Article pubs.acs.org/IECR
Effect of Nanoparticles on Flammability, UV Resistance, Biodegradability, and Chemical Resistance of Wood Polymer Nanocomposite Biplab K. Deka,† Manabendra Mandal,‡ and Tarun K. Maji*,† †
Department of Chemical Sciences, Tezpur University, Assam-784 028, India Department of Molecular Biology and Biotechnology, Tezpur University, Assam- 784 028, India
‡
ABSTRACT: Wood polymer nanocomposite (WPNC) was developed by using high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC), wood flour (WF), polyethylene-co-glycidyl methacrylate (PE-co-GMA), and different nanoparticles viz. nanoclay, SiO2, and ZnO. The distribution of nanoparticles was examined by X-ray diffraction (XRD) study. The change in surface morphology due to the addition of compatibilizer and nanoparticles was studied by scanning electron microscopy (SEM). The surface modification of nanoparticles by organic surfactant and their interaction with polymer and wood was studied by Fourier transform infrared spectroscopy (FTIR). The UV resistance property was improved after the incorporation of clay, SiO2, and ZnO. Bacterial degradation of WPC was found to increase linearly with the incorporation of clay and nanoparticles. The degraded samples showed lower mechanical properties. Flame retarding property, chemical resistance, and water vapor resistance were found maximum in WPC loaded with 3 phr each of clay, SiO2, and ZnO.
1. INTRODUCTION Wood polymer composites (WPC) have evoked considerable interest in recent years.1 The polymers that are used in WPC are mainly high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polystyrene (PS), etc. These polymers have much lower water uptake capacity and hence they retard the degradation process. The entire product manufactured from these nonrenewable polymeric components is not biodegradable. The incorporation of wood flour into the polymer matrix improves the biodegradability and weatherability. Their uses range from different household items to different exterior products viz. automobile industries, different outdoor applications such as decking, railing, fencing, docks, and landscaping timbers, etc., and indoor applications.2 They have relatively high strength and stiffness, low density, low cost, low CO2 emission, and superior biodegradability and renewability. Moreover, they can also be used widely with other materials to improve various properties. Among the different types of plastics, high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), and polyvinyl chloride (PVC) are mostly used in industries. The waste plastic materials thrown away in the form of carry bags, boxes, and packaging film cause a serious threat to the environment. One of the processes to reduce this environmental pollution is by recycling and reusing the plastics. The properties can be improved significantly if composites are developed by combining these waste materials with some cellulosic materials. Nal, Phragmites karka, a nonconventional plant, is widely available in the forest of North Eastern part of India. This plant does not have any economical value. It is mainly used for domestic fuel purposes. Nal can be made into value-added material suitable for preparation of structural components by treating it with waste plastic materials. Different structural © 2012 American Chemical Society
components including windows, window profiles, table tops, and partition walls, etc., can be extensively made from that composite material. Solution blending is one of the processes to mix varieties of plastic materials. The effectiveness of this process for mixing various kinds of plastics can be enhanced by the use of a mixture of solvents. The percentages of individual polymers in the blend and their physical characteristics need to be known to optimize the solvent ratio. But it is difficult to segregate different kinds of plastics from waste plastics. Therefore, the optimization of solvent ratio can be determined properly only if a mixture of known percentages of virgin HDPE, LDPE, PP, PVC, etc. is used as starting waste plastic material. Despite having plastic components an increase in biodegradation of WPC has been reported in the literature.3,4 The fungal degradation of WPC has been studied by Schirp and Walcott.5 A major concern with WPC is that wood in the composite remains susceptible to microbial degradation. Wood contains cellulose, pectin, and lignin as constituents of its composition. The bacteria collect the sole carbon source from all these constituents of wood. To retard the microbial attack to the WPC different additives are added, which leads to decreasing the degradation of the WPC.6,7 The interactions occuring at the interface of the components of wood polymer composite often determine the properties of the composite. An interfacial phase separation always occurs in WPC due to the hydrophobic nature of polymer and hydrophilic nature of wood. To improve the interfacial adhesions certain types of chemicals called compatibilizers are used. A compatibilizer is a compound that can interact with the Received: Revised: Accepted: Published: 11881
February 6, 2012 August 17, 2012 August 24, 2012 August 24, 2012 dx.doi.org/10.1021/ie3003123 | Ind. Eng. Chem. Res. 2012, 51, 11881−11891
Industrial & Engineering Chemistry Research
Article
