**1. Introduction**

Molten thermotropic liquid crystalline polymers have physical properties that are dependent on both small molecule liquid crystals and flexible chain polymers. Liquid crystalline polymers (LCPs) are typical examples of self-ordered polymeric systems, due largely to their intrinsic molecular anisotropy. The properties of LCPs are strongly influenced by flow-induced changes in the degree of molecular orientation during processing [1].

Blends containing small amounts of a thermotropic liquid crystalline polymer (TLCP) in a matrix of thermoplastic have attracted technical interest in recent years for two main reasons. Firstly, by the use of TLCP to enhance the mechanical properties of the matrix polymer through in situ formation of fibrous TLCP dispersion during processing, it may be possible to develop 'self-reinforced' composites that exploit the outstanding tensile properties of fibres made from LCPs. Secondly, it is known that TLCP can act as a flow modifier, resulting in a substantial reduction in pressure drop during melt extrusion. Previous studies by Chan et al.[2] have shown that a small amount of TLCP (1.0 wt %) added to high molecular weight polyethylene (HMMPE, Chevron Phillips Marlex® HXM TR570) caused drastic bulk viscosity reduction (> 95.0%) to occur at 190 oC, when TLCP was in its nematic phase. A significant improvement in extrudate surface smoothness has also been observed, coupled with an increase in the processing window from 34 1/s to up to 1000 1/s. Whitehouse et al. [3] blended 0.2%, 0.5% and 2.0% TLCP with high density polyethylene (HDPE, Chevron Phillips Marlex® HMN 6060), and the blends were then rheologically

characterized at 185 oC when the TLCP was in the nematic regime; substantial viscosity reductions of between 85% and 90% compared with pure HDPE were observed.

Micro-Rheological Study on Fully Exfoliated Organoclay Modified Thermotropic Liquid Crystalline Polymer and Its Viscosity Reduction Effect on High Molecular Mass Polyethylene 277

In this study, the organoclay-modified TLCP (TC3 white) is prepared by a method combining ultra-sonication, centrifugation, solution casting and heating-shearing separation. TC3 white has a very high degree of dispersion of organoclay but without any loss in the degree of liquid crystallinity of TLCP. The effects of the fully exfoliated organoclay on the thermal and rheological properties of TLCP are investigated in detail. Based on this material, we characterize the rheological behaviour of purified TLCP and TC3 white with 1 wt% in HMMPE matrix by a capillary rheometer at 190 oC and 230 oC, where the TLCP has its nematic and nematic-isotropic biphase structures. Schematic drawings of the conformation of organoclay, TLCP molecules and polyethylene molecules before and after yielding are shown. A binary flow pattern model with simulated results is presented and the predicted results show good consistency with

The HMMPE, Chevron Phillips Marlex® HXM TR571, with a melt flow index (MFI) of 2.5g/10 min (ASTM D1238, 190 ºC/21.6 kg) was kindly supplied by Phillips Petroleum International Inc., USA. The TLCP, a copolymer containing 30% p-hydroxybenzoic acid, 35% hydroquinone and 35% sebacic acid (HBA/HQ/SA), used here was synthesized and kindly supplied by B. P. Chemicals Ltd, UK. The as-received TLCP is a light brown powder that has been characterized previously [20]. The Organoclay, Closite 20A modified by dimethyl dihydrogenated tallow ammonium ions, was kindly supplied by

The as-received dried TLCP powder was dissolved into chloroform and followed by mechanically stirred at room temperature overnight. The deionized water was added to the mixture and was mechanically stirred for several minutes. Water extraction was repeated several times to remove any water soluble content, e.g. pure sebacic acid; the subsequent solution was subjected to centrifugal separation (KUBOTA 2010, Japan) at a speed of 3,800 rpm for 1800 seconds. Three layers of solution were obtained. The bottom layer was a brownish precipitate which was believed to be a mixture of HBA, HBA rich TLCP, catalyst or other heavier components in the TLCP powder. The top layer was a white cloudy layer, which was believed to be a SA rich TLCP component. The middle colorless portion was extracted. To obtain more thorough purification, the whole centrifugal separation and extraction processes were repeated several times. The TLCP powder was precipitated out by dropping the extracted solution into methanol. The TLCP fine powder was filtered out and

dried at 120 oC for 3 days to remove any residual solvent contents.

experimental data.

