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Name: Haley
Status: student
Grade: 9-12
Location: OR
Country: USA
Date: April 7, 2011


Question:
What happens when a plasticizer is applied to a plastic as a additive? What happens to the polymer structure? Does the polymer change chemically at all?



Replies:
Hi Haley,

The polymer molecules do not change their primary structure (the atoms and the bonds), but it does change its secondary and tertiary structure. The plasticizer disrupts the crystallinity of the polymer and disrupts the polymer-polymer bonding structure, which is what causes the macroscopic part to become "softer".

Hope this helps, Burr Zimmerman


Haley,

Think of polymers as a very long, often linear, connected strands of atoms. You could imagine a single polymeric molecule as being a long piece of thread, or a very long string of beads. When many polymeric strands are put together, they tend to entangle with each other - much like many different threads will form an entangle ball of yarn. This makes it difficult for any individual strand to move.

If energy is applied to a single polymer strand so that it tends to move in a particular direction and there is already another polymer strand in that direction, then in order for the first polymer strand to move, the second polymer strand must move also. This is why polymers tend to be very viscous (in either solid or liquid form) at normal temperatures.

Plasticizers are small molecules that do not bind with the polymer. Since they are small and have low intermolecular interaction, they tend to be mobile - able to move easily through the strands. Now, when a polymer tries to move and a plasticizer is in the location where the polymer strand is trying to go, the plasticizer can move aside with little energy, and the polymer strand can move into the plasticizer location with less energy.

Thus, a plasticizer does not really change the polymer molecular structure. Rather, it lowers the energy requirements for bulk mobility.

Greg (Roberto Gregorius) Canisius College


Hi Haley,

Plasticizers are added to some types of plastic, to make them more flexible. The most common example is Polyvinyl Chloride, which is quite hard an brittle in the pure state. Commonly, plasticizers such as Polyvinyl Acetate are added to achieve varying degrees of flexibility as desired. Most other common plastics such as ABS, polystyrene, polycarbonate, polyethylene, polypropylene, and others, do not have plasticizers mixed with them.

The plasticizer material is simply mixed with the plastic and forms a sort of "alloy", not unlike what happens when two different metals are mixed. The base polymer does not change chemically. Typically, a plasticizer works by fitting between the long chains of a polymer's molecules, and causes them to separate slightly. This reduces the strong attraction between polymer chains, and results in increased flexibility.

Over time, and especially with exposure to solvents, some of the plasticizer can be dissolved (or "leached") away, and the polymer will then become less flexible. A good example of this is seen with ordinary clear, flexible "vinyl" tubing. It was once common to use this tubing to carry gasoline (for example, to carry gasoline from the tank of a motorcycle to its carburetor). The result was that over time, the gasoline dissolved and removed much of the plasticizer, resulting in the tubing reverting back to nearly pure polyvinyl chloride and becoming very hard and brittle.

Regards, Bob Wilson



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