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Resumo(s)
O processo convencional de branqueamento de malha 100% algodão com peróxido de
hidrogénio em meio alcalino está associado a um elevado consumo energético e a um impacto
ambiental significativo, devido, sobretudo, à necessidade de temperaturas elevadas de
processamento e à utilização de hidróxido de sódio para promover a ativação da espécie
oxidante. A presente dissertação, desenvolvida na empresa Aquitex, teve como objetivo
investigar alternativas mais sustentáveis a este processo, visando a redução da temperatura do
processo e a diminuição ou eliminação da utilização do hidróxido de sódio, contribuindo, assim,
para a redução do consumo energético e do impacto ambiental associado aos efluentes.
Para este efeito, foram exploradas duas vias de oxidação distintas. Na via enzimática recorreuse
à lacase e à peroxidase, bem como aos respetivos mediadores, selecionadas pela sua
capacidade de atuar em condições moderadas de pH e temperatura. A via química baseou-se
na utilização do oxone, um sal triplo, selecionado pelo seu elevado potencial oxidante. Para
este sistema foram exploradas diferentes estratégias de ativação, nomeadamente térmica,
alcalina e catalítica, bem como a possibilidade de geração de ácido peracético pela combinação
do oxone com peróxido de hidrogénio. Em ambas as vias, foram avaliados os efeitos da
temperatura, do pH, da concentração dos sistemas oxidantes e do tipo e da dosagem dos
produtos auxiliares. O desempenho do branqueamento foi avaliado pelo grau de branco,
determinado usando a escala Berger, adotando como referência o limiar de aceitação industrial
de um branqueamento eficaz, correspondente a valores superiores a 60.
Os resultados obtidos mostraram que nenhuma das vias investigadas permitiu atingir, de forma
satisfatória e reprodutível, o limiar mínimo de 60 graus de branco. Na via enzimática, a
utilização de concentrações consideradas economicamente viáveis para aplicação industrial,
não proporcionaram ganhos de brancura relevantes, tendo sido alcançado um valor máximo de
apenas 23 graus de branco. Por sua vez, a via baseada no oxone, apresentou,
independentemente das condições testadas, incluindo temperaturas elevadas e diferentes
estratégias de ativação, valores de brancura na ordem dos 50 graus de branco. Conclui-se, assim,
que, nas condições experimentais e nos intervalos de concentração estudados, não foi possível
substituir o processo convencional de branqueamento sem comprometer significativamente o
desempenho em termos de brancura.
The conventional bleaching process of 100% cotton knitted fabric with hydrogen peroxide in an alkaline medium is associated with high energy consumption and a significant environmental impact, mainly due to the need for high processing temperatures and the use of sodium hydroxide to promote the activation of the oxidising species. The present dissertation, developed at Aquitex, aimed to investigate more sustainable alternatives to this process, seeking to reduce the process temperature and decrease or eliminate the use of sodium hydroxide, thus contributing to the reduction of energy consumption and the environmental impact associated with effluents. For this purpose, two distinct oxidation routes were explored. In the enzymatic route, laccase and peroxidase, as well as their respective mediators, were used, selected for their ability to act under moderate pH and temperature conditions. The chemical route was based on the use of oxone, a triple salt selected for its high oxidising potential. For this system, different activation strategies were explored, namely thermal, alkaline and catalytic activation, as well as the possibility of generating peracetic acid through the combination of oxone with hydrogen peroxide. In both routes, the effects of temperature, pH, concentration of the oxidising systems, and the type and dosage of the auxiliary products were evaluated. The bleaching performance was assessed by the degree of whiteness, determined using the Berger scale, adopting as reference the industrial acceptance threshold for effective bleaching, corresponding to values higher than 60. The results obtained showed that none of the investigated routes allowed the minimum threshold of 60 degrees of whiteness to be achieved in a satisfactory and reproducible manner. In the enzymatic route, the use of concentrations considered economically viable for industrial application did not provide relevant gains in whiteness, with a maximum value of only 23 degrees of whiteness being achieved. In turn, the route based on oxone presented, regardless of the tested conditions, including high temperatures and different activation strategies, whiteness values in the order of 50 degrees of whiteness. It is therefore concluded that, under the experimental conditions and concentration ranges studied, it was not possible to replace the conventional bleaching process without significantly compromising the performance in terms of whiteness.
The conventional bleaching process of 100% cotton knitted fabric with hydrogen peroxide in an alkaline medium is associated with high energy consumption and a significant environmental impact, mainly due to the need for high processing temperatures and the use of sodium hydroxide to promote the activation of the oxidising species. The present dissertation, developed at Aquitex, aimed to investigate more sustainable alternatives to this process, seeking to reduce the process temperature and decrease or eliminate the use of sodium hydroxide, thus contributing to the reduction of energy consumption and the environmental impact associated with effluents. For this purpose, two distinct oxidation routes were explored. In the enzymatic route, laccase and peroxidase, as well as their respective mediators, were used, selected for their ability to act under moderate pH and temperature conditions. The chemical route was based on the use of oxone, a triple salt selected for its high oxidising potential. For this system, different activation strategies were explored, namely thermal, alkaline and catalytic activation, as well as the possibility of generating peracetic acid through the combination of oxone with hydrogen peroxide. In both routes, the effects of temperature, pH, concentration of the oxidising systems, and the type and dosage of the auxiliary products were evaluated. The bleaching performance was assessed by the degree of whiteness, determined using the Berger scale, adopting as reference the industrial acceptance threshold for effective bleaching, corresponding to values higher than 60. The results obtained showed that none of the investigated routes allowed the minimum threshold of 60 degrees of whiteness to be achieved in a satisfactory and reproducible manner. In the enzymatic route, the use of concentrations considered economically viable for industrial application did not provide relevant gains in whiteness, with a maximum value of only 23 degrees of whiteness being achieved. In turn, the route based on oxone presented, regardless of the tested conditions, including high temperatures and different activation strategies, whiteness values in the order of 50 degrees of whiteness. It is therefore concluded that, under the experimental conditions and concentration ranges studied, it was not possible to replace the conventional bleaching process without significantly compromising the performance in terms of whiteness.
Descrição
Palavras-chave
Bleaching Cotton Textile Oxidation Oxone Oxidoreductases Branqueamento Algodão Têxtil Oxidação Oxone Oxirredutases