Meaning
The decrease in the temperature at which an amorphous polymer transitions from a hard, glassy state to a flexible, rubbery state occurs when small molecules disperse within the polymer matrix. This thermal phenomenon is termed glass transition suppression, and it is caused by the lubricating action of plasticizers or absorbed solvents. It increases the free volume between the polymer chains, allowing them to move more freely at lower temperatures.
Such a reduction is important in formulating flexible vinyls or when polymers absorb moisture or organic solvents from their environment.
Plasticizer Action
Formulators exploit glass transition suppression to modify the mechanical properties of brittle resins. The addition of high-boiling esters to polyvinyl chloride shifts the glass transition temperature below room temperature. This change transforms a rigid engineering plastic into a flexible, elastomeric film.
However, the plasticizer must remain compatible over the product lifetime to avoid migration and subsequent embrittlement.
Environmental Influence
Absorbed moisture in hydrophilic polymers such as polyamides results in unintended glass transition suppression. During storage or service, water molecules act as an internal plasticizer, lowering the transition point. This absorption shifts the mechanical performance from high modulus to high ductility, affecting part stiffness.
Engineers must account for this shift when designing load-bearing components exposed to humid conditions.
Processing Effect
Moulding processes must adapt to the suppressed transition temperature. Lower temperatures are required for part ejection. This extends the cooling cycle.
Ejection from the mould becomes challenging.
