The Effect of Acrylic Acid on Tensile and Morphology ...

Available online at www.sciencedirect.com

ScienceDirect Procedia Chemistry 19 (2016) 401 – 405

5th International Conference on Recent Advances in Materials, Minerals and Environment (RAMM) & 2nd International Postgraduate Conference on Materials, Mineral and Polymer (MAMIP), 4-6 August 2015

The Effect of Acrylic Acid on Tensile and Morphology Properties of Wollastonite Filled High Density Polyethylene/Natural Rubber Composites I. Yuhaidaa, H. Salmahb, I. Hanafic, Z. Firuzd c

a,b,d School of Materials Engineering, University Malaysia Perlis, Perlis, Malaysia School of Materials and Mineral Resources Engineering, University Sains Malaysia, Penang, Malaysia

Abstract Inorganic filler manufactured for incorporation into thermoplastic elastomers usually are surface treated with organic reagents in order to improve the interfacial adhesion between filler and the matrix. In the present paper, the effects of acrylic acid (AA) on tensile and morphology properties of wollastonite (WS) filled high density polyethylene (HDPE)/Natural Rubber (NR) composites were studied. The untreated and treated HDPE/NR/WS composites were melt-blending at 180 °C with rotor speed of 50 rpm for 10 minutes. The composites were tensile-tested according to ASTM D638 and the etched surfaces were observed using scanning electron microscope (SEM). Tensile strength and elongation at break of the compositesdecreased upon the addition of wollastonite, but Young’s modulus improves. The results of this study showed that the treated composites are found to have better tensile properties than the untreated composites. The morphology of treated composite showed better interfacial interaction between HDPE/NR and wollastonite. © byby Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2016 2016The TheAuthors. Authors.Published Published Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia. Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia Keywords:Thermoplastic elastomers; Wollastonite; Acrylic acid

1. Introduction Thermoplastic elastomers (TPEs) are polymeric materials that generally possess the processability of thermoplastics with outstanding mechanical properties and the elasticity of rubber. This unique combination of properties and easy processing allows the preparation of objects with complex shapes and smoothsurfaces using

1876-6196 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia doi:10.1016/j.proche.2016.03.030

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common plastic processing equipment1. The TPEs make useful products such as in many automotive parts, footwear, cables, sealants and adhesives, hoses, coated fabrics, tubings and sheetings2. Thermoplastic Natural Rubber (TPNR) is a TPE prepared by melt mixing natural rubber with a polyolefin at different proportions and it is an excellent way to add values tonatural rubber (NR). The most well known materials used to prepare TPNRs are polypropylene3,4, low density polyethylene5,6 and high density polyethylene7,8. NR and HDPE blends combines the excellent processing characteristics of HDPE and elastic properties of NR that can be used in automobile components and other industrial applications9. The addition of inorganic fillers is one of the most common methods in modifying thermoplastic elastomers1. Inorganic fillers are often added into thermoplastic elastomers formulation to enhance processability, permeability, mechanical and thermal properties as well as lower the cost of the compounds10. Wollastonite belongs to an interesting new class of functional materials. It is a form of the naturally occurring mineralwhite calcium silicate (CaSiO 3) with high aspect ratio (its aspect ratio usually 5-20). It is relatively a hard material (Mohhardness of 4.5–5.0) with a specific gravity of 2.78–2.9111. Because of its acicular nature, wollastonite is a promising reinforcement for thermoplastic such as polypropylene12,13. Like most inorganic fillers, wollastonitehas polar, hydrophilic, and high free energy surface and is incompatible with thermoplastics, leading to deteriorated mechanical properties, such as low toughness. Due to these characters, a treatment of the particles are needed to achieve a good dispersion of the filler particles and satisfactory mechanical properties14. The purpose of the present work was to study the effect of using acrylic acid treated wollastonite in thermoplastic elastomercomposition based on HDPE/NR blend on tensile strength and morphology. 2. Materials 2.1. Materials High-density polyethylene (HDPE) was procured by Lotte Chemical Titan Sdn. Bhd., Malaysia. HDPE homopolymer used in this study was blow molding grade Titanzex HB6200 with a density of 0.956 g/cm3 and a melt flow index MFI 0.45 g/10 min. Natural rubber (NR) was purchased from Rubber Research Institute of Malaysia (RRIM). NR is an SMRL grade with a density of 0.93 g/cm3. Wollastonite powders with an average particle size of 40 μm was obtained from Ipoh Ceramics Sdn. Bhd. The acrylic acid was obtained from Aldrich, Malaysia. 2.2. Preparation of treated wollastonite Wollastonite filler was chemically treated through a reaction with a solution mixture of acrylic acid in an ethanol. Wollastonite was gradually added to the acrylic acid solution and stirred for 2 h. The solution was left for 24 h, then filtered and dried at 80 °C for 24 h. 2.3. Preparation of HDPE/NR/wollastonite composites Thermoplastic natural rubber (TPNR) matrix was prepared from high-density polyethylene (HDPE), natural rubber (NR) in a ratio of 70:30 by melt blending. HDPE/NR/wollastonite composites were prepared in a Brabender plasticoder at 180 °C and a rotor speed of 50 rpm. HDPE was loaded first to start the melt mixing for 3 min. Then, NR was added and the mixing continued for another 4 min. After 7 min, the wollastonite was added and the mixing continued for another 3 min until the mixing torque stabilized. The total mixing time was 10 min for the blends. The HDPE/NR/wollastonite composites were taken out and compression-moulded into a 1.0 mm thick mould in an electrically heated hydraulic press. The hot-press procedure involved preheating at 180 °C for 4 min followed by


