Abstract:

Objective Bio-polyamide 56 (PA56) is a new type of bio-based fiber with insufficient basic spinning data. The content ratio (blending ratio) of each component fiber of blended yarn is an important factor that affects its mechanical properties and yarn function. By means of theoretical models, the relationship between yarn strength and blending ratio can be predicted, thereby speeding up production process design and shortening production lead time. This research aims to study the influence of fiber content on the mechanical properties of PA56 staple fiber/cotton blended yarn and establish its strength prediction model.

Method Cotton fiber and PA56 staple fiber were mixed to produce various blended yarns. Pure PA56 staple fiber yarn, pure cotton yarn and PA56 staple fiber/cotton blended yarn with various blending ratios were prepared on the ring spinning machine. In addition, the mechanical properties of the PA56 staple fiber and cotton fiber, and all pure yarns and blended yarns were evaluated. Prediction models for breaking strength of blended yarn were established by using pure yarn (model 1) and fiber (model 2), respectively.

Results By combining with the tensile breaking strength curves of the PA56 staple fiber pure yarn and cotton pure yarn (Fig.2) the pure yarn breaking strength predicted blended yarn strength curve (model 1) was drawn, and the predicted breaking strength expression of blended yarn was established as shown in equation 3. It could be seen that the predicted breaking strength of blended yarn decreased first and then increased with the increase of cotton content. Using model 1, the breaking strength of blended yarn was found to be the smallest when the cotton content was 52.8% (Fig.3). On the other hand, the breaking strength curve of the fiber predicted blended yarn (model 2) could be built by the tensile breaking strength curve of the PA56 staple fiber and cotton fiber (Fig.4 and the equation 3). The trend of model 2 resembled that of model 1, but the predicted minimum blended yarn breaking strength was associated to cotton content 47.9% (Fig.5). In order to verify the accuracy of the prediction model, the consistency between the measured value and the predicted value was obtained by testing the breaking strength of the PA56 staple fiber/cotton blended yarns with different cotton content (Tab.3, Fig.6). The results showed that model 1 was closer to the measured value, while model 2 was smaller than the latter. In order to modify model 2, it was proposed to use the utilization rate of fiber strength in pure yarn. The utilization rate of cotton fiber strength in pure cotton yarn was 45%, and the utilization rate of PA56 staple fiber strength in PA56 pure yarn was 40%. Furthermore, the modified fiber model of the prediction breaking strength of blended yarn (Fig.7) was obtained by combining model 2 and equation 4. The trend of the modified model 2 and the predicted minimum breaking strength cotton content of 50.9% were very close to model 1.

Conclusion The minimum breaking strength point and overall trend of blended yarn on the prediction curve of the pure yarn were well fitted with the trial spinning data, so that the model 1 can predict the breaking strength of the PA56 staple fiber/ cotton blended yarn. The model 2 needed to be modified by using the utilization rate of the fiber strength in pure yarn. The results of the modified model 2 were similar to those of the model 1. Therefor, the modified fiber model could quickly complete the prediction of blended yarn strength without the pure spinning processing flow, and it was very suitable for blending ratio design and product development of blended yarn, especially PA56 staple fiber blended yarn.

Key words: bio-polyamide 56, polyamide/cotton blended yarn, prediction model of blended yarn strength, minimum strength point, utilization rate of fiber strength