Hybrid glass fibre reinforced composites with micro and poly-diallyldimethylammonium chloride (PDDA) functionalized nano silica inclusions Júlio C. Santos a , Luciano M.G. Vieira a , Túlio H. Panzera a,⇑ , Marco A. Schiavon b , André L. Christoforo a , Fabrizio Scarpa c a Department of Mechanical Engineering, Federal University of São João del Rei – UFSJ, Brazil b Department of Natural Sciences, Federal University of São João del Rei, Brazil c Department of Aerospace Engineering, Advanced Composites Centre for Innovation and Science, University of Bristol, UK article info Article history: Received 31 July 2014 Accepted 19 September 2014 Available online 30 September 2014 Keywords: Hybrid Particle-reinforcement Statistical methods Mechanical testing Chemical/thermal analysis abstract This work investigates the effect of using functionalised poly-diallyldimethylammonium chloride (PDDA) silica micro and nanoparticles on the apparent density, tensile and flexural strength and modulus of hybrid glass fibre reinforced composites. The work is carried out using a Design of Experiment (DoE) approach on a population of 60 composite specimens produced according the size of the nanoparticles and their weight fraction. A 2% of weight fraction of functionalised silica nanoparticles is shown to reduce the flexural strength and density of the composites, but to maximise significantly both the tensile, flex- ural modulus and tensile strength of the hybrid glass fibre materials. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Glass fibre-reinforced composites (GFRCs) constitute a signifi- cantly less expensive alternative to carbon fibre-reinforced com- posites (CFRC). GFRCs are however not extensively used in high performance applications due to their relatively low stiffness and durability [1]. In general, interlaminar stresses created by the pres- ence of cracks and defects can propagate rapidly due to the lack of fibres along the transverse direction of fibre-reinforced compos- ites. Several methods have been evaluated to perform toughening – i.e., the enhancement of the interlaminar fracture toughness and mitigation of the delamination process. Toughening can be achieved by the modification of the polymer with the temperature, by using chemical admixtures [2] and nano or micro inorganic par- ticle inclusions [3–7]. Failure of laminated composites is a complex phenomenon that involves matrix cracking, delamination and fibre breaking [8]. Particular types of reinforcement by using particles have been proposed in open literature, including hybridization through micro-scaled [8] and nano-scaled inclusions (i.e. carbon nanotubes, graphene sheets, alumina, titanium oxide and silica particles [9–13]). The fatigue life of hybrid glass fibre reinforced composites (HGFRC) with 10 wt% of silica nanoparticles is almost three to four times higher than analogous GFRCs made with pris- tine epoxy matrix only [14]. Unidirectional glass/epoxy composite containing silica nanoparticles also dramatically increased their longitudinal compressive strength, while at the same time showing an enhancement of the longitudinal and transverse tensile strengths [9]. Tsai and Cheng have postulated that the enhance- ment of the mechanical performance of HGFRCs might be attrib- uted to the increment of the fraction of the epoxy matrix directly affected by the reinforcement from the silica particles [13]. Uddin and Sun have concluded the dispersion of the particles is a domi- nant factor in determining the mechanical properties of HGFRCs reinforced with silica nanocomposites [15]. Nano-particles exhibit a significant tendency to aggregate between them or around larger particles (wall-effect). It is difficult in general to achieve a non- aggregated nano-particle system due to the high surface free energy, which can be caused by the particle geometry and the molecular configuration. Different mechanical and chemical dis- persion methods have been proposed to disperse inorganic nano- particles in organic solvents or resins [16]. This work describes the use of poly-diallyldimethylammonium chloride (PDDA) as an alternative surface agent to disperse silica micro and nanoparticles into an epoxy polymer. A Design of http://dx.doi.org/10.1016/j.matdes.2014.09.052 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Mechanical Engineering, Federal University of São João del Rei – UFSJ, Praça Frei Orlando 170, 36.307-352 São João Del Rei, Brazil. Tel.: +55 (32)33792603. E-mail address: panzera@ufsj.edu.br (T.H. Panzera). Materials and Design 65 (2015) 543–549 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes