Melt rheology and structure-property relationship

The measurement of rheological properties of any polymeric material under molten state is crucial to gain fundamental understanding of the processability of that material. In the case of polymer/layered siUcate nanocomposites, the measurements of melt rheological properties are not only important to understand the knowledge of the processabiUty of these materials, but are also helpful 

The terminal regions slope of the master curves for G and G are presented in Table 3.7. The slope of and in the terminal region of the master curves of PLA matrix was 1.85 and 1, respectively, and these values are in the range expected for polydisperse polymers. On the other hand, the slopes of G and G were considerably lower for all PLACNs compared to those of pure PLA. In fact, for PLACNs with high C18MMT content, G becomes nearly independent at low atut and exceeds G , characteristic of materials exhibiting a pseudo-solid-like behaviour. 

The dynamic complex viscosity 7 master curves for the pure PLA and nanocomposites, based on linear dynamic oscillatory shear measurements, are 

15 (a) Reduced frequency dependence storage modulus (G ) and loss modulus (6 ) of neat PLA and various nanocomposites.(b) Reduced frequency dependence of complex viscosity of neat PLA and nanocomposites. ° Reproduced from Sinha Ray and Okamoto by permission of Wiley-VCH Verlag GmbH, Germany. 

Melt rheological properties of PCL-based nanocomposites were first reported by Krishnamoorti and Giannelis in the case of delaminated structures prepared by in-situ intercalative polymerization. Recently, Lepoittevin et a/. reported the detail melt rheology properties of PCL-based nanocomposites prepared by melt intercalation method. The rheological behaviour of the PCL filled with 3wt.% of MMT-AIk and MMT-(OH)2 was significantly different compared to the unfilled PCL and PCL/MMT-Na nanocomposites, for which the power law observed at low frequencies agrees with expectation for thermoplastics. The frequency dependence of G and G was, however, perturbed by organically modified MMT. The effect was dramatic in the case of G which drops from 2 to 0.14 and 0.24 for MMT-(OH)2 and MMT-AIk, respectively. 

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