Plastics requirements

Plasticizer Efficiency. This is a measure of the concentration of plasticizer required to impart a specified softness to PVC. Such a softness of material may be measured as a British Standard Softness (BSS) or a Shore hardness (Pig. 1). Por a given acid constituent of plasticizer ester, ie, phthalate, adipate, etc, plasticizer efficiency decreases as the carbon number of the alcohol chain increases, eg, for phthalate esters efficiency decreases in the order DBP > DIHP > DOP > DINP > DIDP > DTDP. An additional six parts per hundred in PVC of DIDP rather than DOP is required to give a hardness of Shore 80 when ah. other formulation ingredients remain constant. The consequence of this depends on the overall formulation and product costs. In addition to size of the carbon number of the alcohol chain, the amount of branching is also significant the more linear isomers are of greater efficiency. 

Total energy (elastic plus plastic) required to take specimen to point of necking... 

The second factor listed above that affects the growth of plastics, namely improved capability, is self-explanatory, but the third, the decrease in relative costs for plastics, requires some explanation, particularly as this may have relevance to future prospects. 

Polytetrafluorethylene (p.t.f.e.) This polymer does not absorb water, has no solvents and is almost completely inert to chemical attack molten alkali metals and sodium in liquid ammonia are the rare exceptions. Furthermore it does not soften below 320°C, is electrically inert and has a very low coefficient of friction. It is more expensive than general purpose plastics, requires special fabrication techniques, is degraded by high energy radiation, and has a low creep resistance. 

This same situation exists with plastics. To be successful with plastics requires experience with their melt behavior, melt-flow behavior during processing, and the process controls needed to ensure meeting the dimensions that can be achieved in a complete processing operation. Based on the plastic to be used and the equipment available for processing, certain combinations will make it possible to meet extremely tight tolerances. 

Many of the basic plastics require additives that will improve their resistance to supporting combustion. These improvements vary in degree, and the designer must be cautioned not to over specify the requirement for... 

To produce and process plastics requires less energy than practically any other material (Fig. 9-8). In contrast, glass requires much more energy than any of the materials listed. 

All plastics are polymers, long molecules made of repeating units. Because polymers are extremely stable, they resist reaction. Most conventional plastics require hundreds or even thousands of years to break down. 

Polymer rheology can respond nonllnearly to shear rates, as shown in Fig. 3.4. As discussed above, a Newtonian material has a linear relationship between shear stress and shear rate, and the slope of the response Is the shear viscosity. Many polymers at very low shear rates approach a Newtonian response. As the shear rate is increased most commercial polymers have a decrease in the rate of stress increase. That is, the extension of the shear stress function tends to have a lower local slope as the shear rate is increased. This Is an example of a pseudoplastic material, also known as a shear-thinning material. Pseudoplastic materials show a decrease in shear viscosity as the shear rate increases. Dilatant materials Increase in shear viscosity as the shear rate increases. Finally, a Bingham plastic requires an initial shear stress, to, before it will flow, and then it reacts to shear rate in the same manner as a Newtonian polymer. It thus appears as an elastic material until it begins to flow and then responds like a viscous fluid. All of these viscous responses may be observed when dealing with commercial and experimental polymers. 

The concentration of hydrogen in the polymer during irradiation is low, on the order of 10"6 mole per cc. This is far lower than the concentrations of plasticizers required to cause any significant changes in polymer creep behavior. 

Conventional tin and glass containers can be satisfactorily treated by steam or hot air. Paper, cardboard, and heat-sensitive plastics require subtler techniques. Experiments with Co60 gamma rays indicate that 200,000 r. are sufficient to inactivate vegetative contaminants, while the customary 2 X 10 r. are required for spore formers. These doses are considerably below those that would be expected to have any effect on the physical properties of these materials (Sec. IIIC5). 

It has been shown that the thus rubber bound antioxidant can reduce the amount of plasticizer required for compounding and that the ozone resistance of a vulcanizate containing a p-phenylene diamine modified PIB is superior to that of other vulcanizates (71). 

Efficiency. The term plasticizer efficiency is used to relate a desirable modification of the properties of a given product to the amount of plasticizer required to achieve this effect. For example, the efficiency of various plasticizers in plasticizing a given polymer may be expressed in terms of the depression of the glass temperature by a given mole, or volume fraction of plasticizer. Therefore, there is no absolute value for the efficiency of a certain plasticizer, and the relative efficiency of different plasticizers will depend on which polymer property is used to measure plasticizer efficiency. 

Polymers, plasticizers, stabilizers, and ionic impurities were blended by masticating 5 to 15 min. on a 6 inches x 12 inches two-roll differential-speed mill, adjusting the temperature between 40° and 175°C. according to the thermal plasticity requirements of the different compositions. 

Milled sheets were molded into 6 inch discs 35 mils thick by preheating 1 min., pressing 1 min. at a temperature between 115° and 205°C. according to the thermal plasticity requirements of the different compositions, and cooling 1 min. under pressure before removing from the mold. Pure Hycar 1032 was too rubbery to form good moldings and was therefore cast into film from 20% solution in methyl ethyl ketone. 

Bingham plastics require a finite amount of shear stress before deformation begins, then the deformation rate is linear. Mathematically,... 

Aryl-aliphatic copolyamides (Ar-Al-PA) are industrial technical polymers whose uses as transparent plastics require performances in terms of temperature behaviour, or resistance to solvents and stress cracking. The transparency of materials necessitates a completely amorphous structure, which is obtained by using not only para-substituted phenyl rings, but also meta-substituted phenyl rings that decrease the chain regularity. 

Acetyl, phthalyl 6 CAP (Eastman Comp.) Aquateric (Lehmann Voss) Organic solution Aqueous dispersion (pseudolatices) Sensitive to hydrolysis, 5-30% plasticizer required Micronized powder (0.05-3 pm)... 

Since in general they are poor conductors of heat plastics require large inputs of energy as heat to bring them to the working temperatures the amounts of heat needed differ between materials—essentially because of their molecular structures and crystallinity—as illustrated in Table XI. 

Unlike clay-based systems, modem ceramics require additives, termed binders, to provide the plasticity required for ductile-forming methods to be used. These organic additives serve to modify the rheological behavior of the ceramic suspensions and impart handling strength to the green, as-formed ceramic bodies. Their... 

Transparency. Some applications of plastics require transparency. Amorphous plastics should be able to transmit light. Some factors which prevent transparency include unsatura-tion/light absorption, crystallinity, fillers and reinforcing fibers, and use of rubber particles to increase impact strength. The plastics most often used for their transparency are poly(4-methylpentene-l) (TPX), poly(methyl methacrylate) (almost equal to glass), cellulose acetate, propionate, and butyrate, polycarbonate, and polysulfones (slightly yellow). As a research challenge, it is quite possible that fillers and rubber particles could... 

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