Construction of an accelerated aging device for polyethylene against chlorinated water

Abstract

In this invention, a device has been developed to measure the resistance of polyethylene to chlorinated water and to observe the rate of surface degradation and reduction of the antioxidant and additive package in polyethylene. Municipal tap water typically contains small amounts (about 1-3 ppm) of free chlorine as a disinfectant to help maintain water health. However, the presence of chlorine as a strong oxidizing agent, even in small amounts, can cause the consumption of antioxidants in polyethylene and, in the long term, weaken its properties and lead to pipe failure. Therefore, it is essential and inevitable to measure the resistance of polyethylene to chlorinated water and have a high confidence that the pipe will have a life span of at least 50 years before mass production of the pipe. The device made in this invention is actually a small-scale device that can simulate the service life conditions of pipes used in urban water supply systems in the laboratory and on dumbbell-shaped samples. In this way, the aging test time is significantly reduced and its results can be used to find the optimal formulation that has the highest resistance to chlorinated water. This device consists of a tank for storing and heating chlorinated water, inside which is a holder for storing dumbbell-shaped samples. In order to maintain constant water characteristics including temperature, pH, ORP and chlorine concentration, the water flow is continuously rotating and circulating, and all these parameters are measured and controlled with each water cycle. This device is capable of performing accelerated aging operations at different temperatures and chlorine concentrations, as well as on other materials such as cross-linked polyethylene (PEX), polybutylene (PB) and polypropylene (PP).

Description

Description of the invention Title of the invention (as stated in the declaration) Construction of an accelerated aging device for polyethylene against chlorinated water Technical background of the relevant invention The above invention is in the field of water and wastewater engineering, mechanics, electronics and chemistry. The device made in this invention benefits from various fields of engineering science. Because it has hardware parts related to water and mechanics engineering and also has programming for controlled operation. Reactions related to water chlorination and oxidative degradation of polyethylene are also in the field of chemistry and polymer science. Technical problem and statement of invention objectives Municipal water can contain various types of microorganisms that, without proper treatment, can lead to problems and diseases in humans. Therefore, the use of disinfectants such as chlorine gas (Cl2), chlorine dioxide (ClO2) and sodium hypochlorite (NaClO) is necessary to destroy or inactivate pathogenic microorganisms. Today, the use of polyethylene pipes in municipal water supply networks is very common; but chlorination of water, even in small concentrations, has a great impact on the long-term performance of polyethylene water pipes, both in static and dynamic states, and causes their destruction and shortening of their lifespan. In fact, contact of polyethylene pipes with chlorinated water reduces the amount of antioxidants or completely consumes them (to a depth of approximately 1 mm of the pipe). Therefore, the rate of antioxidant depletion is a very important factor in determining the resistance of the pipe to chlorinated water because pipe degradation begins when all antioxidants in the polyethylene are completely consumed.Antioxidant consumption can occur in two ways: 1- migration from the polymer into the water and 2- consumption on the polymer surface by oxidizing agents (penetration of the oxidizing agent into the polymer is also possible). It should be noted that the rate of antioxidant reduction due to destruction by disinfectants is much higher than its reduction due to migration into the surrounding environment. Polyethylene and polypropylene are economically the most important products of the petrochemical industry. Since a large volume of polyethylene produced by petrochemicals and various companies is used in the pipe and fittings industry and water tankers, the reduction in the lifespan of pipes and their brittleness due to contact with water containing disinfectants is a crisis in this industry. Antioxidants that are commonly used in polyolefins do not necessarily provide the necessary resistance to disinfectants in water, and the development of new additive packages is necessary to enhance their resistance and, consequently, increase the lifespan of the pipe. In view of this, it is of great importance to provide a reliable laboratory method for estimating the lifespan of newly developed compounds. ASTM F2263 provides a method for testing polyethylene pipes and measuring their oxidation resistance to the disinfectant Cl2. However, in general, all related articles and patents use the method mentioned in this standard to measure the life of polyethylene pipes against other chlorinated disinfectants such as ClO2 or NaClO. According