Quantitative Analysis of Meridional Peaks

At e = 0 the long periods of the 4 samples are identical. The increase of L(e) is much slower than expected from the macroscopic strain. At 30 % strain ( = 0.3) L has only grown by 10%. The data is more scattered for the samples containing MMT. The shape evolution of the L-peak of these samples (Fig. 5.4) shows that the asymmetric long period distribution is non-affinely strained. Thus the most probable L is no measure of the average nanoscopic strain of the semicrystalline morphology (i.e. of the long period distribution hcairn, 3) that has its maximum at (ri2, r ) = (0, L)), but it only reflects the deformation of the well-correlated stacks which are 

The width AL of hca rn, fz) in rs-direction describes the heterogeneity of the stacking of crystalline and amorphous domains. Data are presented in Fig. 5.10. Addition of MMT increases the heterogeneity of hca considerably. Thus the nanodomain stacking of PP is distorted by the MMT. Compatibilization leads to a relative reduction, indicating attenuation of the distorting effect of MMT on the semi-crystalline structure. 

With increasing strain the pure PP exhibits a moderate monotonous broadening. The MMT samples start with a slight homogenization of the stacks up to e = 0.07 that is followed by a distinct loss of uniformity when the materials are above the yield. At high strain, compatibilization (PP-i-lcMMT, PP-i-hcMMT) even further attenuates the distortion introduced by MMT. The asymmetry of hca(r i = 0, r3 is not considered and cannot be quantified from a peak fit that is based on a second-order polynomial only. 

Nevertheless, although the mechanical properties of the 4 materials are very similar, monitoring of the straining experiments by SAXS has shown that the semicrystalline nanostructure and its evolution vary considerably. The relative variations from material to material indicate that the dominant troublesome effect of blending MMT and the studied metallocene polypropylene grade is not the interfacial incompatibility between filler and matrix, but the alteration of the adjusted nanostructure of the matrix grade by the filler. 

A decrease of crystallite size may be considered a decrease of filler particle size in the amorphous matrix. Theories of particulate reinforcement predict no influence of the filler size on the mechanical properties, although frequently an increase is empirically found [74]. On the other hand, Sumita et al. [75] report that for polypropylene also the opposite behavior can be observed. The reason may be that below a certain crystallite size further reduction will probably lead to weakening of the filler particle. 

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