Isotactic polypropylene, diffusion

Gas diffusion from a donor stream—in which the analyte chemically is converted to a volatile species—into an acceptor stream, where the two streams run in parallel separated by a suitable gas-permeable membrane, is a highly selective technique particularly well suited for adaptation into FI A, because in nonsegmented streams the diffusion unit can be made extremely small and the flow rates may be considerably reduced. Although in the first FI A gas-diffusion method, developed by Baadenhuijsen and Seuren-Jacobs [57] for the determination of carbon dioxide in plasma, a nonporous dimethyl silicone rubber membrane was used, hydrophobic microporous membranes such as Teflon or isotactic polypropylene have proven to be more versatile diffusion barriers, since they can be used for a greater variety of gases. 

Diffusion Coefficients of 2-Hydroxy-4-Octoxybenzophenone (UV 531) in Isotactic Polypropylene... 

The kinetics of oxidation of isotactic polypropylene was investigated in circulating apparatus with freeze-volatile products of oxidation at the temperature of liquid nitrogen. When the film thickness is less than 60 microns maximum rate of oxidation of the sample is proportional to its thickness. Consequently, at a thickness of less than 60 microns ( 1<60 mcm) kinetic regime is realized, i.e. diffusion of oxygen is a rapid process and does not affect the rate of oxidation. On the contrary, for 1 > 200 microns oxidation occurs in the diffusion regime and the maximum speed calculated for 1 cm the surface is practically independent of the thickness. 

Isotactic polypropylene (iPP) is generally regarded as a semicrystalline polymer since its wide angle X-ray diffraction patterns show the characteristics of both a crystalline phase (as indicated by the sharp reflections) and an amorphous phase (as indicated by a diffuse halo). 

In aU calculations the presence of a crystalline phase was assumed to affect neither the solubility of the probe in the amorphous regions nor the diffusion coefficients. Examination of Figure 5.17 shows that the higher the crystallinity of the stationary phase, the less pronounced is the deviation from linearity and consequently the less pronounced is the glass transition (decrease of film thickness has the same effect). The impossibility of detecting a glass transition in polymers of high crystallinity, such as isotactic polypropylene [170], is believed to be due to this phenomenon. 

Schwartz and co-workers [97] used isothermal differential thermal analysis to study the diffusion of Irganox 1330 (1,3,5 tris (3,5 di-tor -butyl-4-hydroxyl benzyl) mesitylene) in extruded sheets of isotactic polypropylene (iPP). Studies were conducted over the temperature range 80-120 °C. The measurements showed a clear relation between oxidation induction time and oxidation maximum time [both determined by isothermal dynamic thermal analysis (DTA)] and the concentration of stabiliser. It was possible to calculate the diffusion coefficients and the activation energy of diffusion of Irganox 1330 in iPP by measuring the oxidation maximum times across stacks of iPP sheets. 

Figure 4.11 Raman spectra of polypropylene particles obtained in situ on three different alumina-supported catalysts by using the Raman microscope (488 nm excitation). The microscope allows fluorescence from he alumina support to be avoided. (Interestingly, these samples fluoresced worse when using the FT-Raman system than with the visible laser system, a result found to be quite common with catalyst samples.) The variation in polymer tacticity is evident in the three spectra the very weak, diffuse upper spectrum is characteristic of atactic material the strong, sharp lower spectrum indicates highly isotactic polypropylene and the middle spectrum indicates...

LID Li, D., Liu, T., Zhao, L., and Yuan, W., Solubility and diffusivity of caibon dioxide in solid-state isotactic polypropylene by the piessnre-decay method, Ind. Eng. Chem. Res.,AZ,l l, 2009. 

From the Arrhenius plot, the activation energy for diffusion of erucamide from PA-12 was found to be 156 kJ mol. Using the same method, the activation energy of isotactic polypropylene, i-PP, was calculated to be 117 kJ mol. ... 

Dobini, M., O. CrccHErn. G. P. Vjcyuuo, and E. Bua Diffusion of thiodipropioiuc esteis and h3rdroxybenzc enones in isotactic polypropylene. European Polymer J. 3, 473 (1967). 

INTERFACIAL CATALYSIS plays a very important part in surface (interfacial) degradation. Oxidation can be catalyzed by various metals. Catalysis can start at metal/polymer interfaces and metal ions can diffuse into the polymer. The catalytic action by copper or its oxides, for instance, during oxidative degradation of polyethylene and isotactic polypropylene, respectively, has been studied in detail. Some relevant results will be briefly discussed here. 

Similar situations as in the case of isotactic polystyrene are encountered during the oxidation of polyethylene and polypropylene films. For the latter case, flakes of different thickness were used. The functional relationship between sample thickness and rate of oxidation was similar as in the previous case. Here, oxygen diffuses from both sides into the flakes (there is no agitation and [O2] = constant in the film). 

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