Critical material properties

An important question for any modeling effort, especially one aimed at a quantitative description of complex transport processes, is the level of accuracy of the model. As will become evident in the discussion of transport models and specific calculations, the values for thermophysical properties and transport coefficients must be known, as well as the dependence of these coefficients on temperature and pressure. Information is lacking for this data base. Critical material properties for semiconductor materials are not known... 

Hlinak AJ, Kuriyan K, Morris KR, Reklaitis GV, Basu PK. 2006. Understanding critical material properties for solid dosage form design. J. Pharm. Innov. 1(1) 12-17. 

However, some excipients have multiple functions. For example, microcrystalline cellulose can function as a filler, a binder, and a disintegrant. As seen in Table 7.3, a typical low-dose formulation could include more than 85% filler—binders. Thus, physical and chemical properties for these specialty excipients are extremely important in a low-dose formulation for manufacturability, product performance, and longterm stability. Because the poor physicomechanical properties of components are not altered during manufacture as they are in the wet or dry granulation process, critical material properties and their impact on product quality attributes should be well characterized and understood.23 Discussion in this section will focus on fillers-binders. For those requiring more information on excipients, several excellent books and review articles are available in the literature.24-27... 

We have shown that strength and stability can be obtained under selected conditions in nanostructured and dispersion reinforced systems. However, for structural applications, a balance of properties is critical - fracture and fatigue behavior of these systems are not well-established. Processing scale-up is another big challenge in these systems most of the properties have been demonstrated on laboratory-scale materials. Process scale-up is required to produce useful quantities of materials for sub-scale component demonstration as well as design property evaluation. The retention of useful microstructures, microstructural homogeneity as well as critical material properties has to be demonstrated in scaled-up materials. While our focus has been on structural applications, there may be other non-structural or functional applications for these systems. Future investigations will be focused on such opportunities. 

The critical material properties for refractory oxides are dictated by a given application. In some applications, thermal expansion and strength may be most important while in other situations melting temperature and thermal conductivity are important. In general, the most important material properties for refractory oxides include melting temperature, thermal expansion coefficient, thermal diffusivity and conductivity, elastic modulus, and heat capacity. 

This standard is for polymers, blends of polymers, copolymers, terpolymers and alloys. It considers plastic parts that have been produced under a material identity control system. Molders/fabricators are required not to employ such additives/flame retardants that would adversely affect critical material properties. A detailed discussion on national and international fire protection regulations and test methods for plastics is presented by Troitzsch [1983]. 

The use of underfill adhesives has resulted in the development of the draft version of J-STD-030, Guideline for Selection and Application of Underfill Material for Flip Chip and Other Micropackages. The guideline covers critical material properties for underfill materials to assure compatibility in underfill applications for reliable electronic assemblies as well as selected process-related qualification tests such as thermal cycling. Table 6.9 summarizes selected materials requirements for underfill adhesives from the proposed JEDEC J-STD-030. ... 

Of these barriers, the one that is most overlooked is the first. Many of the new thermoplastic materials coming into the market place are blends and alloys that are specifically engineered to provide a combination of the properties of the individual polymers. Often these materials combine crystalline and amorphous polymers with an impact modifier. The products of these marriages often contain a maze of phase boimdaries that result in light scattering (miUdness) equivalent to as much as 0.5% titanium dioxide. Obtaining high chroma colors (e.g., some electrical code colors or even a jet black) in the presence ofthis inherent miUdness becomes an expensive proposition. Often so much color has to be added to the material formulation that critical material properties are affected - a double whammy, cost and performance. 

The main focus of this chapter is to examine the critical material properties that influence polymeric binder and filler-binder performance of directly compressible excipients, and how these material properties can be optimized and integrated with other functionalities via particle engineering. 

However, for performance at very high frequencies, lower D /Df materials are preferred. While low Dij/Df materials have been available for many years, the advent of lead-free assembly has complicated material selection, and in these applications not only are the laminate and Dt properties critical, but their thermal properties are just as important. Critical material properties for lead-free assembly compatibility will be discussed in a subsequent chapter. Figures 9.32 and 9.33 provide Df and Djj data for three different low Dk/Df materials that are also compatible with lead-free assembly. 

The behavior of the hydrogel at short and long timescales can be studied by measurement of the moduli of the material as a function of frequency. The frequency dependence of the moduh is a critical hydrogel parameter since a single material can look quite solid-like (G G") at a high frequency (short timescale) but behave much more liquid-hke (G" > G ) at low frequency (long timescale). Gelation kinetics and final gel stiffness are critical material properties that directly impact the application of the material. 

In a similar vein, I would encourage those engaged in material selection to formally document their selection process using a Material Properties Effects Analysis (MPEA). MPEA involves a systemized approach to material selection, where materials are carefully evaluated for their effect on the system. However, instead of evaluating the effect of failure, the process is used to evaluate the effect of specific material properties. The intent is to determine the critical material properties of the materials that are used in the system. 

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