The appearance retention properties of poly (vinyl chloride) compounds during weathering

Abstract

Damage to poly (vinyl chloride) (PVC) compounds due to thermal degradation during processing has an important influence on its subsequent weatherability. High melt temperatures and/or high residence times cause white PVC to become more yellow and colored PVC to fade and bleach more upon weathering. If high melt temperatures are used, then short residence times are needed to maintain excellent weatherability. In addition to careful consideration of extrusion conditions, stream‐lined equipment is necessary to produce extrudate of uniform thermal history. Also, relatively high thermal stabilizer levels help reduce thermal damage and, therefore, improve weatherability. Impact resistance is better retained when processing occurs at higher melt temperatures. A reasonable compromise between extrusion rate and temperature must be reached to provide for adequate color and impact retention.

Photodegradation of plasticized poly(vinyl chloride) stabilized by different types of thermal stabilizers

“…Although thermal stabilizers almost all take effect by replacing labile chlorine atoms in PVC chains or react with HCl generated from degradation [8], the ability to prevent thermal damage is distinct for different thermal stabilizers, which will largely influence the ultimate outdoor application of the products. Isner et al [9] investigated the appearance retention properties of PVC compounds during weathering and pointed that the thermal history during processing had an important effect on the subsequent weatherability of PVC, especially on the color stability.…”

Critical Review of Polymeric Building Envelope Materials: Degradation, Durability and Service Life Prediction

“…As mentioned earlier, a common cladding material is PVC-U. Isner and Summers [82] completed a study related to the effect of production conditions on the weathering rate of PVC siding, where the weathering rate was determined by the overall colour change as per ASTM D 1925-70. Three experiments were run to investigate the effects of different stabiliser amounts, production rate and melt temperatures on the stability of the product.…”

The chemical mechanisms of outdoor weathering in polyvinyl chloride

“…Often the spectrum can be resolved into a series of absorption maxima each representing a polyene sequence, (C = C)n, where n = 2, 3,4, 5, etc., double bonds (4). Indeed, damage to PVC due to thermal degradation has been shown to cause poor subsequent weathering (5).…”

“…Of particular importance are those structures associated with double bonds or conjugated double bonds because they absorb light as well as contain weak bonds that can be broken. Indeed, the literature shows that degraded or nearly degraded PVC which would contain many double bonds due to loss of HC1 is very susceptible to further degradation by weathering (5). Breaking of a chemical bond leads to two free radicals, the start of weathering degradation.…”

“…Thermal degradation of PVC during processing must be minimized to avoid weathering degradation (5). Stabilizer must be higher than usual in weathering compounds and equipment must be streamlined to avoid degradation (5). Ultraviolet absorbers must be used in large amounts to protect the PVC.…”