TLCP blends

As recognized by others in the case of TLCP blends, it may be detrimental to fiber formation if the matrix and TLCP are too compatible [12,13,49-51]. This can... 

Figure 4 SEM photographs of fractured surfaces of PEI-TLCP blend fibers at the draw ratio of 1 (x 3000). The samples were fractured after freezing in liquid nitrogen. The amount of PEsl in the blends are (A) 0 phr, (B) 0.75 phr, (C) 1.5 phr, (D) 2.25 phr, (E) 3.75 phr, and (F) 7.5 phr. Source Ref. 11.

Figure 10 Normalized impact strength versus PEsI content for PEI-TLCP blend. Draw ratio is 4. Source Ref. 11.

This chapter focuses on recent developments in rheological and mechanical examinations of TLCP blends. Although most of the data presented are taken from actual works done at the Institute of Polymers and Processing of Zhejiang University, Hangzhou, China, this is merely a matter of accessibility and in no way implies that this data is the best or only data of this nature available. 

Nobile et al. [3] reported that viscosity of a polycar-bonate-TLCP blend can increase or decrease in the same system at the same temperature, depending on the shear condition. At very low shear rates the viscosity was found to increase with TLCP loading, whereas at high shear rates a significant drop was observed. But in all of these cases, the way in which the TLCPs alter the bulk polymer flow is not yet well understood. 

The purpose of our study was to model the steady-state (capillary) flow behavior of TP-TLCP blends by a generalized mathematical function based on some of the shear-induced morphological features. Our attention was primarily confined to incompatible systems. 

Figure 5 Comparison of theoretical viscosity curves with experimental value points of PES/TLCP blends for fixed shear stress t.

Table 1 Parameters Provided by Fitting the Experimental Data to Eq. (7) for PES-TLCP Blends...

Equation (7) depicts the viscosity decrease independent of the chemical features of materials. Also for fixed T, Figs. 7 and 8 demonstrate a further example of a poly-amide-TLCP blend with different weight ratios. The rheological data in Fig. 7 were taken from Siegmann et al. [1]. It is obvious that the lowest blend viscosity is obtained at a TLCP loading of only 5%. This result is... 

The parameters were also evaluated by fitting the rheological data to Eq. (7) and are listed in Table 2. It appears to be natural that both the e and 8 values were significantly lower than those of the PES-TLCP blend, previously discussed. 

In this section, we examine fibrillation behavior of a polycarbonate (PC)-TLCP blend by injection molding. 

The formation of a fibrillar structure in TLCP blends makes the mechanical properties of this kind of composites similar to those of conventional fiber reinforced thermoplastics [11,26]. However, because the molecular orientation and fibrillation of TLCPs are generally flow-induced, the formation, distribution, and alignment of these droplets and fibers are considerably more processing-dependent. We do not know ... 

Gopakumar et al. [10] reported the in situ compatibilization of poly(phenylene sulfide) (PPS)/wholly aromatic thermotropic liquid crystalline polymer (TLCP) Vectra A950 blends by reactive extrusion. The authors prepared the in situ compatibilized PPS/TLCP blends in a twin-screw extruder by reactive blending of PPS and TLCP in the presence of dicarboxyl-terminated poly(phenylene sulfide) (DCTPPS). Block copolymer was formed during reactive blending, by transesterification reaction between carboxyl... 

The free volume of thermoplastic miscible blends has also been determined as a function of blend composition (Zhou et al. 2003 Campbell et al. 1997 Roland and Ngai 1991). Those studies have shown that the degree of blend miscibility alters the free volume behavior as a function of blend composition. On the other hand, Hsieh et al. (2000) have studied a number of blends containing only thermotropic liquid crystalline polymers TLCP s as the only components. That work showed that regardless of their various miscibilities, TLCP blends tend to display smaller, fewer free volume sites than expected from a weighted average. This observation has been ascribed to the intrinsic affinity of nematic TLCP s. 

