Data for Processing Description of Crystallizable Polymers

Research project P 14402 Data for Processing Description of Crystallizable Polymers Gerhard EDER 26.6.2000 As is well known, crystallization in polymer melts is considerably enhanced by all kinds of flow. But this means, that consequences of previous flow can be recognized in the cross-sections of almost all plastic manufactures which are made in traditional industrial processes like injection molding. All the mentioned products also show the marks, which are left behind the unavoidable cooling processes which must finally lead to the necessary solidification. The obtained structures determine the quality of the product (warping, fracture mechanism, tensile strength, ...). Thus there is a strong need for understanding of the underlying processes of structure development in order to be able to optimize the manufacturing process and to end up with better products. This understanding, however, goes hand in hand with the ability to integrate interfering transport phenomena as there are heat transfer, rheology and crystallization kinetics. Whereas less critical parameters like densities, heat diffusivities and latent heats can be measured and introduced in calculations without too much risk, the situation is extremely critical with respect to the parameters of crystallization kinetics, as there are nucleation rates and growth speeds as strong functions of temperature and flow (histories). Growth speeds sometimes also show directional dependences, if flow is at stake. And just these parameters are manly responsible for the structures (morphologies) obtained in the final product. In the past the behavior of melts has been investigated in stationary state (i.e. at rest) and under rather extreme conditions of flow, mainly at Linz University. In this connection (fast) shear flow has been preferred for practical reason. A treatment of (fast) elongational flow is on the road. With respect to milder flow conditions, however, not much is known at present. Wolkowicz has stated long ago, that in contrast too fast flow, where (highly oriented) shish-kebab structures are created, in mild flow only the number of neclei is increased with respect to the quiescent melt. This number obviously depends on the flow conditions, like flow rate, flow time, or, more accurately, on the whole flow history. The task of the present project is to vary the said parameters systematically together with temperature, in order to get more insight in the solidification process. The machines for the investigation of shear flow have been developed already, and for elongational flow they are in a far going state. They should work under serious conditions even better, than under the extreme conditions as used up to now.