Dynamic viscoelastic behavior of polypropylene/polybutene‐1 blends and its correlation with morphology

Abstract

In this study the rheology, morphology, and interfacial interaction of polypropylene (PP)/polybutene‐1 (PB‐1) blends in different percentages of PB‐1 are investigated. The morphology of cryo‐fractured surfaces of samples was studied by scanning electron microscopy (SEM). The SEM images showed a droplet‐matrix structure in all range of compositions and the size of dispersed phase increased proportionally with PB‐1 content. The miscibility of blends at various compositions is evaluated by viscoelastic parameters determined by dynamic oscillation rheometry in the linear viscoelastic region. A distinct Newtonian plateau at low frequencies is observed and the variations of complex viscosity (η*) against angular frequency (ω) for all blends are in agreement with Cross model. The complex viscosity of samples at various percentages of PB‐1 showed the log‐additivity mixing rule behavior in low frequencies and positive‐negative deviation behavior (PNDB) at high shear rates. The phenomena such as decrease in the sensitivity of storage modulus to shear rate in the terminal region, the deviation of Cole–Cole plots from the semi‐circular shape, and the tail in relaxation spectrums at high relaxation times are the evidences of two phase heterogenous morphology. The effect of time–temperature on the phase behavior is studied and the interfacial tension between matrix and dispersed phase was evaluated by using emulsion theoretical models. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The impact of viscoelastic behavior and viscosity ratio on the phase behavior and morphology of polypropylene/polybutene‐1 blends

“…a–b. No considerable differences were observed between the predictions of Palierne and Bousmina models, such as in PPB4 blends . The interfacial tension between PP and PB‐1 at 180°C determined by Eq .…”

“…a–c, respectively. A droplet‐matrix morphology is obvious for all samples and the size of droplets in the PPB1 blends are smaller than PPB4 , owing to the coalescence phenomena as a reverse process in mixing in polymer blends. At 10 wt%, in both sets of blends, the fine droplets of PB‐1 resin homogeneously dispersed in the PP matrix, with a volume‐average radius of droplets ( R v ) of about 30 nm for PPB1 and 40 nm for PPB4.…”

“…Graebling et al has found that the secondary plateau at low frequency is related to size, and the amount of dispersed phase and the width of this plateau are related to particle size distribution. The secondary plateau in storage modulus that appeared for PPB4 blends (with lower viscosity ratio and a coarse morphology), containing 20–60 wt% of PB‐1 , disappeared in the PPB1 blends with very fine droplets.…”

“…In addition, it is reported that the Cole‐Cole plot is invalid for analyzing the miscibility of the polymer blend when the dispersed phase does not have enough time to relax during the dynamic frequency sweep test. The Cole‐Cole plots of PBP1 blends in all compositions are semicircular, in which their shapes change in PPB4 samples with a lower viscosity ratio than 1 (Fig. ).…”

“…Rheology is known as an effective means to characterize the phase behavior of multicomponent systems [16]. The compatibility, phase behavior, and flow properties of PP/PB-1 blends have been investigated at various temperatures and compositions [17][18][19][20][21] and it is shown that these blends are incompatible in all ranges of compositions.…”