PREPARATION OF RIGID POLYURETHANE FOAMS FROM POLYETHER AND POLYESTER POLYOL MIXTURE

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1 1 PREPARATION OF RIGID POLYURETHANE FOAMS FROM POLYETHER AND POLYESTER POLYOL MIXTURE Supachai Dhavavarodom 1 * and Nuanphun Chantarasiri 2 1 Program in Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University, Bangkok 103, Thailand 2 Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 103, Thailand * Author for correspondence; supachai.d@irpc.co.th, Tel , Fax Abstract: The use of rigid polyurethane foam (RPUF) has been growing rapidly in many industries due to its excellent combination of energy conservation, good mechanical strength with lighter weight than other traditional materials. In this research, a RPUF formulated system having an excellent low density and thermal conductivity has been developed by using polyether and polyester polyol mixture, isocyanate compound, catalyst and surfactant. Moreover, a utilization of distilled water as a choice of an alternative blowing agent replaced for some of HCFC141b was selected. Density, thermal conductivity, mechanical property and cell morphology of them were investigated together with the adjustment of the cream time, gel time and tackfree time suited for an industrial use. It was found that the formulation of parts by weight of polyester polyols, pbw of distilled water and pbw of HCFC141b showed an excellent low density and thermal conductivity 1. Introduction The major use of RPUF is in the construction and thermal insulation industries, where their superior longterm thermal insulation properties combined with good mechanical properties offer many benefits. An important way to save thermal energy in commercial buildings is to use proper thermal insulation. Every building material resists thermal transfer to some extent, but RPUF provide the best insulation available. One of the first architectural design considerations is insulation, because of the high cost of both air conditioning system in warm climate area and heating system in cool climate area, and thus the need for greater insulating efficiency. While in the thermal insulation industry, an increasing world population will require more efficient use of food, with the emphasis on better food preservation to avoid waste. This can only be done through more efficient insulation during transport and storage [1,2]. RPUF are prepared by mixing, under controlled conditions, polyols, isocyanate compound, blowing agents and a variety of additives such as catalysts, surfactants, water and, optionally, fire retardants. A wide range of polyols is used, normally in combination with polymeric 4,4diphenylmethane diisocyanate (MDI), and the additives are typically preblended into the polyol. The formation of a highly crosslinked homogeneous glassy network structure is crucial for the final properties of RPUF, as it leads to good heat stability, high compression strength at low density and good barrier properties. Obtaining optimum processing and end properties at the same time cannot usually be achieved using a single polyol and the same holds for catalysts and blowing agents. Many studies have demonstrated the use of water as a sole blowing agent [35] or use in combination with other physical blowing agent such as hydrochlorofluorocarbon or hydrocarbon in RPUF [6,7]. They also have had many papers revealed the use of polyol mixtures in RPUF formulated system [6,8,9]. In this study, the RPUF from polyether and polyester polyol mixture has been prepared and analyzed in terms of reaction reactivity, density, cell morphology, mechanical property and thermal conductivity. It provides an excellent balance of properties and also has significant advantages over the existing industrial product, such as environmental concerning and cost effectiveness. 2. Materials and Methods 2.1 Materials The polyether polyols and polyester polyol, polymeric MDI, catalyst, surfactant and blowing agent were supported from IRPC Polyol Co., Ltd. (Rayong, Thailand). All compounding ingredients were commercial chemicals, used without further purification. The characteristics of the materials are shown in Table Sample preparations The RPUF samples with various compositions in polyol mixture were prepared by mechanical mixing technique in two steps of the mixing. In the first mixing step, polyol mixture, catalyst, surfactant and blowing agent were mixed together in a 0 ml plastic bottle with a mechanical stirrer at 00 rpm for minute. Then, in the second mixing step, the isocyanate compound was added into the mixed polyol obtained from the first mixing step. The mixture was immediately stirred by mechanical stirrer at 00 rpm for 10 seconds. After that, the mixture was poured into the plastic bag and rised up freely for reaction reactivity observation. Cream time, gel time and tack free time were measured. The foams were kept at room temperature for 48 hours before free rise density and morphology analysis. While the foams for mechanical property and thermal conductivity analysis were obtained from pouring the mixed reactant into the Pure and Applied Chemistry International Conference 12 (PACCON 12)

