Extrusion Grade Research Articles

Processing and Properties of Polycarbonate/Liquid Crystal Polymer Blends

Abstract Rheological and mechanical properties, structural characteristics, extrusion and injection molding behavior of blends of polycarbonate (PC) with a thermotropic, wholly aromatic copolyesteramide have been investigated. The processability of polycarbonate is remarkably improved by addition of small contents of liquid crystal polymer. All the flow curves of the blends lie between those of the pure components. In the processing conditions adopted, the LCP particles are easily elongated in the flow direction. In this direction the elastic modulus rises remarkably with LCP content. The modulus-composition curve is, however, lower than that expected on the basis of an additive rule due to the incompatibility and poor adhesion between the two phases. Finally, injection molding of this extrusion grade PC has been easily performed by adding small contents of LCP. The impact strength values of the injection molding samples of these blends are only slightly lower than that of the pure PC.

Optimal Processes for Crystal Polystyrene

Abstract Styrenic polymers can be produced by many techniques, but relatively few have proven successful on a commercial scale. In recent years, the so-called bulk, continuous process has dominated industrial production and has largely replaced competitive routes such as suspension and emulsion. It is now used for most molding and extrusion grades of crystal polystyrene, for rubber- modified polystyrene, for styrene-acrylonitrile copolymer, and for certain varieties of ABS. The historic definition of “bulk” supposed use of the neat, undiluted monomers, but more recent terminology follows industrial practice in allowing substantial amounts of solvents (e.g., ethylbenzene) as chain- transfer agents and processing aids [l].

Molecular structure, crystallization behavior, and morphology of fractions obtained from an extrusion grade high‐density polyethylene

AbstractAn extrusion‐grade of high density polyethylene (HOPE) (3 ethyl groups per 1000 carbons) has been divided into 16 fractions by preparative GPC and selective p‐xylene extraction. The fractions, with molecular weights ranging from 900 to 1,000,000, have been studied by IR spectros‐copy, DSC, WAXS, polarized microscopy, and small‐angle light scattering (SALS), The average degree of chain branching (percent C2H5) is 0.5 percent for the part of the sample having a molecular weight lower than 10,000 and it decreases monotonically with increasing molecular weight, finally approaching 0.1 percent C2H5. A crystallinity depression with respect to linear PE equivalent to 20 percent/(percent C2H5) is recorded for all samples except for the very low molecular weight samples for which the crystallinity depression is much larger (30 to 35 percent/ (percent C2H5)). The unit cell volume increases with increasing percent C2H5, presumably due to the inclusion of ethyl groups in the crystals as interstitlals at 2gl kinks. The concentration of ethyl groups in the crystals (ϵc) unanimously follows the relationship: ϵc(percent) = 0.32 + 0.25 log(percent C2H5) except for the low molecular weight fractions which have significantly lower values for ϵc. Our admittedly speculative explanation for this major discrepancy between high and low molecular weight samples is based on the idea that segments with ethyl groups close to chain ends have a greater difficulty in crystallizing than segments containing ethyl groups located at positions far from the chain ends. The fractions obtained from the extrusion‐grade HDPE show a solidification temperature depression with respect to linear PE which can only be explained by the presence of chain branches in these samples. The depression is particularly pronounced for the low molecular weight samples as is expected from the data on molecular structure. Well‐developed non‐banded spherulites are observed in rapidly cooled (crystallized at about 35 K supercooling), low molecular weight samples (6,000 < Mw < 8,000)from the extrusion‐grade HDPE in contrast to the axialites observed in linear PE of the same molecular weight and thermal treatment. This discrepancy in morphology has been related to the presence of ethyl groups in the extrusion grade HDPE fractions. Higher molecular weight samples (20,000 < Mw < 1,000,000)from the extrusion‐grade HDPE and linear PE both display well‐developed banded spherulites of similar nature as is expected due to the similarity in molecular structure of the two sets of sample.

Processing–mechanical property relationships in injection moldings of polybutylene

AbstractTwo unfilled nonpigmented extrusion grades of polybutylene have been injection‐molded into a tensile bar mold under a wide range of barrel and mold temperatures. The overall structure of the moldings has been determined and correlated with processing conditions. The short term tensile mechanical properties of the moldings have been ascertained and correlated with molding structure. For low mold temperatures, the Young's modulus and tensile strength of injection moldings of polybutylene are controlled by the extent of and structure within the highly oriented skin. Low barrel temperatures can give rise to highly crystalline thick skins that treble the Young's modulus and fracture stress, when compared to high barrel temperature moldings. Increasing the mold temperature introduces a brittle response in polybutylene injection moldings. Modulus is controlled, at the high mold temperatures, by the skin thickness and by the crystallinity of the material comprising the core of the molding.