Chapter 7 Chapter 7 Conclusions and Future Scopes
1.9 Mechanical Properties of Composites
Similar characterization techniques have been employed for characterizing the different nanocomposites by several researchers. Where, different characterization techniques such as, the UV/visible spectroscopy, Contact Angle Goniometer, XRD, Rheometer, DSC, Fourier Transform Infrared (FTIR) spectroscopy, SEM, Atomic Force Microscope (AFM), TGA, TEM, DMA etc. techniques revealed the intrinsic properties of the nanocomposites.
Chapter 1 Introduction and Literature Review Chabert et al., 2003) and glass transition temperature to figure out the behavior of filler-
matrix interface etc. (Jin et al., 2001; Sohn et al., 2003; Kanny et al., 2008). Kanny et al., (2008) studied the dynamic mechanical properties of clay–polypropylene nanocomposites.
They have observed that, at 20ºC the storage modulus of polypropylene increases when percentage incorporation of nanoclay shoots up to 3%. Sohn et al., (2003) have also shown the dynamic elastic modulus increases with the loading percentage of filler materials.
Jin et al., (2001) have extensively studied on the dynamic mechanical behavior of MWNTs/PMMA (Polymethyl Methacrylate) composites at different temperatures. They observed that the increment of loading percentage of MWNTs in PMMA composites, the storage modulus is increased particularly at higher temperatures and loss factor of the composite shows some broadening. Similarly, Allaoui et al., (2002) have demonstrated on the MWNT/epoxy composite that the Young’s modulus and the yield strength have been doubled and quadrupled (4th time) for composites with respectively 1 and 4 wt% nanotubes, compared to the pure resin matrix samples. Goh et al., (2003) have extensively studied on the dynamic mechanical properties of multi-walled carbon nanotube/phenoxy resin composite. They found that if dispersion of MWNTs are maintained upto 14% in phenoxy resin, the storage modulus can be reached more than 600 MPa. Tang et al., (2003) have examined the mechanical properties of MWNT/HDPE nanocomposites thin plate. They employed small punch test technique. In this technique a small disk of the material is prepared and is clamped over a circular guide hole between two rigid dies. The specimen is then subjected to a lateral indenter driven at a constant displacement rate through the guide hole as the indenter force and displacement are recorded. They concluded that the loading configuration involves lateral bending and large, biaxial deformation, although the experimental results do not directly yield the usual mechanical properties such as yield stress, elastic modulus, etc. Furthermore, the small punch test results show that the stiffness, the yield strength, and the fracture toughness of MWNT/HDPE composite films all increase with the increasing percentage of MWNTs. Zou et al., (2004) have reported examining the mechanical properties on the MWNT/HDPE composites with MWNT content of 1.0%, the elongation–content curve shows a transition, the tensile strength and modulus of the composites versus MWNTs content shows a similar tendency to that of the impact strength. They also claimed that the flexural properties of HPSM (HDPE/PEG/SiO2/MWNTs), unlikely the tension and impact results, the flexural strength and the corresponding modulus increased with the MWNTs content.
TH-1430_09610309
Manchado et al., (2005) reported that the percentage SWNTs and Carbon Black (CB) increases in the polypropylene polymer, the Young’s modulus and max. strength gradually increases upto a certain limit. The tensile modulus goes from 0.85 GPa for pure polypropylene to 1.19 GPa at the loading of 0.75 wt% SWNTs in nanocomposites. However, further increase in the loading percentage of SWNTs allowing the tensile modulus as well as ultimate strength remarkably decreased. They also observed that the storage modulus of the composite gradually increases with increase of the loading percentages of SWNTs.
Similar observations have been made by Zeng et al., (2006) that increasing the MWNTs content from 1.0–30.0 wt% into Nylon1010 increases the corresponding Young’s modulus from 27.4% (1301 MPa) to 87.3% (1912 MPa), respectively but the elongation at break drastically changes with increasing the % of MWNTs. And for DMA test they reported that the storage modulus of the materials increases significantly upon addition of MWNTs. The composite with 1.0 wt% MWNTs displays 105% increment of storage modulus over pristine Nylon1010 polymer. Zhang et al., (2006) investigated the mechanical and dynamic mechanical analysis on the SWNTs/HDPE nanocomposites. They observed that the addition of 0.5 wt%
SWNTs leads to the increase of tensile strength and initial modulus by approx. 30% and 20%, respectively. And the loading level of 2.6 wt% causes the increment of 65% and 50%, respectively. Hence, they concluded that the high increases of the mechanical properties in the said composites are attributed to the homogeneous dispersion of SWNTs in HDPE. To the mechanical properties point of view, it is shown that the enhancement of tensile properties of different polymer composites can be done by the incorporation of MWNTs as well as SWNTs. Xiao et al., (2007) reported that CNT based low density polyethylene (LDPE) composite yields higher stress with higher % of CNT, at the same time they reported that 1- 5% of CNT gives the fair strain % and at the same time, modulus is improved with higher % of CNTs.
Bao and Tjong (2008) prepared the polypropylene nanocomposites which filled with 0.1, 0.3, 0.5 and 1.0 wt% MWNTs. They tested the nanocomposite samples at various strain rates up to post-yielding using strain gage extensometer to measure the axial strain of the specimens in low strain region (≤0.02). The cross-head speeds were kept in the range of 0.05–
500mm/min. They observed that the additions of very small amounts of MWNTs to polypropylene improve its yield strength, Young’s modulus and stiffness significantly. The stiffness of polypropylene increases dramatically by 31% by adding 0.3–0.5 wt% MWNTs.
In dynamic mechanical analysis, the effect of MWNTs of only 0.3–0.5 wt% is observed that the storage modulus shoots up from 1.88 to 2.5 GPa i.e. 33% more over pure polypropylene.
Chapter 1 Introduction and Literature Review Along with, at different temperature and different strain rate, tensile behaviors of
nanocomposites were discussed in this work. Prashantha et al., (2008) also have shown similar results on MWNTs/polypropylene composites. Similar explanations have been given by many researchers that CNTs can directly influence the reinforcement of any kind of polymer composites. Thus, past literatures established the fact that the mechanical properties and dynamical properties of polymer composites can be enhanced by incorporation of CNTs for any certain of percentage.