Framework for Treatment of Coconut Coir Fibres through Physico-chemical Techniques

Coconut fibres have recently been used in numerous civil engineering applications, mostly in pavement structures as geotextiles. However, their performance is usually lower than the elements made with synthetic fibres, primarily due to their inherent variable characteristics, which mostly depend on the maturity level and pre-processing of the fibres. In this study, an effort is made to develop a framework for enhancing the characteristics of coir, considering the age of the fibres (immature and mature) as well as the treatment techniques. The treatment methods such as washing and boiling; alkali treatment with sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)₂); acidic treatment with acetic acid (CH₃COOH); and grafting with methyl methacrylate (MMA) were optimised for their concentration and soaking duration. The washing of the fibres generally results in a slight reduction in the diameter of the fibres due to the removal of surface impurities. Further, during the chemical treatments (NaOH and Ca(OH)₂), the particles get deposited on the fibres, resulting in improved absolute density. Thus, the reduction in diameter and the increase in absolute density of the fibres after the treatment process results in improved mechanical characteristics. The results indicated a superiority of chemical treatments over physical methods and grafting techniques. Post alkali treatment with Ca(OH)₂, unwashed mature and immature fibres demonstrated a 40.5% and 40.3% increase in tensile strength, while the treatment with NaOH resulted in an increase in the failure strain by 53% and 18%, respectively, under optimised conditions compared to unwashed fibres. Treatment with Ca(OH)₂ demonstrated higher tensile strength under optimised conditions; however, beyond the optimised treatment duration, a drastic reduction in the strength was observed, whereas NaOH-treated fibres exhibited a gradual decrease in the tensile strength. Though alkali treatments could enhance the properties of coir fibres, an excessive concentration or soaking duration was found to affect the fibres’ physical and mechanical characteristics adversely. For mature fibres, the optimum parameters (strength and failure strain) were obtained for 5% concentration of NaOH solution with a soaking period of 5 h, while for immature fibres, 6 h soaking duration was found to be optimum. Based on this comprehensive study, a framework is proposed which could be readily adopted for enhancing the quality of coir fibres.