Accelerated aging detection method and device for thermal forming cup

Abstract

The invention relates to the technical field of thermal forming cup detection, and discloses an accelerated aging detection method and device for a thermal forming cup, and the detection method comprises the steps: setting a specific temperature and humidity accelerated aging condition, adopting two mechanical property detection modes of a cup pinching embrittlement test and a cup body stiffness embrittlement test, and synchronously monitoring the melt index evolution of a sample, and realizing conversion of the natural shelf life based on the acceleration factor. The method mainly solves the problem of pre-judging the validity period of the degradable thermal forming cup, and realizes rapid and accurate detection of the aging performance of the degradable thermal forming cup. The method is short in detection period and visual and reliable in result, can effectively pre-judge the brittle rupture risk of the thermal forming cup in the use period, provides a scientific basis for product quality control and shelf life labeling, and is particularly suitable for aging performance evaluation of degradation type thermal forming cups such as PLA (polylactic acid) and the like.

Description

Technical Field

[0001] This invention relates to the field of thermoformed cup testing technology, specifically to an accelerated aging testing method and apparatus for thermoformed cups. Background Technology

[0002] Thermoformed cups, such as PLA cold cups, are widely used due to their environmental friendliness and biodegradability. However, degradable materials are susceptible to hydrolysis under the influence of temperature and humidity in natural environments, leading to molecular chain breakage, decreased mechanical properties, and ultimately brittleness. This not only affects the user experience but may also cause cuts due to sharp edges. Traditional non-degradable plastic products have long shelf lives and do not require specialized aging tests; however, the shelf life of degradable thermoformed cups varies greatly depending on the properties of raw materials and manufacturing processes, necessitating a rapid and effective aging detection method to predict their shelf life.

[0003] Current technologies lack standardized accelerated aging testing methods for degradable thermoformed cups. Conventional natural aging tests take over 12 months, which is inefficient and cannot meet the timeliness requirements of product development and quality control. Therefore, developing an accelerated aging testing method with a short testing cycle and reliable results to accurately predict the risk of cracking and shelf life of thermoformed cups has become an urgent technical problem to be solved in this field.

[0004] In view of this, in-depth research was conducted on the above-mentioned issues, which led to the creation of this case. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an accelerated aging detection method and apparatus for thermoformed cups, which can effectively solve the aforementioned technical problems.

[0006] To achieve the above objectives, the present invention provides the following technical solution: An accelerated aging test method for thermoformed cups includes the following steps: S1. Test preparation: Select two sets of thermoformed cup samples to be tested and prepare the testing instruments; S2. Accelerated aging treatment: Place the two sets of samples to be tested into a constant temperature and humidity test chamber. Set the temperature of the constant temperature and humidity test chamber to 53℃±2℃ and the humidity to 85%±2℃. Accelerated aging is carried out in 24-hour cycles. S3. Performance Testing: Two sets of samples were taken according to the test cycle, cooled at room temperature for 15 minutes, and then tested separately. The cup was tested for brittleness and the cup body was tested for stiffness, and the number of days after the first brittleness appeared was recorded. S4. Melt Index Test: Simultaneously test the melt index of the accelerated aging sample and record the number of aging days at which melt collapse occurs. S5. Shelf life estimation: Based on the number of days of brittle fracture and melt flow index collapse under accelerated aging conditions, combined with the acceleration factor, the natural shelf life of the sample is calculated.

[0007] Furthermore, the steps described in step S3 The specific procedures for the cup crushing test include: (1) Use a vernier caliper to measure the diameter of the cup at half its height and calculate the radius. Mark two sets of test points symmetrically at this height, with the distance between the two points in each set equal to the radius. (2) After the cup has undergone one test cycle of accelerated aging, remove the cup and place it at room temperature to cool for 15 minutes; (3) After pinching the cup body to fit each test point, release it, adjust the 45-degree angle and repeat the operation. Observe and record the number of aging days after the sample cracks.

[0008] Furthermore, the specific procedures for the cup body stiffness and brittleness test described in step S3 include: (1) Cut off two-thirds of the flat area of ​​the cup body from the sample after accelerated aging and cooling, and divide the cut area into two parts for later use; (2) Set the test speed of the paper cup and bowl stiffness tester to 50 mm / min and the test depth to 20 mm. Fix the spare sample on the fixture and place it in the middle of the probes at both ends of the paper cup and bowl stiffness tester to start the test. Record the number of aging days when the sample breaks or becomes completely brittle and cannot be tested.

[0009] Furthermore, the accelerated aging treatment described in step S2 is performed in 24-hour test cycles, and at least one sample is taken out after each cycle for testing in steps S3 and S4.

