Solvent molding

Methods. Individual solutions of the blend components in dioxane (or tetrahydrofuran) were mixed, and stirred for about 12 hours before casting into a Teflon mold. Solvent evaporation proceeded under ambient conditions for 24 hours followed by transferral to a vacuum oven at 60°C for further removal of solvent. The dried blends were then stored in a vacuum desiccator over P2O5. 

By heating and polymerizing monomer solution at several tens of °C for several hours, a polymer is formed that has 3D crosslinking. By boiling this in saline solution after removal from the mold, solvent and residual monomer are extracted and removed. Finally, a highly hydrated hydrogel is prepared by hydration. 

Cold isostatic pressing Cold press molding Cold solvent cleaning Cold War... 

Polyimides for use ia molded products and high temperature films can be produced by the reaction of pyromelHtic dianhydride [89-32-7] and 4,4 -diaminodiphenyl ether [13174-32-8] ia DMAC to form a polyamide that can be converted iato a polyimide (13). DMAC can also be used as a spinning solvent for polyimides. AdditionaUy, polymers containing over 50% vinyHdene chloride are soluble up to 20% at elevated temperatures ia DMAC. Such solutions are useful ia preparing fibers (14). 

The fluid plasticizer (solvent) consists of an energetic compound, eg, nitroglycerin, an inert carrier, and a stabilizer. The system is evacuated to remove volatiles, moisture, and air, and the plasticizer is then pressurized and passed slowly upward through the powder bed while the powder is held stationary by a pressure plate on the powder column. Casting solvent may also be added from the top of the mold. 

AcryHc resins are often ceU-cast (11). In this process no solvent is used, but the fluid monomers are passed into a cell or mold where polymerization takes place to form a soHd sheet. Heavy sections can be produced in this fashion. Formation of cast acryHc is moving toward modified continuous-based casting to increase productivity. Dmm casting on a commercial scale has almost disappeared. 

A. J. Woytek and. E. Gentilecore, "A New Blow Mol ding Process to Reduce Solvent Permeation of Polyolefin Containers," paper no. 13 presented at ddpances in Blow Molding Conference Rubber and Plastics Institute, London, Dec. 6,1977. 

Preservatives. Most products must contain preservatives to ensure that yeasts, molds, and bacteria do not thrive in them. These preservatives include alcohol, methylparaben, propylparaben, DMDM hydantoin, diazohdinyl urea, and imidazohdinyl urea. The parabens have limited solubiUty in water, eg, 0.25% for methylparaben and 0.05% for propylparaben (22). If these levels are exceeded in the formula, then the addition of solvents is needed to ensure clear, stable products. 

Suspension Polymers. Methacrylate suspension polymers are characterized by thek composition and particle-size distribution. Screen analysis is the most common method for determining particle size. Melt-flow characteristics under various conditions of heat and pressure are important for polymers intended for extmsion or injection molding appHcations. Suspension polymers prepared as ion-exchange resins are characterized by thek ion-exchange capacity, density (apparent and wet), solvent sweUing, moisture holding capacity, porosity, and salt-spHtting characteristics (105). 

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aUphatic and aromatic hydrocarbons promote crazing of stressed molded samples. Eor these reasons, care must be exercised in the choice of solvents for painting and coating operations. Eor sheet appHcations, polycarbonate is commonly coated with a sihcone—sihcate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

Noryl is a rigid dimensionally stable material. Dimensional stabiUty results from a combination of low mold shrinkage, low coefficient of thermal expansion (5.9 x 10 per° C), good creep resistance (0.6—0.8% in 300 h at 13.8 MPa (2000 psi)), and the lowest water absorption rate of any of the engineering thermoplastics (0.07% in 24 h at room temperature). Noryl resins are completely stable to hydrolysis. They are not affected by aqueous acids or bases and have good resistance to some organic solvents, but they are attacked by aromatic or chlorinated aUphatic compounds. 

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

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