Much research has been done all over the world on the use of natural fibers as a reinforcing material for the preparation of various types of composite materials. However, due to the incompatibility between fibers and polymer matrices, the tendency to aggregate during processing and the poor resistance to moisture reduce the use of natural fibers as reinforcements in polymers. For this purpose, in the present research work, the use of pretreated natural fibers in polymer matrix composites was studied.
Also, the effect of surface modification of natural fibers on the mechanical properties of bamboo fiber reinforced polymer composites has also been discussed. The advantages of natural fibers over man-made fibers include low density, low cost, recyclability and biodegradability [1-3]. The natural fibers consist of cellulose, hemi-cellulose, lignin, pectin, wax and water-soluble substances.
The chemical composition of natural fibers can vary with the growing conditions and testing methods even for the same type of fiber. According to the source of origin, natural fibers can be classified into three categories such as animal fibers, vegetable fibers and mineral fibers. As can be seen from table 1.2, the tensile strength of glass fibers is significantly higher than natural fibers, even though the modulus is of the same order of magnitude.
However, if we consider the specific modulus of natural fibers (modulus/specific gravity), natural fibers show values that are comparable or better than those of glass fibers.
![Table 1.1 Composition of few natural fibers [7, 8]](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10558294.0/11.918.137.783.645.959/table-1-1-composition-of-few-natural-fibers.webp)
LITERATURE SURVEY
- Objectives of the present research work
- Preparation of composites
- Mechanical testing of composites
- Scanning electron microscopy (SEM)
A few researchers have reported that the mechanical properties of composites are improved by increasing the interfacial strength. The mechanical properties of fiber-reinforced composites can be improved by peroxide-induced graft copolymerization of polyethylene onto cellulosic surfaces [32]. The effects of different chemical treatments on fiber-reinforced polymer composites have been studied by few researchers [33-34].
The effect of chemical treatment on the mechanical behavior of banana fiber reinforced polyester composites has been studied and it was reported that the mechanical properties of various alkali treated banana fiber composites showed improved fiber-matrix interactions [35]. The effect of chemical treatment on the elastic and dynamic mechanical behavior of LDPE reinforced with short sisal fibers has been studied and it was reported that the cardanol derivative of toluene di-isocyanate treatment decreased the hydrophilic nature of sisal fiber and increased the tensile properties of sisal. -LDPE compounds [36]. The effect of benzoyl peroxide treatment on short sisal fiber reinforced polyethylene composites has been studied and reported that the improvement in tensile properties is due to peroxide induced grafting [28].
Their study showed that the mechanical properties of natural fiber-reinforced composites were improved by different bonding agents. Chemically treated thermoplastic composites reinforced with natural fibers offer improved mechanical and physical properties under extreme conditions. The effect of chemical treatment on the impact behavior of natural fiber reinforced polymer composites has been studied by a few researchers [38, 42].
The effect of silane treatment on the physical and mechanical properties of sisal fiber reinforced epoxy composites was reported by Bisanda and Ansell [43]. An extensive literature review revealed that although the literature is rich in research on mechanical behavior of chemically treated natural fiber reinforced composites, the effect of chemical treatment on short bamboo fiber reinforced polymer composites has hardly been found. To study the influence of chemical treatments on the mechanical behavior of short bamboo fiber reinforced epoxy composites.
This chapter describes the details of the processing of the composites and the experimental procedures followed for their characterization. After manufacturing the composites, the test specimens were subjected to various mechanical tests according to ASTM standards. The impact properties of the polymeric materials are related to the toughness of the material as a whole.
MECHANICAL CHRACTERISTICS OF COMPOSITES
RESULTS & DISCUSSION
Mechanical characteristics of composites
The tensile modulus, an indicator of the relative stiffness of a material, can be obtained from a stress strain diagram[47]. The tensile test is a measurement of the property of a material to withstand forces that tend to pull it apart and to determine how much the material stretches before breaking. The tensile strength of short bamboo fiber/epoxy composites at different fiber loadings is described in.
During the alkali treatment, waxes, hemicellulose and some of the lignin present on the fiber surface are removed. Boiling the fiber with aqueous NaOH roughens the surface of the fiber due to the removal of lignin and hemicellulose. It is observed that the flexural strength for different fiber weight ratios of the composites is higher when alkaline boiled fibers are used in the composites.
From Table 4.3 it is clearly evident that the flexural strength composites are higher than those of the matrix. It is also observed from the table that the flexural strength increases with increasing fiber content in the composite as shown in figure 4.4. Variation of flexural strength of untreated, aqueous, and silane-treated NaOH-treated boiled bamboo fiber.
