Physical Properties of Bio-Based Polyurethane Foams From Bio-Based Succinate Polyols

Transcription

1 Physical Properties of Bio-Based Polyurethane Foams from Bio-Based Succinate Polyols Physical Properties of Bio-Based Polyurethane Foams From Bio-Based Succinate Polyols Tatcha Sonjui 1 and Nantana Jiratumnukul 2* 1 Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok, Thailand Research Unit of Advanced Ceramic and Polymeric Materials, National Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, Chulalongkorn University, Bangkok, Thailand Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok, Thailand Received: 7 April 2015, Accepted: 18 June 2015 Summary The goal of this work is to study the physical properties of bio-based polyurethane (PU) foams prepared from synthesized bio-based succinate polyols. Bio-based succinate polyols were synthesized by condensation reaction using succinic acid (SA) and four types of glycols that are diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TTEG) and glycerol (Gly). The effects of glycol types (single or mixed glycols) used in the prepared polyols toward physical properties of PU foams were studied. Physical and mechanical properties of the prepared PU foams were taken relatively to PU foam obtained from a commercial polyol. The results revealed that hydroxyl number (OH number) and viscosity of prepared polyols decreased as the length of the glycol chains increased (DEG < TEG < TTEG). However, the polyols prepared from mixed glycols showed higher viscosity than those prepared from single glycol. Optical micrographs images showed that the PU foams prepared from mixed-glycol polyols had smaller cell dimension and more closed cell contents compared to ones prepared from single-glycol polyols. Foam formation time and density of foams prepared from DEG-glycerol mixed glycol polyol were similar to one prepared from commercial polyol (POLIMAXX A8360). Moreover, compressive strength of foam was higher than one prepared from commercial polyol. Keywords: Bio-based polyurethane, Polyurethane foam, Succinic acid, Bio-based succinate polyol * nantanaj@gmail.com Smithers Information Ltd Cellular Polymers, Vol. 34, No. 6,

2 Tatcha Sonjui and Nantana Jiratumnukul INTRODUCTION Polyurethanes (PUs) are versatile materials that is widely used in many applications because of their properties can be readily tailored by the composition and type of their components [1-3]. PU foam is one of the most widely used polymeric foams in the world, finding applications in almost all modern industries. PU foams are classified on the basis of their commercially available forms such as flexible PU foams and rigid PU foams. PU foam is usually synthesized by the reaction of diisocyanate with polyol. In general, blowing agent, catalyst and surfactant are also employed to regulate the properties of the foam and morphology of the cell structures [4]. Recently, there are lots of intensive interests in synthesis of polyol from natural resources such as vegetable oils and natural fats because of their important availability, sustainability, biodegradability, and added values. Succinic acid (SA), from fermentation of sugars, has been noted as one of the most important value added chemicals from biomass, from which many chemicals can be derived [5]. The objective of this research is to study the physical properties of bio-based polyurethane (PU) foams prepared from synthesized bio-based succinate polyols. Bio-based succinate polyols were synthesized by condensation reaction using succinic acid (SA) and four types of glycols that are diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TTEG) and glycerol (Gly). The effects of glycol types (single or mixed glycols) used in the prepared polyols toward physical properties of PU foams were studied. The functionality, viscosity, acid number and hydroxyl number (OH number) of prepared polyols were examined. Bio-based PU foams were prepared using the synthesized bio-based succinate polyols reacted with methylene diphenyl diisocyanate (MDI). Mechanical and physical properties of prepared PU foams were investigated relatively to PU foam prepared from a conventional polyol from petrochemicals. EXPERIMENTAL Materials Succinic acid (SA) was purchased from UNIVAR. Diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TTEG) and glycerol (Gly) were purchased from Sigma Aldrich. Commercial methylene diphenyl diisocyanate (MDI) (Suprasec 5005) which is a liquid at room temperature and N, N-dimethyl cyclohexylamine catalyst (DMCHA) were provided from Huntsman International. Silicone surfactant, Tegostab B8462, used in this study was donated by 354 Cellular Polymers, Vol. 34, No. 6, 2015

