Retting and Chemical Treatment of Natural Fibers–A Review

Natural fibers are extracted from plant sources by different retting methods such as microbial, enzymatic, chemical, mechanical and physical. Microbial retting further consists of water, ribbon and dew retting. Microbial retting methods are time consuming and not eco-friendly, though they are extremely simple and low cost. Enzymatic retting is quicker, eco-friendly and produces high-quality fibers. Chemical retting is quicker and produces good fiber when process is well controlled. Mechanical retting is suitable for mass production though they produce low or moderate quality fibers. Physical methods such as steam explosion produce good quality fibers though the lengths are shorter and there is a limitation on the steam pressure values. Extracted raw natural fibers inspite of their advantages such as biodegradability, recyclability, low density, etc. have limitations such as higher moisture absorption and poor compatibility with the polymer matrix. To tackle these issues, they are chemically treated to modify their surfaces. Different chemical treatments are available such as alkali, silane, acetylation, benzoylation, bleaching, etc. Alkali treatment produces rougher surface and better bonding with polymer matrix, silane treatment produces new chemical linkages with polymer chain. Similarly, benzoylation and acetylation too have positive effects on the natural fiber compatibility with the polymer matrix.