Mechanical property improvement

Since thermotropic LCPs have recently been used in applications requiring high modulus and strength, much effort has been expended to improve the processability 

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The data provided by Toyota Research Group of Japan on polyamide-MMT nanocomposites indicate tensile strength improvements of approximately 40%-50% at 23°C and modulus improvement of about 70% at the same temperature. Heat distortion temperature has been shown to increase from 65°C for the unmodified polyamide to 152°C for the nanoclay-modified material, all the above having been achieved with just a 5% loading of MMT clay. Similar mechanical property improvements were presented for polymethyl methacrylate-clay hybrids [27]. 

In all of these cases, it does seem that the law that you do not get something for nothing applies. The conductivity decreases as would be expected from percolation theory, if the conducting polymer is dispersed, and according to the volume fraction if it forms a network. The mechanical properties improve as one might expect from an additivity rule applied to the two components. 

The molecular weight of the thermoplastic affects the flexural properties and the Glc. For example, a molecular weight ranging from 30,000 to 50,000 Da for an aromatic polyether gave the best mechanical properties improvement for a blend with Compimide 796-TM 123 [114]. 

Experimental studies have established that for conducting polymers, the electrical properties and the mechanical properties improve together, in a correlated manner, as the degree of chain extension and chain alignment are improved. Polyacetylene remains the prototype example. 

Previous work on powder consolidation by ECAE has been reported by several research groups [2-5], Past work has shown the method to have promise by finding that near-full consolidation occurs after the first pass and that mechanical properties improve quickly and can reach near peak values after only two passes. 

As mentioned before, the development of SiC whisker reinforced alumina was promoted because the mechanical property improvements observed with the incorporation of SiC whiskers into ceramic matrices were unprecedented. For example, the fiacture toughness of alumina was increased from 3.0 MPaVm to 8.5 MPaVm with the addition of 20 v/o whiskers. The increases in toughness for various whisker contents are shown in Fig. 7. The data is summarized from a number of reported studies and so reflect some of the variations in raw materials and processing methods. The results also reflect the maximum toughening... 

While these materials do contain two crystalline phases, it appears that small quantities of amorphous polyethylene are important in the mechanical property improvements noted above. It should be noted that the amorphous portions of polyethylene have a glass temperature near — 80°C, compared to — 10°C (Nielsen, 1962, p. 16) for polypropylene. 

Kim, M.-S., Fisher, J. G., Lee, H.-Y. and Kang, S.-J. L., Diffusion-induced interface migration and mechanical property improvement in the lead magnesium niobate-lead titanate system, J. Am. Ceram. Soc., 86, 1988-900, 2003. 

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