PasEffect of Erosion on Water Absorption and Morphology for Treated Date Palm Fiber-Reinforced Polyester Composites
Ali S. Hammood
University of Kufa, Faculty of Engineering, Materials Engineering Department
Abstract-- In this study, a composite material contains a matrix (Polyester resin) and a natural fiber (Date Palm) was prepared .The volume fraction for date palm fibers was 40% in all prepared composite materials. All samples were prepared by hand layup process, A chemical treatment with at 5% concentration Maleic acid solutions for 20 hours is conducted, and tested under erosion conditions. The results showed a weight with time due to presence of voids on the surface of composite. Also, the increasing of drying time leads to decrease water absorption in case of longitudinal direction and transverse direction for date palm fibers in composite materials.
Index Term-- Date palm fiber, Erosion, Water absorption, Morphology, Composite Material.
Natural fibers have become an attractive alternative to synthetic reinforcements for fiber/polymer composites from both ecologically and economically point of view [1, 2]. This is mainly due to the advantages of the natural fibers over the synthetics, e.g. low density, non-toxic, non-harm to the skin and eyes, renewable resources, low cost, good acoustic and thermal insulation properties, and good mechanical properties. Due to the importance and the interest of natural fibers, many attempts have recently made to investigate the potential of using different types of natural fibers such as sugarcane , oil palm , and banana . The possibility of replacing fibers of man- made with natural fibers is currently of interest. Natural fibers composite are price-driven commodity composites that provide useable structural properties at a relatively low cost . Natural fibers could be one of the most useful alternative reinforcement to the synthetic fibers such as glass, boron, carbon, and Kevlar . The advantages of natural fibers over conventional fibers are good specific strength and modulus, low density, enhanced energy recovery, economical viability, good biodegradability, require low energy input in their manufacture, reduced dermal and respiratory irritation [8,9]. In spite of the many advantages of natural fibers, they also exhibit some undesirable characteristics. Low thermal resistance and highly anisotropic properties are the main disadvantages associated with natural fibers . Natural fiber composites are more susceptible to environment attack than synthetic fiber composites because of their structure of natural fibers, which consist of cellulose, lignin, hemicelluloses, and pectin . Natural fiber mechanical characteristics are influenced by parameters such as the chemical composition, crystal structure, the degree of crystallinity, the spiral angle of the fibrils, the porosity content, and the degree of polymerization . Date palm fibers (DPF) are natural woven mat of crossed fibers of different diameters surrounding the palm tree stem . Date palm fibers are available in the Middle East in huge amounts . The properties of composites depend on the matrix and fibers, and on their interfacial compatibility. On the other hand, many researchers have reported that the mechanical efficiency of the fiber'reinforced polymer composites depends on the fiber'matrix interface and the ability to transfer stress from the matrix to fiber [10, 13, 14]. In other words, interface bonding between natural fibers and polymer matrix is the core stone to determine the mechanical behavior of the composites [15, 16]. However, recent reported works found that natural fibers lack of good interfacial adhesion with synthetic matrices [17, 18]. Inasmuch, natural fibers tend to be strong polar and hydrophilic materials due to the nature of the fibers since they are rich in cellulose, hemicelluloses, pectin's and lignin, i.e. fibers are hydroxy1 groups and polymers exhibit significant hydrophobicity . To overcome this issue, chemical treatments such as acetylating, bleaching and alkali treatment found to be good candidate to improve the interfacial adhesion of the natural fiber'matrix [19- 21].
Mwaikambo and Ansell  reported that alkalization changes surface topography of the fibers and its crystallographic structure by removing impurities of surface, which also may improve the adhesion of the fiber-matrix. According to their findings, care must be exercised in selecting the soda concentration for treatment process. Srivastava and Shembekar  showed that the fracture toughness of epoxy resin could be improved by addition of fly ash particles as filler. Polymer composites are increasingly used in engineering applications such as gears, pump impellers where the components undergo erosive wear. Srivastava and Pawar  studied the effect of additives and impingement angle and eroding particle velocity on erosive wear of neat Eglass fiber reinforced epoxy resin composite materials and composites with 2 and 4 g fly ash additive particles. They concluded that the erosive wear rate of GFRP composite with 4 g fly ash is the lowest and that the maximum erosion occurs at 60'' impingement angle. H''geret al.  carried out erosion test for several thermoset and thermoplastics composites and observed a semiductile behavior. Maximum erosion is observed at 60'' impingement angle for most of the tested composites. Rajesh et al.  studied erosive wear of five different polyamides and observed that all polyamides showed maximum erosion wear at 30'' impingement angle indicating a ductile failure behavior. Zahavi and Schmitt  and Miyazaki and Takeda  also studied the erosive behavior of fiber reinforced polymer composites and concluded that the maximum erosion rate is at 90'' impingement angle. This study aims to investigate the potential of using date palm fibers as reinforcement instead of artificial fibers in polymeric materials and study Erosion behavior, as well as the morphology of composite also Current search contributes in preserving the environment by using green natural fibers leads to maintaining the sustainability of the resources.
2. EXPERIMENTAL PROCEDURES
2-1 Preparation of Materials
2-1-1 Reinforced Materials
Raw mat surrounding the date palm tree stem was collected from a date palm farm (Berhi type) in Iraq. The fibers were separated from the meshes manually then washed with a distilled water to remove the contaminants and adhering dust and dirt. The extracted date palm fibers were air-dried for 24 h at 25 ''C then submerged in salt water (3.5% NaCl) for 48 hour, then exposure to drying temperature in oven (50''C) for a periodic time until it became dry and then were cut to the desired dimensions into equal sizes. So it became ready to use in this research. Table 2.1 summarizes the physical and mechanical properties for date palm fibers in this study.
