Plastic comparisons

Figure 10.52 shows that addition of the plasticizer decreased dehydrochlorination rate of PVC. Crosslinking rate was reduced with the presence of plasticizers. Also, the carbonyl group formation was slower in the presence of a plasticizer. Comparison of data presented by the same authors for the effect of radiation above and below 290 nm stresses importance of wavelength selection on the results obtained. When studies were conducted with an unfiltered mercury lamp, presence of phthalates increased the carbonyl group formation. 

Change in elastic properties of SPU-1, SPU-2, SPU-5, SPU-6 on swelhng was studied on samples swollen to equihbrimn in plasticizers. Comparison of data shows the lowest values of modulus for all samples swollen in TBP (Table 10.15). TBP mptures domains of hard blocks. The values of the modulus, E, for SPUs swollen in TBP are determined by their density of chemical network and volume fractions of polymer at coefficient of Eq. [10.31] n = 1/3. There was no chemical network in SPU-6 (the sample was completely dissolved). 

Fig. xn-2. Comparison of actual contact areas for (a) metal-on-metal and (b) plastic-on-metal. (From Ref. 2.)... 

AUiedSignal Inc., Technical Bulletin, Engineering Plastics, HAEAR ECTFE Eluoropolymer Resins Comparison Data, Morristown, N.J. 

Mechanical properties of plastics can be determined by short, single-point quaUty control tests and longer, generally multipoint or multiple condition procedures that relate to fundamental polymer properties. Single-point tests iaclude tensile, compressive, flexural, shear, and impact properties of plastics creep, heat aging, creep mpture, and environmental stress-crackiag tests usually result ia multipoint curves or tables for comparison of the original response to post-exposure response. 

Airborne organic sihcon has been detected in samples collected at Barrow, Alaska (509). Organic sihcon levels corresponding to an airborne concentration of 8 ng/m were detected. As a comparison, these samples were deterrnined to hold approximately 20 ng/m of phthalate-based plasticizers. 

Vinyl compares favorably to other packaging materials. In 1992, a lifecycle assessment comparison of specific packages made from glass, paperboard, paper, and selected plastics concluded that vinyl was the material that has the lowest production energy and carbon dioxide emissions, as well as the lowest fossil fuel and raw material requirements of the plastics studied (169). Vinyl saves more than 34 million Btu per 1000 pounds manufactured compared to the highest energy-consuming plastic (170). 

A Comparison of Ethylene Glycol with Propylene Glycol, Union Carbide Chemicals and Plastics Co., Inc., Danbury, Conn., 1989. 

The process zone is a measure of the yield stress or plasticity of the material in comparison to its brittleness. Yielding within the process zone may take place either plastically or by dimise microcracking, depending on the brittleness of the material. For plastic yielding, / is also referred to as the plastic zone size. 

FIG. 26-39 Definition of the venting capability EF of an explosion door in comparison with a plastic foil rupture disk. 

Plastic Materials In comparison with metalhc materials, the use of plastics is limited to relatively moderate temperatures and pressures [230°C (450°F) is considered high for plastics]. Plastics are also less resistant to mechanical abuse and have nigh expansion rates, low strengths (thermoplastics), and onlv fair resistance to solvents. However, they are lightweight, are good thermal and elec trical insiilators, are easy to fabricate and install, and have low fric tion factors. 

We first consider strain localization as discussed in Section 6.1. The material deformation action is assumed to be confined to planes that are thin in comparison to their spacing d. Let the thickness of the deformation region be given by h then the amount of local plastic shear strain in the deformation is approximately Ji djh)y, where y is the macroscale plastic shear strain in the shock process. In a planar shock wave in materials of low strength y e, where e = 1 — Po/P is the volumetric strain. On the micromechanical scale y, is accommodated by the motion of dislocations, or y, bN v(z). The average separation of mobile dislocations is simply L = Every time a disloca-... 

If (as with body panels) elastic deflection is what counts, the logical comparison is for a panel of equal stiffness. And if, instead, it is resistance to plastic flow which counts (as with bumpers) then the proper thing to do is to compare sections with equal resistance to plastic flow. 

In addition to plastics materials, many fibres, surface coatings and rubbers are also basically high polymers, whilst in nature itself there is an abundance of polymeric material. Proteins, cellulose, starch, lignin and natural rubber are high polymers. The detailed structures of these materials are complex and highly sophisticated in comparison the synthetic polymers produced by man are crude in the quality of their molecular architecture. 

It is interesting to note that although the market for natural rubber has grown considerably, that for the other diene rubbers has either been of slow growth or has declined. Data for approximate overall plastics production (not from IlSRP data) have also been included as a comparison of the relative sizes of the rubber and plastics markets. 

Typical values for the principal properties of cellulose acetate compounds are tabulated in Table 22.2 in comparison with other cellulosic plastics. Since cellulose acetate is seldom used today in applications where detailed knowledge of physical properties are required these are given without further comment. 

In contrast, most equipment can safely tolerate higher degrees of heat density than those defined for personnel. However, if anything vulnerable to overheating problems is involved, such as low melting point construction materials (e.g., aluminum or plastic), heat-sensitive streams, flammable vapor spaces, or electrical equipment, then the effect of radiant heat on them may need to be evaluated. When this evaluation is required, the necessary heat balance is performed to determine the resulting surface temperature, for comparison with acceptable temperatures for the equipment. 

The other principal thermal properties of plastics which are relevant to design are thermal conductivity and coefficient of thermal expansion. Compared with most materials, plastics offer very low values of thermal conductivity, particularly if they are foamed. Fig. 1.10 shows comparisons between the thermal conductivity of a selection of metals, plastics and building materials. In contrast to their low conductivity, plastics have high coefficients of expansion when compared with metals. This is illustrated in Fig. 1.11 and Table 1.8 gives fuller information on the thermal properties of pl tics and metals. 

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