Effects of different treatments on the interface of HDPE/lignocellulosic fiber composites

We studied the chemical and mechanical characteristics of composites made up of HDPE (high-density polyethylene) and lignocellulosic fibers (in the presence or absence of a coupling agent). Interfacial morphology and esterification reactions between aspen fibers and the coupling agent were analyzed by means of Fourier Transform Infrared Spectrophotometry (FTIR) and Scanning Electron Microscopy (SEM). The variation of absorption in spectral bands (related to water absorption, glycosidic bonds in the cellulose backbone, hydroxyl and vinyl contents, and the formation of ether bonds) was determined in order to assess the influence of the coupling agents as well as the lignocellulosic fiber content. SEM micrographs were used in order to show the “bridge effect”, brought about by the coupling agent between the HDPE matrix and the reinforcement of lignocellulosic fibers. Mechanical properties, such as tensile strength, Young modulus, elongation at breaking point and toughness, were also analyzed. Finally, the differences observed between the various composites studied were explained by some specific adhesion mechanisms (including interdiffusion, adsorption-wettability and chemical bonds).