Crosslinked PVA Nanofibers Reinforced with Cellulose Nanocrystals: Water Interactions and Thermomechanical Properties Maria Soledad Peresin, 1 * Arja-Helena Vesterinen, 2 Youssef Habibi, 1y Leena-Sisko Johansson, 3 Joel J. Pawlak, 1 Alexander A. Nevzorov, 4 Orlando J. Rojas 1,3 1 Department of Forest Biomaterials, North Carolina State University, Raleigh North Carolina 27695-8005 2 Department of Biotechnology and Chemical Technology, School of Chemical Technology, Aalto University, FI-00076, Aalto Espoo, Finland 3 Department of Forest Products Technology, School of Chemical Technology, Aalto University, FI-00076, Aalto Espoo, Finland 4 Department of Chemistry, North Carolina State University, Campus box 8204, Raleigh North Carolina 27695-8204 *Present address: VTT - Technical Research Centre of Finland, Biologinkuja 7, P.O. Box 1000, FI-02044 VTT Espoo, Finland †Present address: CRP Henri Tudor, 29, avenue J.F, Kennedy L-1855 Luxembourg Correspondence to: O.J. Rojas (ojrojas@ncsu.edu). ABSTRACT: Acid-catalyzed vapor phase esterification with maleic anhydride was used to improve the integrity and thermo-mechanical properties of fiber webs based on poly(vinyl alcohol), PVA. The fibers were produced by electrospinning PVA from aqueous disper- sions containing cellulose nanocrystals (CNCs). The effect of esterification and CNC loading on the structure and solvent resistance of the electrospun fibers was investigated. Chemical characterization of the fibers (FTIR, NMR) indicated the formation of ester bonds between hydroxyl groups belonging to neighboring molecules. Thermomechanical properties after chemical modification were analyzed using thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. An 80% improve- ment in the ultimate strength was achieved for CNC-loaded, crosslinked PVA fiber webs measured at 90% air relative humidity. Besides the ultra-high surface area, the composite PVA fiber webs were water resistant and presented excellent mechanical properties. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40334. KEYWORDS: cellulose and other wood products; composites; electrospinning; hydrophilic polymers; nanoparticles; nanowires and nanocrystals Received 31 July 2013; accepted 17 December 2013 DOI: 10.1002/app.40334 INTRODUCTION Film formation, processability and hydrophilicity of polyhydroxy polymers such as poly(vinyl alcohol) (PVA) make them some of the most commonly used polymers in industry. 1 They are also noted for their biocompatibility and biodegradability. 2,3 PVA has good transparency and antielectrostatic properties. 4 The hydro- philic nature of PVA is a factor in membrane permeation of water and hydrated salts. In fact, PVA-based membranes have reduced fouling by adhesion of nonpolar molecules, microbes and fulvic acids. 1 However, a major drawback for deployment of PVA in aqueous media is its high degree of swelling and solubility. This makes water stability of PVA a highly desirable property. Due to their very high surface area-to-volume ratio nanoscale and microscale fiber membranes are very attractive in filtration media. Such sizes can confer extremely high surface cohesion that allows entrapping particles as small as the sizes of the pores. 5,6 A method commonly used to produce such fine fibers is electrospinning. Electrospinning of PVA has been studied intensely 7–9 ; however, as was highlighted before, fiber webs of PVA dissolve in water, which limits their application in aqueous systems or environments with high relative humidity. 10 Modifi- cation of polyvinyl alcohol can expand end use applications 11 and crosslinking is one route to overcome water sensitivity issues. Several methods have been reported to improve the mechanical integrity of PVA membranes in water, and their selectivity in the case of salt-rejection systems. 1,12 In all the methods proposed, the main target has been to obtain three- dimensional PVA networks. 13 These include physical and chemi- cal modification of PVA by heat treatment, 1,14 freeze–thaw to induce crystallization, 1,15 irradiation, 16 radical polymerization– peroxidisulphate, 12 and acid-catalyzed dehydration through V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2014, DOI: 10.1002/APP.40334 40334 (1 of 12)