[0010] Furthermore, the test frequency for melt index monitoring in step S4 is consistent with that for mechanical property brittle fracture testing. When the melt flow rate meter cannot measure the melt index of the sample, it is determined to be a melt index collapse.

[0011] Furthermore, the shelf life calculation in step S5 is based on the number of days the sample first shows brittleness or melt flow index collapse under accelerated aging conditions, combined with the fact that 1 day of acceleration by the acceleration factor corresponds to 1 month of natural aging.

[0012] Furthermore, the thermoformed cup to be tested is a PLA biodegradable thermoformed cup.

[0013] Furthermore, the number of days of brittle fracture mentioned in step S3 is based on the number of days on which brittle fracture first appears in the monitoring results of each test cycle. When the results of the cup crushing test and the cup body stiffness crushing test are inconsistent, the earlier number of days of brittle fracture shall be used as the basis for mechanical performance failure.

[0014] A testing device based on the accelerated aging test method for the above-mentioned thermoformed cup includes: Programmable temperature and humidity test chambers are used to construct a stable and controllable accelerated aging environment to simulate the key factors that cause natural aging of materials. The paper cup and bowl stiffness tester is used to quantitatively test the rigidity and resistance to brittleness of thermoformed cups and to identify mechanical failure points. Melt flow rate meter is used to quantitatively monitor the degree of molecular chain degradation of thermoformed cup materials, measure melt flow index, and provide a basis for judging microscopic failure.

[0015] This invention provides a method and apparatus for accelerated aging testing of thermoformed cups. It has the following beneficial effects: This invention accelerates the aging process under specific temperature and humidity conditions, shortening the aging process in a natural environment from 12 months to 12-30 days, significantly improving testing efficiency and meeting the quality control needs of product development and mass production.

[0016] This invention achieves a quantitative assessment of the degree of material degradation through two mechanical property tests and melt flow index monitoring. The results of the three tests corroborate each other, avoiding the limitations of a single test and ensuring the accuracy of shelf life prediction.

[0017] This invention specifically designs a testing method for the structural characteristics of thermoformed cups, and is especially suitable for degradable materials such as PLA. It solves the problem of poor compatibility of traditional testing methods with degradable thermoformed products. At the same time, it can predict the risk of brittleness and avoid safety hazards caused by product brittleness during consumer use.

[0018] The testing instruments used in this invention are all conventional testing equipment, and the testing procedures are standardized, making it easy for enterprises to promote and apply them without requiring complex professional operating skills. Attached Figure Description

[0019] Figure 1 for Images showing the state of the cup cracking during a squeeze test; Figure 2 This is a diagram showing the state of the cup body cracking during a rigidity and brittleness test. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Verification of the accelerating factor under accelerated aging: Prepare four groups of samples A, B, C and D of the same model but different batches, with each group consisting of 30 PLA ​​biodegradable thermoformed cups.

[0022] Samples A, B, and C were subjected to natural aging. Specifically, they were placed in an environment with normal temperature and humidity (20-36℃, 58-85%) for one month as the testing cycle. During each testing cycle, two cups of samples from each group were taken and tested separately. The cup was subjected to a squeezing crack test and a cup body stiffness crack test, and the melt index data was recorded.

[0023] Sample D was placed in a constant temperature and humidity test chamber, with the ambient temperature set to 53℃ and humidity to 85%. A 24-hour test cycle was used, and two cup samples were taken out for testing during each cycle. The cup was subjected to a squeezing crack test and a cup body stiffness crack test, and the melt index data was recorded.

[0024] The above experimental data are recorded in Table 1 below:

[0025] Table 1. Test data of accelerating factors under accelerated aging. The above data shows that: PLA cup products The cracking of the cup due to aging occurred after 12 days of accelerated aging at 53℃ and 85% humidity, or after 12 months of natural aging. Therefore, the aging acceleration factor of the PLA cup under these conditions is: 1 day at 53℃ and 85% humidity = 1 month under natural aging. Example

[0026] Two sets of thermoformed cup samples were selected for testing. Both are PLA biodegradable thermoformed cold cups. The specific information is as follows: Sample E: Batch number 2025061501, a total of 60 complete samples, with no initial damage or deformation; Sample F: Batch number 2025061502, a total of 60 complete samples, made from the same batch of raw materials as Sample A, but produced at different times to ensure sample consistency.

[0027] The testing equipment includes: a programmable temperature and humidity test chamber (model THC-1000) with a temperature control accuracy of ±1℃ and a humidity control accuracy of ±1%, capable of stably maintaining an environment of 53℃±2℃ and 85%±2℃ humidity; a paper cup / bowl stiffness tester (model TDY-10) with a speed adjustment range of 0-100mm / min and a test depth adjustment range of 0-50mm, set to a test speed of 50mm / min and a test depth of 20mm after calibration; and a melt flow rate meter (model XNR-400C) with a test temperature range of 50-400℃, set to a test temperature of 190℃ for PLA material, with a load of 2.16kg.