in two separate beakers containing ethanol−water mixture and stirred at 80 °C for 3 h. These mixtures were added slowly to the two flasks containing SiO2 and ZnO mixture under stirring condition. The stirring was continued for 6 h. The mixtures from both the flasks were then filtered separately and washed with deionized water several times. The filtrate was collected, dried in vacuum oven at 45 °C, ground, stored in a separate ampule, and kept in a desiccator to avoid moisture absorption. 2.4. Bacterial Media. Mineral salt medium with the following composition was prepared for bacterial growth: 4.75 g of KH2PO4, 2.0 g of Na2HPO4, 2.0 g of (NH4)2SO4, 1.2 g of MgSO4·7H2O, 100 mg of MnSO4·5H2O, 100 mg of CuSO4·7H2O, 70 mg of ZnSO4·7H2O, 10 mg of H3BO3·5H2O, 10 mg of MoO3, 1 mg of FeSO4·7H2O, and 0.5 mg of CaCl2·2H2O dissolved in 1000 mL of demineralized water. Three mL of this liquid culture medium was poured into a 50-mL conical test tube and was sterilized by autoclave at 121 °C and 15 lbf pressure for 15 min. The autoclaved media were then allowed to cool to room temperature and composite samples were added into the media under sterile condition inside a laminar air flow hood. Media containing only polymer samples were also cultured as negative control. 2.5. Bacterial Strains. Bacillus sp. Cd-3 culture was grown using nutrient broth at 37 °C for 18 h. One mL of bacterial cultures was centrifuged at 6000 rpm for 20 min at room temperature and the pellets were washed with 0.9% NaCl and resuspended in 1 mL of mineral salt medium. Then 0.5 mL of the culture medium containing 1 × 108/mL microbes was inoculated to the test tube containing 50 mL of media for each test. The test tubes were then incubated under sterile condition at 37 °C and 100 rpm for the degradation study. 2.6. Preparation of Wood Polymer Nanocomposite. The minimum ratio of xylene and THF, at which a homogeneous solution of HDPE, LDPE, PP, and PVC was obtained, was optimized as 70:30. Six grams each of HDPE, LDPE, and PP (1:1:1) were added slowly to 105 mL of xylene taken in a flask fitted with a spiral condenser at room temperature. This was followed by the addition of the PE-coGMA (5 phr). The temperature of the flask was increased from room temperature to 130 °C in order to make a homogeneous solution. Now, another solution containing 3 g of PVC in 35 mL of tetrahydrofuran (THF) was prepared. The temperature of the polymer solution containing HDPE, LDPE, and PP was brought down to 120 °C. To this, PVC solution was added gradually and stirring was continued at 120 °C (approximately) for 1 h. A known quantity of CTAB modified SiO2 nanopowder (1−5 phr) and ZnO (1−5 phr) was dispersed in 15 mL of tetrahydrofuran (THF) solution by sonication. This dispersed mixture was added gradually to the polymer solution under stirring condition. Oven-dried wood flour (WF) (40 phr) was added slowly to this solution. The whole mixture was stirred for another 1 h. The mixture was transferred in a tray, dried, and ground. The composite sheets were obtained by compression molding press (Santec, New Delhi) at 150 °C under a pressure of 80 MPa. Polymer blend (HDPE + LDPE + PP + PVC), polymer blend/5phr PE-co-GMA and polymer blend/5phr PE-co-GMA/ 40phr wood were designated as PB, PB/G5, and PB/G5/W40. WPC filled with 3 phr nanoclay and 1, 3, and 5 phr each of SiO2 and ZnO were designated as PB/G5/W40/N3/S1/Z1, PB/G5/W40/N3/S3/Z3, and PB/G5/W40/N3/S5/Z5.
hydrophobic polymer through their nonpolar group and with the hydrophilic wood flour (WF) through their polar group. This leads to an improvement in interfacial adhesion that enhances the properties.8 Different types of compatibilizers such as glycidyl methacrylate (GMA), polyethylene grafted glycidyl methacrylate (PE-g-GMA), and maleic anhydridegrafted polypropylene (MAPP), etc., are reported to enhance the compatibility among different polymers and WF.9−11 As WPC is used in different outdoor applications, it is very important to improve the ultraviolet resistant property of the composite. Although polymers are less susceptible to UV attack but after the incorporation of wood flour, its UV degradation increase to a desirable amount. This gives an inferior product for outdoor application, so it is very essential to improve the UV resistance property of the WPC. Clay nanolayers are broadly used to shield UV irradiation of polymer composite. To improve the UV stability of WPC, ZnO nanoparticles are also widely used.12 Other nanoparticles such as SiO2 and TiO2 are also used to improve the UV resistance property of WPC. Maji and Deka 13 used nanoclay in combination with TiO 2 nanoparticles to improve UV resistance of wood polymer composite. SiO2 can also enhance the mechanical as well as thermal properties of the composite. SiO2 nanoparticles extensively increase the tensile and impact strength of epoxy nanocomposite.14 In the present investigation, WPC has been developed by using HDPE, LDPE, PP, and PVC blend and Phragmites karka wood flour. The effect of nanoclay, SiO2, and ZnO nanoparticles on the final properties of the composite has been studied. The change in mechanical properties along with the morphological changes after UV degradation and microbial degradation has also been reported.
2. EXPERIMENTAL SECTION 2.1. Materials. HDPE and LDPE (grade PE/20/TK/CN) were obtained from Plast Alloys India Ltd. (Harayana, India). PP homopolymer (grade H110MA, MFI 11 g/10 min and PVC (grade SPVC FS: 6701) were purchased from Reliance Industries Ltd. (Mumbai, India) and Finolex Industries Ltd. (Pune, India), respectively. The compatibilizers poly(ethyleneco-glycidyl methacrylate) (PE-co-GMA) and N-cetyl-N,N,Ntrimethyl ammonium bromide (CTAB) were supplied by Otto Chemicals, Mumbai, India and Central Drug House (P) Ltd., Delhi, India, respectively. Nanomer (clay modified by 15−35 wt % octadecylamine and 0.5−5 wt % aminopropyltriethoxy silane, Sigma-Aldrich, USA), SiO2 nanopowder (5−15 nm, 99.5% trace metals basis) (Aldrich, China), and ZnO nanopowder (
