Weathering and light stability: UV irradiation weathering refers to the process of degradation of materials due to exposure to ultraviolet light. This type of weathering is accelerated compared to natural weathering, where UV radiation, condensation and moist heat.
Some factors of natural weathering include:
Degradation (yellowing, cracks, fissures, color change, loss of shine, delamination, loss of adhesion, warping, embrittlement, formation of bubbles and loss of some physical properties) organic materials (polymeric) are those that suffer from the combination of the above factors, creating the force of the action of weathering.
Weathering degradation is typically initiated by sunlight and can be accelerated by heat and affected by the presence of water (humidity, dew, rain).
Light stability of organic samples with or without weathering factors affects organic materials used in industry, including paints and coatings, plastics, packaging, textiles, consumer and household items, additives and dyes, architectural and building materials, inks and printing materials, electronics, and a variety of automotive components.
A related concept is light stability, or lightfastness, which refers to the ability of a material to withstand two of the three (sunlight, heat, and water) forces of weathering. Light stability tests do not involve liquid water and are often used to test fabrics (carpets, curtains, sofas, etc.) and interior materials.
When we discuss sunlight as a force of weathering, we typically refer to ultraviolet light (UV-A/UV-B). Although it represents only about 7% of the total energy of the sun, UV is responsible for practically all polymer degradation. The EQNA UV chambers, Equilam NA, were designed to meet the intensity of UV-A and UV-B irradiation separately or together, using UV 421 and with a radiation intensity greater than solar, in order to reduce the test time. With this, we can expand the studies to minimize the degradation of materials and/or develop additives that can even inhibit degradation.
ASTM, SAE, DIN, ISO standards have developed some accelerated weathering test standards that the industry/research centers among other agencies have adopted as accelerated test standards.
EQNA UV weathering test chambers are used to simulate and accelerate this process, reproducing extreme environmental conditions in a short period. The EQNA UV chamber was designed to simulate in the laboratory the 3 factors that initiate the force of the action of weathering in accordance with technical standards. Using UV-A, UV-B, UV-C and UV 421 lamps with a higher radiation intensity than solar radiation, in the presence of heat and water, the degradation of materials is accelerated, simulating a few years of exposure of the sample to the real atmosphere in just a few hours of testing.
Laboratory test x Real atmosphere correlation: The most common question we receive at EQNA is, “How many hours of the sample exposure in the EQNA UV correspond to (1,2, 3,5, 10, 20) years outdoors?”. The simple answer is that there is no simple relationship between laboratory tests and real weathering conditions. The difficulty is that there is not yet technology to perfectly reproduce large climate variations, variations in the radiation spectrum, pollutants, geographic position, among other factors found in the real atmosphere.
By accelerating the strength of the weathering action in the EQNA UV chamber, you can obtain faster results on the durability of the product. Accelerated weathering testing is fast, repeatable, reliable and convenient, making it excellent for quality control, qualification and research, and development. It is an excellent decision-making tool to help determine the best product/material.
Difference between outdoor and indoor environments.
The nature of sunlight received by products in outdoor environments depends on several factors:
– Time of year, time of day, latitude, cloud cover, pollutants, and altitude, among others.
The nature of sunlight received by products in indoor environments depends on several factors:
– The passage of solar radiation through window glass (indoors) filters out some of the short-wave UV light, depending on its thickness and tint, among others.
The spectral sensitivity of materials is also critical for degradation to occur; the material must be able to absorb incident radiation, and the light must have sufficient energy to cause chemical bonds to break.
Heat, temperature, and temperature variation affect photochemical reactions caused by incident sunlight; they are not simple one-step reactions. Primary reactions caused by sunlight should not be affected by heat; secondary reactions often are. In some cases, a small increase in temperature can double the rate of some chemical reactions. Thermal cycling in outdoor environments can change the surface temperature of a material within minutes, causing physical stress to assemblies and coatings.
Water: Can affect chemical reactions accelerating them and leading to increased oxygen transport. Water can also cause physical effects such as erosion, absorption, freeze/thaw stress, thermal shock, and material loss by impact. Water can be present in the form of dew (condensation), relative humidity, and rain.
