Poly moldings

Polyethylene films as packaging ma terial plastic squeeze bottles are molded from high density poly ethylene... 

Properties Poly(methyl methacrylate) Cast sheet Impact- modified Heat- resistant Alkyd, molded Acrylic poly(vinyl chloride) alloy ... 

Properties Nylon 6/9, molding and extrusion Nylon 6/12 Nylon 11, molding and extrusion Nylon 12, molding and extrusion Aromatic nylon (aramid), molded and unfilled Poly(amide- imide), unfilled... 

The beater additive process starts with a very dilute aqueous slurry of fibrous nitrocellulose, kraft process woodpulp, and a stabilizer such as diphenylamine in a felting tank. A solution of resin such as poly(vinyl acetate) is added to the slurry of these components. The next step, felting, involves use of a fine metal screen in the shape of the inner dimensions of the final molded part. The screen is lowered into the slurry. A vacuum is appHed which causes the fibrous materials to be deposited on the form. The form is pulled out after a required thickness of felt is deposited, and the wet, low density felt removed from the form. The felt is then molded in a matched metal mold by the appHcation of heat and pressure which serves to remove moisture, set the resin, and press the fibers into near final shape (180—182). 

Tetraethylene glycol may be used direcdy as a plasticizer or modified by esterification with fatty acids to produce plasticizers (qv). Tetraethylene glycol is used directly to plasticize separation membranes, such as siHcone mbber, poly(vinyl acetate), and ceUulose triacetate. Ceramic materials utilize tetraethylene glycol as plasticizing agents in resistant refractory plastics and molded ceramics. It is also employed to improve the physical properties of cyanoacrylate and polyacrylonitrile adhesives, and is chemically modified to form polyisocyanate, polymethacrylate, and to contain siHcone compounds used for adhesives. 

Bulk Polymerization. This is the method of choice for the manufacture of poly(methyl methacrylate) sheets, rods, and tubes, and molding and extmsion compounds. In methyl methacrylate bulk polymerization, an auto acceleration is observed beginning at 20—50% conversion. At this point, there is also a corresponding increase in the molecular weight of the polymer formed. This acceleration, which continues up to high conversion, is known as the Trommsdorff effect, and is attributed to the increase in viscosity of the mixture to such an extent that the diffusion rate, and therefore the termination reaction of the growing radicals, is reduced. This reduced termination rate ultimately results in a polymerization rate that is limited only by the diffusion rate of the monomer. Detailed kinetic data on the bulk polymerization of methyl methacrylate can be found in Reference 42. 

Phthahc anhydride (1) is the commercial form of phthaUc acid (2). The worldwide production capacity for the anhydride was ca 3.5 x 10 metric tons ia 1993, and it was used ia the manufacture of plasticizers (qv), unsaturated polyesters, and alkyd resins (qv) (see Polyesters, unsaturated). Sales of terephthahc acid (3) and its dimethyl ester are by far the largest of any of the benzenepolycarboxyhc acids 14.3 x 10 t were produced in 1993. This is 80% of the total toimage of ah. commercial forms of the benzenepolycarboxyhc acids. Terephthahc acid is used almost exclusively for the manufacture of poly(ethylene terephthalate), which then is formed into textiles, films, containers, and molded articles. Isophthahc acid (4) and trimehitic anhydride (5) are commercial products, but their worldwide production capacities are an order of magnitude smaller than for terephthahc acid and its dimethyl ester. Isophthahc acid is used primarily in the production of unsaturated polyesters and as a comonomer in saturated polyesters. Trimehitic anhydride is used mainly to make esters for high performance poly(vinyl chloride) plasticizers. Trimesic acid (6), pyromehitic dianhydride (7), and hernimehitic acid (8) have specialized commercial apphcations. The rest of the benzenepolycarboxyhc acids are not available commercially. 

Soft-drink bottles made from poly(ethylene terephthalate) (PET) are usuady made by stretch-blow mol ding in a two-step process. Eirst, a test-tube-shaped preform is molded, which is then reheated to just above its glass-transition temperature, stretched, and blown. Stretching the PET produces biaxial orientation, which improves transparency, strength, and toughness of the botde (54,56). A one-step process is used for many custom containers that are injection stretch-blow molded. 

