Additive | Antioxidant

Antioxidant Masterbatch

Antioxidant Masterbatch consists of a concentrated mixture of pigments and/or encapsulated additives manufactured by heating a carrier resin and then cooling it and cutting it into granules. The masterbatch thus allows the transformer to colour and give characteristics to the natural polymer economically in the plastics transformation process.

Antioxidant Masterbatch | Technical Advantages | Shelf Life

• Prevents problems of agglomeration of additives or colourants as well as dispersion problems.
• Does not contain solvents and therefore has a longer shelf life.
• Contains an average of 40-65% additive, but the range can reach 15-80% in extreme cases.
• A 25kg bag processes up to one tonne of raw material. Thus, the relatively dilute nature of the materbatches allows for greater precision when dosing small quantities.

Carrier and Dosage

The carrier of the masterbatch should be identical/compatible with the polymer. For example, EVA or LDPE is a carrier compatible with polyolefins and nylon, just as polystyrene is used as a carrier for ABS, SAN and sometimes polycarbonates.

In this sense, when the masterbatch carrier is incompatible with the raw material, changes may occur in the properties of the processed material. The processor must specify the characteristics of the raw material. The percentage of use of masterbatches in relation to the raw material is between 1 and 5 %. Colour and additive masterbatches can be combined.

Adverse effects

• Adverse effects sometimes occur, such as the masterbatch separating from the raw material in the machine hopper.
• The masterbatch, solid or liquid, is added directly to the machine spindle via a peristaltic pump.
• The use of liquid masterbatches also makes it possible to obtain highly precise dosages and rapid colour changes between production runs.

Antioxidant Masterbatch | Transformation processes

Masterbatches are compatible with most processes, with the exception of rotational moulding, plastisol and other liquid resin systems.

Antioxidants are used to protect polymers from degradation, both during processing (=short term stabilization) and during use (=long term stabilization). Polymer degradation generally results in gel formation and changing melt flow index, loss of mechanical and esthetical properties (crazing, gloss reduction, chalking), and discoloration.

Generally during polymer degradation free radicals are formed, resulting in uncontrolled chain reactions. Anti-oxidants are used to decrease the amount of free radicals by different mechanisms e.g. by avoiding the formation of free radicals using complexing agents or hydroperoxide decomposers, or by decreasing the amount of radicals using radical scavengers or hydrogen donors.

A complete range of anti-oxidants exist, starting from cheaper, general purpose anti-oxidants, up to anti-oxidants specially designed for high end applications like hot water pipes. High end anti-oxidants typically have better properties towards discoloration (yellowing/pinking), migration/chalking or hydrolisation.

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