Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation

Transcription

1 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon*, M.N. Mohamad Ibrahim*, I.A. Rahman ** and A.A. Abdullah*** Chemical Engineering, School of Engineering and Information Technology, Universiti Malaysia Sabah, UMS Road, Kota Kinabalu, Sabah, Malaysia *School of Chemical Sciences, Universiti Sains Malaysia, Penang, Malaysia **School of Dental Sciences, Health Campus, Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia ***Malaysian Institute Pharmaceutical & Nutraceutical, MOSTI, Bayan Lepas 11900, Penang,Malaysia Received: 20 July 2011, Accepted: 7 September 2011 Summary In this study, synthesized polyols from refined cooking oil, one of the ingredients in producing polyurethane (PU) foam, were investigated. The effects of reaction time, ph and type of solvents used on the properties of the polyols were characterized by using gas chromatography mass spectrometry (GC-MS), Fourier transform infrared (FTIR) spectroscopy and gel permeation chromatography (GPC). Further studies were carried out by using the synthesized polyols in combination with other chemicals for PU foam formation. The characterizations of the PU foams were performed through chemical, morphological and thermal analyses. The results showed that the polyols were synthesized successfully from refined cooking oil by using epoxidation and the hydroxylation process. 50% of the unsaturated fatty acids in the refined cooking oil were converted to saturated fatty acids and hydroxyl compounds as the reaction time increased up to five hours. However, the chemical contents in the polyols did not show significant changes as the ph value increased from ph3 to ph7. Using different types of solvent in the process showed that the hydroxyl content of the polyols ranged between 57 to 69 mg KOH/ g, with M w in the range of to g mol -1. The results also revealed that not all the synthesized polyols were suitable for *Corresponding author: Coswald Stephen Sipaut, css@ums.edu.my Smithers Rapra Technology, 2012 Cellular Polymers, Vol. 31, No. 1,

2 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah PU foam formation. It is recommended in this study that the minimum hydroxyl content and molecular weight of the synthesized polyol required for PU foam formation is 69 mg KOH/ g and g mol -1 respectively. The properties of PU foam are highly dependent on the polyol and the water (blowing agent) content. Keywords: Polyol, Refined cooking oil, Epoxidation, Hydroxylation, Polyurethane foam INTRODUCTION Polyurethanes are versatile thermoset plastics that can be made into different kinds of forms. They are produced by using polyols and isocyanate compounds as the main components and other components such as catalyst, foaming agent and surfactant. The active hydrogen containing groups react with the isocyanates to provide basic step-growth polymerization. Polyurethane foam can be divided to flexible, semi-rigid and rigid foams. The major areas of applications are furniture cushioning, mattresses, protective padding in car compartments and insulation materials in refrigerators and freezers. About 90% of the polyols used for the production of polyurethane foam worldwide are based on polyethers derived from ethylene or propylene oxides which are obtained from petrochemicals. In 1999, the total market for polyether polyols was 3.4 million tons with 95% (3.25 million tons) of which was used for polyurethane applications. The consumption of polyols is expected to follow the growth in gross domestic product (GDP) closely. The production of polyols from petrochemicals requires a great deal of energy and the process is costly and adversely affects the environment. As a result, there is a pressing need to find an alternative source of polyols for polyurethane manufacture. Lately, the use of renewable resources as a substitute for petrochemicals has gained considerable importance. There have been several attempts to produce polyols from natural oils instead of petroleum for the manufacture of polyurethane. The advantages include renewable, readily available and more environmentally friendly biobased polyols [1]. One of the early methods of preparing polyols from various vegetable oils was based on the transesterification of the fatty acid in triglycerides with polyol such as glycerol, glycerin, pentaerythritol, a-methylglucoside or sucrose. Unfortunately, premature degradation occurred in this process as a result of high temperatures and a relatively long reaction time [2]. Hydroformylation offers another method to prepare polyols whereby aldehyde functional vegetable oil that is first obtained is then hydrogenated to alcohol. Polyurethanes prepared from these polyols have different mechanical properties depending on the type of catalyst used [3]. 20 Cellular Polymers, Vol. 31, No. 1, 2012

