The effect of mixing on the modes of dispersion and rheological properties of two‐phase polymer blends in extrusion

Abstract

SynopsisAn experimental study was carried out to investigate the effect of mixing on the state of dispersion and rheological properties in the two-phase flow of polymer blends. For the study, blends of polystyrene and polypropylene were used, and two mixing devices were employed a single-screw extruder combined with a "static mixer," and a twin-screw compounding machine. Materials of various blending ratios were extruded a t a constant temperature (200'C) through a capillary die having an LID ratio of 20 (D = 0.125 in.). The state of dispersion in the two-phase system was investigated from pictures taken of the microstructure of the extrudate samples. It was found that different mixing devices have a profound influence on the state of dispersion of one polymer in another. Also determined were the rheological properties of the two-phase system investigated, from wall normal stress measurements. Our results show that, when shear stress is used as a parameter, the melt viscosity goes through a minimum, whereas the melt elasticity goes through a maximum. This is regardless of the type of mixing device employed, although the shapes of the c w e a are affected by the type employed. It is suggested that shear stress, instead of shear rate, be used in correlating the viscoelastic properties of two-phase polymer systems.

Morphology and permeability in extruded polypropylene/ethylene vinyl‐alcohol copolymer blends

“…The viscosities that Lepoutre [40] obtained for the PP/EVOH blend system were lower than the respective homopolymer viseosities, which led to designating the blends as negatively deviating. This deviation from the additivity rule has also been observed for other blend systems [27,28,29,39].…”

“…Han [29] PS/PP Danesi [30] PP/EP Vinogradov POM/CPA [31][32][33] Krasnikova PP/PS [34] Tsebrenko POM/CEVAc [35] Lyngaae-PE/PP Jorgensen À<l,""l À""l Table 2.6). Micrographs of samples produced under controlled processing conditions (blow-molded container and extruded sheet) showed that the nylon material was not distributed as a homogeneous, unifcrm blend, ~ut rather as multiple layers, or platelets, along the wall thickness.…”

“…It is suggested in the literature [8,22,23,29] that a three-stage meteri ng screw should adequately achieve a proper degree of mechanical mixing, considering that a certain droplet size is necessary to obtain a fibr illed or l amj nar microstructure. On the other hand, when a compatibilizer is used in the blend system, it might be necessary to employ a mixing screw to ensure sufficient wetting of the dispersed EVOH phase wi th the incorporated interfacial agent.…”

Melt rheological properties of polypropylene-maleated polypropylene blends. I. Steady flow by capillary

“…Blends of polypropylene (PP) for improving properties suited to some specific application were extensively studied with a large number of polymers, including polyethylene, [1][2][3][4][5] polycarbonate, 6 polyamide, [7][8][9][10] polystyrene, 11,12 acrylonitrile-butadienestyrene (ABS), 13 ethylene-vinyl acetate (EVA), 14 elastomers. [15][16][17][18] However, the blends of PP and PP grafted with maleic anhydride (PP-g-MA) seem to have been scantily studied.…”

Capillary flow behavior of bicomponent polymer blends

“…Figure 5 indicates the correlation between e and the apparent shear stress Tw for the P-E and P-M systems. In this case, v~ was used instead of because, as pointed out by Han [10], the variation in ? is not continuous due to the formation of discontinuous phases of micro-structure between two polymers.…”