compressing for 4 min at the same temperature and subsequent cooling under pressure for another 4 min. A similar procedure was conducted for the preparation of treated HDPE/NR/wollastonite composites. The formulations of untreated and treated HDPE/NR/wollastonite composites are given in Table 1. Table 1. Formulation of untreated and treated HDPE/NR/wollastonite composites at different filler loading. Materials

Untreated composites

Treated composites

HDPE (phr)

70

70

NR (phr)

30

30

Wollastonite (phr)

0, 10, 20, 30, 40

10, 20, 30, 40

Acrylic acid (wt. %)

-

3

2.4. Composites characterization 2.4.1 Tensile properties Tensile properties were measured using an Instron 5569 universal tester, at a cross-head speed of 10 mm/min and was performed at 25 ± 3 °C. Dumbell shaped specimens were cut according to ASTM D638. The tensile strength, Young’s modulus and elongation at break were obtained and the average value was reported. 2.4.2 Morphology analysis The morphology of the tensile fractured surface of the HDPE/NR/wollastonite composites were investigated with a scanning electron microscope (SEM),model JSM 6260 LE. The fracture ends of specimens were mounted on aluminium stubs and sputter coated with palladium to avoid electrostatic charging during scanning process. 3. Results and discussions 3.1. Tensile properties The tensile properties of treated and untreated HDPE/NR/wollastonite composites as a function of filler loading are displayed in Fig. 1. As shown in Fig. 1(a), the tensile strength of the composites decreased upon increasing filler loading.Wollastonite has polar, hydrophilic and is incompatible with thermoplastics. When filler loading increased, the tendency of the filler-filler interaction increased rather than filler-matrix interaction. This could lead to agglomeration due to the difficulties to achieve homogenous dispersion of filler at higher filler loading. This might be attributed of a poor adhesion between wollastonite fillers and HDPE/NR matrix and the major reason for the poor performance in tensile strength. This poor adhesion created weak interface regions, resulting in debonding and frictional pull-out. However, due to the presence of acrylic acid on the wollastonite surface, the tensile strength of treated composites had higher values than the untreated composites with the same filler loading. It was found that the tensile strength of the treated composites increased by 16% compared to the untreated composites. These results indicated that the hydroxyl group of wollastonite attached to the carboxylic group of acrylic acid. This caused a better interfacial adhesion between treated wollastonite filler with the HDPE/NR matrix, hence improved the stress transfer and increased the composite performance. Fig. 1(b) shows the Young’s modulus of HDPE/NR/wollastonite composites at different filler loading. The increasing of filler loading significantly increased the Young’s modulus of the untreated and treated composites.This is due to addition of rigid particles to a polymer matrix can easily improve the modulus since the rigidity of wollastonite fillers is higher compared to HDPE/NR matrix. Hence, the Young’s modulus of the treated HDPE/NR/wollastonite composites was higher than untreated composites. This was attributed to the improvement of interfacial adhesion between wollastonite filler and HDPE/NR matrix.

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Fig. 1(c) shows elongation at break of treated and untreated HDPE/NR/wollastonite composites at different filler loading. The elongation at break of the HDPE/NR/wollastoninte composites decreased with the increasing of filler loading. This results clearly indicate that the ductility of the composites reduced as the filler loading increased. However, the treated composites were found to have higher value of elonagtion at break than the untreated composites, indicating of improved surface adhesion of wollastonite fillers and HDPE/NR matrix with the presence of acrylic acid.

Fig. 1. Effect of wollastonite loading on (a) tensile strength ;(b) Young’s modulus ;(c) elongation at break of untreated and treated HDPE/NR/wollastonite composites.

