What is Weatherability?
Weathering is defined as: To discolor, disintegrate, wear, or otherwise affect adversely by exposure. Weatherability is a measured characteristic that shows how well a product performs during exposure to outdoor weather conditions (ultraviolet light, rain, snow, high and low temperatures, humidity, environmental pollution and acidity in the air). How do you create a weatherable product?
This begins at the raw material stage. Raw PVC resin, by itself, is not a weatherable material. Ingredients are added to the resin to form a PVC compound. Such additives as UV inhibitors, pigments, and Ti02 (Titanium Dioxide) all contribute to protecting the PVC from degradation and unacceptable discoloration, therefore, providing a good weatherable product. Other additives impart impact resistance, anti-brittling and enhanced strength characteristics. The formula must be compounded and processed properly to achieve its good, long-term durability and weathering properties. A compound is weatherable if the “pigment package” (individual substances used to color) within the compound is weatherable. For instance, 4 approved pigments are used in our compound to achieve our white color. Each one of these pigments must be weatherable in order to make the entire compound weatherable. Then, it is critical in the blending process (during the manufacture of the compound) that precise amounts are added to the recipe every time the batch is run. This ensures consistent color and weathering.
Vinyl is one of the world's oldest plastics. Known in laboratories since the early 1900's, it was first commercially produced in the 1920's. At the time, it was merely thought of as an interesting substitute for natural rubber. In fact, one of the first commercial uses was as a rubber substitute in electrical wire insulation because rubber could dry out and crumble over time. In the 1930's, rigid vinyl was developed but it wasn't until the 1950's that rigid vinyl saw its first uses in the United States.
More than 60% of the polyvinyl chloride (PVC) resin produced in the United States, today, is used in building and construction and related industries. Commonly known as vinyl, its popularity in this market can be attributed chiefly to its competitive, stable cost base and wide processing capability. Vinyl has many inherent characteristics that make it an ideal choice for a variety of building and construction applications:
- Ease of molding or shaping
- Durability under all environmental conditions
- Good mechanical strength and toughness
- Excellent resistance to abrasion
- Good chemical and electrical resistance
- Good barrier to gases
- Excellent flame retardant characteristics
- Easy to color and decorate
Vinyl is the most versatile plastic on the market today -- primarily because it's the only polymer that is always mixed with other ingredients before being formed into a product. With a careful balance of the right additives, vinyl compounds can be formulated to make tough, rigid items like pipe, and flexible items like vinyl membrane. Depending on the additives used, vinyl products can be crystal clear, opaque or virtually any color.
Rigid PVC was the first plastic to be used in the construction industry and has become this industry's leading plastic. Pipe, pipefittings and conduit account for approximately 70% of PVC construction sales. Other major applications include siding, window and door profiles, electrical wire and cable insulation, flooring, and vinyl membranes for roofing and environmental containment liners.
As polyvinyl chloride windows and doors have gained more acceptance in the marketplace and are being sold into many different climatic regions, questions continue to arise about vinyl's suitability for areas with a warmer (or cooler) climate, very high (or low) humidity, salt air or pollution, etc.
Questions like: Will the PVC disintegrate and disappear in a week, a year, or a decade? Will heat turn the framing into a soft, melted material unrecognizable as a window? Will the window's color change from white to yellow or brown to beige? If the PVC framing is hit with some object, will a chunk break off, leaving a jagged gap where there once was a smooth surface? How well will my windows perform over time? How well will they weather?
Most of these concerns are material based and can be addressed in the formulation of the compound. Rigid PVC without additives is brittle and translucent, discolors under ultraviolet light, and does not weather well over time. Other concerns are in product design and function: how much surface is exposed, what loads--wind, gravity, stresses--are expected, and how reinforcing can help ensure long-term durability.
Heat Deflection/Distortion (HDT)
The UV or IR (infrared) wavelength of sunlight is about the only condition that affects PVC. Other elements, such as moisture or salt air, have no effect on most PVC windows.
UV affects the impact strength and color retention of the window, but most of the degradation is just on the extrusion surface, affecting appearance only.
UV-caused degradation can be controlled with the right compounding and extrusion process. Co-extruded exterior surfaces, exterior-laminated films or other resin-blends also can improve the weathering characteristics, while still keeping within the definition of a PVC extrusion.
The more critical factor is heat build-up from IR that can cause distortion of the framing materials. But design, reinforcing, or using materials with higher heat-distortion resistance numbers can help prevent this problem. White and pastel-colored extrusions generally will perform in all U.S. climates, while darker colors may absorb more heat. Heat build-up above the ambient air temperature, caused by the sun's heating, is typically dependent on a product's pigmentation (color). All of NT Window's PVC compounds used in our window frames are low heat build-up formulations. This helps prevent high surface temperatures and increases resistance of the product to heat distortion.