Effect of Surface-Treated ZnO on Mechanical and Morphological Properties of High Density Polyethylene/ZnO Nanocomposites

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1 Paper Code: pp011 TIChE International Conference 2011 Effect of Surface-Treated ZnO on Mechanical and Morphological Properties of High Density Polyethylene/ZnO Nanocomposites Pannida Kijkobchai *, Sirirat Wacharawichanant Department of Chemical Engineering, Faculty of Engineering and Industrial Technology Silpakorn University, Nakhon Pathom, 73000, Thailand * Abstract This work studied the effect of untreated ZnO (p-zno) and surface-treated ZnO (t-zno) on mechanical and morphological properties of high density polyethylene (HDPE)/ZnO nanocomposites. Two different silane coupling agents, Vinyltriethoxysilne (VTES) and 3-Aminopropyltriethoxysilne (APTES), were used to treat ZnO. HDPE/ZnO nanocomposites were prepared by melted compounding in an internal mixer. The results found that the tensile strength of HDPE/t-ZnO nanocomposites increased after adding t-zno 1 wt% in HDPE matrix and then decreased with increasing t-zno content. Young s modulus of HDPE/t VTES -ZnO nanocomposites increased with increasing t VTES -ZnO content while the addition of t APTES -ZnO, Young s modulus did not change. The dispersion of ZnO particles in HDPE matrix was observed by SEM, it found that the dispersion of ZnO particle was good when an addition of p-zno low content in the HDPE matrix. But t-zno particles with VTES or APTES did not improve the particle dispersion. Keyword: Vinyltriethoxysilane, 3-Aminopropyltriethoxysilane, Zinc Oxide, High Density Polyethylene, Silane coupling agent 1

2 1. Introduction Polyolefins are the low-cost, easy-processing and most widely used general polymeric materials. Through blending, filling and reinforcing, it is possible to get the high performance of polyolefin- based materials. High density polyethylene (HDPE) is the most crystalline of the commercial polyethylene. HDPE distributes well balanced mechanical properties which make it ideal for industrial applications. Polyethylene (PE) is a widely used material in outdoor applications, so its life time is determined by various environmental factors as solar radiation, temperature, thermal cycling, humidity, weather, pollutants, but most importantly by ultra-violet (UV) radiation. Its highly crystalline structure, in comparison to other kinds of PE, results in very high tensile strength. On the other hand, HDPE offers a good barrier for humidity and resistance to abrasion and corrosion, and it presents inertness to the most of chemicals. Additionally, it has light weight and low thermal conductivity. To enhance some of the above mentioned properties, polymer materials have been filled with several inorganic compounds. However, the larger the filler the more imperfect is the structure. Thus, as the fillers become smaller and smaller, structural perfection can be achieved [1]. The key factor, which affects the performance of composites, is the interfacial compatibility between the components. Usually, the compatibility between polyolefins and polar materials is poor because polyethylene does not have any polar groups in its backbone to interact with the ZnO surface for dispersion and inert. This poor compatibility in the blends often results in bad mechanical properties. There are a lot of methods developed to improve or modify the affinity between the component [2]. Polymer composites filled with inorganic or organic fillers could be widely used in the industries including electronics, packaging, medical and health cares, tools, and automobile, etc., due to their superior mechanical, thermal, optical, and electrical properties compared to those of pure polymeric materials. Inorganic polymer composites have the advantages of the polymeric properties together with the characteristics of the inorganic particles. The homogeneous dispersion of the filler particles in the polymeric matrix may improve the material characteristics [3]. Inorganic nanoparticles are very easy to agglomerate in mediums and show poor dispersion in polymers, hence the applications of many nanosized particles are largely limited. From the practical point of view, these nanoparticles have to be dispersed in polymer matrix to form nanocomposites for the purpose of gaining stability and processability. To prevent the formation of agglomerated nanoparticles in polymers, the combination of inorganic particles with polymers is usually accomplished by surface modification. There are two methods of surface grafting: one is that the endfunctionalized polymers are grafted to the surface of inorganic particles; the other is that the polymer is grafted onto the surface of inorganic particles. As regards with the first method, metal oxide nanoparticles having reactive hydroxyl groups on the surfaces, surface grafting is carried out by the reaction of reactive polymers (having isocyanate, alkoxy silane, etc.) with the hydroxyl groups. As to the second method, the polymerization of vinyl monomers can be initiated by introducing the reactive groups such as azo groups, peroxyester groups onto the surface of inorganic particles. In addition, the double bonds introduced onto the surface of inorganic particles can also copolymerize with other vinyl monomers. The introduction of the initiating groups onto the surface of the inorganic particles usually need multi-step synthesis, while the introduction of the double bonds can be achieved by one-step synthesis using silane coupling agent containing double bonds to modify the surface of the inorganic particles[4]. The widespread use of silane treatment can be attributed to the availability of a wide range of endgroups. Thus, the interaction between the inorganic surface and the matrix polymer can be tuned by selecting the appropriate end groups [5]. There are a variety of ways to produce a crosslinked material. The usual peroxide crosslinking or irradiation crosslinking, the utilisation of silane-water crosslinking has gained much attention in recent years. The crosslinking reaction involves hydrolysis of the alkoxy groups with moisture, followed by condensation of the formed hydroxyl groups to produce stable siloxane linkages[6]. In the present work, we attempt to further investigate the effect of surface-treated ZnO with 3- Aminopropyltriethoxysilne (APTES) and Vinyltriethoxysilne (VTES) on the properties of HDPE. HDPE has been used widely due to the excellent ductile behavior, is selected as the matrix Material 2. Experiment HDPE (POLENE V1160) with a density of 0.95 g/cm3 and a melt flow rate of g/10min (190 C, 2.16 kg) was produced by IRPC Public Co., Ltd. ZnO (5.96 g/cm3) with an average particle size 63 nm produced by Aldrich company. The two silane coupling agents of Vinyl triethoxysilane (VTES 97%, density: g/cm 3, boiling point: 217 C) and 3- Aminopropyltriethoxysilane were (APTES 99%, density: g/cm 3, boiling point: 217 C) supplied by S.M. Chemical Supplies company. pp011-2

