Using a purposely modified torsional dynamic rheometer with a closed cavity, I investigated composites of poly(vinyl chloride) (PVC) and green coconut fibers (GCFs) with Fourier transform (FT) rheometry, a new dynamic test technique that resolves the complex dynamic response of materials submitted to harmonic strain into their main and harmonic components. Because of instrument limitations in the low-strain region, torque signal harmonic components had to be corrected to yield results that suited established theoretical considerations. The preparation method of the composites had major effects on their linear and nonlinear viscoelastic responses; essentially, no homogeneous material could be prepared by dry blending plus extrusion, in contrast to dry blending plus mixing, which is the recommended technique; this was likely because PVC plasticization was then achieved. One of the most important rheological characteristics of the PVC-GCF composites was the quasidisappearance of the linear viscoelastic behavior. Nevertheless, an easy extrapolation technique was used to extract linear modulus data from the FT results, which led me to the conclusion that the reinforcing effect of the GCFs was essentially hydrodynamic with little, if any, interfacial interaction between the polymer matrix and the fibers. The results gathered from nonlinear viscoelastic properties, as obtained through FT rheometry, supplement this conclusion. (c) 2006 Wiley Periodicals, Inc.