Effect of LCP and rPET as Reinforcing Materials on Rheology, Morphology, and Thermal Properties of in situ Microfibrillar-Reinforced Elastomer Composites Sunan Saikrasun, 1 Panpirada Limpisawasdi, 1 Taweechai Amornsakchai 2 1 Department of Chemistry and Center of Excellence for Innovation in Chemistry, Mahasarakham University, Mahasarakham 44150, Thailand 2 Center for Alternative Energy, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Mahidol University, Bangkok 10400, Thailand Received 6 February 2008; accepted 11 November 2008 DOI 10.1002/app.29715 Published online 11 February 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Microfibrillar-reinforced elastomer compo- sites based on two dispersed phases, liquid crystalline poly- mer (LCP) and recycled poly(ethylene terephthalate)(rPET), and styrene-(ethylene butylene)-styrene (SEBS) were pre- pared using extrusion process. The rheological behavior, morphology, and thermal stability of SEBS/LCP and SEBS/ rPET blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thin- ning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into SEBS significantly improved the processability by bring- ing down the melt viscosity of the blend system. The fibril- lation of LCP dispersed phase was clearly observed in as- extruded strand with addition of LCP up to 20–30 wt %. Although the viscosity ratio of SEBS/rPET system is very low (0.03), rPET domains mostly appeared as droplets in as- extruded strand. The results obtained from thermogravimet- ric analysis suggested that an addition of LCP and rPET into the elastomer matrix improved the thermal resistance significantly in air but not in nitrogen. The simultaneous DSC profiles revealed that the thermal degradation of all polymers examined were endothermic and exothermic in nitrogen and in air, respectively. V V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1897–1908, 2009 Key words: elastomer; composites; liquid crystalline polymer (LCP); thermal degradation; recycled PET (rPET); thermal stability INTRODUCTION Blending two or more polymers is a versatile way of developing new materials with a desirable combina- tion of properties. Among such blending systems, immiscible blends of thermotropic liquid crystalline polymers (TLCPs) with thermoplastics or thermo- plastic elastomers (TPEs) have received much atten- tion over the past 2 decades. 1–3 TLCPs are known to possess superior physical properties, such as high strength, good thermal properties, and low melt vis- cosity. Under appropriate shear or elongational flow field, dispersed TLCP droplets can be elongated and frozen in the matrix after cooling. This type of blend is called in situ composite. 4 Two major advantages gained by the addition of small amount of TLCP into a polymer matrix are improved processability and enhancement of mechanical properties. How- ever, the main problem to be investigated for these types of the blends is to find the optimum process- ing conditions, composition of the blend component, viscosity ratio (dispersed phase to matrix phase), and fabrication techniques to obtain a fibrillar mor- phology of the dispersed phase. Despite the numer- ous advantages of TLCP as a minor blend component, which can improve the melt processabil- ity and enhance mechanical properties, TLCPs are often too expensive for general engineering applica- tions. On the other hand, there are considerable sup- plies of engineering plastics in the form of post consumer scraps, which are a low cost source of raw material for forming polymer blends. 5 An alternative way is to find a substitute for TLCPs in fiber-rein- forced composite application as a new type of proc- essing route. Poly(ethylene terephthalate) (PET) is one of the most important polymers for industrial production because of rapid growth in its uses. It is regarded as an excellent material for many applications and is widely used for making containers (bottles) for liquids. It has excellent tensile and impact strength, Journal of Applied Polymer Science, Vol. 112, 1897–1908 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: S. Saikrasun (sunan.s@msu.ac.th). Contract grant sponsor: Office of Commission on Higher Education and Thailand Research Fund; contract grant number: MRG5080415.