Synthesis and Characterization New Polyurethane Membrane From Hydroxylated Rubber Seed Oil

Marlina¹, Saiful¹, Rahmi¹, Sitti Saleha¹ and Salfauqi Nurman²

¹Chemistry Department of Mathematics and Sciences Faculty, Syiah Kuala University, Banda Aceh, Indonesia.

²Agriculture Industrial Technology Department  of Agriculture Technology Faculty, Serambi MekkahUniversity, Banda Aceh, Indonesia.

Corresponding Author E-mail: marlina_rachman@yahoo.com

DOI : http://dx.doi.org/10.13005/ojc/330122

New polyurethane membrane from hydroxylated rubber seed oil has been preparedin this study. Hydroxylated process of rubber seed oil improved 135.30%  of hydroxyl number and decreased 73.91% of iodine number of rubber seed oil. Optimum polyurethane membrane was obtained at the composition of hydroxylated rubber seed oil:hexamethylene-1,6-diisocyanate was 5:7 v/w. The membrane was homogeneous, dry, smooth, slightly stiff and brownish yellow. The flux and rejection factor of the membrane were  0,544L / m².h.bar and 98.86%, respectively. FTIR spectra indicated the formation of urethane bond (N-H at 3308 cm^-1). Thermal analysis showed two stages of decomposition at 223^oC and 386^oC. The membrane exhibited a strong and elastic properties with a tensile strength of 1.13 kgf/mm2 and elongation 215.36%.

Rubber seed oil; Hexamethylene-1,6-diisocyanate; Synthesis; Polyurethane membrane; Characterization

Introduction 

Indonesia is an agricultural country which has a wide range of biological, one of them is rubber plant (Heveabrasiliensis)¹. The products of rubber plant are only put emphasis on the processing of latex and trunks, while other products such as its seed has not received more attention. Rubber seeds are the byproducts of rubber plantations which can be utilized for biodiesel^2,3. To improve the diversification of plant products,  an effort is needed to increase the added value of these plants.

Rubber seed contains 40.76% (w/w) of oil. Rubber seed oil contains 38.59% of oleic acid, 41.06% of linoleic acid, 10.43% of stearic acid and  9.92% of palmitic acid. Rubber seed oil has a hydroxy number 40.33 mgKOH/g and 154.05 gI₂/g of iodine number⁴. Rubber seed oil has a color (lovinbond) 22R; 23,2Y, 0.916 of specific gravity (30 ° C), 43.62 mg KOH/g of acid number, free fatty acids 21.4, 202.91 mg KOH/g saponification number and 136.21 g I₂/100 g of iodine numbers⁵.

Hydroxylation process is the addition of a hydroxy group into a compound by performing addition -OH group to the double bond⁶. The reaction takes place in two stages, where the first stage is protonated alkene to produce a carbocation. The second stage is nucleophilic addition to the carbocation. Both of reactions take place according to Markovnikov rule. Hydroxylation process in vegetable oils can increase the concentration of hydroxyl⁶.

In our previous research, polyurethane membranes have been prepared by using vegetable oil. The free fatty acids and oxidized fatty acids of  castor oil were used as a source of hydroxyl and 2,4-toluene diisocyanate (TDI) as the source of isocyanate⁷. polyurethane membrane of rubber seed oil with HMDI have to be synthesized, the resulting membrane has a homogeneous, dry, elastic, brownish yellow, wavy with the  flux and  rejection factor were 0544 L/m².h.bar and of 100%, respectively⁴. Therefore, in this study hydroxylated rubber seed oil and hexamethylene-1,6-diisocyanate (HMDI) were used for polyurethane membrane preparation.

Materials and Methods 

Materials

The raw material was rubber seed taken from the plantation residents in the village Gunong Kleng, Meureubo, West Aceh, Aceh Province, Indonesia. Chemicals used were hexamethylene-1,6-diisocyanate (HMDI) purchased from Merck, chloroform, acetic acid, KOH, KI, Na₂S₂O₃, starch indicator, n-hexane, NaCl, H₂SO₄, and methanol were purchased from Sigma–Aldrich.

