Single-walled carbon nanotubes were added to two different grades of polypropylene to produce composites. The composites were then melt-spun into fibers, and the fibers were tested with both a conventional tensile pull tester and dynamic mechanical analysis. The changes in tensile properties were related to the grade of polypropylene used. In addition to fibers being made from the mixes, coarse extrudates (i.e., undrawn, gravity-spun filaments) were also produced. Density measurements on these extrudatesshowed that the addition of nanotubes increased the composite density in a highly nonlinear manner, which suggested interaction between the polypropylene and the carbon nanotubes.

Polybutylene (PB-1) fibers were spun at spinning speeds of 250-2500 m/min. A tensile tester was used to analyze the stress-strain behavior of these fibers. In addition, birefringence and the effect of aging were examined. A DMA (dynamic mechanical analyzer) was used to measure the storage modulus and loss modulus of the fibers. Nonwoven mats of the fibers were prepared and compression tests were run on these mats. The properties of the polybutylene fibers and mats were compared with the properties of common polypropylene fibers and mats.

Other crystalline polymer pairs have been studied wherein a synergism was found in their mechanical properties. For example, PP/HDPE was studied by Noel and Carley (1975) in a wide range of compositions. They found that very low amounts of HDPE caused a maximum in the tensile modulus and strength of the blends. They concluded that, when the HDPE component is less than 10%, the HDPE acts as a stiffener. In contrast, small amounts of PP were found to make the blend ductile. Stell et al. (1976) studied polymer blends of PS/HDPE in stretched films. These authors found that the mechanical properties of the films (tensile strength and elongation at break) were best when the films were quenched right after hot stretching. Blends of polybutylene (PB-1) and polypropylene were used to produce fibers at spinning speeds of 800-2100 m/min. Concentrations ranged from 0% PP to 100% PP. The stress-strain behavior of the resultant fibers was examined, and the fibers were analyzed for crystallinity via DSC (differential scanning calorimetry). Fibers produced from blends of PB-1/PP show mechanical properties that are in between the properties of the pure polymers. The tensile strength of 50% PB-1 fibers is comparable to the tensile strength of pure PP fibers. Fibers produced from blend compositions of 25 and 75% have higher tensile strengths than pure PP fibers, although these blend compositions have lower tensile strengths than pure PB fibers. The present study is concerned with crystalline blends of PB-1/PP and characterization of the fibers produced from these blends. Although this type of blend has been studied over the years, especially in the form of thin films and molded samples, there is little research on the characteristics of fibers formed from this particular blend. Foglia (1969) concluded that the PB-1/PP blends are "highly compatible in all proportions under normal operating conditions". In later studies, Siegmann (1979; 1982) examined the interactions of both components and found that the presence of PP in PB depresses the melting temperature of both components in the blend. From thermal analysis he found that PP and PB-1 seemed to crystallize separately with no evidence of cocrystallization. In addition, he reported that the crystallinity ratio of PB-1/PP is not linear with respect to percentage of composition. Siegmann also ran X-ray analyses that supported his conclusion that crystallinity ratio is not linear with respect to composition percentage. In addition, the X-ray results showed that the crystalline size did not change with the ratio of the polymers present in the blend. Siegmann suggested that the morphology of the blends changes from spherulite to branched crystallites as the composition changes.