Polymer 185 (2019) 121946 Available online 31 October 2019 0032-3861/© 2019 Elsevier Ltd. All rights reserved. Covalent grafting of unfunctionalized pristine MWCNT with Nylon-6 by microwave assist in-situ polymerization Roberto Ya~ nez-Macias a , Ernesto Hernandez-Hernandez a , Carlos A. Gallardo-Vega a , Raquel Ledezma-Rodríguez a , Ronald F. Ziolo a , Yucundo Mendoza-Tolentino b , Salvador Fern� andez-Tavizon a , Carlos A. Avila-Orta a , Zureima Garcia-Hernandez a, ** , Pablo Gonzalez-Morones a, * a Centro de Investigaci� on en Química Aplicada (CIQA), Blvd, Enrique Reyna Hermosillo, #140. San Jos� e de los Cerritos, C.P. 25294, Saltillo, Coahuila, Mexico b Universidad Tecnol� ogica del Valle del Mezquital (UTVM), Carretera Ixmiquilpan-Capula Km, 4, Col. El Nith, 42300, Ixmiquilpan, Hidalgo, Mexico A R T I C L E INFO Keywords: Microwave synthesis Hybrid polymer nanocomposite Nanohybrid MWCNT-Polymer In-situ polymerization ABSTRACT Covalent grafting of nylon-6 (Ny-6) and pristine multi-walled carbon nanotubes (MWCNT-P) was performed in- situ via microwave assist polymerization (MAP) of ε-caprolactam and 6-aminocaproic acid at different power and time conditions. The results showed that the microwave dielectric heating of the MWCNT-P activates the nanotube vacancies to react with the amine group of 6-aminocaproic acid at 175 � C. When the reaction tem- perature reaches 230 � C, Ny-6 polymerization ensues, simultaneously, with insertion of Ny-6 chains on the amine-activated MWCNT to obtain a nanohybrid, MWCNT-Ny, with a grafted Ny-6 coating of 14 nm. The hy- bridization reaction therein affects the entire polymerization process and the molecular weight and yield of both the hybrid and Ny-6. Raman, XPS and electrical conductivity data for the MWCNT-Ny flms show that the nanotube structure remains intact in the flms which display an electrical surface conductivity range of 0.47–0.06 S/m. The compatibility and dispersion of the MWCNT-Ny nanohybrid in Ny-6, as observed by crys- tallization and fusion of the so-formed hybrid polymer nanocomposite, HPNC, exceed those obtained by con- ventional methods of preparation using ultrasound and functionalized nanotubes. 1. Introduction Interest in polymer nanocomposite materials may be attributed to their useful mechanical, electrical, thermal, optical and processing properties and in subsequent applications in a broad range of societal sectors including transportation, communications, construction, mem- brane fltration and consumer goods and in industries such as automo- tive, aeronautical, manufacturing, utilities and agriculture [1–6]. A valuable synthetic and rapidly growing alternative for energy effcient and fast assembly of nanomaterials, such as nanoparticles (NP), polymer nanocomposites (PNC), hybrid polymer nanocomposites (HPNC), and organic molecules, is microwave-assist chemistry [7–11]. The micro- wave synthesis of HPNC in particular has attracted considerable atten- tion since it was shown that the covalent bonding that occurs between the nanoparticle and the polymer in the HPNC enhances property per- formance, such as in thermal conductivity, for example, by several orders of magnitude [12–14]. Some of the advantages of the microwave (MW) heating technique are quantitative yields, a signifcant reduction in reaction time, more selective generation of by-products, disuse of solvents, cost reductions and lower environmental impact [15–17]. Additionally, the dispersion and compatibility of nanoparticles with a polymer through in-situ polymerization and crosslinking is a more effcient process than tradi- tional mixing and blending techniques, particularly when using “graft- ing from” and “grafting to” strategies, among others, for direct syntheses [18–23]. The two primary methods for the synthesis of HPNCs that utilize different thermoplastic matrices, such as nylon 6, polyethylene tere- phthalate, methyl methacrylate, and epoxide resins, use either precursor or prefunctionalized nanoparticles. In the frst method, nanoparticle precursor salts and monomers are mixed and treated with MW irradia- tion whereby polymerization takes place as well as NP formation * Corresponding author. ** Corresponding author. E-mail addresses: zureima.garcia@ciqa.edu.mx (Z. Garcia-Hernandez), pablo.gonzalez@ciqa.edu.mx (P. Gonzalez-Morones). Contents lists available at ScienceDirect Polymer journal homepage: http://www.elsevier.com/locate/polymer https://doi.org/10.1016/j.polymer.2019.121946 Received 30 May 2019; Received in revised form 10 October 2019; Accepted 25 October 2019