This paper discusses the usage of thiourea dioxide to modify the residual terminal amino groups of amino acid in laccase. The effect of modified-laccase/glutamate treatment on the microstructure and properties of old newspaper deinked pulp was investigated by means of fourier transform infrared spectroscopy and headspace gas chromatography. Results showed that after the modified-laccase/glutamate treatment, the content of carboxyl groups in pulp increased remarkably by 20.8 %. Microscope images showed the fiber filamentation was more obvious, and fibrils content on the fiber surface increased. The fiber quality analyse indicated that fiber coarseness decreased notably but length and width changed a little. The paper physical analysis showed that the paper strength properties had improved remarkably while whiteness decreased slightly.
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