PREPARATION AND SOME PROPERTIES OF POLYETHYLENE/VERMICULITE NANOCOMPOSITES

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1 PREPARATION AND SOME PROPERTIES OF POLYETHYLENE/VERMICULITE NANOCOMPOSITES Marianna HUNDÁKOVÁ a,b, Marta VALÁŠKOVÁ a,b, Erich PAZDZIORA c, Petr SLOBODIAN d, Dušan KIMMER e a, b VSB-Technical University of Ostrava, Ostrava, Czech Republic, EU, marianna.hundakova@vsb.cz c Institute of Public Health in Ostrava, Ostrava, Czech Republic, EU, erich.pazdziora@zu.cz d UTB-FT, Polymer Centre,Zlin, Czech Republic, EU, slobodian@ft.utb.cz e SPUR a.s., Zlin, Czech Republic, EU, Dusan.Kimmer@spur.cz Abstract The high aspect ratio of layered silicate nanoparticles is very convenient to modify the properties of the polymer, but the hydrophilic nature of silicate surfaces impedes their homogeneous dispersion in the organic polymer phase. The hydrophilic clay minerals are commonly treated with ammonium cations with long alkyl chains to improve the compatibility between the silicate layers and the polymer matrix. In this study, clay mineral vermiculite (V) was used as a clay nanofiller to the polyethylene (PE) and the functional and mechanical properties of PE/V nanocomposite plates were characterized. Vermiculite has been modified to the role of nanofiller with organic dodecylamine (DA) compounds in various concentrations. Exfoliation of modified vermiculite nanofiller in PE was studied on the nanocomposite plates using X-ray diffraction analysis. The quality of nanofiller distribution in polymer matrix was observed using light microscopy. Changes in mechanical properties of the PE/VDA nanocomposites in comparison with the pure PE were studied on the data from the Creep measurements. The antibacterial activity of the surfaces of composite plates was tested on the Gram-positive bacteria Enterococcus faecalis. Keywords: Polyethylene, vermiculite, x-ray diffraction, creep characteristics, antibacterial activity. 1 INTRODUCTION Clay minerals may be used as fillers during the preparation of polymer/clay mineral nanocomposites to improve their stiffness, strength, toughness or thermal stability [1,2,3]. The hydrophilic nature of silicate surface makes their homogenous dispersion in the organophilic polymer impossible. Therefore, clay minerals are often modified with organic compounds as alkyl amines (octadecylamine, hexadecylamine, dodecylamine etc.) or quartery ammonium salts (hexadecyltrimethylammonium bromide, cetyltrimethylammonium chloride etc.) to make them hydrophobic and compatible with the polymer [1,2,3,4,5]. Antimicrobial activity of organoclays based on effect of organic cations against broad spectrum of microorganisms was studied [6,7]. This study presents structure and characterization of vermiculite intercalated with dodecylamine used as nanofiller to the polyethylene matrix together with the level of vermiculite dispersed in PE, antibacterial action, structure changes and creep characteristics of nanocomposite.

2 2 MATERIALS AND METHODS 2.1 Materials Vermiculite from Brazil (fy Grena, Czech Republic) was milled in planetary mill, sieved to the fraction < 40 µm (marked as V) and subsequently milled in jet mill (Sturtevant Micronizer ) at the pressure of compressed air 350 kpa (marked as Vj). The structural formula for the half unit cell composition of V calculated from the elemental analysis was: (Si 3.08 Al 0.92 )(Mg 2.44 Fe Fe Ti 0.06Al 0.04 )O 10 (OH) 2 K 0.18 Ca 0.15 Na Dodecylamine (DA) 97% (fy Sigma Aldrich, Co) and ethanol 96% (fy Vitrum, Czech Republic) were used for V modification. Polyethylene (PE) for composites preparation was prepared as the mixture of three low density polyethylenes (LDPE). Their ratio was 33 wt. % of Bralen VA powder, 42 wt. % of Bralen VA granulated and 25 wt. % of Bralen FB2-17 powder (fy Slovnaft, Slovak Republic). 2.2 Sample preparation Organo-Vermiculite nanofillers V (30g) was mixed with 30 wt.%, 10 wt.% and 3 wt.% of DA in mortar for 20 min. The mixture was placed to the drying oven preheated to 80 C. After 2 hour, the mixture was removed from the oven and ethanol was added. After evaporation of ethanol, sample was crushed in mortar and milled in jet mill. Prepared samples were marked as VDA30, VDA10 and VDA3, respectively. Polyethylene/Vermiculite composites Composites were prepared in Brabender GmbH & Co. KG, type The mixtures of PE with vermiculite samples Vj, VDA3, VDA10 and VDA30 at the ratio PE:V:DA = 90:7:(0; 0.3; 1 and 3) were slowly poured into the Brabender kneading chamber heated to 160 C. Heavy kneading the mixture was carried out for a total of 10 minutes in two velocity intervals, first for 2 min at 10 rpm and the next 8 min at 50 rpm. The matter was scratched from the kneading chamber. The composite foils of size 100 x 100 mm and a thickness of 1 mm were pressed at 160 C from the stiff matter. 2.3 Methods The elemental composition of V was determined by the X-ray fluorescence elemental analysis (XRF) on energy dispersive spectrometer SPECTRO X LAB. The X-ray powder diffraction (XRD) patterns were measured on the X-ray diffractometer from INEL equipped with a curved position-sensitive detector CPSD 120 (reflection mode, Ge-monochromator, CuKα 1 radiation) in ambient atmosphere under constant conditions (2000 s, 35 kv, 20 ma). The Infrared (IR) spectra were obtained by Fourier transformed infrared spectroscopy (IRS) on a Nicolet 6700 in the spectral range cm -1. The images of the powder samples were performed by Scanning electron microscopy (SEM) on PHILIPS XL-30 equipped with energy dispersive spectrometer EDS. The images of composite foils were performed by Light microscopy (LM) on Olympus BX51 equipped with camera Olympus UC30, using bright field polarized light at transition mode. 2.4 Antibacterial test Antibacterial effect of prepared composites was tested on Gram-positive (G + ) bacteria strain Enterococus faecalis. Suspension with density 1.5x10 8 in 1000 µl was prepared and applied on polyethylene composite foils (50 x 50 mm) in volume 25 µl and also on control pure polyethylene foil. Foils were placed in the laminar box to dry and covered with aluminium foil to protect. The first fingerprints on blood agar plates in Petri dishes were made after drying for 1 hour. The foils were gradually impressions always on the three discs with blood agar. Cultivations took place in thermostat at 35 C for 24 hours. The numbers of colony forming units (CFU) of all three fingerprints were recorded. If the number of CFU was in countless (CN) result was expressed as 3xCN (countless number). The next fingerprints were made after 3, 6, 8, 24, 48 and 96 hours of total exposure.

