Tolylene 2,4 Diisocyanates (TDI) of analytical grade (95%), Dibutyltin dilaurate (DLDBT), Methyl isobutyl ketone (MIBK) is purchased from Sigma- Aldrich, Germany. Castor oil (CO) is procured from local markets. Castor oil is only the natural oil polyol available in the market, which is produced directly from a plant sources without chemical modifications. An alga is extracted from the sea rack, which is glued to the rock surface. The algae is dried and crushed into powder form. Before mixing algae with polymer, it was screened by sieve mesh size 300 micro to get uniform particle size. The filler density is estimated as 1.27 g/ml.
2.2 Synthesis of PU/Algae biocomposites
50 ml of methyl iso butyl ketone (MIBK) solvent is placed in the necked round bottom flask. Calculated amounts of tolylene 2,4 disocyanates (TDI), castor oil (CO) and 3 drops of catalyst dibutyltin dilaurate (DLDBT) are added to MIBK solvent as per standard procedure (Madhukar, et al., 2015). The flask is then kept on digital hot plate fitted with a condenser. The temperature is maintained between 60–70oC and stirred at 1200 RPM. The reaction between the aromatic TDI isocyanates, which is having two isocyanates groups (NCO) and a hydroxyl group (present in the castor oil) in the presence of catalyst DLDBT produce urethane groups as shown in the equation 1.
The algae powder is added to the PU solution after 30 minutes of mixing with different polymer-algae weight ratios (100/0, 97.5/2.5, 95/5, 92.5/7.5 and 90/10). PU/algae is stirred again for 1 hour. The resulting viscous solution poured into clean glass mold of dimension of 20×10×4 cm to get the uniform polymer film. The solution is cooled and dried slowly under ambient temperature overnight. The created PU sheet in the glass mold has been post cured in the electric oven at 60oC for 5 hours. The prepared biocomposite sheets are taken out and stored for characterization and experimentations.
2.3 Collection of OPW
Oil Produced water (OPW) is collected from (Oxy-Oman) site (Makizina) for this experimental purpose. Mukhaizna field is located in Oman’s south central interior and it is producing very high viscosity oil. The initial boron and other multi component concentrations areestimated using plasma atomic emission spectrometry (ICP). The initial boron concentration in the produced water is obtained as 6.44 mg/l. The initial pH value of OPW sample is measured as 7.19.
2.4 PU/Algae Characterization
ASTM D792–08 method is used to determine the experimental density of the specimens. The weight of the specimen is taken in the air and in immersed water at room temperature to determine the specific gravity. Accordingly calculated the density of PU/Algae polymer specimens. The theoretical density is calculated for thecomposites by the weight additive principle as shown in equation 2Madhukar, et al., 2015).
ρ = ω1+ω2 (2) Where ρ is the density of composite, ω1, ρ1, ω2, ρ2 are the weight fraction, thedensity of the filler and neat polymer respectively.
The chemical resistance of PU/Algae polymer composites is studied in the various chemical reagents such as acids, basis, salts and organic solvents. Uniform surface area of PU/Algae composites istaken and immersed in the prepared chemical solutions for 7 days under laboratory environment. After 7 days, the specimens are removed and wiped with tissue papers and weighted. Then, the percentage weight changes are calculated. Also, surface to mass of the specimens are estimated. The morphological behavior, chemical composition and crystalline structure of the PU/algae composites is investigated by using scanning electron microscopy (SEM) technique with an operating voltage of 15 kV, magnification of 1000x and quality resolution of 10 microns. FTIR spectroscopy is used to analyze the physiochemical properties of synthesized PU/Algae composites as per standard procedure in the range of wave number 600 to 4000 cm–1 (Marek, 1993).
A thermal property of polymer is investigated by using thermal gravimetric analysis (TGA) in order to determine the test conditions and the behavior of the polymer with increasing temperature. The sample is cut into a small piece and after that loaded into sample ceramics pan to complete thermal analysis. The nitrogen gas grade 5 is used as purge gas and it is supplied at aconstant flow rate 100ml/min. The thermal analysis in TGA is started in the temperature range between 32 and 38°C and the final temperature considered for this analysis is 800°C. The heating rate is customized at 10°C/min. The thermograms are interpreted for all composites by using TA instrument explorer software universal V4.7A.
2.5 Boron adsorption characteristics
The treated oil produced water (OPW) is analyzed to examine the boron adsorption efficiency for different PU/algae composites. The adsorbent dosage is fixed as 1 gram in 50 ml of OPW for all PU compositions. The agitation is adjusted at 100 RPM to assist the contact between adsorbent and theuntreated OPW for 72 hrs. The final boron concentration is obtained using plasma atomic emission spectrometry (ICP) and then the removal efficiencies are estimated.