Effect of Mixing Sequence of Polymer and Nanofillers on Thermo Mechanical as well as Morphological Property of the Nanocomposites

Blends of polybutylene terephthalate (PBT) and thermo tropic liquid crystalline polymer (LCP) and blend of PBT, LCP and nanosilica have been prepared by melt mixing technique.Polymer composites made by engineering thermoplastic PBT and reinforcing polymer LCP has been extruded in presence of nanosilica in different mixing sequence. Here the mixing sequence of PBT, LCP and nanosilica has been picked out so as to study the different changes that can be observed in the characteristics in each of the system.The resultant mixtures are then compression moulded in high temperature range.Microstructures of the blends have been studied by Field Emission Scanning Electron Microscope (FESEM). Thermal properties and dynamicbehaviour of the composites have been analyzed by Thermo gravimetric Analysis (TGA) and Dynamic Mechanical Thermal Analyser (DMTA), respectively. From the TGA analysis it is evident that PNL has superior thermal stability than the other nanocomposites. FESEM analysis revealed that the nanosilica prefers the low viscous LCP phase than the high viscous PBT. PNL has the highest tensile modulus among all the nano composites due to migration of nanosilica from high viscous PBT to low viscous LCP phase. There is a remarkable enhancement in storage modulus value is observed in case of PNL system than the other nano composites.


Introduction
In the advent of rigid rod-like molecules and due to their spontaneous molecular orientation the thermo tropic liquid crystalline polymers (TLCPs) gains impressive rheological (low melt viscosity), thermal, and dynamic mechanical stability and thereby making them useful for a number of specialized application in conjunction with other thermoplastics.Recently studies onpolyblendssystem have been the subject of numerous investigations.Blending of LCP with other polymers are attractive for number of reasons, the most important of which is in the case of processibility and in situ fibrillation offered by the LCP component to the isotropic polymers (Siegmann, Dagan, & Kenig, 1985;Isayeb & Modic, 1987;Kiss, 1987).Polymer composites based on engineering thermoplastics have excellent wide ranging properties for which they are extensively applied in automobile industries, electronics, electrical appliances and many other fields.Nanoparticles have an extremely high surface to volume ratio which dramatically changes their properties when compared with their bulk sized equivalents.It also changes the way in which the nanoparticles bond with the bulk material.The result is that the composite can be many times improved with respect to the component parts.Some nanocomposite materials have been shown to be several times tougher and improved thermal and mechanical property than the bulk component materials (Ishida, Campbell, & Blackwell, 2000;Beecroft & Ober, 1997;Messersmith & Giannelis, 1995).Nano-sized filler such as nanosilica, nano clay, carbon black have been reported to have unique influence on the morphology of immiscible blends (Messersmith & Giannelis, 1995;Steinmann, Gronisk, Friedrich, 2002;Wang, Li, Chen, Yuan, Yang, & Yuan, 2007).It has been reported nanosilica and nano clay has a compatibilization effect in immiscible polymer blend (Steinmann, Gronisk, & Friedrich, 2002;Wang, Li, Chen, Yuan, Yang, & Yuan, 2007;Zhang, Yang, & Fu, 2004).Polymer blending presents the most attractive route for the production of high performance materials with desired property while suppressing the unwanted properties of individual component.Most of the engineering thermoplastics (polycarbonate, polyethersulfone, polybutylene terephthalate, polypropylene oxide) are very difficult to process due to their high processing temperature as well as melt viscosity and are not compatible with each other.To improve the processibility these thermoplastics are often blended with the polymer of lower viscosity like liquid crystalline polymer (LCP) and to minimize the phase separation in binary or multi component system, some compatibiliser is to be added during blending (Sahoo, Das, Pandey, & Mathur, 2002;Datta & Weiss, 1991;Jose, Thomas, Biju, Koshy, & Karger-Kocsis, 2008).The properties of LCP/polymer composites fall far short of expectations, mainly due to poor interfacial adhesion between the dispersed LCP phase and the thermoplastic matrix phase (Datta & Weiss, 1996).Several approaches have been attempted to enhance the interfacial bonding between the two phases (Bassett & Yee, 1990;Datta, Chen, & Baird, 1993).The best way to avoid the above mentioned problem is to incorporate a compatibiliser, which can ensure better adhesion and hence reduces the interfacial tension.PBT is a semi crystalline engineering thermoplastic.PBToffers good electrical properties and good mechanical properties including high strength, rigidity, and toughness and chemical resistance to a wide range of chemicals, solvents, oils and greases.Polybutylene Terephthalate (PBT) has excellent dimensional stability, low moisture absorption, and powerful insulation resistance.Since the processing temperature of PBT is very high so the compatibiliser for this type of blend system should be thermally stable.(Han, Pan, Dong, & Zhang, 2011).Lai et al. has shown that PEEK nanocomposite filled with the modified silica would show higher storage modulus values as compared with those of the unmodified counterparts, also suggesting that the better dispersion of the nano-sized silica could reduce the polymer domain size and make greater improvement on the modulus of the PEEK matrix (Lai, Kuo, Huang, & Chen, 2007).
Here in this work we have shown that mixing sequence had a major role in the dispersion and migration of the nanofillers in the polymer blends.In this article a comprehensive study is carried out to investigate and highlight the thermal, rheological, and morphological properties of PBT/LCP and PBT/LCP/nanosilica blend systems.Here one blend system (PL) and the nanocomposite systems (PLN, LNP, PNL) have been prepared by melt blending process.This paper mainly highlights about the migration of nanofillers to the low viscous medium (LCP) and for this how the thermomechanical, morphological propertiesare altered for different composite system.