Instrumentation

FTIR spectra of rubber seed oil and polyurethane membrane used (Agilent resolution pro cary 630 FTIR spectrometer), membrane morphology viewed using SEM (Tabletop microscope 3000), thermal analysis of polyurethane membrane using TGA and DTA (SDT Q600) and mechanical strength of the membrane was tested with (Control computer series 10-100 KN)

Rubber seed oil extraction process

Rubber seeds were cleaned, peeled, dried at room temperature and crushed into powder. Rubber oil extraction was carried out by n-hexane at 80° C for 4 hours. A rotary evaporator was used to separate the rubber seed oil and n-hexane at 60 ° C for 30 minutes.

Hydroxylation process of rubber seed oil

25 mL of rubber seed oil was added to 2.5 mL of H₂SO₄ 35%, then stirred for 90 minutes, and then chloroform was added to separate the remaining water phase.  5 grams of anhydrous Na₂SO₄ was added to the organic phase and then filtered. The filtrate obtained was evaporated using a rotary evaporator and the oil obtained was characterized.

Preparation of polyurethane membrane

5 mL of hydroxylated rubber seed oil and 1,6-hexamethylene diisocyanate (with a series of composition) were mixtured by using a magnetic stirrer at a temperature of 90-100°C for 60 min. Then poured in a petri dish, cured an oven at a temperature of 115-120°C for 8 hours. Once the membrane was formed, then the membrane was released in the flowing water with the aid of a spatula.

Result and Discussiong

Characterization of hydroxylated rubber seed oil

Hydroxylation process of rubber seed oil was conducted by using water in acidic solutions. H⁺ as a catalyst break the double bond of rubber seed oil resulting in the addition reaction with -OH groups from water. The proposed of addition reaction of linoleic acid can be seen in Fig 1.

Hydroxylated rubber seed oil has a hydroxyl number  94,903 mgKOH/g and iodine number 40.185 gI₂/g. There was an increase for the hydroxyl number and a decrease in iodine number of 40.333 mgKOH/g and 154.052 gI₂/g⁴. Hydroxylation process has improved hydroxyl number amount up to 135.30%.

FTIR spectra of rubber seed oil and hydroxylated rubber seed oil are shown in Fig 2. The -OH groups of  hydroxylated rubber seed oil at wave number 3400 cm^-1 was appear broader comparing to the spectrum of rubber seed oil. Peak of -CH alkene bond at wave number 3010 cm^-1 in the spectrum of rubber seed oil seems clearer with high intensity comparing the spectrum of hydroxylated rubber seed oil. It shows that the hydroxylation process of rubber seed oil has reduced the number of double bonds and those results also supported by reduction of  iodine number.

Figure 1: The Proposed of addition reaction Click here to View figure

Figure 2: FTIR spectra of  (a) rubber seed oil and (b) hydroxylated rubber seed oil Click here to View figure

Polyurethane membranepreparation

The preparation of a polyurethane membrane from hydroxylated rubber seed oil and hexamethylene-1,6-diisocyanate through addition reaction can be seen in Fig 3. The visual results of the membrane with HMDI composition is shown in Table 1.

Table 1 shows the visual of polyurethane membrane with composition variation of HMDI.The optimum composition ofhydroxylated rubber seed oil and HMDI was 5: 7 v / w with a polymerization temperature of 90-100°C and a curing temperature of 115-120°C. It showed better results than the other variations. The obtained polyurethane membrane was homogeneous, smooth, dry (not greasy), a little rigid and brownish yellow

Characterization of polyurethane membrane

Filtration processes was done by using mercury-contaminated water. The membrane surface area was 22.051 cm² with a pressure of 20 bar and a filtration time of 20 minutes. The results of the flux and rejection factors can be seen in Table 2.

Rejection factor was obtained by calculating the concentration of mercury in the feed and permeate using atomic absorption spectrophotometry (AAS). Decoys are used in the form of mercury-contaminated water with a mercury concentration of 0.0703 ppb, resulting permeate contains 0.0008 ppb mercury. So that the resulting rejection factor was 98.86%.

Table 1: Variations in composition in the preparation of polyurethane membrane

¹ HRSO : Hydroxylated rubber seed oil

² HMDI : Hexamethylene-1,6-diisocyanate

Figure 3: Suggested Hydroxylated reaction between linoleic acid and hexamethylene-1,6diisocyanate Click here to View figure

Table 2: Results of flux and rejection factor