In order to utilize polypropylene staple fiber as textile material and to develop novel spun yarn with good functionality, we investigated how to construct a three-layered structure of composite single yarn and/or adopt the production method of triplet spun yarn using an experimental ring spinning frame. The unique spinning conditions were not only the types of staple fibers but also the arrangement and the distances of three rovings and the twist level of yarn. The following results were obtained: (1) By adopting the production method of triplet spun yarn with three rovings made from the different types of fibers in the arrangement of different rovings under the spinning condition with an equal distance of roving, the yarn combining side-by-side and sheath-core structures could be constructed by one point of yarn formation and one twisting process without the device for controlling of spinning tension; (2) In the spinning method of staple-core spun yarn, it was necessary to control the difference between spinning tensions of the sheath layer with side-by-side structure and the staple-core layer under the spinning condition with the lower twist level of yarn; (3) For constructing the staple-core layer from polypropylene fiber with greater torsional rigidity, it was important not only to control the greater length of drafted fiber strands for the sheath layer but also to choose the fineness and cut length of the sheath and the core fibers and the composition ratio of polypropylene fiber and to have the greater spindle speed in the spinning frame.

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An excessive computational time is required to perform accurate numerical simulations for flow kinematics in a FRP processing, e.g., one week. In contrast, when the eco-strategy of numerical solution proposed here is used, it would take a so much shorter computational time, less than 10 minutes. The predictions will be also useful for the practical purpose in a fiber composite processing, thus the numerical solution strategy would have some potential.
Furthermore, it is well known that the addition of slender particles to a Newtonian liquid can drastically change the flow kinematics even at very low concentrations. Why does such a phenomenon occur? Estimation of flow energy consumption makes it clear that slender particle dispersion can flow through a complex geometry by smaller energy consumption owing to a change in its flow kinematics. In particular, contribution of extensional deformation to flow energy saving becomes dominant. It is, therefore, concluded that slender particle dispersions are so smart.

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