Biconstituent Fiber Systems

A second important type of biconstituent fiber is a semicompatible blend on nylon 66 with nylon 61 (I referring to isophthalic acid), with nylon 61 

The crystalline bicomponent and biconstituent blends considered above may also be compared to the polyallomer block copolymers (Section 6.8), which consist of two crystalline components linked together by chemical bonds rather than by mechanical mixing. In all cases, the constituents are independently crystallizable. Melt-blending theory is considered in Section 9.6. 

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Figure 9.3. Classification of bicomponent and biconstituent fibers. (Allied Chemical Corp., advertising literature) (A) Bicomponent system (B) skin-core system (C) matrix-fibril system.

These systems, whose phase characteristics resemble those of the polyblends discussed in Chapter 3, can be prepared by first blending the molten polymers together until the minor component is dispersed in the form of droplets that are small in comparison to the fiber diameter desired (Allied Chemical Corp., n.d. Buckley and Phillips, 1969 Hayes, 1969 Mumford and Nevin, 1967 Papero et a/.,1967). The material is then melt-spun and drawn in order to orient both constituents and cause the dispersed phase to form elongated cylinders or fibrils. For satisfactory dispersion, the viscosities of both components must be comparable (for a discussion of rheological effects in molten polymer blends, see Section 9.6). An important biconstituent system is based on a combination of nylon 6 with a linear polyester poly(ethylene terephthalate), with nylon 6 as the continuous phase (Buckley and Phillips, 1969). As shown in Figure 9.5, fibrils of polyester... 

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