to this standard, pipe samples are installed in a device and chlorinated water with a specified pH, ORP, chlorine concentration, pressure, flow rate and temperature flows through them until the samples fail due to oxidative damage. The data on the time of pipe failure due to oxidative damage are measured at different temperatures and hoop stresses and are analyzed and extrapolated to the final hoop temperature and stress (at the time of use) using the method mentioned in this standard. This standard does not provide any explanation about the structure and various components of the device that must operate under these conditions.Another point is that the time it takes to conduct this test and reach the final result, which is the estimated life span of the pipe, is very long, on the scale of several months. As is known, the production of pipes and their testing according to the ASTM F2263 standard is very time-consuming and, in addition, requires a lot of raw materials. In addition, when developing a new formulation or synthesizing polyethylene with improved resistance to chlorine, it is usually necessary to design experiments and test several dozen samples until the optimal sample is finally selected and mass-produced. Testing each of the initial samples according to this standard (“tubular” sample) means several years of study time, which is practically unreasonable and the results obtained from it will be useless. Therefore, in the early stages of designing a polyethylene formulation or structure, there is a need for another device that, although it works similarly to the standard, but its samples are not tubular and significantly reduces the testing time. Therefore, the aim of this invention is to build a small-scale device to perform accelerated aging tests on "dumbbell-shaped" samples and to be effective in finding the optimal formulation of polyethylene with high resistance to chlorine. This device observes all stages of water circulation under specific pH, ORP, chlorine concentration and temperature conditions and, with the help of existing sensors and programming done in PLC (Programmable Logic Controller), it always controls each of the water characteristics and keeps them within the required range. Dumbbell samples that have been exposed to chlorinated water with a specific chlorine concentration, temperature and pH in the main tank of the device can be removed from the tank at specific time intervals and their various properties, including mechanical properties (tensile strength and percentage of elongation at break), OOT (oxidation onset temperature) and surface chemistry (using FT-IR) can be examined. The amount of reduction in mechanical properties and OOT of the samples can be a criterion for selecting the optimal formulation.In this way, the samples that show the least loss in mechanical properties after a certain time compared to the sample that has not been exposed to chlorinated water have a better formulation and their resistance to water disinfectants that are oxidizing is greater. In this way, this device actually makes a relative comparison between different formulations and does not measure the lifespan, but it saves a lot of time in selecting the optimal formulation. If desired, the selected formulation can be converted into pipes of specific dimensions by a twin-screw extruder in the next step and, with the help of another device that complies with all the process conditions mentioned in the standard, including the pressure and flow rate inside the pipe (not the subject of this invention), subjected to an accelerated aging test and the lifespan of the pipe can be estimated. A description of the state of the prior art and the history of developments related to the claimed invention. Since in recent years, urban water supply pipes all over the world have been replaced by plastic pipes, it has become very important to examine their properties and measure their oxidation resistance to disinfectants. Many researchers have tried to find a suitable method to provide a process or device for this purpose. These efforts have included performing aging tests on polyethylene samples in the form of pipes, dumbbells, films, tapes, etc., based on two different methods: the static or stagnant method (Stagnation) and the circulation method. In the study by Mitroka et al. [Polym Degrad Stab, 2013, 98, 1369], accelerated aging test was performed on HDPE dumbbell samples and then the change in polymer properties was investigated. The selected chlorine concentrations were 50, 250 and 500 ppm, pH = 6.5 and the aging time of the samples was 160 days (1840 hours). Each dumbbell sample was immersed in chlorinated water in a separate 500 ml glass bottle and the solution in the bottle was replaced every 3 days. Also, pH, free chlorine concentration and alkalinity were measured. As it is known, the samples are exposed to still chlorinated water and although the free chlorine concentration in the water is initially adjusted, chlorine in the water is unstable and its concentration decreases over time. Therefore, this method is not very accurate. Montes et al. [Polym Degrad Stab, 2012, 97, 149] cut PERT / Al / PERT tubes into 10 cm lengths