3 3 RESULTS AND DISCUSSION 3.1 Structure characteristics The XRD patterns in Fig. 1 show structure changes of V after modification with DA and also after mixing with PE. The basal reflections (002) of Vj with values d = 1.43 nm and d = 1.24 nm correspond to the interlayer material with two layer and one layer of water molecules, respectively. The other basal reflection with value d = 2.15 nm proved mix-layered hydrate domains in the interlayer [8,9]. The XRD patterns of samples VDA3, VDA10 and VDA30 (Fig. 1 d, f, h) show decreased intensities of the basal reflection d (002) =1.43 nm opposite relative intensity of Vj (100%) with shift at VDA 30 to d = 1.47 and 1.39 nm which showed inhomogeneous structure. Samples VDA10 and VDA 30 showed in comparison with original Vj expansion of the profiles of the basal reflection and shift to the higher interlayer (d = 2.21 nm). Also a new reflection of phase with low water content is supposed base on the reflection with d = 1,13 nm (VDA10), d = 1.11 nm (VDA30). These significant changes confirmed the intercalation of DA to vermiculite interlayer and exfoliation of vermiculite layered structure. The XRD pattern of PE (Fig. 1 b) proved present of crystalline region with reflections values d = 0.42 nm and d = 0.38 nm over the amorphous region between θ [10]. XRD patterns of the composites PE/VDA10 and PE/VDA30 (Fig. 1 g, i) differ from others. The basal reflection with d = 1.43 nm of V disappeared and the new peaks with d = 3.26 nm, d = 2.32 nm may correspond to the disturbance of vermiculite crystalline structure, further intercalation of PE to the VDA interlayer and good exfoliation of VDA nanofiller in PE matrix. Fig. 1 XRD patterns region with basal 002 reflection of nanofillers and composites Vj (a), PE (b), PE/Vj (c), VDA3 (d), PE/VDA3 (e), VDA10 (f), PE/VDA10 (g), VDA30 (h) and PE/VDA30 (i). The dashed line represents the XRD pattern of pure DA.

4 3.2 Morphology of nanofiller Morphology of V significantly changed after intercalation DA in Fig. 2. Characteristic vermiculite lamellar morphology (Fig. 2a) was disturbed after jet milling (Fig. 2b) and the particles size was reduced (under ca 20 µm). The sample VDA30 after jet milling showed disappearance of the lamellar structure and confirmed exfoliation (Fig. 2c) to the very small particles (under ca 5 µm). 3.3 Creep characteristics Fig. 2 SEM images of the samples V (a), Vj (b) and VDA30 (c). The reinforcing effect of filler onto polymeric matrix was tested by creep measurements applying constant stress of app. 1 MPa at temperature 25 C. The examples of measured data presented in Fig. 3 and Tab. 1 comparing pure PE matrix with selected nanocomposites. The results represent time-depended creep compliance data with significant modification of mechanical properties when presence of vermiculite based fillers increases rigidity of PE matrix. These differences can be quantified for example using initial tensile creep modulus representing elastic part of deformation presented in Table 1.Their values increased from 25 % to 70 % compared to pure PE with the highest reinforcement effect PE/VD3 nanocomposite. Fig. 3 Tensile creep and reverse (marked r) tensile creep compliance data for pure PE and PE/vermiculite nanofillers composites.

