Reinforcement with Other Compounds

Other reinforcing agents either have been used to reduce the thermal degradation of polymers or do not have an effect on it. These include calcium carbonate in polyvinyl acetate [65,73] and polymethyl methacrylate [69,71] and titanium dioxide-magnesium oxide in polyethylene [78]. 

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BP. These nitrile alloy membranes are compounded from PVC, flexibilized by the addition of butadiene—acrylonitrile copolymers, PVC, and other proprietary ingredients. Typically reinforced with polyester scrim, NBP membranes are 1 mm thick and have a width of 1.5 m. They ate ptedominandy used in mechanically fastened roofing systems. NBP membranes exhibit excellent teat and puncture resistance as well as good weatherabihty, and remain flexible at low temperatures. They ate resistant to most chemicals but ate sensitive to aromatic hydrocarbons. The sheet is usually offered in light colors. The physical characteristics of NBP membranes have been described (15). 

PVC. Poly(vinyl chloride) (PVC), a very versatile polymer, is manufactured by the polymerisation of vinyl chloride monomer, a gaseous substance obtained from the reaction of ethylene with oxygen and hydrochloric acid. In its most basic form, the resin is a relatively hard material that requites the addition of other compounds, commonly plasticisers and stabilisers as well as certain other ingredients, to produce the desired physical properties for roofing use. The membranes come in both reinforced and nonreinforced constmctions, but since the 1980s the direction has been toward offering only reinforced membranes. The membrane thickness typically mns from 0.8—1.5 mm and widths typically in the range of 1.5—4.6 m. 

B4C boron carbide has a melting point of 2450 °C and a hardness somewhere between those of SiC and diamond. This makes the material a suitable abrasive. It is used in heads of sand blasting equipment, in mortars and in armour plating. For the latter application a B4C plate is provided on both sides with a plastic which has been reinforced with glass fibre. This is done to reduce the risk of splintering. Boron carbide is also used as the raw material for many other boron compounds ... 

In comparison with other thermoplastics, polyamides have superior mechanical properties, vibration and chemical resistance, and high dielectric properties. The superior antifrictional characteristics of cast PA-6 allow us to use it for bearings instead of bronze, cast iron, steel, babbit, reinforced phenolic compounds, and other materials. 

Fluorosilicones can be compounded by the addition of mineral fillers and pigments. Fillers for such compounds are most commonly silicas (silicon dioxide), because they are compatible with the elastomeric silicon-oxygen backbone and thermally very stable. They range in surface areas from 0.54 to 400 m2/g and average particle size from 100 to 6 nm. Because of these properties, they offer a great deal of flexibility in reinforcement. Thus, cured compounds can have Durometer A hardness from 40 to 80. Other fillers commonly used in fluorosilicones are calcium carbonate, titanium dioxide, and zinc oxide. 

Chemically, all forms contain linalyl acetate, linalool and 1,8-cineole, along with many other compounds. Further analysis of each type reveals their differences in amounts of chemical components. The situation is illustrated by comparing published data for principal constituents and then seeing how these are reinforced by an actual GC chromatogram. This is shown in Table 7.1 the main figure is the published data while figures in brackets are those taken from the GC analysis of actual oil samples (cis- and trans-ocimene are minor hydrocarbon components, but are included as they are often used as markers for the authenticity of lavender oils). In all cases the amounts of compounds in the hybrid (Lavandula intermedia) are in between those of the true (Lavandula angustifolia) and the spike (Lavandula latifolia). 

The materials being reviewed in this book, as in the industry, are identified by different terms such as polymer, plastic, resin, elastomer, reinforced plastic (RP), and composite unreinforced or reinforced plastic. They are somewhat synonymous. Polymers, the basic ingredients in plastics, can be defined as high molecular weight organic chemical compounds, synthetic or natural substances consisting of molecules. Practically all of these polymers are compounded with other products (additives, fillers, reinforcements, etc.) to provide many different properties and/or processing capabilities. Thus plastics is the correct technical term to use except in very few applications where only the polymer is used to fabricate products. 

Nearly symmetrical molecules deserve special mention. Benzene and piperazine are uncharged and have no dipole moment, so the Born-Kirkwood-Onsager model predicts AGs — 0- However, AM1-SM2 predicts —0.5 and —7.8 kcal/mol, respectively, in good agreement with the experimental -0.9 and -7.4 kcal/mol. In benzene the result comes as the sum of a hydrophobic AGcds = 1.4 kcal/mol and a hydrophilic AGe p = —2.0 kcal/mol whereas in piperazine both terms are hydrophilic (AG ds 4.1 kcal/mol, AGg p = —3.7 kcal/ mol), and they reinforce each other. Similar reinforcement occurs in many other compounds [e.g., p-bromophenol (AGs -4.4 kcal/mol, AGg p = —2.7 kcal/mol)], in which case AM1-SM2 predicts AGs 7.0 kcal/mol versus an experimental value of —7.1 kcal/mol. 

Finally, the inductive and resonance effects in compounds having the general structure C6Hs-Y=Z (with Z more electronegative than Y) are both electron withdrawing in other words, the two effects reinforce each other. This is true for benzaldehyde (C HsCHO) and all other compounds that contain a carbonyl group directly bonded to the benzene ring. 

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