A study of Rodrun LC3000/PP blends under different stationary and non-stationary shear conditions: the influence of LCP content and processing temperature

Susana Filipe^1,2, João Maia¹ , Catarina Rosa Leal³,
Maria Teresa Cidade²

¹ IPC – Institute for Polymers and Composites, Polymer Engineering Department, University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal

²Materials Science Department and CENIMAT, New University of Lisbon, Campus da Caparica, 2829-516 Caparica, Portugal

³ISEL, Polytechnical Institut of Lisbon, Scientific Area of Physics, Rua Conselheiro Emídio Navarro,1,1949-014 Lisboa, Portugal and C.F.M.C.- Lisbon University, Av. Prof. Gama Pinto 2, P-1649-003 Lisboa, Portugal

Abstract

Blends containing liquid crystalline polymers and thermoplastics have been a topic of great interest for the scientific community due to their excellent performance and properties and thus, promising use in industrial applications. For that reason, from the eighties until today, these systems were widely studied and characterized in terms of their mechanical, morphological, and rheological properties under stationary conditions but not under non-stationary ones which are, in fact, those most relevant to processing sequences. Thus, despite all the published work on this subject, there is still a need to study the response of the materials under the latter conditions.

The transient shear measurements performed on the blends of Rodrun LC3000 and PP showed an overshoot for the transient stress, the magnitude of which increases with increasing LCP content. This overshoot is attributed to the orientation and deformation of the LCP structures.

The results obtained for the blends by Large Amplitude Oscillatory Shear, LAOS, were revealed to be highly sensitive (compared with those observed in steady shear measurements) not only to the LCP content, but also to the processing temperature. From the rheological point of view an unusual behavior was observed for these systems, which was characterized by an increase of the viscosity and storage modulus with the increase of the LCP content at low frequencies, but a decrease at high frequencies. The traditional and well-known decrease of steady shear viscosity and mechanical improvement, induced by the addition of liquid crystalline polymer to the thermoplastic, was also observed.