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Summary: Polymer‐layered silicate nanocomposites (PLSN), based on polyamide 6 (PA6) and montmorillonite (MMT) modified with an octadecylammonium salt, were produced via melt compounding in a co‐rotating twin‐screw extruder. Wide angle X‐ray diffraction (WAXD) and TEM revealed a PLSN containing 3.3% by weight (wt.‐%) of MMT to exhibit a mixed exfoliated/intercalated morphology, consisting mainly of individual silicate lamellae together with some intercalated stacks, resulting in a mean value of 1.8 lamellae per particle. In contrast, a PLSN containing a higher level of 7.2 wt.‐% MMT exhibited a more ordered intercalated structure, consisting mainly of a distribution of lamellae stacks with a mean value of 3.8 lamellae per particle. The dispersion of MMT in the PLSN generated very large polymer–filler interfacial areas, resulting in significant increase in the volume of constrained PA6 chain segments. Consequently, significant changes in the ratio of α/γ crystallites and in the thermal behaviour of the matrix PA6 were observed during WAXD, DSC and dynamic‐mechanical thermal analysis (DMTA) studies of the PLSN. In particular, damping data from DMTA showed relaxations between Tg and Tm resulting from amorphous polymer chain segments constrained at the polymer–filler interface, indicating the formation of a continuous phase of constrained polymer. In contrast, a PA6 microcomposite formed using unmodified MMT generated much lower polymer–filler interfacial area, with most of the MMT residing within large, poorly wetted aggregates. Consequently, changes to the thermal behaviour of the matrix PA6 were much less significant than those induced in the PLSN.Shear storage modulus (G′) versus temperature data for the matrix PA6, the 5T and 10T PLSN and the 5P microcomposite.magnified imageShear storage modulus (G′) versus temperature data for the matrix PA6, the 5T and 10T PLSN and the 5P microcomposite.

The effects of montmorillonite (MMT) addition level on the tensile properties of PA6-MMT polymer-layered silicate nanocomposites (PLSN) were quantified using factorial experimental design (FED) to fit experimental data to a series of polynomial response equations.Tensile behaviour, determined via FED, was related to the morphologies of the PLSN and compared to additional experimental data, determined for both a PLSN produced as a confirmation experiment and a PA6-MMT microcomposite of equivalent MMT content. In general, the PLSN displayed mechanical behaviour in keeping with their mixed exfoliated lamellae/intercalated lamellae-stack composite morphology and with the formation of a continuous phase of constrained polymer at a MMT loading of approximately 4 wt.-%. The data generated by the FED response equation for tensile modulus were compared to the predictions of the Halpin-Tsai composite theory model. A modification to the Halpin-Tsai model was made in order to take account of changes in the distribution of the number (n) of lamellae in the stack particles. Using experimental data for n, the composite moduli of the PLSN were successfully modelled as summations of the contributions of each particle fraction of varying n.

Composites based on polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS triblock thermoplastic elastomer) and magnesium hydroxide (Mg(OH)2) (5–60 wt.‐%) have been prepared by twin screw extrusion. Interfacial modifiers included dispersants, i.e., isostearic acid, oleic acid, stearic acid; and coupling agents, i.e., maleanised polybutadiene and vinyltriethoxysilane. In each case, approximately one monolayer of treatment was used. A dual bore motor driven extrusion rheometer was used for assessment shear and elongation flow behavior (Cogswell's method) over a shear rate range of 100 s−1 to 5 000 s−1. Untreated filler and filler treated with coupling agents gave composites that become increasingly pseudoplastic as filler level increased. Fatty acid structure was shown to have some influence over the level of melt viscosity reduction normally associated with such treatments; stearic acid gave the most pronounced reduction in melt viscosity possibly due to the tightly packed monolayer. Elongational flow properties, determined using Cogswell's method, indicated significant chain extension/branching of the bulk matrix when high levels of untreated filler were present and long range filler‐matrix interaction in composites modified with maleanised polybutadiene.Elongational viscosity versus extensional stress (obtained by Cogswell's method) for SBS blended with filler surface treatments (□) unfilled matrix, and unfilled matrix plus (•) Hist and (▵) MPBD.magnified imageElongational viscosity versus extensional stress (obtained by Cogswell's method) for SBS blended with filler surface treatments (□) unfilled matrix, and unfilled matrix plus (•) Hist and (▵) MPBD.