3 2.2. Surface treatment of ZnO particle with VTES and APTES Prior to melt blending of HDPE and ZnO, ZnO needs to be chemically modified to improve the compatibility between HDPE and ZnO and to obtain the homogeneous distribution of ZnO in composites. Surface treatment of ZnO surface was carried out in liquid phase. ZnO powders were treated with a silane coupling agent as follows: 2.5 g of VTES or APTES (80 wt% ZnO) in solution (ethanol:h 2 O) 10:1 was stirred for 1 hr. The obtained solution containing the silane coupling agent was added to 0.5 g of ZnO and 50 g of deionizer water which ultrasonic for 30 min and stirred for 1 hr. The rotation speed was 650 rpm. After mixing, the mixture were dried in an oven at 110 o C for 24 hrs. The molecular structure of silane coupling agent as shown in Fig. 1. from Lloyd instruments. The tensile test was performed at crosshead speed 50 mm/min 2.6. Scanning electronic microscope (SEM) SEM with a MX 2000S Camscan, was taken to study the morphology of the HDPE/ZnO composites and to evaluate the dispersion quality of ZnO particles, the tensile-fractured surface of HDPE/ZnO composites with and without VTES and APTES obtained from tensile test were examined. All specimens were coated with a thin Au film before SEM observations. 3. Results and discussion 3.1. Fourier transform infrared spectrometer (FT-IR) Fig. 1. The chemical formula of silane coupling (a) VTES (b) APTES 2.3. Sample preparation Pure HDPE, pure ZnO particles (p-zno) and ZnO surface treated with VTES (t VTES -ZnO) and APTES (t APTES -ZnO) were dried in an oven at 110 o C for 3 hrs before melt mixing. Melt blending of different compositions of ZnO/HDPE composites was conducted by using an internal mixing with the setting temperature of 180 o C. The melt blending time was 8min and the rotor speed was 50 rpm. In this study, the contents of ZnO were 0.5, 1, 2 and 4 wt%. After that, the composites were compression molded into standard dumb-bell tensile bars the mold temperature was kept at 165 o C for 20 min Fourier transform infrared spectrometer (FT-IR) The infared spectra of original and modified ZnO were conducted using FT-IR spectroscopy to observe the surface functional groups of the samples as shown in Figure 2. The spectra of the ZnO particles treated and untreated with VTES and APTES were analyzed by a FT-IR spectroscopy and ZnO particles dispersed in a matrix of KBr, followed by compression to consolidate the formation of the pellet. FT-IR spectra were obtained in the wave-number range from 400 to 4000 cm Mechanical test Tensile tests were conducted according to ASTM D 638 with a universal tensile testing machine LR 50k Fig. 2 show the FT-IR spectra of p-zno, VTES, t VTES -ZnO, APTES and t APTES -ZnO, respectively. There is a broad peak with a maximum at 3400 cm -1 attributed to the surface hydroxyl groups and a strong absorbance at cm -1 attributed to the Si-O-Si (silaoxane groups). Assignments of IR bands of fumed silica are also given in Table 1[16]. Fig. 2. FT-IR spectra of (a) p-zno, (b) VTES, (c) t VTES -ZnO, (d) APTES and (e) t APTES -ZnO. Table 1 IR vibration bands of fume silica [17] Wavenumber(cm -1 ) ~3400 ~ ~ Mechanical properties Peak assignment Si-OH vibration(stretching) -OH bending (molecular H 2 O) Si-O-Si asymmetric stretching vibration Si-O(H.H 2 O) bending In-plane bending (geminol) The strength of a material is defined as the maximum stress that the material can sustain under uniaxial tensile loading. For micro- and nano-particulate composites this relies on the effectiveness of stress transfer between matrix and fillers. Factors like particle size, particle/matrix interfacial strength and particle loading that significantly affect the composite strength are pp011-3

