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Synergistic effect of nano TiO2 and nanoclay on the ultraviolet degradation and physical properties of wood polymer nanocomposites Ankita Hazarika, and Tarun Kumar Maji Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie401596h • Publication Date (Web): 26 Aug 2013 Downloaded from http://pubs.acs.org on September 2, 2013
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Industrial & Engineering Chemistry Research
Synergistic effect of nano TiO2 and nanoclay on the ultraviolet degradation and physical properties of wood polymer nanocomposites
Ankita Hazarika, Tarun K. Maji*
Department of Chemical Sciences, Tezpur University, Assam-784028, India
Corresponding Author *E-mail:
[email protected]; tel.: +91 3712 267007, ext 5053; fax: +91 3712 267005.
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ABSTRACT: Wood polymer nanocomposite (WPNC) was prepared by impregnating melamine formaldehyde-furfuryl alcohol (MFFA) copolymer, dimethylol dihydroxy ethylene urea (DMDHEU), a crosslinking agent, nanoclay, nano TiO2 and a renewable polymer obtained as a gum from the plant Moringa oleifera into wood (Ficus hispida). Fourier Transform Infrared Spectroscopy (FTIR) and Xray diffractometry (XRD) were used to confirm the surface modification of TiO2 and interfacial interaction between wood, polymer, crosslinker and nanoparticles. The uniform distribution of nanoclay and TiO2 was evidenced by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). Remarkable improvement in ultraviolet resistance properties was observed as manifested by lower weight loss, carbonyl index, lignin index, crystallinity index values, SEM study and lower loss in mechanical properties. WPNC treated with 3 phr each of nanoclay, TiO2 and the plant gum enhanced significantly the mechanical, flame retardancy, thermal stability and decreased water uptake capacity. Keywords: Nanocomposites, wood, UV resistance, plant polymer
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1. INTRODUCTION Modification of wood by the formation of nanocomposites through in situ polymerization has been studied comprehensively in recent years.1 The cell wall of wood is mainly composed of biopolymers i.e. cellulose, hemicellulose and lignin. The glucose units of cellulose and hemicellulose are linked by glycosidic linkage and the free hydroxyl groups in cellulose help in easy formation of hydrogen bonding with water which causes swelling of wood.2 But lignin is an aromatic compound, polymers of phenyl propane unit, and has least tendency to absorb water.3 All the components of wood are susceptible to UV degradation. However lignin is the primary components of wood responsible for degradation due to the presence of chromophoric functional groups.4 These groups absorb light, generate long-lived triplet states, and thus assist in its degradation. Moreover, lignin can form free radicals as intermediates on UV exposure and the process of degradation is stimulated by moisture and atmospheric oxygen.5 Chemical treatment such as formation of wood polymer composites (WPC) is one potential ways to overcome the drawbacks allied with the properties of wood.6 Nanofillers based WPC as in situ nanoreinforcement offers new opportunities in the overall properties of the composites. Wood modified with nanoclay has been reported to improve dimensional stability, water repellency, surface hardness and modulus of elasticity.7 Combination of nanoclay with other metal nanoparticles will influence the properties of the composites considerably as reported by Laachachia et al. while studying the properties of PMMA nanocomposites prepared with TiO2 and nanoclay.8 Ultraviolet resistant property is one of the desirable properties of WPC as it is mainly used for outdoor applications. Among the different nanofillers, TiO2 nanopowder is increasingly being investigated to improve UV stability and durability of the composites. TiO2 reinforcement can improve physiochemical, mechanical and abrasion resistance properties making the nanocomposites a 3
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promising category of products.9 Most of the reports have addressed the enhancement in properties of wood such as weather resistance and antimicrobial activity of wood by the use of TiO2 sols through sol-gel methods.10,11 Using water as a solvent instead of using petroleum based organic solvent has rejuvenated the awareness for a sustainable environment. Furfuryl alcohol derived from renewable feedstock improves durability, dimensional stability and hardness of wood.12 But it cannot influence the bending strength and the modulus of elasticity (MOE) of the treated wood. Melamine formaldehyde is one of the important thermoset resins due to its advantageous properties such as high hardness, stiffness and low flammability.13 Mantanis et al.14,15 has reported that the cell wall of wood is permanently swelled by low molecular weight monomers that are capable of forming hydrogen bonds. Similarly, MFFA, which is a low molecular weight and low viscosity prepolymer, has the capacity to swell the cell wall of wood and hence the prepolymer penetrates easily into the cell wall. The prepolymer contains abundant hydroxyl groups, polymerizes in the cell wall and can be grafted permanently into the cell wall of wood through their hydroxyl groups. Flame retardants are incorporated in WPC to achieve fire resistance which is one of the most desired properties of wood. Polymeric flame retardants obtained from a renewable resource i.e. from a local plant Moringa oleifera can diminish the leaching problem and is also ecofriendly.16 Very few reports are available on the use of gum from Moringa oleifera as flame retardant. Considerable improvement in flame retardancy and biodegradability of starch based biodegradable film modified with gum polymer has been reported by Jana et al.17 This work is focused on modification of Ficus hispida, a lower grade soft wood, by vacuum impregnation of melamine formaldehyde copolymer; 1,3-dimethylol 4,5-dihydroxy ethylene urea crosslinking agent; CTAB modified TiO2; plant polymer in presence of nanoclay. The main objective 4
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of the article is to study the synergistic effect of the nanoparticles and plant polymer on the properties of the composites.
2. EXPERIMENTAL 2.1. Materials Fig wood (Ficus hispida) and plant polymer was collected locally. Melamine, Maleic anhydride, furfuryl alcohol, glyoxal and formaldehyde were purchased from Merck (Mumbai, India). Nanoclay [clay modified by 15–35 wt.% octadecylamine and 0.5–5 wt.% aminopropyltriethoxy silane, Sigma–Aldrich, (USA)] N-Cetyl-N,N,N-Trimethyl Ammonium Bromide (CTAB) (Central Drug house (P) Ltd., Delhi, India), and TiO2 nanopowder (
