Publisher Summary This chapter outlines the reasons why polyolefins are blended, modified rheologically, or melt mixed. Polyolefins constitute a group ofpolymers of complex macromolecular structure. Typical examples of commercial polyolefin blends are impact-resistant polypropylene, super thin, highly orientable film grades of polyolefins, polyolefins for high-speed cable covering, and blow molding of environmental stress cracking resistant containers. The chapter also highlights the behavior of polyolefin blends in processing. The behavior of a blend during processing and the properties of its products are influenced by mechano-chemical processes and the melt shearing in the processing equipment. Low-density polyethylene (LDPE) used in the manufacture of blends are usually delivered in granulate form prepared by mixing granulates from various batches. A polyolefin blend manufactured from LDPE displays excessively high extrudate swelling and low critical shear rate during processing. Processing leads to transformations in the super molecular structure of the blends. These transformations are divided into three main types—structure changes because of orientation effects, which may be further influenced by the thermal history of the melt; structural changes because of generation of fibrillar and lamellar forms; and redistribution of the blend components because of shearing flow. Properties of micro heterogeneous polyolefin blends display several characteristic features—nonlinear dependence on composition (non-additivity), strong dependence on the degree of orientation and rheothermal treatment, and substantial flexibility for change to suit particular applications using fillers and compatibilizers. The chapter concludes with a review of various analytical techniques that have been used not only for polyolefins but also for other systems as well.

Polyolefin Blends: Rheology, Melt Mixing, and Applications

Polycarbonate (PC) blended with a polymer-modifier polycarbonate–polydimethylsiloxane (PC–PDMS) of polyblock structure having equal molar ratios of soft (PDMS) and hard (PC) blocks have been investigated. The kinetics of adhesional interaction in blends and the analysis of interphase interaction conducted by using the relaxation spectrometry showed that intensive interactions between phases can occur. At a concentration of the modifier ≤5 wt %, these effects can lead to a partial compatibility of the components. The phase separation comes to completion when PC–PDMS content reaches 7 to 10 wt %. Here the impact strength of the blends improves compared with homopolycarbonate; this factor becomes less sensitive to the notch pattern or surface defects. The micro-heterogeneous blends would fail by the multiple crazing mechanism. The mode of temperature vs impact strength relationship depends on the concentration of the modifier. Low shearing rates applied to the PC blends containing 3 to 7 wt % of PC–PDMS results in a lower melt flow index compared with that for a neat PC. The blends were more sensitive to shearing stresses than the homopolycarbonate. Therefore, they have lower viscosity at a high shearing rate than PC. Introduction of PC–PDMS into PC did not change its thermal stability significantly. The modifier inhibited the chemical crosslinking of PC chains if the melt had been kept for a long period. The optimal mechanical properties combined with improved processability were found in blends containing 7 to 10 wt % of PC–PDMS. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 858–869, 2000

Compatibility, adhesional interaction of components, impact strength, and rheological behavior of polycarbonate/polycarbonate-siloxane block copolymer

For the experiments there have been prepared such microheterogeneous mixtures of isotactic polypropylene with polyethylene and of polyvinylchloride with polyethylene which contained maximum 60 volume per cent of dispersed phase component (iPP; PVC respectively) at 160°C for various diffusion times, whereat with sufficient exactness the tetrahedric lattice model could be applied. From the dependence of the mixture excess volume on dispersed phase volume fraction, calculated from additive and real densities, the volume fraction at the maximum dilatation (Φ
 m
 ) was determined. At supposing theFickian course of the mutual diffusion, it was possible to calculate the thickness of the interphase layer. It was stated that for both polymer pairs the diffusion after 15 min had been practically stopped. This phenomenon, which could be explained by the kinetic hindrances during the interpenetration of the different nature polymer segments, is resulting in the deviation from theFickian course of diffusion.

J. Letz

Papers

Attempt for the diffused interphase layer determination from the volume changes of microheterogeneous polymer mixtures