[0028] A total of 120 samples, including samples E and F, were evenly placed in a programmable constant temperature and humidity test chamber with a spacing of ≥5cm between samples to avoid uneven temperature and humidity contact caused by stacking and compression. The test chamber temperature was set to 53℃ and the humidity to 85%. The equipment was started to carry out continuous accelerated aging, with a test cycle of 24 hours, and continued to run until the samples showed obvious brittleness or melt index collapse.

[0029] After each test cycle, two samples were taken from each of samples E and F, cooled to room temperature for 15 minutes, and then tested separately. Cup crush test and cup body stiffness crush test.

[0030] (1) Cup-squeezing brittleness test: The diameter of the sample at half its height was measured with vernier calipers. The diameter of this batch of cups was found to be 72mm, and the calculated radius was 36mm. Two sets of test points were symmetrically marked at half the height of the cup, with the distance between the two points in each set strictly controlled at 36mm. The cup body was pinched between the thumb and forefinger, and each set of test points was pinched together until they were completely in contact, then slowly released. The cup was adjusted clockwise by 45 degrees, and the pinching and releasing operation was repeated for the other set of test points. The sample status was observed and recorded cycle by cycle: In the first 27 test cycles, samples E and F did not show any cracking. In the 28th test cycle, samples E and F both showed longitudinal micro-cracks in the cup body for the first time after the pinching operation. The condition of the two sets of samples was recorded. The cups cracked after being squeezed for 28 days.

[0031] (2) Cup body stiffness and brittleness test: From the samples cooled at the same time, cut off two-thirds of the cup body, specifically the flat area within the upper and lower two-thirds of the cup body, 4cm from the cup mouth and 2cm from the cup bottom. Each sample was cut into 2 pieces for later use, ensuring that the spare samples were free of wrinkles and damage. The spare samples were fixed on the special fixture of the paper cup and bowl stiffness tester, ensuring that the center of the sample was aligned with the center of the probes at both ends of the instrument. The instrument was started and tested at the set parameters of 50mm / min speed and 20mm depth. The test results were recorded cycle by cycle. Samples E and F taken out in the 25th test cycle did not break during the test. Samples E and F taken out in the 26th test cycle both broke when the probe pressure reached a depth of 18mm, and the stiffness and brittleness days were recorded as 26 days. The sample taken out in the 30th test cycle was completely brittle and could not be tested because it was directly crushed after being pressed. The number of days of complete brittleness was recorded as 30 days.

[0032] Melt flow index (MFI) testing: Simultaneously with performance testing, after each test cycle, an unmarked, undamaged, flat area of ​​the sample cup was immediately cut and placed in a melt flow rate meter for MFI testing. The testing frequency was consistent with the mechanical property brittleness test. During the first 26 test cycles, the MFI of samples E and F continuously increased, gradually rising from an initial value of 31.2 g / 10 min to 58.7 g / 10 min. During the 27th test cycle, the instrument displayed no valid MFI data, indicating MFI collapse. The number of days for MFI collapse was recorded as 27 days for both groups of samples.

[0033] Based on the acceleration factor set according to this invention, and combined with test data: the mechanical property failure criterion is that the stiffness brittle fracture occurs earlier than... The number of days for cup crushing was set at 26 days as the mechanical performance failure benchmark; the microscopic failure benchmark was set at 27 days for melt index collapse.

[0034] Shelf life calculation: Taking the median value between mechanical failure and microscopic failure, the natural shelf life of this model of PLA thermoformed cold cup is estimated to be 26.5 months. Considering the actual application scenario, the final shelf life is marked as 26 months.

[0035] The following conclusions can be drawn from the above Example 1: Under the conditions of this accelerated aging test, as the melt flow index of PLA products gradually increased over time until it collapsed, the test samples entered a significant degradation stage when the melt flow index entered the collapse phase, accompanied by the simultaneous failure of mechanical properties (stiffness, crush resistance). Observations showed that the loss of stiffness in all products occurred 1-3 days earlier than the crush cup cracking, indicating that the material first loses rigidity and then loses toughness. This phenomenon is consistent with the theory that the increase in brittleness caused by the decrease in polymer molecular weight is consistent with this.

[0036] The detection method of this invention also conducts a stiffness and brittleness test on PLA cold cups. The results show that the stiffness and brittleness data are consistent with the changes in aging melt index and cup-squeezing brittleness. Therefore, for products such as PLA cold caps that have undergone severe deformation after aging and are difficult to simulate cracking tests by means of direct use such as cup-squeezing or fastening, the aging performance of different raw materials can be compared through the stiffness and brittleness test results, and the comparison results of the superior and inferior aging performance can be obtained.

