Rigid Polyurethane Foam Composites

In the first part of this work, the expandable graphite (EG) with different particle size filled rigid pol(?)urethane (RPUF) foam was obtained. The EG particles were pulverized to ac(?)eve different sizes using an ultra-high-speed mixer. The microstructure of particles was observed by a scanning electron microscope (SEM). EG particles show an irregular flake structure. With the increase of the mixing time, the EG particles become circular and the collapses and cracks in the EG surfaces produce. Many exfoliated graphite flakes are observed, whose thickness reduces with increasing the pulverization time. The particle sizes of the processed EG are much smaller than that of the unprocessed EG. Sizes of EG particles are estimated using SEM micrographs and an image analysis system. The average diameter and average area of the EG particles rapidly decrease with the increase of mixing time. For example, the average area was decreased to 7424.4μm~2 from 39661.5μm~2 after a 4 min mixing time, and further decreased to 1422.4μm~2 after 13min. The expansion volume of the EG particles reduces resulting from the decrease of particle sizes and the weight ratio of the graphite to oxidant. The EG particles after thermal expansion reveal the loose structure, and the space between the carbon sheets is many times wider than the lots among the graphite flakes, and the thickness of the EG layer is less than 100 nm. The effects of different expandable graphite particle sizes on the fire-retardant properties of high-density (RPUF) (0.45 g/cm~3) were studied. It is surprised that the large EGO (as received) and EG4 particles can both improve the fire-retardant properties of RPUF composite efficiently but the fine EG13 particles not. For example, when the EG is 20 wt% the LOI value of the EGO/RPUF and EG4/RPUF increased rapidly to 39.5 from 22.5 of pure RPUF compared to 23.5 for EG13/RPUF. The char morphology of the composites showed that the expanded...