Fibre reinforced composites contents

George et al. [27] studied stress relaxation behaviour of pineapple fibre-reinforced polyethylene composites. They found stress relaxation to be decreased with an increase of fibre content due to better reinforcing effect It is also reported by George et al. [28] that properties of fibre-reinforced composites depend on many factors like fibre-matrix adhesion, volume fraction of fibre, fibre aspect ratio, fibre orientation as well as stress transfer efficiency of the interface. Luo and Netravah [29] found an increase in the mechanical properties of green composites prepared from PALFs and poly(hydroxybutyrate-co-valerate) resin (a biodegradable polymer) with the fibres in the longitudinal direction. However, the researchers reported a negative effect of the fibres on the properties in the transverse direction. 

Another important aspect is the moisture content of natural fibres. These fibres are hydrophilic and absorb water. The moisture content can be as high as 20%, but in most cases it will be in the range of 5-10%. Lack of good interfacial adhesion with the polymer phase, due to the inherently poor compatibility and the ability of the hydrophilic cellulose fibres to disperse with the hydrophobic resins, makes the use of cellulose-based fibre-reinforced composites less attractive. During processing, the presence of water can create voids in the matrix and also lead to a poor adhesion of the fibres with the hydrophobic resin. The hydrophilic nature of natural fibres can be a problem in the finished composites as well. 

This process has been described in a previous chapter as a means to process unreinforced resins. Fibre-reinforced composites can be fabricated in a similar way. The resin and fibre can be combined by usual hand lay-up or spray-up techniques. Glass fibre content up to 70 wt% or 50 vol% can be achieved for fibre composites processed by this technique. Press moulding offers obvious advantages like fast cycle time, good finish, structural integrity and high reinforcement content. 

Further, the rule of mixture type models can be applied for estimating tensile and notched impact strength of sisal fibre reinforced composites. The agreement of the two simple models is good for evaluating the influences of fibre length and content. 

ISO DIS 14,127. Composites- -Determination of resin, fibre and void content for composites reinforced by carbon fibre. 

Summerscales. J., and Fry, S.. Poisson s ratio in fibre reinforced polymer composites with high void content. J. Material Science Letters, 13. 912 -914 (1994). 

FIGURE 16. Thermal conductivity at 50 °C versus fibre volume content and versus density of short fibre reinforced C/C-SiC composites... 

Pineapple leaf fibre (PALF), which is rich in cellulose, relatively inexpensive and abundantly available has the potential for polymer-reinforced composite. PALF at present is a waste product of pineapple cultivation. Hence, without any additional cost input, pineapple fibres can be obtained for industrial purposes. Among various natural fibres, PALFs exhibit excellent mechanical properties. These fibres are multicellular and lignocellulosic. They are extracted from the leaves of the plant Ananus cosomus belonging to the Bromeliaceae family by retting. The main chemical constituents of pineapple fibres are cellulose (70-82%), lignin (5-12%) and ash (1.1%). The superior mechanical properties of PALFs are associated with their high cellulose content. 

The creep and fatigue behaviour for natural fibre-reinforced plastics is less weU understood than for glass fibre-reinforced plastics because of the lack of systematic and detailed information. Limited information is currently available oti the effects on the fatigue behaviour of natural fibre-reinforced plastics of different composite parameters such as fibre type, the quality of fibre-matrix adhesion and fibre properties and their content. 

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