3 Physical Properties of Bio-Based Polyurethane Foams from Bio-Based Succinate Polyols Goldschmidt Chemical. Distilled water was used as the blowing agent. Commercial polyol (POLIMAXX A8360) were supported by IRPC polyol. All materials were used as received without further purification. Preparation of Bio-based Succinate Polyols The bio-based succinate polyols were prepared from SA with four types of glycols that are diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (TTEG) and glycerol (Gly) as shown in Table 1. The synthesized polyols were separated into two groups as SA with single glycol (DEG, TEG, and TTEG) and SA with mixed glycols (DEG, TEG and TTEG were mixed with Gly separately). To a 250 ml round bottomed flask, equipped with a magnetic stirrer, thermocouple and distillation condenser, the reactants were added and heated to 190 C for 1 h under atmosphere. The pressured was then reduced to 160 mmhg for 1 h, the catalyst was added to the mixture and the reaction temperature were kept at 190 C under reduced pressure to remove water from the reaction [6]. The reaction mixtures were taken every hour to monitor the acid values. Reactions were completed when the acid values were less than 2.0 mgkoh g -1, and the foam formation times were recorded. Table 1. Polyols formulation of bio-based succinate polyols Group Component Molar ratio Functionality Single-glycol polyols SA:DEG SA:TEG SA:TTEG 1:2 2 Mixed-glycol polyols SA:DEG:Gly SA:TEG:Gly SA:TTEG:Gly 1:1.5: Preparation of Bio-based Polyurethane Foams The various PU foams were prepared by mixing various synthesized polyols with MDI. The NCO index (isocyanate equivalents/polyol equivalents) was fixed at 1.0. The basic formulations used to prepare foams in this study are given in Table 2. First, the ingredients in component B were all mixed simultaneously by stirring for 30 s at 2000 rpm in a disposable paper cup. The mixture was allowed to degas for 2 min. Then the component A (MDI) was added and mixed for 10 s at the same speed. The reacting mixture was then poured quickly into an uncovered mold to foam freely at room temperature and was allowed to cure at room temperature for 7 days. After curing, the foam materials were cut and used as samples in various testing. Cellular Polymers, Vol. 34, No. 6,

4 Tatcha Sonjui and Nantana Jiratumnukul Table 2. Foaming formulation of bio-based polyurethane foams Ingredients Component A Isocyanate index b of MDI Component B Succinate polyol DMCHA (gelling catalyst) TEGOSTAB B 8462 (Surfactant) Distilled water (Blowing agent) Concentration, php a a The concentration of all ingredients are expressed in parts per hundred parts of polyol, which conventionally dictates that the sum of all polyols adds up to 100 parts b The amount of isocyanate is based on the isocyanate index. The isocyanate index is the amount of isocyanate used relative to the theoretical equivalent amount Characterization The viscosity of the synthesized bio-based succinate polyols were measured at 25 C using a Brookfield viscometer. Hydroxyl numbers (OH numbers) of the synthesized polyols were examined in accordance with ASTM D4724. The functionality of the synthesized polyols and the PU foam samples prepared from the synthesized polyols were investigated using Fourier transform infrared spectroscopy (FTIR) (Nicolet 6700). Kinetics of the foam formation are followed by the physical change of some properties such as cream time, gel time, and tack- free time [7]. The cream time corresponds to the start of bubble rise and hence rise color of the mixture becomes cream like from dark brown due to the introduction of foam bubbles. Rise time is the time that foam reach to its largest volume or maximum height. At tack- free time, the outer surface of the foam loses its stickiness and the foam can be removed from the mold. These times were measured by a digital stopwatch. The cellular morphology and cell dimensions of prepared foams were observed using an optical microscope (OM) (Model SZ-CTV Olympus; Tokyo, Japan). Thin slices, less than 1 mm, were cut from each foam sample. Images were captured by an online color video camera (Model SSC-E458P Sony; Tokyo, Japan). The captured images were analyzed to measure cell dimensions by manually selecting the cell windows using an image analysis software (Image Pro Express version 6.0; Media Cybernetics, Silver Spring, MD). Only those cell windows for which the entire window came into focus were taken. Fifty measurements were made for each specimen [8]. Density of the foams were measured according to ASTM D 1622 with sample size of mm 3 (width length thickness). Compression strength was determined by ASTM 356 Cellular Polymers, Vol. 34, No. 6, 2015

