The Influence of Different Retting Processes on the Strength of Fibres obtained from Poliostigma raticulatum, Grewia mollis, Cissus populnea and Hibiscus sabdariffa

Abstract

The extraction of vegetable fibres from different parts of plants has been a major focal point in the search for natural fibres that would substitute synthetic fibres. Fibres from Poliostigma reticulatum, Grewia mollis, Cissus populnea and Hibiscus sabdariffa were extracted by water and chemical retting. In chemical retting different concentrations of NaOH and NH 4 OH were used. The extracted fibres were further purified and their tensile strength measured. The pH of water was measured as retting progresses and observed to increase as the retting time increases. This was ascribed to the secretion of enzymes by microorganisms as they acted on the mucilaginous matter of the bast with the resultant loosening of the fibres. The tensile strength of the fibres was determined using the Shirley Testometric 220D and was observed to gradual decline as the retting time increases. This was attributed to the continual removal of non-fibrous matter and the freeing of the fibres in the composite. However, beyond the fifth week of retting, no appreciable change in tensile strength was observed. This suggested that most of the non-fibrous matter have been solublized and utilized as source of nutrients and energy by the microorganisms. Acidic metabolites were produced due to microbial activities may have changed the pH of the medium and subsequently hindered their growth. In chemical retting, as the concentration of the medium increases the strength of the fibres decreases to a minimum then remain constant. This was accredited to the breakdown of inter- molecular bonds between non-fibrous substances and the fibres. And subsequently, the non-fibrous components separate from the fibres and dissolved in the medium revealing the actual fibres strength. It was therefore, opined that retted fibres in water, 5% NH 4 OH and 15% NaOH are clearer and lustrous for all sample except those from Kargo.