and filled them with a chlorinated water solution (sodium hypochlorite at concentrations of 0, 1, 25, and 100 ppm). The samples were then placed in an oven at 70 °C for 270 days.The pH of the water in all experiments was greater than 8. In this study, the chlorine concentration also decreased continuously with time and did not remain constant. Azhdar et al. [Polym Test, 2009, 28: 661] used a liquid hydrocarbon called Squalane containing the antioxidant Irganox 1010 to investigate the consumption time of the antioxidant using the OIT test. Cl2 or ClO2 was used for chlorination of water and the free chlorine concentration was selected to be 10 ppm. Also, the pH was 6.8 and the temperature was 70˚C. The samples were immersed in a glass reactor equipped with a condenser and the volume of water in the reactor was 50 ml. There is a heater with a temperature sensor around the glass reactor to provide its temperature. In this study, in order to improve the static method, the pH of the water and the chlorine concentration were regularly measured by pH electrode and titration, respectively, but in fact, there is no automatic program to regularly adjust these parameters by injecting acid or a more concentrated chlorine solution. The exposure time of the samples was also 5 hours so that the amount of decrease in chlorine concentration during this period was small.In patent US20120031495A1 from Basell, polyethylene samples were molded into sheets and cut into 2 cm wide strips, then placed in an aqueous solution containing 20 ppm ClO2 at 60 °C and pH = 6.5 for 200 hours. After this time, the samples were removed from the chlorinated solutions and their OIT was measured as a measure of chlorine resistance. Yu et al. [Polym Degrad Stab, 2015, 111, 1] exposed medium density polyethylene strip samples containing 8 different phenolic antioxidants (with a wt.% concentration of 0.1) to chlorinated water containing 10 ppm ClO2, pH=6.8, and temperature of 70˚C, and measured the rate of antioxidant consumption using OIT measurement. The effect of aging in hot chlorinated water on the mechanical properties of four different polypropylenes was investigated by Fischer et al. [Mater Today Proc, 2019, 10, 385]. The chlorine concentration was 5 ppm (Cl2 or NaClO) and the temperature was 60 °C. The device used by this group is a small tabletop device with a glass water bath in which the sample holder is placed. The various sensors are placed and placed in the lid of this water bath, so the sensors are also at the same temperature of 60 °C, which reduces their life. A control system for the bath is provided, which, based on the data it receives from the sensors, issues commands for the injection of water storage solutions, pH control, and chlorine concentration control. The dimensions of the samples that can be tested with this device include two samples: strip samples with a length of 150 mm, a width of 2 mm, and a thickness of 0.1 mm, and EWF test samples with dimensions of 80 mm long, 30 mm wide, and 0.1 mm thick. Which, as is clear, is different from the dimensions of mechanical test specimens based on the ASTM D638 standard. Bredacs et al. [Proceedings PPXVII, 2016], at the PCCL laboratory in Austria, have designed a device that is an accelerated aging method for polyethylene samples exposed to 1 ppm of ClO2. Although in some experiments they have also used 100 ppm of NaClO. The samples are in the form of dumbbells and are immersed in water with a temperature of 60˚C, pH = 6.8 and ORP = 550 mV. They have used a prefabricated device called DULCOMARIN II, manufactured by ProMinent, to measure and control various parameters during the experiment. This device is usually used for water purification in private swimming pools. As mentioned, this device is completely ready-made and therefore the part of measuring and controlling the water characteristics was not designed by this group but only a ready-made device installed alongside other equipment of the device. Also, the ClO2 storage solution was prepared by another ready-made device called Legio Zon CDL, manufactured by ProMinent. Another notable point is that they have only provided a general outline of their device and have not specified the details of the device's design. Also, in another study, Bredacs et al. [Polym Degrad Stab, 2018, 157, 80], immersed dumbbell samples with a thickness of 0.3 mm (based on ASTM D1708-13) and 1 mm (based on ISO 18488) in ClO2 solutions with concentrations of 5 and 10 ppm. The solution temperature was 60 °C and pH = 6.8. The circulating flow rate was selected as 50 lit / h. The maximum temperature that can be operated with this device is 60 °C and temperatures higher than that cannot be tested. Also, this device is suitable for testing small dumbbell samples and its sample chamber is also very small. The different parts of this device include storage solution tanks, a dumbbell sample tank, a unit for making ClO2, and a unit for measuring and controlling water characteristics. As in the previous work of this group, the water characteristics measurement and control unit was performed by the DULCOMARIN II device, and this group did not perform the design work of this part. As described, the