Commercially available plastic resins and rubber compounds are rarely used in pure form. Generally, to be useful, these polymer materials contain various types of additives at specific concentrations. There are numerous unique classifications of additives that are used in plastic and rubber materials. It is common for polymer materials to contain several combinations of additives in concentration ranges from parts per million to high percentage values. 

Additives serve a wide variety of purposes when incorporated into polymer materials. Additive packages can include air release agents, fillers, flame retardants, heat stabilizers, and lubricants, to name a few. These additives are intentionally incorporated into polymers to tailor their performance, processing and long-term stability. 

However, the use of additives can also create unintended consequences for the manufacturer. The additives have the potential to generate excessive costs and reduce profit margins, yield out-of-compliance products, and cause alleged patent infringement. Let's take a look at how the use of additives can lead to unintended consequences. 

Verification testing

Although there are starting point formulations and ranges of concentration that are offered by the manufacturers of the additives, it is important to produce trial plastic resins or rubber compounds and verify the functional performance. Manufacturers of additives may recommend higher loading levels than are required. However, too much of a good thing can be quite bad, both for the bottom line and for the performance of the finished product. Therefore, experimentation and evaluation are required to tune the additive level to optimally meet the needs of the specific application in a cost effective manner. 

In addition, the particular combination of additives can have positive or negative synergistic effects that cannot be entirely predicted. This risk further supports the need for systematic formulation development, performance verification, and composition optimization. It is possible that an intentional ingredient contains a measurable amount of a minor ingredient. For example, if didecyl phthalate is used at a modest level to plasticize a child care article, as defined by the Consumer Product Safety Commission, that phthalate may contain dioctyl phthalate (DnOP or DEHP) as an impurity. Because the ban on this plasticizer requires that the DnOP or DEHP concentration be below 0.1%, one could end up in the unintentional situation wherein the didecyl phthalate incorporated into the polymer has also inadvertently caused DnOP or DEHP to be incorporated at a level in excess of 0.1%, thus creating a non-compliant product. 

Understanding the actual composition

Minor ingredients, contained in additives, can also create situations wherein a manufacturer is alleged to infringe on a patent. This condition can occur as a result of ingredients that are a trace component of an additive. It is the responsibility of manufacturers to fully understand the actual composition of the products they make and sell. Particularly dangerous to an unsuspecting manufacturer is phrasing within relevant patents that state, "a composition containing *a chemical ingredient*..." with no established lower limit of the concentration of the chemical ingredient within the patent. This is in contrast to patents that state, "a composition containing 3 to 8% by weight of *a chemical ingredient*..." In the first example, detection of any amount of the chemical ingredient, 100 parts per million for example, may be interpreted as an infringing composition of matter.  In contrast, 100 parts per million of the chemical does not infringe on the patent that claimed "3 to 8% by weight."

The selection of additives for a particular application is based on the attribute that each additive contributes. The formulator must balance cost, physical properties, processing characteristics, and toxicity, for example. Truly, much of the "magic" of high performing polymer materials is in the additives package. Therefore, proper additives selection is crucial for safe, properly functioning, cost effective products that meet customer expectations.

Table 1: Additives used in plastic and rubber materials

Jim Rancourt is the Founder of Polymer Solutions Incorporated, an independent testing laboratory that has been serving high-consequence clients since 1987.  The ISO 17025 accredited, FDA registered, and GMP compliant PSI laboratories provide spectroscopy, microscopy, chromatography, thermal analysis, physical testing, wet chemistry, technical consulting, and expert witness services.