Additive properties method, determination glass transition temperature

Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and infrared spectroscopy are the common techniques used in the characterization of the structure of the congealed solid. Thermal analytic methods, such as DSC and differential microcalorimetric analysis (DMA), are routinely used to determine the effect of solutes, solvents, and other additives on the thermomechanical properties of polymers such as glass transition temperature (Tg) and melting point. The X-ray diffraction method is used to detect the crystalline structure of solids. The infrared technique is powerful in detecting interactions, such as complexation, reaction, and hydrogen bonding, in both the solid and solution states. 

In addition to the above methods, 82 of polymer can be determined from a threshold of sedimentation and by critical opalescence. In recent years the method of inverse gas-liquid chromatography has been used to evaluate 82 of polymers. One may also use some empirical ratios relating solubility parameters of polymers with some of their physical properties, such as, surface tension and glass transition temperature. ... 

This chapter discusses the form and parameterization of the potential energy terms that are used for the atomistic simulation of polymers. The sum of potential terms constitutes a molecular force field that can be used in molecular mechanics, molecular dynamics, and Monte Carlo simulations of polymeric systems. Molecular simulation methods can be used to determine such properties as PVT data, selfdiffusion coefficients, modulus, phase equilibrium, x-ray and neutron diffraction spectra, small molecule solubility, and glass transition temperatures with considerable accuracy and reliability using current force fields. Included in the coverage of Chapter 4 is a review of the fundamentals of molecular mechanics and a survey of the most widely used force fields for the simulation of polymer systems. In addition, references to the use of specific force fields in the study of important polymer groups are given. 

Differential scanning calorimetry (DSC) directly measures the heat flow to a sample as a function of temperature. A sample of the material weighing 5 to 10 g (18-36 oz.) is placed on a sample pan and heated in a time- and temperature-controlled manner. The temperature usually is increased linearly at a predetermined rate. The DSC method is used to determine specific heats (see Fig. 9-4), glass transition temperatures (see Fig 9-5), melting points (see Fig. 9-6), and melting profiles, percent crystallinity, degree of cure, purity, thermal properties of heat-seal packaging and hot-melt adhesives, effectiveness of plasticizers, effects of additives and fillers (see Fig. 9-7), and thermal history. 

While pressure sensitive adhesive performance at various temperatures can be determined by practical tests, as described above, it is also possible to predict the temperature performance of pressure sensitive adhesives. The polymers used in pressure sensitive adhesives will have a variety of glass transition temperatures (Tg), and for a pressure sensitive adhesive to be effective, the formulated mass must have a Tg of between 50°C and 70°C below the temperature at which the adhesive is to be used. At the same time, however, the Tg cannot be so low that the adhesive mass is so soft that it fails cohesively even at room temperature. A variety of analytical techniques used to determine the Tg of the adhesive mass include Differential Scanning Calorimetry (DSC), Differential Thermal Analysis (DTA), and Dynamic Mechanical Analysis (DMA). Of these, the most commonly used method is DMA. DMA will measure the bulk properties of the adhesive mass, which will include the base polymer and any additives in it. It does not take into consideration any interfacial relationships between the adhesive and the surfaces to which it is bonded. 

Changes in physical state may be observed from changes in thermodynamic quantities, which can be measured by calorimetric techniques, dilatometry, and thermal analysis. Spectroscopic methods are also available for the determination of changes in molecular mobility around transition temperatures. In addition to the changes in thermodynamic quantities and molecular mobility, a glass transition has significant effects on mechanical and dielectric properties. 

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