Received: 24 September 2008, Revised: 1 December 2008, Accepted: 18 December 2008, Published online in Wiley InterScience: 3 February 2009 Influence of liquid crystalline polymer and recycled PET as minor blending components on rheological behavior, morphology, and thermal properties of thermoplastic blends Supattra Kayaisang a , Taweechai Amornsakchai b and Sunan Saikrasun a * In this study, the potential of recycled poly(ethylene terepthalate) (rPET) as a well-defined reinforcing material for the in situ microfibrillar-reinforced composite (iMFC) was investigated in comparison with that of liquid crystalline polymer (LCP). Each dispersed phase (LCP or rPET) was melt blended with high density polyethylene (PE) by using extrusion process. The rheological behavior, morphology, and the thermal stability of LCP/PE and rPET/PE blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of LCP or rPET into PE significantly improved the processability. A potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as-extruded strand. Although the viscosity ratio of the rPET/PE system was lower than that of the LCP/PE blend system, most rPET domains appeared as small droplets. An addition of LCP and rPET into the PE matrix improved the thermal resistance significantly in air but not in nitrogen. The obtained results suggested the high potential of rPET as a processing aid and good thermally resistant material similar to LCP. Copyright ß 2009 John Wiley & Sons, Ltd. Keywords: in situ composite; liquid crystalline polymer; rheology; thermal property; recycled PET; polyethylene INTRODUCTION Blending of liquid crystalline polymers (LCPs) with commercial thermoplastics, resulting in a so-called in situ microfibrillar- reinforced composite (iMFC), [1] has been known to exhibit excellent mechanical properties because of the self-reinforcing effect of LCP fibrils. The mechanical properties of the resultant in situ composites are generally controlled by their morphology, which in turn depends on the rheological properties of the blends and its components including the processing condition and the blend composition. A requirement for the deformation of the polymer dispersed phase in the molten state is that the viscosity ratio (dispersed phase to matrix phase) should be less than unity. [2,3] The understanding of phase behavior is an essential information for the expectation of fibrillation and selecting the suitable fabricating technique in order to obtain the composite products with desirable properties. Two major advantages gained by the addition of small amount of LCP into a polymer matrix are improved processability by bringing down the melt viscosity of the blend system and enhancement of mechanical properties. [4–6] Despite the numerous advantages of LCP as a minor blend component, which can improve the melt processability and enhance mechanical properties, LCPs are often too expensive for general engineering applications. On the other hand, there are considerable supply of engineering plastics in the form of post-consumer scraps, which are a low cost source of raw material for forming polymer blends. [7] An alternative way is to find a substitute for LCPs in fiber-reinforced composite application as a new type of processing route. Polyethylene terephthalate (PET) is one of the most important polymers and has been widely employed in many cases for its high strength and modulus. PET is basically used for manufactur- ing films, fibers, and containers, with the latter application being the most important due to the superlative characteristics offered by this material in packaging: high transparency, in blown containers, good mechanical properties for minimum thickness walls, dimensional stability during handling (even at high temperatures), relatively low cost (price per container), low permeability level of gases, and solvent resistance. [8,9] However, in the past few decades, the plastics have entered overbearingly and diffusely into our lives, being widely used particularly in the fields of packaging and building. This has caused increasing concern regarding the environment in relation to the problem of plastic waste disposal. In this regard, it is particularly fortunate (www.interscience.wiley.com) DOI: 10.1002/pat.1389 Research Article * Correspondence to: S. Saikrasun, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahasarakham University, Mahasarakham 44150, Thailand. E-mail: sunan.s@msu.ac.th a S. Kayaisang, S. Saikrasun Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahasarakham University, Mahasarakham 44150, Thailand b T. Amornsakchai Center for Alternative Energy, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand Polym. Adv. Technol. 2009, 20 1136–1145 Copyright ß 2009 John Wiley & Sons, Ltd. 1136