[tone999]

Q. Briefly describe what is meant by the glass-transistion temperature (Tg) for plastics and how the Tg of polyvinyl chloride is significantly altered by use of an additive.

A. The temperature at which an amorphous solid, becomes brittle on cooling, or soft on heating.
PVC in its pure form is a hard and rigid material with additives it can transform it into a soft flexible material.

Is this good enough? Is it even correct?

[DrCMS]

So what do the additives do to the Tg raise it or lower it?
What are the additives called?

[typhoon2028]

In your explanation of Tg, you may want to reference how the heat capacity changes.  In addition, you might want to explain how glass transition differs from melting.

[tone999]

Do the additives lower the Tg of PVC, yes? Is plasticisers the main additive?

[typhoon2028]

Yes plasticizers lower the Tg.

PVC has many several additives.

[tone999]

Thanks guys