devices that have been previously made in relation to the purpose of this invention each have disadvantages. For example, a separate compartment is not provided for the sensors, or the maximum temperature that can be tested with them is 60˚C and higher temperatures cannot be selected. However, the device made in this patent, in addition to eliminating these disadvantages, has other outstanding advantages and features that will be described in the following sections. Providing a solution to an existing technical problem along with an accurate, sufficient, and integrated description of the invention Polyethylene pipes used in urban water supply systems must have a lifespan of at least 50 years and must not leak or break before that. Any polyethylene compound that is to be used in the water pipe production process and installed in building plumbing must first be ensured of its proper performance and then mass-produced. However, as mentioned, there is no device that can measure the resistance of pipe-grade polyethylene to chlorinated water. Such a device must have the ability to keep all the parameters effective in the oxidative degradation of polyethylene, such as temperature, pH, and chlorine concentration, constant so that the test is sufficiently accurate. Also, in order to shorten the test time, the values ​​of these quantities are selected much higher than the actual state (pipe service time) to create accelerated aging operations for the samples. This device is designed to test dumbbell-shaped samples and find the optimal formulation. Since experimental design methods such as RSM are usually used to find the optimal formulation, the number of samples is usually large and producing all of them in the form of tubes consumes a lot of raw materials. Also, to perform extrapolation and find the life time of the tubes according to the standard, at least 18 data are required under different temperature and pressure conditions, the duration of some of which may reach 6 months. Therefore, in addition to imposing a very high cost, performing tube tests on all formulations is also not reasonable in terms of time. The overall design of this device is shown in Figure 1, and the process is described below: Tank (1): In this device, a large corrosion-resistant tank (1) is provided, in which chlorinated water with appropriate permitted concentrations is initially prepared and poured into distilled water by adding a certain amount of concentrated Joule water (8-20% by weight). The control unit of the device (11), which is actually a PLC-type electrical panel, is installed next to the device and is connected to its various parts. The task of the PLC (11) is to measure the water characteristics and control them at predetermined values. An electric drain valve (3) is provided under the tank (1) that can be turned on when the tank (1) needs to be completely drained and all the water inside is drained. Also, when a command is received from the PLC stating that some of the water in the tank (1) needs to be drained, this electric valve (3) is turned on by the PLC (11) command and the water is drained. The water is heated through a belt-type thermal jacket (4) that is wrapped around the tank (1). The temperature sensor (5) inside the tank (1) measures the temperature of the water inside it and sends the value to the PLC (11).PLC (11) also issues a command to the thermal jacket (4) to stay on or turn off, depending on the difference between the temperature of the sensor (5) and the desired temperature. At the top of the tank (1), there is a relief valve (6) which is for safety purposes and if the internal pressure exceeds the permissible limit (2 bar), it releases the pressure by discharging some gas and after adjusting the pressure, it is re-sealed. A pressure gauge (7) is also installed on the lid of the tank (1). The outer body of the tank (1) is completely covered with rock wool insulation to prevent heat loss. Mixing the components inside the tank (1): To have a homogeneous fluid with uniform temperature, pH, and chlorine concentration at all points, proper mixing is required. To achieve this, a stirrer (8) will be placed inside the tank (1) and its rotation can be adjusted. Adjusting the water level inside the tank (1): In this device, a 6-point height gauge (9) is considered, which has points HH, HL, LH and LL. At point HH, all tank inlets are closed and the drain valve (3) is opened. The distance between point HL and LH is actually the desired water level inside the tank (1). Point LL is also the lowest suitable water level, and at values ​​lower than that, the water level may fall below the level of the dumbbell samples, which causes some of the samples to not be exposed to chlorinated water and is therefore not desirable. At this point, the drain valve (3) is closed and only the inlets to the tank (1) remain open. In addition to these points, there are two points at the highest and lowest achievable limits of the tank (1), and if any of the units does not function properly and the water level changes too much, the device will alarm at these points and the inlet and outlet valves will all be closed, and in fact, the device will stop functioning. Dumbbell