Question

Draw a log modulus–temperature plot for an amorphous polymer. What are the five regions of viscoelasticity, and where do they fit? To which regions do the following belong at room temperature: chewing gum, rubber bands, Plexiglas®?

Answer 1

viscoelastic curve represents the relationship between a sample's temperature and its modulus. The modulus is a measure of the sample's resistance to being deformed by an imposed stress. The curve is divided into main regions(A-E).

A - Glass. The material is rigid, yet brittle if not reinforced by chemical crosslinks or crystallites. Polystyrene and plexiglass are amorphous glasses at room temperature.

B - Glass Transition Zone. The material starts to become compliant over time (at constant temperature), or in a narrow temperature range.

C - Rubber. The material is very flexible, capable of being stretched to several times its original dimensions without breaking. Commercial rubbers are chemically crosslinked to keep them from softening at elevated temperatures.Rubber band belong to this category

D - Rubbery Flow Zone. The material becomes tacky, and will spread like a liquid if pressure is applied. Pressure-sensitive adhesives are designed to exhibit this behavior at room temperature. Chewing gum belong to this category

E - Polymer Melt. As the polymeric material is heated beyond the rubbery flow zone its viscosity steadily decreases. As the viscosity (resistance to flow) decreases, so does the materials modulus. This is the processing region of the viscoelastic curve.