Tensile Properties, Single Crystals

Solid-state extrusion has also yielded some of the highest properties for uniaxially oriented morphologies. Tensile moduli (210 GPa) nearing the theoretical value of a polyethylene single crystal have been attained.f ... 

Several authors have analyzed the miscibility of iPP and PB-1, by means of different analytical approaches. Piloz et al. (16) found a single, composition-dependent, glass transition behavior for these blends, and concluded that they are compatible in the amorphous state. Sjegmann (17,18) reported that the composition dependence of tensile properties evidences a high degree of compatibility of iPP and PB-1 and observed a marked effect of the composition on the morphology of melt-crystallized samples. Conversely, the analysis of the crystallized blends indicates the presence of separated crystal phases of the two polymers, even if a mutual influence during the crystallization cannot be excluded. 

The above results have obvious implications for the biosynthesis of cellulose mlcrofIbrlls. The parallel chain structure of cellulose I rules out any kind of regularly folded chain structure, and reveals the mlcrofibrils to be extended chain polymer single crystals, which leads to optimum tensile properties. Work by Brown and co-workers (22) on the mechanism of biosynthesis points to synthesis of arrays of cellulose chains from banks of enzyme complexes on the cell wall. These complexes produce a bundle of chains with the same sense, which crystallize almost immediately afterwards to form cellulose I mlcroflbrlls there is no opportunity to rearrange to form a more stable anti-parallel cellulose II structure. Electron microscopy by Hleta et al. (23) confirms the parallel sense of cellulose chains within the individual mlcroflbrlls stains reactive at the reducing end of the cellulose molecule stain only one end of the mlcroflbrll. 

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