i want to understand the principle.
when plasticizer added to polymer, why tg falls?
please let me know?
The answers are already there. Plasticers sit in between chains and minimize secondary interactions so that the polymer chain segments are relatively free to move. That means the chain segments maintain their mobility up to lower temperature than normal. On further cooling the plasticizer imparted mobility also freezes to undergo glass transition. Thus Tg depression occurs.
Probably, an addition of plasticizer increases the mobility of polymeric chain by disrupting the chain entanglements and cohesive forces among them. As a result, the polymer becomes soft and pliable.The change in molecular dynamics causes the glass transition temperature of polymers to drop down.
This is exactly the effect to be expected by adding a plasticizer. The latter may also break some secondary bondings in the polymer network, so that the individual chains don't do hydrogen bonds between them, for example. As a consequence, the chains can move far easier than before, from where the drop of Tg which is the temperature above which mobility starts. With a higher mobility, it is clear that the polymer is soft at lower temperatures than before, i.e., Tg is lower with plasticizers.
Alain
Plasticizers acts as lubricant to improve the polymer chain mobility at lower temperatures by decreasing the friction between the chains through intercalation phenomena and sometimes even they can dismiss the secondary interactions with their ability to interact with polymer chains.
Dear all;
Tg is a second order transition at localized segments of the polymer chains; most probably of a crank-shaft movement. This needs a sufficient space or volume to be possible. This is normally seen when the thermal energy is sufficient to provide an additional spacing which favor this motion. A plasticizer acts in similar manner, it goes beneath the macromolecules and reducing there secondary forces and create additional free volume for localized rotational motion.
At the Tg motion of the whole chains are not possible since still not enough energy. The motion of the whole macromolecules is a feature of melting Tm. Regards
diisononyl phthalate (DINP)
diisodecyl phthalate (DIDP)
di-2-ethylhexyl phthalate (DEHP, sometimes also referred to as DOP
all are stabilizer for PVC
A plasticizer is a liquid that is added to a material (usually a resin or elastomer)
making that material softer, more flexible (by decreasing the glass-transition
temperature Tg of the polymer), and easier to process.
Plasticizer comes in two types. 1) Internal and 2) External
Internal plasticizer is a inherent part of polymer backbone chain and forms part of product modifying the polymer or monomer so that the flexibility of the polymer is increased.
The external plasticizing route is more common because of lower overall costs. This type of plasticizer are generally low volatile substances. They sit between two polymeric chains thereby increasing distance between them and hence increasing mobility. This type of plasticizer comes in two types:- Primary and Secondary.
A primary plasticizer, when added to a polymer, causes elongation and softness to be increased.A secondary plasticizer, when added
to the polymer alone, does not bring about these changes and may have limited
compatibility with the polymer. However, when added to the polymer in combination with a primary plasticizer, secondary plasticizers enhance the plasticizing performance of the primary plasticizer. Secondary plasticizers are also known as extenders.
So basically as softness, mobility and flexibilty of polymer increases, Tg decreases with it. For further literature you can refer this attached file.
Plasticizers are long chains that depart the main polymeric chains from each another, therefore their movement is easier. Tg is the temperature at which the polymer chains begin to move, so, by addition of plasticizer the movement will occur at lower temperatures.
when adding plasticizer to PVC, the crystalline decreased, so the Tg decrease.
The answers are already there. Plasticers sit in between chains and minimize secondary interactions so that the polymer chain segments are relatively free to move. That means the chain segments maintain their mobility up to lower temperature than normal. On further cooling the plasticizer imparted mobility also freezes to undergo glass transition. Thus Tg depression occurs.
Plasticizers typically work by embedding themselves between polymer chains, pushing them apart therefore increasing the free volume of the polymer material which in turn lowers the glass transition temperature by allowing for the segmental diffusion to occur at a lower temperature.
PVC is an example of a material where plasticizers are used to optimize mechanical properties which are also affected by the free volume within the material allowing PVC products to range from stiff and rigid to relatively flexible.
PVC is a brittle polymer. Therefore plasticizer is added to reduce the Tg. This addition also makes the processing better without degradation. The plasticizer sits in between polymer chains. It reduces the secondary interaction between polymer segments. At Tg the segmental motion starts. As the secondary interaction is reduced by plasticizer, the segmental mobility needs less energy and the Tg goes to lower temperature.
when plasticizer added to polymer like PVC, improved flexibility and durability. Then viscosity decreas and increasing the free volume and thus significantly lowering the TG the glass transition temperature for plastic (PVC).
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