Novel flame retardant epoxy/clay nanocomposites prepared with a pre-ground phosphorus-containing organoclay

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J.C. Tang Department of Cosmetic Science, Chin Min Institute of Technology, Tou-Fen Township, Miao-Li County 351, Taiwan, Republic of China

Y.W. Wu and H.S. Chen Department of Chemistry and Center for Nanotechnology, Chung Yuan Christian University, Chung-Li City, Taoyuan County 320, Taiwan, Republic of China (Received 31 July 2007; accepted 30 January 2008)

A series of novel epoxy/clay nanocomposites (EPOCg-x) were prepared with a selected epoxy resin and x wt% of a mechanically ground phosphorus-containing organoclay (POCg). The results of x-ray diffraction (XRD), Fourier transform infrared, and field emission scanning electron microscopy measurements showed that POCg was size-reduced, and its silicate layers were disordered by the grinding process. The results of XRD and transmission electron microscopy of the nanocomposites suggested that the POCg particles were well-dispersed in the epoxy matrix with a combination of intercalation and destruction platelet structures. The as-prepared nanocomposites remained thermally stable above 376 °C. Furthermore, the storage modulus in the glass state, surface hardness, char residue, and limiting oxygen index (LOI) of the as-prepared nanocomposite were all significantly increased with increasing the POCg content. The large increment of LOI, 10 units higher than that of neat epoxy, indicated that an extraordinary enhancement on flame retardancy was obtained from EPOCg-5.

I. INTRODUCTION

Epoxy resins are useful material because of their interesting properties, such as good mechanical behavior, electrical properties, adhesive strength and chemical resistance, ease of processing, and low cost. These have led epoxy resins to a wide range of applications in surface coatings, semiconductor and insulating materials for electrical devices, and structural reinforced composites for aerospace, marine vehicles, and automobiles. However, the brittle and combustible characteristics hindered their potential applications in other fields. Therefore, modification by addition with inorganic fillers to form the epoxy nanocomposites is generally used to improve its physical and mechanical properties.1–12 In particular, epoxy/clay nanocomposites have been studied extensively in recent years. This is mainly because the addition of a small amount of clay particles usually resulted in significant improvement in thermal properties,1–3 mechanical properties,4,5 barrier properties,6–8 and flame retardant properties9–11 of the pure epoxy. Similar to the a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0215 1618 J. Mater. Res., Vol. 23, No. 6, Jun 2008 http://journals.cambridge.org Downloaded: 28 Mar 2015

other polymer/clay nanocomoposites,13–16 the improvements were related to the dispersion efficiency and the degree of exfoliation of the clay in the epoxy matrix as well as the compatibility of the clay with the polymer matrix. Therefore, many research groups have used different methods to facilitate clay exfoliation and found that different processin