Plastic Additives
Additives are usually added into polymers to modify and improve certain characteristics, such as stiffness, strength, color, weatherability, flammability, arc resistance for electrical applications, and ease of subsequent processing. These additives are described below:
1. Fillers
Fillers are particles added to plastics to lower the consumption of more expensive binder material or to better some properties of the mixture material. Formerly, because of their lower cost, fillers also reduce the overall cost per unit weight of the polymer. Today, it has been proven that fillers are also able to enhance technical properties of the products. The effectiveness of filler depends on the nature of the bond between the filler material and the polymer chains. Most thermoplastics and some thermosetting plastics contain fillers.
Fillers are generally wood flour, silica flour, various minerals, powdered mica, and short fibers of cellulose, glass, and asbestos. Depending on their type, fillers improve the strength, hardness, toughness, abrasion resistance, and stiffness of plastics. These properties are maximized at various percentages of different types of polymer/filler combinations.
2. Plasticizers
Plasticizers are low-molecular-weight solvents (with high boiling points, i.e., nonvolatile) that reduce the strength of the secondary bonds between the long-chain molecules of the polymer, and give flexibility and softness to the polymer by lowering the glass-transition temperature. The most common application is in PVC, which remains flexible during its many uses.
3.Stabilizers
Polymers are considered to get weathered due to the direct or indirect impact of heat and ultraviolet light. So, stabilizers are used directly or by combinations to avoid making polymers rigid and brittle. A typical example of protection against ultraviolet radiation is the compounding of rubber with carbon black (soot). The carbon black absorbs a high percentage of the ultraviolet radiation. Protection against degradation by oxidation, particularly at elevated temperatures, is done by adding antioxidant to the polymer. Various coatings are another means of protection against degradation.
4. Colorants
The great variety of colors available in plastics is obtained by the addition of colorants. These are either organic(dyes) or inorganic(pigments). The selection of a colorant depends on service temperature and exposure to light. Pigments, which are dispersed particles, generally have greater resistance to temperature and light than dyes do.
5. Flame Retardants
Flame retardants are chemicals used in thermoplastics or thermosets, that inhibit or resist the spread of fire. The flammability of polymers can be reduced either by making them from less flammable raw materials or by adding flame retardants to the compound. Common flame retardants are chlorine, bromine, and phosphorus compounds. The flammability (the ability to support combustion) of polymers varies considerably, depending on their composition, such as the chlorine and fluorine content. Polymethylmethacrylate, for example, continues to burn when ignited, whereas polycarbonate extinguishes itself.
6. Lubricants
Polymers tend to be relatively viscous and “sticky” above their melt temperature. To reduce friction during molding process and to prevent sticking to the molds, lubricants are added to polymers. Lubrication is also important in preventing thin polymer films from sticking together.
7. Polyblends
When polymers are blended with small amounts of rubbery polymers, they can have a rubbery behavior. Usually, rubbery polymers are finely dispersed throughout the polymer and improve its impact strength.
- Material
- Injection Molding
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