4 discussed below [18]. Fig. 3 shows the effect of a silane coupling agent types on the tensile strength of HDPE/ZnO nanocomposites. The result found that the tensile strength of HDPE/p-ZnO increased after added ZnO and reach maximum 1 wt% after that it was constant. While of HDPE/t VTES -ZnO and HDPE/t APTES - ZnO nanocomposites increased and reach maximum 1 wt% of t-zno because the lower content of ZnO was a good dispersion in HDPE and then decreased due to ZnO particles agglomerated and inserted in the chain of polymer. wt% t VTES -ZnO and then increased but lower than Young s modulus of HDPE/p-ZnO nanocomposites. Because t-zno particles were aggregates and the dispersion of t-zno particles was poor. Fig. 5 shows the effect of silane coupling agent types on the stress at break of HDPE/ZnO nanocomposites. The result found that stress at break of HDPE/t VTES -ZnO and HDPE/t APTES -ZnO nanocomposites decrease after added ZnO. While the stress at break of HDPE/p-ZnO nanocomposite increased with increasing ZnO content. The interaction between the ZnO and the HDPE matrix was enhanced when ZnO surface was untreated with the silane coupling agent. When add 0.5% wt ZnO, we found that the stress at of HDPE/t VTES -ZnO and HDPE/t APTES -ZnO nanocomposites were better than HDPE/p-ZnO but higher content of ZnO(4%wt) the stress at of HDPE/t VTES -ZnO and HDPE/t APTES -ZnO nanocomposites were worse than HDPE/p-ZnO. Fig. 3. The effect of the silane coupling agent types on the tensile strength of HDPE/ZnO nanocomposites. Fig. 5. The effect of the silane coupling agent types on the stress at break of HDPE/ZnO nanocomposites. Fig. 4. The effect of the silane coupling agent types on the young s modulus of HDPE/ZnO nanocomposites. Young s modulus is the stiffness (the ratio between stress and strain) of a material at the elastic stage of a tensile test. It is markedly improved by adding microand nano-particles to a polymer matrix since hard particles have much higher stiffness values than the matrix [18]. As expected, addition of ZnO induced the enhancement of the tensile modulus and it increased gradually with increasing of ZnO content, indicating the stiffening effect of ZnO on HDPE due to the high modulus of ZnO. Fig. 4 shows the effect of a silane coupling agent types on the Young s modulus of HDPE/ZnO nanocomposites. The result found that Young s modulus of HDPE/p-ZnO was increased after added ZnO and reach maximum 1 wt% and then slightly decreased. While Young s modulus of HDPE/t APTES -ZnO was constant and Young s modulus of HDPE/ t VTES -ZnO was a minimum after added 1 Fig. 6 show the effect of silane coupling agent types on the %strain at break of HDPE/ZnO nanocomposites. The result found that %strain at break of HDPE/t VTES - ZnO, HDPE/t APTES -ZnO nanocomposites decreased after added ZnO. While the %strain at break of HDPE/p-ZnO nanocomposite increased in a range of wt% content after that it decreased with high ZnO content. The interaction between the ZnO and the HDPE matrix was enhanced when ZnO surface was untreated with the silane coupling agent. pp011-4

