Control of strain hardening of polymer melts under elongational flow

Abstract

This paper includes two topics on the nonlinear elongational flow behavior from the viewpoints of a small amount of long relaxation time mode and physical gelation network structure. First one is polypropylene (PP). PP is a well- balanced material in terms of the physical properties such as the stiffness and heat resistance, and the cost. PP is, however, one of the linear polymers exhibit low melt strength and weak strain hardening. We focused on an introduction of a small amount of high molecular chain in order to enhance the strain hardening under elongational flow. This system showed unusual rheological behavior: strong elasticity, two-step nonlinear damping, strong strain hardening. This polymer system is very complex comparing with conventional PP in terms of the miscibility of the matrix and ultra- high molecular weight component. Another is poly(vinyl chloride)(PVC)/plasticizer systems. PVC forms physical gels in various solvents. We focused on the rheological behavior of high PVC concentration systems, since the physical properties and structure have been extensively studied mainly for low polymer concentration system. PVC/DINP system showed same relaxation exponent n with the value of the low concentration system reported previously. We observed change of the elongational flow behavior of sol-gel system such as PVC/plasticizer system with temperature. These behaviors from the view point of critical gelation phenomena has not been reported so far as much as we know. © 2008 The Society of Rheology, Japan.