sample holder (10): A holder base is completely immersed in chlorinated water inside the tank (1) and a large number of dumbbell samples can be placed in it. Main circulation path (12): To control and maintain the water characteristics, chlorinated water is constantly circulated and all its characteristics are measured and controlled with each rotation. This circulation is carried out through the main pump (14) with a Teflon head that is of the centrifugal type. All pipes used in the construction of the circulation path are made of PTFE, PVDF, titanium or other neutral and corrosion-resistant materials. At the beginning of the main circulation path (12), a ball valve (15) is located, which actually acts as a safety valve so that if a break occurs in the circulation pipe path, the flow is completely closed and the water in the tank is not wasted. A Y-strainer (16) is provided after the pump to remove impurities from the system. This filter (16) has a mesh size of less than 15 µm and must be opened and cleaned at regular intervals. Sub-circulation path (13): Since various sensors are installed in this device and generally the sensors do not function properly at high temperatures and their lifespan is greatly reduced, a sub-circulation path (13) is installed in this device to house the tank containing the sensors (2) and to cool the circulating water before entering it. A needle valve (17) is located at the beginning of this sub-path (13) which sends some of the flow in the main circulation path (12) to this path and its flow rate is adjustable. In the secondary path (13) a circulator (18) is placed which cools the water to 25˚C. Then this water whose temperature has decreased from 80˚C to 25˚C is entered into the tank (2) where the sensors are located. In the tank (2) four sensors of temperature (19), pH (20), ORP (21) and EC (electrical conductivity of water) (22) are installed. Each of these sensors must have a transmitter which is installed in the PLC (11) so that it can issue the necessary control command to maintain the desired values ​​of the relevant parameter. Therefore, all these sensors are connected to the PLC (11). The PLC program (11) is written in such a way that each of the measured values ​​at 25˚C is converted to its actual value at 80˚C. The data of pH, temperature, ORP (chlorine concentration) and electrical conductivity of water must be permanently recorded and reportable. The required accuracy of each of the sensors used is given below: pH sensor: pH measurement and control must have an accuracy of 0.1 or better. ORP sensor: ORP measurement and control must have an accuracy of ±10 mV. Temperature sensor: Temperature measurement and control must have an accuracy of ±1˚C. To know exactly at what temperature each water characteristic was measured, a temperature sensor (19) is placed in the sensor tank (2) which is connected to the PLC (11). Water pH adjustment: In this device, to control the pH and since the pH increases when sodium hypochlorite is added to the water, a dilute solution of HCl acid is considered. This solution is poured into a storage tank (23) made of HDPE, and a peristaltic pump (24) is used to inject it into the tank (1). This peristaltic pump (24) is connected to the PLC (11) and receives commands from it to inject into the tank (1). In fact, if the data that the pH sensor (20) sends to the PLC (11) is greater than the required pH value, a command is sent to the peristaltic pump (24) to inject some acid. Chlorine Concentration Adjustment: This device uses pH (20) and ORP (21) sensor data to adjust the free chlorine concentration in the water. ORP is a measure of the overall oxidation potential of the solution and at any given chlorine concentration, it has a mathematical relationship with pH that can be calculated and used to estimate the chlorine concentration in ppm. To adjust the chlorine concentration and keep it constant, a higher concentration stock solution is poured into a HDPE water storage tank (25) connected to a peristaltic pump (26). The peristaltic pump (26) is connected to the PLC (11) and is commanded to inject into the tank (1). EC sensor (22) and water hardness adjustment: Continuously adding Joule water to the water to keep the chlorine concentration constant and adding acid to adjust the pH will produce new ions in the water, which after a while will make the circulating fluid very hard. To maintain the quality of the water, a part of it must be periodically discarded and replaced with fresh water. The criterion for measuring the quality of the water in this case is the water hardness, which is a convenient method for measuring by measuring the electrical conductivity of the water. In this invention, the electrical conductivity of the water is measured by the EC sensor (22) which is connected to the PLC (11). If the water conductivity exceeds 500 µS (equivalent to 250 ppm water hardness or 25 ˚F), some of the system water must be drained from the solenoid valve (3) under the tank (1). Distilled water storage tank (27): Fresh water is contained in the HDPE water storage tank (27) and water is injected into the tank (1) via a peristaltic pump (28) connected to the water storage