Morphological and thermal analyses of flexible polyurethane foams containing commercial calcium carbonate

www.scielo.br/eq www.ecletica.iq.unesp.br Volume 33, número 2, 2008 Morphological and thermal analyses of flexible polyurethane foams containing commercial calcium carbonate S. S. Sant’Anna1, D. A. Souza1, C. F. Carvalho2, M. I. Yoshida1* Department of Chemistry, UFMG, Av. Antônio Carlos, 6627 – Pampulha, 31270-90, Belo Horizonte – MG. 2 Department of Chemistry, UFOP, Campus Universitário – Morro do Cruzeiro, 35400-000 Ouro Preto – MG. * 1 Abstract: One filler often utilized in flexible polyurethane foams is calcium carbonate (CaCO3) because it is non-abrasiveness, non-toxicity and facilitated pigmentation. However, it is observed that the excess of commercial CaCO3 utilized in industry possibly causing permanent deformations and damaging the quality of the final product. The effect of different concentrations of commercial CaCO3, in flexible foams, was studied. Different concentrations of CaCO3 were used for the synthesis of flexible polyurethane foams, which were submitted to morphological and thermal analyses to verify the alterations provoked by the progressive introduction of this filler. Keywords: polyurethane; flexible foam; calcium carbonate. Introduction The versatility of polyurethane chemistry permits the production of a great variety of materials such as flexible foams, rigid foams, films and molded devices, among others, depending on the initial ingredients used in the synthesis [1]. Flexible polyurethane foams are one of the most important classes of cellular plastic and can be applied in the fabrication of a wide range of materials for different uses such as foam mattresses, pillows, furniture, etc. [2]. When adding a filler to a polymer to form a conjugated biphasic material, the properties of the final material will be intermediate between those of the two components. The tension applied to the polymeric matrix will be transferred in part to the disperse phase, the filler, since it presents properties superior to the pure polymer [3]. Efficient reinforcement is achieved by interactions of the constituents of the biphasic material Ecl. Quím., São Paulo, 33(2): 55-60, 2008 [4-5] via mechanisms of adhesion, which could be: adsorption, chemical bonding and mechanical adhesion. Chemical bonding is the most efficient form of adhesion and occurs with the application of coupling agents on the surface of the filler, which serves as a bridge between the polymer and the reinforcement. In mechanical adhesion, the polymer fills in the grooves of the filler; this adhesion tends to be low unless there is a large number of recesses on the surface of the filler [6]. Several types of materials exist that can be used as filler. Among the inorganic materials utilized as filler, notable ones include: calcium carbonate, aluminum hydroxide, silica, titanium dioxide and talc [6]. Some of the organic materials more commonly used are carbon black [7] and natural fibers [8-9]. In flexible polyurethane foams, the fillers promote an increase in density and resistance to compression. However, they reduce the resiliency and contribute to the increase in permanent defor55 mation. In addition, properties such as tear strength, for example, are significantly affected by the introduction of filler [10]. Accordingly, it is necessary to know the end-use of the material in order to use the correct concentration in the polymer matrix, obtaining a product of reliable quality. In spite of the polyurethane industry widely using calcium carbonate as a filler, generally the quantity used is defined randomly. In the businesses visited in the region of Belo Horizonte in Minas Gerais State - Brazil, no data was available on the influence of this filler on the foam, nor was there any methodology to define the ideal quantity of calcium carbonate that should be added without causing damage to the mechanical properties of the final product. Thus the proposal of the present work was to analyze the morphological, mechanical and thermal behavior when various concentrations of commercial calcium carbonate were introduced into the polymer matrix using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) microanalysis and thermal analysis. Experimental Preparation of flexible foams For the fabrication of the flexible foams, the following components were used: polyether polyol Voranol 4730N (100.00 pph = parts per hundred parts of polyol) and TDI Voranate T-80 (50.00 pph) purchased from Dow Chemical; the silicone surfactant PDMS/POE (0.60 pph) from General Electric; amine Aricat AA 805 purchased from Arinos (0.16 pph) and stannous dioctoate II (Liocat 29, Miracema-Nuodex, 0.30 pph) were used as catalysts in the polymerization and expansion reactions [11-12]; distilled water (3.00 pph); and commercial calcium carbonate (1, 9, 15, 21 and 30 pph) obtained from the mattress manufacturing industries in the region of Belo Horizonte. The stoichiometry of the formulation used in industry was adjusted for the lab-scale fabrication of foams. The isocyanate index used was 132. A Fisatom model 710 shaft stirring device (power: 25W, rotation: 25-200 rpm) was used for stirring. Polyol and the filler were placed in a disposable plastic receptacle, and the mixture was 56 stirred until complete homogenization. Next, the amine, surfactant and water were added. The mixture was submitted to mechanical stirring for 60 seconds. Shortly after the catalyst was added and the mixture was stirred again for 30 seconds. After introducing the isocyanate, the mixture was submitted to 6 seconds of stirring and then poured into a cubical cardboard box (7cm x 7cm x 7cm). The foams were left to cure for seven days. Flexible foams analyses For the instrumental analyses, the following instruments were used: SEM – Jeol JSM-840; microanalysis (EDS) – Jeol-8900 electron probe microanalyzer; thermogravimetric analysis (TG) – Netzsch STA 409EP. SEM — The samples were cut into little pieces (0.5cmx0.5cmx0.5cm) using scissors. Next they were covered with a fine layer of gold to permit observation in SEM since the samples were not conductors. The samples were analyzed under magnifications of 50, 150 and 500x. EDS — The samples of calcium carbonate were covered with a thin layer of carbon and analyzed under with an accelerating voltage of 15 kV and a current of 20 nA. TG — alumina crucible; dynamic atmosphere of air; 100 mL.min-1 gas flow; heating rate of 10ºC min-1; heating range of 25-950ºC. The sample masses were approximately 12 mg. Results and discussion Morphological analysis of commercial calcium carbonate When a filler is introduced into a polymeric material, the ideal is that it has regular granulometry and that its particles are sufficiently small to enable good distribution in the matrix [7]. Figure 1 presents the image obtained in the scanning electron microscopy (SEM) of commercial calcium carbonate at a magnification of 500x. In the image obtained, it was observed that the calcium carbonate presented ir (...truncated)