Determination of the Optimum Coupling Agent Content for Composites based on Hemp and High Density Polyethylene

摘要

It is well known that for polymer composites based on natural fibers, the addition of a coupling agent is necessary to improve fiber dispersion and adhesion with the matrix. Nevertheless, an optimum content must be found which is related to the total surface area created between the fibers and the matrix. But in most cases reported in the literature, a single property (like tensile strength or flexural modulus) is used to determine this optimum value. In this work, high density polyethylene (HDPE) was reinforced with hemp fibers as a typical system. In particular, the addition of a coupling agent based on maleated polyethylene (MAPE) was studied to determine its optimum content. To better detect the specific effect of the selected coupling agent, reinforcement content was limited to 10% wt., while the MAPE content was controlled at different levels (0, 5, 7, 9 and 11% wt. based on total hemp content). Compounding was performed in a twin-screw extruder and the samples were produced by compression molding. From the composites obtained, a complete set of characterization in terms of morphology (SEM), mechanical properties (tension, flexion, and impact), and density (pycnometry) was made. From all the results obtained, it can be shown that 9% wt. MAPE is the optimum content maximizing all the mechanical properties. These results indicate that any physical property can be used to determine the optimum coupling agent content.