Kenaf fibers have been gaining great interest in fabricating composites with thermoset and thermoplastic polymers. However, natural fibers have had limits in their applications due to surface properties and moisture sorption that limit their application in semi-structural exterior components. Natural fibers undergo a retting treatment that uses micro-organisms and moisture to assist in removing material surrounding the fiber bundles to assist in removing the fiber from the stem. These treatments require follow-on surface modifications to reduce water sorption. This study applies a thermochemical modification called torrefaction on kenaf fibers that modifies the fiber chemistry by thermally removing chemical components as a method to reduce water sorption and investigate the thermal changes to the fiber properties. The study evaluates the effect of temperature, time, and atmospheres that were used and how it affects the fiber properties. Two temperatures of 175 °C and 275 °C were used based on chemical decomposition of xylan and cellulose with variates of time, (2 hours and 6 hours), reduced atmospheric pressure of -5 and -20 inches of mercury, and gases of nitrogen and air. The torrefaction results show temperature and time were the key contributors to fiber modifications with temperatures of 175 °C for 2 and 6 hours were less than 10% total mass loss, whereas, temperature experiments of 275 °C for 2 and 6 hours had mass losses from 20-80%. The kenaf fiber performance in water sorption was reduced in all conditions with the best performing fiber treated at 175 °C for 6 hours. Water sorption was reduced between 30-50% depending on the relative humidity of up to 85%. There was significant fiber strength degradation of all samples treated at 275 °C and were very frangible. Fibers treated at 175 °C did have a 40% reduction in fiber strength and the 6 hour treated fibers had a 20% reduction in strain at break. The moduli of 175 °C treatments were statistically indifferent. The results of molded composite panels from sheet molding compound showed a 50% reduction in 24-hour soak water uptake, however, there was a 20% reduction in tensile strength of the 175 °C treated fiber.
|Commitee:||Englund, Karl, Scuderio, Louis, Smith, Lloyd|
|School:||Washington State University|
|School Location:||United States -- Washington|
|Source:||DAI-B 80/07/(E), Dissertation Abstracts International|
|Keywords:||Retting treatment, Thermal changes, Thermoplastic polymers, Water absorption|
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