How to evaluate the stability of PVC stabilizer?

- Feb 22, 2019-

The most important and indispensable materials in PVC products is stabilizers, the stabilizers on the market are basically no longer as before: Triple Salt, double salt, Lead stearate, Barium stearate. In addition to transparent products and a few soft products in the use of Organotin, liquid calcium zinc barium cadmium, composite stabilizer accounted for most of the market, there are calcium-zinc composite stabilizers, lead salt composite stabilizers, hydrotalcite composite stabilizers, rare earth composite stabilizers and so on, after the composite stabilizers become indispensable, then how to evaluate the stability of the stabilizers?

From the use requirements, the stability of PVC stabilizer can be divided into initial stability, long-term stability and residual stability. Initial stability is the color to maintain stability, refers to any production cycle, from the mixture to the output, product color stability or color within the range allowed. The long-term stability is refers to the stability which causes the material decomposition color change because of the accidental breakdown, but does not arrive at the machine to clean up. Residual stability refers to the stability of PVC products during their later use.

From the test method, the stability can be divided into static thermal stability and dynamic thermal stability. Static thermal stability is the ability of heat stabilizers to retard the thermal decomposition of PVC in the presence of only heat or heat and air. Dynamic thermal stability is the ability of thermal stabilizer to retard the thermal decomposition of PVC under the combined action of heat, air and shear force.

Test Method for static thermal stability

1. Static oven test is one of the easiest and fastest methods for initial screening of large quantities of new stabilizers. Cut a small piece from the prepared film and place it on several plates in the hot air circulation oven. The control temperature is 180 °C. take out a plate every once in a while (if set at 1 hour) to test the change of Whiteness and yellowness. In addition, the weatherability of PVC products can be tested by modifying and adding ultraviolet lamp and using acid water spray to set proper temperature.

2. Congo red test method, the static thermal stability of PVC was tested according to GB / t 2917.1-2002, the temperature of oil bath was controlled (1801 °c) , and the time when the lower end of Congo red test paper turned blue was recorded The time of Congo red test paper turning blue was recorded, which reflected the long-term thermal stability of the heat stabilizer to PVC. This method is commonly used in wire and cable industry as the basis for the temperature grade of wire and cable. The method is also used for the residual thermal stability of recycled waste.

Dynamic Thermal Stability Test Method

1. Dynamic double-roll process. The ingredients in the formula are continuously molded on the heating roller in the 180 °C double-roller rubber-mixing process, a small amount of samples are taken off at intervals of 5 or 10 minutes, and the color is checked by the whiteness meter after cooling.

2. Torque rheometer mixing method. The dynamic thermal stability of the material can be determined by setting a certain temperature and rotating speed, comparing the rheological curve of the material from feeding to decomposing and the color of the material block. The method is simple to operate and easy to compare. It is favored by many stabilizer manufacturers and downstream customers.

3. Extruder extrusion. The same formula of different stabilizers, through the barrel of heating, barrel and screw, as well as the mold, nozzle shear, darkening the color of the poor stability of the proof, but this to pass the production test, the waste is inevitable.