**2. Experimental** 

*2.1.1. Materials* 

Southern Clay Products.

*2.1.2. Purification of as-received TLCP* 

**2.1. Materials and samples preparation** 

It is worth noting that even in early studies of polymer blends containing TLCP, researchers had already attempted to introduce inorganic reinforcements into such blend systems [4]. The addition of inorganic fillers not only enhanced the mechanical properties of the blends but also reduced the anisotropy of the resulting materials [5]. Rheological characterization revealed that TLCP could reduce the melt viscosity of glass-filled thermoplastics [6]. Much work has been published on TLCP systems containing different inorganic solid reinforcements, such as glass fibres [7], carbon black [8], whiskers [9] and silica [10]. Most of the studies have used high inorganic solid reinforcement content and have focused on the balance between the mechanical properties and processability of such blends.

Layered silicates have long been used as fillers in polymeric systems to improve mechanical, thermal and other properties in the resulting polymer composites. In layered silicate itself, the local interaction between layers causing the presence of domains similar to those found in studies of liquid crystalline and ordered block copolymer systems have been analyzed by many researchers [11-14].

It seems that intercalation or exfoliation of layered silicates in polymers should induce nanocomposites to exhibit similar rheological behaviour to that found in the nematic state structures in LCPs. Nanocomposites based on thermotropic liquid crystalline polymer and organically modified layered silicate have been studied by several groups with different foci. Zhang et al. [15] synthesized a series of liquid-crystalline copolyester/organically modified montmorillonite nanocomposites by intercalation polycondensation with different surfactant modified clay in LCP. X-ray diffraction and transmission electron microscope studies indicated that, after ion exchange with suitable surfactants, clay formed delaminated morphology and was well dispersed in LCP. Chang et al. [16] reported nanocomposites of TLCP with an alkoxy side-group and an organoclay (Closite 25 A) prepared by the melting intercalation method above the melt transition temperature of TLCP, with liquid crystallinity of the hybrids being lost when the organoclay content exceeded 6.0 %. Vaia et al. [17] directly annealed a powder mixture of TLCP and clay within the nematic region of TLCP under high hydraulic pressure. Reversible intercalation formed, with a loss of liquid crystallinity which was attributed to the confinement of LCP chains on the clay pseudo-2D geometry. An extensive study of a series of nanocomposites with a segmented main-chain liquid crystalline polymer having a pendent pyridyl group (PyHQ12) or a pendent phenylsulfonyl group (PSHQ12) and commercial Closite 20 A or 30B clays by examining rheological and other properties was reported by Huang and Han [18, 19] to demonstrate whether functionality of TLCP was essential to obtain highly dispersed clay in nanocomposites with TLCP as matrix. Only intercalated morphology formed when the nanocomposites were based on a TLCP without functionality. The formation of hydrogen bonds caused a very high degree of dispersion but a considerable loss in the degree of liquid crystallinity in a PyHQ12/30B nanocomposite. From the above studies, it can be seen that functionality in TLCP is necessary to obtain highly dispersed nanocomposites, but at the same time, there is the possibility of loss some degree of liquid crystallinity in the TLCP.

In this study, the organoclay-modified TLCP (TC3 white) is prepared by a method combining ultra-sonication, centrifugation, solution casting and heating-shearing separation. TC3 white has a very high degree of dispersion of organoclay but without any loss in the degree of liquid crystallinity of TLCP. The effects of the fully exfoliated organoclay on the thermal and rheological properties of TLCP are investigated in detail. Based on this material, we characterize the rheological behaviour of purified TLCP and TC3 white with 1 wt% in HMMPE matrix by a capillary rheometer at 190 oC and 230 oC, where the TLCP has its nematic and nematic-isotropic biphase structures. Schematic drawings of the conformation of organoclay, TLCP molecules and polyethylene molecules before and after yielding are shown. A binary flow pattern model with simulated results is presented and the predicted results show good consistency with experimental data.
