Brand New Anti-NOx Solution Fights Yellowing Factors Hidden in the Air

5 Aug, 2021

Author : Specialty Chemical Business Unit

Polyurethane (PU) materials can be made into various products with a wide range of applications, but the nitrogen oxide (NOx) in exhaust gases causes PU to yellow and fade. Weatherability expert Everlight Chemical has launched a new “anti-NOx product” which effectively maintains the attractive appearance of PU products!

Good partners for doing home exercise during pandemic — PU products

Apart from following TV dramas and binge snacking while staying at home during the pandemic, you also need to consider your body shape and health. But what should you do if you can’t go out to exercise? That’s why more and more people are getting hooked on various kinds of home exercise such as online aerobic dancing, online body building courses, or various super-popular “play and slim” Nintendo Switch games such as Ring Fit Adventure, Just Dance, Fitness Boxing, and so on. Not only can you burn calories with these games, you can also have fun with the family. So, they’ve become essential supplies for getting through the pandemic since 2020!

Whether you’re doing home aerobics or ring fit games, these exercises usually involve running, jumping, squatting, and so on. In order to protect your joints and muscles, and to avoid injury, it is best to wear sports shoes or equip yourself with a yoga mat. Did you know that there is a material that provides both good shock absorption and abrasion resistance? So many fitness products, from the sports shoes you wear on your feet to yoga mats and rollers, and even Switch accessories, all need to use this material to be manufactured. That’s right! It’s polyurethane (PU)!

Photo credit：Pexel

PU features and applications

The advantage of polyurethane (usually abbreviated as PU) is that it has excellent physical and chemical properties. Not only is it abrasion- and twist-resistant, but it’s also soft, highly elastic, and easy to be processed. From lightweight soft foam to highly tough shoe soles, all are made with PU. Because of these excellent properties, polyurethane is not only widely used in various kinds of sports equipment, but also in such fields as automotive components, shoe materials, synthetic leather, fibers, dyes and coatings, adhesives, and so on. It can be called one of the most widely used polymer materials!

What causes PU yellowing?

When these PU materials are made into elastomers, foam or synthetic leather, they will also show signs of degradation such as yellowing and fading after exposure to sunlight or high temperatures during the production process. Although these degradation problems encountered during the course of production or processing can be improved by modifying the raw materials or by adding addtives, PU products are still subject to yellowing during storage or transportation. This is the yellowing risk factor often overlooked by people. The main culprit is — the “all-present NOx gas in exhausts”!

Many research reports on PU materials demonstrate that, in order to effectively solve PU yellowing problems, it is necessary to consider such factors as the light, heat and NOx gas present in the environment. However, due to the decline in demand under COVID-19 pandemic impact, storage times of finished products have grown longer. Additionally, delivery times are also significantly lengthened due to the chaotic distribution logistics in land and sea transportation. These factors all make PU products more susceptible to the effects of NOx in exhaust fumes, causing problems such as yellowing and fading in the appearance of products, and they markedly increase manufacturers’ costs in terms of scrap processing and customer complaints.

Why does NOx cause PU yellowing? Currently, there are various divergent opinions as to the precise mechanism of its action. Some theories indicate that NOx may react with the antioxidant BHT (butyl hydroxyl toluene), which is commonly used in the PU synthesis process, to trigger yellowing. There is also evidence showing that NOx itself can cause a free radical chain reaction, in which the molecular structure of polyurethane is attacked, thus causing degradation and yellowing!

Not to worry! Let Everlight Chemical solve PU yellowing problems

The rapid development of industrialization has brought with it a year-on-year increase in exhaust gas emissions and increasingly serious air pollution hazards. In order to effectively solve the yellowing problems with PU products due to increasing amounts of NOx, Everlight Chemical has specially brought out a brand new “Anti-NOx product.” As shown in the figure below, after 48 hours of testing with an anti-air fumigation test (AATCC 23: test method for colorfastness to burnt gas, NOx concentration 4~5ppm), it can be clearly seen that when the Everlight Chemical anti-NOx product was added to a sample of polyester PU (MDI_Base), signs of yellowing were significantly reduced (ΔYi decreased from 34.7 to 10.7), which also proves that the Everlight Chemical anti-NOx product is able to protect polyurethane materials from environmental exhaust gases, and effectively alleviate the yellowing problem of PU products during storage.

Everlight Chemical has also launched a series of products specially designed for polyurethane — Eversorb® UV absorbers & light stabilizers and Everaox® antioxidants, which are able to effectively protect the performance of PU products, improve their weather- and heat-resistance, extend their service life, and increase their product value. If you are interested, please do not hesitate to contact us.