Polyethylene difference spectra

Fig. 8. Line shape analysis of the noncrystalline resonance of the bulk polyethylene with Mv of 3 x 106. A and B correspond to A and E in Fig. 6, respectively, C is the difference spectrum (A-B), and D shows the line shape analysis. In D, the composite curve of the component lines is mostly superimposed on the experimental spectrum...

Bow Tie Trees. An example of the use of the microbeam to investigate the contaminants in a bow tie tree in polyethylene insulation is presented in figure 7 which shows a) the spectrum from the center of the tree, b) the average of spectra from the insulation outside the tree and c) the difference spectrum. The latter clearly shows the presence of aluminum, possibly a shard from the manufacturing process, as well as excess sulphur, chlorine, potassium, calcium, copper and possibly iron. 

Pure polyethylene should not absorb ultraviolet radiation of wavelength above 200 nm since pure paraffins are transparent in that region of the spectrum. However, it is well established [ 20] that even carefully purified polyethylene differs from a simple high molecular weight straight chain paraffin in being to some extent unsaturated. The total unsaturation has been estimated to be about 0.25% C=C by weight [21]. Olefinic unsaturation of different types has been detected by infrared spectroscopy [21, 22] it seems to be mainly of the vinyl type in linear polyethylene, while most unsaturation is of the vinylidene type in branched polyethylene [22]. Attention has also been drawn to the fact that a structure seems to be present in low density polyethylene which leads to a triene on ultraviolet irradiation [23]. 

Figure 4 FTIR microscopy of polyethylene cable insulation. (A) Water-tree, (B) undamaged area, and (C) the difference spectrum (A) (B). (Parker SF (1995) Industrial applications of vibrational spectroscopy and the role of the computer. In George WO and Steele D (eds.) Computing Applications in Molecular Spectroscopy, pp. 181-199. Cambridge The Royal Society of Chemistry reproduced by permission of The Royal Society of Chemistry.)...

For the accentuation of these small differences in the spectra of the stressed and unstressed polymer the absorbance subtraction technique has proved particularly useful. In Fig. 3 this is illustrated with reference to the 972.5 cm absorption band of the v(0—CH2) skeletal vibration of polyethylene terephthalate. Fig. 3 a shows the shape of this absorption band for the unstressed and stressed (300MN/m ) polymer. In the difference spectrum (see Fig. 3 b) the shift of the peak maximum toward lower wavenumbers and the low-frequency tailing are reflected by a pronounced asymmetrical dispersion-shaped profile. 

Fig. 16a and b. FTIR spectra recorded during uniaxial elongation of a hi -doisity polyethylene film at 300 K with unpolarized radiation (a) and absorbance subtraction of successively recorded spectra (b) (a 83% strain, b 50% strain, a-b difference spectrum)... 

Figure 3-32. Multiple internal reflection spectrum in the CHi-bending region at different angle of incidence of a 56 pm-thick film of commercial polyethylene. The spectrum shows the increase of the fraction of conformationally irregular material by increasing penetration depth.

It is very useful to measure FTIR difference absorption spectra, where the spectrometer digitally subtracts an appropriate reference spectrum from a sample spectrum [1048,1222-1224, 1989]. To obtain a difference spectrum in polyethylene, the methylene wagging band at 1369/cm is used as the null wavenumber. An example of such an operation is demonstrated in Figure 10.62. 

Fig. 10.65. IR spectra of carbonyl groups m polyethylene (a) photo-oxidized sample (b) sample before UV irradiation (c) difference spectrum and (d) deconvulted difference spectrum [589].

The ATR method makes it possible to measure infrared spectra from the layer of the order of up to a few micrometers below a surface but it is also possible to extract information on a thinner layer by combining it with the method of difference spectrometry (see Section 6.2.3) in other words, the ATR method can be applied to more surface specific analysis. Figure 13.14a shows the ATR spectrum of polyethylene terephthalate (PET) covered with 0.05 pm-thick film of another material. The ATR spectrum of PET itself is shown in Figure 13.14b and the absorbance difference spectrum obtained by subtracting the spectrum in (b) from that in (a) is shown in Figure 13.14c. This spectrum is mostly due to the thin film covering the PET, and it is inferred from this spectrum that this surface-layer film is made of some kind of polyurethane. 

Here k is the absorption coefficient, d the thickness of the film, and C the concentration of end-groups. Figure 8.8 shows such a difference spectrum recorded by Zhurkov et al. [17, 18] from a polyethylene film ruptured at room temperature. 

Figure 1 shows a positive static SIMS spectrum (obtained using a quadrupole) for polyethylene over the mass range 0—200 amu. The data are plotted as secondary ion intensity on a linear y-axis as a function of their chaige-to-mass ratios (amu). This spectrum can be compared to a similar analysis from polystyrene seen in Figure 2. One can note easily the differences in fragmentation patterns between the...

Vertical surface collectors can readily provide information on relative drift (e.g., the amount of drift from one field trial compared to another). However, it is difficult to obtain absolute data unless the precise collection characteristics are known for the droplet size spectrum at the point of spray collection, wind speed and air turbulence intensity. " The SDTF conducted studies in wind tunnels to compare the collection efficiency of different types of drift collector used in its field studies. These studies showed that collection efficiency on strings was several orders of magnitude higher for 0.8-mm diameter cotton string than for 2-mm diameter polyethylene line and vertical o -cellulose strips or squares. The higher collection efficiency for the cotton... 

Sometimes, small structural differences in morphology of polymer samples can be isolated by using a double subtraction technique. For example, with polyethylene terephthalate) PET, differences in the amorphous phase of the melt-quenched polymer and solution-cast polymer can be isolated by first subtracting out the contribution due to the trans isomer and then subtracting the two difference spectra from each other 214). (Fig. 16) shows the resultingdifference spectrum obtained after the second subtraction. Obviously the two amorphous structures are different from each other. 

In Fig. 4 least-squares fitting with this equation to the experimentally observed spectrum is shown. The dotted line expresses Eq. (7) with rca = 1.81 x 10-8, rcb = 8.42 x 10-8 sec (Here, r is assumed to be 4.71 x 108 Hz2 8)). The observed and calculated spectra superpose with no appreciable deviation. Similar excellent agreement between observed and calculated spectra was obtained for many samples with different molecular weights. Thus, the deviation of spectra for polyethylene in the melt from a single Lorentzian is understood by the distribution of the correlation time. 

Filaments about 0.12 mm in diameter were obtained from unfractionated high-density polyethylene (Mi] = 8.0 x 104) by a melt-spinning at 220 ° C with a draft ratio of about 17. They were next stretched at 100 °C in polyethylene glycol with a molecular weight of 380—400 to different draw ratios, which are defined as the ratios of the drawn length to the original. NMR spectroscopy was carried out for the drawn filaments randomly packed into a glass tube 18 mm diameter. The three-component analysis of the spectrum at different temperatures was performed the results are discussed in relation to the phase structure of samples. 

The unique nature of the alkyl attached to titanium in a polyethylene catalyst has been indicated by Gray (80). Methyltitanium trichloride has an infrared spectrum which is unique and different from the bridged or unbridged methyl of methylaluminum chlorides. Although methyltitanium trichloride is not an effective catalyst to polymerize ethylene, this unique character is an indication of a difference which is developed further in the effective polyethylene catalysts. 

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