Abstract:
To assist forest conservation efforts, panel products made from non-wood lignocellulosic fibre sources that can compete with established wood panels have recently received a lot of attention. The purpose of this research is to develop a process for manufacturing medium density and high density fibreboards (MDF and HDF) capable of full-scale production using kenaf bast fibres. Three different synthetic resins, urea formaldehyde, phenol formaldehyde and melamine urea formaldehyde were initially investigated to select a suitable resin system. Kenaf bast fibres were blow line blended with synthetic and bio-based resins using different resin contents and mat moisture contents to manufacture panels through hot pressing in a pilot plant. The investigation revealed that panels made withMUF resin at 12% resin loading and 12% mat moisture content would have elevated properties in accordance with the American National Standard Institute ANSI A208.2-2009. Comparative analysis has also shown that at same panel densities kenaf fibres are highly permeable, have flat vertical density profiles and are less compressible as compared to wood mats due to kenaf’s stiffness, high density and irregular shapes. The residual stresses developed during panel consolidation were 40-50% lower in kenaf panels compared to those of wood based panels. Further, investigation of the effects of fibre characteristics and panel density on the physicomechanical properties of panels revealed that kenaf fibres were more suitable for high density panels. Transverse air permeability of fibre mats made of different fibre lengths was measured as a function of mat density. Reducing the fibre length improved the permeability of the panels; hence thickness swelling of short fibre panels was better than long fibre panels and a minimum thickness swelling of 7.4% was achieved for panels with short fibres. It was found that kenaf mats had a permeability ten times higher, and required significantly larger compaction pressure at similar mat density compared to wood fibre mats. A relationship between permeability, thickness swelling, and mat density of the panels was determined. Various post-manufacturing hygrothermal treatments were used to reduce the residual stresses and improve the dimensional properties of kenaf MDF/HDF panels. The treatments significantly improved the quality attributes of the panels in terms of dimensional stability. The empirical models developed were of statistically significance and the experimental results were in agreement with the predicted responses. A strong correlation was found between thickness swelling and residual stresses of kenaf panels. Kenaf bio-panels with soy based adhesive were also manufactured on the basis of results obtained from fibre characteristics and permeability data. Bio-panels showed excellent mechanical properties, well above the MDF ANSI A208.2-2009 and hard board ANSI A135.4-2012 standards. However, due to poor dispersion of bio-resin, the panels showed mediocre dimensional properties. There is a strong indication from the results of this thesis that kenaf could be a promising alternative fibre source for composite panel production at a commercial level.