Spectra rubber, natural

Figure 5.9 GALDI mass spectrum of natural rubber (from toluene/THF solution) on silver doped graphite matrix. The signal spacing of 68 Da corresponds to the isoprene monomer...

Also, the high mobility present in elastomers creats a weak dipolar coupling so that the cross polarization is inefficient and results in weak enhancement compared to standard free induction decay spectra. As far as material identification is concerned, the spectrum resulting from acquiring a standard pulsed free induction decay at an elevated temperature is adequate. Further research will probably show the narrow lines from the magic angle spectra of natural rubber may allow assignments to lesser components. ... 

Fig. 31. Stacked plot of the heteronuclear two-dimensional J-resolved spectrum of cured, carbon black filled, natural rubber. The proton flip experiment was used with high-power proton decoupling during the detection time. The experiment was performed with the sample spinning at the magic angle (reprinted from Ref. 1911 with permission)...

Fig. 49. Standard 13C NMR spectrum (top) and DEPT spectra of sulfur cured natural rubber (6h at 138 °C). The label T indicates peaks from trans-polyisoprene units, X marks residual peaks from other subspectra and arrows indicate peaks due to crosslink sites (adapted from Ref. 194>)...

The system Cl-buty 1-natural rubber (or cw-polyisoprene) could not be resolved by differential solvent techniques because the polymeric solubility parameters were too similar. At one end of the spectrum—i.e., with styrene at — 25 °C—natural rubber could be highly swollen while restricting the chlorobutyl swell, but the reverse was not possible, as indicated by the swelling volumes in the trimethylpentane. As displayed in Table II, attempts to use a highly symmetrically branched hydrocarbon with a very low solubility parameter, served only to reduce both the swelling of natural rubber and chlorobutyl. (Neopentane is a gas above 10°C and a solid below — 20°C). Therefore, for this report the use of differential solvents in the study of interfacial bonding in blends was limited to systems of Cl-butyl and cw-polybutadiene or SBR. 

The effect of particle size and spinning of the NMR tube were studied for the latex state 13C-NMR of natural rubber latex fractionated by particle size [134], High-resolution spectrum was obtained by measurement without sample spinning. The diffusion constant of Brownian motion was found to be a dominant factor governing the intensity and halfwidth of the signals. As the particle size decreased and temperature of measurement was raised, the intensity of signals increased and was comparable to the theoretical value, which was observed by the addition of triethylene glycol as an internal standard. 

A similar experiment has been performed [68] but under MAS conditions. For a series of crosslinked natural rubber samples (A - FI), 13C edited 1H spinning sidebands have been extracted from the 2D spectrum. These sideband pattern are encoded by the residual dipolar couplings of the corresponding functional groups and are presented in Figure 14.12. 

At normal temperature polymers generally react so slowly with oxygen that the oxidation only becomes apparent after a long time. For instance, if polystyrene is stored in air in the dark for a few years, the UV spectrum does not change perceptibly. On the other hand, if UV light under similar conditions irradiates the same polymer for 12 days, there appear strong bands in the spectrum. The same applies to other polymers such as polyethylene and natural rubber. 

Pyrolysis-field ionization MS performed on natural rubber at 315° C [6] generated the spectrum shown in Figure 6.1.2. The results from Py-FI MS show that the main pyrolysis compounds are oligomers of isoprene corresponding to m/z = (68)k where k =1,2. .. 19. However, at trace level other series are present [6] such as m/z = (68)k +... 

Figure 6.1.2. Py-field ionization MS spectrum of natural rubber at 31C [6],...

Figure 2. ESR spectrum resulting from deformation of natural rubber at —75°C...

Figure 1. Natural rubber cured with 30 phr dlcumyl peroxide. Spectrum (A) obtained under CP-MASS. Spectrum (B) obtained with the CP-MASS experiment with a delay between acquisition of 100 yiAsec, the quartenary carbons are distinguishable at 135 ppm and 45 ppm.

Figure 16. Spectra of natural rubber cross-linked with 25 phr ROOR. Spectrum (A) swollen in benzene to equilibrium swelling. Spectrum obtained under conditions of NFT experiment. Spectrum (B) same sample as (A), obtained under CP-MASS. The asterisk marks resonance of benzene solvent. Spectrum (C) the difference between (A-B).

Our analytical procedure consists of stepwise acetone extraction followed by cyclohexane. Subsequently, the acetone-soluble fraction is partioned between hexane/aqueous ethanol (12,15), and the soluble components are freed of solvents and determined gravimetrically. For lack of specific nomenclature, the botanochemicals isolated by this technique have been referred to as "whole plant oil," "polyphenol," and "polymeric hydrocarbon." Actually, components from these extracts need to be further characterized. However, petroleum refinery processes may be sufficiently insensitive to allow use of carbon-hydrogen rich compounds represented by a broad spectrum of structures. For example, consider the diverse chemicals ranging from methanol to natural rubber which have been converted to gasoline (16). Thus, chemical species may be important if chemical intermediates are being generated but may be nonconsequential for production of fuels, solvents, carbon black, and other basic chemicals. 

FIGURE 3.1 Magnified portion of NMR spectrum of natural rubber vulcanized to half its maximum torque. The peak at 16 ppm arises due to cis-to-trans isomerization (Mori and Koenig, 1998). 

FIGURE 3.21 Isothermal dielectric loss curves for a thermodynamically-miscible blend of 25% 1,2-polybutadiene with natural rubber. Notwithstanding the homogenous morphology, the respective mobiUties of the components differ, whereby two peaks are observed in the spectrum. Reprinted from Alegria et al. (1994). 

For Singapore to become a centre of excellence for polymer education and polymer research and development, at some point in the near future consideration should be given to a honours degree course in polymer science and technology. Also, as the ASEAN Region is the world s major natural rubber producer, rubber should have a much greater profile. These steps would complete the spectrum of polymer education available. 

To produce bio-based plastics there is a broad spectrum of feedstock options. Today, bio-based plastics are mainly based on sugar, starch, vegetable oil and natural rubber, the so-called... 

Two NR samples (cured and uncured) were studied. In all studies, the samples were stretched to 500% elongation. The Fourier-transform Raman spectrum of NR is presented as a function of time of cold soaking at -25C and of strain with respect to laser polarisation. Under both sets of conditions, changes occur in the spectra that can be attributed to crystallisation. Difference spectra showing only those bands due to crystallisation (i.e. spectra of crystalline NR) are presented, which allows the crystallisation process to be discussed with respect to the conditions under which crystallites are formed. A combination of Fourier-transform Raman and Fourier-transform IR depolarisation spectra was used to deduce preliminary assignments for some of the vibrational bands of natural rubber. 40 refs. 

Natural rubber is compatible with paraffinic, naphthenic, and aromatic oil plasticizers. Only butyl rubber has similar compatibility. All other synthetic rubbers are compatible with a limited spectrum of mineral oils. These are recent applications ... 

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