Meaning
A chemical additive protects polymers from oxidative degradation by scavenging free radicals as they form. The primary antioxidant is the first line of defense for a plastic part, reacting with peroxy radicals to stop the chain reaction of breakdown. These molecules are essential for maintaining the physical properties of the plastic during its entire service life.
Chemical Mechanism
Donating a hydrogen atom to a radical turns a reactive species into a stable one. This action by the primary antioxidant prevents the radical from attacking the polymer chain and causing it to break or crosslink. Most of these additives are hindered phenols, which are chosen for their effectiveness and their ability to withstand high processing temperatures.
Long Term Stability
Parts that are exposed to heat or air for long periods require a steady supply of these stabilizers. The primary antioxidant remains in the polymer matrix and continues to work for years, protecting the material from becoming brittle or losing its color. Without this protection, items like automotive parts and outdoor furniture would fail within a few months of use.
Formulation Strategy
Efficiency of a stabilization package is maximized when different types of chemicals are used together. While a primary antioxidant handles the radicals, a secondary one is often added to decompose hydroperoxides. This combination provides a much higher level of protection than either additive could provide alone, ensuring that the plastic remains durable under a wide range of environmental conditions.
Selecting the right blend of chemicals is a necessary step in the design of a new plastic part, as it determines how well the material will age and how long it will maintain its structural integrity.
