Rigid PVC is polyvinyl chloride resin without a plasticizer added. Therefore, rigid PVC is not flexible, which is desired for many end uses like building products and is the material of choice for
window, siding, doors, decking, fencing, and soffit products.
Like Flexible PVC, rigid PVC is compounded with many other ingredients necessary for processing and physical properties. First and foremost, a heat stabilizer must be chosen. Other important additives are colored pigments, lubricants, fillers, protective agents, pesticides and biocides, and impact modifiers.
In most outdoor applications, TiO2 is utilized at up to 10% loadings to increase weatherability as it strongly absorbs in the UV electromagnetic spectrum effectively quenching much of this radiation and thereby protecting the PVC polymer from degradation. Two types of TiO2 are offered. The choice depends on your preference for chalking and colorhold.
Chalking TiO2 products are not encapsulated with amorphous silica or increased levels of alumina, silica or zirconium. Therefore after absorption of the UV radiation, electrons and holes are generated which can catalyze localized degradation. The net effect is maintenance of the PVC’s physical properties, but also "chalking". In many cases, this is actually desired, particularly in white colors where chalk is not objectionable. The chalk actually helps mask the PVC natural yellowing and therefore affords increased brightness.
Chalk resistant TiO2 products are generally encapsulated with amorphous silica and contain increased levels of alumina. The encapsulation forms a barrier to the transfer of electrons and holes to the PVC polymer and results in profiles and moldings with very low chalk rates. Colorhold in the darker colors are also enhanced. Encapsulation also greatly diminishes the abrasivity of the TiO2 product, which can be important for color consistency. Brighter whites are also possible under some transfer conditions.
