Enzymatic modification of secondary sludge by lipase and laccase to improve the nylon/sludge composite properties

Abstract

Secondary sludge from pulp and paper mills can be considered as potential filler for composite industry. Enzymatic modifications of the waste secondary sludge from pulp and paper mills to reduce the hydrophobicity and increase the molecular weight have been carried out by lipase and laccase, respectively. The enzymatic modification was performed to enhance the reinforcing capability of the secondary sludge for further composite production. The lipid content of the secondary sludge, which was measured to be 6 AE 0.5%, was hydrolyzed by lipase from Candida rugosa and the structural changes were followed by Fourier transform infrared (FTIR) spectroscopy. Laccase from Trametes versicolor was tested for its activity and reaction rate in the secondary sludge and the alkali-extracted lignin. Characterization of the sludge before and after the laccase treatment was carried out by FTIR spectroscopy. High pressure size exclusion chromatography (HPSEC) was applied to determine the molecular weight distribution of the lignin samples and also as a means for comparing modified and unmodified samples. Biokinetic parameters for the Michaelis-Menten kinetic model as a function of dissolved oxygen concentrations were determined the K m values to be 3.491 and 2.318 g/m 3 for sludge and the alkali extract, respectively. The FTIR results on the laccase-treated secondary sludge showed clear changes in the molecular structure, which was mainly attributed to the crosslinking reactions and generation of new bonds. Moreover, the HPSEC results revealed that laccase modifies the sludge by increasing the molecular weight. The manufactured nylon/sludge composites showed lower tensile strength for the lipase treated sludge/nylon composite. However, the laccase-treated sludge/nylon composite showed a statistically significant increase in the mechanical strength, which is attributed to the increase in the components molecular weight.

Plant-Based Natural Fibre Reinforced Composites: A Review on Fabrication, Properties and Applications

“…To increase the interfacial bonding between the fibre and the matrix, it is necessary to improve the hydrophobicity of the fibres, the interfacial bonding between matrix and fibre and the roughness [188]. Bonding between fibre and matrix is usually enhanced by a few mechanisms, such as mechanical interlocking, chemical bonding, electrostatic bonding and inter-diffusion bonding [189][190][191][192][193][194][195]. Besides, the other factors such as temperature, pressure, time and resin viscosity seriously affect the properties of the biocomposites [139,[196][197][198].…”