Effects of Melamine Particle Size on Flexible Polyurethane Foam Properties

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The purpose of this paper is to elucidate the relationships between the size of the melamine particles dispersed and the foam properties such as hardness, tensile strength, resiliency, and flammability in the formulation of the flame retarded polyurethane high resilient molded foam. Fine melamine particles, ca. 5 Im in average, were compared with the generally-used large ones, ca. 60 ym in average, for their effects on the properties of the resultant foam. Conventionally-used ACTCOL MF-34M, a polyether-polyol dispersing large melamine particles, and specially-developed ACTOOL MF-34N, a polyether-polyol dispersing fine melamine particles, were employed in this study. The foam with the fine particles showed higher hardness, better tensile properties, and less flammability than that with the larger ones. The resiliency of the foam, however, was slightly low in the fine particle system compares to that in the large particle system. By optical microscopy, we found that the fine particles dispersed everywhere in the foam skeleton and that the large particles were located only in the strut joints because the particles are larger than the strut thickness. With an increase in melamine content, the cellular structure was unchanged in the fine particle system, but in the large particle system the struts became thin and the melamine-embedded joints became thick. The deforming ways of the cellular skeletons were also monitored by optical microscopy during the compression and the stretching of the foams. When the foam was compressed, every part of the skeleton deformed in the fine particle system, and the struts mainly deformed in the large particle system. When the foam was stretched, the struts oriented to the longitudinal direction in the fine particle system, and the melamine-embedded rigid joints inhibited the orientation of the struts in the large particle system. The differences in mechanical properties of the foams obtained were thought to depend on the ways the melamine particles disperse in the cell skeleton. As for the difference in the flammability, the location and the surface area of the particles would be the important factors. The results in this paper indicate that a flame retarded foam with better physical properties can be manufactured by a polyol including melamine particles smaller than the strut thickness of the resultant foam.