Polymer selection properties affecting

Vehicles are selected by two methods. In one a concentrate is designed directiy for a resin system, the resin itself, or a compatible resin. Thus when the concentrate is made there is a minimal effect on the properties of the final color. In PVC, often a plasticizer such as dioctyl phthalate (DOP) is used. In the other method, concentrates are made with a commercial universal concentrate vehicle. Concentrate manufacturers and some resin manufacturers have developed vehicles that can incorporate many types of colorants and can be used across many classes of polymers without adversely affecting final product performance. 

Selected factors affecting crystallinity regarding Tg and Tm are described in Chapter 2. Here we discuss the influence of crystallinity on the mechanical properties of polymers. For thermoplastics the relation between the degree of crystallinity and the physical nature is shown in Table 5.1. The general lack of difference in physical nature shown by largely crystalline polymers at... 

These stabilizers are added to the formulation in order to stabilize the emulsion formed during particle preparation. These stabilizers, however, can also influence the properties of the particles formed. The type and concentration of the stabilizer selected may affect the particle size. Being present at the boundary layer between the water phase and the organic phase during particle formation, the stabilizer can also be incorporated on the particle surface, modifying particle properties such as particle zeta potential and mucoadhesion (203). Other polymers have also been evaluated as stabilizers in earlier studies such as cellulosic derivatives methylcellu-lose (MC), hydroxyethylcellulose ( ), hydroxypropylcellulose (HPC), and hydroxypropylmethylcellulose (HPMC), as well as gelatin type A and B, carbomer and poloxamer (203). 

It has been found that the HNBR/SP nanocomposite provides the best thermal and mechanical properties when HNBR is dissolved in Ch and SP is dispersed in MEK. XRD, AFM,TEM, and optical transmittance studies show that the dispersion of clay is best in the Ch/MEK solvent combination and, hence, polymer-filler interaction is also highest in this system. Thus, rather than implying that the solvent selection directly affects the physical properties of the nanocomposite, solvent acts on the properties through its influence on the developed morphology. 

Some polymers have a specific set of bulk properties that make them ideal for a certain application, but cannot be used because the surface properties are inappropriate. For example, a material may have excellent elasticity but cannot be used in cardiovascular devices because the polymer surface triggers blood clotting. Alternatively, another polymer may have excellent surface biological compatibility but is too brittle for a cardiovascular application. An answer to this problem, like many others, is to select a polymer for its advantageous bulk properties and then carry out property modification reactions on the polymer surface without affecting the bulk material. 

The semihydrogenation of the carbon-carbon triple bond is a particularly valuable and frequently used application of heterogeneous catalysis to synthetic chemistry, and is the subject of several recent re-views. > Catalysts prepared from palladium and nickel are most commonly used, but the form of the catalyst and the conditions of use affect the results (see Section 3.1.1.2). A polymer-bound palladium catalyst, PdCh with poly-4-diphenylphosphinomethylstyrene, is intended to combine the selective properties of mononuclear transition metal complexes with the ease of separating the product from a solid. Whether catalysts of this type will replace the more traditional heterogeneous catalysts remains to be seen. 

Table 2 Properties affecting polymer selection, manufacture, and performance...

By controlling the hydrophobic/hydrophilic equilibrium of the polymers, their selectivity for bacterial cells over red blood cells (RBC) can be improved. This property is related to the effect that the ionic nature and hydrophobic character of these polymers has on cell membrane activity. The length of the alkyl substituents in the polymer repeat units affects antibacterial effectiveness in more hydrophobic polymers (hexyl and higher alkyl chain lengths in the repeat unit), disruption of the membrane integrity occurs more effectively. ROMP is an attractive method of synthesis which is widely used to prepare well-defined polymers with controlled MW and low polydispersity index values (PDl) [27-30]. 

In the area of personal care, solution rheology directly affects how a cosmetic product behaves. In this way, associative polymers can influence a cosmetic s aesthetic properties. Perhaps more importantly, they can influence the appearance of the product, the spreading behavior, the film thickness, and the feel of cosmetics from lotions to gels to shampoos. From the consumer s perspective, products that appear stringy (pituitous) or that ball up on application (pilling) are undesirable (72). Good viscosity control can impart a perceived increase in product concentration that the consumer considers beneficial. A low-viscosity product delivered from a bottle or pump is unacceptable, yet low-viscosity products are a necessity for products that are atomized (aerosols). In most cases, the viscosity manipulation is partly the result of appropriate polymer selection. 

In addition, a change in a specific polymer parameter may affect both processability and basic physical properties and both of these can interact in governing the behaviour of a fabricated article. Comprehensive experimental data are therefore necessary to understand effectively the behaviour of plastic materials and to give a realistic and reliable guide to material and grade selection. 

Blending two or above polymers together is an important way to create synergis-tically new physical properties of the composites in the polymer industry. Furthermore, the multiphase separation is produced by polymer blending, and thus, phase morphology of the polymer blends significantly affects the final properties of the composites. When conductive fillers are added to the immiscible polymer blends, the location of conductive fillers in polymer phases may be various and could lead to different electrical properties of CPCs. In another word, conductive fillers can be selectively located in one of the polymer phases or at the phase interfaces [86-88], which can be controlled to constiuct a desirable conductive network structure in CPCs. 

The stress-strain curves shown in Figure 15.17 just present the general property trends. In reality, the curve shapes may vary from fiber to fiber. For example, the stress-strain curves of natural polymer fibers are affected by the fanning conditions of the plants or animals. Depending on the applications, the processing conditions of synthetic polymer fibers can be selectively adjnsted to produce different physical stractures and mechanical properties. Table 15.2 shows typical tensile strength, modulus and strain-at-break valnes of some commercial fibers. 

The effect of PPO molecular weight on the gas transport properties of dense films as well as integrally skinned asymmetric membranes is significant. Molecular weight parameter of the polymer not only affects the membrane performance, it also influences the mechanical properties of dense films and skin/selective layer integrity of the asymmetric membranes. 

Analyzing the behavior of filled polymers, as any other heterophase systems, two aspects should be distinguished. First, these are the properties of such systems, i.e. their inherent characteristics, independent of a measuring method if, of course, the measurements are correct (to select criteria of correctness of an experiment, carried out with multiphase systems, seems to be an independent and by no means a simple problem). Second, this is a manifestation of these properties when heterophase systems flow in channels of different geometrical form. Behind all this stands the basic applied problem—finding out how the properties of filled polymers, appearing during their flow, affect the properties of finished articles. 

---