Today we take it for granted that polymers can withstand high-speed processing at elevated temperatures and shear rates, and also can take exposure to heat on the job for extended periods without discoloring or embrittlement. It was not always so. In the 1950s, the best antioxidant available was BHT, a low-molecular weight phenolic type that was fugitive and unable to provide long-term protection.
Work on more permanent and effective high-molecular-weight hindered phenolics originated around 1955 at Geigy Chemical’s Industrial Chemicals Div. (today’s Ciba Specialty Chemicals). In early 1963, Geigy launched its new Irganox family, including grades 1076 and 1093, which were initially targeted for PP but with the expectation that they would find use in ABS, HIPS, PVC, acetal, polyesters, and nylons.
Not long after came Irganox 1010, considered the “Cadillac” of antioxidants at the time. It was instrumental in making PP a huge commercial success by extending product lifetimes in higher-heat applications such as food packaging and automotive components.
From the 1970s on, many im proved hindered phenolic antioxidants arrived from companies like Ciba-Geigy, American Cyanamid (now Cytec), Great Lakes Chemical (now Chemtura), Uniroyal (now Chemtura), Ashland Chemical, and Mayzo. They soon proved valuable in other polymers such as PE and rubber-modified polymers like HIPS, ABS, and TPEs. Phenolic antioxidants are also widely used in engineering polymers such as PET, polycarbonate, and nylons. These resins have high processing temperatures and are generally designed to be exposed to heat.
Very few readers of this issue can remember, or even imagine, what it was like when an injection mol...