Polypropylene sample

Table 4. Molecular Weight Characterization Data for Polypropylene Samples ...

The syndiotactic polymer configuration is not obtained in pure form from polymerizations carried out above 20°C and, thus has not been a serious concern to most propylene polymerization catalyst designers. Eor most commercial appHcations of polypropylene, a resin with 96+% isotacticity is desired. Carbon-13 nmr can be used to estimate the isotactic fraction in a polypropylene sample. Another common analytical method is to dissolve the sample in boiling xylene and measure the amount of isotactic polymer that precipitates on cooling. 

Figure 3. Formation of carbonyl group absorption at 1714 cm in polypropylene samples exposed to ozone and UV light (L2).

Figure 4. Kinetics of carbonyl group formation at 1714 cm- in polypropylene samples (0) and ( ) ozone and UV light (L2) (4) and (A) ozone only (0) and ( ) ATR spectra (A) and (A) transmission spectra.

The assumption is made at present that elemental combustion analysis for carbon, hydrogen, and fluorine provides a good approximation to the extent of incorporation of fluoroalkyl residues, i.e. alcohols and ethers. We have ruled out trifluoromethylcarbonyl groups since no evidence is seen for their presence in either the infrared spectra or the 19F-NMR spectra. Thus, our values for percent modification reflect the best fit of the combustion data to an idealized stoichiometry for the product in Equation 1, where (m+n+o) = 100, and the percent modification (% mod.) is given by the expression [100 x (m+o)/(m+n+o)], equivalent to the number of fluoroalkyl residues per one hundred methylenes. An appropriately normalized formula was used to fit the data for polypropylene (sample 10). 

Of course, the stereoselectivity (and hence the isospecificity) of the catalytic models strongly depends on the encumbrance of the jt-ligand, increasing along the following series 3-methyl-cyclopentadienyl (e.g., 3.7 kcal/mol for 10), indenyl (e.g., 4.9 kcal/mol for 13), 4,7-dimethyl-indenyl (e.g., 5.3 kcal/mol for 17), and tetrahydroindenyl (e.g., 5.9 kcal/mol for 18). This is in good qualitative agreement, for instance, with the percent of mmmm pentads evaluated for polypropylene samples obtained for different catalytic systems in strictly similar conditions by Resconi and co-workers.58... 

The effect of heterogeneous nucleation on the crystallization of isotactic polypropylene from the melt can be easily established as follows. A small amount of powdered polypropylene is well mixed with about 0.1 wt% of sodium benzoate in a mortar or by means of an analytical mill. Some of the mixture is transferred with a spatula to a microscope slide and melted at about 250 °C on a hot block. A cover slip is pressed on to the melt with a cork to obtain as thin a film as possible.The sample is held at 200-250 °C for some minutes and then allowed to crystallize at about 130 °C on the hot stage of the microscope an unadulterated polypropylene sample is crystallized in the same way. Both samples are observed under a polarizing microscope during crystallization,the difference in spherulite size between nucleated and untreated polypropylene can be seen very clearly. An ordinary microscope can also be used by placing polarizers on the condenser and eyepiece, and adjusting these to give maximum darkness. 

Fig. 4.5. A comparison of measurements on dilute solutions (in trans-decalin at 150° C, dashed lines) and on the melts (at 210° C, full lines) for two polypropylene samples, as specified in Table 3.3. For the definitions of FSi and see eq. (3.83). Bata are from refs. (74) and (36)...

Fig. 4.6. Doubled extinction angle 2y (closed triangles) and doubled orientation angle 2% (open circles and triangles) as function of shear rate q, and loss angle 6 as a function of angular frequency (closed circles, connected by dashed lines) for the melts of two polypropylene samples. Data of samples are given in Table 3.3. Measurement temperature 210° C (36)...

Fig. 5.4-5 DSC diagram of a polypropylene sample 1, melt peak of the in-situ polymer 2, crystallization of the polymer, 3, melt peak of the recrystallized polymer.

Figure 4 corresponds to a polypropylene sample and Figure 5 to a well-crystallized PET sample. Four integration intervals chosen for the diagrams of the main textile fibers. For PET fibers, they are ... 

When examining the first peak (see curve a in Fig. 5) it was found that it was proportional to the hydroperoxide contents as measured by FTIR, after NO derivatisation of un-aged films. When the sample was treated with S02, to decompose the hydroperoxides, the peak disappeared as shown (see curve b in Fig. 5). The CL curve of the S02 -treated sample has the typical sigmoidal appearance, just like an oxidising polypropylene sample. It was thus concluded that the first peak in the CL curve of the oxidising polyethylene in this study is from hydroperoxides already present in the material before the measurement starts. The second peak is the auto-oxidation. It might be... 

Initiation of a polypropylene sample was also done by placing a piece of copper in contact with a PP film stabilised with the antioxidant system in... 

Figures 8.13 and 8.14 show the HRR and mass loss rate of the polypropylene samples with each silica additive. The addition of low density, large surface area silica, such as fumed silicas and silica gel, to PP and PEO significantly reduced the HRR and mass loss rate. However, the addition of fused silica did not reduce the flammability properties as much as other silicas.

Time to Embrittlement of 0.02-inch Thick Polypropylene Sample, Sulfur Compound hours... 

Figure 4. Oven aging of polypropylene samples stabilized with 0.1% Antioxidant A (—) and B (- -). Logarithmic scale...

Previous static SIMS analyses have also shown (2) that the plasma treatment may induce fragmentation of the polymer backbone and some homogeneization of the polypropylene surface composition. Figure 6a shows static SIMS spectra obtained on a virgin polypropylene sample and Figure 6b on polypropylene which was treated in a N2 plasma for 7 seconds. 

Table 3 Comparison of embrittlement times during photo-oxidation with catalyst residues for polypropylene samples ...

Table 3. Polydispersity index of polypropylene samples obtained with different catalytic systems ...

Water samples were taken from the recreational lakes using polypropylene sample containers which had been acid soaked. The water was filtered over 0.22 pm Millipore filters, and the suspended sediment collected for metal analyses. Heavy metal analyses were also done in the meat portion of the most common fish found in the recreational lakes, i.e. Tilapia nilotica. The fish were caught without baits to avoid contact contaminating their internal organs. 

Fig. 10 Microstructure of rotationally molded polypropylene samples (A) undercured specimen viewed under polarized light microscopy (B) overcured specimen viewed under polarized light microscopy and (C) overcured specimen viewed under fluorescence microscopy. In these pictures, the degraded layer shows higher birefringence. (From Ref.P. )...

Syndiotactic propagation of propylene is know to be catalyzed by homogeneous vanadium catalyst (1 ). In the polypropylene samples prepared with the homogeneous catalysts, the relative population of iso-, hetero- and syndiotactic triads is in accordance with that predicted from the first order Markov model (25, 26). There is no chiral structure around the homogeneous vanadium species. The stereochemistry of the entering monomer is controlled by the chirality of the growing chain end, in contrast with the isotactic propagation. 

Piperazine 2 is also highly synergistic with commercial UV absorbers, as shown in 20 mil-thick compression-molded polypropylene samples aged in a xenon Weather-Ometer. 

Figure 7. Time dependence of concentration of the N-oxyl radicals in polypropylene samples containing different amounts of Tinuvin 770 and Irganox 1010 during irradiation.

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