Aromatic thermotropic liquid crystal polyesters (Ar-TLCP s) and TLCP s containing aliphatic linkages can be compatibilized as binary-TLCP blends by transesterification. The morphology and physical properties of the resultant binary-TLCP blend are dependent on the blockiness, composition and viscosity ratios of the two TLCP components. Polycarbonate (PC) can also be blend compatibilized with either TLCP s or binary-TLCP blends, by transesterification of aliphatic linkages from the TLCP s into the PC. In this work, the degree of selective transesterification is quantified and its effect on TLCP blend compatibility is described... 

Highly aromatic ester-based main-chain TLCP s are useful because of their high strength and modulus, and processability. A limiting factor in the use of these Ar-TLCFs as a reinforcement with commercially available thermoplastic polymers is their incompatibility, as expressed by poor interfacial adhesion [1,4,13,14]. This could be overcome by the utilizing intermediary phases as compatibilizers [5,//]. A binary-TLCP blend can provide for this. 

Various results are reported on binary-TLCP blends that use p(ET/HBA) or the Ar-TLCP p(HBA/HNA) (where HNA hydroxynaphthoic acid) is as a component. In some cases, miscibility is observed [11,15,16,17,18]. In others, the components are shown to have a degreeof compatibility [3,7,8,9,11]. In other blends, the components are completely incompatible [3,19,20]. These studies note the... 

Introduction. A binary-TLCP (Bin-TLCP) blend of an Ar-TLCP with the p(ET/HBA) TLCP is prepared over varying composition. The potentially transesterifiable ET blocks of p(ET/HBA) are blended with the Ar-TLCP to induce a small amount of aliphaticity in the Ar-TLCP. The Bin-TLCP will then be blended with PC to form a ternary blend, with and without the TBOT catalyst. It is anticipated that the TBOT will initiate a block transesterification of ET with the PC, thereby compatibilizing the components of the ternary blend. 

Method and Materials. Bin-TLCP blends of Ar-TLCP Vectra RD-501 p(HBA/HNA/TA/HQ) with Rodrun p(ET/HBA) were produced with the following compositions 30/70, 50/50, 70/30 % wt. The LCP blocks in the binary blend are hydroxybenzoic acid (HBA) hydroxynaphthoic acid (HNA) terephthalic acid(TA) hydroquinone (HQ) ethyleneterephthalate (ET). The Bin-TLCP blend of 70/30 RD-501/Rodrun (abbreviated " RDRR in the figures), was then used in ternary... 

Samples for morphological and thermal studies were pressed at 300 C (for Bin-TLCP blends) or 250 0 (for blends with PC), and cut to size. Specimens were cold-fractured after liquid nitrogen immersion, and the fracture surfaces were analyzed for phase size, dispersion, and interfacial adhesion using SEM. The blend Tg s were measured using tensile-mode DMT A at 1 Hz and a 3 C/min, heating rate. 

Figure 6. DMTA spectra of the Binary-TLCP blends. See text for compositions.

Figure 7. DSC curves of the Binary-TLCP blends during Slow Cool...

Heat-of-Recrystallization as a Function of Composition x/y % wt. Ar-TLCP/p(ET/HBA) Binary-TLCP Blends... 

Further publications are available for supporting data, details and mechanical properties of these blends properties of other binary-TLCP blends of either p(HBA/BP/TA/IA/HQ) or p(HBA/HNA) with p(ET/HBA) s and, a comparison of block structures of p(ET/HBA) s and its affect on blending [26,27]. 

H. Wang, G. Hinrichsen (1997) Influence of processing temperature on morphological and mechanical properties of a polycarbonate/thermotropic liquid crystalline polymer (PC/TLCP) blend, Int. Polym. Proc. 12,26. 

Thermotropic liquid crystalline polymers (TLCPs) have gained increased commercial attention because of their unique properties. These include their low coefficients of thermal expansion, low viscosity, and high modulus, low permeability to gases, low dielectric constants, and chemical resistance. As the demand for these characteristics increases, it is anticipated that the use of TLCPs will grow, rising at a projected annual growth rate of 25 % from an estimated use of ten million pounds in recent years. In expanding the potential uses for TLCPs, it has been found that TLCP/TLCP blends can possess characteristics which are better than those of either individual TLCP (Utracki and Favis 1989). But the better result is only possible if the LCP fibrillation is prominent in the blend system. 

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