Effects of weathering and formulation on the properties of vinyl siding
Authors: Zammarano Mauro , Jhang Song , Kim Ickchan , Goodwin David , Sarti Gianluca , Gardi Stefano , Cardelli Camillo , Sung Li Piin 
Published: September 2024

Vinyl siding has become a popular choice for residential exteriors across the United States. In its insulated form, this siding includes a shell, capstock, and substrate, that encase a foamed material, serving as an efficient insulating material. While it offers a cost-effective solution with numerous advantages, such as improved energy efficiency, easy installation, noise reduction, fire resistance, aesthetic appeal, low maintenance requirements, durability, and protection against external elements like humidity and mold, there are two critical areas for potential improvement. Firstly, its durability can be compromised by outdoor conditions such as sun, heat, rain, wind, dust, and pollutants. This exposure can result in the degradation and cracking of the shell, diminishing its effectiveness as a protective exterior layer. Secondly, fire performance, especially in terms of fire barrier, is a concern. The 2021 International Energy Conservation Code (IECC) introduced a requirement for exterior continuous insulation for walls in most U.S. territory (climate zone 4 and above). Typical insulating materials, such as foamed polystyrene or polyisocyanurate, are highly flammable. In the event of a fire, in vinyl siding a shell material is needed to act as an external fire barrier to delay or prevent insulation ignition. This issue is rising in importance due to the prevalence of wildland-urban interface (WUI) fires. While unplasticized polyvinyl chloride (U-PVC) inherently possesses flame-retardant properties, the current U-PVC compounds used in vinyl siding may not be enough performant for serving as an effective fire barrier, such as especially in cases of cracking due to weathering.This study investigated (1) the weathering of commercial vinyl siding and (2) the impact of various additives (impact modifiers, titanium dioxide, calcium carbonate, stabilizers) on the mechanical performance of U-PVC formulations before and after weathering. Color and gloss retention, the mechanical properties, and the chemical nature of weathering were also studied to understand which additives affected more the weatherability of the item. Weathering experiments were conducted using a Q-Lab Accelerated Weathering Tester (QUV), Simulated Photodegradation via High Energy Radiant Exposure (SPHERE), and natural outdoor exposure in Florida. Mechanical properties were assessed through tensile, elongation, and impact strength tests; chemical properties via Fourier-transformed infrared (FTIR) spectroscopy; and color and gloss evolution were also measured during aging. For studying the fire performances imparted by additives, flammability was examined using micro combustion calorimetry (MCC), and a recently adopted test based on cone calorimetry (ASTM E3367) was specifically performed to evaluate the barrier effect of materials.The results revealed that, regarding durability, mainly the content of titanium dioxide and calcium carbonate significantly influenced the weatherability of the siding due to their chemical nature and interactions with the PVC matrix. Regarding fire performance, MCC revealed a significant effect of various additives but a low to insignificant effect of weathering. In particular, the formulation with the highest calcium carbonate content showed the best performance in MCC. Noticeably, all U-PVC formulations failed to act as an effective fire barrier, exposing the insulation foam underneath due to the melting, flowing, and shrinking of U-PVC during combustion. This underscores the necessity for modifying the U-PVC compounds of the vinyl siding shell to achieve the appropriate barrier effect during combustion.