What factors influence the glass transition temperature of a polymer?
Pressure and free volume. Increase in pressure of surrounding leads to decrease in free volume and ultimately high Tg. Other factors like branching, alkyl chain length, bond interaction, flexibility of polymer chain, film thickness etc. also have significant impact on glass transition temperature of polymers.
How can you increase the glass transition temperature of a polymer?
These can be done by controlling cooling rate and isothermal time during heat treament, and polymer modification, respectively. On the other hand, increasing pressure to polymer will also increas molecular crowing and interaction, resulting increased Tg.
Which of the following polymer will have highest value of TG?
These types of interactions increase the rigidity of polymeric material therefore increase the glass transition temperature. Polyvinyl chloride has higher Tg than polyethylene and Nylon-6 also has higher transition point than polyolefin.
What does low Tg mean?
At temperatures below the Tg, the molecular chains do not have enough energy present to allow them to move around. The lower slope below the Tg is due to the lower heat capacity for the amorphous polymer. Above the Tg, the rubbery, flexible polymer has a higher heat capacity.
What is the Tg of polypropylene?
The glass transition temperature (Tg) is one of the most important thermophysical properties of amorphous polymers….Glass Transition Temperature of some Polymers.
| Polymer | Tg (K)a,b |
|---|---|
| Polypropylene (PP) | 260 (239) |
| Polyethylene (HDPE)* | 148* (148, 186, 238) |
What is TG and TM in polymers?
Tg (glass transition temp ) – the onset of segmental motion of the polymer backbone. The noncrystalline portion of the material exhibits a Tg . · Tm (melting point ) – temp.
What is the glass transition temperature of natural rubber?
-70
What is the effect of heat on thermoplastics?
The plastic begins to soften and lose its stiffness as the material temperature increases and if you heat it long enough or exceed the limit of its operational temperature range, it will begin to distort.
Does heat make plastic brittle?
Chemical failure occurs as a result of exposure to extreme temperatures. If a product is exposed to a very high temperature it can melt and warp. On the other hand, plastic products can become brittle when forced to endure extremely cold environments, which can make them prone to cracking and shattering.
Do polymers expand when heated?
The extent to which the polymer expands or contracts when heated or cooled. They contain strong covalent bonds along the polymer chain and much weaker dispersive forces between the polymer chains. As a result, polymers can expand by differing amounts in different directions.)