The properties of polymer melts are different from those of monomeric materials because polymer materials have crystalline and amorphous regions. In addition, polymer melts exhibit elasticity as well as viscosity. Therefore, the viscoelasticity, crystallinity and temperature of polymer melts must be considered for an accurate simulation of the melt spinning process for crystalline polymers. In this study, we simulated the melt spinning process of Nylon-6 by using the streamline-upwinding finite element method. The non-isothermal Phan-Thien Tanner model proposed by Sugeng and Phan-Thien was employed as a constitutive equation. We investigated the distribution of temperature and crystallinity on the free surface of the filament, and the filament diameter.
The calculations were nearly independent of gravity. The primary normal stress increases and the filament diameter decreases with an increase of take-up speed. The filament diameter obtained by the non-isothermal flow simulation is smaller than that for the isothermal case, and the filament diameter depends on the crystallinity. The filament shape for a purely viscous fluid is the same as that for a viscoelastic one.

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Glass-fiber (GF) reinforced polypropylene (PP) is a very important industrial material. However, as PP is a non-polar polymer, the interfacial adhesion strength between PP and GF is very weak. In order to resolve this problem, maleic acid grafted PP (MA-PP) is generally used. In this way the tensile strength of GFPP can be improved remarkably. Moreover long glass-fiber reinforced PP pellets for injection molding have been recently developed. In spite of these improvements, the strength of GFPP still lags those of other GF reinforced engineering plastics. In order to improve the strength of GFPP, it is necessary to reinforce the weakest of the many interfaces and interphases in the GFPP system. It was found that the interface between the malefic acid grafted PP and the neat matrix PP is the weakest layer. Thus, to reinforce this interface, it is important to increase the entanglement between the MA-PP and PP molecules. It was found that the strength of GFPP could be improved by using high molecular weight MA-PP.

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