Graduate Thesis Or Dissertation
 

Orienting lignocellulosic fibers by means of a magnetic field

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  • Controlling the orientation and spatial distribution of discontinuous fibers in composite materials enables product properties to be tailored to anticipated use. Electric fields are already (albeit rarely) used to affect alignment in lignocellulosic (LC) fiber composites. The use of magnetic fields has not, however, been suggested or explored; this is apparently because LC fibers are essentially non-magnetic. The approach may offer, however, some considerable advantages, as long as ferromagnetism may be imparted to the fibers. In the present research several fiber modification processes were considered and two, electroless nickel plating and spray application of a coating containing nickel in suspension, were investigated in more depth. The latter was chosen to render highly engineered, elongated wood particles responsive to magnetic fields. Individual treated particles were suspended in viscous, newtonian silicone fluids and their rotation under the influence of a controlled magnetic field was video recorded. The magnetic torque on the particle was, under the above conditions, directly proportional to the fluid viscosity, to the particle's angular velocity and to a characteristic shape constant. The maximum of the specific magnetic torque (magnetic torque divided by the shape constant) was found to reflect the influence of field strength and particle Ni-treatment on rotation. Results were scaled to an arbitrarily chosen viscosity for comparison. The dependencies of the magnetic torque found in the present research compare with those theoretically predicted for ellipsoidal and cylindrical bodies. For field strengths ranging from 0.07T to 0.15T (below magnetic saturation) the magnetic torque increased almost linearly with increasing field strength. Magnetic torque was also found to increase nearly linearly with increasing bulk Ni-concentration (5g/kg - 50g/kg). Rotational motion was sometimes impeded at low field strengths and this was attributed to a permanent magnetic moment obtained by the particle. A coercive field strength of 7600A/m supported this hypothesis. Judiciously switched field polarity increased magnetic torque at small alignment angles. The present research indicates that orienting LC fibers with magnetic fields is possible and promising. To study dynamics of fiber motion in low viscosity fluids, such as air, a different experimental method is necessary; however, dependencies of the magnetic torque found in the present study still hold true.
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