5 Physical Properties of Bio-Based Polyurethane Foams from Bio-Based Succinate Polyols D 1621 using a Universal Testing Machine (Ametek, LLOYD) at a crosshead speed of 2.5 mm/min with the sample dimension of mm 3 [9]. The force required for at 10% deformation based on the original thickness has been taken as the compressive strength of the foam. An average of at least three measurements was taken to report. RESULTS AND DISCUSSION Properties of the Synthesized Bio-based Succinate Polyols The viscosity of a polymer is affected by many variables such as the molar mass, structure and conformation of the polymer molecule [10]. The hydroxyl number (OH number) is the amount of available reactive hydroxyl groups on polyol molecules and acid number indicates the amount of carboxylic groups in a chemical compound or in a mixture of compounds. The results of viscosity, OH number and acid number of prepared polyols and commercial polyol are shown in Table 3. It showed that the viscosity and OH number of the polyols decreased as the chain length of glycols increased (DEG < TEG < TTEG). Same trend happened for polyols prepared from single or mixed glycols. This might be because, the amount of hydrogen bond of the polyols decreased as the chain length of the glycol increased. The slip resistance among the molecules decreased, resulting in a lower viscosity [11]. However, the polyols prepared from mixed glycols had higher viscosity than those prepared from single glycols. This was because the glycerol used in mixedglycol polyols containing three hydroxyl groups in one molecule acted as crosslinking agent and provided more branches in polymer chain. As a result, the higher viscosity was obtained. OH numbers of the polyols prepared from Table 3. Physical properties of the synthesized bio-based succinate polyols Group Component Acid number (mgkoh g -1 ) Single-glycol polyols Mixed-glycol polyols SA:DEG SA:TEG SA:TTEG SA:DEG:Gly SA:TEG:Gly SA:TTEG:Gly OH number (mgkoh g -1 ) C (mpa s) ,362 1,175 1,150 POLIMAXX A ,100 Cellular Polymers, Vol. 34, No. 6,

6 Tatcha Sonjui and Nantana Jiratumnukul single glycols and mixed glycols were not significantly different. Moreover, all of the synthesized polyols had the acid numbers less than 2.0 mgkoh g -1 indicated that carboxylic groups from SA were completely reacted. FTIR Spectra FTIR is used to characterize the functional groups present in polymers. The synthesized bio-based succinate polyols spectra are shown in Figure 1(A) and (B). The peak of O-H stretching appeared at 3430 cm -1 indicated that all the synthesized polyols have the hydroxyl groups terminated at the end of the polymer chains. In the C=O stretching region, the peak at 1730 cm -1 are observed. The existence of C-O stretching in O=C-O groups are confirmed by the presence of the peak around cm -1 [12]. Figure 1(C) illustrated the FTIR spectra of PU foams prepared from single-glycol polyols (DEG) and mixed-glycol polyols (DEG and Gly). The wide absorption band at 3350 cm -1 represented stretching vibration of N-H urethane hydrogen bonded. It can be seen that the peak for hydroxyl located at 3430 cm -1 almost disappears after succinate polyols reacted with MDI. The peak at 2200 cm -1 which is a characteristic peak of N=C=O group are hardly observed, this indicated that isocyanate groups of MDI were totally reacted [13]. The peak at 1530 cm -1 can be attributed to N-H stretching of urethane linkage which confirmed that urethane linkages were formed [1]. Morphology of the Bio-based PU Foams The morphology and cellular structure of prepared PU foams were observed using an optical microscope (OM). Figure 2 showed the cubic specimens and OM images of PU foams. It was observed that the cubic specimens of foams prepared using single-glycol polyols had larger pore size than ones prepared using mixed-glycol polyols. Moreover, the pore size of foams increased as the length of glycols chain (DEG < TEG < TTEG) increased. The results of OM images showed that the foams prepared from mixed-glycol polyols had regular cell size and more closed cells of spherical and polyhedral shape contents than those prepared from single-glycol polyols. The average cell dimension, measure by image analysis of OM micrographs, and volume of the foam samples are shown in Table 4. The cell dimension of PU foams, prepared by single or mixed glycol polyols, increased as the chain length of the glycol in polyol used in the foam (DEG < TEG < TTEG) increased. However, foams prepared using mixed-glycol polyols had smaller cell dimensions than ones using single-glycol polyols. The volume of foam rising decreased as the chain length of the glycol 358 Cellular Polymers, Vol. 34, No. 6, 2015

7 Physical Properties of Bio-Based Polyurethane Foams from Bio-Based Succinate Polyols Figure 1. FTIR spectra of the synthesized bio-based succinate polyols from single glycols (A), mixed glycols (B) and PU foams prepared from the synthesized bio-based succinate polyols (C) Cellular Polymers, Vol. 34, No. 6,

