Introduction of control release urea (CRU) in agriculture provides a good significant impact on the environment and economy. The main purpose of controlling the release of urea is to minimize the loss of nutrients to the soil through leaching and to increase the efficiency of nutrient use. There are many types of coating material that have been introduced and used for urea control.
For this research, biopolymer composite material was developed as a coating material because biopolymer composite is more environmentally friendly compared to other coating materials. However, the combination of biopolymer coating materials, which are starch, polyvinyl alcohol (PVA) and citric acid, does not ensure a good uniform release of urea. The uniformity of the coating of the coated urea is crucial to allow the uniform release of urea.
The good coating uniformity of thin film technique should have good wettability properties of biopolymer coating material. The aim of this research is therefore to study the wettability properties of biopolymer coated urea with addition of fillers.
- Background Study
- Problem statement
- Objective
- Scope of Study
- Feasibility of Project
Thus, this experiment will investigate the presence of different fillers in the biopolymer coating material, which are Bentonite, Kaolin, Bentonite Nanoclay and Nanoclay Halloysite. The study of wettability for a single drop of biopolymer with the addition of fillers will help to find the best composition of fillers. The aim of the project is to study the wettability of biopolymer coated urea using variants of fillers.
The experiment will use starch, polyvinyl alcohol (PVA) and citric acid with different fillers; Bentonite, kaolin, bentonite nanoclay and halloysite nanoclay to control the wettability properties of the biopolymer coating solution. The wettability characterization is measured and analyzed with the optical contact angle device (OCA 20) to measure the dynamic contact angle. This project was completed to investigate the wettability property of biopolymer modified with different fillers as a coating material for coated bridges.
The main objective is to discover the effect of different fillers on the wettability property of the biopolymer mixture. A good wettability property will ensure good dispersion, which is critical in the coating process as well as in the Controlled Release Urea (CRU) manufacturing process.
Significant of Control Release Urea
Fillers
- Bentonite as fillers
- Kaolin
- Nanoclay Composite Fillers
In addition, bentonite's other properties are good for hydration, swelling, water absorption, viscosity and thixotropic, making it a valuable material for a wide range of uses and applications, including pharmaceuticals (Collins, 2014). Much of bentonite's usefulness in the drilling and geotechnical engineering industries comes from its unique rheological properties (Hosterman, 1985). Moreover, the application of sodium bentonite to maximize the filler and pozzolanic effect of stabilized peat helps to improve peat in the geological condition of swampy area, especially for highway construction (Wong, Hashim, & Ali, 2013). Therefore, the wide application of bentonite as a filler can possibly be a good filler for urea coating of composite material.
In addition, the particle size distribution of the kaolin helps control the packing density, so it will give a good spread in the paint. Kaolin is hydrophilic and can be dissolved in water, but it can also be chemically modified to make it hydrophobic. Its good property can be tested as a potential filler for urea coating composite material.
The use of nano-filled polymer matrix provides significant improvements in mechanical and physical properties even by introducing small amounts of filler (<10 wt.%) (Ferreira, Reis, Costa, Richardson, & Richardson, 2011). The addition of nanols has been found to help increase the wettability in the contact angle (Hegde, 2009). Nanoparticles such as nanoclays can be used to modify the chemical composition of the surface and will later affect the intermolecular interactions between solid and water such as wetting behavior (Manoudis & Karapanagiotis, 2014).
Wettability characterization of composite
The interfacial tensions are solid-vapor γsv, solid-liquid γsl, and liquid-vapor γlv and θ is the contact angle. According to Myers (1946), there are four direct contact angle measurement techniques that are sissile drop. The commonly used method for measuring contact angle is the sessile drop method which occurs by measuring the angle between the solid surface and the tangent to the drop profile at the drop edge during deposition of a liquid drop on a solid surface (Njobuenwu, Oboho, & Gumus, 2007). .
In addition, the maximum spreading behavior is another character that should be identified in the moisture characterization. The maximum spreading behavior can be measured by identifying the maximum spreading diameter, where Dt at a given time exceeds the initial diameter of the droplet, Do (Samsudin, Ku Shaari, Man, & Sufian, 2012). According to Samsudin et al. 2012) when the liquid droplet impinged on the urea substrate produced the least static, indicating that maximum spreading behavior was achieved.
The better wettability ensures an even distribution of the liquid and the quality of the coating. A wettability relationship exists when a low contact angle will produce a high spreading diameter factor and a low surface tension, indicating good wettability properties.
