Surface resistance, polypropylene

Artificial surfaces must be resistant to cigarette bums, vandaUsm, and other harm. Fire resistance is most critically evaluated by the NBS flooring radiant panel test (10). In this test, a gas-fired panel maintains a heat flux, impinging on the sample to be tested, between 1.1 W/cm at one end and 0.1 W/cm at the other. The result of the bum is reported as the flux needed to sustain flame propagation in the sample. Higher values denote greater resistance to burning results depend on material and surface constmction. Polypropylene turf materials are characterized by critical radiant flux indexes which are considerably lower than those for nylon and acryflc polymers (qv) (11). 

R.S. Bisht, R. Kumar, N. Thaku, Change in surface free energy and surface resistivity of polycarbonate and polypropylene sheets after plasma exposure. Optoelectton. Adv. Mater. 4, 144-147 (2010)... 

Polypropylene materials (PP), because of their electric properties (such as surface resistivity Ps, volume resistivity pv, dielectric loss factor tg8, permittivity e), mechanical properties and resistance to noxious agents (resistance to acids, bases, salts and organic solvents) are used in various industries. Polypropylene materials characterise, also, with the lowest specific density among widely used polymers. Those properties predispose polypropylene to be used as a substrate for composite protective screens shielding people and electric or electronic devices against noxious activity of electromagnetic (EM) fields. Composite shields... 

Not only surface fibres are coated with metal (fig 2a), but also the nonwoven fabrics internal fibres (fig. 2b) and areas between fibres (fig. 2c). Similar crystallization are observable for zinc layers deposited on polypropylene film (fig. 3). A layer obtained in that manner characterises with large sp>eafic surface area, which disperses electromagnetic field and increases shielding coefficient SE at the same time. Cross-section of such compwsite is presented in Fig. 4. It comes to one s attention that metaUic layers on fibre surface are solid and uniform. Best composites characterise with SE 60 dB, which not only stems from low surface resistivity, but also from expanded surface of metaUic layers (fig. 5). 

Table 18.4 Influence of type of polypropylene (homopolymer versus copolymer) and conductive filler on surface resistivity and impact strength of filled composites.

The surface resistivity range of materials is very wide, covering more than 20 orders of magnitude (Figure 1). Pure polypropylene and propylene copolymers are typical insulators with surface resistance in the order of 10 -10 ohm. Materials with such a small conductivity... 

Polypropylene is stiffer and semi-crystalline in nature. It has high heat distortion temperature. It offers excellent chemical and environmental stress cracking resistance and surface hardness. Polypropylene is a low cost material for packaging or gasoline tanks that meets technical requirements such as barrier and mechanical properties [63]. 

Corrosion. Ammonium bifluoride dissolves in aqueous solutions to yield the acidic bifluoride ion the pH of a 5% solution is 3.5. In most cases, NH4HF2 solutions react readily with surface oxide coatings on metals thus NH4HF2 is used in pickling solutions (see Metal surface treatments). Many plastics, such as polyethylene, polypropylene, unplasticized PVC, and carbon brick, are resistant to attack by ammonium bifluoride. 

Alkenylsuccinic anhydrides made from several linear alpha olefins are used in paper sizing, detergents, and other uses. Sulfosuccinic acid esters serve as surface active agents. Alkyd resins (qv) are used as surface coatings. Chlorendric anhydride [115-27-5] is used as a flame resistant component (see Flame retardants). Tetrahydrophthalic acid [88-98-2] and hexahydrophthalic anhydride [85-42-7] have specialty resin appHcations. Gas barrier films made by grafting maleic anhydride to polypropylene [25085-53-4] film are used in food packaging (qv). Poly(maleic anhydride) [24937-72-2] is used as a scale preventer and corrosion inhibitor (see Corrosion and corrosion control). Maleic anhydride forms copolymers with ethylene glycol methyl vinyl ethers which are partially esterified for biomedical and pharmaceutical uses (189) (see Pharmaceuticals). 

Fabric Composition. The method of fabric manufacture dictates many of the characteristics of the sheet, but intrinsic properties are firmly estabhshed by the base polymer selected. Properties such as fiber density, temperature resistance, chemical and light stabiUty, ease of coloration, surface energies, and others are a function of the base polymer. Thus, because nylon absorbs more moisture than polypropylene, spunbonded fabrics made from nylon are more water absorbent than fabrics of polypropylene. 

The use of ABS has in recent years met considerable competition on two fronts, particularly in automotive applications. For lower cost applications, where demands of finish and heat resistance are not too severe, blends of polypropylene and ethylene-propylene rubbers have found application (see Chapters 11 and 31). On the other hand, where enhanced heat resistance and surface hardness are required in conjunction with excellent impact properties, polycarbonate-ABS alloys (see Section 20.8) have found many applications. These materials have also replaced ABS in a number of electrical fittings and housings for business and domestic applications. Where improved heat distortion temperature and good electrical insulation properties (including tracking resistance) are important, then ABS may be replaced by poly(butylene terephthalate). 

It is suggested that the first material to be considered is polypropylene. The polymer has a number of desirable properties, as discussed in Chapter 11. These include low density, reasonable toughness, flexibility and strength at normal room temperatures, good resistance to hot water for a moderate period, low water absorption, translucency and good surface finish. Furthermore, it is one of the cheapest materials currently available. 

Materials such as polyethylene, polypropylene and acetal, which have waxy surfaces, or other crystalline plastics that are very solvent resistant, can be difficult to paint and require special primers or pre-treatments (flame, etc.) for satisfactory adhesion. Many amorphous plastics easily accept a wide variety of paint coatings. 

The most common material of construction is PFA Teflon . This high-purity material has become the material of choice due to its universal chemical resistance, nonstick surface properties, availability and compatibility of parts, and general historical and emotional acceptance. Other materials, such as polyethylene and polypropylene, are becoming more widely... 

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