## 4 Discussion
### Mechanical Properties  
FRP-plywood presented better bending results, in stiffness and strength in both the parallel and the perpendicular direction, with respect toplywood. This is generally attributed to the capacity of fibers and adhesives (FRP) to enhance the mechanical properties oflywood. The bending test stiffness (MOE) and strength (MOR) were higher in the parallel direction than in the perpendicular direction. In the parallel direction, the ER-CF sample presented an increase of 48.2% and 52.8% of the MOE and MOR, respectively. In the perpendicular direction, the ER-CF sample was also the one that presented the greatest increase in MOE (52.0%), but it was the PVA-CF sample that presented the greatest increase in MOR (102.9%). The orientation of the veneers on the surface of theplywood defines the parallel and perpendicular direction of these. The greater strength of the structure of the wood fibers in the longitudinal direction is the cause of the greater strength to bending in the parallel direction of plywood. This gives it a higher MOR and MOE due to the longitudinal tensile and compressive strength of the wood, as well as a lower deflection of the samples during the test [26]. Incorporating FRP in the flexo-tensile surface of the plywood increases its stiffness and strength to parallel and perpendicular bending, changing its failure behavior from a brittle material to a more ductile material [14; 19; 27; 28]. The results obtained were in accordance with those from [PERSON] et al. [19], in which a 15-layered plywood reinforced with basalt fiber and bonded with epoxy resin on the tension side showed, in most instances, a better performance than the control panel. Figure 9: Load–deflection curves of the samples during the Janka hardness test. [PERSON] et al. [16], compared plywood samples reinforced with one and two layers of basalt fiber and bonded with PVA adhesive. The results obtained by these authors were also consistent with those obtained in the present study, where values of bending stiffness and strength of the FRP-plywood were higher than the control panel. With regard to the different behavior of the different adhesives used, similar results were published by [PERSON] et al. [29], who noted that PVA adhesive may impart superior bonding strength in the longitudinal tensile plane compared to the epoxy resin used, due to the intermolecular bonding, while the ER have better tensile properties when loaded in the transverse direction, which can be caused by the stronger thermosetting adhesive used. This performance was observed for MOE and MOR of the BF reinforced samples and for MOE of the CF reinforced samples. So, the material properties and composite performance will be derived from the thermoplastic or thermoset adhesive and from the fiber reinforcement used, but also from the bonding mechanisms between these components [30]. Additionally, the stronger curing state and the brittle nature of the ER can also result in increased strength values in a perpendicular direction [29]. On the contrary, the PVA adhesive is the least brittle among wood bonding adhesives; it has the ability to sustain high deformations without fractures [31], behavior that was evidenced with the higher strength values in the parallel direction. The results with the different adhesives used can lead to different uses of the FRP-plywood depending on the direction of the fiber. Hardness results are presented in Table 5 and are shown in Figures 8 and 9. Janka hardness is an important property to define the end use of FRP-plywood, especially when used as flooring components [32]. The FRP-plywood showed a higher Janka hardness. The PVA-CF sample presented the highest hardness and stiffness values, with increases of 79.0% and 82.9%, respectively. In this case, fibers bonded with PVA, an adhesive with ductile behavior, tend to have higher hardness values than fibers bonded with ER, an adhesive with brittle behavior.