Polyurethane Membranes From Red Seaweeds For Ammonia Adsorption

. Polyurethane (PU) membranes were prepared from red seaweed ( Gracilaria sp .), castor oil, Toluene Diisocyanate (TDI), and added benzoyl peroxide (BPO) additive to improve membrane performance. The membrane is applied for the adsorption of ammonia in the solution. FT-IR analysis showed the presence of functional group N = C = O at a wavenumber of 2276 cm -1 and the O-H functional group at a wave number of 3373.50 cm -1 , indicating the urethane functional group's formation has been formed during membrane polymerization. SEM images showed the morphological structure of the PU membrane, where the more open structure of the PU membrane by the addition of BPO. The DSC and TGA results showed the membrane's thermal stability with the addition of BPO. The PU membrane has an optimum contact time for ammonia uptake of 40 minutes. The adsorption isotherm of ammonia by the PU membrane follows the Freundlich isotherm model. The adsorption capacity of the PU membrane with the addition of BPO additives was 13.2 mg/g, which shows that the adsorption capacity of the PU-BPO membrane has a better performance than a membrane without the addition of the BPO. The PU-BPO membrane could be used as an alternative method of ammonia removal.


INTRODUCTION
Membranes have been developed for various needs in the process of separating a component. Membranes are divided into several types based on their origin, and the membrane consists of natural and synthetic membranes. The advantages obtained with membrane technology include being able to be used continuously, combining membrane devices with other equipment, and separating substances sensitive to temperature changes. [1].
Membranes have various types, one of which is polyurethane. Polyurethane is a polymer with a urethane group (-NHCOO-) obtained from a diisocyanate and a polyol reaction. Polyurethanes are classified as thermoset polymers. In the manufacture of polyurethane, polyols can be sourced from vegetable oils such as rubber seed oil, palm oil, soybean oil, and castor seed oil. [2,3]. Arniza et al. has synthesized polyurethane from polyols derived from the transesterification of palm oil by adding additives in the polymerization process as a chain extender to obtain polyurethane foam with better thermal properties. [4]. Polyurethane membranes are generally made from natural materials to be easily degraded. One example of a natural ingredient that can be used is carrageenan, derived from seaweed.
Seaweed is a large macroalga and includes lower plants and lives in the sea or brackish water. The content of red seaweed is carrageenan, cellulose, protein, fat, carbohydrates, crude fiber, and water [5]. The high carrageenan content in seaweed can be used as a membrane material. Red seaweed has great potential as an alternative membrane material [6]. Currently, the community is still remarkably lacking in using seaweed, which is only as animal feed and the essential ingredient of drinks; seaweed will be used as a polyurethane component because cellulose contains several -OH (polyol) groups. Another polyurethane-forming component is castor oil. Castor oil is a vegetable oil obtained from the seeds of the jatropha plant Ricinus Communis L. Castor oil contains a high -OH group to help form polyurethane.
Another polyurethane-forming component is isocyanate. Toluene diisocyanate (TDI) is the isocyanate compound used to synthesize polyurethane. Toluene diisocyanate is a colorless to pale yellow liquid that has a pungent odor [7]. The addition of additives will improve the performance of the polyurethane membrane. Additives are materials used to improve the quality and properties of polymer products. The addictive substance used in this study is benzoyl peroxide. Benzoyl peroxide is a peroxide compound that is an initiator and a source of free radicals in the polymerization process [8,9].
One source of water pollution is ammonia. Ammonia waste is generally produced from palm oil plantation waste. The content of ammonia will affect the life of biota and can cause a foul odor if it has flowed into the river. Therefore, it is necessary to develop processing methods [10]. Adsorption is one of the most widely used methods to remove waste because this method is easy, efficient, flexible, and does not require high costs. Polyurethane membranes have been applied in various separation processes and their ability as an adsorbent has been studied by many experts [11]. This study wants to see the ability of the PU membrane to adsorb ammonia in water.

Chemicals and Equipment
The materials used in this study were red seaweed taken from pond waters in Kaju, Aceh Besar, Aceh, distilled water, toluene diisocyanate (TDI), methanol, 0.1 N NaOH, NH4Cl, dioxane and benzoyl peroxide (BPO) were purchased from Sigma-Aldrich Co. (USA).
The equipment used in this research are glass, oven, hot plate, blender, fine gauze, Fourier Transform Infra-Red (FTIR), Scanning Electron Microscope (SEM), Differential Scanning Analysis (DSC), Thermal Gravimetric Analysis (TGA) and Tensile Test.

