Processing-induced morphology

The molecular structure of the polymer directly but partly affects the properties of processed articles. The properties of shaped, processed items mainly depend, on the other hand, on changes in the higher-order structures which are very sensitive to the processing conditions of semicrystalline polymers, such as polypropylene (PP). 

The higher-order structures (morphologies) of processed PP which should be considered are crystalline form, lamellar thickness, spherulite size, crystallinity, molecular orientation, crystal orientation, amorphous orientation, dispersion state of blended polymer, length and orientation of filled fibers, crystalline texture (skin-core structure), etc. In this chapter, morphological changes induced by various processing methods are described. 

While the tensile elongation decreases with increasing spherulite size, the yield strength and ultimate tensile strength scarcely depend on it. The tensile modulus, yield strength and hardness increase linearly with increasing crystallinity in contrast to the impact strength. 

The tensile modulus increases with increasing crystallinity. A necessary condition for obtaining transparent sheets is to keep the spherulite size smaller than the wavelength of visible light. This can be achieved by the copolymerization method, by addition of nucleating agents or by quenching. 

A similar morphology to that in sheet extrusion is formed in pipe extrusion, too. The spherulite size and crystallinity increase with increasing bath temperatiue. The molecular orientations in the axial, radial and tangential directions are high at the surfaces and decrease toward the interior. The orientation factors are higher when the melt flow index (MFI) of the PP is lowered or the extrusion speed is increased. 

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Y. S. Kim, L. Dong, M. A. Hickner, B. S. Pivovar, and J. E. McGrath. Processing induced morphological development in hydrated sulfonated poly(arylene ether sulfone) copolymer membranes. Polymer, 44(19) 5729-5736, September 2003. 

Hin Hintze, C. Influence of processing induced morphology on mechanical properties of short ara-mid fibre filled elastomer composites. PhD Thesis, Technische Universitat Dresden, TUD press Verlag, 2013, ISBN 978-3-944331-13-3. 

The SHE cell transformation assay at pH 6.7 is conducted to determine the ability of a test article to induce morphological transformation in cultured SHE cells. The SHE cell transformation assay is one of the most widely used cell transformation assays. The endpoints of this assay are related to the conversion of normal cells into preneoplastic or neoplastic cells. The assay provides a valuable tool in the process of assessment and evaluation of the carcinogenic potential of a test article.2 28... 

The content of desired enzymes at the end of fermentation processes should be as high as possible in order to ease the downstream processing. This may be achieved by a proper choice of microorganisms, optimising the fermentation conditions (e.g. culture media, inducer, morphology, growth rate) or by RDNA technology. 

Capillary forces induce morphological evolution of an interface toward uniform diffusion potential—which is also a condition for constant mean curvature for isotropic free surfaces (Chapter 14). If a microstructure has many internal interfaces, such as one with fine precipitates or a fine grain size, capillary forces drive mass between or across interfaces and cause coarsening (Chapter 15). Capillary-driven processes can occur simultaneously in systems containing both free surfaces and internal interfaces, such as a porous polycrystal. 

The varied and complex steroid-induced morphologic and biochemical changes in the TM have been studied extensively. The result of the various known processes is an increased resistance to aqueous humor outflow resulting in ocular hypertension and, if imtreated, secondary open-angle glaucoma. 

CNTF induces morphological as well as molecular differentiation of neurons. Embryonic mammalian and avian neurons cultured in the presence of CNTF manifest neurofilament-containing processes, although it cannot be ascertained whether CNTF actively stimulates neurite outgrowth or is merely permissive by virtue of its effect on neuronal survival. For several classes of molluscan neurons, however, the situation is clearer. These neurons survive without neurite extension in the absence of CNTF, but rapidly acquire neurites when CNTF is added to the culture medium (Bulloch et al., 1992). 

This section aims at discussing the behavior of blends from a general point of view, looking at the impact of blending on processability, flow-induced morphology and the effect of forming on properties. 

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