Evaluation of load transfer in the cellulosic fiber/polymer interphase using a micro-raman tensile test
Published: 2007
Abstract:
The objectives of this research were (1) to use a Raman micro-spectroscopic technique to determine the tensile stress distribution of a cellulosic-fiber/polymer droplet interphase, and (2) to examine if the stress profile could be used to evaluate load transfer in fiber/polymer adhesion. Cellulosic fibers were treated with various salines (amino, phenylamino, phenyl, and octadecyl functionalities) and a styrene-maleic anhydide copolymer to creat different interphases upon bonding with polystyrene. A single fiber, bonded with a micro-droplet of polystyrene in the mid-span region of its gage length, was strained in tension. Raman spectra was collected at five-micrometer intervals along the embedded region of the fiber. The stress-dependent peak of cellulose was analyzed for frequency shift so that the local tensil stress in the interface region could be determined. Results showed that the local tensile stresses of the strained fiber were lower in the embedded region combared to the exposed region, suggesting a transfer of load from the fiber to the matrix polymer. A deeper and sharper decline of the stress profile was observed when the fiber/droplet interaction was enhanced. Further analyses, involving conversion of tensile stress profiles to shear stress distributions in the interphase, confirmed that the micro-Raman/tensile test can be employed to evaluate fiber/matrix interfacial bonding in composites. This success signifies the possibility of evaluating adhesion between cellulosic fibers and brittle polymers, which is difficult to study using common micromechanical tests. Use of the micro-Raman technique can improve our understanding of wood/polymer adhesion.
Documents: