Abstract The content of carbon black in polyethylene was determined by GB13021《Determination of carbon black content in polyethylene pipe and pipe (thermal weight loss method)》and thermogravimetric analyzer. The results of the two methods were compared. The results showed that both methods had good repeatability and accuracy, and the results were basically the same. The results obtained by using different methods can be mutually referenced. Key words GB13021, thermogravimetric analysis according to law, carbon black content In addition, the carbon black content in polyethylene was determined by two methods of GB13021, polyethylene pipe and tube carbon black content determination (thermal gravimetric method) and thermo gravimetric analyzer. Compared with the measurement results of the two methods of the surface, the two methods have good repeatability And accuracy. The measurement results are basically the same, the determination results obtained by different methods can reference each other Key wordsGB13021, thermal gravimetric analysis, carbon black content In recent years, polyethylene pipe has become the world's second-largest consumer of plastic pipes after PVC, and is widely used in water supply, agricultural irrigation, gas transmission, sewage disposal, oil fields, chemical engineering, and communications. The additive-free polyethylene is poor in weather resistance and sunlight exposure, so carbon black will be added in actual use [1]. Carbon black enables the material to have sufficient resistance to UV aging. When the carbon black content is 2.0% to 3.0%, it can effectively prevent the influence of ultraviolet rays [2]. Because the content of carbon black has an important influence on polyethylene pipes, many standards have stipulated the content of carbon black in polyethylene. For the purpose of R&D production and sales, the content of carbon black is an indicator that polyethylene pipes must be tested. At present, the test method for the content of carbon black in pipeline plastics is mainly implemented in GB13021-1991 [3]. The use of thermogravimetric analyzer is a commonly used thermal analysis method. It is very convenient to measure the composition of polymers. The commonly used standard is ASTM E1131–2008 [4]. Thermogravimetric analyzer can also be used to determine the carbon black content in polyethylene. . At present, these two methods coexist. Different laboratories often use different methods to test, and there is a problem that the results of carbon black content analysis cannot be directly compared. The author used the above two methods to determine the content of carbon black in the same batch of polyethylene pellets. The advantages and disadvantages of different test methods, measurement repeatability, and the consistency of the test results of the two methods were discussed. The test method for carbon black content The choice provides a reference. 1 experimental section 1.1 Major Instruments and Materials Carbon Black Analyzer: HS-TH-3500, Shanghai Heyin Instrument Technology Co., Ltd.; Mechanical Analytical Balance: Accuracy 0.0001g, Shanghai Tianping Instrument Factory; Thermogravimetric Analyzer: STA449C; German Nachi Company; Electronic Balance: M2P, Sartorius, Germany; Polyethylene: Commercially available. 1.2 Experimental Methods 1.2.1 GB13021 method Weigh the sample mass m1 (1 ± 0.05) g placed in the sample boat, the sample boat into the carbon black content analyzer, adjust the nitrogen flow 130mL/min, heated to 600 °C under nitrogen protection, constant temperature pyrolysis for 30min, After being taken out, it is placed in a desiccator and cooled to room temperature. The mass m2 is weighed, then placed in a muffle furnace and calcined for 10 minutes at 950° C., taken out into a desiccator and cooled to room temperature, and the mass m3 is weighed. Carbon black content c (%) Calculated according to formula (1). 1.2.2 Thermogravimetric Analyzer Method Weigh the sample quality (10 ± 0.05) mg into the sample rack, close the heating furnace, set the temperature program, the room temperature rose to 550 °C in nitrogen atmosphere, converted to oxygen, heated to 750 °C in an oxygen atmosphere, the computer Automatically collect sample quality changes during warming. 