Making Seaweed Flour
The procedure for making seaweed flour refers to the research of Marlina (2010). Red seaweed smells fishy and must be soaked in fresh water for 24 hours. After cleaning, the seaweed is boiled using aquadest with a ratio of seaweed to aqua dest of 1:15 (w/v). The seaweed was crushed in a blender and hot aquadest was added in a ratio of 1:30 (w/v). The result is filtered with gauze. The residue obtained was soaked by adding methanol in a ratio of 2.5:1 (w/v) for 24 hours and filtered with gauze. The filter results obtained wet seaweed flour, then dried at room temperature for 24 hours and milled using ball milling to produce a sample that is shaped like flour and green in color. To determine the presence of carrageenan content in seaweed flour, a qualitative analysis test of seaweed flour was carried out referring to the research of Marlina (2010). Red seaweed was dissolved in 0.1 N NaOH and then stirred to form a gel indicating the presence of carrageenan.

Polyurethane Membrane Manufacturing
Polyurethane membranes were synthesized from seaweed flour as a source of polyol and toluene diisocyanate (TDI) as a source of -NCO. In this study, the dope solution (membrane base material) was made from 0.2 grams of seaweed flour, added 1 gram of castor oil and then dissolved with 10 mL of dioxane solvent with variations in concentration to TDI of 1, 2, 3, 4 and 5 mL v/v). The membrane was printed on petri glass and allowed to dry at room temperature for 24 hours. After drying, the membrane was soaked in warm water until the membrane was separated from the Petri dish glass. To improve the adsorption performance of polyurethane membranes, BPO additives were added with concentrations of 0.01, 0.02 and 0.03 grams. The membrane was made from 0.2 grams of seaweed flour, added 1 gram of castor oil and then dissolved with 10 mL of dioxane solvent with an optimum TDI concentration. The membrane was printed on petri glass and allowed to dry at room temperature for 24 hours. After drying, the membrane was soaked in warm water until the membrane was separated from the petri dish glass.

Mechanical Properties
Polyurethane membranes with 1 mL TDI and BPO additive polyurethane membranes with variations of 0.01, 0.02 and 0.03 grams were tested for tensile strength and % elongation. The tensile test was carried out at the Physic Laboratory of Syiah Kuala University.

Fourier Transform Infra-Red (FTIR) Spectroscopy
Optimum TDI polyurethane membrane and polyurethane membrane with the addition of optimum BPO were cut to a size of 1x1 cm and characterized their chemical structure using Fourier Transform Infra-Red (FTIR) Spectroscopy. The range of wave numbers used is 4000 -450 cm -1 .

Scanning Electron Microscope (SEM)
Optimum TDI polyurethane membranes and polyurethane membranes with the addition of optimum BPO were cut to a size of 1x1 cm and characterized using a Scanning Electron Microscope (SEM) to view the membrane surface with a magnification of 1,000x and 10,000x.

Differential Scanning Calorimetry (DSC) and Thermal Gravimetry Analysis (TGA)
Optimum TDI polyurethane membrane and polyurethane membrane with the addition of optimum BPO were tested for thermal analysis using DSC and TGA.

Determination of Optimum Contact time for ammonia adsorption
Membranes with the optimum TDI concentrations and membranes with BPO concentrations of 0.01, 0.02 and 0.03 grams. cut and put into a beaker. A 25 mL of ammonia solution was put into a beaker containing the membrane. Then allowed to stand at room temperature with time variations of 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 minutes. 10 mL of the adsorption solution was taken and 3 mL of Nessler's reagent was added and allowed to stand for 5 minutes and then the absorbance value was measured using a UV-Vis spectrophotometer.

Concentration variation in ammonia adsorption
The membrane adsorption capacities were evaluated with variations in the concentration of ammonia solution. The membrane was cut and the weight of the membrane was weighed and then put into a beaker. A total of 25 mL of ammonia solution with various concentrations of 20, 25, 30, 35, 40, and 45 ppm were put into a beaker containing a membrane in the optimum contact time. Ten mL of the aliquot solution was taken and 3 mL of Nessler's reagent was added and allowed to stand for 5 minutes and then the absorbance value was measured using a UV-Vis spectrophotometer.