[0037] The experiments conducted using the detection method of this invention provided a detailed study on the degradation and aging evolution of PLA in cold cups. The analysis revealed a high correlation between the gradual increase in melt index until collapse and the time to brittle failure during the aging process. The two trends were consistent and mutually corroborative. While the performance fluctuations of PLA raw materials are generally greater than those of traditional plastics, and the products themselves are affected by variations in product thickness and design, raw material formulation, production processes, and transportation and storage conditions, the shelf life estimates for products made from different raw materials obtained through this test are still relatively reliable.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for accelerated aging testing of thermoformed cups, characterized in that, Includes the following steps: S1. Test preparation: Select two sets of thermoformed cup samples to be tested and prepare the testing instruments; S2. Accelerated aging treatment: Place the two sets of samples to be tested into a constant temperature and humidity test chamber. Set the temperature of the constant temperature and humidity test chamber to 53℃±2℃ and the humidity to 85%±2℃. Accelerated aging is carried out in 24-hour cycles. S3. Performance Testing: Two sets of samples were taken according to the test cycle, cooled at room temperature for 15 minutes, and then tested separately. The cup was tested for brittleness and the cup body was tested for stiffness, and the number of days after the first brittleness appeared was recorded. S4. Melt Index Test: Simultaneously test the melt index of the accelerated aging sample and record the number of aging days at which melt collapse occurs. S5. Shelf life estimation: Based on the number of days of brittle fracture and melt flow index collapse under accelerated aging conditions, combined with the acceleration factor, the natural shelf life of the sample is calculated.

2. The accelerated aging test method for a thermoformed cup according to claim 1, characterized in that, The steps described in step S3 The specific procedures for the cup crushing test include: Measure the diameter of the cup at half its height using vernier calipers and calculate the radius. Mark two sets of test points symmetrically at this height, with the distance between the two points in each set equal to the radius. After the cup has undergone one test cycle of accelerated aging, remove the cup and let it cool at room temperature for 15 minutes. After squeezing the cup body to fit each test point, release it, adjust the angle to 45 degrees and repeat the operation. Observe and record the number of aging days after the sample cracks.

3. The accelerated aging test method for a thermoformed cup according to claim 1, characterized in that, The specific procedures for the cup body stiffness and brittleness test described in step S3 include: Cut off two-thirds of the flat area of ​​the cup body from the sample after accelerated aging and cooling, and divide the cut area into 2 parts for later use; Set the test speed of the paper cup and bowl stiffness tester to 50 mm / min and the test depth to 20 mm. Fix the spare sample on the fixture and place it in the middle of the probes at both ends of the paper cup and bowl stiffness tester to start the test. Record the number of aging days when the sample breaks or becomes completely brittle and cannot be tested.

4. The accelerated aging test method for a thermoformed cup according to claim 1, characterized in that, The accelerated aging treatment described in step S2 is performed in 24-hour test cycles. At least one sample is taken out after each cycle for testing in steps S3 and S4.

5. The accelerated aging test method for a thermoformed cup according to claim 1, characterized in that, The test frequency for melt index monitoring in step S4 is consistent with that for mechanical property brittle fracture testing. When the melt flow rate meter cannot measure the melt index of the sample, it is determined to be melt index collapse.

6. The accelerated aging test method for a thermoformed cup according to claim 1, characterized in that, The shelf life estimation in step S5 is based on the number of days when the sample first shows brittleness or melt flow index collapse under accelerated aging conditions, combined with the fact that 1 day of acceleration by the acceleration factor corresponds to 1 month of natural aging.

7. The accelerated aging test method for a thermoformed cup according to claim 1, characterized in that, The thermoformed cup to be tested is a PLA biodegradable thermoformed cup.

8. The accelerated aging test method for a thermoformed cup according to claim 1, characterized in that, The number of days of brittle fracture mentioned in step S3 is based on the number of days on which brittle fracture first appears in the monitoring results of each test cycle. When the results of the cup crushing test and the cup body stiffness crushing test are inconsistent, the earlier number of days of brittle fracture shall be used as the basis for mechanical performance failure.

9. A testing device for the accelerated aging testing method of thermoformed cups according to any one of claims 1-8, characterized in that... ,include: Programmable temperature and humidity test chambers are used to construct a stable and controllable accelerated aging environment to simulate the key factors that cause natural aging of materials. The paper cup and bowl stiffness tester is used to quantitatively test the rigidity and resistance to brittleness of thermoformed cups and to identify mechanical failure points. Melt flow rate meter is used to quantitatively monitor the degree of molecular chain degradation of thermoformed cup materials, measure melt flow index, and provide a basis for judging microscopic failure.

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