tank (27). The injection of fresh water into the tank (1) is based on data obtained from the altimeter (9). When the water level in the tank (1) decreases (due to the opening of the drain valve (3)), a command is sent to the PLC (11) and the PLC (11) sends a command to the peristaltic pump (28) connected to the fresh water tank (27) to turn on and pour fresh water into the tank (1). Finally, the water that has passed through both the main (12) and secondary (13) circulation paths returns to the tank (1), and this process is repeated over and over again until all water characteristics remain constant. Explanation of shapes, maps and diagrams Figure 1: Design diagram of the device showing all the different components and their locations. (1): Large corrosion-resistant tank (2): Sensors tank (3): Electric drain valve (4): Thermal jacket with belt (5): Temperature sensor inside the tank (1) (6): Relief Valve (7): Barometer (8): Agitator inside the tank (9): Altimeter (10): Dumbbell sample holder (11): PLC (12): Main circulation path (14): Main pump with Teflon head (15): Ball valve (16): Y-strainer filter (17): Needle valve (18): Circulator (19): Temperature sensor (20): pH sensor (21): ORP sensor (22): EC sensor (electrical conductivity of water) and water hardness adjustment (23): Dilute HCl acid solution storage tank (24): Peristaltic pump (25): Javel water storage tank (26): Peristaltic pump (27): Distilled water storage tank (28): Peristaltic pump Figure 2: Design of the dumbbell sample holder: (a) Front view of the holder, (b) Top view of the holder and cross-section of the main tank, and (c) Arrangement of dumbbells in the holder. A clear and precise statement of the advantages of the claimed invention over prior inventions. In this invention, a new device has been designed and manufactured to test the resistance of pipe-grade polyethylene to chlorinated water, which can test the behavior of polyethylene by performing an accelerated aging method against disinfectants. Since the production of pipes and their testing according to the ASTM F2263 standard is very time-consuming (about several months) and, in addition, requires a lot of raw materials, there is a need for a smaller-scale device that can reduce the time spent conducting research to find the optimal formulation. Therefore, the device presented in this invention simulates the service conditions of pipes, including temperature, pH, ORP, and chlorine concentration of water, and applies these conditions to "dumbbell"-shaped samples.In this way, the machine operator can remove the samples from the machine at short intervals (one to several weeks) according to his needs and perform the required tests such as mechanical properties, OOT or OIT, and FT-IR on them, and examine the reduction in mechanical properties due to chlorine degradation, the amount of antioxidant consumption, and the formation of polar groups resulting from the oxidative degradation of polyethylene, respectively. Another major advantage of this device is that all test conditions including temperature, pH, ORP and chlorine concentration of the circulating water are kept constant throughout the test, and therefore the results obtained are highly accurate and precise. The most important point among these is that the chlorine concentration remains constant because chlorine in water is unstable and its concentration decreases with time or temperature increase. The device made in this invention has the advantage that it can keep the chlorine concentration constant throughout the test with appropriate accuracy. This device is very suitable for petrochemical companies and pipe and fitting manufacturers by assisting in the research stages of developing new grades or controlling the quality of existing grades, and it increases the quality of products, increases added value, and helps enter global markets. In addition, it helps to completely replace metal and cast iron pipes in urban water supply systems with polyethylene pipes. Description of at least one implementation method for implementing the invention The water used in this device is deionized or distilled water. For example, its pH is chosen to be 6.8 ± 0.2, free chlorine concentration is 5 ± 0.2 ppm, and its ORP is < 825 mV. The water temperature is 80 ± 1 °C. Concentrated sodium hypochlorite (NaClO) (14% by weight) is used to produce chlorinated water. Dumbbell samples are injection molded to ASTM D638 dimensions and are installed inside the main tank of the machine in a section designated as a dumbbell sample holder. The holder is designed so that the dumbbells are not under additional tension but are completely fixed. Chlorinated water is circulated by a pump in the main path. The water temperature in the tank where the sensors are installed is set to 25˚C. Dilute HCl acid (0.05-1%) is used to adjust the pH of the water, and NaClO solution (with a concentration of 100-2000 ppm) is used to adjust the chlorine concentration and ORP of the water. If any of the sensors measure values ​​below the optimum value, their controller or the device PLC sends the necessary commands. For example, if the pH is higher than 6.8, the PLC sends a command to the peristaltic pump