Characterization of coir fiber powder (cocos nucifera L.) as an environmentally friendly inhibitor pigment for organic coatings

Abstract

The reuse of an agricultural by-product in consense with the development of green coatings, motivated the characterization of coconut fiber powder, as a renewable inhibitor pigment. Coconut microfibers are a new, efficient, eco-friendly inhibitor pigment. The aim of this work to homogenize the particle size - MESH 250 -, the fiber was milled and sieved. The coconut fiber powder underwent an alkaline treatment, with immersion in sodium hydroxide solution - NaOH 5% (w/w) - for 24 h. The morphological characterization of untreated microfiber (UM) and treated microfiber (TM) were performed using laser diffraction and scanning electron microscopy (SEM). The compositions of the UM and TM samples were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and their thermal decomposition by the thermogravimetric analysis (TG/DG). The samples were characterized as a coating pigment in terms of density, oil absorption, and CPVC. Weight loss and potentiodynamic polarization curves tests were performed for understanding the inhibitory effect of fiber powder samples. Despite the high oil absorption of the samples (UM-95.73, TM-99.46) it has a low density, therefore presenting CPVC values that allow the formulation of coatings with ideal PVC. The FTIR showed that the untreated microfiber samples had lignocellulosic matrix and tannins in their composition, the treated sample showed removal of some materials from the structure, increasing the lignin concentration. The mass loss and potentiodynamic assays showed an inhibition efficiency of approximately 70% for UM and 90% for TM.