Characterization of the moisture absorption and thermal ageing behaviour of polymeric composite systems using Raman spectroscopy

Advanced polymeric materials and their respective composites are fast becoming one of the world's most frequently used engineering materials. They find application in the manufacture of e.g. boat hulls, high performance motor vehicles, aircraft components and sports goods. Their high specific strength and specific stiffness give them the edge in applications where weight savings are critical, but their long-term durability is often questioned. These materials are susceptible to environmental conditions such as temperature and humidity. There is also a lack of relevant data, due to the long time-scales required for testing. In this study, the Raman technique has been used to monitor the degradation of two composite systems, namely: a rubber toughened vinylester material used in the marine industry and a high temperature bismaleimide/carbon fibre aerospace composite. Preliminary Raman studies show that the toughening rubber particles dispersed in the cured vinylester resin are leached out during hygrothermal ageing. The weight gain during ageing suggests that this leaching process occurs concurrently with the absorption of water molecules. An increase in the degree of cross-linking is observed when bismaleimide/carbon fibre composite is aged at high temperature. This cross- linking tendency decreases with increasing depth within the carbon fibre bundle.

A controllable simple method for production of polymeric nanofiberous composite via single nozzle jet electrospinning

A special Micro-Nano fiberous composite structure composed of nano- and micro-scale fiber of Polycaprolactone (PCL) and Gelatin produced by using single nozzle electrospinning instrument. By controlling the solution (polymer concentration and polymer composition percent) and processing parameters of electrospinning (feed rate and electrostatic field), different portion of nano and micro fibers in the structure is achieved. This method can result a one-stage method of fabrication of Micro-Nano fiberous composite structure instead of previously used twostage process or using additional facility to produce structure near-similar to this composite structure. The resulting materials finely mingle nano- and micro fibers together, rather than simply juxtaposing them, as is commonly found in the literature. The results obtained from SEM, Flow Porosimetry, and DMA led the authors to confirm that the structure has very versatile and improved properties for many applications like cell culture scaffolds. These favourable mechanical and structural properties can provide easier opening of spaces for cell penetration to deeper levels of the scaffold and withstand to tensions during to clinical handling.

Proton conductive composite membranes

In this work we investigated the synthesis of composite organic and inorganic membranes for proton conduction. Particles derived from metal alkoxides (M(OR)n) sol-gel processes (Ti, Zr, W with phosphoric acid) were embedded in polymeric matrices of poly-vinyl alcohol, (3-glycidoxypropyl)-trimethoxysilane and ethylene glycol. The structure of the composite membranes was complex as several IR peaks were convoluted, indicating the assignment of several functional groups. However, the peaks assigned to OH groups reduced in intensity in the composite membranes, indicating that cross-linking of hydroxyl groups in the organic and inorganic phases of the membrane may have occurred. The particles allowed for re-arrangement of the polymer matrix, as crystallinity was reduced compared to a polymer blank membrane. The composite membrane process resulted in homogeneous dispersion of nanoparticles into the polymer film. Proton conduction of the inorganic phase was mainly dominated by titania. Binary mixtures of titania phosphate (sample name TiP) resulted in proton conduction of 7.15 × 10−2 S.cm−1, one order of magnitude higher than zirconia phosphate (ZrP). The addition of Zr and W to TiP forming ternary or quaternary phases also led to lower proton conduction as compared to TiP. Similar trends were also observed for the composite membranes, though the TiP composite membrane proton conduction reduced after several hours of testing at 50°C, which was mainly attributed to acid leaching.

Knitted strain sensor textiles of highly conductive all-polymeric fibers

A scaled-up fiber wet-spinning production of electrically conductive and highly stretchable PU/PEDOT:PSS fibers is demonstrated for the first time. The PU/PEDOT:PSS fibers possess the mechanical properties appropriate for knitting various textile structures. The knitted textiles exhibit strain sensing properties that were dependent upon the number of PU/PEDOT:PSS fibers used in knitting. The knitted textiles show sensitivity (as measured by the gauge factor) that increases with the number of PU/PEDOT:PSS fibers deployed. A highly stable sensor response was observed when four PU/PEDOT:PSS fibers were co-knitted with a commercial Spandex yarn. The knitted textile sensor can distinguish different magnitudes of applied strain with cyclically repeatable sensor responses at applied strains of up to 160%. When used in conjunction with a commercial wireless transmitter, the knitted textile responded well to the magnitude of bending deformations, demonstrating potential for remote strain sensing applications. The feasibility of an all-polymeric knitted textile wearable strain sensor was demonstrated in a knee sleeve prototype with application in personal training and rehabilitation following injury.

Amino-functionalized mesoporous silica based polyethersulfone-polyvinylpyrrolidone composite membranes for elevated temperature proton exchange membrane fuel cells

It is important to find alternative membranes to the state-of-the-art polybenzimidazole based high temperature proton exchange membranes with high proton conductivity at elevated temperature but with simple synthesis procedures. In this work, inorganic-organic nanostructured hybrid membranes are developed based on a polyethersulfone-polyvinylpyrrolidone (PES-PVP) polymeric matrix with hollow mesoporous silica (HMS), amino-functionalized hollow mesoporous silica (NH2-HMS) and amino-functionalized mesoporous silica (NH2-meso-silica). The composite membranes show a significant increase in proton conductivity and a decrease in the activation energy for proton diffusion in comparison with the phosphoric acid (H3PO4, PA) doped PES-PVP membrane. And the composite membrane with NH2-HMS shows the best performance under the conditions in this study, achieving the highest proton conductivity of 1.52 × 10-1 S cm-1 and highest peak power density of 480 mW cm-2 at 180 °C under anhydrous conditions, which is 92.7% higher than that of the PA doped PES-PVP membrane at identical conditions. Such enhancement results from the facilitated proton transportation in the ordered mesoporous channels via the hydrogen bond between the -NH2 groups and H3PO4. The high water retention capability of silica materials with a hollow structure also contributes to the decrease of the activation of proton diffusion. Consequently, the results show promising potential of the NH2-HMS based PES-PVP composite membrane for the elevated temperature proton exchange membrane fuel cells.