Polymer Categories

Figure 4. Representative chain configurations for F-F (a) and F-S (b) polymer classes. MD simulations [100] are obtained for isolated chains and are only meant for illustrative purposes. The polymerization index N is taken as iV = 100. The monomer structure is assumed to be common for these two polymer categories and is depicted in Fig. 3b. The bending energies b and are chosen in the simulations as E /ksT = Es/k T = 0, and Eb/k T = 0, Es/ksT = 200 for F-F and F-S polymer classes, respectively.

The chemical reaction that takes place during solidification of thermosets also leads to considerable thermal effects. In a hardened state, their thermal data are similar to the ones of amorphous thermoplastics. Figure 2.8 shows the specific heat graphs for the three polymer categories. 

Specific heat curves for selected polymers of the three general polymer categories. 

Table VI compares the key properties of these two types of thermotropic polymers category by category. The samples compared had the same melting ranges, but were very different in reduced viscosities and solubility characteristics. The data compared were those processed under the most favorable conditions. Interestingly enough, the as-spun fibers from the polyester-carbonate can be heat-treated more efficiently than those fibers (of same tenacity) spun from the polyester. Both of them gave fiber properties far superior to those of nylons and polyethylene terephthalate. These two classes of polymers also had comparative properties (such as tensile strength, tensile modulus, flex modulus, notched Izod impact strength) as plastics and their properties were far superior to most plastics without any reinforcement.

This chapter deals with processability tests for the two general polymer categories, rubbers and plastics. Not surprisingly, there are many similarities in the processing of the two types of material, but there are also many differences arising from their structural differences, differences in the processing methods and because of the separate development of the two industries. International and national standards for the two types of material are separate, and generally the apparatus used is specific to one material type. Consequently, rubbers and plastics are dealt with here sequentially, and it is left to the interested reader to contrast and compare the appoaches taken. 

Organic glasses belong to the polymer category since they are formed by polymer chains interacting through VDW (thermoplastics) or VDW and covalent bonds (thermosets). 

Different types of reactors and reaction conditions are used for PE and PP manufacturing processes. Choice of the reactors and process conditions are determined primarily by the specifications of the desired products. It is important to note that within the broad polymer categories such as HDPE, LLDPE, PP, etc., subcategories differing from each other in terms of a range of polymer properties exist. Different manufacturing processes must meet those product specifications and balance the rate of production with the market demand. 

Most commonly available natural polymers (category 1 above) are extracted from agricultural or forest plants and trees. Examples are cellulose, starch, pectins, and proteins. These are cell-wall, plant-storage (starch), or structural polymers. AH are by nature hydrophilic and somewhat crystaUine all factors may cause processing and performance problems. 

In industrial practice, polymer categories may be based on a variety of considerations. Producers of polymers may well use a compositional basis like the one used in the various sections here and in Chapter 16. Raw materials and techniques for many products may be common to one such group. However, users of polymers often create categories by performance properties such as those summarized in Section 11.1. Within a major industry, polymers compete on a price and performance basis. As an example, in the... 

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