Production And Characterisation Of A Bio-Composite From Cotton Stalk Fibre And Phenol Formaldehyde Resin

Abstract

Cotton stalks are a by-product of cotton farming. Approximately two to three tonnes of cotton stalk are generated per hectare of cotton farmed, making available in Zimbabwe about a million tonnes of cotton stalks every season. The cotton stalk is normally burnt to avoid pest infestations such as pink bollworm and mealybug, but this pollutes air emitting greenhouse gases. The current study, therefore, aims at finding an alternative use of the cotton stalks through production of a bio-composite based on phenol formaldehyde resin. Cotton stalks were collected from Umguza cotton farming district in Zimbabwe. The stalks were subjected to natural retting for 3 weeks followed by manual decortications to extract fibres. The fibre yield from extraction process was about 23%. The physical and mechanical properties of extracted fibres were characterized and categorized according to their relative position along the cotton stalk as top section, middle section and root section fibres. The cotton stalk fibres had a light brownish colour and their fibre length was determined as 8.18 cm. The moisture regain of the fibres was 11.14%, 10.68% and 10.20% for root, middle and top fibres, respectively. The fibres had an average diameter of 0.23 mm, breaking extension of 1.5% and density of 1.45g/cm 3 . The test results were analysed using Statistical Package for the Social Science and Minitab statistical software. The fibres were used to fabricate a composite using phenol formaldehyde resin following a hand layout process. The mass fraction (M f ) was increased from 0-38%and the density maintained between 650-900 kg/m 3 . The cost of producing the bio-composite was $5.80/m 2 which was cheaper than boards available in the market which cost approximately $5.56/m 2 . The board tensile strength varied between 2.3 MPa to 6.8 MPa depending on the M f while the flexural strength ranged between 46.39-170.00MPa. From the determined properties of the fabricated composite, it can be concluded that it has adequate mechanical properties comparable to solid wood in several applications such as ceiling panels, partition boards and table tops. As a recommendation steam explosion for fibre extraction can be studied as faster method to extract cotton stalk fibres. As further study the shive that is a by-product from fibre extraction can be ground and used as a potential composite filler material.