Influence of Compatibilizer on Notched Impact Strength and Fractography of HDPE–Organoclay Composites Waraporn Rattanawijan, 1 Taweechai Amornsakchai, 1,2 Pornsawan Amornsakchai, 3 Pinsupha Petiraksakul 4 1 Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Salaya, Nakonpathom 73170, Thailand 2 Center for Alternative Energy, Faculty of Science, Mahidol University, Salaya, Nakonpathom 73170, Thailand 3 Department of Chemistry, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand 4 Department of Materials Technology, Faculty of Science, Ramkhamhaeng University, Huamark, Bangkapi, Bangkok 10240, Thailand Received 6 July 2008; accepted 27 January 2009 DOI 10.1002/app.30181 Published online 17 April 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The focus of this study was the notched impact property of high-density polyethylene (HDPE)– organoclay composites and the resultant morphology of impact-fractured surfaces. Composites with a different organoclay content and degree of organoclay dispersion were compared with neat HDPE under identical condi- tions. The degree of organoclay dispersion was controlled through the use of a compatibilizer, maleic anhydride grafted polyethylene. It was found that the addition of organoclay can slightly increase the elastic modulus and notched impact strength of the composite. When the level of organoclay dispersion was improved by using compati- bilizer, elastic modulus and toughness further increased. A significant increase in yield strength was also notable. The presence of organoclay was found to suppress strain hardening of the matrix during tensile testing. The impact- fractured surfaces of failed specimens were studied with scanning electron microscopy. The micromechanism for the increased toughness of HDPE–organoclay composites was discussed. V V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1887–1897, 2009 Key words: polyethylene composites; organoclay; impact property; fractography INTRODUCTION High-density polyethylene (HDPE) is one of the im- portant semicrystalline polymeric materials that is widely used because of its low costs and ease of processing. 1 HDPE, as other polymers, is frequently used in mineral-filled forms to reduce the cost of the polymer and to modify mechanical properties, espe- cially modulus. 2 There are also other advantages such as improved heat distortion temperature and better mold shrinkage. 3 In recent years, there has been a great deal of interests in nanocomposites from HDPE and other low-cost commodity poly- mers. One of the reinforcements that is widely used in polymer nanocomposites is organically modified layered silicates or organoclay. Since organoclay pri- mary platelets have a very large aspect ratio, it is expected that a significant level of improvement in mechanical property may be obtained with low organoclay loading (typically less than 5 wt %). 4 However, the effect of organoclay on tensile proper- ties varies from polymer to polymer. For nylon, the improvement in modulus can be as high as 200% due to the strong polar–polar interaction. 5,6 For non- polar polymers such as polyethylene or polypropyl- ene, the level of improvement is much lesser and varies, depending on the level of degree of disper- sion. 7–10 Another important mechanical property that could determine the application of a material is impact strength. HDPE is generally known to be quite tough at normal temperatures and moderate rates of deformation. It is, however, notch-brittle at low temperatures and under impact loading. 11 The addition of mineral fillers will generally have embrittling effects by sharply decreasing the poly- mer impact energy. Similarly, HDPE nanocomposites also have poor impact strength due to the present of rigid particles. It is clear that there is a need for HDPE with high modulus and high impact strength. Most studies of modification using rigid particu- late fillers report a significant decrease in toughness compared with neat polymers. An increase in Journal of Applied Polymer Science, Vol. 113, 1887–1897 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: T. Amornsakchai (sctam@mahidol.ac. th). Contract grant sponsor: Thailand Research Fund; contract grant number: RSA4580038. Contract grant sponsor: Center for Innovation in Chemistry: Postgraduate Education and Research Program in Chemistry (PERCH-CIC), Commission on Higher Education, Ministry of Education.