James L. Schwendeman

Preparation and Properties of Open Pore Polyurethane (OPP)

Open-pore polyurethane (OPP) structures again fall into the last category wherein there are small interconnecting pores between randomly packed chains of spheres. Open-pore-polyurethane structures are not like the conventional foams that have unit cells, but consists rather of a network structure of entangled chains of spheres (--11-’ diameter), with interconnected pores (5-lop, formed by the interstices between the chains of spheres). The Chemical Reactions in the Formation

The Counter-Pressure Process for Molding Bead Polystyrene Foam

The process for conventional molding of polystyrene bead foam blocks is well known to most but will be reviewed briefly as background for discussion of the counter-pressure process. The sequence of events in the commercial process is shown in Figure 1. 1. Pre-Expand Beads to Desired Apparent Density Polystyrene beads containing pentane pneumatogen are pre-expanded in one of several types of steam or air equipment to the apparent density that is desired in the final molded product. Sojourn time and temperature in the pre-expander is adjusted to obtain beads which are expanded to the desired degree. 2. Allow Beads to Recuperate About 24 Hours It is desirable to allow the beads to recuperate after pre-expansion at least overnight. This is especially important in the case of very low density moldings where apparently significant diffusion of atmospheric air into the pre-expanded bead takes place and tends to equilibrate the gas pressure inside the bead with that outside.

Evaluation of Four Foaming Techniques for Inflating a PK-2 Life Raft

man life raft (termed the &dquo;PK-2&dquo; by the Navy). The PK-2 life raft is shown in Figure 1. The PK-2 and similar gas-inflated, rubberized cloth rafts have been used successfully for more than 20 years in emergencies at sea. Although dependable in most respects, the gas-inflated life raft is easily damaged (tears or rips in deployment, enemy action, sharks, etc). Operational requirements of the foam system to be developed in this study were: 1. Rapid inflation (10 seconds at 70 ° F and 30 seconds at -20 ° F ) , 2. Operation over a wide temperature range (-20°F to 160°F), 3. Buoyancy sufficient to support 265 pounds at sea, 4. Resistance to damage, 5. Size (0.3 cu ft) and weight (7 lb ) of the undeployed raft to approximate closely the present PK-2 life raft. 1-Approach I 2-Approach II 3-Approach III 4-Approach IV 1-Use of preformed flexible foam as a means for deploying and inflating the raft. 2-Use of two-component liquid urethane reactants in conjunction with simplified mixing equipment to produce rigid and semi-rigid foam-inflating material.