Hybrid silicate nanofillers: Impact on morphology and performance of EVA copolymer upon in vitro physiological fluid exposure Azlin Fazlina Osman, 1 Asna Rasyidah Abdul Hamid, 1 Md. Rakibuddin, 2 Goh Khung Weng, 1 Rajakumar Ananthakrishnan, 2 Supri A. Ghani, 3 Zaleha Mustafa 4 1 Center of Excellence Geopolymer and Green Technology (CEGeoGTech), School of Materials Engineering, Universiti Malaysia Perlis, Arau, Perlis 02600, Malaysia 2 Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, India 3 Faculty of Engineering Technology, Universiti Malaysia Perlis, Kampus UniCITI, S. Chuchuh, Padang Besar Perlis, Malaysia 4 Advanced Manufacturing Centre, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, Durian Tunggal, Melaka 76100, Malaysia Correspondence to: A. F. Osman (E-mail: azlin@unimap.edu.my) ABSTRACT: Ethyl vinyl acetate (EVA) copolymers are recyclable plastics with exceptional biocompatibility, thus they are potent candi- date materials for biomedical applications. In this study, improvement in the EVA biostability was aimed by the incorporation of hybrid nanofillers. EVA copolymer incorporating 3 wt % organically modified montmorillonite/bentonite (OMMT/Bent) hybrid nanofillers in different ratios (3:0, 2.75:0.25, 2.5:0.5, 2.25:0.75, 2:1 and 0:3 in wt %) were prepared by melt compounding process and then analyzed for their biostability upon in vitro physiological fluid exposure. Results indicated that the addition of OMMT 2.75 / Bent 0.25 hybrid nanofillers can reduce the degradation of the EVA copolymer under physiological fluid environment through hydro- philic bentonite–vinyl acetate interactions. The obtained nanocomposite material achieved the best retention in tensile and thermal properties upon 4 weeks exposure in the in vitro physiological fluid. The findings indicate the potential of using the hybrid OMMT/ Bent nanofillers for biostability enhancement of the EVA while reducing the nanocomposite production costs through the addition of cheaper natural bentonite as co-nanofiller with the OMMT. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44640. KEYWORDS: biomedical applications; composites; copolymers; degradation; structure-property relationships Received 6 September 2016; accepted 7 November 2016 DOI: 10.1002/app.44640 INTRODUCTION Ethylene vinyl acetate (EVA) copolymer is a polymeric material that exhibits low modulus and high flexibility similar to elasto- meric materials, yet it can be processed like other thermoplas- tic. 1 EVA is biocompatible, offers excellent optical clarity, barrier properties, low-temperature toughness and stress-crack resis- tance. 1,2 These superior properties of EVA which have been applied in various applications such as flexible packaging, cable and wire, hose and tube, photovoltaic encapsulants and adhesive as well as biomedical devices. 1,2 However, to be used as implantable material, further improvement in EVA mechanical performance and biostability is needed. This is to ensure the durability of the insulation material, so that the frequency of replacement and follow-up care of the implantable device can be reduced. The enhancement in EVA performance as implant- able insulation material can be achieved by adding small amount of nanofillers as reinforcing and toughening filler. 3–5 Nanoclays are the most frequently employed nanofiller for polymers because they are abundant, cheap and own tailorable surface chemistry. However, when dealing with the multi- component polymer such as the EVA, the interactions between individual co-monomer chains with the nanofiller is the critical point to obtain the desired mechanical, thermal, thermome- chanical and barrier properties enhancement. 5–9 The polarity different between the ethylene and vinyl acetate (VA) co- monomers may affect their degree of interactions with the nanofiller. Therefore, in this project, hybrid nanofillers compris- ing unmodified bentonite (Bent) (hydrophilic) and OMMT (hydrophobic surface) were introduced into the host EVA copol- ymer in order to optimize nanofiller interactions with both the ethylene (hydrophobic) and the VA (hydrophilic) co-monomers. It was observed by previously published studies that synergistic effects obtained from hybrid fillers can allow the enhancement in mechanical and thermal properties of the host polymers. 10–12 However, there is no published research concerning the effect of hybrid nanofillers to biostability aspect of host polymers as V C 2016 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.44640 44640 (1 of 15)