Industrial Crops and Products 70 (2015) 170–177 Contents lists available at ScienceDirect Industrial Crops and Products jo u r n al homep age: www.elsevier.com/locate/indcrop Inﬂuence of storage conditions on starch/PVA ﬁlms containing cellulose nanoﬁbers Denis Mihaela Panaitescu ∗ , Adriana Nicoleta Frone ∗ , Marius Ghiurea, Ioana Chiulan Polymer Department, National Institute for R&D in Chemistry and Petrochemistry ICECHIM, 202 Splaiul Independentei, 060021 Bucharest, Romania a r t i c l e i n f o Article history: Received 9 December 2014 Received in revised form 17 February 2015 Accepted 11 March 2015 Keywords: Starch/PVA ﬁlms Cellulose nanoﬁbers AFM Mechanical properties a b s t r a c t Cellulose nanoﬁbers (CN) with high aspect ratio were obtained and their transverse modulus (Et) was determined for the ﬁrst time by peak force (PF) QNM (quantitative nanomechanical mapping). The PF QNM value of Et (18.8 GPa) was comparable with that of cellulose determined by other methods. CN were used as reinforcements in starch/poly(vinyl alcohol) (S/PVA) cross-linked ﬁlms and the inﬂuence of storage conditions on the properties of these ﬁlms was investigated in this paper. It was found that over 4 wt%, CN form a real network and hinder starch recrystallization. CN determined a signiﬁcant increase of strength and stiffness of S/PVA depending on storage conditions. Two fold increase of modulus was observed in thermal treated samples compared to fresh ones and the increase of both strength and modulus in samples exposed to humid atmosphere. PF QNM successfully explains the inﬂuence of moisture on the properties of the ﬁlms exposed to humid atmosphere, emphasizing new well organized sub-micron amorphous formations on their surface. Starch ﬁlms with 7 wt% CN showed strength and stiffness close to that of polyoleﬁnes (19.5 MPa and 1199 MPa, respectively), and can be seen as a low cost “green” substitute for application in food packaging and conservation. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Bio-derived ﬁlms and coatings have become hot topics in both research and industry because of the ever-increasing requirement of functional properties and the growing awareness about environ- mental issues (Belgacem and Gandini, 2008; Belhassen et al., 2014; Bledzki et al., 2009; Ghanbarzadeh et al., 2011; Svagan et al., 2009; Thakur et al., 2014). The disposal of synthetic packaging materials exerts a huge pressure on the environment and, therefore, replac- ing these synthetic products with “green” versions obtained from non-food crops is essential for reducing environmental pollution. Starch/polyvinyl alcohol blends and composites have been widely investigated for the production of “green materials” for packag- ing, agricultural and medical applications (Das et al., 2010; Dean et al., 2008; Majdzadeh-Ardakani and Nazari, 2010; Misic et al., 2012). Starch (S), composed of two distinct polymers, amylose and amylopectin, in approximate proportion of 25/75 in corn starch granules is highly biodegradable. Poly(vinyl alcohol) (PVA), the largest synthetic water soluble polymer produced in the world, has valuable properties such as biodegradability, biocompatibility, ∗ Corresponding authors. Tel.: +40 213163068; fax: +40 213123493. E-mail addresses: panaitescu@icf.ro (D.M. Panaitescu), ciucu adriana@yahoo.com (A.N. Frone). chemical resistance, and good mechanical properties (Awada et al., 2014; Frone et al., 2011). However, the biodegradation process of pure PVA is quite slow, particularly under anaerobic conditions and its cost is high. In S/PVA blends, the ﬁrst acts as a promoter for mate- rial biodegradation and contributes with its low-cost, abundant supply and ease of physical and chemical modiﬁcation. However, the mechanical properties and water resistance of pure starch and starch/PVA blends are poor and starch retrogradation, further lim- its their application. Cross-linking (Das et al., 2010) and micro- or nano-reinforcements (Majdzadeh-Ardakani and Nazari, 2010; Dean et al., 2008; Versino and García, 2014) were mostly tested to enhance their performance. Cellulose nanoﬁbers (CN) are valuable reinforcing agents for polymers because of their remarkable mechanical properties, besides the abundance of sources including agro-industrial waste, renewability, and biodegradability (Angles and Dufresne, 2000; Roohani et al., 2008; Thakur et al., 2014). CN were tested for improv- ing the mechanical properties of starch (Hietala et al., 2013; Moran et al., 2013; Yakimets et al., 2007). Five percent (w/w) CN were enough for doubling the modulus of elasticity of potato starch ﬁlm prepared by solution casting (Moran et al., 2013). Higher amount of CN (10 wt%) was necessary for the same increase of modulus in thermoplastic starch prepared by twin-screw extrusion (Hietala et al., 2013). Water greatly inﬂuences the mechanical properties of http://dx.doi.org/10.1016/j.indcrop.2015.03.028 0926-6690/© 2015 Elsevier B.V. All rights reserved.