5 Tab. 1 Composition of composites and values of initial tensile creep modulus Sample/ Composition PE (wt.%) V (wt.%) DA (wt.%) Initial tensile creep modulus E (t) (MPa) PE PE/Vj PE/VDA PE/VDA PE/VDA Distribution of nanofiller in PE The images of composites obtained by light microscopy in Fig. 4 showed differences among the nanofiller particles distribution in polyethylene matrix. The largest number of visible particles was observed in the sample PE/Vj with approximate average size > 100 μm 3 %, > 80 μm 3 %, > 60 μm 9 %, > 40 μm 16 %, > 20 μm 29 % and < 20 μm 40 %. The particles in PE formed agglomerates. The amount of visible particles with higher average size increased in order PE/Vj > PE/VDA3 > PE/VDA10 > PE/VDA30. The nanofiller VDA30 was very well distributed in PE which was confirmed with the XRD analysis Fig. 4 Images of composites PE/Vj (a), PE/VDA3 (b), PE/VDA10 (c) and PE/VDA30 (d) with highlight vermiculite filler particles. The size of the observed area is 1.8 x 1.3 mm at magnification 4x. 3.5 Antibacterial activity Results of antibacterial activity testing of prepared composites against G + bacteria E. faecalis in Tab. 2 showed that PE/Vj, PE/VDA3 and PE/VDA10 had no inhibit effect on bacterial growth over 24 hours. After 48 hours the number of survived bacterial colonies decreased. The nanocomposite PE/VDA30 inhibited

6 bacterial growth already after 1 hour and after 24 hours no bacteria survived and have remained stable over the whole experiment period of 96 hours. Antibacterial effect increased with an increasing content of DA. The exception was the PE/Vj where the action was influenced by the surface properties of foils. A smooth surface of pure PE allowed the bacteria to survive and multiply throughout the experiment. Tab. 2 Average number of bacterial colonies E. faecalis survived on the three tested composite plates (CN = coutless number). Time 1 h 3 h 6 h 8 h 24 h 48 h 72 h 96 h Number of colonies PE CN CN CN CN CN CN CN CN PE/Vj CN CN CN CN CN PE/VDA3 CN CN CN CN CN PE/VDA10 CN CN CN CN CN PE/VDA CONCLUSION The polyethylene/vermiculite nanocomposites were prepared and characterized. The XRD patterns confirmed dodecylamine intercalated to the interlayer of vermiculite. The layered structure of vermiculite was disturbed after exfoliation in the melted PE. Dodecylamine increased content positively influenced homogeneous distribution of vermiculite particles in PE. The creep experiment confirmed the rigidity of PE matrix with the vermiculite nanofillers. The antibacterial test showed action of all prepared composites against Enterococcus faecalis. ACKNOWLEDGEMENT This work was supported by projects: Ministry of Education, Youth and Sport of Czech Republic SP2012/43, Czech Grant Agency P210/11/2215 and IT4Innovations Centre of Excellence project reg. no.cz.1.05/1.1.00/ LITERATURE [1] RAO, Y., POCHAN, J.M. Mechanics of polymer-clay nanocomposites. Macromolecules, 2007, vol.40, p [2] GOMES, E.V.D., VISCONTE, L.L.Y., PACHECO, E.B.A.V. Thermal characterization of polypropylene/vermiculite composites. J. Therm. Anal. Caloritm., 2009, vol. 97, p [3] GOPAKUMAR, T.G., LEE, J.A., KONTOPOULOU, M., PARENT, J.S. Influence of clay exfoliation on the physical properties of montmorillonite/polyethylene composites. Polymer, 2002, vol. 43, p [4] WANG, K.H., COI, M.H., KOO, CH.M., CHOI, Y.S., CHUNG I.J. Synthesis and characterization of maleated polyethylene/clay nanocomposites. Polymer, 2001, vol. 42, p [5] VALÁŠKOVÁ, M., SIMHA MARTYNKOVÁ, G., MATĚJKA, V., BARABASZOVÁ, K., PLEVOVÁ, E., MĚŘÍNSKÁ, D. Organovermiculite nanofillers in polypropylene. Appl. Clay Sci., 2009, vol. 43, p [6] NIGMATULLIN, R., GAO, F., KONOVALOVA, V. Polymer-layered silicate nanocomposites in the design of antimicrobial materials. J. Mater. Sci., 2008, vol. 43, p [7] HUGO, W.B., RUSSELL, A.D. In: Russell, A.D., Hugo, W.B., Ayliff, G.A.J. (eds.). Principles and practise of disinfection preservation and sterilization. 1999, Blackwell Science, Oxford. [8] WALKER, G.F. Mechanism of dehydration of Mg-vermiculite. Clays Clay Min., 1956, vol. 4, p [9] MARCOS, C., ARANGO, Y.C., RODRIGUEZ, I. X-ray diffraction studies of the thermal behaviour of commercial vermiculites. Appl. Clay Sci., 2009, vol. 42, p [10] DAS-GUPTA, D.K. Polyethylene: Structure, morphology molecular motion and dielectric behavior. IEEE Electrical Insulation Magazine, 1994, vol. 10, no. 3, p