editor 2018-05-09 Browse ()

The influence of heat stabilizers on the transparency of PVC is influenced by the following factors

1. Refractive index of stabilizer

If the visible light refractive index of heat stabilizer and PVC resin is the same or similar to 1.52-1.55, then the transparency of PVC products is better, otherwise the transparency is lower.

2. Linear length of stabilizer molecules (molecular clusters)

The linear length of the heat stabilizer molecule (or molecular group) is less than the visible light wavelength of 400-735nm, resulting in less refracted light and higher transparency. Conversely, the transparency is lower.

3. The "solubility" of heat stabilizers in PVC, i.e. compatibility

Compatibility refers to the mutual affinity between two or more substances when mixed. Good compatibility means it is possible to achieve molecular level dispersion. Heat stabilizers have good compatibility with PVC resin in the molten state. Unable to form two phases, that is, there is no interface or the interface is not obvious, the refracted light is less, and the transparency of PVC products is higher. Liquid stabilizers have better compatibility with PVC than corresponding solid metal soaps, and their molecular linear length is also smaller, resulting in higher transparency of PVC.

The transparency of liquid organotin heat stabilizers is the best, because both the heat stabilizer itself that has not participated in the heat stabilization reaction and the R2SnCl2 generated after participating in the stabilization reaction have good compatibility in PVC resin. The stearic acid soaps of Ba/Zn, Ba/Cd, and Ca/Zn have certain compatibility in PVC and relatively high light transmittance. However, due to their limited compatibility and long molecular linearity, the products produced after thermal stabilization are typical metal salts such as CaCl2 and BaCl2, which have poor compatibility with PVC. Therefore, when used in large quantities, they become cloudy due to the presence of more refracted light, affecting their light transmittance.

Tribasic lead sulfate and dibasic lead phosphite with extremely poor compatibility have relatively large molecular clusters, making PVC products opaque.

Lead stearate, due to its certain compatibility, becomes semi transparent when used in small amounts.