Pre-expanded particles

Patent Number US 6166096 A1 20001226 PRE-EXPANDED PARTICLES OF POLYPROPYLENE RESIN, PROCESS FOR PRODUCING THE SAME AND PROCESS FOR PRODUCING IN-MOULD FOAMED ARTICLES THEREFROM... 

Patent Number US 6130266 A1 20001010 PRE-EXPANDED PARTICLES OF PROPYLENE RESIN, PROCESS FOR PREPARING THE SAME AND FLOW-RESTRICTING DEVICE... 

Patent Number EP 1016690 A2 20000705 WATER-CONTAINING POLYPROPYLENE RESIN COMPOSITION AND PRE-EXPANDED PARTICLES MADE THEREOF... 

Stuart, J.B. Skarke, S.C. Ogita, T. et al. Flame retardant polyolefin resin pre-expanded particles and in-mold foamed articles prepared therefrom, PCT US Patent 6,822,023 assigned to Kaneka Corporation, 2001. 

Isotactic Polystyrene. The familiar steam molding of pre-expanded particles has so far not been applied successfully to isotactic polystyrene. However, the polymer has been foamed, according to three disclosed methods. For example, finely divided acetone-insoluble polymer, with a melting point in excess of 200°C., is blended with a liquid selected from methylene chloride, aromatic hydrocarbons, or halogenated aromatic hydrocarbons. This blend is then heated (84). A mixture of molten polymer and methyl chloride, propane, or butane is suddenly depressurized (8). Foam may also be generated in a continuous manner directly from a butyllithium-initiated polymerization conducted in the presence of a 4/1 blend of benzene and petroleum ether (15). 

Thermoplastic foams are closed cell foams that are pre-expanded particles before they are processed to a finished product (Figure 1.190 and Figure 1.191). 

Liquid carbon dioxide (purity 99, 95 Vol %) was undercooled (W2) to avoid cavitation in the membran pump (P). After the compression to pre-expansion pressure, the fluid is heated to the extraction temperature (W3). The supercritical fluid loaded with anthracene leaves the extractor (V = 0,6 1). With a additional heat exchanger (W4), the solution is heated to pre-expansion temperature. In the separation vessel, the supercritical solution is expanded through a nozzle. The expanded gas will be condensed (Wl) and recompressed or let off. After the experiment, the separation vessel is opened and the particles were collected. The particle size is measured by laser diffraction spectroscopy (Malvern Master Sizer X). 

At constant pre-expansion pressure, the post-expansion pressure was varied from 5 bar til 60 bar. As it is shown in figure 4 at constant pre-expansion temperature T = 110 °C, there is no provable influence of the post-expansion pressure on the particle size distribution for these three pre-expansion pressures. It is not necessary to expand the supercritical solution til atmospherical pressure, the gas could be expanded to 60 bar and recompressed. 

The expandable polystyrene particles, based on suspension polymerization, are converted into foam in three steps pre-foaming, temporary storage and final... 

In the experiments that followed, the pre- and post-expansion temperature, pressure and composition were systematically perturbed around their values in this base case and the results were compared to identify the effects of each variable on the morphology and size of the precipitated Naphthalene particles. The pre-expansion temperature, while varied, was kept high enough in all experiments so that the jet of expanded fluid downstream of the nozzle was not visible, i.e. no condensation of carbon dioxide occurred upon expansion. Tbe base case post-expansion pressure corresponds roughly to the solubility minimum of Naphthalene in CO2 at 45 C (2). All of the experiments performed in this study are listed in Table I (Run 1 is the above mentioned base case). 

The ideal-gas equation describes how gases behave but not why they behave as they do. Why does a gas expand when heated at constant pressure Or why does its pressure increase when the gas is compressed at constant temperature To understand the physical properties of gases, we need a model that helps us picture what happens to gas particles when conditions such as pres.sure or temperature change. Such a model, known as the kinetic-molecular theory of gases, was developed over a period of about 100 years, culminating in 1857 when Rudolf Clausius (1822—1888) published a complete and satisfactory form of the theory. 

In the event that the sohds in the suspension are either too fine, even for the most efficient of filter fabrics, pre-coating the filter cloth with filter aids such as diatomaceous earth or expanded perlite will significantly enhance particle capture. In similar vein, where filtration conditions are difficult due to slimy suspensions, such agents are often added as body feed... 

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