8 Tatcha Sonjui and Nantana Jiratumnukul in polyol increased. All of foams prepared using single-glycol polyols were found to have CO 2 gas releasing during the foam formation while the foams prepared using mixed-glycol polyols were not. This might be because the effect of glycerol in mixed-glycol polyols that acted as crosslinking agent causing PU foams had more polymer network, resulting PU foams had regular and smaller cell size [14]. Moreover, morphology of the foams prepared by single-glycol polyols was not good since the foams had less volume than those prepared by mixed-glycol polyols. This is because small amount of CO 2 gas was released during the foam formation causing the thick cell wall of PU foams with singleglycol polyols. Due to the lower viscosity of single-glycol polyols, the polymer could not maintain the CO 2 gas generated during foam formation resulting less volume of foam rising. The higher viscosity of mixed-glycol polyols reduced cell drainage by gravity at the initial foaming stage leading to a smaller cell size and higher closed cell contents occurred [15]. Figure 2. Cubic specimens and OM images of the prepared PU foams from the synthesized bio-based succinate polyols 360 Cellular Polymers, Vol. 34, No. 6, 2015

9 Physical Properties of Bio-Based Polyurethane Foams from Bio-Based Succinate Polyols Table 4. Cell dimension and volume of the foam samples Foam type cell dimension (mm) volume SA:DEG SA:TEG SA:TTEG SA:DEG:Gly SA:TEG:Gly SA:TTEG:Gly Foam Formation Time ± ± ± ± ± ± / / / / / /10.00 POLIMAXX A ± /10.00 There are various types of times that involve during foam formation. Cream time is the time when the polyol and isocyanate mixture begins to change from the liquid state to a creamy and starts to expand subsequently. Rise time is the time that foam reach to its largest volume or maximum height. Tack free time is the time taken from the beginning as the formulation is poured till the point that the outer skin of the foam mass loses its stickiness or adhesive quality [7]. Foam formation time of the prepared PU foams are shown in Figure 3(A). It was found that, the foam formation time increased as the chain length of glycol in polyols used in the foam increased (DEG < TEG < TTEG). This phenomenon was found in all foams prepared from single or mixed-glycol polyols. This indicated that the lower hydroxyl contents of the long chain polyols provided lower reactivity relative to the short chain polyols. Moreover, PU foam prepared from DEG-glycerol mixed glycol polyol showed shortest tack free time used in foam formation and the tack free time were similar to the foam prepared from commercial polyol (POLIMAXX A8360). Density of the Bio-based PU Foams Density is an important parameter to control the mechanical properties of foams. The bulk densities of prepared PU foams are shown in Figure 3(B). The results showed that density of PU foams decreased as the chain length of glycol in polyol used in the foam increased (DEG < TEG < TTEG). Foams prepared with single-glycol polyols had higher density than those prepared from mixed-glycol polyols. The blowing reaction of PURFs had effect to the foam density since the reaction released CO 2 gas causing the foam rise toward the top of a mold. The lower viscosity of single-glycol polyols caused the polymer could not maintain the CO 2 gas generated during foam formation cause the small amount of CO 2 was released. As a result, the lower volume of foam rising was obtained [7]. Therefore the density of PU foams prepared with single-glycol polyols were higher than those foams prepared with mixed-glycol polyols. Cellular Polymers, Vol. 34, No. 6,

10 Tatcha Sonjui and Nantana Jiratumnukul Figure 3. Foam formation time (A), bulk density (B) and compressive strength (C) of the prepared PU foams from the synthesized bio-based succinate polyols 362 Cellular Polymers, Vol. 34, No. 6, 2015

