What are the ingredients in plastics?

Plastic materials offer a wide variety of properties and design flexibility that have made them the material of choice for making many different products. From injection molded toys to machined bearings or bushings, plastics are allowing for creative ideas to become realities in a more affordable way to solve difficult problems. There are times when a plastic material by itself, may not be able to meet all of the demands of particular application. When an alternative material becomes cost prohibitive or will not work either, there are some options that can make the palstic material suitable for use.

Different things can be introduced to help enhance a specific property or set of properties to help the plastics sheet, rod, tube or film bridge the gap in performance. In this article, we will endeavor to explain and/or clarify some commonly used and confused terms.

Additives:

Additives are a general term referring to anything added to a plastic.  This term covers both fillers and reinforcements. The term additives refers to a wide range of chemicals that are added to plastics. The major categories of additives are antioxidants, antistatic agents, colorants, coupling agents, curing agents, flame retardants, foaming/blowing agents, heat stabilizers, impact modifiers, lubricants, nucleating agents, plasticizers, preservatives, processing aids and UV stabilizers. Most additives are compounded into base material prior to manufacturing.

Reinforcements:

Reinforcements are used to improve tensile strength, flex strength and stiffness of a material. There are many reasons for adding reinforcements. One important reason is to produce dramatic improvements in the physical properties of the base material. Reinforcements are often confused with fillers. Fillers are small particles and contribute only slightly to strength (see next section). On the other hand, reinforcements are ingredients that increase strength, impact resistance and stiffness. One major reason for the confusion is that some materials may act as a filler, reinforcement or both.

Fillers:

Fillers are things added to plastics to control other properties such as impact modifiers, lubricants, glass beads, MoS2 and the like. The term filler is often confusing. Filler was originally selected to describe any additive used to fill space in the polymer to lower cost. Because some fillers can be more expensive that the base material, the word extender can be misleading. The terms dilutant and enhancer are sometimes used to describe the addition of fillers. Ambiguity of terms and and overlapping of function add to the problem. For our purposes, a filler will mean any minute particle from various sources, functions, composition and morphology.

According to ASTM, a filler is a relatively inert material added to a plastic to modify its strength, permanence, working properties or other qualities or to lower costs. Fillers can be both organic and inorganic ingredients of plastic resins. They can increase bulk or viscosity, replace more costly ingredients, reduce mold shrinkage and improve physical properties of the composite item.