Crystallinity studies of polyamides by infrared, specific volume and X‐ray methods

Abstract

Examination of the infrared absorption of three nylons, polyhexamethylene sebacamide, polyhexamethylene adipamide, and polycaproamide (nylon 6,10, 6,6, and 6, respectively) revealed the existence of bands associated with crystalline order. These discoveries were utilized in the study of crystallinity of nylon 6,10 and nylon 6 in conjunction with x‐ray and specific volume methods. The work falls into three parts. Part I deals with elementary consideration of dichroism and deduces a method of comparing the intensity of an infrared band in a drawn sample of polymer with that of a disoriented sample. A theory of dichroism in materials that have rotational symmetry about one direction is formulated. The question of measuring the absolute intensity of an infrared band is briefly considered. In Part II the crystallinity content of nylon 6,10 (a polymer chosen for its suitability for testing the method) is determined by using the 940 cm.−1 band and specific volume measurements. The effects of annealing and drawing are studied. Proportionality between change in specific volume and change in infrared absorption is confirmed by experiment up to an annealing temperature of 180°C. Above this temperature specific volume measurements give too high a crystallinity figure. Cold‐drawing is found to be connected with a reduction of crystallinity, and can produce voids. The crystallinity of our samples varied between 20 and 55%. The significance of these figures—absolute and relative—is discussed. An absolute figure of 1.052 for the amorphous density of nylon 6,10 is deduced. Part III deals with nylon 6. The infrared spectrum in the 7.5–12.5 μ region is examined and several of the bands are classified as crystalline or noncrystalline. Variation of these bands is studied when the polymer is annealed, drawn, and melted. Both annealing and cold‐drawing increase crystallinity content. In the drawn samples the crystallites are found to be better oriented than the noncrystalline parts. The direction of the transition moment of the 935 cm.−1 band is determined. X‐ray results reveal a new type of ordering corresponding to a state of packing intermediate between randomness and full crystalline order. Infrared bands at 990 and 720 cm.−1 are found to be connected with this state of order. Direct evidence is obtained that the molecules possess an order in the quenched amorphous state. The density of amorphous nylon 6,10 calculated from this ordering is in complete agreement with the figure deduced in Part II.

Annealing of melt-crystallized nylon 6

“…It can be due to the different thermal treatment of the samples used for the analysis. The extrapolated density of an amorphous phase of nylon 6 is 1.099 g/cm 3, which is within the range of values given by Sandeman and Keller [8] and Illers [7].…”

Structure characterization of heat set and drawn polyamide 66 fibers by FTIR spectroscopy

“…Relatively few studies have been reported concerning the measurement of crystallinity and molecular orientation of polyamides by infrared spectroscopy [9][10][11][12]. Usually, the crystallinity determination of semicrystalline polymers by infrared spectroscopy has been carried out by calibrating against another method [13,14], and the determination of crystallinity by infrared alone has been done only for a few polymers [15,16]. The purpose of the present study is to characterize some fundamental microstructure properties of PA66 fibers such as crystallinity and molecular orientation using infrared spectroscopy.…”

Amorphous and crystalline phase interaction during the Brill transition in nylon 66

“…It is preceded by gradual crystallographic changes, occurring over a relatively wide temperature range and entailing dimensional changes of the triclinic crystallographic unit cell, wherein the room temperature spacings of 0.44 nm (d 100 ) and 0.37 nm (d 010/110 ) are shifted to lower and higher values, respectively. At the transition point the two diffraction maxima are replaced by one with a spacing of 0.42 nm [6][7][8]. Over the years since its discovery, the Brill transition has been studied for various types of even-even and odd-even polyamides [9][10][11][12][13] and for different crystallization conditions [10].…”