3 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation Another alternative method to prepare polyols is based on oxidizing an olefin having a carbonyl group with molecular oxygen, followed by hydrolysis and the reduction of the acetal (or ketal) to an alcohol. Although this method appears to be complicated and must be run at high pressures, good yields are reported. Petrovic proposed to improve canola and soy-based polyols with the ozonolysis reaction to produce primary hydroxy groups at the carbon-ended part of the fatty acid moieties [4]. However, this can lead to by-product formation with mixtures of four to eight carbons that can be a problem in waste disposal or purification for marketable materials. The process is then further modified by using single step ozonolysis. Fringuelli et al. reported on a method to convert alkenes into 1,2-diols using peroxy acids in deionized water [5]. The process involves the epoxidation of the alkene, followed by the opening of the epoxide ring by acid or base hydrolysis to produce the diol. They also stated that the synthesis does not require any organic solvent [6]. Another method consists of using a consecutive two-step process involving epoxidation and hydroxylation for the manufacturing of natural oil-based polyols from vegetable or animal oil. Peroxyacid is used to form an epoxidized natural oil, which is then added to a mixture of alcohol, water and fluoroboric acid to undergo hydroxylation to form a natural oil-based polyol. The polyols synthesized may be reacted with isocyanate to form polyurethane [7]. However, the process does not contain precise descriptions concerning the critical steps in affecting the quality of the products. Therefore, the process can be further improved by studying the effect of ph, reaction time and type of solvent used. Cooking oils have been used by human beings for food and a variety of end use applications. They are made of triglycerides containing both saturated and unsaturated moieties which can be modified and used to synthesize polyols [8]. The triglycerides can be converted to diol functional compounds which can then react with isocyanates to form polyurethane. The main objective of this research is to synthesize and characterize polyols from refined cooking oil as one of the ingredients in producing polyurethane foam. These synthesized polyols are then used in polyurethane foam formulations. The expansion properties of the polyurethane foam are further investigated using only a selected synthesized polyol. Cellular Polymers, Vol. 31, No. 1,

4 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah EXPERIMENTAL Materials The refined cooking oil was obtained from a local grocery store with the brand name Labour Refined Cooking Oil. It is a refined palm olein, consisting of 45% monounsaturated compounds, 12% polyunsaturated compounds and 43% saturated compounds. It was used without further purification to synthesize polyester-based polyols by the conversion of unsaturated compounds to hydroxyl groups. Peroxy acid was the main reagent used in the epoxidation reaction. It was formed in-situ by reacting hydrogen peroxide (30%) and sulfuric acid with glacial acetic acid. During the epoxidation reaction, the peroxy acid reacted with the double bond compounds to form epoxides at the reaction temperature range of 25 C to 200 C. Fluoroboric acid (50% solutions in water) supplied by Acros Organics was used as the acid catalyst in the hydroxylation reaction. A mixture of methanol and isopropanol supplied by Systerm and R&M Chemicals Company respectively was used in excess amounts in hydroxylation to prevent polymerization. Another component in the hydroxylation process is water, which will react with the epoxides to form hydroxyl groups. Isocyanate is the main component in producing polyurethane foam. Isomer mixtures of 2,4- and 4,4-diphenylmethane diisocyanate (MDI), manufactured by Merck was used in this study. All the foam formulations used a fixed concentration of 75 parts to 100 parts of polyol. The blowing agent used for the polyurethane foaming process was chemically produced by the addition of distilled water into the formulations and reacted with the isocyanate to generate carbon dioxide gas (CO 2 ). CO 2 is the source of gas for PU foam formation. The concentration of water used ranged from 0 up to 0.4 parts to 100 parts of polyol. Polydimethysiloxane manufactured by Acros Organics was selected as the surfactant in the polyurethane foam formation. It is a silicone-based surfactant designed to lower surface tension, promote the generation of bubbles during mixing and stabilize cell window. All foam formulations used a fixed concentration of 0.4 parts to 100 parts of polyol. The catalyst used in polyurethane foam formation was N,N,N,N - tetramethyl-1,6-hexanediamine (99%) manufactured by Acros Organics. All foam formulations used a fixed concentration of 1.0 part to 100 parts of polyol. 22 Cellular Polymers, Vol. 31, No. 1, 2012

