Gas injection consolidation of miniature natural fiber beams

Graduation date: 2003The internal structure of natural fiber composites can be manipulated by controlling the spatial distribution of fiber orientation and internal chemical and thermodynamic conditions during their consolidation. Objects highly tailored to specific service demands may thereby be produced. Techniques to form miniature structural beams from oriented hemp and random wood fiber networks with phenol formaldehyde (PF) adhesive have been explored. Beams have been consolidated in a specially developed rectangular gas injection pressing system using ammonia as a softening agent and an ester as a low-temperature adhesive catalyst. A range of natural fiber and adhesive types for use in producing the small composite beams are reviewed and hemp and wood fibers selected. Anatomical, tensile strength, and bonding characteristics of hemp fibers are explored. Adhesion kinetics of PF adhesive with both individual hemp strands and fiber networks in the presence of methyl formate at 50°C was also studied. Methyl formate was found to hasten the rate of strength development and final network strength by 51% and 22% respectively. The presence of waxy epidermal surfaces on hemp fibers has been found to limit strength of PF adhesive-to-fiber bonds to approximately 1 .OMPa, while opposing surfaces bond well (4.5MPa). The effect of testing temperature on the strength of partially cured PF resin-to-wood bonds was investigated to explore the possibility of reducing hot pressing time in conventional hot pressing processes of wood-based composite manufacturing and also to take advantage of temperature control that may be affected in sealed pressing methods. The shear strength of partially cured PF-to-wood bonds was found to be significantly increased by reducing temperature. This temperature effect was greatest at the beginning of bond formation and progressively decreased to zero with increasing isothermal cure. Chemicals have been selected to sequentially stimulate fiber softening (anhydrous ammonia) and adhesion (methyl formate) in the sealed pressing system under near-ambient temperature conditions. It was found that density gradients can be created within beams by injecting ammonia from one platen. Stress analysis of a density graded beam showed that such a beam performs more efficiently than homogeneous beams of the same weight