$3 Morphology The morphology of fracture surfaces of tensile specimens of HDPE/ZnO composites was examined by SEM. Fig.$

5 Fig. 6. The effect of the silane coupling agent types on the % strain at break of HDPE/ZnO nanocomposites. 3.3 Morphology The morphology of fracture surfaces of tensile specimens of HDPE/ZnO composites was examined by SEM. Fig.7 shows the micrographs of the tensile fracture surfaces of the composites filled with 2wt% p- ZnO, t VTES -ZnO and t APTES -ZnO respectively. It was observed that the dispersion of p-zno particles was relatively good and uniformly dispersed throughout the entire polymer matrix. while t-zno particles agglomerated to each other to become a cluster of ZnO. HDPE/t APTES -ZnO was more aggregate than HDPE/t VTES -ZnO, it has influence the tensile properties. So it supports the result from tensile properties. 4. Conclusion The effect of ZnO surface treated with VTES and APTES on mechanical and morphological properties of HDPE/ZnO nanocomposites. The results found that tensile strength of HDPE/t-ZnO nanocomposites increased after adding t-zno and reach at 1 wt% and then decreased. But Young s modulus of the nanocomposites increased with increasing t VTES -ZnO content and did not change when adding t APTES -ZnO in HDPE matrix. The dispersion of p-zno particles in HDPE matrix, it found that dispersion of particle was a good, addition of p-zno high content effect of a few agglomerates in HDPE matrix. The result showed that surface treatment of ZnO particle with VTES and APTES did not improve the particle dispersion References [1] I. Grigoriadou, K. M. Paraskevopoulos, K. Chrissafis, E. Pavlidou, T.-G. Stamkopoulos, D. Bikiaris, Effect of different nanoparticles on HDPE UV stability, Polym. Degrad. Stab. 96 (2011) [2] S. Wu, G. Ji, J. Shen, A study on ultraviolet irradiation modification of high-density polyethylene and its effect in the compatibility of HDPE/PVA fibre composites, Mater. Lett. 57 (2003) [3] J. Jung, J. Kim, Y. R. Uhm, J.-K. Jeon, S. Lee, H.M. Lee, C.K. Rhee, Preparations and thermal properties of micro- and nano- BN dispersed HDPE composites, Thermochim. Acta 499 (2010) 8 14 [4] E. Tang, H. Liu, L. Sun, E. Zheng, G. Cheng, Fabrication of zinc oxide/poly(styrene) grafted nanocomposite latex and its dispersion, Eu. Polym. J. 43 (2007) [5] M. Hashimoto, H. Takadama, M. Mizuno, T. Kokubo, Enhancement of mechanical strength of TiO 2 /high-density polyethylene composites for bone repair with silane-coupling Treatment, Mater. Res. Bull. 41 (2006) [6] K. Sirisinha, S. Chimdist, Comparison of techniques for determining crosslinking in silane-water crosslinked materials, Polymer Testing 25 (2006) [7] O. H. Lin, H. M. Akil, Z. M. Ishak, Characterization and properties of activated nanosilica/polypropylene composites with coupling agents, polym. Comp.(2009) Fig. 7. SEM micrographs a) pure HDPE, b) HDPE/ p-zno 2 wt%, c) HDPE/t VTES -ZnO 2 wt% /, d) HDPE/t APTES -ZnO 2 wt%. pp011-5

PROPERTIES OF THERMOPLASTIC CASSAVA STARCH MODIFIED BY PECTIN

E_E0026 1 PROPERTIES OF THERMOPLASTIC CASSAVA STARCH MODIFIED BY PECTIN Worawan Pattanasin, Jutarat Prachayawarakorn* Department of Chemistry, Faculty of Science, King Mongkut s Institute of Technology