2 2 Table 1: Characteristics of the starting materials Materials a Equivalent Weight Role Polymeric 4,4 diphenylmethane diisocyanate 136 NCO content = 31 (polymeric MDI) Polyether polyol OH value = 440 mg KOH/g Polyether polyol 2 1 OH value = 450 mg KOH/g Polyether polyol 3 50 OH value = 11 mg KOH/g Polyester polyol 160 OH value = 350 mg KOH/g Polydimethyl siloxane Surfactant Dimethylcyclohexylamine (DMCHA) Catalyst Distilled water 9 Chemical blowing agent 1,1dichloro1fluoroethane (HCFC141b) Physical blowing agent a All materials were supported by IRPC Polyol Co., Ltd., Rayong, Thailand close mold (0 x 0 x 110 mm) to produce the foams with controlling the core density 3642 kg/m 3. To investigate the effect of the polyester polyols content on the properties of the RPUFs, the amount of polyester polyols was varied from 0 to pbw while the amount of catalyst, physical blowing agent, chemical blowing agent and surfactant were fixed at 1.0,, 1.5 and 1.5 pbw, respectively. The amount of polymeric MDI required for the reaction with polyols mixture and chemical blowing agent was calculated from the equivalent weight. For the completion of the reaction, excess polymeric MDI (NCO/OH = 1.) was used. After the optimum formulations of good appearance were achieved, the next investigation of the effect of the blowing agent by increasing chemical blowing agent to and pbw and decreasing HCFC 141b to pbw were carried out. The amount of catalyst, polyol mixture and surfactant were fixed at 1.0, and 1.5 pbw, respectively. The amount of catalyst was varied from 1.0 to 0.75 and 0.5 pbw were investigated at the same time. The amount of polymeric MDI required for the reaction with polyols mixture and chemical blowing agent was calculated from the equivalent weight. For the completion of the reaction, excess polymeric MDI (NCO/OH = 1.) was used. 2.3 Analytical Procedure The reactivity of RPUF polymerization reaction was obtained by measuring cream time (CT), gel time (GT) and tack free time (TFT). The cream time was the starting point of blowing and therefore was the time when the color of mixed reactants was brightened. The gel time was the starting point when the stable spatial shape was formed by the reaction of forming urethane and urea linkage and the crosslinking reaction. The tack free time was the time when the perfectly crosslinked RPUF could be detached from the mold. The free rise density (FRD) of RPUF samples was measured according to ASTM D16 by using cutting cylinder. The size of the specimen was a cylindrical shape with the 0 mm diameter width and 800 mm length. While the size of the core density specimen was x x mm (width x length x thickness). The densities of five specimens per sample were measured and averaged. The morphology of the RPUF sample was studied with a Philips XL scanning electron microscope. The samples were cut and gold sputtered before scanning in both parallel and perpendicular to the rising direction. The accelerating voltage was kv. The mechanical properties of the RPUF samples were measured under ambient conditions with a Lloyd LRX 5K universal testing machine. A compressive test was performed according to ASTM D1621. The size of the specimen was 50 x 50 x 50 mm (width x length x thickness) and the speed of crosshead movement was 5.00 mm/min. The force required for 10% deformation based on the original thickness has been taken as the compression strength of the foam. The strengths of five specimens per sample were measured and averaged for each mechanical test. The thermal conductivity property of the RPUF samples was measured with Netzsch Heat Flow Meter (HFM 436) analyzer according to ASTM C Results and Discussion 3.1 Preparation of RPUF RPUF were prepared by free rising method in order to study the reactivity of RPUF polymerization reaction while the overpacking specimens were prepared for mechanical and thermal conductivity property analysis. The formulations and reactivity results are tabulated in Table 2. Pure and Applied Chemistry International Conference 12 (PACCON 12)

