Solid-plastic forming

Applicability Most hazardous waste slurried in water can be mixed directly with cement, and the suspended solids will be incorporated into the rigid matrices of the hardened concrete. This process is especially effective for waste with high levels of toxic metals since at the pH of the cement mixture, most multivalent cations are converted into insoluble hydroxides or carbonates. Metal ions also may be incorporated into the crystalline structure of the cement minerals that form. Materials in the waste (such as sulfides, asbestos, latex and solid plastic wastes) may actually increase the strength and stability of the waste concrete. It is also effective for high-volume, low-toxic, radioactive wastes. 

Ratio of the volume of loose molding compound to the volume of the same amount in molded solid form ratio of density of solid plastic component to apparent density of loose molding compound. 

Solid-Phase Forming (Cold Forming) of Plastics , PLASTEC Rept R42 (1972) 36) A.F. 

Results obtained for two mixed plastics are summarized in Table 4. A balance exists between process temperature, plastics feed rate, and product yields (67). For example, lower temperatures increase wax formation due to incomplete depolymerization. Slower feed rates and increased residence times reduce wax formation and increase the yield of liquids. The data summarized in Table 4 illustrate that the addition of PET to a HDPE PP PS mixture changes the performance of the Conrad process. Compared to the reference HDPE PP PS mixture, increased amounts of solids are formed. These are 95% terephthalic acid and 5% mono- and bis-hydroxyethyl esters. At higher temperatures, apparendy enough water remains to promote decarboxylation. 

Plastics and polymers take much of the production of the petrochemical industiy in the form of monomers such as styrene, acrylates, and vinyl chloride. The products of this enormous industry are everything made of plastic including solid plastics for household goods and furniture, fibres for clothes (24 million tonnes per annum), elastic polymers for car tyres, light bubble-filled polymers for packing, and so on. Companies such as BASE, Dupont, Amoco, Monsanto, Laporte, floechst, and ICT are leaders here, Worldwide polymer production approaches 100 million tonnes per annum and PVC manufacture alone employs over 50 000 people to make over 20 million tonnes per annum. 

Reaction injection molding (RIM) is a fast, low-pressure, low-temperature, low-cost process for one-step conversion of reactive liquids into large finished solid plastic products. Liquid polyol and liquid diisocyanate are mixed by impingement, pumped instantly to fill a large mold cavity, and polymerize/ cure rapidly to form a thermoset polyurethane product. The cured polymer may be a stiffly flexible product such as automotive bumper covers, front ends, and trim or a rigid foamed product such as furniture and housings (cabinets) for computers, business machines, TY and radio. 

Either crystalline and amorphous types (Chapter 1) can be used with flow molding because the plastic is melted prior to forming. The forming temperature is usually lower than for injection molding or extrusion. Plastics need not be trimmed, as the composite is compression-molded to completely fill the mold cavity (Chapter 14). Very important, the flow molding process permits more complex parts to be formed than solid-state forming. The process cycle time is usually about 1 min. 

One essential difference between casting and molding processes is that pressure need not be used in casting (although large-volume, complex parts can be made by low pressure and/or vacuum casting methods). Another difference is that the starting material is usually in liquid form rather than the usual solid plastic used in other processes. There is also the difference that the liquid could be a monomer rather than the plastic used in most other processes and in turn the monomer is converted to a polymer/plastic (Chapter 1). 

In general the work required to form new surface area of a solid (plastic and elastic) is given by the expression [14]... 

A final technique presented for the continuous production of solid dosage forms is extrusion/ spheronization—a technique producing spherical agglomerates of very uniform size. The process is based on low-pressure extrusion and shaping the moist, plastic extrudate into spheres in a spheronizer. These spheres (pellets) are, in most cases, coated after drying and filled into hard gelatin capsules or compressed into... 

Shah PS, Zatz JL. Plasticization of cellulose esters used in the coating of sustained release solid dosage forms. Drug Dev Ind Pharm 1992 18 1759-1772. 

The advantage over povidone in solid dosage forms lies mainly in its lower hygroscopicity and higher plasticity (see Sections 4.2.4.4 and 4.4.2.4). Copovidone is seldom used in liquid dosage forms, apart from sprays. 

A cellular plastic is defined as a two-phase gas-solid plastic system whose apparent density is decreased substantially by the presence of numerous cells or voids disposed throughout its mass. These cells or voids are chiefly formed by using CBAs, PBAs, microballoons, or fillers containing gases or liquids. If these cells are discrete and the gas phase of each is independent of that of the other cells, the material is termed closed cell. 

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