5 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation Synthesis of Polyol Polyols were synthesized from refined cooking oil using a consecutive twostep process involving epoxidation and the hydroxylation process. Epoxidation Process 500 g of cooking oil was added into a round bottom flask equipped with a temperature control, a reflux condenser and a stirrer. Approximately 75 g of glacial acetic acid and 6.36 g of 50% solution of sulfuric acid were added into the reactor. After the reactor system was brought up to a temperature of 70 C, 243 g of hydrogen peroxide solution was added. The temperature of the reactor was then increased to 100 C with vigorous stirring. The effect of different reaction times was conducted at one hour, three hours and five hours prior to the final addition of hydrogen peroxide. After the set reaction time was reached, the contents of the reactor system were transferred to a separatory funnel and allowed to cool down. A separate layer of sample was obtained with water at the bottom layer and crude partially epoxidized oil at the upper layer. The epoxidized oil was then collected and rinsed with distilled water several times. The epoxidized oil was then transferred into a few beakers and the desired amount of sodium methoxide was added to obtain each sample of different ph value i.e. ph3, ph5 and ph7. Each of the mixture was then stirred for two hours to obtain homogenous samples. These samples were then used in the hydroxylation process. Hydroxylation Process 330 g of solvent, 83 g of water and 6.73 g of fluoroboric acid were added to the reactor. Three types of solvents were used in each experiment, i.e. methanol, isopropanol and 1:1 ratio of methanol to isopropanol. The ingredients were thoroughly mixed while the reactor system was brought to 80 C. Then 510 g of the partially epoxidized oil prepared from the epoxidation process was quickly added and vigorously stirred. After 60 minutes of reaction time, 10 g of sodium methoxide was added to neutralize the acids in the content. This mixture was stirred further for one hour at 100 C to remove water and alcohol residuals and the final recovered polyol was obtained. Table 1 shows the conditions used for synthesizing each polyol sample. The samples were labeled from Sample A to G at different reaction time, ph and type of solvent used. The selected polyol formulations were then used in polyurethane foam formation. Cellular Polymers, Vol. 31, No. 1,

6 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah Table 1. Conditions used for synthesizing polyol samples Sample Reaction Time (hr) Sodium Methoxide Used (g) Solvent A 1 40 (ph3) 1:1 methanol:isopropanol B 3 40 (ph3) 1:1 methanol:isopropanol C 5 40 (ph3) 1:1 methanol:isopropanol D 5 80 (ph5) 1:1 methanol:isopropanol E (ph7) 1:1 methanol:isopropanol F 5 40 (ph3) Methanol G 5 40 (ph3) Isopropanol Preparation of Polyurethane Foam The PU foams were prepared by pre-mixing the synthesized polyol, polydimethylsiloxane, N,N,N,N -tetramethylhexanediamine and distilled water according to formulations listed in Table 2. The modified MDI (2, 4 -MDI and 4, 4 -MDI) was then added to the mixture, followed by vigorous stirring for 15 seconds and the reaction was allowed to proceed. The PU foam samples were allowed to cure for at least 24 hours at room temperature before they were cut to the desired dimensions for characterizations. Table 2. Weight recipe for the foam formulations Components Parts by weight F1 F2 F3 F4 F5 Polyol ,4 - and 4,4 -MDI N,N,N,N tetramethylhexanediamine (catalyst) Polydimethylsiloxane (surfactant) Water Characterizations Gas Chromatography Mass Spectrometry Analysis (GC-MS) analysis was performed to investigate the compositions of fatty acid moieties in the oil and the compositions of synthesized polyols. 100 mg of sample was dissolved with 10 ml of hexane and 100 µl of 2 M methanolic potassium hydroxide in a 24 Cellular Polymers, Vol. 31, No. 1, 2012

