosity, fluctuations in output, and discrepancies in product performance during the later stages of continuous processing.

[0098] As can be seen from Examples 1 to 3, this invention, by first grouping multiple batches of recycled polypropylene with similar initial melt flow rates and then conducting equal-condition thermal residence induction tests, exposes low-stability reserve batches that are difficult to detect before feeding. Furthermore, by delaying the flow transition rate... Stable reserve depletion rate and batch instability characterization values Batch stability is assessed, and the total amount of stability-restoring components added is determined based on the restoration strength level. Then, based on... and The amounts of antioxidant stabilizing components and chain stabilizing components were determined separately to ensure that the repair target and repair intensity corresponded to the degree of thermal residence-triggered melt flow transition.

[0099] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for restoring the stability of recycled polypropylene through multiple batch cyclic processing, characterized in that, Includes the following steps: S1. Pre-treat multiple batches of recycled polypropylene separately, and detect the initial melt flow rate of each batch of recycled polypropylene. and the initial melt flow rate Multiple batches of recycled polypropylene within the same defined range are grouped into the same repair group; S2. Perform a heat retention induction test on each batch of recycled polypropylene in the group to be repaired, and detect the initial melt flow rate before heat retention. and initial oxidation induction time And detect the melt flow rate after heat hold. Oxidation induction time after heat retention ; S3, based on the initial melt flow rate and the melt flow rate after the heat residence Calculate the delayed flow transition rate According to the initial oxidation induction time and the oxidation induction time after heat residence Calculate the rate of decline of stable reserves And according to the said delayed flow transition rate and the stable reserve decay rate Determine batch instability characterization values ; S4. Based on the batch instability characterization values With setting an instability threshold Based on the comparison results, the corresponding recycled polypropylene batches are determined to be either heat-stable batches or heat-stable triggered low-stability reserve batches, and the batch instability characterization values ​​are used as a basis for classification. Determine the repair intensity level of the aforementioned heat-induced low-stability reserve batch; S5. According to the repair strength level, add the stability repair component to the heat-induced low-stability reserve batch, and perform melt mixing, extrusion, cooling and granulation to obtain repaired recycled polypropylene granules. S6. Perform a heat retention verification test on the repaired recycled polypropylene particles and calculate the instability characterization value after repair. And based on the instability characterization values ​​after repair Determine whether the corresponding batch of recycled polypropylene has been repaired and is qualified.

2. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claim 1, characterized in that, In step S1, the pretreatment includes crushing, washing, drying and preliminary homogenization of the recycled polypropylene waste plastic.

3. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claim 1, characterized in that, In step S1, batches of recycled polypropylene that satisfy the following formula are grouped into the same group to be repaired: in, The target melt flow rate, To allow for the initial melt flow rate deviation, The initial melt flow rate.

4. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claim 1, characterized in that, In step S2, the melting temperature, the heat residence time, and the equipment rotation speed or shear rate used to characterize the shearing action in the heat residence induction test are determined according to the target melt reprocessing conditions of the corresponding recycled polypropylene batch.

5. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claim 1, characterized in that, In step S3, the delayed flow transition rate Calculate according to the following formula: The stable reserve decay rate Calculate according to the following formula: The batch instability characterization value Calculate according to the following formula: in, To delay the flow transition rate, This represents the melt flow rate after thermal residence. The initial melt flow rate; To stabilize the reserve decay rate, The initial oxidation induction time. This refers to the oxidation induction time after heat retention; This represents the batch instability characterization value.

6. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claim 1, characterized in that, In step S4, when the batch instability characterization value Greater than the set instability threshold When the corresponding recycled polypropylene batch is identified as a heat-induced low-stability reserve batch, and the batch's instability characterization value is... Not greater than the set instability threshold At that time, the corresponding recycled polypropylene batch will be classified as a heat-stable batch.

7. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claim 1, characterized in that, In step S4, the repair strength level includes light repair batches, moderate repair batches, and heavy repair batches; when Greater than And not greater than the first repair threshold When this occurs, the corresponding recycled polypropylene batch will be classified as a slightly repaired batch; when Greater than And not greater than the second repair threshold When the corresponding recycled polypropylene batch is identified as a moderately repaired batch; when Greater than At that time, the corresponding recycled polypropylene batch will be identified as a heavily rehabilitated batch; among which, .

8. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claim 7, characterized in that, In step S5, the stability repair component includes an antioxidant stabilizing component and a chain stabilizing component, and the total amount of the stability repair component added is 0.1% to 2.5% of the mass of the recycled polypropylene.

9. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claim 8, characterized in that, The amount of stability-restoring component added for the mild, moderate, and severe repair batches increases sequentially; the amount of antioxidant stabilizing component added is based on the stability reserve decay rate. It is determined that the amount of the chain-stabilizing component added is based on the delayed flow transition rate. Sure.

10. The method for restoring the stability of recycled polypropylene through multiple batch cyclic processing according to claims 3 and 8, characterized in that, In step S6, the hot residence verification test includes detecting the initial melt flow rate after repair. Melt flow rate after repair and heat retention Initial oxidation induction time after repair and the oxidation induction time after heat retention following repair and according to , , and Calculate the instability characterization value after repair ; When the instability characterization value after repair Not greater than the set instability threshold And satisfy At that time, the corresponding batch of recycled polypropylene was deemed to have passed the repair test. When the instability characterization value after repair Greater than the set instability threshold If the corresponding recycled polypropylene batch is not identified as a severely repaired batch, the repair strength level of the corresponding recycled polypropylene batch shall be increased and stability repair shall be carried out again. When the instability characterization value after repair Greater than the set instability threshold When the corresponding recycled polypropylene batch has been identified as a heavily repaired batch, the amount of stability repair component added is adjusted within the range of 0.1% to 2.5% of the total amount of stability repair component added, and stability repair is carried out again.

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