Page 381 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

PLASTICS ADDITIVES 5.61

vent such sliding. Antislip agents for polyolefin films are often materials such as
oleamide in PE or erucamide in PP, used at about 0.05 percent.
• Antifog agents are added to films to keep moisture condensation from clouding them
and preventing the passage of light. Typical uses are in polyolefins, polystyrene, PVC,
and polyester films, as an aid in marketing refrigerated and frozen foods, and in plastic
film for greenhouses. These are hydrophilic organic compounds such as mono- and dig-
lycerides, higher-polyol partial esters, and ethoxylated phenols and fatty alcohols and
acids, used at 0.5 to 4.0 percent, at a cost of $0.80 to 4.00 per pound. They adsorb mois-
ture and spread it into a continuous transparent surface film rather than the opacifying
droplets that normally form on a low-polarity plastic surface.
• Water repellants are sometimes used in surface treatments such as isobutyl trimethoxy
silane.

5.12.3 Degassing Agents
Compounding and mixing of liquid systems often traps air, or volatile liquids that volatil-
ize during processing, forming bubbles and other flaws in the finished products. Several
types of additives are used to remove these volatiles before they cause trouble.

• Humidity eliminators are used to absorb moisture from PVC plastisols and other liquid
systems, to prevent blistering, bubbles, and craters. A typical system would be a combi-
nation of calcium oxide plus a wetting agent.
• Air-release agents are added to liquid epoxy, polyester, and polyurethane systems to re-
move air bubbles before cure. These function by their surface activity. They are mostly
proprietary compositions.
• Antifoam agents are added to latexes to prevent air from producing foam that would ruin
the dried final coatings. Typical antifoams are octyl alcohol and liquid silicones. They
must be chosen with care to avoid negative effects on adhesion and decoration of the
finished products.

5.12.4 Oxygen Scavengers
These may be added to PET bottle resins to protect the contents against attack by atmo-
spheric oxygen. They are mostly proprietary.

5.12.5 Epoxy Diluents
When an epoxy resin formulation is too viscous for the intended process, it may be
thinned by adding low-molecular-weight liquids. These are preferably mono- or diepoxy
monomers, smaller than conventional bisphenol epoxy molecules, which can react right
into the finished resin without sacrifice of properties. Some formulators may use nonreac-
tive diluents, but these may detract from finished properties.

5.12.6 Fragrances
Chemical fragrances are added to products either to produce a desired odor (“decorative”)
or to mask an undesirable odor (“functional”) in a material or an environment. They are
generally perfume oils that are masterbatched into thermoplastics, often combined with

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2006 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.