Polymer studies pressure

Because chromophores orientation is important for creating anisotropy and optical nonlinearities, intensive studies have been performed to understand induced molecular orientation and relaxation processes in polymers. To gain further insight into the physics of thin polymer films and the effects of molecular orientation in solid polymers, studies at high pressure could be beneficial. Pressure as a thermodynamic parameter is widely used to study... 

Polymer miscibihty has been the subject of numerous studies. Pressure is a thermodynamic parameter that can affect the phase behavior of polymer mixture and that can be used to enhance the miscibility of polymers. This properly may have an important apphcation in controlhng microstructure. The phase behavior of blends and block copolymers under pressure has recently received significant attention 1-3). 

The identification of polymer blends is illustrated by the DTA curve in Figure 7.48. Chiu (154) studied a physical mixture of seven commercial polymers high-pressure polyethylene (HPEE), low-pressure polyethylene (LPPE), polypropylene (PP), polyoxymethylene (POM), Nylon 6, Nylon 66, and polytetrafluoroethylene (PTFE). Each component shows its own characteristic melting endothermic peak, at 108,127,165,174,220,257, and 340°C, respectively. Polytetrafluoroethylene also has a low-temperature crystalline transition at about 20°C. The unique ability of DTA to identify this polymer mixture is exceeded by the fact that only 8 mg of sample was employed in the determination. 

The breakthrough volxame trends for many sorbate types on the porous polymeric sorbents indicate a limited trapping capacity in the supercritical fluid CO2 above 200 atmospheres. Fractionation and selective retention on these sorbents seems only possible below this specified pressure limit for the odoriferous solutes examined in this study. Adsorbent surface area appears to be the most significant factor contributing to the retention of sorbates on these sorbents as well as activated carbon. For certain synthetic adsorbents (Tenax, XAD-2) employed in this study, pressure-induced morphological changes in the polymer matrix lead to an increase in the sorption capacity, and hence to an increase in breakthrough volumes at intermediate pressures. 

Y. Xiong and E. Kiran, High-pressure light scattering apparatus to study pressure-induced phase separation in polymer solutions. Rev. Sci. Instrum., 69, 1463-1471 (1998). 

It has been long realized that there are two regimes of injection mold filling. These involve a slowly expanding front or jetting into a mold. Oda et aL [Ol] have shown that jetting into a mold is the result of the polymer or compound having a low extrudate swell. The often complex occurrence of this swell is associated with the melt temperature and its variations in runners. Isayev and his coworkers [13, 14, 16] have extensively studied pressure... 

A variant of the technique devised by Ishizawa et al examines the transmission pattern of an He-Ne laser beam to study pressure dependence of LCST with high accuracy . Coupled with titration methods (that is varying composition by addition of solvent or solution), turbidimetry has been used to good effect to study cloud point curves in polymeri-polymerj-solvent and ionic polymer systems and to obtain solubility parameters for copolymers in mixed solvents. ... 

More recently, Silva et al. (2010) provided a new and fundamental level of understanding about the SPIF of polymers by setting up a theoretical framework that allows the influence of major operative parameters and their mutual interaction to be studied both qualitatively and quantitatively. The theoretical framework is based on membrane analysis with in-plane contact friction forces and is capable of modelling the cold plastic deformation of polymers with pressure-sensitive yield surfaces. 

Thermal evolution analysis is an excellent tool for polymer studies complementary to other thermal techniques such as DTA, TG and pyrolysis. Its applications include thermal degradation studies, determination of additives and contaminants, polymer composition and structure identifications. With small variations, the apparatus can also be used for vapour pressure measurements, and for determination of odorous materials in polymer systems. Coupling of TEA to GC for the identification of effluents is practicable and useful. TEA-CT-GC was used for the analysis of volatiles from ABS 10 ppb of styrene but negligible acrylonitrile was detected in the headspace of a typical ABS resin [42]. 

The influenee of pressure and temperature on fluid phase relations in the system ethylene/polyethylene being well documented in a qualitative sense [90-94], the effect of molar mass (distribution) is usually left out of consideration. Only De Loos et al. [95, 97] studied fluid phase relations in terms of cloud points and critical points in the system ethylene/linear PE for eight well-characterized polymer samples. Pressures ranged up to 2000 bar, temperatures were between 390 and 450 K, and a polymer concentration range of 0 to 30 wt% was studied. The weight-average molar masses varied from 3.7 to 118 kg mol. Cloud points were determined visually and critical points were measured with the phase volume ratio method. 

Besides temperature and polymer composition, pressure is a third parameter needed to completely determine the thermodynamic equilibrium state of a binary mixture. So far, only a few systematic SANS studies exist for polymer blends in external pressure fields [34-41]. Those experiments were also performed in our laboratory for which a temperature-pressure cell was developed for in-situ investigations allowing pressure and temperature fields between 0.1 < P(MPa) < 200 and - 20 < T(°C) < 200, respectively. A temperature control better than 0.01 K allowed also precise exploration of thermal composition fluctuations near the critical point [34]. 

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