Carbohydrate Polymers 87 (2012) 2367–2375 Contents lists available at SciVerse ScienceDirect Carbohydrate Polymers jo u rn al hom epa ge: www.elsevier.com/locate/carbpol Investigation on the surface properties of chemically modified natural fibers using inverse gas chromatography Nereida Cordeiro a , Mariana Ornelas a , Alireza Ashori b,∗ , Shabnam Sheshmani c , Hor Norouzi c a Competence Center in Exact Science and Engineering, University of Madeira, Funchal, Portugal b Department of Chemical Technologies, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran c Department of Chemistry, Shahr-e-Rey Branch, Islamic Azad University, Tehran, Iran a r t i c l e i n f o Article history: Received 21 September 2011 Received in revised form 21 October 2011 Accepted 2 November 2011 Available online 9 November 2011 Keywords: Alkaline treatment Fibers modification Inverse gas chromatography Surface properties a b s t r a c t This paper presents the application of inverse gas chromatography (IGC) technique for characterization and comparison of the surface properties of the natural fibers as reinforcement fillers in wood plas- tic composites. The effects of chemical modification using 1% NaOH were also studied. The fibers used for this work were Iranian cultivated eucalyptus, spruce, bagasse, and wheat straw. Chemical composi- tion of fibers was found to be modified after treatment as characterized by Fourier transform infrared spectroscopy (FTIR). The crystallinity of fibers and the specific interaction was improved by the alkaline treatment, with more relevance to the agro-fibers. The IGC shows also a general increase in the wettability of the modified fiber when compared with the raw (unmodified) samples. Alkaline treatment achieves the best overall improvement in the properties evaluated of the agro-fibers when compared to the wood fibers. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Composite materials based on natural fibers, namely wood plas- tic composites (WPCs), demonstrate remarkable environmental and economical advantages (Ziaei Tabari, Nourbakhsh, & Ashori 2011). Although the use of wood flour in plastic composites has several advantages over inorganic fillers, several drawbacks (limi- tations) of natural fibers such as low compatibility and low thermal stability, greatly reduce the overall performance of WPCs (Hamzeh, Ashori, & Mirzaei, 2011). Wood, the most durable organic material, is a three dimensional polymeric composite, made up mainly of cellulose, hemicellulose and lignin. All species of wood and other plant tissues contain small to moderate quantities of chemical substances in addition to the macromolecules, namely extractives. Extractives content in most temperate and tropical wood species are 4–10% and 20% of the dry weight, respectively (Sjöström, 1993). Although extractives con- tribute merely a few percent to the entire wood composition, they have significant influence on its properties (Sheshmani, Ashori, & Farhani, 2012). It is well known that the performance, for example the mechan- ical properties, of WPCs depend on the properties of the individual components and their interfacial compatibility. The interface between hydrophobic plastic and hydrophilic wood is typically ∗ Corresponding author. Tel.: +98 228 2276637; fax: +98 228 2276265. E-mail address: ashori@irost.org (A. Ashori). weak and fails to transfer stress. The effective use of wood particles in WPCs requires a fundamental understanding of the structural and chemical characteristics of wood. For example, a few reports have been published about the effects of wood extractives on the strength properties of the resulting WPCs (Kim, Harper, & Taylor, 2009; Shebani, van Reenena, & Meincken, 2009; Sheshmani et al., 2012). Wood extractives are hydrophobic substances with low molecular weights. In the preparation of WPCs, wood flour is thoroughly mixed with a thermoplastic at high temperatures, e.g. 170 ◦ C. At such high temperature, wood extractives may tend to migrate to the wood flour surface, thus accumulating in the wood- plastic interphase (Nourbakhsh, Ashori, Ziaei Tabari, & Rezaei, 2010). In recent years, inverse gas chromatography (IGC) has been used to characterize and optimize the interaction of natural fibers and polymer composites (Cordeiro, Gouveia, & Jacob John, 2011; Cordeiro, Gouveia, Moraes, & Amico, 2011; Tze, Wålinder, & Gardner, 2006). The technique uses a solid phase packed into a column, and the column is placed in an oven. The temperature is controlled, as a gas mobile phase flows through the column where an inert carrier gas contains “infinitely dilute” samples of probe gases. A detector measures the time required for the probe gases to go through the packed column. The retention time is then related to thermodynamic quantities to characterize the solid phase sample. The fiber/matrix acid base interaction can be quantified using IGC by matching the acidic parameter (K a ) of one component with the basic component (K b ) of the other component, and then, measuring the enthalpy of adsorption of the resin onto the fibers 0144-8617/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2011.11.001