Nanocomposites of polystyrene (PS) with up to 20 wt% organoclay were prepared by melt compounding in a co‐rotating, intermeshing twin‐screw extruder. Three grades of PS with different molecular weights were used. In this paper we discuss preparation and characterization of the mixtures. Residence time and its distribution were measured by ultrasonics (US). They were found to be independent of the PS grade, but the US attenuation and sound velocity varied with the organoclay loading. According to the XRD diffraction data, the organoclay was dispersed into two types of platelet stacks evidenced by the diffraction peaks at about 2θ = 2.1 and 5.5°, i.e., with the interlayer spacings of d001 = 4.20 and 1.6 nm, respectively. Since neat organoclay has d001 = 1.93 nm, the first peak indicates intercalation by PS and the other a collapse of the interlamellar gallery during compounding. The XRD spectra depended on the organoclay content, but not on PS grade. According to TEM analysis, the degree of intercalation of organoclay in the polymer matrix is highest for the low‐molecular‐weight polystyrene. TEM results also confirm the collapse of interlamellar spacing in parts of the samples. FT‐IR spectroscopy showed that there was some thermal degradation of the onium compound present in the nanoclay. Polym. Eng. Sci. 44:1046–1060, 2004. © 2004 Society of Plastics Engineers.

We discuss the effects of the melt compounding variables, matrix molecular weight and organoclay content on the X‐ray diffraction (XRD) and mechanical properties of polystyrene (PS)/organoclay nanocomposites (PNC) prepared in a twin‐screw extruder. An increase of residence time reduced the height of the first XRD peak and increased that of the second peak. Barrel temperature and screw configuration had a little influence on the tensile properties and impact strength. Young's modulus increased with organoclay content and it was almost independent of matrix PS molecular weight. The stress‐at‐break and impact strength decreased with organoclay content and increased with PS molecular weight. Young's modulus and impact strength decreased with residence time. Since the slopes of these dependencies for PNC were similar to that of the neat PS, the matrix degradation seems to play the major role. The relationship between impact strength and elongation at break of PNC showed high dependency on matrix grade. However, better empirical correlation was observed between the impact and tensile strengths. According to theoretical model of Ji et al. [32], the Young's modulus vs. clay concentration dependence indicated the presence of low interphase thickness. POLYM. ENG. SCI. 45:827–837, 2005. © 2005 Society of Plastics Engineers

The extrusion foaming process involves several critical steps, in which the physical foaming agent plays a significant role: plasticization, solubility, nucleation and bubble growth. Although these aspects can be studied by different techniques, a novel method based on ultrasonic sensors has proven to provide valuable information with respect to the thermoplastic foaming process. This technique can be either used off-line as a characterization tool to improve our understanding of the foaming agent characteristics, or it can be installed in-line, on the extrusion line, as a control device. Review of the different applications of this technique will be covered in this paper, with numerous examples given to the mixture of PS with CO2. The degree of plasticization of the polymer as a function of the blowing agent concentration will be addressed first, followed by the detection of the conditions prone to induce nucleation, in terms of pressure, temperature, type of nucleating agents and flow conditions. The evaluation of the kinetics of bubble growth will also be explored.

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