THE INFLUENCE OF RECYCLED MATERIAL ON THE CRYSTALLIZATION KINETICS OFTHERMOPLASTIC POLYMERS

The injection moulding of semi-crystalline thermoplastic polymers requ ires an exact knowledge of the thermodynamic data and of the crystalli zation kinetics. The behaviour of the polymer melt during rapid coolin g in the mould determines, to a great extent, the quality and usabilit y of a final product. Technical raw materials are often equipped with nucleating agents in order to obtain crystallization within the desire d temperature range and at the required rate. The use of recycled mate rial (regranulate) shows an analogous effect such as the addition of n ucleating agents, i.e. crystallization begins at a higher temperature and a higher crystallization rate is detected compared to materials wi thout added regranulate. Heat flux DSC was used to study the crystalli zation of polyamides, polyolefins and polyoxymethylene during cooling at various cooling rates. Although the temperature gradients and press ures which occur in the processing machine cannot be realised in DSC t ests, the DSC results reproduce the direction of influence of the regr anulate additive very clearly.