A high molecular weight polymer mixture was obtained from a sequential Ziegler–Natta polymerization of styrene and propylene. After removing unwanted homopolymers from the reaction product, the remaining copolymer was subjected to extensive molecular and morphological characterization. The results of these experiments indicate that the purified material is a diblock copolymer of isotactic polystyrene and isotactic polypropylene, with each block having a molecular weight in the range of 225,000 g/mol. This block copolymer was incorporated in varying amounts into blends of isotactic polystyrene and isotactic polypropylene homopolymers. At low concentrations of copolymer (<20 wt %), the diblock functions as a dispersing agent, significantly reducing the size of domains in the heterogeneous blends. At higher copolymer concentrations, a dramatic improvement in the adhesion across the domain boundaries is also observed. The favorable effects of the copolymer on mechanical properties are demonstrated in the results of tensile impact experiments.
Samples of isotactic polypropylene having different morphologies and crystallinities were prepared and subjected to stress‐relaxation experiments at different levels of strain. The relaxation moduli were determined in the range of temperature between – 20 and 40°C over a period of time from 1 to 1000 seconds. Using the time‐temperature superposition principle, the activation energy values of the shift factors aT were determined and the master curves were obtained for the various structures. Increasing crystallinity and/or crystalline aggregate size increases the relaxation modulus of the material and changes both shape and location of the spectrum of relaxation times so that no simple method can be found to correlate the various master curves.
SynopsisTwo low-density polyethylenes, a linear low-pressure (LLDPE) and a branched high-pressure (LDPE), have been compared. Their shear and extensional behavior and melt fracture phenomena have been investigated, and some mechanical and optical properties of their blown films have been measured. The rheological analysis showed major differences between the samples, both in shear viscosity and in elongational viscosity. The LLDPE exhibited two types of melt fracture, the first of which-a fine scale extrudate roughness-was not shown by the LDPE and appeared a t a very low shear rate. The concomitance in LLDPE of a high shear viscosity and a low elongational viscosity and the presence of melt fracture at low shear rate resulted in its more difficult processing into film. The mechanical properties of the LLDPE film approached those of high-density polyethylene while the optical characteristics were in the range of LDPE. Such a coexistence of properties makes LLDPE an interesting material for film production.
A model for the solids conveying zone of a plasticating extruder is presented. The flow of solid granules is studied in the framework ofthermomechanics of media with affine structure, and assimilated to plane steady flow of an incompressible viscous fluid with spherical indeformable structure. Simple constitutive equations are accepted, along with those kinematical assumptions which stem directly from the geometry of the system. The resulting balance equations are given a dimensionless form, and integrated so as to arrive at closed-form solutions for velocity, spin and temperature of granules. A discussion of the influence of the adimensional parameters relevant to the problem is presented; this discussion is supplemented with some examples. Finally, various developments and refinements of the present model are proposed.* Most n f the results contained In the present nnte were the object 01 a communication presented at the Joint Meeting ofthe British, Netherlands and Italian Societies nt Rheology on Polymer Processing and Rheometry, Pisa 13th-15th April 1977, under the title: "Thermomechanics of plasticating extrusion: 1-Solids conveying znne " ' By solids conveyingzone we mean the zone from the section where the unld granular polymer IS supplied througlr the Impper to the section where firstly melting occurs.'The importance nt alluwing tor shearing flow in the solid fed 1s pointed nut by Pearsnn (2). in contrast, current theories derived from Darnell and Mol see the solid fed as a plug which rigidly slides down the channel. The reader IS referred to Ref. (5). Ch. 4, lor an exposition of the theory of Darnell and Ma1 (61, later extended by Schneider (7); the analysis nl Lovegrove and Williams (8), which develops along the same basic ideas, IS summarized briefly by Pearsnn in Ref.(1). 8 The need for a rational basis of rules for scale-up is stressed by Pearson in Ref. (1,2).
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