Métodos de quantificação de grupos carboxílicos e carbonílicos em polpa de celulose kraft branqueada

• Autor(a) principal: Cazal, Cristiane de Melo
• Data de Publicação: 2006
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2062
• topic: Oximação; Celulose kraft; Polpa kraft; Oximation; Kraft cellulose; Kraft pulp; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ORGANICA

Bleached pulp quality is evaluated by many parameters but brightness is by for one of the most significant ones. However, exposure of bleached pulp to light, heat, humidity, chemicals and oxygen can causes darkening or yellowing of the pulp, a process also known as brightness reversion. The reasons why brightness reversion occur are not yet well defined. Carbonyl and carboxyl groups present in pulp may contribute to the yellowing processes. Thus, the quantitative determination of these groups is important to evaluate the quality of bleached pulp. This work aimed at evaluating different methods for carbonyl and carboxyl groups determination in bleached kraft pulp. Carboxyl groups were measured by new methodology using the direct potentiometric titration, where the method TAPPI (T 237 om-93) was used for validation of developed method. Carbonyl groups determination carbonyl groups was made by the oximation and copper number (TAPPI T 430 om-94) methods. In the oximation method the conditions for pulp oximation reaction were optimized, incluing pH, hydroxylamine hydrochloride (NH2OH.HCl) concentration and reaction time. Pulp samples of kraft bleached industrial and oxidized with ozone (O3), sodium periodate (NaIO4) and NaIO4/sodium chlorite (NaClO2) were used. The analysis for FT-IR spectroscopy was also investigated as a qualitative tool for characterization of samples of cellulose pulp bleached industrial and oxidized with O3 and NaIO4/NaClO2. Excellent correlation (r = 0.9956) was observed between the adapted potentiometric titration and TAPPI T 237 om-93 methods; however, the results found for the potentiometric titration method were 22% larger than found them in the TAPPI method. The potentiometric titration was elected the most viable considering execution easiness, analysis time, reagents cost and accuracy. The oximation method was not showed adequate for quantitative analysis of carbonyl groups in bleached kraft pulp. The optimal conditions for oximation reaction were pH 5.0, 48 h of reaction under agitation and 0.1 mol of NH2OH.HCl/2 g of pulp. Pulps oxidized with sodium periodate (NaIO4) were more reactive towards oximation than pulp oxidized with ozone, due the nature of formed carbonyl. The FT-IR spectroscopy was not showed an useful qualitative tool for determination of carbonyl groups in cellulose bleached commercial. The identification of carbonyl groups in the infrared spectrum of samples oxidized with NaIO4 was more difficult in relation to the samples oxidized with O3. Taken together, the results showed that the oximation method should not be used for determination of carboxyl groups content; although, the direct potentiometric titration method showed a promising technique for quantitative determination of carboxyl groups in bleached kraft pulp samples.