7 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation 20 ml test tube. The test tube was then closed, vortexed at room temperature for 30 seconds and centrifuged. The clear supernatant was then transferred for GC injection and the GC-MS conditions were described elsewhere [9]. Hydroxyl value, defined as the mg of potassium hydroxide equivalent to the hydroxyl content of 1 g of sample, was determined by ASTM test method D1957 [10]. The chemical characterizations of polyols and polyurethane foams were conducted using infrared spectroscopy, by using a resolution of 4.0 cm -1 to obtain infrared spectra. 2.5 g of polyol was first dissolved with tetrahydrofuran in 50 ml volumetric flask. One drop of the solution was placed as a thin film between polished sodium chloride (NaCl) plates which were then transferred to a sampling holder located in the Fourier Transform Infrared Spectroscopy Analysis (FTIR). For solid samples such as polyurethane foams, the Attenuated Total Reflectance (ATR) system attached to the FTIR was used. Sixteen consecutive scans from 400 cm -1 to 4000 cm -1 were taken for each sample. Then the active groups contained in the samples were investigated. Gel Permeation Chromatography (GPC) was used to determine the molecular weight distribution of the polyol samples. A sample concentration of 1.0 mg ml -1 was dissolved in chloroform (HPLC grade) and filtered through membrane filters with pore sizes of not less than 0.4 µm. Polystyrene standards with low dispersity were used to construct a calibration curve and chloroform was used as the eluent at a flow rate of 0.8 ml min -1 [11]. The value of the number of average molar mass (M n ), weight average molar mass (M w ) and polydispersity (PD) obtained was studied for its molecular weight distribution. The cellular structure of the foam specimens was analyzed using Scanning Electron Microscope (SEM) image. The mean apparent cell size of the foam was estimated from the SEM images by a modified cell count method described elsewhere [12]. Foam density was determined by measuring the weight and volume of the regular shape parallelepiped samples of 20 mm x 20 mm x 10 mm free of skin, voids or other irregularities [13]. Thermogravimetric Analysis (TGA) was used to determine the PU foam thermal stability and its fraction of volatile components by monitoring the weight change that occurred as a specimen was heated from 30 C to final temperature of 900 C at 20 ml min -1 nitrogen flow rate. Differential Scanning Calorimetry (DSC) was used to investigate the glass transition temperature of the polyurethane foam. Each sample was weighed between 10 to 15 mg and encapsulated in an aluminium pan and an empty aluminium pan was used as a reference sample. The specimen and the Cellular Polymers, Vol. 31, No. 1,

8 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah reference pan were then placed in the test chamber and heated at 20 C min -1 over a temperature range of -30 C to 200 C in a flowing stream of nitrogen at 30 ml min -1 [14]. RESULTS AND DISCUSSION Synthesis of Polyols All the polyols were synthesized successfully from refined cooking oil using epoxidation and hydroxylation reactions. Gas Chromatography Mass Spectrometry Analysis The content of the fatty acids in the refined cooking oil and the synthesized polyols were determined by using Gas Chromatography Mass Spectrometry (GC-MS). The major constituents in the cooking oil are oleic acid (52.2%), palmitic acid (33.0%), followed by linoleic acid (10.4%), stearic acid (3.8%) and myristic acid (0.6%). As the cooking oil consisted of large amounts of unsaturated acid content (approximately 62.6%), this is favorable for the synthesis of polyols by the conversion of the unsaturated portions to hydroxyl groups through epoxidation and hydroxylation reactions. Figure 1 shows the effect of reaction time on the content changes in the cooking oil components. The results indicated that linoleic acid was not found after one hour of reaction time. However, the oleic acid content was only reduced as the reaction time increased up to three hours. This means that the minimum reaction time required for the process was three hours for unsaturated fatty acids to be converted to saturated compound or hydroxyl compound. The saturated fatty acids contents for myristic acid and stearic acid remained unchanged when reaction time increased. This is because the reaction only occurred in unsaturated fatty acids that contained C=C double bonds. However, palmitic acid content increased to 63% at three hours of reaction time and reduced to 34% at five hours of reaction time. This is possibly due to the reverse reaction which occurred at five hours of reaction time and the incomplete hydroxylation process which led to the presence of intermediate products, i.e. oxiraneoctanoic acid. In order to ensure that the synthesizing process was long enough to complete the reaction, five hours of reaction time was used for the work to study the effect of ph and solvent used on the chemical changes in the component. 26 Cellular Polymers, Vol. 31, No. 1, 2012

