EFFECTIVENESS OF ENZYMATIC TREATMENT ON A CONTINUOUS FLAX FIBRE REINFORCED COMPOSITES
Topic(s) : Material science
Co-authors :
Giulia RONCONI (ITALY), Alexander BEHRENS (GERMANY), Regine HIRSCHBERG , Marco ZANELLI (ITALY), Pietro RUSSO (ITALY), Nina GRAUPNER (GERMANY), Jörg MÜSSIG (GERMANY), Francesco MOLLICA , Valentina MAZZANTI (ITALY)Abstract :
The present study shows a different approach to the manufacturing of a unidirectional composite, reinforced with bast fibres. A unidirectional flax fibre reinforced poly-(lactic acid) laminae were obtained by filament winding followed by compression moulding. The filament winding methodology was used to avoid fibre misalignment. Maintaining the same fibre loading (30 wt.%), two different cases were investigated: untreated and enzymatically treated fibres. The enzymatic treatment promotes the opening of the fibre bundle. In fact, pectinase is able to partially remove the middle lamella that holds the different elementary fibres together.
Tensile specimens were then cut from the laminae tested in accordance with ASTM D3039 at 0°, 10° and 90° with respect to fiber direction. From a macro-mechanical point of view, the influence of bundle opening and fibre fineness on the tensile tests was studied, and the results showed a significantly higher longitudinal tensile strength in light of the enzymatic fibre treatment. The improved aspect ratio of reinforcing fibre leads to properties from 170 MPa for untreated fibre reinforcement up to 185 MPa for the treated fibre. This last result is also confirmed by the single fibre tensile test, which shows an improvement in tensile strength and Young’s modulus in the enzymatically treated fibres. This enhancement is ranging from 380 MPa for untreated fibre up to 430 MPa for treated fibre.
On the other hand, at the micro-mechanical level, microbond tests were carried out in order to measure the interfacial shear strength (IFSS). In this case, the treatment effect was merely to clean the surface of the fibres. The untreated fibres showed a higher apparent IFSS due to their rougher surface. As a result, the apparent IFSS decreases slightly, from 20 MPa for the untreated fibre down to 15 MPa for the treated fibre. Furthermore, this aspect is also reflected in the shear properties of the composite. In fact, the samples of the composite with 10° fibre orientation showed a lower stress at break in the case of the treated fibres than in the case of the untreated fibres. This indicates that the load transfer between the fibre and the matrix is less effective.
There is then a consistent trend in the micro and macro characterization, which underlines the lower shear properties in the composite reinforced with treated fibres. In other words, the fibre/matrix interfacial behaviour is clearly influenced by the fibre surface and plays a significant role in the mechanical properties.
Tensile specimens were then cut from the laminae tested in accordance with ASTM D3039 at 0°, 10° and 90° with respect to fiber direction. From a macro-mechanical point of view, the influence of bundle opening and fibre fineness on the tensile tests was studied, and the results showed a significantly higher longitudinal tensile strength in light of the enzymatic fibre treatment. The improved aspect ratio of reinforcing fibre leads to properties from 170 MPa for untreated fibre reinforcement up to 185 MPa for the treated fibre. This last result is also confirmed by the single fibre tensile test, which shows an improvement in tensile strength and Young’s modulus in the enzymatically treated fibres. This enhancement is ranging from 380 MPa for untreated fibre up to 430 MPa for treated fibre.
On the other hand, at the micro-mechanical level, microbond tests were carried out in order to measure the interfacial shear strength (IFSS). In this case, the treatment effect was merely to clean the surface of the fibres. The untreated fibres showed a higher apparent IFSS due to their rougher surface. As a result, the apparent IFSS decreases slightly, from 20 MPa for the untreated fibre down to 15 MPa for the treated fibre. Furthermore, this aspect is also reflected in the shear properties of the composite. In fact, the samples of the composite with 10° fibre orientation showed a lower stress at break in the case of the treated fibres than in the case of the untreated fibres. This indicates that the load transfer between the fibre and the matrix is less effective.
There is then a consistent trend in the micro and macro characterization, which underlines the lower shear properties in the composite reinforced with treated fibres. In other words, the fibre/matrix interfacial behaviour is clearly influenced by the fibre surface and plays a significant role in the mechanical properties.