Chemical and Biomolecular Engineering

Official blog of the Lehigh University Chemical Engineers

Glass Transition in Polymers

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I’m currently taking Physical Polymer Science class as my Chemistry 300 level class requirement. In order to graduate, you need to have 3 credit hours of ChE 300 levels or higher. Polymers are so common in everyday uses, it is everywhere. For example, it made the plastic bottles that we use, credit card that we swipe, or gums that we chew. In Polymers lately, I’ve learned some fundamentals of glass transition states in polymers.

The glass transition is something that is unique to polymers. There’s a certain temperature where the property of the polymer will be changed differently. The temperature is called the glass transition temperature, Tg. When a polymer is cooled below this temperature, it’ll become hard and brittle and easy to break. When the polymer is above this temperature, it’s soft and rubbery. Some polymers are used above Tg and some are used below Tg, depending on where we use it from. Also, Tg varies for different polymers. Glass transition is different from melting though. Melting only happens in crystalline polymers, where polymers chains are lined up in ordered crystals. Glass transition is unique to largely amorphous polymers, where chains are randomly coiled around and in solid state. So therefore, when a polymer has both crystalline portion and amorphous portion, the crystalline portion will undergo melting, and amorphous portion will undergo glass transition. Here’s a short video showing a piece of gum experiencing glass transition.

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Author: Jerry Jin

Hello, My name is Jerry Jin. I'm a senior at Lehigh University pursuing a degree in Chemical Engineering. I'm from Allentown, PA, but I was born in Shanghai, China. I moved here when I was fourteen years old. I'm currently the secretary for Southeast Asia at Lehigh Club, and treasurer for SASE. I'm also on the Lehigh Ultimate Frisbee Team and I enjoy being spontaneous.

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