Characterization of PP/Mg(OH) 2 and PP/Nanoclay Composites with Supercritical CO 2 (scco 2 )

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This article was downloaded by: [Marmara Universitesi] On: 25 August 2011, At: 04:31 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered

1 This article was downloaded by: [Marmara Universitesi] On: 25 August 2011, At: 04:31 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Polymer-Plastics Technology and Engineering Publication details, including instructions for authors and subscription information: Characterization of PP/Mg(OH) 2 and PP/Nanoclay Composites with Supercritical CO 2 (scco 2 ) Münir Taşdemir a, Gerard T. Caneba b, Rajesh Tıwarı b & Bo Wang c a Marmara University, Technology Faculty, Ziverbey, Istanbul, Turkey b Michigan Technological University, Chemical Engineering Faculty, Houghton, MI, USA c Cascade Engineering, Inc., Grand Rapids, MI, USA Available online: 12 Jul 2011 To cite this article: Münir Taşdemir, Gerard T. Caneba, Rajesh Tıwarı & Bo Wang (2011): Characterization of PP/Mg(OH) 2 and PP/Nanoclay Composites with Supercritical CO 2 (scco 2 ), Polymer-Plastics Technology and Engineering, 50:10, To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan, sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Polymer-Plastics Technology and Engineering, 50: , 2011 Copyright # Taylor & Francis Group, LLC ISSN: print= online DOI: / Characterization of PP/Mg(OH) 2 and PP/Nanoclay Composites with Supercritical CO 2 (scco 2 ) Münir Taşdemir 1, Gerard T. Caneba 2, Rajesh Tıwarı 2, and Bo Wang 3 1 Marmara University, Technology Faculty, Ziverbey, Istanbul, Turkey 2 Michigan Technological University, Chemical Engineering Faculty, Houghton, MI, USA 3 Cascade Engineering, Inc., Grand Rapids, MI, USA In this article, supercritical carbon dioxide (scco 2 ) is used to form a high density microcellular foam structure to reduce the polymer use and facilitate dispersion of Mg(OH) 2 and Nanoclay fillers. A twin-screw extruder system was used to predistribute the inorganic filler from the PP polymer, resulting composite PP/filler pellets. This followed by the use of a single-screw extruder wherein supercritical carbon dioxide is introduced in the formulation. Finally the resulting foam PP/filler/CO 2 pellets are injection molded into test samples. The structure and properties of the composites are characterized using a scanning electron microscopy (SEM), Differential scanning calorimetry (DSC), and density measurements. Furthermore, PP/Clay/Mg(OH) 2 polymer composites are subjected to examinations to obtain their yield and tensile strengths, elasticity modulus, % elongation, Izod impact strength, hardness, Heat deflection temperature (HDT), Vicat softening point and Melt flow index (MFI). Keywords Cloisite 25A; Magnesium hydroxide; Polypropylene; Supercritical carbon dioxide INTRODUCTION CO 2 is the most widely used supercritical fluid because of its non-toxicity and low critical temperature and pressure [1]. Recently, supercritical fluids (SCFs) have been used in polymer processing, especially in polymer extrusion, due to their unique sorption characteristics. Applications of gas or SCFs to polymer processing originally have been found in the foam industry. Supercritical carbon dioxide is now well established as a solvent for use in extraction. This is for a number of reasons. It can generally penetrate a solid sample faster than liquid solvents because of its relatively high diffusion rates, and can rapidly transport dissolved solutes from the sample matrix because of its relatively low viscosity. There are also of course less solvent residues present in the products [2]. Foaming process variables affect three stages of foaming such as the formation of uniform polymer=gas solution, cell nucleation, and cell growth, Address correspondence to Münir Taşdemir, Marmara University, Technology Faculty, Ziverbey, Istanbul, Turkey. munir@marmara.edu.tr and therefore have impact on the cellular structure and ultimate properties of the foam products [3]. Thermoplastic foams exhibit a two-phase cellular structure (i.e., a solid polymer matrix and a gaseous phase) created by the expansion of a blowing agent. This cellular structure provides unique properties, such as light weight and low thermal conductivity, which enable foamed plastics to be used effectively for various industrial applications [4]. Because of the outstanding functional characteristics and relatively low material costs, PP foams have been considered to be one of the most promising candidates among thermoplastic foams for industrial applications. PP is resistant to chemicals and abrasion, and has a number of advantages over polystyrene and polyethylene [5]. A vast amount of research, particularly in the area of polymeric foams, has been focused in studying the relation between the processing conditions in extrusion and the final polymer morphology when CO 2 is introduced. The initial concentration, solubility, and diffusivity of the gas in the polymer melt all have a direct effect on the final properties of the foam [1 3,6 13]. In this article, we explore a supercritical carbon dioxide processing method that utilizes CO 2 to disperse Mg(OH) 2 and Nanoclay into the PP matrix. The structure and properties of the composites are characterized using a scanning electron microscopy (SEM), Differential scanning calorimetry (DSC), and density measurements. Furthermore, PP=Clay= Mg(OH) 2 polymer composites were subjected to examinations to obtain their elasticity modulus, elongation at break, tensile yield strength, elongation at yield, strength at break, Izod impact strength, hardness, heat deflection temperature (HDT), Vicat softening point and melt flow index (MFI). EXPERIMENTAL Compositions and Materials Eight different polymer composites were prepared. Compositions of PP, PP=Mg(OH) 2 =CO 2, PP=Clay=CO 2 and PP=Clay=Mg(OH) 2 =CO 2 polymer composites that were formed are given in Table

