Plastics Molding & Manufacturing/Plastic Additives
The plastic material itself do not have any desired properties when moulded . Therefore, the plastic material are added with additives to made the final plastic products to be more usable in specific situations
There are two types of additives usually used for the plastic additives: Filler and Reinforcement
Fillers are any additives mixed with a base resin to change the properties of that base resin. Fillers are added to a base resin for many reasons.
2 types of colorants are used for plastics: dyes and pigments that are available as organic and inorganic compounds. The major difference between dyes and pigments is their respective degree of solubility. Dyes tend to be soluble in plastics, while pigments, being insoluble, are simply well dispersed throughout the plastic mass
Plasticizers act as internal lubricants in that they overcome the natural attractive forces between molecular chains of the plastic and minimize the physical bonding of the molecules. As a result, In general, the more plasticizer added to a resin, the greater the flexibility.The most common plasticizers are phthalates, epoxies, adipate diesters, sebacates, and polyesters.
Stabilizers are used for inhibit degradation of the plastic material, either while being processed or in end-use environments. Stabilizers are available in both solid and liquid form and are usually blended in the initial compounding phase of resin manufacture. The most common stabilizers are lead, organotin, cadmium, tin salts, and others.
Antioxidants are used to minimize the deterioration when exposed to heat, light, or various chemicals through reducing the normal tendency of oxygen to combine chemically with hydrocarbons, the basic building blocks of plastic materials. The deterioration will results in brittleness, unstable melt flow properties, loss of tensile properties, and discoloration. Their use can increase the end-use life of a plastic product by up to 10 times .The more common organic chemicals used as antioxidants are phenols,arylamines, phosphites, and various sulfur compounds.
Flame retardants are compounded to the thermoplastic materials (thermoset materials are inherently flame retardant) works on four basic principles: (i) Insulation (ii) Create an endothermic cooling reaction (iii) Coat the base plastic (thereby excluding oxygen) (iv) React with other materials to combat combustion The most common chemicals are both organic and inorganic including such as antimony, boron, halogens, bromine, nitrogen, and phosphates.
Ultraviolet (UV) Light AbsorbersEdit
UV light absorbers are used to stabilize color and lengthen the life of a product by minimizing the degradation effects caused by sunlight which eventually degrades virtually every plastic material. This degradation is manifested by discoloration and loss of physical properties of the plastic product. Black (in any form, whether paint, dye, or carbon black) is the most effective UV absorber, but its use is limited to products that can be black in color. UV absorption capability will be depleted as time goes. Common UV absorbers include benzophenones (especially for clear materials), alkylated hindered phenol, and benzotriazoles.
Antistatic agents are used to reduce the buildup of electrostatic charges on the surface of plastic products or materials by increasing surface conductivity. The most common antistatic agents for plastics include amines, quaternary ammonium compounds, phosphate esters, and polyethylene glycol esters. They are usually classified on the basis of level of concentration required and their effectiveness at low humidity.
A blowing agent (also called foaming agent) are used to produce a cellular structure in a plastic mass, thereby reducing the density and weight of the product. The chemical blowing agents are the most common and range from simple salts (such as ammonium or sodium bicarbonate) to complex nitrogen-releasing materials such as azodicarbonamide, the N-nitroso compounds,and sulfonyl hydrazides.
Lubricants are used to enhance resin processing characteristics and to improve the surface appearance of molded products. They generally fall into five major categories: metallic stearates, fatty acid amides and esters, fatty acids, hydrocarbon waxes, and low-molecular-weight polyethylene.
In summary, the addition of a filler will increase the production cost and reduce the processibility of a plastic material.
Reinforcements are added for increasing only the strength of the base resin. So, a reinforcement could be considered a filler, but fillers are not necessarily reinforcements.
- Anti-microbials - To prevent deterioration of plastic materials where part of the material might be susceptible to microbiological attack.
- Fillers - To reinforce the plastic injection mould
- Flowing agents - To improve injection flow and mouldability
- Release agents - To improve mould releases
- Flame Retardants - To make the plastic products more resistant to the burning