This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014 New J. Chem. Cite this: DOI: 10.1039/c4nj01558d Tough hyperbranched epoxy/neem-oil-modified OMMT thermosetting nanocomposite with an antimicrobial attribute Bibekananda De, a Kuldeep Gupta, b Manabendra Mandal b and Niranjan Karak* a In the present study, a high performance, tough, antimicrobial, hyperbranched epoxy nanocomposite is fabricated by the incorporation of neem oil-immobilized organo-modified montmorillonite nanoclay. The immobilization of neem oil with organo-modified montmorillonite nanoclay is performed by the combined effect of mechanical and ultrasonic forces under ambient conditions. This immobilization is confirmed by FTIR and XRD studies. FTIR, XRD, SEM and TEM analyses also confirm the formation of the exfoliated nanocomposite. The dose-dependent enhancements of tensile strength (50%), elongation at break (3-fold), toughness (5.5-fold) and thermal stability (20 1C) of the pristine epoxy thermoset are observed for the nanocomposite. Antimicrobial studies are performed by growth curve and zone-of- inhibition analyses against different bacteria and a fungus at different doses of neem oil-immobilized organo-modified montmorillonite nanoclay. The nanocomposite with 50 wt% neem oil-immobilized organo-modified montmorillonite nanoclay (2.5 wt%) shows significant activity against biofilm formation compared to the pristine thermoset. Thus, the studied nanocomposite has strong potential as a high- performance functional material. Introduction Polymer nanocomposites are one of the most active areas of development in the domain of nanotechnology and materials science. The incorporation of nanoclays into various polymers to enhance properties like mechanical, thermal, physical, barrier, have been extensively reported over the last two decades. 1–3 The high surface area, favorable intercalation chemistry and natural availability of nanoclays make them the most popular among all the nanomaterials. 4,5 They have a high tendency to absorb or intercalate different bio-molecules like drugs or biocides, 6,7 organo-molecules 8 or different nanoparticles 9,10 between their layer structures, and thus recently they have attracted consider- able attention in the biological field. However, high moisture absorption and incompatibility with hydrophobic polymers restrain the incorporation of clay particles into the polymer matrix. Thus, organically modified clay is largely used in polymer nanocomposites, and this modification can be performed either by surface functionalization or by the cation exchange process. 11–13 The modification of clay is mainly performed to achieve improved properties as well as to obtain a new set of desired properties. Among different matrices for the fabrication of polymer–clay nanocomposites, epoxy resins are extensively used. Furthermore, the design of hyperbranched architecture in the epoxy structure offers a golden feather into it. This is because of their high solubility, low viscosity, and high reactivity, in addition to the fact that thermosets also possess high tensile strength, high modulus, high stiffness, high thermal stability and high chemical resis- tance. 14–16 However, such approaches cannot properly address the main drawback of low toughness or the highly brittle nature of the epoxy thermoset. Thus, this observation prompted researchers to investigate further modification of the conventional OMMT in such a way that the abovementioned problem of epoxy thermoset can be addressed. On the other hand antimicrobial polymer nanocomposites are promising materials in advanced surface coatings for destructing microorganism in different fields including marine industries because of slow release of the active agents. Tradi- tionally, antimicrobial materials contain one or more toxic compounds like biocides and metal nanoparticles, which may cause human health as well as environmental hazards due to leaching problem. 17–19 Therefore, a natural antibiotic- or biopesticide-immobilized, clay-reinforced polymer nanocomposite is preferred, although no such report is found, except our earlier report. 6 Moreover, the active agent used earlier, H. aromatica, had the problem of volatility and availability. On the other hand, a Advanced Polymer and Nanomaterial Laboratory, Department of Chemical Sciences, Tezpur University, Napaam-784028, Assam, India. E-mail: karakniranjan@yahoo.com; Fax: +91-3712-267006 b Department of Molecular Biology and Biotechnology, Tezpur University, Napaam-784028, Assam, India. E-mail: mandal@tezu.ernet.in Received (in Montpellier, France) 11th September 2014, Accepted 24th October 2014 DOI: 10.1039/c4nj01558d www.rsc.org/njc NJC PAPER Published on 24 October 2014. Downloaded by Tezpur University on 13/11/2014 09:36:59. View Article Online View Journal