PVC finished products are used in different industries. The evaluation and testing of PVC calcium zinc stabilizers require different methods depending on their performance. In general, there are two main methods: static and dynamic. The static method includes Congo red test paper method, aging oven test, and electromotive force method, while the dynamic method includes torque rheometer test and dynamic double roll test.
1. Congo Red Test Paper Method
Using an oil bath with built-in glycerol, the PVC to be tested is mixed evenly with a heat stabilizer and placed in a small test tube. The material is shaken slightly to make it firm, and then placed in an oil bath. The temperature of glycerol in the PVC calcium zinc stabilizer oil bath is set in advance to about 170 ℃, so that the upper surface of the PVC material in the small test tube is level with the upper surface of glycerol. Above the small test tube, a plug with a thin glass tube is inserted, and the glass tube is transparent from top to bottom. The Congo red test paper is rolled and inserted below the glass tube, so that the lower edge of the Congo red test paper is about cm away from the upper edge of the PVC material. After the experiment begins, record the time from when the Congo red test strip is placed in the test tube to when it turns blue, which is the thermal stability time. The basic theory of this experiment is that PVC will rapidly decompose at a temperature of about 170 ℃, but due to the addition of a heat stabilizer, its decomposition is inhibited. As time goes on, the heat stabilizer will be consumed. When consumption is complete, PVC will rapidly decompose and release HCl gas. At this time, the Congo red reagent in the test tube will change color due to its easy reaction with HCl. Record the time at this time and judge the effectiveness of the heat stabilizer based on the length of time.
2. Static oven test
Prepare high-speed mixed samples of PVC powder and other processing aids (such as lubricants, impact modifiers, fillers, etc.) in addition to PVC calcium zinc stabilizers. Take a certain amount of the above sample, add different heat stabilizers to PVC calcium zinc stabilizer in a certain proportion, mix well, and then add to the double stick mixture
The preparation of test pieces on the mixer is generally carried out without adding plasticizers. The double roll temperature is set at 160-180 ℃, and when adding plasticizers, the roll temperature is generally around 140 ℃. By repeatedly pressing with two sticks, a uniform PVC sample is obtained, followed by cutting to obtain PVC samples of a certain size containing different heat stabilizers. Place different PVC test pieces on a fixed device and then place them in a constant temperature (usually 180 ℃) oven. Record the color change of the test pieces every 10 minutes or 15 minutes until they turn black.
Through oven aging tests, the effectiveness of heat stabilizers on PVC thermal stability can be determined, especially their ability to suppress color changes. It is generally believed that when PVC is heated, the color will undergo a series of changes from light to dark, including white yellow brown brown black. The degradation situation can be determined by the color of PVC over a certain period of time.
3. Electric potential method (conductivity method)
The experimental device mainly consists of four parts. The right side is an inert gas device, which generally uses nitrogen, but sometimes also air. The difference is that when using nitrogen protection, PVC calcium zinc stabilizer can avoid the degradation of PVC mother chains caused by oxygen oxidation in the air. The experimental heating device is generally an oil bath at around 180 ℃. A mixture of PVC and heat stabilizers is placed inside the oil bath. When HCl gas is generated, it will enter the NaOH solution on the left side along with the inert gas. NaOH quickly absorbs HCl, causing the pH value of the solution to change. By recording the pH meter’s changes over time, the effect of different heat stabilizers can be determined. In the experimental results, the pH t curve obtained by processing is divided into an induction period and a growth period, and the length of the induction period varies with the effectiveness of the heat stabilizer.
4. Torque rheometer
The torque rheometer is a typical small-scale instrument that simulates the actual processing of PVC. There is a closed processing box on the outside of the instrument, and the temperature of the processing box and the speed of the two internal rollers can be controlled through a computer connected to the instrument. The material mass added to the torque rheometer is generally 60-80 g, which varies according to different instrument models. The experimental steps are as follows: prepare masterbatch containing different heat stabilizers in advance, and the basic masterbatch formula generally includes ACR in addition to PVC CPE、CaCO3、TiO、 Lubricants, etc. The torque rheometer is set to temperature in advance. When it reaches the specified temperature and the speed is stable, the weighed mixture is added to the processing box, quickly closed, and various parameters on the connected computer are recorded, which is the rheological curve. After processing, different appearance features of the extruded material can also be obtained, such as whiteness, whether it is formed, smoothness, etc. By using these parameters, the industrial potential of the corresponding heat stabilizer can be determined. A suitable heat stabilizer should have appropriate torque and plasticization time, and the product should be well formed with high whiteness and smooth surface. The torque rheometer has built a convenient bridge between laboratory research and industrial large-scale production.
5. Dynamic double roll test
As a type of auxiliary method for dynamically measuring the effect of heat stabilizers, dynamic double rollers are used in the absence of a rheometer, and a double roller tablet pressing instrument is selected in the experiment. Add high-speed mixed powder into it and press it into shape. Repeatedly extrude the obtained sample. Until the test piece turns black, record the time it takes for it to completely turn black, which is called the blackening time. To determine the thermal stability effect of different heat stabilizers on PVC by comparing the duration of blackening.
Post time: Jun-20-2024
