Effect of glass compositional variables on the structure and properties of phosphate glass/polyamide 11 hybrids

The blending of polymers is a relatively inexpensive method of manipulating their properties and is common practice in the industry. Phosphate glass/polymer hybrids are an emerging class of nanomaterial with peculiar characteristics derived from nano-micro interactions of their components. Inorganic phosphate glasses are made up of chain-like molecules and are similar to polymer chains in their structure. These glasses are also unique in exhibiting similar processing temperatures to polymers, which opens up the possibility of co-processing and of greatly extending the range of obtainable properties. Both components being fluid during processing allow controlling and tailoring hybrid morphologies, and avoiding the problem of the intractable viscosity inherent from a high solid filler concentration. This work investigates the blending of an organic semi-crystalline polymer, polyamide 11 (PA 11), with different compositions of phosphate glasses. Experimental and theoretical studies of miscibility and phase behaviour of these unusual blends were analysed. In particular the research investigated the effect of glass composition on the rheological and thermo-chemical properties and nano/microstructure of these new materials, focusing on the tin fluoride (SnF2) content in the glasses. The Flory Huggins equilibrium depression point model was employed to correlate and predict miscibility behaviour in these new systems. The experimental results showed that a high amount of SnF2 could act as a proper compatibilizer for the novel Rilsan ® PA 11 matrix. Experiments showed that the halogen content lowered the glass transition temperature (Tg) and softening point (Ts) of the glasses, allowing both phases being fluid during melt-blending. However the water stability of the glasses was improved with increasing SnF2 content in the network. The particle size of glass in the hybrids was inversely correlated with SnF2 in the glass composition. This phenomenon resulted in lowering the equilibrium melting point (Tm0) in the hybrids. The load force (F) generated during the extrusion process and the hybrid viscosities decreased, without compromising chemical and thermal stability of the materials. The Tg of PA 11, measured as shifts of the major peak in dissipation factor against temperature plot, was inversely correlated with SnF2 content in the
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glass composition, phenomenon often attributed to the partial miscibility of components in a system. The stiffness of the hybrid was improved by higher amount of SnF2 in the glass compositions with polyamide reinforced by the glass having the lowest Tg (60 SnF2 mol%). The longitudinal storage modulus was inversely correlated with temperature for PA 11 and all hybrids and increased with melting each phosphate glass with the polymer matrix. The storage modulus increased with SnF2 content in the glass composition in the matrix at lower temperature and reached a constant value for all hybrids at higher temperature. The viscosity and shear modulus decreased and increased respectively with increasing angular frequency. Shear modulus of polyamide matrix was lowered by each phosphate glass. All samples showed a small upturn in the modulus versus angular frequency curve at the lowest viscosities, behaviour related to the presence of yield stress in the hybrids, more evident in the hybrids with the highest content of SnF2 in the glass.