Caracterização de extrativos de madeira de eucalyptus e depósitos de pitch envolvidos na fabricação de celulose e papel

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The objective of this work was to study the chemical composition of lipophilic extracts from eucalyptus wood and compare it with the composition of dirt specks found in cellulose pulp. Gas chromatography coupled with mass spectrometry (GC-MS) and analytical pyrolysis were the main techniques used in the study. The exhaustive extraction of wood was carried out to evaluate the influence of different solvents and the extraction time on the determination of lipophilic extract content in seven types of eucalyptus wood, consisting of three species (E. urophilla, E. urograndis and E. camaldulensis) and four E. urograndis clones. It was found that both acetone and toluene:ethanol mixture can be used in the determination of total extract content in eucalyptus wood, whereas the lipophilic extract content can be determined by dichloromethane or chloroform in direct extractions, or still by determining the total extract content (with acetone or toluene:ethanol) and re-dissolve them in dichloromethane. Following, a detailed chemical characterization of the lipophilic extracts of the seven types of wood was carried out before and after hydrolysis. First, the chemical composition was compared among the three species E. urophylla, E. urograndis and E. camaldulensis. E. urophylla showed the lowest lipophilic extract content (0.48% m/m), which is a decisive factor from the point of view of pitch formation. A total of 57 compounds were identified in the three extracts, whose main chemical classes were fatty acids and steroids, followed by long-chain alcohols and aromatic compounds. Some compounds of these families came esterified and as glycosides. Numerous compounds identified in the extracts are of high interest, since they have already been found in pitch deposits, standing out --sitosterol, palmitic, oleic, linoleic acids and and -hydroxylated acids. Then, the comparison of the chemical composition among the four E. urograndis clones was accomplished. Although the percentages of extracts were very similar (approximately 0.47%), their chemical compositions were shown very different. The chemical composition of lipophilic extracts from eucalyptus wood with different times of storage in the field was also evaluated. At each period of 20, 40, 60, 100, 140 and 180 days after cutting, the content and chemical composition of lipophilic extracts were determined by GC-MS. The lipophilic extract content reduced with period of storage, with the largest decrease occurring at 60 days. The main reason for this reduction is the decrease in the content of fatty acids and steroids mainly, particularly of 16- and 18-carbon acids and -sitosterol and -sitostanol. These variations have a direct impact on the industrial wood processing, particularly on pitch deposition. Analytical pyrolysis (Pi-GC-MS) was used to analyze a series of dirt speck samples collected from bleached cellulose pulp. Different reference materials such as rubber from several parts of the plant, cellulose fiber and additives were used to investigate the possible sources of these specks. Principal component analysis was used to establish a relationship between pyrograms of these samples with the pyrograms of the specks. The results showed that the samples of rubber containing Teflon were the origin of numerous pecks in the pulp. This was confirmed by the efficient clustering of samples containing tetrafluoroethane by the principal component analysis. This methodology can serve as a complementary tool for the procedure already used in the plant for correct speck characterization. This methodology has been used again for the characterization of a group of specks in cellulose pulp and of rubbers used in the industrial process. The data were compared with the ones obtained by infrared spectroscopy (IR). Analytical pyrolysis was shown a more informative technique than IR, because it allowed the differentiation between pairs of samples (specks and rubber) that showed similar spectra in the infrared. Finally, the results showed that the analytical pyrolysis technique used for characterization of specks in pulp is efficient and complementary to IR

ASSUNTO(S)

química orgânica teses. quimica vegetal teses. madeira quimica teses. pirolise teses.

ACESSO AO ARTIGO

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