9 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation Figure 1. Effect of reaction time on the contents of the compositions present in synthesized polyols The effect of ph value on the chemical contents in the synthesized polyols is shown in Figure 2. It was found that the chemical contents for both saturated and unsaturated fatty acids did not show significant changes. Hence, it is suggested that ph value does not play an important role in synthesizing polyols. From these results, ph3 was selected and used for subsequent work, i.e. the effect of solvent used on chemical changes in the refined cooking oil components. Figure 2. Effect of ph on the contents of the compositions present in synthesized polyols Cellular Polymers, Vol. 31, No. 1,

10 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah Methanol, isopropanol and a combination of methanol with isopropanol in the ratio of 1:1 were selected as the solvent in the preparation of polyols from refined cooking oil. From the results shown in Figure 3, oleic acid was not found in the synthesized polyol when methanol or isopropanol was used. This means that the unsaturated fatty acids had been removed. For comparison on the presence of the intermediate product, oxiraneoctanoic acid, the content was very high in Sample C (using 1:1 methanol:propanol as solvent) and Sample F (using methanol as solvent). However, it was not found in Sample G (using isopropanol as solvent). This suggests that oxiraneoctanoic acid could be diminished by using isopropanol as an interaction medium. In addition, it was found that approximately 5% of hydroxyl compound, i.e. octadecanoic acid, 9,10-dihydroxy was contained in Sample G and 3% in Sample F. However, isopropanol is more favorable to be used compared to methanol as using methanol will cause the presence of oxiraneoctanoic acid. Hydroxyl compound is favorable when the synthesized polyol is used for PU foam formation. Figure 3. Effect of solvent on the contents of compositions present in synthesized polyols Hydroxyl Content The results indicate that the hydroxyl value increased rapidly from 9 mg KOH/g to 57 mg KOH/g as the reaction time increased up to one hour. At three hours of reaction time, the hydroxyl number presented slightly increased. This suggests that the hydroxyl compound was generated in the sample. This result was supported by the results obtained from GC-MS analysis where hydroxyl compounds were present at the reaction time of three hours. 28 Cellular Polymers, Vol. 31, No. 1, 2012

11 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation It was observed that the hydroxyl values were nearly constant at ph3, ph5 and ph7 with the content ranging from 56 to 57 mg KOH/g. This shows that the hydroxyl content in the synthesized polyol was not affected by different ph conditions. The highest hydroxyl value was obtained when isopropanol was used, with a content of 69 mg KOH/g. This indicates that isopropanol is the most suitable interaction medium in generating a higher hydroxyl content for polyol. This was also in agreement with the study by Petrovic et al. [7] which showed that the use of isopropanol would create a higher hydroxyl number and higher viscosities in vegetable oil-based polyol. Fourier Transform Infrared Spectroscopy Analysis Figure 4 displays the Fourier Transform Infrared Spectroscopy (FTIR) spectra of refined cooking oil and the synthesized polyol at different reaction times. Peak stretching vibrations of the aliphatic ether group (C-O-C group) at 1070 cm -1 only appeared in the synthesized polyol. This suggests that some reaction occurred to form aliphatic ether linkage during epoxidation and the hydroxylation process. The peak at 3400 to 3510 cm -1 attributed to OH stretching vibrations becoming more apparent at longer reaction times. This also supported the phenomena that the C=C bond had reacted and converted to C-OH bonding or forming oligomer with other compounds. Figure 4. FTIR spectra of polyols synthesized from cooking oil at different reaction times Cellular Polymers, Vol. 31, No. 1,

12 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah In addition, there were absorption bands in the region of 2850 to 3000 cm -1 due to the stretching of C-H bonds in aliphatic carbons and in 1450 and 1375 cm -1 characteristic of the bending vibrations of the methylene groups in the polyol chain. Similar observations were also found in the study by Caroline et al. [15] of polyol recovered from PU foam. Figure 5 shows the FTIR spectra of synthesized polyols using different solvents. Among the synthesized samples, the sample using isopropanol as the solvent showed the most apparent absorption peak at 3400 to 3510 cm -1 and this represented the increases in the hydroxyl content. However, the actual amount of the hydroxyl content was not defined from the FTIR spectra quantitatively. The spectra were only used to determine the presence of functional groups in the synthesized samples. Figure 5. FTIR spectra of polyols synthesized from cooking oil using different solvents Gel Permeation Chromatography Analysis Figure 6 presents the variation in M w and PD of the synthesized polyols when the reaction time increased up to five hours. The M w value did not show much changes when the reaction time was increased to three hours. However, the M w value increased more significantly at five hours of the reaction time. The polydispersity of the synthesized samples increased to 1.08 at three hours of reaction time but reduced to 1.03 at five hours of reaction time. 30 Cellular Polymers, Vol. 31, No. 1, 2012