Red Seaweed Flour
Samples of red seaweed have a fishy smell, and they need to be soaked for 24 hours to remove the fishy smell. The red seaweed sample was boiled for 15 minutes so that it was easier to grind it using a blender until it became a coarse red seaweed slurry. The coarse red seaweed slurry is then soaked using methanol to attract unwanted substances so that only carrageenan is produced. Then the residue obtained was dried and to produce fine red seaweed flour, a ball milling process was carried out for 15 hours. The carrageenan content in red seaweed flour can be identified by conducting a qualitative analysis using NaOH to detect the presence of carrageenan as a source of polyurethane membrane formation. The results obtained were samples of red seaweed flour formed a gel which indicated a positive presence of carrageenan in red seaweed flour. Gel formation is caused by a double helical structure at low temperatures. Kappa carrageenan is very sensitive to NaOH and will form a strong gel when reacted with NaOH [12]. The Carrageenan identification reaction using NaOH reagent is as follows:

POLYURETHANE MEMBRANE MANUFACTURE
The red seaweed flour that has been produced is used as a component in the manufacture of polyurethane membranes where the polyol (-OH) content in red seaweed flour will bind to the isocyanate group owned by TDI. The chemical reaction between red seaweed flour and TDI alone does not form a strong, homogeneous polyurethane membrane. The process of making PU membranes from red seaweed flour requires the addition of castor oil to form a perfect PU membrane. Because the addition of castor oil is an essential factor in producing PU membranes from red seaweed flour. The composition of castor oil used in this study is 1 mL. In addition, different concentrations of TDI were carried out, namely 1, 2, 3, 4, and 5 mL (v/v), to obtain the best membrane PU.
The results obtained were a membrane with a composition without TDI and castor oil did not form a membrane and was shaped like flour, a membrane with a composition of 0 mL TDI and castor oil produced a hard membrane, difficult to remove from the mold and shaped like flour after being removed from the mold. The membrane with the composition of 1 mL TDI and castor oil produced a very good membrane physically, elastic but still slightly brittle. The membrane with the composition of TDI 2, 3, 4, 5 mL and castor oil produced a membrane that has physical properties that are hard, easy to crack, stiff and very brittle. Based on the results of polyurethane membranes with variations in the concentration of TDI, it can be seen that the greater the concentration of TDI added, the more fragile the resulting membrane can be. This is because the hard segment of the polyurethane membrane is formed more than the soft part so that the resulting membrane is less elastic or brittle. .
The previously produced membrane with a TDI concentration of 1 mL has the best (optimum) composition compared to other TDI composition membranes. However, the membrane structure still has poor physical properties, so adding BPO additives is necessary. The addition of BPO aims to improve the performance of the polyurethane membrane. BPO was added with different concentration variations, namely 0.01, 0.02, 0.03, and 0.04 grams.
Polyurethane membranes added with BPO at concentrations of 0.01, 0.02, and 0.03 grams produced a homogeneous, elastic membrane and was easy to remove from the mold. This shows that the addition of BPO produces a membrane with better physical properties than the membrane without the addition of BPO. However, the membrane, adding 0.04 grams of BPO resulted in a rigid membrane. This shows that a membrane with a high BPO composition of 0.03 grams will produce a membrane with poor physical properties. The resulting membrane was tested for characterization

Tensile Strength
The tensile test is a method used to determine the strength of the membrane against external forces that can damage the membrane. Tensile testing is carried out by applying a force in the opposite direction to the membrane, refers to ASTM D-368. The results of the analysis of the tensile strength of the PU membrane can be seen in Figure 2. The optimum TDI PU membrane has a tensile strength of 7.50 Kgf/mm 2 and is slightly elastic with an elongation percentage of 7.70. The membrane adding 0.01 gram of BPO has a tensile strength of 5.58 Kgf/mm2 and is more elastic with the percentage of elongation obtained at 21.80. The membrane adding 0.02 gram of BPO has a tensile strength of 4.04 Kgf/mm 2 and is more elastic with the percentage of elongation obtained at 21.80. The membrane, with the addition of 0.03 gram of BPO has a tensile strength of 7.63 Kgf/mm 2 and is slightly elastic with a percent elongation obtained of 13.90. Based on these data, the membrane with the addition of 0.03 gram of BPO produces good tensile strength, so it can be applied to the separation process using higher pressure.

Fourier Transform Infrared (FT-IR)
FT-IR characterization determines the functional groups present in a material and proves the formation of polyurethane bonds. The FT-IR test was conducted on the optimum polyurethane membrane and 0.03-gram BPO polyurethane membrane. The resulting FTIR spectrum overlaps due to the two polyurethane membranes having the same functional group but different intensity.

