Measuring Polymer Exemptions with Gel Permeation Chromatography

In 1976, the Toxic Substances Control Act (TSCA) was implemented which empowered the EPA with the authority to require accurate reporting and record-keeping. This was primarily designed to address key hazardous chemicals such as asbestos, lead, and polychlorinated biphenyls (PCBs). Yet the scope also covered typically inert polymeric materials. To promote the manufacture of safer polymers and allow regulatory oversight to focus on higher risk substances, the polymer exemption was written into the TSCA.

In this article, we will explore the polymer exemption in more detail and show how gel permeation chromatography (GPC) can help manufacturers confirm regulatory compliance.

 

What is the Polymer Exemption?

The polymer exemption streamlines the manufacturing and importing process by exempting certain substances from the premanufacture notification requirements of the TSCA. These are established in section five. Qualifying for the exemption requires written certification of compliance – which can be challenging, given that the EPA does not make an independent review. Instead, businesses must correctly interpret the exemption and demonstrate how their polymer meets compliance parameters. This requires a detailed understanding of the chemical identity of the polymer to prove it meets at least one of three exemption requirements:

1. It is a polyester manufactured from a list of acceptable reactants;
2. It is a polymer with a number average molecular weight (MW_n) within a range of 1000 – 10,000, with specific weight percentages for oligomers in the polymeric chain;
3. It is a polymer with a molecular weight of 10,000 or more, comprising an oligomer content of less than five or two weight percent depending on the weight maximum.

The definitions outlined above should only serve as a general impression of the exemption conditions. There are contingencies and complications that should be born in mind when demonstrating compliance. This is why it is often best to rely on a third-party lab testing partner when seeking a polymer exemption.

 

Gel Permeation Chromatography in Polymer Testing

Gel permeation chromatography is one of the leading techniques used to characterize polymeric substances by molecular weight. At RQM+ Service Labs, we have worked extensively with manufacturers to help them demonstrate compliance with polymer exemptions as a function of MW using gel permeation chromatography.

During standardized gel permeation chromatography, samples are dissolved in a solvent and chromatographically separated based on molecular size. Similar to size exclusion chromatography (SEC), the stationary packing medium in the chromatographic column comprises material designed to eliminate chemical interactions between the mobile and stationary phases, ensuring all separations are based purely on size.

At RQM+ Service Labs, we use a 100% divinyl benzene (DVB) resin in our gel permeation chromatography columns, ensuring flawless analytical results for a full spectrum of molecular weight determinations, including distribution and number average. If you would like to learn more about measuring polymer exemptions with gel permeation chromatography, simply contact a member of the RQM+ Service Labs team today.