1. EXPERIMENTAL INVESTIGATION ON MECHANICAL PROPERTIES OF NATURAL FIBRE
RESULTS AND DISCUSSION
Morphology of the reinforcements
Raw materials such as NaOH treated sugarcane fibers, HCl treated sugarcane fibers and coconut shell fillers are separately analysed in the SEM to understand the surface morphological features. The NaOH-treated fiber surfaces are observed to be smooth, as seen in Fig. 1(a) whereas the HCl treated fiber surfaces appear to be damaged with the lot of fragments due to the acidic nature of hydrochloric acid as seen in Fig. 1(b). The coconut shell powders appear to be a honeycomb structure, as seen in Fig. 1(c).
2. Mechanical properties
Fig 2: (a)Tensile and (b) Flexural strength of Composites
The effects of HCl and NaOH treatment on the fibres are completely opposite. On the one hand, NaOH treatment of fibres shows significant strengthening of the composites through the strong matrix and fiber bonding through chemical and mechanical bonding. NaOH treated fibers increases the tensile strength of the composite. On the other hand, HCl treatment leads to the significant damage to the fiber by absorbing the electrons due to its acidic nature. The presence of (OH-) group in the sodium hydroxide donates electrons to the fiber material during chemical treatment. The electron transfer modifies the fiber surface through exposing several cellulose sites which facilitates the chemical bonding and improves the wettability with the matrix as shown in Fig. 1 (a). Further it helps to reduce the moisture absorption and imparts the hydrophobicity. The damage may be due to the chloride (Cl-) erosion effects. Further, it was found that there are several local pockets of porosities in the HCl treated fiber reinforced composites, as seen in Fig. 1(b). The porosities are strength limiting defects. Further, the damaged fibres do not bond well during the curing process resulting poor interfaces in the composites. Flexural results show that NaOH treated sugarcane fibers with fillers provides better flexural properties when compared to untreated and HCl treated sugarcane fiber composites.
EXPERIMENTAL INVESTIGATION ON MECHANICAL PROPERTIES OF NATURAL FIBRE
REINFORCED POLYMER COMPOSITES
K.Gokul1, T. Rajasekaran2
1,2Department of Mechanical Engineering, SRM University, Kattankulathur –
INTRODUCTION
The potential use of natural fibers has also been attractive in developing countries, where they are often available in tropical plants and agricultural wastes that currently have limited economic value [1]. Continuous development in the production of natural fibre composites mainly focused on mechanical improvement and reduction of structural defects to ensure durability, reliability, cost reduction and increased production rates [2]. The development of natural fibre reinforced biodegradable polymer composites promotes the use of environmentally friendly materials. The use of green materials provides alternative way to solve the problems associated with agriculture residues [3]. The mechanical properties of treated and untreated sugarcane fiber polyester composites was examined with respect to chemical treatments. Interfacial bonding between sugarcane fiber and polyester matrix enhanced by chemical treatments. Improvement in mechanical properties was found in NaOH treated sugarcane fiber composites than HCl treated sugarcane fiber composites [4].
EXPERIMENTAL DETAILS
Sugarcane bagasse fibers were collected from local juice shops. Fiber extraction was carried out by manual process. Sugarcane bagasse was used in the three forms: (1) untreated, (2) treated with 4 vol% sodium hydroxide (NaOH) and (3) treated with 4 vol% hydrochloric acid (HCl) for 180 min. Coconut shell powder was used as a filler to prepare composites. Unsaturated polyester was selected as the matrix supplied by Sakthi Fiber Glass, Chennai. Ethyl Ketone Peroxide (MEKP) and Cobalt Naphthenate were added to the matrix by manual stirring to improve the bonding characteristics with the fibers. Sugarcane fiber composites were prepared by hand layup process. The tensile and flexural tests was carried out according to ASTM D 3039 and ASTM D 790 under computerized universal testing machine (TUE-CN-200, Hitech India) respectively. The morphology of the treated fibers and secondary fillers was studied under scanning electron microscope (SEM) (FEI Quanta 200 FEG).
ABSTRACT
Natural fibre composites becoming very popular because of less density, availability, cheap and biodegradable in nature compared to synthetic fibres and conventional materials. Composites offer high levels of specific stiffness and strength as well as an adjustable energy absorption capacity. This study was planned to observe the mechanical characteristics of sugarcane fibers with fillers of untreated, HCl treated and NaOH treated sugarcane fibre composites. The mechanical properties of the prepared composite material using those sugarcane fibers was evaluated and then the results are discussed. To study the mechanical characteristics such as tensile and flexural tests are performed as per ASTM standards. It is observed that the NaOH treated sugarcane fiber composite with fillers showing better mechanical properties when compared to all other combinations.
CONCLUSION
The NaOH treated sugarcane fiber reinforced polyester matrix composites are found to provide superior tensile and impact properties due to the strong interface bonding established by the fiber and the matrix.
The NaOH treatment cleans the surface of the fiber and modifies by the fiber surface through OH- functional groups. In contrast, HCl treatment of the fibers deteriorates the surface of the fiber by absorbing the electrons. The damaged surface results in weak bonding causing poor mechanical properties.
From the SEM analysis of the surface of the sugarcane fiber, it may be concluded that the surface condition of the sugarcane fibres decides the bonding with the matrix. The fiber pull-outs and porosities are less in the NaOH treated sugarcane reinforced composites. The fiber failure is the main mechanism of failure in the tensile test whereas the fiber debonding from the matrix is the main source of failure in the flexural test.
REFERENCES
[1] Andressa Cecília Milanese, Maria Odila Hilário Cioffi, H. J. C. V. “Thermal and mechanical behaviour of sisal/phenolic composites, Composites: Part B 43 (2012) 2843–2850.
[2] Essabir, H., et al. "Structural, mechanical and thermal properties of bio-based hybrid composites from waste coir residues: Fibers and shell particles." Mechanics of Materials 93 (2016):
[3] Mulinari, Daniella Regina, et al. "Sugarcane bagasse cellulose/HDPE composites obtained by extrusion." Composites Science and Technology69.2 (2009):
[4] Rajasekaran T, and K. Gokul. "Evaluation of mechanical characteristics of treated and untreated sugarcane fiber composites." Journal of chemical and Pharmaceutical Sciences 9.1 (2016)
Fig 1: High magnification images of (a) NaOH treated fibres, (b) HCl treated fibres and (c) Coconut shell filler