P. K. Rohatgi

Alkali treatment of coir fibres for coir-polyester composites.

Coir fibres were subjected to alkali treatment with a view to improving the wettability of coir fibres by a commercially available resin such as polyester. Tensile strength of the fibres increases by 15% when the fibres are soaked in 5% aqueous solution of NaOH at 28±1° C for 72 to 76 h after which it shows a gradual decrease. This decrease is much more pronounced when the alkali is replenished after every 24 h. SEM observations showed the removal of cuticle and tyloses from the surface of coir as a result of alkali treatment, resulting in a rough fibre surface with regularly spaced pits. The debonding stress of alkali-treated fibres from polyester matrix was 90% higher than that of untreated fibres from the same matrix. Untreated fibres tended to float in the polyester whereas alkali-treated fibres were uniformly dispersed in polyester. Incorporation of 0.30 volume fraction of untreated and treated fibres in polyester resulted in composites having 11% and less 5% porosity, respectively. Flexural strength, modulus and impact strength of composites containing alkali-treated fibres were 40% higher than those containing the same volume fractions of untreated fibres. Longitudinal ultrasonic velocity and sound attenuation measurements indicated less fibre segregation and better fibre-matrix bonding in composites containing alkali-treated fibres.

Wear and abrasion of cast Al-Alumina particle composites

Abstract Wear rates for cast aluminium and Al-Si alloys containing up to 5 wt.% γ-Al 2 O 3 particles (100 μm size) were determined under conditions of adhesive wear and abrasive wear against a hardened steel disc and an alumina abrasive cloth sheet respectively. The adhesive wear rate of aluminium containing 5 wt.% A1 2 O 3 dispersions is similar to that of Al-11.8Si eutectic alloy and slightly higher than that of A1-16Si hypereutectic alloy. Al-3wt. %Al 2 O 3 and Al-5wt.%Al 2 O 3 composites perform better than Al-11.8Si and Al-16Si hypereutectic alloys under abrasive wear conditions. Al-11.8Si and Al-16Si alloys have a lower abrasive wear resistance than pure aluminium. The results indicate that Al 2 O 3 particles can be used as a substitute for silicon as the hard dispersed phase in aluminium for wear-resistant and abrasion-resistant applications.

Structure property studies of fibres from various parts of the coconut tree

Fibres from different structural parts of the coconut palm tree (Cocos nucifera, linn.) have been examined for properties such as size, density, electrical resistivity, ultimate tensile strength, initial modulus and percentage elongation. The stress-strain diagrams, fracture mode, microfibrillar angle as well as cellulose and lignin contents of these fibres have been determined. The observed properties have been related to the internal structure and chemical composition of the fibres. Some potential uses of these fibres have been listed.

Mechanical properties of banana fibres (Musa sepientum)

The stress—strain curve for banana fibre is determined. Properties such as the initial modulus (YM), ultimate tensile strength (UTS) and percentage elongation are evaluated as a function of fibre diameter, test length and speed of testing. It is found that YM, UTS and % elongation show little variation in their values for fibres of diameter ranging from 50 to 250 μm. The UTS and breaking strain are found to decrease with an increase in the test length while both breaking strength and breaking strain remain constant with the increase of speed of testing from 0.5 to 100 × 10−3 m and thereafter they both decrease. These observed properties are explained on the basis of the internal structure of the fibre, namely, the number of cells, spiral angle and the number of defects. Scanning electron microscopic (SEM) studies of the fractured surfaces of these fibres indiacte that the failure is due to pull-out of microfibrils accompanied by tearing of cell walls; the tendency for fibre pull-out seems to decrease with increasing speed of testing.

Sunhemp fibre reinforced polyester.

This paper describes the tensile and impact behaviour of polyester composites reinforced with continuous unidirectional sunhemp fibres of plant origin. The tensile strength and Youngs modulus of sunhemp fibre were found to be 389 MPa and 35.4 GPa, respectively. Tensile strength of composites containing up to 0.4 fibre volume fraction (Vf) were found to increase linearly with (Vf) and the results showed good agreement with the rule of mixtures. The work of fracture, as determined by Izod impact test, was also found to increase linearly with (Vf) and the work of fracture for 0.24 (Vf) composite was found to be approximately 21 kJ m−2. The analysis of various energy absorbing mechanisms during impact fracture showed that fibre pull out and interface fracture were the major contributions towards the high toughness of these composites. The results of this study indicate that sunhemp fibres have potential as reinforcing fillers in plastics in order to produce inexpensive materials with a high toughness.