3 Group # TABLE 1 Composition of the PP-clay-Mg (OH) 2 -CO 2 polymer composites Polypropylene (PP) (%) CHARACTERIZATION OF NANOCLAY COMPOSITIONS 1065 Clay (Cloisite 25A) (%) Magnesium hydroxide Mg(OH) 2 (%) Carbon dioxide (CO 2 ) (ml=min C) (Second extrusion run) TABLE 2 Extrusion and injection conditions of the PP-clay- Mg(OH) 2 -CO 2 polymer composites Process Extrusion Injection Temperature ( C) Pressure (bar) Waiting time in mold (s) 10 Screw speed (rpm) Mold temperature ( C) 40 PP (SG702) was supplied by Basell (Basell polyolefins, Rotterdam, The Netherlands). Its density is 0.9 g=cm 3, MFR value is 18 g=10 min (230 C=2.16 Kg), yield strength is 21 MPa, Izod Impact (notched) is 2.3 J=cm and heat deflaction temparature is (0.46 MPa) 90 C. Clay (Cloisite 25A) was supplied by Southern Clay Products Inc. (Gonzales, Texas USA). Its density is 1.87 g=cm 3, Hardness is 83 Shore D, yield strength is 101 MPa, Izod Impact (notched) is 0.27 J=cm, heat deflection temperature is (0.46 MPa) 96 C and particle size is (50%) 6.00 m. Magnesium hydroxide, Mg(OH) 2 (MagShield S) was supplied by Martin Marietta Magnesia Specialties (Baltimore, MD USA). Its density is 3.58 g=cm 3, Magnesium hydroxide content is 98.5%, specific gravity is 2.36 and particle size FIG. 1. Schematic diagram of the extrusion system. is 17.0 m. Carbon dioxide (Liquid CO 2 ) was supplied by Universal Industrial Gases Inc. (Pennsylvania, USA) with 99.99% purity. Its molecular weight is and boiling point is 78.5 C (@ kpa). Composite Preparation Mg(OH) 2 is hydrophilic and absorb moisture. Therefore, Mg(OH) 2 was dried in a Yamato Vacuum oven ADP-31 (Yamato=VWR Scientific Products, Japan) at TABLE 3 Mechanical properties of the PP-clay-Mg(OH) 2 -CO 2 polymer composite Mechanical properties Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Elasticity modulus (MPa) break (%) Tensile yield strength (MPa) yield (%) Strength at break (MPa) Hardness (Shore D) Izod impact strength (kj=m 2 ) (notched)

4 1066 M. TAŞDEMIR ET AL. FIG. 2. Mechanical properties of the PP-Mg(OH) 2 -CO 2 polymer composite. FIG. 3. Thermal properties of the PP-25A-Mg(OH) 2 -CO 2 polymer composites.