Scanning Electron Microscope (SEM)
SEM characterization on membranes serves to determine the surface morphology of a material. The composition of the PU membrane printing solution greatly influences the structure of the PU membrane. The composition of the PU membrane printing solution itself is determined based on the chemical reaction of polyurethane bond formation [14]. SEM images were analyzed for PU membranes with optimum composition. PU membrane SEM test results of red seaweed flour are shown in Figure 4.
The SEM Image in Figure 4 shows the differences in structure and morphology of the PU and PU-BPO membranes. The PU membrane has a denser structure and the formation of flakes on the surface of the membrane. In comparison, the PU-BPO membrane has a more open and porous membrane surface structure. Both membranes did not find macrovoid formation indicating a PU membrane with a strong structure, as evidenced by the results of the tensile strength and elongation analysis. . the optimum polyurethane membrane was endothermic at a temperature of 326.09 o C, at that temperature the water content, dioxane solvent, and castor oil were removed from the optimum polyurethane membrane. At a temperature of 355.07 o C, an exothermic process occurred, indicating that the polyurethane membrane was starting to decompose or be damaged. This is evidenced in the TGA graph, where there is a weight loss of 99.56% on the optimum polyurethane membrane. Meanwhile, the polyurethane-0.03 BPO membrane was endothermic at a temperature of 331.50 o C at that temperature; the water content, dioxane solvent and castor oil were removed from the 0.03 BPO polyurethane membrane. At a temperature of 356.18 o C, an exothermic process occurs, indicating that the membrane is starting to decompose or be damaged. This is evidenced in the TGA graph, where a weight loss of 96.53% on the 0.03 BPO polyurethane membrane. Time is one of the factors that affect adsorption. The effect of contact time was carried out by varying the time (5,10,15,20,25,30,35,40,45, and 50) tested on the optimum polyurethane membrane and polyurethane membrane with the addition of BPO (0.01; 0.02 and 0.03 grams). The concentration of the NH3-N solution used in the adsorption test was 25 ppm, because it was adjusted to the concentration of NH4 + in palm oil liquid waste. The results of adsorption on the effect of contact time can be seen in Figure 6. Figure 6 (a) shows the adsorption data obtained, namely an increase in adsorption up to 40 minutes with an optimum adsorption capacity of 64.3% with an adsorption capacity of 12.2 mg/g. .6%, and 70% with adsorption capacities of 12.7 mg/g, 12.8 mg/g, and 13,257 mg/g respectively. The presence of an active site on the membrane caused the increase in membrane adsorption of ammonia. As the contact time between the membrane and ammonia increases, the active site decreases, decreasing adsorption until it reaches an equilibrium position between the adsorption and desorption rates of ammonia at 45 and 50 minutes. So it can be concluded that the 40th minute is the optimum time for each membrane. The membrane with the addition of 0.03 gram of BPO, had a higher percent adsorption so that the membrane would be used for further adsorption processes. Therefor, ammonia adsorption on the PU-BPO membrane has a specific isotherm pattern, according to its adsorption properties. The adsorption isotherm serves to determine the maximum adsorption capacity. Based on calculations for the Langmuir and Freundlich isotherms, the adsorption isotherm model shows that the NH4 + adsorption process is closer to the Freundlich isotherm and comparable with reported in literature [14,15].
Polyurethane membrane with BPO concentration and optimum contact time will be used to test the effect of concentration. Variations in the solution concentration used were 25 ppm, 30 ppm, 35 ppm, 40 ppm, and 45 ppm. The membrane adsorption was carried out at the optimum contact time previously obtained, which was 40 minutes. The adsorption results on the effect of concentration can be seen in Figure 6(b).  Figure 7 was illustrated that the adsorption capacity decreases as the ammonia concentration increases. The most significant adsorption percentage occurred in a solution with a concentration of 25 ppm, total ammonia removal of 81.1%, and an adsorption capacity of 15.358 mg/g. Furthermore, increasing concentration causes a decrease in the total removal of ammonia and the adsorption capacity of the membrane. This decrease is due to the PU-BPO membrane having the maximum active side that ammonia can access. The adsorption capacity can be increased by determining the optimal ratio between the adsorbent and analyte. However, the ability of the PU-BPO membrane to reduce ammonia in water is relatively promising, and carrying out a two-stage adsorption process will enable the PU-BPO membrane to remove ammonia levels in water, reaching 99%.

CONCLUSIONS
A red seaweed-based polyurethane membrane with the addition of benzoyl peroxide has been successfully made, with the composition of red seaweed, TDI, castor oil, and benzoyl peroxide, namely 0.2: 1: 1: 0.03 (w/v/w). The addition of benzoyl peroxide (BPO) to the polyurethane membrane makes the surface of the membrane more open and increases the performance of the polyurethane membrane in the adsorption of NH3-N. Polyurethane membranes derived from red seaweed can be an alternative for removing ammonia.