Fabrication and Characterization
The Mg alloy reinforcements were in the form of fibers/wires that were 300 цт in diameter. Once they were arranged directionally a solution of PLA dissolved in chloroform was poured on them and left to dry in air for 12 h. Then the lamina stacking method was employed as described in . To further increase the mechanical strength of the alloy fibers micro arc oxidization (MAO) treatment was performed on a batch of fibers, which were used to fabricate a separate set of PLA/Mg alloy treated scaffolds. The volume fraction of the fibers in the composites was 5%, 10%, 20% and 40%. Finally, pure PLA scaffolds, again using the lamina stacking method were fabricated to use as the control group and better understand the effect of the Mg alloy and Mg alloy treated reinforcements.
Scanning electron microscopy, shown in Fig. 4.7 revealed that the PLA had a uniform structure into which the fibers were directionally distributed in a uniform manner. The difference between the MAO treated fibers is that their surface was coated with a porous structure which allowed for better adhesion with the PLA as it could penetrate into the pores and result in a stronger interface.
Inclusion of the untreated fibers in the PLA resulted in a significant increase in the tensile strength of PLA. Performing tension tests indicated that the pure PLA scaffold had a tensile strength of 46 MPa and increasing the fiber content continually increased it to 50 MPa (5% fibers), 65 MPa (10% fibers), 80 MPa (20% fibers), and 108 MPa (40% fibers). Three point bending was further used to determine the bending strength which was found to be 88 MPa for PLA and increased with fiber addition to 99 MPa (5% fibers), 119 MPa (10% fibers), 136 MPa (20% fibers), and 190 MPa (40% fibers). This increase in strength was further enhanced for the composites fabricated with the MAO treated reinforcements. Particularly, for the 20% MAO treated composite the tensile strength was 100 MPa, i.e. 14% higher than without surface modification and the bending strength was 150 MPa, i.e. 11% higher than the untreated case . As mentioned MAO treatment resulted in better PLA/fiber bonding and therefore the interface strength was increased which enhances the overall composite strength.