It is clearly seen in the figure that the flexural strength increases with the carbon fiber content. It is observed from the figure that the flexural properties of bamboo fiber reinforced composites were significantly lower than those of long bamboo fiber reinforced composites and therefore to improve the properties, treatment is generally required for short bamboo fiber reinforced composites. . A possible improvement in the bond between the reinforcement and the matrix is made by alkali treatment which increased the flexural properties of the composites.
The impact strength of composites is not greatly improved by either alkali treatment or silane treatment. Although the flexural strength of alkali-treated bamboo composites is higher than that of silane treatment, there is little difference in impact strength between the two composites. The effect of fiber reinforcement on the impact strength of composites is more complicated than flexural and tensile strength, as impact strength is attributed to energy consumption during failure.
Surface morphology of the composites
Successful fabrications of a new class of epoxy-based composites reinforced with short bamboo fibers have been made. It has been observed that the mechanical properties of composites such as hardness, tensile strength, flexural strength and impact strength etc. treatment bamboo fiber composites have been studied.
The variation of tensile strength, tensile modulus and flexural properties of these composites is studied with different mass ratios. These tensile, modulus and flexural properties are observed to improve with increased fiber loading in the composites. They also investigated the effect of alkali treatment of bamboo fibers on tensile, modular and flexural properties and found that the properties increased with alkali treatment and silane treatment.
It was found that both bamboo fiber reinforced composites showed better tensile, modulus and flexural properties than untreated bamboo fiber composites. This is due to the fact that the alkali treatment improves the adhesion of the fiber surface by removing the hemi-cellulose, thereby creating roughness. This work can be further extended to study other aspects such as using other types of chemical treatments to modify the surface of bamboo fiber reinforced polymer composites and evaluate their mechanical behavior, and the obtained experimental findings can be similarly analyzed.
Recent Developments in Chemical Modification and Characterization of Natural Fiber Reinforced Composites, Polymer Composites, 29(2), pp.187-207. C., "Effect of water absorption on dimensional and impact energy of jute fiber reinforced polypropylene" Journal of Material Science Letters vol 16 (1997) pp 462-464. Uma, Bhagawan S S and Thomas S, "Mechanical properties of pineapple leaf fiber-reinforced polyester composite" Journal of Applied Polymer Science 64 (1997) pp 1739-1748.
Shin F G, Xian x j, Zheng W P, Yipp M W "Analyses of mechanical properties and microstructure of bamboo-epoxy composites" material science journal, vol 24, pp-3483-3490. Torres F.G., Diaz R.M., Morphological characterization of natural fiber reinforced thermoplastics (NFRTP) processed by extrusion, compression and rotational molding, Polymers and Polymer Composites pp- 705-718. Torres F.G., Aguirre M., Rotational molding and powder processing of natural fiber reinforced thermoplastics, International Polymer Processing pp- 204–210.
Torres F.G., Ochoa B., Machicao E., Single-screw extrusion of natural fiber reinforced thermoplastics (NFRTP), International Polymer Processing pp- 33–40. George J, Bhagawan S.S and Thomas S, (1998) "Enhanced interaction in chemically modified pineapple leaf fiber reinforced polyethylene composites". -Gonzalez A., Cervantes-Uc J.M, Olayo R., and Herrera-Franco P.J. 1999) "Chemical modification of henequen fibers with organosilane coupling agent" Composite Part B, vol 30, pp- 321-331.
Denes, Proceedings of the Third International Symposium on Natural Polymers and Composites–ISNaPol/2000 and Workshop on Advances in Production and Processing of Cellulosic Fibers and Natural Polymers, 14-17 May 2000. Pothan L.A., George C.N., Jacob M. and Thomas S., “Effect of Chemical Modification on Mechanical and Electrical Properties of Banana Fiber Polyester Composite” Journal of Composite Material, Vol 41, (2007). Wang B., Panigrahi S., Tabil L. and Crerar W, "Pretreatment of flax fiber for use in rotationally molded biocomposites".
Sreekala M.S., Kumaran M.G., Joseph S., Jacob M. and Thomas S., “Oil Palm Fiber Reinforced Phenol Formaldehyde Composites: Influence of Fiber Surface Modifications on Mechanical Performance” Applied Composite. Vazquez, "Effects of alkali fiber treatment on resin transfer molding processing and mechanical properties of jute-vinylester composites" Journal of Composite Materials vol pp 1729 -1741. Effect of Silane Treatment on Mechanical and Physical Properties of Sisal-Epoxy Composites” Composites Science and Technology, Volume 41, Issue 2, 1991, p. 165-178.
![Table 1.2 Properties of natural fibers [9]](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10558294.0/12.918.134.785.470.1064/table-1-2-properties-of-natural-fibers-9.webp)
