ASTM D2117, Hot Stage Microscopy, & A Holiday Puzzle

What is our favorite type of science? The type of science that allows for the fusion of creativity and great scientific practices. Yes—creativity has a clear role in analytical chemistry. This curious and creative aspect of who we are often manifests itself in the way we solve our clients toughest problems, when the approach and answers aren’t abundantly clear from the onset. We also know this is one of the aspects of who we are that our clients value most!

Since we love a really good challenge—a “puzzle” if you will—we decided to challenge our clients to solve a puzzle this holiday season, a jigsaw puzzle to be specific. We picked an image that tells the story of who we are and what we do. We also hope that this puzzle is a great excuse to sit down, relax, and enjoy the holiday season.

What exactly is this intricate image found on the jigsaw puzzle? Great question!

The quick answer: The puzzle image is polypropylene under cross-polarized transmitted light, which is called birefringence.

The long answer: This image is a sample that was being tested for compliance with 21 CFR 177.1520 Polyolefins for Food Contact. CFR stands for “Code of Federal Regulations”, which means this test is required by the United States federal government when a polyolefin material comes in contact with food as part of packaging or it’s in-use application.

This particular CFR requires melting point determination in accordance with ASTM D2117. ASTM stands for American Society of Testing and Materials, and these standards are a way to create consistency in testing across different industries. It keeps results comparable and relevant to each other, as they are standardized. In this specific ASTM standard, hot stage microscopy is the required analytical technique.

Hot stage microscopy is a technique in which the “stage”—or area the sample rests on for imaging—is heated and cooled at a controlled rate. This allows us to observe the performance of the sample in response to varied temperatures, while being magnified. Pretty cool, huh?

ASTM D2117 requires approximately 2mg of sample, which must be melted and pressed between the glass slide and glass cover slip. The sample is then cooled at a gradual rate, allowing recrystallization to occur, creating birefringence. This sample was cooled at the extremely slow pace of 0.1°C/min overnight. This allows not just recrystallization, but formation of the nice round spherulites with radiant birefringence. They resemble individual little circular snowflakes (Let it snow!). The sample is then gradually heated and the melting point is determined when the birefringence disappears. You can watch the progression of the disappearing spherulites in the images below.

We are thankful that each and every day in our labs is an opportunity to solve the toughest of materials science challenges for our clients around the world. On behalf of the curious and creative scientists of Polymer Solutions, we wish our clients the happiest of holidays!

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