PEN film for audio- and videotape and various electronic appHcations and blow molded PEN containers for hot-fill appHcations are already being marketed in Japan. NDA is unlikely to ever become as inexpensive as terephthaUc acid but novel NDA-based polyesters will become available if a market need exists. One example could be the experimental polyester PBN (Celanese Corp.) this is the NDA analogue of PBT, poly(l,4-butylene naphthalene-2,6-dicarboxylate) [28779-82-0]. It has a high rate of crystallization, faster even than that of PBT, and its combination of physical properties is weU-suited for injection molding. 

Properties of PET Molding Resins. The fliU crystal stmcture of poly(ethylene terephthalate) has been estabhshed by x-ray diffraction (134—137). It forms triclinic crystals with one polymer chain per unit cell. The original cell parameters were estabhshed in 1954 (134) and numerous groups have re-examined it over the years. Cell parameters are a = 0.444 nm, b = 0.591 nm, and c = 1.067 nm a = 100°, (3 = 117°, and 7 = 112° and density = 1.52 g/cm. One difficulty is determining when crystallinity is fliUy developed. PET has been aimealed at up to 290°C for 2 years (137). 

Thermoplasticity. High molecular weight poly(ethylene oxide) can be molded, extmded, or calendered by means of conventional thermoplastic processing equipment (13). Films of poly(ethylene oxide) can be produced by the blown-film extmsion process and, in addition to complete water solubiUty, have the typical physical properties shown in Table 3. Films of poly(ethylene oxide) tend to orient under stress, resulting in high strength in the draw direction. The physical properties, melting behavior, and crystallinity of drawn films have been studied by several researchers (14—17). 

Thermoplastic Processing. Poly(ethylene oxide) resins can be thermoplasticaHy formed into soHd products, eg, films, tapes, plugs, retainers, and fillers (qv). Through the use of plasticizers (qv), poly(ethylene oxide) can be extmded, molded, and calendered on conventional thermoplastic... 

Other bacterial strains identified as biodegrading poly(vinyl alcohol) iaclude Flavobacterium (95) 2in.dFicinetobacter (96) and many others, as well as fungi, molds, and yeasts (97). Industrial evaluations at Du Pont (98) and Air Products (99) iadicate that over 90% of poly(vinyl alcohol) entering wastewater treatment plants is removed, and hence no environmental pollution is likely. 

Small amounts of TAIC together with DAP have been used to cure unsaturated polyesters in glass-reinforced thermo sets (131). It has been used with polyfunctional methacrylate esters in anaerobic adhesives (132). TAIC and vinyl acetate are copolymerized in aqueous suspension, and vinyl alcohol copolymer gels are made from the products (133). Electron cure of poly(ethylene terephthalate) moldings containing TAIC improves heat resistance and transparency (134). 

An example is poly(bis(p-carboxyphenoxy)propane) (PCPP) which has been prepared as a copolymer with various levels of sebacic anhydride (SA). Injection molded samples of poly (anhydride) / dmg mixtures display 2ero-order kinetics in both polymer erosion and dmg release. Degradation of these polymers simply releases the dicarboxyhc acid monomers (54). Preliminary toxicological evaluations showed that the polymers and degradation products had acceptable biocompatibiUty and did not exhibit cytotoxicity or mutagenicity (55). 

Fig. 12. Viscosity at different temperatures measured by a capillary viscometer injection-molding grade of poly(methyl methacrylate) (43). To convert N/m to psi, multiply by 145 to convert (N-s)/m to (dyn-s)/cm (P), multiply by 10.

Heat-SensitiZingProcess. Another process used to make latex mbber articles of thicker section involves sensitizing the compound so that it coagulates when heated to a given temperature, then using heated molds to build the article to the desired thickness. Ammonia-preserved latex is used in this process, and polyether, polythioether, or poly(vinyl methyl ether) (PVME) can be used as heat-sensitizing agents. 

The poly(vinyl acetal) prepared from acetaldehyde was developed in the early 1940s by Shawinigan Chemicals, Ltd., of Canada and sold under the trade name Alvar. Early uses included injection-molded articles, coatings for paper and textiles, and replacement for shellac. Production peaked in the early 1950s and then decreased as a result of competition from less expensive resins such as poly(vinyl chloride) (see Vinyl polymers, poly(vinyl chloride)). 

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