Polyallylamineemontmorillonite as super flame retardant coating assemblies by layer-by layer deposition on polyamide Kadir Apaydin a, b , Abdelghani Laachachi a, * , Vincent Ball a , Maude Jimenez b , Serge Bourbigot b , Valérie Toniazzo a , David Ruch a a Department for Advanced Materials and Structures, Laboratoire de Technologies Industrielles, Centre de Recherche Public Henri Tudor, 66 rue de Luxembourg, L-4002 Esch-sur-Alzette, Luxembourg b UMET-ISP, UMR 8207, ENSCL, Université Lille Nord de France, BP 90108, 59652 Villeneuve d’Ascq Cedex, France article info Article history: Received 10 August 2012 Received in revised form 18 October 2012 Accepted 20 November 2012 Available online 29 November 2012 Keywords: Layer-by-layer assembly Clay Flame retardant Polyamide abstract In this paper, a polyamide-6 (PA6) substrate has been coated with a flame retardant film, made from polyallylamine (PAH) (polycation) and montmorillonite (MMT) (polyanion), elaborated by Layer-by-Layer (LbL) technique. The (PAHeMMT) n assembly (with n the number of bilayers deposited) exhibits an exponential growth regime. At n ¼ 20 bilayers deposition of PAH and MMT, the film reaches a consid- erable thickness of w5 mm with the alignment of MMT in the direction parallel to the substrate. Scanning Electron Microscopy (SEM) analysis of the cross-section and Atomic Force Microscopy (AFM) analysis display a regular and continuous morphology of the obtained films. Thermogravimetric analysis shows that the presence of (PAHeMMT) n films at 10 and 20 bilayers enhances the thermal stability of the polyamide substrate. Cone calorimetry evidences excellent reaction to fire of the material since peak of heat release rate (HRR) is decreased by more than 60% in the presence of 20 bilayers of PAHeMMT film in comparison with uncoated PA6. Continuous charred layer was observed during the combustion and the thickness of the coating at the end of the combustion test is twice higher than that of the initial thickness. The presence of this expanded charred layer at the surface acts as protective limiting heat and mass transfer. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Layer-by-Layer (LbL) deposition technique consists of alter- nating deposition of polyanions and polycations on a solid substrate leading to the formation of polyelectrolyte multilayer films. This technique was discovered in 1966 by Iler [1] and developed by Decher et al. [2] in the 90’s. Nowadays, this popular technique is widely used in various fields such as drug delivery [3,4], anti-reflection [5,6], electrochromic [7e9], oxygen barrier [10e17] and it is only in recent years that this technique has been considered to design flame retardant coatings [15,18e26]. Li et al. [18] have been the first to study the flammability of coatings made from branched polyethylenimine (BPEI) and Laponite clay designed by LbL deposition on cotton fabrics. High-pH BPEI and low-pH clay produced the thickest films (5 nm/bilayer). It was shown by thermogravimetric analysis and vertical flame testing (VFT) that the clay coating delays the degra- dation of the cotton by providing a sheath like ceramic barrier. In the other work, Li et al. [19] have studied the flame retardant behavior of branched polyethyleneimine (BPEI) (at pH ¼ 7 or 10) e MMT (0.2 or 1wt%) assemblies deposited onto the cotton fabrics. The VFT results showed that the residues from 20 bilayers coated fabrics are heavier, have preserved the fabric structure and provide significant char. Microcombustion calorimeter (MCC) data revealed that all the coated fabrics decrease the total heat release (THR) and heat release capacity (HRC). In this case the BPEI pH 10/1% MMT coatings displayed the best MCC results (HRC decreases by 20%). Then Li et al. [20], also demonstrated that the polyhedral oligomeric silsesquioxanes (POSS) ( or þ) coupled to aminopropyl silses- quioxanes oligomer (APþ) improved the fire performance of the cotton fabrics. In this work, several fire methods were used to evaluate the fire performance of this system. VFT results showed that all coatings yield char residue when increasing the number of bilayers. Moreover, MCC data revealed that the maximum reduc- tion of peak of heat release rate (pHRR) (20%) was observed for the (APþ/POSS) 20 coatings. Following the pill test, the (APþ/POSS) * Corresponding author. Tel.: þ352 42 59 91 591; fax: þ352 42 59 91 4555. E-mail address: abdelghani.laachachi@tudor.lu (A. Laachachi). Contents lists available at SciVerse ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymdegradstab.2012.11.006 Polymer Degradation and Stability 98 (2013) 627e634