Issues and challenges in injection molding of LFBC
The behavior of the developed biocomposites is significantly influenced by the orientation, dispersion, and size of the lignocellulosic fibers within the biocomposite. Issues and challenges have thus been divided into the three following subsections.
Distribution and orientation of natural fibers
In order to develop biocomposites exhibiting exceptional mechanical behavior, the lignocellulosic fibers should ideally be oriented in the direction of applied load. The orientation of lignocellulosic fibers during injection molding is influenced by the fiber—matrix melt flow within the mold. However, in the case of injection molded LFBC, complex fluid flow is observed. During mold filling, the shear flow experienced by the fiber—matrix mixture close to the mold walls, tends to align the fibers in the direction of the flow. This phenomenon is observed for a certain thickness below the surface. However, near the core, bulk deformation of the fiber— matrix flow takes place, which orients the fibers randomly in the direction perpendicular to the applied load (Singh and Chaitanya, 2015). Fig. 9.7 depicts fiber orientation behavior of injection molded sisal fiber-reinforced PLA biocomposites. Fig. 9.7A represents a schematic of fiber orientation at a mid-cross-sectional plane
Figure 9.7 Fiber orientation in injection molded LFBC.
parallel to the direction of flow. Fig. 9.7B represents the sisal fiber orientation in the cross-sectional plane perpendicular to the direction of flow. It can be observed from both the figures that the fibers near the mold walls tend to align in the direction of the applied load, while the fibers near the core align randomly. It was also observed that short lignocellulosic fibers are more likely to orient and disperse themselves in the direction of the applied load compared to long fibers (Chaitanya and Singh, 2016b). Hence, during loading, the fibers aligned in the direction of applied load bear more load as compared to the randomly aligned fibers, affecting the overall load-bearing capability of the injection molded biocomposite.