13 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation The effect of ph value on molecular weight distribution is illustrated in Figure 7. The resulting plot shows almost a flat line for both the M w value and polydispersity at ph3, ph5 and ph7. This suggests that the molecular weight distribution for the synthesized polyol was not affected by ph conditions. The role of the solvent in affecting the molecular weight distribution for the synthesized samples is presented in Figure 8. Between the two types of solvents and the combination used, M w value achieved the highest value when isopropanol was used. This indicates that the fraction of higher molecular Figure 6. Variation in weight average molecular weight (M w ) and polydispersity (PD) of polyols synthesized at different reaction time Figure 7. Variation in weight average molecular weight (M w ) and polydispersity (PD) of polyols synthesized at different ph values Cellular Polymers, Vol. 31, No. 1,

14 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah Figure 8. Variation in weight average molecular weight (M w ) and polydispersity (PD) of polyols synthesized using different solvents weight could be obtained with the addition of isopropanol as an interaction medium. For all the synthesized polyols, the polydispersity value was higher than 1. This suggests that when the PD value increased, the molecular weight distribution became broader. Polyurethane Foam Polyurethane (PU) foams were prepared by using the synthesized polyols in combination with other chemicals that are commercially available. However, most of the foams produced collapsed during the foaming process. The only foam sample that could be generated was based on the polyol that had been synthesized using isopropanol, i.e. Sample G. Hence, this selected formulation is used to further investigate the expansion characteristic and its properties at various water contents. Fourier Transform Infrared Spectroscopy Analysis The FTIR spectra of the polyurethane foams generated at different water content are presented in Figure 9. It was found that all the PU foams produced showed almost similar types of peak. The absorption bands at 3300 cm -1 and 1735 cm -1 attributed to N-H peak and C=O peak respectively were identified for all the PU foams generated. This suggests that reaction occurred between the isocyanate (MDI) and hydroxyl compounds to produce PU foam. In all the 32 Cellular Polymers, Vol. 31, No. 1, 2012

15 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation Figure 9. Comparison of FTIR spectra of polyurethane foam at different formulations with standard spectra for polyurethane cases, the absence of the peak in the range of 2000 to 2300 cm -1 indicates that all the isocyanate groups had reacted. In addition, the combination of urethane carbonyl (NH-CO-O) and esteric carbonyl (CO-O) vibrations at 1735 cm -1 [16] and the stretching vibrations of the C-O-C band at 1176 cm -1 were observed. This was the strong evidence for the formation of urethane linkage. The spectrums of the synthesized PU were compared with the spectrum of PU obtained from the database as illustrated in Figure 9. The spectrum of the synthesized PU presented a higher relative intensity of 2920 cm -1 and 2850 cm -1 peaks than the PU spectrum obtained from the database. This may be due to the use of aliphatic polyol synthesized from refined cooking oil which contributed to the long aliphatic chain in PU. Morphological Properties As shown in Figure 10, the cell structure and the cell sizes for the polyurethane foams produced were confirmed by the morphological analysis performed by SEM. The samples were designated as F1 to F5 with water content ranging from 0 up to 0.4 parts to 100 parts of polyol. The foams of Samples F1 and F2 consisted of a relatively fine and uniform cell structure with a cell size approximately ± 24% µm in diameter compared to Sample F4 with Cellular Polymers, Vol. 31, No. 1,

16 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah Figure 10. SEM micrographs of polyurethane foams with varying contents of water. Magnification: 30 x for Sample F1-F4 and 50 x for Sample F5 752 ± 28% µm in diameter. At a lower level of water concentration, the cell structure produced was round in shape. At a higher water content, the cell was dodecahedral. This suggests that the cell structure was more uniform at low water content and the cell size became bigger when the water content increased. The maximum cell size could be achieved by using 0.3 parts per weight of water content. 34 Cellular Polymers, Vol. 31, No. 1, 2012

