【Popular Science on Polymers and Materials】--008 Bubble gum needs to be chewed before blowing bubbles+jlszhoujidai

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This post was last edited by ljtjbx on 2015-11-9 08:02. Many people like to chew bubble gum; it’s quite hard when first put in the mouth, but after continuous chewing it becomes very soft, and it’s then possible to blow bubbles from it And why is that? Here we learn another characteristic unique to polymer materials—the glass transition. Generally, polymer materials have three mechanical states at different temperatures: the glassy state, the high-elastic state, and the viscous flow state. At lower temperatures, the material is in a rigid solid state, similar to glass; under external forces, it undergoes only very slight deformation. This state is known as the glassy state. When the temperature rises to a certain level, the deformation of the material increases significantly, and within a certain temperature range thereafter, the deformation remains relatively stable. This state is known as the hyperelastic state. As the temperature continues to rise, the degree of deformation increases again, and the material gradually turns into a viscous fluid; at this point, the deformation cannot be reversed, and this state is known as the viscous flow state. We usually refer to the transition between the glassy state and the high-elastic state as the glass transition, and the temperature at which this transition occurs is known as the glass transition temperature, or simply the glass temperature. The main component of bubble gum is polyvinyl acetate, whose glass transition temperature is around 28 degrees Celsius. Under normal conditions, the temperature is below this value, so the bubble gum has little fluidity and maintains its shape; however, when chewed in the mouth, the temperature rises above the glass transition temperature, causing the bubble gum to undergo a glass transition from a glassy state to a highly elastic state. That’s why it’s not possible to blow bubbles at first when starting to chew bubble gum – only after the temperature rises and the gum becomes softer can bubbles be blown.