LCP/PET blends

Hashmi, S.A.R. and Kitano, T. (2007) Shear rate dependence of viscosity and first normal stress difference of LCP/PET blends at solid and molten states of LCP.J. Appl. Polym. Sd 104 (4), 2212-2218. 

Hashimi S, Takeshi K (2007) Shear rate dependence of viscosity and first nramal stress difference of LCP/PET blends at solid and molten states of LCP. J Appl Polym Sd 104 2212-2218 Hsies TT, Tiu C, Simon GP, Wu RW (1999) Rheology and miscibilily of thermotropic liquid crystalline polymer blends. J Non-Newt Fluid Mech 86 15-35 Isayev A1 (2012) Liquid crystalline composite. In Luigi N, Borzacchiello A (eds) Wiley Encyclopedia of composites, 2nd edn. Wiley, New York Isayev AI, Nicolais L (2011) Liquid crystalline composite. Wiley Encyclopedia of composites. Wiley, New York... 

PC being polyester may also undergo trans-reaction with another polyester, polyester-amide or polyamide. Lin and Yee studied such reactions in blends of a Uquid crystalUne copolyesteramide (LCP, Vectra B950) with PC or PET.i i Due to transesterification, the PC/LCP blends were slightly miscible, with misdbihty increasing with time and temperature, T < 340°C.The trans-reaction also reduced LCP crystallinity. The DSC-determined decomposition temperature of LCP/PET blend was about 400°C. The exchange reactions between LCP and PC or PET improves the interfacial adhesion in these immiscible blends thus they may be used for in situ formation of compatibilizing copolymers. The reactions are rather slow and need to be accelerated by, for example, an ionic catalyst. 

This article is an overview of the novel technology of self-reinforced LCPs with polyesters, poly(ethylene terephthalate) (PET) and poly(ethylene naphtha-late) (PEN) [10-13, 21, 23], LCP/polyester blends in a polyester matrix form in situ fibrils which improve the mechanical properties. LCPs have an inherently low melt viscosity, and provide LCP/polyester blends that effectively lower the melt viscosity during melt spinning [24], and fast injection-molding cycles. The miscibility between the LCP and polyesters can be controlled by the degree of transesterification [25] in the reactive extrusion step, and fibril formation in LCP-reinforced polyester fibers has been studied. 

Table 20.6 The kinetic parameters of the LCP/PET and LCP/PEN blends at each temperature [44], From Park, J. K., Park, Y. H., Kim, D. J. and Kim, S. H., Crystallization Kinetics of TLCP with polyester blends , J. Korean Fiber Soc., 37, 69-76 (2000). Reproduced by permission of The Korean Fiber Society...

PEN/LCP Melt blended/mechanical properties/DSC/ DMA/SEM/evidence for transreaction between PEN and PET segments of LCP Xie et al. 2001b... 

This concept was explored by Lee and DiBenedetto (1992) who introduced a second LCP as a compatibUizing agent in order to improve the interfacial adhesion and dispersion between components of incompatible LCP/thermoplastic blends. The primary reason that the LCP and thermoplastic polymers are immiscible is due to molecular conformation differences or entropy effects. The concept for using a second LCP in such blends is that the two LCP s will be miscible due to entropy effects and the second LCP and the thermoplastic polymer will adhere due to specific interactions. The LCP coupling agent used in this work was a copolymer of PET and HBA known as PHB60. Blends of an LCP with both polycarbonate (PC) and PET were prepared with and without the addition of the second LCP... 

The shear viscosities of some of the investigated LCP/polymer blends, measured at a shear rate of 24 s are shown in Figure 1 as a function of the LCP content For all the blends, a considerable decrease of melt viscosity was observed as a result of the LCP addition. This is in agreement with literature data (i). A minimum is seen for some of the viscosity/composition curves (cf. NY/VB and PET/VA). This was shown to occur when the LCP s viscosity is higher than, or similar to, that of the matrix (5,4). 

Injection-molded articles tend to exhibit skin-core and multi-layer morphologies in which the LCP domain aspect ratio varies considerably with location within the part. The hierarchy of structures found within LCP/TP blends was elucidated by Silverstein et al. who said the microdomains form domains, the domains form microlayers, the microlayers form sublayers, and the sublayers form a layered structure . The structural hierarchy in PET/CLP blends was characterized by Narh who found good agreement of fibril length observed in sublayers with a numerical prediction. 

---