17 Synthesis and Characterization of Polyols from Refined Cooking Oil for Polyurethane Foam Formation The cell size of Sample F3 was not determined due to the non-cellular and poorer cell structure. However, there was still interconnectivity between the pores. It can be seen that there were particles which adhered onto the cell walls in Sample F5 as shown in Figure 10. These particles were probably unreacted compounds that remained in the PU foam. Some remnants of the collapsed cell walls could be seen at the cell edges. This indicated that too much CO 2 gas was generated from the high water content which caused the foaming process to become unstable. The cell expansion process is faster than stabilization during the mixing process. Foam Density The density of the PU foams are presented in Table 3. It was observed that when the water content increased, the density of the polyurethane foams decreased from 108 kg m -3 to 56 kg m -3. This was in good agreement with the results obtained from morphological studies in which the foam with a smaller cell size with thicker cell wall would lead to a higher density value. No density value was measured for Sample F5 due to the non uniformity of the foam sample. The foam seemed to collapse when the water content of 0.4 parts per weight was used. Therefore, the optimum expansion of the PU foam produced was less than 0.4 parts per weight. Thermogravimetric Analysis All the polyurethane foams synthesized exhibited similar profiles in which the onset of degradation began at a temperature of 300 C, followed by an increase in the degradation rate until a temperature of 500 C. From 500 C to 900 C, the samples appeared to be more stable with 10% of residue. This reveals that the differences of the water content used did not cause any significant changes on the thermal degradation profile. Differential Scanning Calorimetry Analysis The thermal properties of polyurethane foams were studied by differential scanning calorimetry (DSC) and are summarized in Table 3. The DSC curves with glass transition point (T g ) were detected for all the samples and within the range of 50.8 to 60.5 C. The T g was found to increase with the increase of water content in PU foam formulations. This suggests the occurrence of soft segments and hard segments fractions in PU foam. During the process of polymerization, oligomers might act as chain extenders to change the Cellular Polymers, Vol. 31, No. 1,

18 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah fractions of the soft and hard segments in the PU foam. The increase of the water content would lead to more chain extenders formation. Hence, the glass transition point increased with the increase of water content. Table 3. Thermal and physical properties of polyurethane foams Sample Designation T g ( C) Density (kg/m 3 ) Cell Size (µm) F ± ± 24% F ± ± 27% F a - a F ± ± 28% F ± a a: no density/ cell size data obtained due to the non uniformity of the foam synthesized CONCLUSIONS Polyols have been synthesized successfully from refined cooking oil by using epoxidation and the hydroxylation process based on the results in GC-MS, FTIR and GPC. From these results, it can be concluded that 50% of unsaturated fatty acids in refined cooking oil was converted to saturated fatty acids as the reaction time increased up to five hours. However, the chemical contents in the polyols did not show significant changes as the ph value increased from ph3 to ph7. Using different types of solvent in the process showed that the hydroxyl content of the polyol ranged from 57 to 69 mg KOH/ g, with M w in the range of g mol -1. This revealed that the type of solvent used was a key parameter in synthesizing polyols. From the study, it was found that not all synthesized polyols could be used in PU foam formation. It is highly dependent on the hydroxyl content and the average molecular weight. Therefore, it is recommended that the minimum hydroxyl content and molecular weight of the synthesized polyol required for the PU foam formation is 69 mg KOH/ g and g mol -1 respectively. The properties of PU foam are highly dependent on the polyol and the water (blowing agent) content. Acknowledgement The authors also wish to thank to Ministry of Higher Education Malaysia for the FRGS grant no FRG0211-TK The corresponding author also wishes to thank Universiti Malaysia Sabah for promotion, new working places and support for this research. 36 Cellular Polymers, Vol. 31, No. 1, 2012

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20 C.S. Sipaut, S. Murni, S. Saalah, T.C. Hoon, M.N. Mohamad Ibrahim, I.A. Rahman and A.A. Abdullah 38 Cellular Polymers, Vol. 31, No. 1, 2012