Plastics classes

Chapter 661 of the USP provides criteria for the interchangeability of low- and high-density polyethylene for dry, oral dosage forms. In addition, there are standards for polyethylene terephthalate bottles and polyethylene terephthalate G bottles. USP criteria for interchangeability are listed in Table 17. These criteria allow usage of alternate materials in the same plastic class to be used prior to obtaining prior stability data. 

Generally, it is believed that many plastics classed as insulators become partial conductors when "hot and wet" (12). The UV and thermally cured solder masks in Table III show a dramatic loss of insulation resistance after seven days at 85°C and 95% relative humidity (RH). All the test boards recovered most of their initial insulation resistance after 24 hours at ambient conditions. Table IV shows that an additional exposure to 85°C at ambient humidity produces an increase in insulation resistance. 

The second is that representative samples of the material are independently tested according to a method described in USP 23. In the Biological Test for Plastics Class VI (70 °C), the test sample is extracted at 70 °C in a range of solutions, and both these extracts and the test material itself are checked for direct biological reactivity, leading to a pass/faU result. 

It is useful to note that individual polyurethane elastomer classes are truly compatible with only specific plasticizer classes. Polyether-based urethanes are compatible with phthalate ester plasticizers such as dioctyl-phthalate (DOP) and its analogues, whilst polyester-based urethanes are only compatible with benzoate ester-type plasticizers. 

Nylon A class of synthetic fibres and plastics, polyamides. Manufactured by condensation polymerization of ct, oj-aminomonocarboxylic acids or of aliphatic diamines with aliphatic dicarboxylic acids. Also rormed specifically, e.g. from caprolactam. The different Nylons are identified by reference to the carbon numbers of the diacid and diamine (e.g. Nylon 66 is from hexamethylene diamine and adipic acid). Thermoplastic materials with high m.p., insolubility, toughness, impact resistance, low friction. Used in monofilaments, textiles, cables, insulation and in packing materials. U.S. production 1983 11 megatonnes. 

The polymers of the 2-cyanoacryhc esters, more commonly known as the alkyl 2-cyaiioacrylates, are hard glassy resins that exhibit excellent adhesion to a wide variety of materials. The polymers are spontaneously formed when their Hquid precursors or monomers are placed between two closely fitting surfaces. The spontaneous polymerisation of these very reactive Hquids and the excellent adhesion properties of the cured resins combine to make these compounds a unique class of single-component, ambient-temperature-curing adhesives of great versatiUty. The materials that can be bonded mn the gamut from metals, plastics, most elastomers, fabrics, and woods to many ceramics. 

One of the principal classes of flame retardants used in plastics and textiles is that of phosphorus, phosphorus—nitrogen, and phosphorus—halogen compounds (see also Flame retardants for textiles). Detailed reviews of phosphoms flame retardants have been pubhshed (1—6) (see also Phosphorus compounds). 

PCTFE plastic is available in products that conform to ASTM 1430-89 Type 1 (Grades 1 and 2) and is suitable for processing into parts that meet MIL-P 46036 (Federal Specification LP-385C was canceled 1988). Standards for fabricated forms are available for compression molded heavy sections (AMS-3645 Class C), thin-walled tubing, rod, sheet, and molded shapes (AMS-3650). PCTFE plastics have been approved for use in contact with food by the FDA (55). 

Perhaps the simplest examination done is the physical match. A small fragment of wood, plastic, or other material is recovered and fitted into a large piece found on the suspect or at the scene of the crime (39). Other examinations result ordy in demonstrating class characteristics (40). Such information may be used in a prosecution as circumstantial evidence in a trial. However, it is important that the forensic scientist neither inflate nor minimize (41,42) its importance. 

Typical chemical stmctures and representative sources of different classes of synthetics are given in Table 6. Properties and uses of representative synthetics foUow in Table 7. In addition to considering thek physical properties, selection is needed of appropriate paints, seals, hoses, plastics, and electrical insulation to avoid problems with the pronounced solvency and plasticizing action of many of these synthetic oils. 

Polyolefins are manufactured and used in much greater quantity than any other class of plastics. The principal polyolefins are polyethylenes of various densities (LDPE, LLDPE, HDPE) and polypropylene (PP) (see Olefin polymers). 

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