connected to the HCl storage tank to turn on and the acid injection continues until the pH reaches the desired level. Therefore, the device has the ability to keep all the parameters effective in the aging process of the samples constant and the test can continue for a desired period of time (from one day to several months). The samples can be removed from the device at specific intervals and various identification tests can be performed on them. Explicit mention of the industrial application of the invention The device made in this invention is used by petrochemical companies producing pipe-grade polyethylene and companies producing polyethylene pipes to test the resistance of synthetic polyethylene and compounds produced from it to chlorine. Using this device, the service conditions of pipes used in urban water supply systems can be simulated in the laboratory and on dumbbell-shaped samples. Because in order to achieve a polyethylene compound that can provide a minimum service life of 50 years when used as a pipe, it is necessary to design a special formulation that contains various antioxidants or other additives, or even changes need to be made to the structure of the polyethylene chain during polymerization. Every new polyethylene material and compound that is produced as a pipe grade must be tested by this device before mass production to measure its resistance to chlorinated water and ensure its proper performance during service. Brief description of the invention In this invention, a device has been developed to measure the resistance of polyethylene to chlorinated water and observe the rate of surface degradation and reduction of the antioxidant package and additives in polyethylene. Urban tap water typically contains small amounts (about 1-3 ppm) of free chlorine as a disinfectant to help maintain water health. However, the presence of chlorine as a strong oxidizing agent, even in small amounts, can cause the consumption of antioxidants in polyethylene and, in the long term, weaken its properties and lead to pipe failure. Therefore, measuring the resistance of polyethylene to chlorinated water and having a high degree of confidence that the pipe will last at least 50 years is essential and inevitable before mass production of pipes. The device developed in this invention is actually a small-scale device that can simulate the service life conditions of pipes used in urban water supply systems in the laboratory and on dumbbell-shaped samples.In this way, the aging test time is significantly reduced and its results can be used to find the optimal formulation that has the highest resistance to chlorinated water. This device consists of a tank for storing and heating chlorinated water, in which a dumbbell-shaped sample holder is placed. In order to maintain constant water characteristics including temperature, pH, ORP and chlorine concentration, the water flow is continuously rotating and circulating, and all these parameters are measured and controlled with each water rotation. This device is capable of performing accelerated aging operations at different temperatures and chlorine concentrations, as well as on other materials such as cross-linked polyethylene (PEX), polybutylene (PB) and polypropylene (PP).

Claims

Claim What is claimed: Claim 1) What is claimed is a device for accelerated aging of polyethylene and evaluation of its oxidation resistance to chlorinated water. This device consists of the following components: a- A main tank for immersing samples in chlorinated water; b- pH, ORP (oxidation and reduction potential), temperature and EC (electrical conductivity of water) sensors for continuous measurement of water characteristics; c- A main circulation path; d- Three storage tanks for storing pure water, dilute acid and concentrated chlorine solution; e- A PLC electrical panel connected to all electrical equipment of the device and sensors. Claim 2) A device according to claim 1, in which the aging operation can be performed at a chlorine concentration of 1-10 ppm and the device has the ability to keep the chlorine concentration constant at the set value throughout the aging test. Claim 3) A device according to claim 1, which has a side path parallel to the main circulation path and the flow rate of the flow entering it is controlled by a needle valve and flowmeter at the beginning of the path and the following components are located therein: - A circulator for cooling the water to a temperature of 25 degrees Celsius; - A small tank after the circulator, for placing sensors for measuring water characteristics (pH, ORP and EC) and having a temperature sensor for measuring the temperature of the water inside the small tank. Claim 4) A device according to claim 1, wherein the main tank is equipped with the following equipment: - a height sensor to maintain the water level within a certain range; - a pressure gauge to indicate the air pressure inside the tank; - a safety valve to release the pressure; - an electric drain valve; - a water temperature sensor inside the tank; - a stirrer. Claim 5) The main tank according to claim 4, wherein the heat required to heat the water is provided by a belt heater or rod elements.

Images