During the last century, natural fibers and particulates are used as reinforcement in polymer composite that has been continuously growing in the composite industry. This polymer matrix composite has wide range of applications in hostile environment where they are exposed to external attacks such as solid particle erosion. Also, the mechanical properties of different polymer composites show the best alternate to replace the metal material. In the present investigation, an attempt has been made to improve the mechanical and tribological behaviour of polymer matrix composite using wood apple shell particles as a filler material in polymer matrix. Also the temperature variation of the dynamic-mechanical parameters of epoxy matrix composites incorporated with 5, 10, 15, and 20 wt% of wood apple shell particles was investigated by DMA test. It is clearly observed that the incorporation of wood apple shell particles tends to increase the tensile strength, flexural strength, erosive wear resistance, and viscoelastic stiffness of the polymer composite. To validate the results, SEM of the polymer matrix composite has been studied.
Bio and industrial waste are finding increased application under different conditions in which they may be utilised as value-added products. Many scientists are looking for new and alternative materials due to the paucity of metals. Their survey reveals that natural waste products have the potential to replace the conventional materials. These natural waste products include banana, bamboo, coconut shell, oil palm shell, jute, rice husk, and henequen, which are attractive due to their low cost, easy fabrication, high strength to weight ratio, better thermal and insulating properties, renewable, completely or partially recyclable, and biodegradable [
Many investigations have been made by the researchers on the potential of the natural fillers as reinforcements for composites. Bujang et al. [
Numerous research works are carried out on various filler materials that can give good dispersion and interfacial adhesion between the filler and polymer matrices. In this work, we fabricated an epoxy composite using a new natural filler material, that is, wood apple shell particulate, because particulate reinforced polymer composites are very attractive due to the ease of manufacturing and mould ability. Anusha [
Wood apple (
Wood apple shell.
The main aim of this research was to investigate the influence of wood apple shell particles on mechanical and tribological properties of epoxy composites and also study the temperature variation of the dynamic-mechanical parameters such as storage modulus and loss modulus of epoxy matrix composites incorporated with wood apple shell particles by DMA tests.
The wood apple shell (WAS) used in this study is washed several times with distilled water to remove the impurities and waste. The shell material was dried at 110°C for 48 h in an oven to remove excess water content and moisture. After drying, the raw materials were crushed into small pieces with the help of a crusher. After crushing the small pieces of shell materials, and finally converted into fine granular size particles by ball mill for 48 h. The particle size used in this experiment was 212-1
Wood apple shell particles.
Proximate analysis is one of the most important characterization methods to analyse the biofiller. It consists of determining moisture, ash, volatile matter, and fixed carbon contents of the biomass. The proximate analysis of wood apple shell particles is presented in Table
Proximate analysis (% by mass) of wood apple shell particles.
Sample | Wood apple shell |
---|---|
Fixed carbon | 19.21 |
Moisture | 6.6 |
Ash | 0.85 |
Volatile | 73.34 |
The ultimate analysis of a sample determines the elemental compositions (carbon (C), hydrogen (H), nitrogen (N), and sulphur (S) contents) of the sample which is presented in Table
Ultimate analysis of wood apple shell particles.
Sample | Wood apple shell |
---|---|
C | 52.59 |
H | 6.355 |
N | 0.34 |
S | 0.00 |
Chemical composition of wood apple shell particles.
Sample | Wood apple shell |
---|---|
Cellulose | 39.54 |
Hemicellulose | 26.06 |
Lignin | 29.86 |
Ash | 0.9 |
A wooden mold of
Epoxy LY 556 (bisphenol-A-diglycidyl-ether) is used in the present studies, chemically belonging to the “epoxide” family, is used as the matrix material. The epoxy resin and the hardener are supplied by Ciba Geigy India Ltd.
Ten percentage of hardener HY951 is mixed in the resin earlier to reinforcement. A proper stirring is done with mechanical stirrer for uniform mixing of particulates. Then the mixture of particulate and epoxy along with hardener was poured into the mould and after few minutes 30 kg of load is applied on the composite for 24 h for better increase of strength. Due to applying of load some amount of the polymer may squeezed out from the mould for this care has taken to ensure no polymer may squeeze out from mould. When the composite was hardened it was removed from the mould and cut with a diamond cutter according to ASTM standard for different tests.
In terms of weight fraction the theoretical density of the composite materials can be calculated using Agarwal and Broutman [
However the actual density of the composite materials in terms of weight fraction is determined experimentally by (
Density and void contain of wood apple shell.
% of filler | Actual density (g/cc) | Theoretical density (g/cc) | Volume fraction of voids (%) |
---|---|---|---|
Epoxy | 1.1800 | 1.2 | 1.66 |
5 | 1.1799 | 1.193 | 1.06 |
10 | 1.1755 | 1.185 | 0.83 |
15 | 1.1725 | 1.178 | 0.48 |
20 | 1.18 | 1.171 | 0.76 |
Consider
The volume fraction of voids
The tensile tests are conducted according to the ASTM D638-99 standard. The dumbbell-shaped samples for tensile test are cut with a circular diamond blade. The tensile specimen is placed in the testing machine and a care has to be taken taken when aligning the longitudinal axis of the specimen. Servohydraulic controlled INSTRON H10KS dynamic material testing system is used for tensile testing.