Experimental Details
In this section the materials used in this study has been mentioned.This section also contains brief discussion about the characterization techniques adopted for thermal, rheological, morphological and of PBT/LCP and PBT/LCP/nano-silica nanocomposite system.

Materials Used
(1) The thermo tropic LCP used in this study was Vectra A950 supplied by Ticona (Shelby, NC).This LCP is a wholly aromatic co polyester consisting of 25 mol % of 2, 6 -hydroxynaphthoic acid (HNA) and 75 mol% of p-hydroxybenzoic acid (HBA).The molecular weight could not be determined because it was difficult to find a suitable solvent in which it can be dissolved.
(3) Nano silica was indigenously developed in the laboratory of Materials Science Centre, Indian Institute of Technology Kharagpur, India.

Preparation of PBT/LCP/nano-silica Nanocomposites
Prior to the mixing of PBT and LCP were kept at 80°C and nanosilica was kept at 150°C for 12h.PBT/LCP composite with nanosilica were prepared by melt blending method in an internal mixture, equipped with two sigma type counter rotating rotors, at 285°C and 100 rpm.The mixing was done for five minutes.A binary blend of PBT/LCP was also prepared under the same condition for comparison of properties with the ternary and quaternary blends.Samples for the mechanical testing were prepared by compression moulding, at 285°C and 10 MPa pressure.Then the samples were rapidly cooled to room temperature.The compounding formulations of the nanocomposites are presented in Table 1.

Thermo-gravimetric Analysis (TG Analysis)
Thermo-gravimetric analysis is conducted using a DuPont TGA-2100 thermal analyzer at 100°C to 650°C with a heating rate of 10°C/min.

Mechanical Testing
Tensile tests were carried out on a dumb-bell shaped samples using a Hounsfield HS 10 KS (universal testing machine) operated at room temperature with a gauge length of 35 mm and a crosshead speed of 5 mm/min.Tensile values reported here are an average of the result for test run on at least four specimen.

Field Emission Scanning Electron Microscopy (FESEM)
Fracture surfaces are analyzed by Field Emission Scanning Electron Microscope (Tescan, Vega LSU) to reveal the fracture mechanism of the blend systems.Before the analysis samples are gold coated to make it conducting.

DSC Study
Figure 1 shows the DSC plots of PBT and its composites.Pure PBT showed an endothermic peak around 227°C corresponding to its melting temperature.Incorporation of Nanosilica in PBT matrix showed a slight deviation in the melting temperature.However, for PBT/LCP blend system there are two endothermic peaks were observed.The peak at around 110°C corresponds to the T g of LCP which indicated towards the incompatible nature of the two blend partners.Incorporation of Nanosilica in the PBT/LCP blend shows two peaks in the melting range of PBT.This might be due to the non-uniform dispersion of Nanosilica in the PBT phase.Addition of Nanosilica first in PBT phase, followed by LCP addition shows no sign of bifurcation of melting peak of PBT.Similarly addition of Nanosilica first to the LCP phase followed by PBT addition showed no bifurcation.This indicates that the Nanosilica dispersion was better in case of two step mixing but it could not be clear from the DSC analysis that in which phase these nanofillers were dispersed.To further explore the dispersion state of Nanosilica in PBT/LCP matrix, FESEM analysis was carried out and discussed in the following section. www.ccsen

Conclus
The blend blending p was also fo nanocomp evident th highest sto

Raference
Figure 2 s Figure 2a droplets ar due to the PBT and L support the ellipsoidal percent of two polym better adhe Similar typ remained morpholog LCP phase the phase a during mix the LCP p was first m and hence dispersion migration out and the Polyphosphazene compatibilised PEI/LCP (Bose, Pramanik, Das, Ranjan, & Saxena, 2010), PES/LCP (Bose, Mukharjee, Das, & Saxena, 2009) studied by Bose et al. and PEI /LCP (Nayek, Sahoo, Karthikeyan, Das, Saxena, & Ranjan, 2011) studied by Nayek et al.Nanosilica is one of the most common nano-fillers used in the preparation of nano composite.Han et al has shown that The formation of a high-performance SiO 2 network by well dispersed silica (formed by the surface modification) has improved the thermal stability of LLDPE

Table 1 .
Showing the Composition of the nanocomposites along with PL blend Dynamic mechanical analysis (DMA) was performed in a TA instrument DMA 2980 dynamic mechanical analyzer model in a single cantilever bending mode with a frequency of 1 Hz and a heating rate of 10 °C/min.The temperature dependence of storage modulus E/ was measured from 20°C to 150°C.