3 4 Table 2: Composition, Reactivity and Free Rise Density of RPUF RPUF Polyether Polyester DMCHA HCFC Water Reaction time (sec.) Sample a polyol Polyol 141b CT GT TFT mixture Com. b F12 F13 F14 F15 F16 F F18 F19 F131 F132 F133 F134 F141 F142 F143 F144 F151 F152 F153 F154 F1531 F1532 F1533 F1541 F1542 F FRD ( kg/m 3 ) Foam Appearance Small shrink. Small shrink. High Small High Small Small a Other chemicals: Surfactant 1.5 pbw and polymeric MDI with Isocyanate index 1.2 were used in all samples. b Commercial system was supplied from IRPC Polyol, Co., Ltd. 3.2 Reactivity and Free rise density RPUF formulations were studied by variation of polyester polyols amount (F11F19) as shown in Table 1. It was found that F1315 gave low FRD foam with good foam appearance. Therefore, these formulations were further used in the next experiment by variation of physical and chemical blowing agent amount. It was also observed that F153 and F154, which pbw of polyester polyol was used, gave fast reactivity together with low FRD and good appearance. These formulations were selected to use for finetuning the catalyst amount to suit the industrial requirement and also for study in compressive strength analysis and thermal conductivity analysis. Among all RPUF formulations, F1533 showed the best results of reactivity and FRD, which required slow CT, GT and fast TFT as industry required, whereas it consumed low level of HCFC 141b and catalyst dosage. Figure 1 Compressive strength and thermal conductivity properties of RPUF Pure and Applied Chemistry International Conference 12 (PACCON 12)

4 4 3.3 Mechanical property and thermal conductivity Figure 1 shows the mechanical property of RPUF obtained from the molded fabrication at core density of ~3642 kg/m 3. It was found that many RPUF samples achieved the better compressive strength than that of the commercial product. In addition, the thermal conductivity is less than that of the commercial product. These are two of the most important properties of RPUF for insulation application. 3.4 Morphology Cell morphology of the RPUF from molded and free rising methods are shown in Figure 2 and 3, respectively. Cell structure of the molded method had an isotropic structure, which had a spherical shape in all directions. In contrast with the one obtained from free rising method, it had an anisotropic structure. It was an ellipsoidal shape which showed the elongated cell in parallel and the spherical cell in perpendicular to the foam rising direction. 2a) 2b) Figure 2. Cell morphology of molded RPUF in a) parallel and b) perpendicular to foam rising direction. 3a) 3b) while the commercial one consumed HCFC141b pbw. and water 1.5 pbw. F1533 is the best formulation when considers in all properties results and cost competitiveness since it composed of a high level of polyester polyol and also consumed less catalyst while an acceptable reactivity, low FRD, good mechanical property and excellent thermal conductivity property were achieved. Acknowledgements Program in Petrochemistry and Polymer Science, Department of Chemistry, Faculty of Science, Chulalongkorn University, IRPC Polyol Co., Ltd. and IRPC Public Company Limited are acknowledged for all of knowledge advice, materials and also financial support for this research. References [1] K. Dedecker, J. Deschaght and G. Biesmans In: S. Lee and D. Randall, Editors, The Huntsman Polyurethanes Book, Wiley, Italy (10), 9 and 96. [2] M. Szycher, Szycher's Handbook of Polyurethanes, CRC Press, Florida (1999), Chapter 8, 146. [3] W.J. Seo, H.C. Jung, J.C. Hyun, W.N. Kim, Y.B. Lee, K.H. Choe and S.B. Kim, J. Appl. Polym. Sci. 90 (03) [4] W.J. Seo, J.H. Park, Y.T. Sung, D.H. Hwang, W.N. Kim and H.S. Lee, J. Appl. Polym. Sci. 93 (04) [5] M. Thirumal, D. Khastgir, N.K. Singha, B.S. Manjunath and Y.P. Naik, J. Appl. Polym. Sci. 108 (08) [6] J.F. Jin, Y.L. Chen, D.N. Wang, C.P. Hu, S. Zhu and L. Vanoverloop, Anal. Sci. (08) [7] J. Luna, D. Shieh and A.D. Leon, API Conference Proceeding, Salt Lake City, Utah, USA (06) [8] W.R. White, J.A. Mullins, T.B. Lee, K. McLellan and R.J. Wierzbicki, U.S. Pat. 5,684,057 (1997). [9] C.A. McAdams and S. Farmer, J. Cell. Plast. 39 (03) Figure 3. Cell morphology of free rising RPUF in a) parallel and b) perpendicular to foam rising direction. 4. Conclusions PU formulations with an improvement of low FRD, high compressive strength together with low thermal conductivity properties were achieved by partially adding polyester polyol into polyether polyol mixture together with a finetuning of catalyst and blowing agent system. HCFC 141b blowing agent could be partially substituted by water in which it can be found in the Table 2 that F1531 to F1533 consumed HCFC141b pbw. and water pbw. Pure and Applied Chemistry International Conference 12 (PACCON 12)

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