Abrasive wear of cast aluminium alloy-zircon particle composites

The abrasive wear rates of particulate composites of an Al-11.8Si-4Mg alloy containing up to 0.35 volume fraction of zircon particles (average size, 100 μm) were measured on an 80 grit aloxide cloth sheet as a function of the volume fraction of zircon, the applied load and the number of passes over the abrasive paper. When the volume fraction of zircon is above a critical value of 0.09, the abrasive wear resistance (reciprocal of the wear rate) increases with the volume fraction of zircon according to the rule of mixtures. When the volume fraction is fixed, the abrasive wear resistance increases with the number of passes possibly because of blunting of the alumina particles of the abrasive cloth. No improvement in the abrasive wear resistance of composites over the matrix alloy was observed when the volume fraction of zircon was below 0.09. Scanning electron microscopy studies of the abraded surfaces of composites revealed fractured zircon particles but no evidence of filler particle pull-outs or debonding at the interface was obtained.

Bibliography Resource structure properties of natural cellulosic fibres — an annotated bibliography

We present a review of the work on the structure and properties of some natural lignocellulosic fibres with a classified list of references on resource, structure, physico-mechanical properties and on the uses of these fibres. This list of references includes papers published in scientific journals and in the proceedings of conferences.

Fabrication and properties of natural fibre-reinforced polyester composites

Abstract An attempt has been made to find new uses for natural fibres — one renewable resource which is otherwise under-utilized. The structure and properties of the fibres, and the fabrication and physical and mechanical properties of their polyester-based composites are described. The performance of these composites is evaluated after exposure to indoor and outdoor weathering by both destructive and non-destructive testing methods. The preparation of various consumer articles such as a voltage stabilizer cover, mirror casing, a projector cover and roofing are also reported. This study demonstrates the potential of natural fibres for non-conventional applications and points out some of their limitations.

The UPAL process: a direct method of preparing cast aluminium alloy-graphite particle composites

A direct method of preparing cast aluminium alloy-graphite particle composites using uncoated graphite particles is reported. The method consists of introducing and dispersing uncoated but suitably pretreated graphite particles in aluminium alloy melts, and casting the resulting composite melts in suitable permanent moulds. The optical pretreatment required for the dispersion of the uncoated graphite particles in aluminium alloy melts consists of heating the graphite particles to 400° C in air for 1 h just prior to their dispersion in the melts. The effects of alloying elements such as Si, Cu and Mg on the dispersability of pretreated graphite in molten aluminium have also been reported. It was found that additions of about 0.5% Mg or 5% Si significantly improve the dispersability of graphite particles in aluminium alloy melts as indicated by the high recoveries of graphite in the castings of these composites. It was also possible to disperse upto 3% graphite in LM 13 alloy melts and retain the graphite particles in a well distributed fashion in the castings using the pre-heat-treated graphite particles. The observations in this study have been related to the information presently available on wetting between graphite and molten aluminium in the presence of different elements and our own thermogravimetric analysis studies on graphite particles. Physical and mechanical properties of LM 13-3% graphite composite made using pre-heat-treated graphite powder, were found to be adequate for many applications, including pistons which have been successfully used in internal combustion engines.

Mechanical behaviour of coir fibres under tensile load

Stress-strain curves of coir fibres have been determined. Mechanical properties including initial modulus, strength and percentage elongation of coir fibres have been evaluated as functions of retting treatment (during retting the coconut husks are soaked in saline water for a period of about six months to facilitate the extraction of fibres presumably due to a bacterial process), fibre diameter, gauge length and strain rate. No significant differences in mechanical properties were observed between retted and unretted fibres. The strength and percentage elongation seem to increase for both retted and unretted fibres up to a fibre diameter of 0.2×10−3 m whereafter they remain almost constant. On the other hand, moduli seem to decrease with increase in diameter of the fibre. The observed modulus values and percentage elongation have been related to microfibrillar angle. Observed strength values have been explained on the basis of structural changes occurring with an increase in the diameter of the fibre. Scanning electron/microscope studies have indicated that the failure of the fibre is due to the fracture of the cells themselves accompanied by the uncoiling of microfibrills. There is no appreciable variation in strength and percentage elongation with strain rates for any one diameter of the fibre. On the other hand, with increase in gauge length, a decrease in both strength and percentage elongation at break has been observed. These have been attributed to an increase of probability of defects and localized deformation and gentle necking, respectively.