In order to determine the flexural properties of the composites a three-point bending test is carried out according to D790-99 standard. Bending property of wood composite is very necessary for structural application to avoid failure. The rectangular samples for bend test are cut by using diamond cutter and followed by grinding. The span of 70 mm and a crosshead speed used for the flexural tests (three-point bending) is 5 mm/min. The machine is designed to elongate the specimen at a constant rate and to continuously and simultaneously measure the instantaneous applied load and the resulting elongations using an extensometer. The flexural strength was calculated by the formula:
The value of interlaminar shear strength (ILSS) was found out by using short beam shear test method as per the ASTM standard D 2344-84. Load is applied at the rate of 1.3 mm/min. The force applied at the time of failure was recorded and the stresses were determined using
Dynamic mechanical analysis (DMA) is a powerful technique to investigate thermal and mechanical properties of polymers. The specimens generally deform sinusoidally in response to an applied oscillating force. The resultant strain in specimen due to the sinusoidal load depends upon both elastic and viscous behavior of the specimen. In this study, the storage modulus
The erosion test was conducted on erosion wear test rig according to the ASTM G76-95 standard test method. In the erosion test apparatus, dry and compressed air is used to accelerate the abrasive particles to strike the test specimen and pressure changes at the nozzle are adjusted with a pressure regulator and controlled with a manometer. Angular silica sand abrasive particles with the average size range 150–250
Experimental condition for the erosion test.
Test parameters | |
---|---|
Erodent | Silica sand |
Erodent size ( |
|
Erodent shape | Angular |
Hardness of silica particles (HV) |
|
Impingement angle ( |
30, 45, 60 and 90 |
Impact velocity (m/s) | 48 |
Erodent feed rate (gm/min) |
|
Test temperature | RT |
Nozzle to sample distance (mm) | 10 |
Density of the composites decreases with increasing the filler content as compared to polymer; this is due to the lighter density of filler material (1.068 g/cc). The void content decreases with increasing filler content up to 15 wt% this may be due to addition of less hydrophilic filler material. Beyond 15 wt% the void content slightly increases; this is due to imbalance of filler and matrix weight percentage shown in Table
The mechanical properties of a composite depend on the nature of the filler, resin, resin-filler adhesion, and cross-linking agents and not the least on the method of the processing. Therefore, any improvement in the property is evaluated as compared to that of the polymer matrix undergone the same processing. The fillers are impregnated by the liquid resin usually at room temperature and then treated with some cross-linking agent for hardening. Usually with an increase in the filler content in the composition, the tensile and flexural property gradually improves. Beyond certain limit of the filler content, however, depending on the method of processing, the adhesion between the resin and the filler decreases resulting in the decrease in the strength of final products [
Figure
Effect of tensile strength of composite.
Figure
Effect of flexural strength of composite.
Epoxy resin has excellent adhesion to a large number of materials and could be further strengthened with the addition of fiber or particulates. The improved strength of the epoxy due to filler addition and a comparison of optimum results obtained in many natural fillers with wood apple shell are shown in Table
Mechanical properties of some epoxy polymer composites.
Resin | Filler (particles) | Corresponding filler content (wt%) | Tensile strength (MPa) | Flexural strength (MPa) | Reference |
---|---|---|---|---|---|
|
|
|
|
|
|
Epoxy | Coconut shell | 20 | 30.60 | 63.45 | [ |
Epoxy | Orange peel | 20 | 25.85 | 62.35 | [ |
Epoxy | Ipomoea carnea | 30 | 23.75 | 52.47 | [ |
Epoxy | Pineapple-leaf | 30 | — | 80.2 | [ |
Generally ILSS increases with the reduction of void fraction. From the ILSS results shown in Figure
Effect of ILSS of composite.
Figure
Variation of the storage modulus with the temperature for the pure epoxy and the composites reinforced with different volume fractions of wood apple shell particles.
Figure
Variation of the loss modulus with the temperature for the pure epoxy and the composites reinforced with different volume fractions of wood apple shell particles.
Effect of impingement angle on the erosion wear rate of the composites at impact velocity 48 m/s.
Figure
The state of dispersion of wood apple particles into the resin matrix plays a significant role on the mechanical properties of the composite. SEM is used to evaluate the particle dispersion in the composite. The morphology of the composites was investigated using a scanning electron microscope (SEM) (JEOL jsm-6480lv) at an accelerating voltage of 15 kV).
Figure
SEM of 15 wt% flexural specimen.
SEM of 20 wt% flexural specimen.
SEM analysis of different composites (5, 10, 15, and 20 wt%) with constant impact velocity 48 m/s and impingement angle 45° is shown in Figures
SEM of eroded composite surface (impact velocity 48 m/s, 5 wt% filler, and impact 45° angle).
SEM of eroded composite surface (impact velocity 48 m/s, 10 wt% filler, and impact 45° angle).
SEM of eroded composite surface (impact velocity 48 m/s, 15 wt% filler, and impact 45° angle).
SEM of eroded composite surface (impact velocity 48 m/s, 20 wt% filler, and impact 45° angle).
Density and void contents of the wood apple shell particulates composites decrease with increasing the filler content as compared to polymer. With the addition of wood apple shell particles in epoxy resin the tensile and flexural strength increases. However wood apple shell particulates epoxy composite shows better mechanical strength than other polymer. The increase of the filler plays an important role in improving the ILSS of the mechanical behavior of composites. The improvements of ILSS up to optimum filler content, that is, 15 wt%, indicated better interfacial interaction and effective load transfer between filler and epoxy resin due to better dispersion. Study of influence of impingement angle on erosion rate of the composites filled with different weight percentages of filler loading reveals their semiductile nature with respect to erosion wear. The peak erosion rate is found to be occurring at 45° to 60° impingement angle for all the composite samples under various experimental conditions irrespective of filler loading. DMA investigations on wood apple shell particles filled composites exhibit the better storage modulus than neat epoxy composite. From the SEM analysis it is clearly observed that there is a formation of micro cracks, voids, and poor interfacial bonding which causes the reduction in strength these defects can be overcome by employing other fabrication techniques.
The authors declare that there is no conflict of interests regarding the publication of this paper.