3.2. Morphology Fig. 2(a) and (b) shows SEM micrographs of tensile fracture surfaces of untreated and treated HDPE/NR/wollastonite composites containing 20 php of wollastonite. The micrograph of the untreated HDPE/NR/wollastonite composites shows a presence of wollastonite large particles within the HDPE/NR matrix, provides evidence of the poor interaction of the filler and the matrix. This was due to low filler-matrix interfacial adhesion which leads easy removal of fillers, thus caused a reduction in tensile strength. Less filler pull-out can be observed in the acrylic acid treated HDPE/NR/wollastonite composites. The wollastonite fillers was dispersed more effectively compared to the untreated HDPE/NR/wollastonite composites, suggesting that the surface treatment increase the affinity of the filler to the HDPE/NR composites.


Fig. 2. SEM micrographs of HDPE/NR/wollastonite composites with 20 php filler loading, (a) untreated composites and (b) treated composites.

4. Conclusions HDPE/NR/wollastonite composites chemically treated with acrylic acid were prepared. The tensile study showed that the presence of wollastonite reduced tensile strength and the elongation at break of the HDPE/NR composites. However, it increased the Young’s modulus upon addition of wollastonite with the maximum value at 40 php filler loading. At a similar loading, the treated HDPE/NR/wollastonite composites were found to have a higher tensile strength, Young’s modulus and elongation at break as compared to the untreated HDPE/NR/wollastonite composites. The SEM micrographs showed a better fillerdispersion and interfacial adhesion in HDPE/NR matrix with the presence of acrylic acid. References 1. Jiri GD, Handbook of Thermoplastic Elastomers. New Hampshire and Prague: Andrew Publishing; 2007. 2. Robert CS, Ink K. Thermoplastic Elastomers. 2012. Thermoplastic Elastomers, Thermoplastic Elastomers, Prof. Adel El-Sonbati (Ed.), ISBN: 978-953-51-0346-2, InTech, Available from:http://www.intechopen.com/books/thermoplastic-elastomers/thermoplastic-elastomers. 3. Samia B, Farid R. Dynamic mchanical and thermal properties of a chemically modified polypropylene/natural rubber thermoplastic elastomer blend. J Polym Testing 2014;36:54-61. 4. Anoma T, Charoen N, Kannika CS , Jacques N. Effect of different type of peroxides on rheological, mechanical, and morphological properties of thermoplastic vulcanizates based on natural rubber/polypropylene blends. J Polym Testing 2007;26:537-546. 5. Hanafi I, JM Nizam, HPS Abdul Khalil. The effect of compatbilizer on the mechanical properties and mass swell of white rice husk ash filled natural rubber/linear low density polyethylene blends. J Polym Testing 2001:20:125-133. 6. Supak M, Sirilux P. Preparation of natural rubber (NR) latex/low density polyethylene (LDPE) blown film and its properties. J Polym Testing 2011;30;716-725. 7. Skulrat P, Charoen N, Azizon K, Suda K. Influences of blend compatibilizers on dynamic, mechanical, and morphological properties of dynamically cured maleated natural rubber and high-density polyethylene blends. J Material Properties 2008;27:566-580. 8. Pongdhorn SO, Chakrit S, Promsak S, Puchong T. Properties and recyclabilityof thermoplastic elastomer prepared from natural rubber powder (NRP) and high density polyethylene (HDPE). J Polym Testing 2010;29:346-351. 9. Worawan P, Charoen N, Kannika S. Thermoplastic natural rubber based on oil extended NR and HDPE blends: Blend compatibilizer, phase inversion composition and mechanical properties. J Polym Testing 2008;27:621-631. 10. Hugo MT, Daiane T, Fabricio C, Vanda FR, Sonia MBN. Use of wollastonite in a thermoplastic elastomer composition. J Polym Testing 2013;32:1373-1378. 11. Honglong X, Gaosheng W, Mengyan H, Bowen C. Modification of wollastonite by acid treatment and alkali-induced redeposition for use as papermaking filler. J Powder Technology 2015;276:193-199. 12. Ming-Rui M, Qiang D. Effect of pimelic acid on the crystallization, morphology and mechanical properties of polypropylene/wollastonite composites. J Materials Sci Eng A 2008:492:177-184. 13. AS Luyt, MD Dramićanin, Ž Antić, V Djoković. Morphology, mechanical and thermal properties of composites of polypropylene and nanostructured wollastonite filler. J Polym Testing 2009;28:348–356. 14. Mathieu B, Marianna K. Preparation and characterization of thermoplastic olefin/nanosilica composites using a silane-grafted polypropylene matrix. J Polym 2009;50:2472-2480. 15. Shao-Yun F, Xi-Qiao F, Bernd L, Yiu-Wing M. Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate-polymer composites. J Composites Part B 2008;39:933-961.

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