Effects of Bromination-Dehydrobromination on the Microstructure of Isotropic Pitch Precursors for Carbon Fibers

In this work, isotropic pitch precursors are synthesized by the bromination-debromination method with ethylene bottom oil (EO) as the raw material and bromine as the initiator for pitch formation and condensation reactions. The aggregation structure, molecular weight distribution, and molecular structure of isotropic pitch precursors are characterized by thermal mechanical analyzer (TMA), MALDI TOF-MS, and 13C NMR, respectively, for revealing the mechanism of synthesis of isotropic pitch precursors. The results show that at low bromine concentrations, polycyclic aromatic hydrocarbons (PAHs) were mainly ordered in cross-linked structures by bromination-debromination through substitution reactions of side chains. The condensed reactivity can be improved by the effect of bromine, meaning that condensation reaction was aggravated by the method of bromination-dehydrobromination. In the presence of excess bromine, the cross-linked stereo structure of PAHs changed to the planar structure of condensed PAHs, which was not conducive to the subsequent spinning and preparation of carbon fibers.

Characterization of lipophilic wood extractives from clones of Eucalyptus urograndis cultivate in Brazil

The chemical compositions of the lipophilic extractives from four clones of Eucalyptus urograndis cultivated in Brazil were studied by gas chromatography-mass spectrometry (GC-MS) before and after alkaline hydrolysis. The four E. urograndis clones showed similar amounts of dichloromethane soluble (lipophilic) extractives (0.38-0.55% w/w). The major groups of compounds identified in the lipophilic fraction of extractives consisted mainly of fatty acids (mainly palmitic linoleic and oleic acids and small amounts of a- and w-hydroxyacids), steroids (mainly b-sitosterol, b-sitostanol), followed by minor amounts long chain aliphatic alcohols, hydrocarbons and aromatic compounds. The relative abundances of these groups were similar for three of the clones with exception of the clone Ugc, which was shown to have much higher amounts of fatty acids and sterols. The high amounts of extractives found in these clones, and particularly of Ugc, when compared with other Eucalyptus species, suggests an increased risk of pitch formation during bleached pulp production.

Natural clonal variation of wood extractives in Populus tremuloides

Analysis of the potential genetic variation in quaking aspen (Populus tremuloides Michx.) wood extractives was performed by sampling nine natural clones at breast height. Significant clonal differences were found not only in the levels of total acetone extractives but also in the levels of sterols–triterpenes, steryl esters–waxes, and triglycerides, all of which are known to contribute to pitch formation in pulping and papermaking. In addition, extractive compounds known to elicit toxic effects in aquatic organisms showed statistically significant differences between natural aspen clones. In some cases (e.g., flavonoids), these compounds formed a part of the defense system in the living tree and, thus, were affected in part by the presence of decayed wood.