Physical and mechanical properties for date palm
(g/cm'') Young's Modulus (GPa) Tensile Strength
(MPa) Elongation at break
Date Palm 1-1.98 2.7- 5.8 95-190 2.5-5.0
2-1-2 Treatment for Date palm
After drying, the date palm fibers immersed in maleic acid. Used American maleic (Old Dutch) in 5% constant concentration, where date palm immerses in maleic acid for 20 hours. Chemical treatment with maleic acid is necessary to remove the plant matrix surrounding date-palm fibers (lignin)
and to make date-palm fibers surface relatively rough for providing better adhesion with the polyester resin matrix by increasing the amount of matrix filling the valleys existed on the outer of the surface of the fibers.
2-1-3 Matrix Material (Resin)
The Polyester resin, which is used in this work, was in the form of transparent adhesive liquid at room temperature. The physical and mechanical properties for polyester material are summarized in Table 2.2. It is a type of thermosetting polymers which transform from liquid state to solid state with the additional of hardener to it. The hardener is (Methyl Ethyl Keton Peroxide Mekp), which is form of transparent liquid add to polyester resin in percentage (2 grams) for each (10 grams) of resin materials at 25''C. The drying time for samples one and two is about 15 minutes, while the drying time for samples three and four is about 30 minutes.
Physical and Mechanical properties for polyester material .
Specific Weight Thermal conductiviy
W/m''C Specifc Heat
J/Kg.K Coefficient of Thermal Expansion
10^-6 Tensile Strength
MPa Percent El.
1.15 0.17 710-920 100-180 41.4-89.7 < 2.6
2-2 Sample Preparation
Use simple hand lay-up method to prepare the composite samples as shown in Figure 2.1, The die made from wood with dimensions were 125 mm length, 90 mm wide and 20 mm thick. The date palm fibers (40% from matrix material with hardener) were placed on the female die, the mixing for resin with hardener it slow and continue for 8-10 minute until the mix is becomes homogenous and then the mix poured on die in the form of stream from one side. The prepared composite sample was then cured for 1 h in oven and the final shape of composite sample was obtained.
Fig. 2.1. Hand lay-up method
Specimens of suitable dimensions are cut using a diamond cutter for testing. Almost care has been taken to maintain homogeneity of the composites samples.
2-4 Erosion Test
Erosion test was accomplished by using erosion device In this test, the erosion percent of the composite samples in different directions (vertical and transverse) is computed.
2-4-2 Test Procedure
The test was run at the upper tank that contained the water tube and the nozzle fixture while the sample is fixed. The water concentrate on the sample by the tube water throw nozzle with specific diameter from the lower tank by plunger submerged in water push water with press and high flow rate according to the plunger capacity. All tests were carried out at a 40 m/sec impingement speed at 25''C. The change in weight of the composite material determined by weighing the samples before and after the erosion test by using a balance with an accuracy of 1*10^-4 . Each erosive test was performed twice and average erosion rate values were calculated.
2-5 Scanning Electron Microscopy
Scanning Electron Microscope (SEM) JEOL JSM-5600Awas used to study composite morphology, fiber morphology, fiber morphology, and fiber-cross section structure of the eroded surface of the composite samples. The samples were frozen in liquid nitrogen, mounted, coated with gold/palladium to enhance the conductivity of samples and observed using an applied voltage of 10 KV.
3. Results and discussions
The results obtained from this experimental study evaluate the effect of erosion on the composite materials.
3-1 The weight gain for Composite Samples in different direction after erosion
The weight gain can be calculated by using the formula:
Weight gain = W ' Wo / A 
W: the weight of specimen for each periodic time.
A: surface area of the specimen.
Different models have been developed in order to interpret the behavior of water absorption of the materials. For one-dimensional absorption of water, each specimen is exposed on both sides to the same environment and the total moisture content G was calculated as follows [8, 11, 30, 31]:
Where mi is the initial weight of moisture when the material is fully saturated, in equilibrium with its environment. D is the diffusivity of mass in the composite. This is an effective diffusivity since all the heterogeneities of the composites have been neglected. h is thickness of specimen and t is the time and J is the summation index. The coefficient of diffusion is an important parameter in Fick's law. The liquid diffusion into another material is commonly described by Fick's law [8, 11, 32].
where C is the concentration of the liquid, D is diffusion coefficient of the material absorbing the liquid, t is time, and X is the distance term.
Solving the diffusion equation for the moisture weight, and rearranging in terms of the percent moisture content, the following relationship is obtained :
Where Mm is the equilibrium moisture content of the sample. Using the weight gain data of the composite material with respect to time, the coefficient of diffusion can be calculated using the following formula :
Where d is sample thickness in mm and t70 is time taken to reach 70% saturation in seconds .
To correlate the experimental behavior of water uptake of the theoretical behavior, computer modeling by 3 Dimension Finite Difference Method based on Fickian Diffusion [11, 33] was used and computed with experimental results. The water absorption in this composite material is in excellent agreement with theoretical behavior predicted by the model . It was noticed that the absorption of water is thus demonstrated to be Fickian behavior in this composite material.
The coefficient of absorption or solubility S is defined as:
S = Me / Mi (6)
Where Me is the water weight taken up at equilibrium and Mi is the initial weight of the sample. The values of S for individual samples were calculated and their average value was found to be 0.17.
Similarly coefficient of permeability P, which represents the combined effects of sorption and diffusion, is defined as :
P = D S (7)
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