# Fabrication of Low-Twist and High-Strength Metallic Fibre Hybrid Spun Yarns
## 3 Results and Discussion
### Effect of the Twist on Tensile Properties of Yarns  
The tensile properties of MFHSYs are discussed in four sections corresponding to the objectives of the experimental design (Table 3). The tensile properties of MFHSYs from PS1 to PS3 are shown in Figure 2. The tenacity and elongation at the break of yarns are found to increase with the increase in TC. Under the optimum level of TC, this proportional increase in tensile properties is generally predictable. However, this predictable behaviour is only true within a specific range of defined parameters, distinctive to the material, composition, yarn count and processing parameters. What stands out in this figure is the stepwise decreasing trend of the relative increase in tenacity. It can be seen that, for the first step of increase in TC from 2.3 to 2.8, the tenacity is increased from 24.41 cN tex\({}^{-1}\) to 25.51 cN tex\({}^{-1}\) (about 4.51% improvement is realised). While for a further rise in TC from 2.8 to 3.3, there is only a small rise of tenacity about 2.3% reaching maximum of 26.09 cN tex\({}^{-1}\). This behaviour may indicate that as TC rises over 3.3, the further increase in tenacity could be unpredictable. The regression analysis was used to predict the extent of the relationshipbetween the dependent variable of tensile properties and the independent variable of TC, and the results are given in Table 5. Though the positive sign of slope coefficient and fairly higher value R\({}^{2}\) in regression equation revealed a strong positive interaction of tensile properties and TC. However, the results are based on only three set points. The increase in tensile properties of yarns with increasing TC could be attributed to the improved packing density and, consequently, increase in resistance to the slippage of fibres in the yarn [33; 34; 35]. The increase in the tenacity with increasing TC occurs only up to a certain level of TC, called optimum TC [36; 37]. According to Equation (1), the greater the value of TC, the greater the twist level in the yarn for a fixed yarn count will be. Consequently, the twist angle (helix angle of surface fibres around the yarn axis) of fibres is also increased, thus producing a contraction in yarn length, commonly designated as twist contraction [38; 39]. This twist contraction is further responsible for building a more compact yarn structure with a somewhat coarser yarn count (Ne), as seen from a line chart in Figure 2, where yarn count has decreased stepwise from 10.22 s Ne to 10.16 s Ne and 9.98 s Ne with an increase in TC. In addition, it should be noted that the actual TTI of yarn is also related to the spindle speed and front roller delivery of the ring spinning machine by the following Equation (2). \[\text{TPI}=\text{Ns}/\text{Vd} \tag{2}\]  
where:  
Ns: Spindle speed (rpm);  
Vd: Front roller delivery rate (inches/min). From Equations (1) and (2), the yarn delivery rate can be described as per Equation (3). \[\text{Vd}=\text{Ns}/\text{TC}\times\sqrt{\text{Ne}} \tag{3}\]  
Figure 2: Effect of TC on tensile properties of conventional ring-spun MFHSYs. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Factors**} & \multicolumn{2}{c}{**Tenacity**} & \multicolumn{2}{c}{**Elongation \%**} \\ \cline{2-5}  & **Regression Equation** & **R\({}^{2}\)** & **Regression Equation** & **R\({}^{2}\)** \\ \hline TC & y = 0.84x + 23.657 & 0.9691 & y = 0.415x + 8.6933 & 1 \\ \hline Yarn count, Ne & y = \(-\)1.255x + 27.033 & 0.8439 & y = \(-\)0.685x + 10.523 & 0.938 \\ \hline No. of Plies & y = 0.625x + 25.293 & 0.8154 & y = \(-\)0.18x + 10.067 & 0.7915 \\ \hline \hline \end{tabular} R\({}^{2}\) = coefficient of determination.  
\end{table} 
Table 5: Linear regression analysis of tensile properties for ring-spun and plied MFHSYs. It can be seen that for a given yarn count, the yarn delivery rate or productivity is inversely related to the yarn TC.