Hybrid yarns have reinforcing and matrix-forming filaments combined together in order to reduce the problems associated with high melt viscosity of thermoplastic matrices. Among hybrid yarns, commingled and air-textured yarns, which are produced with air jets have demonstrated high flexibility and good mixing of constituent filaments. Many research findings have been reported on the structure and properties of intermingled and air-textured yarns having low-modulus apparelgrade filaments. The relationships between air jet, filament yarn, and the processing parameters are critically reviewed. It is emphasized that there is an immediate need to study the mixing behavior of combination of high-and low-modulus filaments in air jet, which has not been investigated in detail in the published literature, in order to improve the mixing of these filaments. The methods used to characterize hybrid yarns are discussed. The need to study and improve the stability of the hybrid yarns in terms of maintaining the level of mixing of constituent filaments across the cross section is also established.
Commingling is becoming an important method for developing thermoplastic composites, which demonstrate significant advantages over thermoset composites in several applications including aerospace, marine, sporting, and automotive industries. Although the commingling technique has a very high potential to produce towpregs with a good blending of matrix and reinforcing fibers, it has been reported that these towpregs tend to de-mingle due to nonuniform stretching during textile and other preforming processes, leading to the segregation of stiffer reinforcing fibers and matrix-forming fibers, which in turn results in poor mechanical properties. Therefore, the current research focuses on the enhancement of stability and homogeneity of commingled yarns during subsequent processing. An attempt has been made to study the effect of the commingling process variables, namely air pressure and volume fraction of matrix-forming fibers on the structure and properties of Glass/Polypropylene, Glass/Polyester, and Glass/Nylon commingled yarns. In this paper, nips are classified into different categories based on their structure. The causes of occurrence and their effect on the commingled yarn properties are identified. Other parameters including nip frequency, nip length, and degree of interlacing are also studied in relation to the process parameters. The results show that commingling process parameters as well as the type of matrix-forming fibers significantly affect the structure and properties of commingled yarns.
In this study, a computational fluid dynamics (CFD) model is applied to study the airflow patterns inside the commingling jets, for different configurations. The CFD package, FLUENT 6.1, is used to predict the two-dimensional flow field inside a yarn channel. The parameters viz. velocity profile, pressure gradient, and air particle trajectory, obtained from this CFD analysis give important information for further analysis. The design parameters of commingling jets are related to the flow characteristics and their effect on the structure and properties of Glass/Nylon commingled yarns. The results show that the number of air orifice and the angle of orifice have significant effect on the airflow profile inside the jet and consequently on the structure of the commingled yarns. The jet orifice angle affects the axial velocity. The effect of air pressure is also important, since the nip frequency of commingled yarns is a function of the speed of rotation of the vortex and it is observed that with increase in air pressure, axial and tangential velocities in the nozzle increase. This work shows that, the CFD modeling can be used to optimize nozzle design parameters to develop commingled yarns with better properties.
The influence of glass-fiber (GF)/polypropylene (PP) commingled yarn structure on the impregnation quality of laminates is investigated by characterizing the microstructure and mechanical properties of the laminates. For this study, the degree of interlacing of the commingled yarns is taken as a measure of the structure of commingled yarns. Properties of laminates made by compression molding of commingled yarns are compared with those of laminates made with two other methods of composite manufacturing: film stacking and side-by-side (SBS) winding of glass roving and PP yarns. The results show that the degree of interlacing has a significant influence on the void content, fiber impregnation, and tensile behavior of composites made from commingled yarns. Laminates made from SBS and film stacking show more voids and dry fibers than those made from commingled yarns for the same consolidation conditions.
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