Natural Fibre Composites: Laccase-Enzyme Treatment of Flax Fibres for improved Interfacial Strength
Topic(s) : Material science
Co-authors :
Hanna BRODOWSKY (GERMANY), Anne HENNIGAbstract :
Natural plant fibres are more sustainable than other reinforcement fibres, as the carbon dioxide footprint during production is far lower than that of synthetic reinforcement fibres. Especially flax or hemp fibres provide an attractive reinforcement of polymer matrices, as they combine high specific strength and modulus with low machine wear and reasonable prices, especially in applications where high damping is valued.
In any composite, the interphase between fibre and matrix is the region of highest stresses, therefore a tailored adhesion between fibre and matrix is essential for any composites’ properties. Modifying the fibre surface can increase the adhesion and thereby enhance the mechanical properties of composites. Good results have been achieved with sodium hydroxide treatments followed by a sizing of silane bonding agents and film formers chosen in correspondence to the studied matrix.
In the present study, a novel sustainable surface treatment is presented: the fungal enzyme laccase was utilized with the aim of covalently binding the coupling agent dopamine to fibre surfaces. Laccase catalyzes the ring opening reaction, enabling the dopamine to bond to lignin present in the natural plant fibres (flax). The goal is to improve the interfacial strength and permit bonding with the epoxy matrix. SEM and AFM micrographs showed that the modification changes the surface morphology, indicating a deposition of dopamine on the surface. Fibre tensile tests, which were performed as control to check whether the fibre structure was damaged during the treatment, showed that no decrease in tensile strength or modulus occurred.
The present study compares two methods of determining the interfacial shear stress in natural fibre reinforced composites: the single fibre fragmentation test and the single fibre pullout test. In the observed samples, single fibre fragmentation test data of fracture mode and fragment length scatter when compared to single fibre pull-out data. In single fibre pullout tests, force displacement curves are measured on single fibres embedded into a matrix droplet. Evaluating the local interfacial shear strength (IFSS) during fracture showed a 30% increase in IFSS due to the laccase-mediated bonding of the coupling agent dopamine. These results demonstrate that a laccase induced dopamine treatment modifies flax fibres sustainably and increases the interfacial strength towards epoxy. The method also permitted an evaluation of the frictional stress occurring after surface failure. These results demonstrate that a laccase + dopamine treatment modifies flax fibres sustainably and increases the interfacial strength towards epoxy.
In any composite, the interphase between fibre and matrix is the region of highest stresses, therefore a tailored adhesion between fibre and matrix is essential for any composites’ properties. Modifying the fibre surface can increase the adhesion and thereby enhance the mechanical properties of composites. Good results have been achieved with sodium hydroxide treatments followed by a sizing of silane bonding agents and film formers chosen in correspondence to the studied matrix.
In the present study, a novel sustainable surface treatment is presented: the fungal enzyme laccase was utilized with the aim of covalently binding the coupling agent dopamine to fibre surfaces. Laccase catalyzes the ring opening reaction, enabling the dopamine to bond to lignin present in the natural plant fibres (flax). The goal is to improve the interfacial strength and permit bonding with the epoxy matrix. SEM and AFM micrographs showed that the modification changes the surface morphology, indicating a deposition of dopamine on the surface. Fibre tensile tests, which were performed as control to check whether the fibre structure was damaged during the treatment, showed that no decrease in tensile strength or modulus occurred.
The present study compares two methods of determining the interfacial shear stress in natural fibre reinforced composites: the single fibre fragmentation test and the single fibre pullout test. In the observed samples, single fibre fragmentation test data of fracture mode and fragment length scatter when compared to single fibre pull-out data. In single fibre pullout tests, force displacement curves are measured on single fibres embedded into a matrix droplet. Evaluating the local interfacial shear strength (IFSS) during fracture showed a 30% increase in IFSS due to the laccase-mediated bonding of the coupling agent dopamine. These results demonstrate that a laccase induced dopamine treatment modifies flax fibres sustainably and increases the interfacial strength towards epoxy. The method also permitted an evaluation of the frictional stress occurring after surface failure. These results demonstrate that a laccase + dopamine treatment modifies flax fibres sustainably and increases the interfacial strength towards epoxy.