Structure and formation of cellulosic chars

Abstract

SynopsisThe formation and structure of chars produced on heating of cellulose, lignin, and wood have been investigated by FTIR and CP/MAS 13C-NMR, and the results have been discussed in conjunction with parallel permanganate oxidation studies reported before. These data show that when cellulose is heated for 5 min within the temperature range of 325-350°C, the IR bands associated with hydroxyl and glycosidic groups in cbllulose disappear, and new bands signal the formation of unsaturation and carbonyl groups by dehydration and rearrangement. The NMR data also show the disappearance of the glycosyl carbons at 60-110 ppm and the appearance of methyl and other paraffinic carbons at 0-60 ppm, aromatic carbons at 110-170 ppm, carboxyl carbons at 170-190 ppm, and carbonyl carbons at 190-220 ppm. On heating at 400OC the IR and NMR signals for the glycosyl groups completely disappear, the signals for carbonyl and carboxyl groups diminish, and those for the aromatic and paraffinic groups expand. At this stage the char contains about 69% aromatic and 27% paraffinic carbons. At the temperature range of 400-50O0C the paraffinic carbon content is reduced to 12%, and a highly aromatic (88%) char is produced. This is consistent with the permanganate oxidation studies which show the production of polycyclic aromatic structures resulting from extensive condensation and crosslinking at these temperatures. The chars produced from wood and lignin at 400°C had about the same aromatic carbon content as the corresponding cellulose char; however, the char yields were higher due to the presence of the methoxy phenyl groups that survive the heating process, as indicated by strong NMR signals at 55 and 148 ppm.

Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

“…There were also small increases in the intensity of the phenolic region and a broad alkyl signal comprised of methyl and short-chain alkyl substituents of the aromatic C. With increasing temperature, the aromatic character of the chars increased, as phenolic, Csubstituted aromatic and alkyl structures decreased. Our NMR results follow the general trends seen in previous charring studies of cellulose (Pastorova et al, 1994;Sekiguchi et al, 1983), pectin (Sharma et al, 2001), wood (Solum et al, 1995;Baldock and Smernik, in press) and other lignocellulosic materials (Maroto-Valer et al, 1996;Freitas et al, 1999Freitas et al, , 2001Knicker et al, 1996), the results of course varying slightly with different combinations of time, temperature, sample particle size, and an inert vs. oxidizing atmosphere.…”

“…However, our results are in line with previous findings by Susott (1982), that mass loss pattern, and thus thermal stability, of wood seems to be mainly controlled by its cellulose and less by its lignin content and structure. During charring, cellulose undergoes thermal degradation (dehydration and fragmentation) to volatiles (mainly CO, CO 2 , and H 2 O) and tar (mainly levoglucosan) that can further undergo condensation reactions to form alkyl and aromatic C (BC) (Shafizadeh, 1968(Shafizadeh, , 1982Sekiguchi et al, 1983;Shafizadeh and Sekiguchi, 1983;Banyasz et al, 2001;Elias et al, 2001). Our results showed that both wood samples had their highest mass loss in the same temperature range as both holocellulose samples (340-480 C).…”

“…The smaller mass loss of softwood compared to hardwood can be explained by its lower cellulose and higher lignin content (Mackay and Roberts, 1982;Susott, 1982;Shafizadeh, 1982;Sekiguchi et al, 1983;Jakab et al, 1997). Further, mass loss of woods may be affected by differences in ash content and composition (Mingle and Boubel, 1968;Shafizadeh and Sekiguchi, 1983;Jakab et al, 1997) and initial bulk density (Vo¨lker and Rieckmann, 2002).…”

“…Previous studies have included charring of individual wood components, such as cellulose (Shafizadeh, 1968;Pastorova et al, 1994;Sekiguchi et al, 1983;Banyasz et al, 2001;Vo¨lker and Rieckmann, 2002), pectin (Sharma et al, 2001), lignin (Oren et al, 1984), woody peat (Freitas et al, 1999), grass (Knicker et al, 1996) and rice hulls (Freitas et al, 2001). Only a few studies exist for wood charring (Solum et al, 1995;Baldock and Smernik, 2002).…”

Effects of Ultrasonic Cleaning and Chemical Pre-treatment on the Characteristics of Fast-stabilized Rayon Fabrics

“…둘째, 질량손실과 직접적으로 관계되는 dehydration 반응이 보다 낮은 온도에서 발생하도록 촉진시 키며, polyconjugation 탄소구조의 형성 및 aromatic 구 조의 형성을 보다 낮은 온도에서 진행되도록 해준다. 셋째, 탄소섬유의 제조에 촉매/난연제의 사용은 탄화율 을 높여줄 뿐만 아니라 분해반응에 의해서 제어되는 최종 섬유의 기계적 특성을 향상시키는데도 기여한다 [8,9]. 이러한 촉매로는 종종 염(salt)이 사용된다.…”