Information on the noncrystalline phase of nascent iPP given by slow calorimetry

Nascent isotactic polypropylene (iPP) has a lower crystallinity and a different X-ray pattern than recrystallized iPP. Heat flows during the melting of nascent highly stereoregular iPP samples are recorded with a Setaram C80 calorimeter over a wide T range (30–280 °C). The rate of heating–cooling is 1–3 K/h, i.e., much lower than with conventional DSC. Melting is performed after annealing at 30 < Tannealing < 140 °C and with or without substrate. The main peak, that found by DSC, is associated with melting of monoclinic crystals and gives an enthalpy ΔHDSC. Two other peaks, usually above and below the main peak, are observed. These are associated with a slower process of disordering a physical network, which was produced in the sample during polymerization. The sum of ΔHDSC and ΔHnetwork equals ΔHtotal. When melting is complete ΔHtotal is equal to ΔH0, the heat of fusion of perfect iPP crystals. This work presents new information on: (i) the noncrystalline phase of nascent iPP and the heat content of a semicrystalline polymer; (ii) the modifications of the melting process due to strain development, brought about by expansion in the material during the temperature ramp when a physical network is present; and (iii) the effect of a substrate on the polymer melting process. Keywords: nascent iPP, slow calorimetry, strain-melting, change of enthalpy, substrates.

Effect of Crystallinity of PET and Nylon 66 Fibers on Plasma Etching and Dyeability Characteristics

We investigated the correlation between crystallinity and plasma susceptibility for PET and nylon 66 fibers. Plasma susceptibility is measured by the weight loss observed when fibers of varying crystallinity are exposed to air plasma. We varied the crystallinity of samples by annealing fibers at different temperatures. Plasma susceptibility and dyeability as a function of the crystallinity of fibers showed a striking resemblance: both decreased with increasing crystallinity up to a threshold crystallinity, above which there were appreciable increases. Plasma susceptibilities of these fibers, under the conditions used in this investigation, are believed to be proportional to the dyeable non-crystalline region, but not to the total noncrystalline phase of fibers.

AEM investigation of the noncrystalline phase in a mullite/zirconia/titania composite

Reaction sintering of zircon and alumina has emerged as an economically attractive route for obtaining high toughness zirconia composites. To reduce sintering temperatures various techniques such as the use of fine reactive powders, hot pressing and sintering additives such as MgO and TiO2 have been used. All these techniques have their potential disadvantages and it has been argued that the use of an additive capable of acting in solid solution will prove beneficial to the microstructure without any associated problems.