2 Results and Discussion 2.1 Comparison of Measurement Results Determine the content of carbon black in polyethylene according to 1.2.1. The results are shown in Table 1. Determine the thermogravimetric curve of polyethylene samples according to 1.2.2 (see Figure 1). According to the percentage of weight loss at each step of the curve, the decomposition mechanism of the sample and the content of each component can be judged. As the temperature rises, the polyethylene cracks and continues until the mass at 550°C is constant, because the carbon black does not react in high purity nitrogen. At this time, the gas is switched, oxygen is introduced, the carbon black reacts completely, and the sample quality is again Constant. The mass loss that occurs when oxygen is switched from 550°C to 650°C is the carbon black content in polyethylene. After 650°C quality stability, the remaining material is ash in polyethylene. The results of determination of the carbon black content in polyethylene samples are shown in Table 1. From the test results, the relative standard deviations of the two test methods are all less than 3%, indicating that both methods have good repeatability. The relative standard deviation of the thermogravimetric analyzer method is slightly larger than the relative standard deviation of GB13021. With the thermogravimetric analyzer method sample size is less, the sample is not uniform. The consistency of the test results of the two methods can be performed using the following method [5]: Suppose the test results of the two test methods are x11, x12...x1n, the average is x1, the standard deviation is S1; x21, x22...x2n, average The value is x2 and the standard deviation is S2. If you consider xx12- as a random variable, the basic rules of variance are: Therefore, if xx2S12(x1x2)-G-, it is considered that the two sets of data are consistent. Substituting the data in Table 1 into the formula can calculate: xx0.8212-=, 2S(x1-x2)=0.83, and the calculation result shows that the two sets of data are consistent. The results of the two method tests are consistent and can be used to compare with each other. 2.2 Thermogravimetric Analyzer Accuracy The thermogravimetric analyzer automatically records the real-time sample quality in the analysis process. The human factors are small, and the accuracy of the thermal weight loss can be verified with the standard CaC2O4. CaC2O4·H2O with the increase of temperature will produce the following three steps of chemical reaction: CaC2O4 · H2O (solid) = CaC2O4 (solid) + H2O (gas) (3) CaC2O4 (solid) = CaCO3 (solid) + CO (gas) ( 4) CaCO3 (Solid) = CaO (Solid) + CO2 (Gas) (5) In each step of the reaction, gas is released, and the weight loss occurs. According to the chemical equation and the molecular weight, the chemical reaction of each step can be calculated. Loss of weight theory. The chemical reaction of each step of CaC2O4·H2O can be reflected on the thermal weight loss curve. The weight loss and theoretical values ​​of CaC2O4·H2O obtained with the thermogravimetric analyzer are shown in Table 2. It can be seen from Table 2 that the relative deviation of the thermogravimetric analyzer in the range of 550 to 750°C is 1.3%, and the measurement accuracy is high. The thermogravimetric analyzer method and the GB13021 method for measuring carbon black content are reliable. The thermogravimetric analyzer method is quick and easy, but the relative standard deviation of the measurement is larger than that of the GB13021 test method because the amount of sample used during the thermogravimetric analysis is only 10 mg. If the carbon black in the sample is not uniformly distributed, the thermogravimetric analyzer is used to measure the relative standard deviation. Carbon black in polyethylene increases the standard deviation of the test. It is recommended that when analyzing the content of carbon black by thermogravimetric analysis, samples from multiple polyethylene particles should be sampled as much as possible and the sample volume should be appropriately increased. 3 Conclusion From the experimental process and analysis results, we can see that the two different methods for carbon black content analysis have the following characteristics: (1) Both test methods can be used to determine the carbon black content in polyethylene. The results are basically consistent and comparable. (2) GB13021 method test carbon black content test repeatability is good, but the use of carbon black analyzer and muffle furnace two devices, the experimental process requires cooling and weighing 3 times, operation more complex than the thermal analyzer. (3) The thermogravimetric analysis method is easy and fast to operate, and the result is intuitive. However, due to the small amount of sample used, the standard deviation of the test results is large, and abnormal values ​​tend to occur in the test. Sampling from multiple particles should be performed to increase the sample volume as much as possible. The number of tests is at least 2 times. When there are two large deviations, increase the number of tests. A linear-motion bearing or linear slide is a bearing designed to provide free motion in one direction. There are many different types of Linear Motion Bearings. Linear Motion Bearings Linear Motion Bearings,Linear Motion Ball Bearing,Motion Ball Bearing,Linear Guide Motion Ningbo Ritbearing Imp & Exp Co.,Ltd. , https://www.nbbearing.de
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