5 CHARACTERIZATION OF NANOCLAY COMPOSITIONS C for 24 h before being blended with PP. Mechanical premixing of solid compositions was done using a LB-5601 liquid-solids blender (The Patterson-Kelley Co., Inc. east Stroudsburg, PA USA) brand batch blender at 10 min. Samples with various proportions of polymer composites were produced between C at bar pressure, and a production rate of 25 rpm, with a CWB co-rotating twin-screw extruder (L=D ratio is 10:1, C.W. Brabender Instrument Inc., S. Hackensack, NJ). Test samples of the granulated polymeric blends were made in Nissei FS120S18ASE (FD Technology Sdn. Bhd.- Kedah, Malaysia) injection machine. Extrusion and injection conditions are given in Table 2. Supercritical Carbon Dioxide (scco 2 ) Processing CO 2 was injected into the polymer melt at varying rates in the extruder barrel using the 260D syringe pump (Teledyne Isco, Inc. Lincoln, NE, USA). The injected gas amount was controlled at a level less than the solubility limit at the processing temperature and pressure. The polymer feed rate was controlled by the feeder. The barrel pressure at the injection point was monitored for a stable injection of CO 2. Finally, the extruded foamed filament was cooled in a water bath. Schematic diagram of the extrusion system is shown in Figure 1. Test Procedure Composite specimens were conditioned at 23 C and 50% humidity for 24 h before testing (ASTM D618). Tensile tests were performed according to ASTM D638 specification. They were carried out using a Zwick Z010 (Zwick GmbH, Ulm-Germany) testing machine with a load cell capacity of 10 kn at a cross-head speed of 50 mm=min. The tensile strength, elastic modulus and % elongation were determined from the stress strain curves. Hardness test were done according to the ASTM D2240 method with Zwick hardness measurement equipment. To investigate fracture behavior, Izod impact test (notched) was done at room temperature according to the ASTM D256 method with Zwick B5113 impact test device (Zwick GmbH & Co. KG Ulm, Germany). Flow behavior testing of all the mixtures was done according to ISO 1133 standard with Zwick 4100 MFI equipment. Thermal transition temperatures were determined through a TA Instruments DSC 2920 (TA Instruments, West Sussex, England) test equipment in a nitrogen atmosphere. Starting point was at 30 C, end point was at 300 C, and the heat rate was at 20 C=min. Fractured surfaces of the composites were coated with about 40 Å thick Gold layer using the POLARON SC 7640 (Gala Instrumente GmbH, Bad Schwalbach-Germany). The surfaces of the prepared samples were observed by the JEOL-JSM (JEOL Ltd., Tokyo, Japan) scanning electron microscopy (SEM) at an acceleration voltage of 5 10 kv. Heat deflection temperature tests were done according to ISO 307 standard using the CEAST 6521 (Ceast SpA Pianezza, Italy) HDT test equipment. Five samples were tested in each set and the average value was reported. Density Measurements of Test Samples Densities of the polymer samples were measured using a variation of the ASTM C sink-float method [15]. Liquid solutions of densities equal to those of the polymer samples were first obtained, and then the densities of this solution were taken. The experiments were planned in such a way that the lightest samples were measured first than heavier samples. An open vessel was first filled with distilled water than the sample was immersed in the water at room temperature. FIG. 4. DSC curves of the PP-Mg(OH) 2 -CO 2 polymer composites.

$1068 M. TAŞDEMIR ET AL. FIG. 5. SEM micrographs revealing the appearance of fracture surfaces of the PP-Clay-Mg(OH) 2 -CO 2 polymer composite.$ The syringe was used to obtain the density of the solution: 5 ml solution was taken using the syringe and placed in sealed bottle.

The syringe was used to obtain the density of the solution: 5 ml solution was taken using the syringe and placed in sealed bottle.

6 1068 M. TAŞDEMIR ET AL. FIG. 5. SEM micrographs revealing the appearance of fracture surfaces of the PP-Clay-Mg(OH) 2 -CO 2 polymer composite. If sample floated, isopropanol was added until the sample sank. If, on the other hand, the sample sank, then glycerol was added until it floated. The syringe was used to obtain the density of the solution: 5 ml solution was taken using the syringe and placed in sealed bottle. Liquid density was obtained through measuments of weight of the solution in the bottle with its known volume (5 ml). To test for data consistency, duplicate density meassurements were done, and it was observed that density data were accurate to values within g=cm 3. RESULTS AND DISCUSSION Mechanical properties of polymer composites produced with PP, Clay, Mg(OH) 2 and CO 2 are indicated in Table 3. First and foremost, test samples made from composites with CO 2 had good dimensional integrity relative to the FIG. 6. Energy dispersive X-ray spectroscopy (EDS) spectra of: (a) Mg(OH) 2 and (b) Clay particulates in the polymer composites.

