Effect of morphology on shear viscosity for binary blends of polycarbonate and polystyrene

Abstract

The structure and rheological properties of binary blends of polycarbonate (PC) and polystyrene (PS) were investigated using various PS samples with different molecular weights, namely PS1k (Mw = 1,000), PS53k (Mw = 53,000), and PS240k (Mw = 240,000). The blends with PS53k and PS240k show phase‐separated structures, whereas the blend with PS1k is miscible. The shear viscosity decreases greatly on addition of PS53k and PS240k, especially at high shear rates, which would be a great advantage at processing operations. Because the nonlinear response occurs in the small strain region for multilayered films of PC and PS240k, the origin of the significant viscosity drop for the phase‐separated system is interfacial slippage at the phase boundary.

Viscosity decrease by interfacial slippage between immiscible polymers

“…[ 40 ] The viscosity data measured by the different dies were identical for all samples, demonstrating that wall slippage did not occur even for PP‐H/PS‐L. The same result was obtained previously [ 33,34 ] using bisphenol‐A PC blends with low‐viscosity PS. It has been well known that the steady‐state shear viscosity of conventional PP corresponds with the complex viscosity calculated using the oscillatory modulus; that is, the Cox‐Merz rule is applicable.…”

“…The viscoelastic properties for PS‐H and PS‐L were summarized in preceding papers. [ 33,34 ] The zero‐shear viscosities at 190°C for the materials are 1.1 × 10 4 Pa s for PP‐H, 5.5 × 10 1 Pa s for PP‐L, 9.0 × 10 4 Pa s for PS‐H, 1.8 × 10 −1 Pa s for PS‐L, and 6.0 × 10 1 Pa s for PE‐L.…”

“…In the latter case, adding low‐molecular‐weight compounds has been employed as a conventional method, which largely reduces the shear viscosity in the low shear rate region. [ 32,33 ] A well‐known material for achieving this is a plasticizer. Furthermore, adding polystyrene (PS) with a low molecular weight was recently found to greatly decrease the shear stress of bisphenol‐A polycarbonate (PC).…”

“…Furthermore, adding polystyrene (PS) with a low molecular weight was recently found to greatly decrease the shear stress of bisphenol‐A polycarbonate (PC). [ 33,34 ] For PC blends with PS, the decrease in shear viscosity was significant at high shear rate, that is, at high shear stress. This is different from the system with a plasticizer, and is an attractive method for increasing the flowability when injection molding.…”

“…Although the shape of droplets was affected by the distance from the die wall, the deformed droplets provided a large interfacial area available for slippage. [ 33 ] This concept is applicable to various immiscible blend systems.…”