A polyacrylonitrile sample of molecular weight 78,000 was dissolved into a 15% solution in 70% aqueous HNO3, spun into an undrawn model filament with diameter 0.3 mm. using a 30% aqueous HNO3 as the coagulation bath. The fresh filament was drawn 4–16× in water at various temperatures (40, 65, and 75°C.) and then steamed at 90–180°C. Dynamic mechanical tests were carried out on these filaments at 138 cps and it was found that the steamed filaments had a new transition at about 160°C. in addition to the two well‐known transitions at 60–70°C. (β) and 110°C. (αa), although the unsteamed samples had only the two absorptions, αa and β. This newly found transition was designated αx. The αx was measured at 3.5, 11, and 110 cps from which the activation energy of this relaxational motion was estimated to be 95 kcal./mole. The αx peak height was lowered by stretching and recovered on resteaming; the change in the peak height was paralleled by the changes in the x‐ray crystallinity produced by the stretching and the resteaming. These phenomena lead us to a conclusion that the region contributing to the αx absorption is of considerably higher order than that of the αa transition with an activation energy about 50 kcal./mole and intimately related to the crystallinity, although it cannot be connected directly to the crystalline region itself because a single crystal mat did not show the αx.
Polypropylene film was biaxially stretched in one step in air at 140°C or 152°C, and the deformation was studied optically. A linear relation held between Δnss and vA−½ for vA > 10, at both temperatures, where Δnss is the birefringence with respect to the normal to the film and vA is the degree of stretching expressed as the factor by which the area of the film is increased. Extrapolation of data in this linear region yielded a value of 20 × 10−3 for −Δnss at infinite vA. Since it is presumed that the polypropylene molecules lie completely parallel to the film surface when the film is stretched infinitely, −Δnss at vA−½ = 0 must be just half Δn°, the intrinsic birefringence in the case of completely parallel orientation. Thus, Δn° must be 40 × 10−3. This value was obtained experimentally in uniaxial stretching when the birefringence with respect to the direction of drawing was extrapolated to infinite extension. Similar relations held between np, the average of the refractive indices in the two stretching directions, and vA, and between nss, the index normal to the film, and vA. By similar extrapolations, (1/2)(n′γ + n′β) and n′β = n*α′ were estimated, and thence nα′ was obtained. Here, n′α and n′β are the refractive indices along the c axis (molecular chain axis) and b axis. All these optical parameters refer to a density of 0.900 g/cm3. Hence by applying a density correction to those values, the principal refractive indices and the intrinsic birefringence of polypropylene crystal were evaluated as follows: nα = 1.5522, nβ = n*α = 1.5106 and Δnc° = 4.16 × 10−3, where n*α is the refractive index prependicular to the b and c axes of the crystal.
synopsisA polypropylene film was stretched a t 1O&16O0C., quenched to room temperature, and then restretched a t the same temperature perpendicularly to the first stretching. The reorientation behavior was investigated by using optical and x-ray methods. During the restretching the monoaxiaI orientation caused by the stretching is converted into a new monoaxial orientation through a balanced state, where npp = npi > ns.. The more or less parallel orientation to the film surface of the polypropylene molecules, brought about by the first stretching, proceeds further on restretching. nss is a h e a r function of the degree of stretching in area VA. The inclination of this line is independent of the type of deformation, stretching, or restretching, provided the temperature is kept constant. At 160OC. the plot of nss versus thickness is less steep than it is a t 100 or 130OC. The overall reorientation apparently proceeds according to Kratky's first deformation law. The x-ray pattern of a restretched film is a four-point diagram which indicates the existence of a pair of reorientation axes inclined symmetrically against the stretching axis. The inclination grows larger with restretching, and the axes merge into the restretching axis at extreme restretching. This phenomenon is less pronounced when the restretching is carried out a t higher temperatures. The density of the restretched film is determined mainly by the stretching temperature, but extreme restretching has a tendency to lower it very slightly.
synopsisFour samples of poly(ethy1ene terephthalate) film of various crystallinities and orientation were dyed with p-nitroaniline and disperse dyes. When these films were heated under a 2-3 X lo-* mm Hg vacuum at a specified temperature T, the dye sublimed out of the dyed specimen. The amount (Mr/Mm) of sublimed dye is in linear proportion to the square root of the sublimation time, t1I2, where M t and Mm are the amounts of dye sublimed for times t and t = 0 3 . The diffusion coefficient D, calculated from the slope of the above plot, is independent of the dye concentration of the film.When log D is plotted against l/T"K over the temperature range 320-520°K, the relation is composed of two to four intersecting lines with the slope decreasing with elevation of temperature and with the breaks a t about 89"-98", 122"-135", 155' and 175"-176°C. the first is the glass transition temperature T , the second and the fourth are the amorphous transitions corresponding to the crystalline transition points, i.e., the cold crystallization temperature and the smectic-triclinic transition temperature. With some exceptions, these amorphous transitions are found also by dilatometry and electrical conductivity measurements. The apparent activation energy for diffusion decreases from about 100 kcal/mole for the glass state to 22-24 kcal/mole for the region above 180°C. The activation energy for each region changes slightly with the size of dye molecule and the crystallinity and orient,at,ion of the film.These breaks are the amorphous transitions:
SynopsisThe orientation factor by infrared dichroism of polypropylene film was compared with the other orientation factors. After the correction of imperfect polarization and the suitable choice of the base line, it was found that infrared dichroism is a reliable indicator of the orientation factor. Orientation factors obtained from the 998 and 842 cm.-l bands agreed with the x-ray orientation factor, and that from the 975 cm.-l band agreed with the optical orientation factor.
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