The Function of Plasticizers

Plasticizers are used mainly (about 80%) in PVC compounds, both flexible and rigid, which is unprocessable without a plasticizer. Over the years, certain of them have been withdrawn on the grounds of potential toxicity. Recently, phthalates have come under intense pressure due to fears of carcinogenicity and oestrogen interference. 

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Chloroparaffines are used, for instance, in coolants and lubricants in the metalworking industry and as additives in paints, plastics and rubber. They fulfil the function of plasticizer and flame retardant. 

MAIN FUNCTIONS PERFORMED BY PLASTICIZERS A short list of the functions of plasticizers in epoxy resins includes ... 

Copolymers wet and adhere well to nonporous surfaces, such as plastics and metals. They form soft, flexible films, in contrast to the tough, horny films formed by homopolymers, and are more water-resistant. As the ratio of comonomer to vinyl acetate increases, the variety of plastics to which the copolymer adheres also increases. Comonomers containing functional groups often adhere to specific surfaces for example, carboxyl containing polymers adhere well to metals. 

The initial strain hardening rate (df/dy)o is given as a function of plastic strain rate for strain rates up to 10 s (which includes shock compression to 5.4 GPa) as [38]... 

It is widely appreciated that the deterioration of metal and plastic implant materials within the body is one of the most important aspects of implant surgery. This particular application of materials places an almost unique demand on the resistance to deterioration. The reasons are basically twofold, for not only may the environmental effects alter the structure and properties of the material, which may itself affect the function of the implant and hence the well-being of the patient, but also the by-products of any structural change may have harmful effects on the patient... 

As an example, for room-temperature applications most metals can be considered to be truly elastic. When stresses beyond the yield point are permitted in the design, permanent deformation is considered to be a function only of applied load and can be determined directly from the stress-strain diagram. The behavior of most plastics is much more dependent on the time of application of the load, the past history of loading, the current and past temperature cycles, and the environmental conditions. Ignorance of these conditions has resulted in the appearance on the market of plastic products that were improperly designed. Fortunately, product performance has been greatly improved as the amount of technical information on the mechanical properties of plastics has increased in the past half century. More importantly, designers have become more familiar with the behavior of plastics rather than... 

The function that plastics serve in most applications is that of a dielectric or insulator that separates two conductors with an electrical field between them. The field can be a steady direct current (DC) field or an alternating current (AC) field and the frequency range may vary such as from 0 to 1010 Hz. 

Thin to large wall Designing around TP problems is the joint responsibility of the product and mold designers. For example, one way to handle the problem of thin to large area walls is by the inclusion of long ribs into the product in the direction of plastic flow. These ribs are not a functional requirement of the product but they act as auxiliary runners attached to the product to facilitate plastic flow in difficult to fill areas. In some instances the ribs may be used as a surface decoration like a corrugation or they may be on the concealed side of the product where they are stiffeners. 

With the application of plastics in combination with other materials, the coefficient of expansion plays an important role in making design allowances for expansions (also contractions) of various materials at different temperatures so that satisfactory functions of products are ensured. 

Information on molecular orientation can be useful in two primary ways. First, it is possible to use the orientation functions or averages to gain an understanding of the mechanisms of plastic deformation. Secondly the orientation averages can provide a basis for understanding the influence of molecular orientation on physical properties, especially mechanical properties. 

Figure 3.6 Sound velocity in polystyrene/HCFC 142b before phase separation as a function of temperature. The blowing agent concentrations (wt%) are indicated. After Sahnoune el al. [189]. Reproduced by permission of the Society of Plastic...

Packaging trends involve lower cost, more functionality, volume growth, shorter product life-cycles and increased value. Rigid plastic packaging now dominates markets which were previously the exclusive realms of materials such as glass and metal, despite the fact that some technical aspects of plastic are still inferior to those of such traditional materials, e.g. the failure of plastics to withstand high temperatures without deforming, or barrier properties of a standard comparable to that... 

In addition to functionality, skeletal structure and the physical make-up of the coal was found to be important in achieving high conversions at short time. Neavel has previously called attention to the importance of plasticity in coal liquefaction... 

Gregory, and it still applies - if you take a radio and delete a transistor from it and the result is that instead of a symphony you get a howl, you can t conclude that the function of the transistor was a howl suppressor. That is one of the major problems of knock-out studies, that they are compounded by the fact that if you take a transistor out of a radio it can t self-repair. In a developing animal, if you take out a gene, then what you get is compensatory plasticity, other processes taking over as well. So the interpretation of any of those knock-out studies is immensely complicated. 

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