Nano-structured polymer-glass hybrid coatings

The increased attention received by polymer nanocomposites in recent years, has opened the way to research on nanostructured glass polymer hybrids for coating applications. Using polyamide 11 and adding fillers (in this case glass) at the nanometre length scale can lead to innovative modifications to the polymer matrix, giving rise to new structures and properties. This could develop new materials with enhanced properties and may enlarge the coating market to other application areas.
Some of the main obstacles to overcome are the control of glass particle size to obtain suitable dispersions on the nanoscale with interaction between components. Nanoscale structures require the development of optimal hybrid precursors. Finding a way to develop the hybrids using melt compounding methods like extrusion, particle size processes and coating techniques have been investigated in this research. The nanostructured hybrids are made using macroscopic fillers, which avoids problems with current regulations on ultra-fine particles.
Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy indicate the glass structure during synthesis of tin fluoride phosphate glass was pyrophosphate, mainly built up from phosphate tetrahedral units with one bridging oxygens present within a particular phosphate tetrahedron Qଵ end groups with a low concentration of phosphate tetrahedral units with two bridging oxygens Qଶ polymeric chains. However,
sub-optimal melting produced significantly higher concentrations of phosphate tetrahedral units with no bridging oxygens present within a particular phosphate tetrahedron Q଴ orthophosphate structural units. The variations in NH and P − OH vibrations in the spectra revealed that a critical time and temperature of melting were necessary for the conversion of NHସHଶPOସ to produce sufficient PଶOହ for glass forming. During melting, PଶOହ and SnFଶ formed a low-temperature melt, which facilitated melting of the SnO and promoted the formation of a more stable glass structure. The fluorine breaks the P − O − P bonds and induces depolymerisation. The density of the glass reached a maximum at 450 °C for 25 min driven by the need for conversion of NHସHଶPOସ to PଶOହ and miscibility of SnO in the melt. Inadequate melting times and temperatures gave low glass transition temperature (Tg) values because of weak F − Sn and F − P linkages. Glass stability improved with melting
due to increased PଶOହ and SnO miscibility enabling stronger Sn − O − P linkages.
The results show that melting conditions during synthesis strongly influence critical glass properties and also provide an understanding of optimum processing necessary for future industrial scale-up. Novel hybrids of tin fluoride phosphate (TFP) glass (composition of 50% SnFଶ + 20% SnO + 30% PଶOହ) were synthesized with polyamide 11 and their morphology and mechanical properties investigated. Hybridization was achieved by melt blending up to 25 vol% of glass using different compounding conditions (temperature, screw speed and residence time). Scanning electron microscopy (SEM) showed that the morphology was greatly influenced by the extrusion processing temperature and the glass content. Transmission electron microscopy (TEM) studies revealed nanoparticles of 40 nm in size and suggested good compatibility. In order to determine the existence of miscibility between hybrid components, measurement of the loss tangent using a Dynamic Mechanical Analysis (DMA), was carried out. The presence of two transition peaks in the hybrid containing 34 vol% tin fluoride phosphate glass implied an immiscible system showing heterogeneously distributed regions of very different molecular mobilities. Contrary to the plasticizer effect reported in the literature for some polyamide 6 - TFP glass hybrids, the measurements of mechanical properties by DMA showed a reinforcement effect of glass in the polymer. This was reflected by the increase of storage modulus (Εᇱ) at low and high temperatures in hybrids containing 13, 18 and 25 vol% tin fluoride phosphate glasses, achieving the highest modulus at 25 vol%. Tensile testing revealed a pronounced reduction in ductility for high glass contents.
Finally, the first TFP- PA11 hybrid coating was developed with enhanced fire resistance and adhesion to the metal. Hardness and abrasion tests using different glass Tgs showed an influence of the glass Tg on the final coating application.