Polymer structure modification external plasticization

The antiplasticization phenomenon is presumably common to all the polymers exhibiting a relatively strong (5 transition, well separated from the a transition. It has been observed for both linear (PVC, polycarbonate, poly-sulphones) and network polymers (amine-crosslinked epoxies). For the case of thermosets, the phenomenon may be a consequence of both internal (change of the network structure) and external (incorporation of miscible additives) modifications of the structure or the composition but it always seems to be a consequence of the plasticization, as shown in Fig. 11.7. 

In contrast to use of the term in other categories of additives, external plasticizers refer to additives blended homogeneously into the resin. The term internal plasticizer refers to modification of the molecular structure of the polymer by incorporating comonomers that provide greater flexibility. 

Such information offers an opportunity to study details of the fibrillation mechanism. The fibers formed by stretching the spherulitic polymer representing nothing other than ribbon formations plastically deformed and oriented towards the mechanical stress that is released by comparatively weak mutual interconditions existing in an earlier formation (Figure 3). This behavior points to the existence of some weak surfaces in the crystalline polymers. Elements of the super-molecular structure detached by action of the external mechanical forces can slide on the weak surfaces. Evidence for the strain-destruction relationship must come from studies of the modification of the contact surfaces of two neighboring spherulites under mechanical stress. 

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