Other Design Applications for Plastics

The long-term stress-strain behavior of polymers is generally more important than shortterm properties where the product is expected to sustain a stress or strain in service. Creep is dearly the most relevant where the product or component is to be subjected to a more or less constant stress. This is the case for a great many uses of rigid plastics and for such products as rubber mountings. Hence, creep data is often an essential design factor for plastics but is only used for other polymer types when particular applications are in mind. 

However, the company offers the ZE 25 System for pilot-plant development of any product, including polymer blends. KraussMaffei Berstorff compounding lines are designed to be tailored to customer s specific product and process requirements. They offer extensive process engineering know-how in all k processing and extrusion applications for plastics and other base materials. 

Designing plastic Basically the general design criteria applicable to plastics are the same as those for metals at elevated temperature that is, design is based on (1) a deformation limit, and (2) a stress limit (for stress-rupture failure). There are, of course, cases where weight is a limiting factor and other cases where short-term properties are important. 

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. 

Polyurethanes have several advantages over competing material in the materials field. The major items of competition are metal, other plastics, and rubbers. Ceramics offer some competition to urethanes. Each of the above groups of materials, including polyurethanes, requires its own design adjustments for successful use in any application. 

A further interesting effect discovered in our laboratories is that the addition of low levels of a second component, or dopant ion, can lead to significant increases in the ionic conductivity [6, 30, 31]. Typically these dopant species, for example, Li, OH , and H" ", are much smaller than the organic ions of the matrix, and since the relaxation times characterizing the motion of these ions are more rapid than those of the bulk matrix itself, these materials may represent a new class of fast ion conductor. The dopant ion effect can be used to design materials for specific applications, for example, Li+ for lithium batteries and H /OH for fuel cells or other specific sensor applications. Finally, we have recently discovered that this dopant effect can also be apphed to molecular plastic crystals such as succinonitrile [32]. Such materials have the added advantage that the ionic conductivity is purely a result of the dopant ions and not of the solvent matrix itself. 

The other validation test that is used to approve containers for use with sensitive preparations is the moisture permeability test. This evaluation is notably more complex in that it sets permeation limits based both on the type of container and the classification of the material being stored within. In general, these tests measure the performance of the packaging system but offer no design guidance. For compendial applications, permeability testing of plastics are described in the USP general chapters (661) and (671) for all types of containers. 

Blends of the commodity polymers with more specialty polymers are limited although many specific examples exist in the patent/open literature. In the design of polymer blends for specific application needs, countless opportunities can be envisioned. Examples may include PE/poly(s-caprolactone) (PCL) blends for biodegradable applications (proposed), polyolefin (PO)/poly(vinyl alcohol) (PVAL) blends for antistatic films, PO/silicone rubber blends for biomedical applications, PO/thermoplastic polyurethane TPU (or other thermoplastic elastomers) for applications similar to plasticized PVC, functionalized PO/thermoset blends. 

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