Experiment Procedure/Approach
- Preparation of Modified Biopolymer coating material
- Preparation of Urea Substrate
- Characterization of modified biopolymer solution
- Surface tension and contact angle measurement
- Maximum spreading
The urea surface sample for urea granules is prepared in preparation for the subsequent characterization of the wettability of the modified biopolymer solution. The urea granules are melted at 130°C until the urea granules melt and become a solution in an aluminum dish. The characterization of the wetting behavior of new modified biopolymer solutions is measured using the OCA 20 measuring device (optical contact angle).
Besides that, it can also provide a representation of wetting envelopes and work with adhesion or contact angle diagram. The device is assembled with 1 ml syringe with 0.51 mm needle tip to be used to dispense the liquid with the drop size range of 2 mm to 0.06 mm (Samsudin et al., 2012). Apart from that, the device is also equipped with a high-speed camera (CCD) to capture the high-speed movement of the drop impact.
The CCD camera is capable of capturing up to 30 frames per second and the built-in software, SCA software, is used to analyze the acquired high-speed digital image data. Normally, the drop method is the standard method used to measure contact angles with the OCA20 device. From the SCA software, the image is captured by the built-in video camera in the OCA20 device.
Later the image will be snapped and the surface tension is measured with the measuring tool using the drop-pendant method. Then, for the contact angle measurement, the position of the urea substrate is calibrated to obtain the clear and sharp focus of the images. The modified biopolymer dispenses at the 2.00 µl dosing rate, so the gravitational effect can be negligible.
The surface tension calculation is calculated based on the Young-Laplace equation using these contact angle measurements (Samsudin et al., 2012). The scattering behavior is observed by calculating the maximum scattering diameter factor using the same OCA20 device. The calculation of the maximum dispersion diameter can be measured by Dt / Do, where Dt is above the initial diameter of the droplet, Do (Samsudin et al., 2012), at a given time.
Surface tension and contact angle measurement
From figure 10, we summarized and concluded the surface tension and contact angle measurements at each of percentages and types of fillers including without fillers. From the surface tension result analysis obtained, the addition of 1% Nanoclay Bentonite filler in coating solution gives the smallest surface tension compared to the other filler. In addition, only 1% and 3% Nanoclay Bentonite gives the surface tension below a non-filler coating solution with 39.92 mN/m and 46.25 mN/m, respectively.
The smallest values of surface tension and contact angle indicated that the intermolecular force between biopolymer molecules is reduced by the addition of fillers. As the intermolecular force between the molecules is reduced, the modified coated solution will become more dispersed and will have a smaller contact angle. From the result, we also found that the relationship between surface tension and contact angle is incorrect.
Both must have the same low value of surface tension and contact angle to be considered as having good wetting properties. As de Young-Dupré noted, the contact angle may be related to the work of adhesion and interfacial or surface tension. The surface tension given by the software may not be correct because the baseline indication is not accurate, but the contact angle result should have accurate values as the contact angle value can be clarified by calculating manually.
Again, based on contact angle analysis, 2%, 3% and 4% of kaolin and other fillers except Nanoclay Bentonite give good indication of contact angle providing less than non-filler contact angle.
Spreading Diameter measurement
Based on the graph, most of the percentages of Halloysite Nanoclay fillers give the largest maximum dispersion diameter compared to other fillers. The addition of Nanoclay Bentonite filler does not give a significant improvement in the maximum dispersion diameter factor because it was drawn under the coating solution without fillers. The addition of kaolin as a filler is optimal at 2%, but other percentages give a worse coating diameter factor.
Good dispersion of the modified biopolymer is important in the coating process, where it will form a thin layer of coating material that will later ensure better uniformity of the urea grain coating. The optimal dispersion diameter factor can be explained as it shows that 3% Halloysite Nanoclay is much less viscous and spreads faster compared to other fillers. This makes the biopolymer solution less viscous and allows the biopolymer solution droplet to disperse more.
Finally, the contact angle analysis shows a significant improvement in the wetting properties of modified biopolymer after the addition of fillers except Nanoclay Bentonite.
Objective relevancy
Suggested future work for expansion and continuation
The effect of citric acid on the structural properties and cytotoxicity of the polyvinyl alcohol/starch films when cast at high temperature.
Project Flow Chart
Gantt Chart and Key Milestone
Experimental Table Matrix
