Fibrils in blends

Polymeric materials have relatively large thermal expansion. However, by incorporating fillers of low a in typical plastics, it is possible to produce a composite having a value of a only one-fifth of the unfilled plastics. Recently the thermal expansivity of a number of in situ composites of polymer liquid crystals and engineering plastics has been studied [14,16, 98, 99]. Choy et al [99] have attempted to correlate the thermal expansivity of a blend with those of its constituents using the Schapery equation for continuous fiber reinforced composites [100] as the PLC fibrils in blends studied are essentially continuous at the draw ratio of 2 = 15. Other authors [14,99] observed that the Takayanagi model [101] explains the thermal expansion. 

Cardinaels R, Moldenaers P. Relaxation of fibrils in blends with one viscoelastic component From bulk to confined conditions. J Polym Sci Part B 2010 48(12) 1372-1379. 

Factors for Liquid Crystalline Polymer Fibrillation in Blends... 

Table 5 compares the tensile properties of Vectra A950 in the form of dispersed fibers and droplets in the matrix by injection molding, microfibril by extrusion and drawing [28], injection molded pure thick sample and pure thin sample, and the pure drawn strand [28]. As exhibited, our calculated fiber modulus with its average of 24 GPa is much higher than that of the thick and thin pure TLCP samples injection molded. It can be explained that in cases of pure TLCP samples the material may only be fibrillated in a very thin skin layer owing to the excellent flow behavior in comparison with that in the blends. However, this modulus value is lower than that of the extruded and drawn pure strand. This can be... 

Fig. 25. The computed average number of unbroken entangled chains n and the force per chain f in fibrils in crazes in blends of X wt. fraction high M PS with low M PS...

Fig. 37. Effect of the diluent molecular weight in blends with 1,800,000 molecular weight PS (X = 0.3) on craze fibril stability (e — ej. The samples were unfiltered and the strain rate used was 5 X 10 s Mc(as2Me) is the critical molecular weight for entanglement effects on the zero-shear-rate viscosity (From Ref. courtesy Macromolecules (ACS))...

After drawing the torsional storage modulus of the blend of LCP60-80 with PPS is remarkably improved in comaprison with that of neat PPS film and its magnitude is comparable with that for the PPS/carbon fiber composite (Figure 19). On the other hand, for the blends of PPS with LCP80 there was no significant enhancement of the properties as the draw ratio was increased. This is due to the lack of fibrils in the latter case. 

Extrasion of LCP containing blends often results in fibrillation in stream-line flow or with orientation. Extraction of the thermoplastic matrix yields... 

The particular orientation of the LCP in the course of flow effects a shear thinning at low shear rates. High shear forces favor the formation of fibrils. In aromatic poly(ester)/LCP blends, the viscosity ratio is more responsive in controlling the morphology." ... 

The formation of fibrils in poly(carbonate) (PC)/LCP blends have been shown to be enhanced by tbe addition of glass beads. Nano silica acts in the same way. For example, in PC/LCP blends the addition of nano silica results in a reduction of the viscosity. The reduction of viscosity is correlated with the fibrillation of tbe LCP which is promoted by nano silica. In blends of LCP and poly(sulfone) the addition of ca. 5% of nano silica effects the formation of long and perfectly orientated fibrils in the capillary flow. The nano silica forms a network in the matrix that increases the elasticity. This effect is responsible for the improvement of the formation of fibrils. 

The formation of fibrils in poly(carbonate) (PC)/ LCP blends has been shown to be enhanced by the addition of glass beads [52,73]. Nano silica acts in the same way. For example, in PC/LCP blends the addition of nano silica results in a reduction of the viscosity... 

From the viewpoint of composite mechanics, the better performances of composites come from the effective reinforcing effect of the reinforcements and effective stress transferring from the mafiix to the reinforcements. The reinforcing LCP fibrils in in situ composites are generated during the melt processing of LCP blends, which is different fi om conventional glass or carbon fiber-reinforced composites. So the formation of LCP fibrils becomes one of the most important aspects in the preparation of in situ composites, except the common interfacial interaction in fiber-reinforced plastics. 

The ring-banded structure of spherulites (Fig. 7) is often seen in blends in which the amorphous components are miscible, i.e. both components are present in the melt at the growth surface, and it is frequently considered that such features are only seen in these situations. Detailed information on ring-banded spherulites is exempHfied in subsequent sections deaUng with individual blend types. To date there is no agreed explanation for the origin of this feature i.e. there is no explanation as to why the fibrils should twist in a regular... 

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