UNCORRECTED PROOF Food Packaging and Shelf Life xxx (2018) xxx-xxx Contents lists available at ScienceDirect Food Packaging and Shelf Life journal homepage: www.elsevier.com Properties of poly(vinyl alcohol) flms as determined by thermal curing and addition of polyfunctional organic acids Massimo Bellelli a , Fabio Licciardello a, b, ⁎ , Andrea Pulvirenti a, b , Patrizia Fava a, b a Department of Life Sciences, University of Modena and Reggio Emilia, Via Amendola 2, 42122, Reggio Emilia, Italy b Centro di Ricerca Interdipartimentale per il Miglioramento e la Valorizzazione delle Risorse Biologiche Agro-Alimentari BIOGEST-SITEIA, University of Modena and Reggio Emilia, Tecnopolo di Reggio Emilia, Piazzale Europa 1, 42124, Reggio Emilia, Italy ARTICLE INFO Keywords: Citric acid Crosslinking Malic acid Plasticizer PVOH ABSTRACT The aim of the study was to assess the effect of the addition of citric and malic acid and heat curing on the me- chanical, physical and optical properties of poly(vinyl alcohol) (PVOH) flms. The addition of the organic acids without successive thermal treatments has a mere plasticising effect, while their application with heat curing has a combined crosslinking and plasticising effect. While conventional plasticizers and crosslinkers improve either extensibility or tensile strength of flms, respectively, the addition of citric and malic acid coupled with heat curing determined good tensile strength and extensibility. Hydrophilicity was significantly reduced by thermal curing and even further reduced with the organic acids addition. The high transparency of the PVOH flms was not affected either by heat-curing, acid addition and their combination, while the use of high curing temperature coupled with acid addition caused a slight yellowing of the flms. The use of citric and malic acid in combina- tion with thermal curing is a viable strategy for tailoring the performances of PVOH flms thus broadening their spectrum of application. 1. Introduction Poly(vinyl alcohol) (PVOH) is a non-toxic, odourless and tasteless polymer with several applications, such as food packaging material (as flm, layer in composite flms, coating for flms of different nature), as a coating agent for food supplements, in the pharmaceutical and cosmet- ics industries and several medical applications, as well as in the paper and textile industries (Demerlis & Schoneker, 2003; Vieira, Altenhofen da Silva, Oliveira dos Santos, & Beppu, 2011). PVOH has been previ- ously evaluated for safety by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) in 2003 at the 61st meeting, and an ADI of 50 mg/kg bw was established. Among its main features, biodegradability has raised interest for this material (Chiellini, Corti, d’Antone, & Solaro, 2003); indeed, even boosted by the recent planetary alert on microplastic pollution, research is seeking for biodegradable packaging solutions which could substitute conventional plastics for food application, considering that recycling is often not feasible for food packaging plastics (Gan & Chow, 2018; Ingrao, Gigli, & Siracusa, 2017). As a material for food packaging, either as stand-alone material or in the formulation of composite flms (Muppala, Kannat, Chawla, & Sharma, 2014), PVOH generally stands out for its excellent flm-form- ing capacity, barrier to gases, optical properties, high tensile strength and fexibility (Park, Park, & Ruckenstein, 2001; Park, Jun, & Marsh, 2001); however, the physical properties of PVOH largely depend on the method of preparation. On the other hand, PVOH is highly hydrophilic and its properties are affected by water acting as plasticizer (Musetti et al., 2014). Hence, research aimed at the improvement of PVOH prop- erties is of paramount importance in order to broaden its range of ap- plication. Previous works have studied the physical and mechanical re- sponse of PVOH flms to curing: this can be performed by heat treat- ment, addition of cross-linking agents or both. Chemical cross-linking agents which have been studied for PVOH are glutaraldehyde, hexam- ethylene diisocyanate, glyoxal and boric acid (Lim et al., 2015). Mul- tifunctional compounds able to react with the hydroxyl groups present in each repeating unit of PVOH may be used as crosslinkers and yield three-dimensional networks, thus enhancing resistance to dissolution in water, improving mechanical and thermal properties (Lim et al., 2015): ⁎ Corresponding author at: Department of Life Sciences, University of Modena and Reggio Emilia, Via Amendola 2, 42122, Reggio Emilia, Italy. Email address: fabio.licciardello@unimore.it (F. Licciardello) https://doi.org/10.1016/j.fpsl.2018.10.004 Received 6 August 2018; Received in revised form 28 September 2018; Accepted 10 October 2018 Available online xxx 2214-2894/ © 2018.