The use of antioxidants in polymer processing can offer better stabilization of the polymer during processing and also prolong its useful life in the end application. Pure Polymers has an extensive range of products which can be used as standalone masterbatches offering gel reductions or die lip build up control in polyethylene film extrusion or process stabilization in the case of polypropylene fiber production where careful control of the MFI is essential to ensure high-quality trouble-free production.
Long term color and thermal stability can be enhanced by selecting the correct package of antioxidants. In addition, to stand-alone masterbatches, this system can be used in multifunctional masterbatches such as in conjunction with UV Stabilizers and Processing Aids Masterbatches to offer both enhanced properties and cost-effectiveness. Application Examples: Tapes, Fibres, Geotextiles, Films, and Injection Mouldings.
• Primary phenolic & secondary phosphate stabilizer packages
• Products specifically designed for film and fibre producers
• Process stabilizers to improve outputs
• Finished product stabilizers to enhance lifetime performance
The degradation of polymers can occur during various stages of the polymer lifecycle from initial manufacture, through to fabrication and then subsequent exposure to the environment. Oxygen is the major cause of polymer degradation and its effect can be accelerated by other factors such as sunlight, heat, mechanical stress and metal ion contaminates.
Polymer degradation during thermal processing and weathering occurs through an autoxidative free radical chain reaction process. This involves the generation of free radicals, then propagation reactions leading to the formation of hydroperoxide, and finally
termination reactions where radicals are consumed. Hydroperoxides are inherently unstable to heat, light, and metal ions, readily decomposing to yield further radicals so continuing the chain
The prior thermal-oxidative history of polymers significantly influences their photo-oxidative behavior in service. Inhibition of this oxidative process is therefore very important and almost all synthetic polymers require stabilization.
Types of Antioxidants Antioxidants are compounds that can interfere with the oxidative cycle thus inhibiting or slowing the oxidative degradation of polymers. There are two main classes of antioxidant depending on the way they act to interrupt the oxidative process illustrated.
These interrupt the primary oxidation cycle by removing the propagating radicals. Such compounds are also called Chain Breaking Antioxidants and examples include the hindered phenols and aromatic amines. Aromatic amines tend to discolor the end product and hence their use in plastics is limited. The phenolic antioxidants, however, are widely used in polymers. Careful selection of the phenolic antioxidant is required as the oxidation products of some phenols may discolor the polymer. The formation of chromophores is directly related to the structure of the phenol and discoloration can therefore be minimized by choosing a phenolic with a specific structure together with the use of suitable co-stabilizers.
These compounds are also called Preventative Antioxidants as they interrupt the oxidative cycle by preventing or inhibiting the formation of free radicals. The most important preventive mechanism is the hydroperoxide decomposition where the hydroperoxides are transformed into non-radical, nonreactive, and thermally stable products. Phosphites or phosphonites, organic Sulphur containing compounds, and thiophosphates are widely used to achieve this, acting as peroxide decomposers.
Choosing the correct system
The choice of antioxidant varies depending on a number of factors, including the base polymer, the extrusion temperature, and the performance targets of the end-use application. The efficiency of an antioxidant upon processing is dependent on its ability to reach the polymer's attacked sites by diffusing through the viscous melt. The compatibility with and the solubility of the additive in the solid polymer, its low volatility, and its resistance to extraction into the environment are also clearly important. Synergism, where a co-operative interaction between antioxidants leads to a greater overall effect, can occur. It may arise from using two chemically similar antioxidants or when two different antioxidant functions are present in the same molecule, or when mechanistically
Oxidative degradation also occurs during the outdoor exposure of plastic products. The photooxidation is initiated by hydroperoxides formed during processing. Hindered phenols are relatively ineffective under photo-oxidative conditions as they are generally unstable to UV light. However, a number of UV stabilizers can act as photo antioxidants and when used with hindered phenolics a synergistic effect is produced resulting in the phenols also being more effective photo antioxidants.
This information is correct to the best of our knowledge, but we would recommend that users make their own assessment to confirm that the material meets their requirements. We accept no liability for any damage, loss, or injury resulting from the use of this information. Freedom from patent rights must not be assumed.