Morphology and tensile properties of PMMA carbon nanotubes nanocomposites and nanocomposites foams Changchun Zeng a,b,⇑ , Nemat Hossieny a,b,1 , Chuck Zhang a,b,2 , Ben Wang a,b,2 , Shawn M. Walsh c a High Performance Materials Institute, Florida State University, 2525 Pottsdamer St., Tallahassee, FL 32310, USA b Department of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer St., Tallahassee, FL 32310, USA c Building 4600, Army Research Laboratory, Aberdeen Proving Ground, MD 21005, USA article info Article history: Received 31 May 2012 Received in revised form 17 February 2013 Accepted 28 March 2013 Available online 11 April 2013 Keywords: A. Polymers A. Nanocomposites A. Carbon nanotubes B. Mechanical properties abstract Poly (methyl methacrylate) (PMMA) and multi-walled carbon nanotubes (MWCNTs) nanocomposites were synthesized and foamed by supercritical carbon dioxide. Morphology and tensile properties of both solid and foamed nanocomposites were investigated. Moderate improvement in the tensile properties was observed in the solid nanocomposites, which depended on carbon nanotube (CNT) dispersion and polymer–CNT interaction. The CNTs had signiﬁcant inﬂuences on the foam cell morphology. Moreover, the convoluted effects of CNT dispersion, polymer–CNT interaction and foam structure differences led to signiﬁcant difference in foam properties. Nanocomposite foam with concurrent increases in tensile strength (40%), tensile modulus (60%) and strain at break (70%) was successfully prepared with the use of 0.5% functionalized CNTs that were well dispersed. The foam showed a ductile failure under tension that involved extensive pore deformation and collapsing, and formation and coalescence of microvoids that were largely responsible for the signiﬁcantly improved tensile toughness. By contrast, foam properties were reduced in the presence of poorly dispersed CNTs that weakly adhered to the matrix. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Polymeric foams are one of the most widely used materials in many applications such as insulation, packaging, ﬂotation and cushion, and shock and sound attenuation [1]. They offer good bal- ance between strength and weight, good thermal and sound insu- lation properties, and energy absorbing capability etc. Recently nanocellular foams were produced and showed unique properties such as ultra-low dielectric constants [2] and signiﬁcantly im- proved toughness [3,4]. Recently foaming of polymer nanocomposites has emerged as a novel means to expand the accessible range of foam morphology, and produce novel multifunctional materials with enhanced prop- erties [5,6]. The impacts of nanoparticles on the polymer foams are mainly twofold: (1) alteration of morphology resulting from the introduction of nanoparticles; and (2) change of properties as a combined effect of morphological change and properties enabled/ enhanced by the nanoparticles. Nanoparticles are highly effective bubbles nucleating agent, leading to foams with higher cell density and smaller cell size. This has been observed in numerous foams prepared by both physical and chemical foaming with different types of nanoparticles [7–15]. The high nucleation efﬁciency of nanoparticles has been shown particularly advantageous for manufacturing microcellular foam (cell size < 10 lm, cell density > 10 9 cells/cc 3 ) [16]. The nucle- ation efﬁciency of the nanoparticles is dependent on the particle dispersion [7–9], particle aspect ratio [10], and particle surface treatment [9]. In many instances it was found that better particle dispersion resulted in higher nucleation efﬁciency, higher cell den- sity and smaller cell size. On the other hand, non-uniform disper- sion of nanoparticle may lead to bimodal cell size distribution [11]. Particle surface curvature and geometry also play important role. Flat surface is more effective than convex surface for bubble nucleation [17]. Moreover, Chen et al. [10] observed higher nucle- ation efﬁciency when a nanoparticle with lower aspect ratio was used. They have attributed this to the higher nucleation efﬁciency of ﬂat tube-ends than the convex side-walls, and the higher frac- tion of tube-ends surfaces in shorter carbon nanotubes. Further- more, the resulting change of foam structure (bubble density, bubble size and size distribution [18,19]) and matrix properties [20] have profound inﬂuence on the foam mechanical properties. 0266-3538/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compscitech.2013.03.024 ⇑ Corresponding author at: Department of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer St., Tallahassee, FL 32310, USA. Tel.: +1 850 410 6273. E-mail address: zeng@eng.fsu.edu (C. Zeng). 1 Current address: Department of Mechanical & Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, ON, Canada M5S 3G8. 2 Current address: H. Milton Stewart School of Industrial & Systems Engineering, Georgia Institute of Technology, 755 Ferst Drive, NW, Atlanta, GA 30332, USA. Composites Science and Technology 82 (2013) 29–37 Contents lists available at SciVerse ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech