Melt Processing of Polymers

Polymers that are difficult to process in the melt, either because the melt viscosity is too high or because they decompose, can often be processed at low temperatures through the addition of a plasticizer, leading to improved flow properties and lower processing temperature. 

If a suitable press is not available, one may improvise as follows The heating plates of two electric irons are first bored to accept a thermocouple and then connected in parallel to the power supply through a variable transformer. A calibration curve is determined for the temperature attained at different voltages. For the preparation of a film the finely powdered polymer is placed, as described 

---

As previously stated, molecular orientation occurs during melt processing of polymers. On removal of the deforming stresses the molecules start to coil up again but the process may not go to equilibrium before the polymer cools to below its Tg. This leads to residual orientation (frozen-in strain) and corresponding frozen-in stresses. 

Fig-1 Schematic illustration of the crystallization and melting processes of polymers. The crystallization process corresponds to processes of disentanglement and chain sliding diffusion. The melting process is the reverse of the crystallization process. Between equilibrium melt and ideal crystal, there exists metastable melt and crystal. Cross marks indicate entanglement... 

Note 1 Phase inversion may be observed during the polymerization or melt processing of polymer blend systems. 

Scheme 1.70. Pro-oxidant activity of alkyl mercaptans (a) and both pro-oxidant and delayed antioxidant activity of diphenyl disulfides (b) during melt processing of polymer PH containing hydroperoxide groups POOH. After Scott (1993b).

OTHER FACTORS AFFECTING THE MELTING PROCESS OF POLYMER CRYSTALS... 

FIGURE 6.1 Mixing in the major routes for melt processing of polymers to finished products. (Reprinted by permission of the publisher from Matthews, 1982.)... 

---