Effect of Coupling Agents on Mechanical Properties and Morphology ...

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132 PHUEAKBUAKHAO, N. et al. Table 1. Chemical structure <strong>of</strong> the selected coupling agents. Abbreviation Name Chemical structure SA AMPTES GPTMS Stearic acid 3-Aminopropyltriethoxy silane 3-Glycidoxypropyltrimethoxy silane CH 3 -(CH 2 ) 15 -CH 2 -COOH NH 2 -CH 2 -CH 2 -CH 2 -Si-(O-CH 2 -CH 3 ) 3 CH 2 -CH-CH 2 -O-CH 2 -CH 2 -CH 2 -Si-(O-CH 3 ) 3 O MA-g-HDPE Maleic anhydride grafted HDPE CHCH 2 n O O O Surface Treatment <strong>of</strong> CaCO 3 with Silane <strong>Coupling</strong> <strong>Agents</strong>. (2) Surface treatment <strong>of</strong> CaCO 3 was carried out in the suspension containing 30 g CaCO 3 and 30 ml n-butanol. The desired volume <strong>of</strong> the silane coupling agent, either AMPTES or GPTMS, to reach 1, 2, 3, 4 and 5 wt.% compositions which respect to CaCO 3 was added to the stirred suspension. After being stirred for 3 h, the slurry was left standing for 3 days. The solvent was removed by vacuum evaporating and dried. The treated CaCO 3 was put into saturated water vapor atmosphere for 10 Preparation <strong>of</strong> r-HDPE/CaCO 3 Composites The r-HDPE was blended with 10 wt.% silane-treated CaCO 3 in a twin screw extruder at 190 °C. The composite pellets were compressionmolded into specimens according to ASTM D256, ASTMD638 and ISO 178. In the case <strong>of</strong> using MA-g-HDPE as a coupling agent, the required amount <strong>of</strong> MA-g- HDPE to reach 1, 2, 3, 4 and 5 wt.% compositions which respect to CaCO 3 was added to the mixture <strong>of</strong> r-HDPE and untreated CaCO 3 before blending in a twin screw extruder. Characterization <strong>of</strong> r-HDPE/CaCO 3 Composites The tensile and flexural properties were determined using an Universal Test Machine (LLOYD Instruments; LR 10 K). The tensile tests were performed at a crosshead speed <strong>of</strong> 50 mm/min with a fixed gauge length <strong>of</strong> 50 mm. For the flexural testing, a three point loading system with a span <strong>of</strong> 64 mm was used and the crosshead speed was set at 50 mm/min. The notched Izod Impact strength was determined using a pendulum energy <strong>of</strong> 10.96 J. The analysis <strong>of</strong> the fractured surface <strong>of</strong> the specimens after the impact test was carried out a using scanning electron microscope (JEOL; JSM 5410 LV). Before observation, the fractured surfaces <strong>of</strong> the tested specimens were vacuum coated with a thin layer <strong>of</strong> gold to make them electrically conductive. Results and Discussion Characterization <strong>of</strong> CaCO 3 Treated with AMPTES and GPTMS The characteristic spectra <strong>of</strong> CaCO 3 before and after treatment with AMPTES and GPTMS are presented in Figure 1 and Figure 2, respectively. Table 2 presents the selected peals assignment. As can be seen in Figure 1, the absorptions at 2926 cm - 1 and 2853 cm -1 attributed to the alkyl chains <strong>of</strong> AMPTES are observed. In addition, there is an increase in absorbance in these bands with the increment <strong>of</strong> AMPTES content, suggesting more coupling level. The peaks in the range <strong>of</strong> 1250-950 cm -1 assigned to Si-O-Si stretching vibration <strong>of</strong> the polysiloxane structure, indicating the incorporation <strong>of</strong> the silane coupling agent into CaCO 3 particles. (8) The similar results are observed for GPTMStreated CaCO 3 as shown in Figure 2.
<strong>Effect</strong> <strong>of</strong> <strong>Coupling</strong> <strong>Agents</strong> on Mechanical Properties and Morphology <strong>of</strong> CaCO 3 -filled Recycled High Density Polyethylene 133 untreated 1 wt.% 2 wt.% 3 wt.% 4 wt.% 5 wt.% treatment <strong>of</strong> CaCO 3 improves the mechanical properties, including tensile strength, flexurall strength, impact strength and elongation at break, <strong>of</strong> the r-HDPE/CaCO 3 composites, compared to untreatment. By treatment with 1 wt.% <strong>of</strong> different coupling agents, SA-treated CaCO3 appears to exhibit the greatest improvement in the mechanical properties <strong>of</strong> the r-HDPE/CaCO 3 composites, particularly impact strength are shown in Figure 3. Table 3 Mechanical properties <strong>of</strong> r-HDPE/10 wt.% CaCO 3 composi ites. (CaCO 3 treated with 1 wt.% coupling agents) Figure 1. Infrared spectra <strong>of</strong> CaCO 3 treated with different content <strong>of</strong> AMPTES. untreated 1 wt.% 2 wt.% 3 wt.% <strong>Coupling</strong> agent Tensile strength Flexural strength Impact strength (MPa) (MPa) (kJ/m 2 ) Untreated Stearic acid AMPTES GPTMS MA-g- HDPE 14. .01 15. .68 15. .16 14. .98 15. .27 19.87 24.93 23.80 23.73 22.75 10.28 13.23 12.03 11.11 11.96 Elongationn at Break (%) 18.77 21.65 21.08 19.52 20.19 4 wt.% 5 wt.% Figure 2. Infrared spectra <strong>of</strong> CaCO 3 treated with different content <strong>of</strong> GPTMS. Table 2. Assignment <strong>of</strong> characteristic bands in the FTIR spec ctra <strong>of</strong> CaCO 3 treated with silane coupling agents Wavelength (cm -1 ) Functional group 2926 - CH 2 Strertching (Asymmetric Vibration) - CH 2853 3 and - CH 2 -C-H Strertching (Symmetric Vibration) 1250-950 Si-O-Si (Polysiloxane) Si-O-Si Strertching Mechanical Properties <strong>of</strong> r-HDPE/CaCO 3 Composites Mechanical properties <strong>of</strong> r-HDPE/untreated CaCO 3 and r-HDPE/treated CaCO 3 compositess are shown in Table 3. In this case, CaCO 3 was treated with the fixed 1 wt.% <strong>of</strong> different coupling agents and the amount <strong>of</strong> CaCO 3 blended to r-HDPE matrix weighed <strong>of</strong> 10% %. It can be seen that surface Figure 3. <strong>Effect</strong> <strong>of</strong> CaCO 3 treated with 1% different coupling agents on the impact strength <strong>of</strong> r-HDPE/CaCO 3 composites. This results may be expounded that a strong chemical bonding between the polar group <strong>of</strong> the stearic acid and CaCO 3 to form calcium stearate enhances the compatibility <strong>of</strong> the polymer matrix and CaCO 3 particles resulting improvement the mechanical properties <strong>of</strong> composites can be achieved, by changes hydrophilic <strong>of</strong> CaCO 3 to hydrophobic. In the case <strong>of</strong> other coupling agents including AMPTES, GPTMS and MA-g-HDPE, the interactionn at interface areas between the polymer matrix and CaCO 3 particles can be achieved by van der waals forces, which are relatively weak compared to chemical bonds. Thus, using a few concentrations <strong>of</strong> coupling agent,
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