7 CHARACTERIZATION OF NANOCLAY COMPOSITIONS 1069 TABLE 4 Thermal properties of the PP-25A-Mg(OH) 2 -CO 2 polymer composite Thermal properties Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 MFI (g=10 min) (220 C 10 kg) Vicat softening point ( C) HDT ( C) PP Tm ( C) TABLE 5 Results of densities of test samples at 21 C S. No. Running sample (PP=MgO þ CO 2 ) Weight of solution (gm) Volume of solution syringe (CC) Density (gm=cm 3 ) 1. (PP) (Pure) (PP=MgO % 3) þ (0.2 ml CO 2 ) (PP=MgO % 3) þ (0.2 ml CO 2 ) (PP=MgO % 5) þ (0.2 ml CO 2 ) (PP=MgO % 5) þ (0.4 ml CO 2 ) (PP=MgO % 5 þ (0.8 ml CO 2 ) (PP þ 25A % 6) þ (0.8 ml CO 2 ) (PP þ 25A % 6) MgO % 3 þ (0.8 ml CO 2 ) shape of mold cavities. This means that the CO 2 was still expanding as the test samples were being solidified in the injection mold. Corresponding mechanical properties of polymer composites produced with PP, Clay, Mg(OH) 2 and CO 2 (shown in Figure 2) indicate lack of significant deterioration of overall mechanical properties on the composite test samples that were processed with CO 2, even compared to that of virgin PP. The thermal properties of polymer composites produced with PP, Clay, Mg(OH) 2 and CO 2 are indicated in Table 4 and Figure 3. DSC results of polymer composites are indicated in Table 4 and Figure 4. Density results of polymer composites produced with PP, Clay, Mg(OH) 2 and CO 2 are indicated in Table 5. Scanning electron micrographs of fractured surfaces of the PP-Clay-Mg(OH) 2 -CO 2 polymer composite taken after Izod impact tests are shown in Figure 5 and energy dispersive X-ray spectroscopy (EDS) spectrums of the polymer composite are given in Figure 6. The micrographs indicate that the Mg(OH) 2 and clay particulates can be slightly detached from the polymer matrix on the fractured surfaces, and they seem to be covered with gas pockets as well. Still, it seems that dimensional integrity of injection molded samples and lack of significance differences in mechanical and thermal properties point toward an attractive set of formulations in these CO 2 -processed composites. CONCLUSIONS The use of CO 2 as processing aid seems to be able to offset inherent disadvantages of incorporation of Mg(OH) 2 and clay particulates in PP matrix. This is evidenced by the lack of significant differences in overall mechanical properties of virgin PP and CO 2 -processed composites. Moreover, resulting injection molded samples have been shown to possess dimensional integrity, due to the continued expansion of CO 2 during the molding operation. ACKNOWLEDGMENTS This work has been supported by the Scientific Research Project Program of Marmara University (Project no. FEN-A ). The authors are grateful to Marmara University for their financial support and the provision of laboratory facilities. Also, acknowledgement is given to the MTU Center for Environmentally Benign Functional Materials (CEBFM) (USA). REFERENCES 1. Tusek, L.; Golob, V.; Knez, Z. Int. J. Polym. Mater. 2000, 47, Zhao, J.J.; Zhao, Y.P.; Yang, B.J. Appl. Polym. Sci. 2008, 109, Zhang, P.; Zhou, N.; Li, B. Polym.-Plast. Technol. Eng. 2007, 46, Klempner, D.; Frish, K.C. Handbook of Polymeric Foams and Foam Technology, Hanser: New York, 1991.

8 1070 M. TAŞDEMIR ET AL. 5. Leaversuch, R.D. Mod. Plast. 1996, 73, Smole, S.M.; Zipper, P. Int. J. Polym. Mater. 2000, 47, Baldwin, D.F.; Park, C.B.; Suh, N.P. Polym. Eng. Sci. 1996, 36, Lee, S.T.J. Cell. Plast. 2001, 37, Park, C.B.; Baldwin, D.F.; Suh, N.P. Polym. Eng. Sci. 1995, 35, Colton, J.S.; Suh, N.P. Polym. Eng. Sci. 1987, 27, Lee, M.; Tzoganakis, C.; Park, C.B. Polym. Eng. Sci. 1998, 38, Wu, Q.; Zhou, N.; Zhan, D. Polym.-Plast. Technol. Eng. 2009, 48, Gao, C.Y.; Zhou, N.Q.; Peng, X.F.; Zhang, P. Polym.-Plast. Technol. Eng. 2006, 45, Lee, J.J.; Cha, S.W. Polym.-Plast. Technol. Eng. 2006, 45, Caneba, G.T. Diffusion and Sorption of Cyclohexane in Styrene- Butadiene Copolymers. M.S. Thesis, University of California Berkeley, 1985.

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