Polymer nanocomposites have different properties depending on dispersion states even at same concentration. The methods of assessing dispersion states as well as controlling dispersion quality are quite important to industrial area. To verify the degree of dispersion, optical analysis, e.g. TEM, XRD, SAXS and also rheological measurements are mainly employed. In rheological measurements, storage modulus (G’) from SAOS (small amplitude oscillatory shear) test is the well-known parameter to represent dispersion quality. G’ at low frequencies (terminal region) exhibits higher values and lower scaling behavior with power (G'∝ωⁿ, n become less than 2 for polymer melt) than matrix polymer as filler content increases. However, SAOS results are not enough to present the degree of dispersion quantitatively. In order to quantify the degree of dispersion, Lim et al.[1] studied PCL nanocomposites with various fillers and then suggested new parameter, NLR (Nonlinear-Linear viscoelastic Ratio) from LAOS (large amplitude oscillatory shear) test. With increasing concentration, NLR values rose and reached a plateau. In this study, we investigated that NLR is valid parameter revealing the degree of dispersion using polypropylene(PP)/clay(C20A) nancomposite with maleic anhydride grafted polypropylene(MAPP). Due to the absence of polar group on backbone, PP is considered poor matrix when mixed with polar filler like clay. MAPP has been utilized as compatibilizer because it is compatible with PP and clay both. We manipulated the contents of MAPP and viscosity of matrix PP to change degree of dispersion. NLR value is raised when MAPP was added and the viscosity of matrix was decreased. It was found that NLR value is related with degree of dispersion of clay.
[1] Lim, H.T, K.H. Ahn, S.J. Lee, J.S. Hong, and K. Hyun, J. Rheol., 57, 767 (2013).
Keywords: Maleic anhydride grafted polypropylene, Cloisite 20A, FT-rheology, NLR, LAOS, Q₀