11 Physical Properties of Bio-Based Polyurethane Foams from Bio-Based Succinate Polyols Compressive Strength of the Bio-based PU Foams Mechanical properties are more important than any other properties of foams when it comes to the real application. Compressive strength property is the most important mechanical property that used to evaluate the strength of the PU foams. The results of compressive strength of prepared PU foams in this study were shown in Figure 3(C). It was observed that, the compressive strength of PU foams decreased when the chain length of glycol in polyol used in the foam increased (DEG < TEG < TTEG). This might be because the longer chain polyols enhanced the flexibility of foams [10]. The longer chain length, the lower hydroxyl contents of polyols resulting provided less in urethane linkage and lower in strength. The high cohesive interaction between these urethane linkages provides rigid structure, resulting PU foam to have better dimensional stability [16]. Foams prepared with mixed-glycol polyols had higher compressive strength than those prepared from singleglycol polyols. Even though the density of foams prepared by single-glycol polyols was higher than mixed-glycol polyols, the compressive strength results were not showed the same trend due to the morphological aspects presented at Figure 2. Small and closed cell do contribute to increase the compressive strength of foams. The PU foam prepared from DEG-glycerol mixed glycol polyol gave the highest compressive strength and was higher than one prepared from commercial polyol. CONCLUSIONS Various bio-based succinate polyols were successfully synthesized from succinic acid with various types of glycols. The bio-based PU foams were also prepared from the synthesized bio-based succinate polyols and methylene diphenyl diisocyanate (MDI). The viscosity and OH number of the prepared polyols decreased as the chain length of the glycols increased (DEG < TEG < TTEG). The polyols prepared from mixed glycols had higher viscosity than those prepared from single glycols. Optical microscope images showed that the foams prepared from mixed-glycol polyols had regular cell size and more closed cells of spherical and polyhedral shape contents than those prepared from single-glycol polyols. However, foams prepared using mixed-glycol polyols had smaller cell dimensions than ones using single-glycol polyols. The cell dimension of PU foams, prepared by single or mixed glycol polyols, increased as the chain length of the glycol in polyol used in the foam increased. The volume of foam rising decreased as the chain length of the glycol in polyol increased. Foam formation time increased as the chain length of glycol in polyol increased. This phenomenon was found in all foams prepared from single or mixed-glycol polyols. The density and compressive strength of PU foams Cellular Polymers, Vol. 34, No. 6,

12 Tatcha Sonjui and Nantana Jiratumnukul decreased as the chain length of the polyols increased. Foams prepared with single-glycol polyols had higher density than those prepared from mixed-glycol polyols. On the other hand, compressive strength of PU foams prepared with single-glycol polyols had lower compressive strength than those prepared from mixed-glycol polyols. This was because small and closed cell foams in mixed-glycol polyols do contribute to increase the compressive strength of foams. The PU foam prepared from DEG-glycerol mixed glycol polyol had similar foam formation time and density compared to one prepared from a commercial polyol (POLIMAXX A8360). Moreover, compressive strength of foam was higher than one prepared from commercial polyol. ACKNOWLEDGEMENTS We wish to thank to the Department of Materials Science, Faculty of Science, Chulalongkorn University and Center for Petroleum, Petrochemicals and Advanced Materials. We also acknowledge the support by Chulalongkorn University. REFERENCES 1. Hapburn, C. Polyurethane Elastomers; Elsevier Oxford Publications, Oertel, G. Polyurethane Handbook; Hanser Publication, Szycher, M. Szycher's Handbook of Polyurethanes; CRC Press Publication: New York, Hakim, A.A.A.; Nassar, M.; Emam, A.; Sultan, M. Mater. Chem. Phys., 129, (2011), Sonnenschein, M.F.; Guillaudeu, S.J.; Landes, B.G.; Wendt, B.L. Polymer, 51, (2010), Ahn, B.D.; Kim, S.H.; Kim, Y.H.; Yang, J.S. J. Appl. Polym. Sci., 82, (2001), Seo, W.J.; Park, J.H.; Sung Y.T.; Hwang D.H.; Kim W.N.; Lee H.S. J Appl Polym Sci, 93, (2004), Mondal, P; Khakhar, D.V. J. Appl. Polym. Sci., 103, (2007), Seo, W.J.; Jung, H.C.; Hyun, J.C.; Kim, W.N.; Lee, Y.B.; Choe, K.H.; Kim, S.B. J. Appl. Polym. Sci., 90, (2003), Zhang, C.; Feng, S. Polym. Int., 53, (2004), Cellular Polymers, Vol. 34, No. 6, 2015

13 Physical Properties of Bio-Based Polyurethane Foams from Bio-Based Succinate Polyols 11. Ionescu, M. Chemistry and Technology of Polyols for Polyurethanes; Rapra Tech. Publications: United Kingdom, Zeng, C; Zhang, N.W.; Ren, J. J. Appl. Polym. Sci., 125, (2012), Narine, S.S.; Kong, X.; Bouzidi, L. J. Amer. Oil. Chem. Soc., 84, (2007), Zhang, L.; Ding, X.; Ou, Y. AASCIT., 1(1), 2014, Tan, S.; Abraham, T.; Ference, D.; Macosko, C.W. Polymer, 52, (2011), Fan, H.; Tekeei, A.; Suppes, G.J.; Hsieh, F.H. J. Appl. Polym., 127, (2013), Cellular Polymers, Vol. 34, No. 6,

14 Tatcha Sonjui and Nantana Jiratumnukul 366 Cellular Polymers, Vol. 34, No. 6, 2015