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The effect of heat stabilizers on the transparency of PVC is determined by the following factors
2018-05-09 10:46
1. Refractive index of stabilizer
Heat stabilizer and PVC resin visible refractive index 1.52~1.55 the same or similar, the PVC products transparency is better, and vice versa transparency is low.
2. Linear length of stabilizer molecules (molecular groups)
The linear length of the heat stabilizer molecule (or molecular group) is less than the visible light wavelength 400 ~ 735nm, less refracted light, higher transparency, and vice versa.
3, heat stabilizer in PVC "solubility", that is, compatibility
By compatibility is meant the mutual affinity of two or more substances when mixed. Good compatibility means that it is possible to achieve molecular dispersion. The heat stabilizer has good compatibility with PVC resin in the molten state. The two phases are not formed, that is, there is no interface or the interface is not obvious, the refraction of light is less, and the transparency of PVC products is higher. Liquid stabilizer than the corresponding solid metal soap in PVC compatibility is better, the molecular linear length is also smaller, so the transparency of PVC is higher.
Liquid organic tin heat stabilizer transparency is the best, this is because whether it is not to participate in the thermal stabilization reaction of the heat stabilizer itself, or has participated in the stabilization reaction after the formation of R2SnCl2 in the PVC resin have good compatibility. However, the stearic acid soaps of Ba/Zn, Ba/Cd and Ca/Zn have certain compatibility and high light transmittance in PVC. However, due to their limited compatibility and long and large molecular linearity, the products after thermal stabilization are typical metal salts such as CaCl2 and BaCl2, which have poor compatibility with PVC. Therefore, when the dosage is large, they become turbid due to more refracted light, which affects their light transmittance.
Tribasic lead sulfate and dibasic lead phosphite with poor compatibility have relatively large molecular groups, so PVC products are not transparent.
However, lead stearate is translucent due to its compatibility.
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