A. E. Woodward

The dynamic mechanical behavior of some nylons

Abstract The dynamic mechanical properties of 6-6 nylon, 6–10 nylon, and a nylon copolymer have been studied in the audio-frequency region over a temperature range extending from about 80°K. to near the melting point by driving rodlike samples in their first transverse mode of oscillation. In all nylon types tested, four dispersion regions are observed, the first three being at temperatures of approximately 170°, 250°, and 350°K. These dispersion regions appear both as peaks in the absorption curve and as relatively sharp drops in the resonance frequency curve. The magnitude and temperature positions of the damping maxima are dependent on the specific nylon type. Over parts of the temperature region the damping of 6-6 nylon depends on the thermal history and water content of the sample. Possible assignments for each of the observed dispersion regions in terms of molecular motion are given. Correlations between the dynamic mechanical data and the results of other physical measurements on the nylons are pointed out.

Effect of Irradiation On Dynamic Mechanical Properties of 6–6 Nylon

Measurements of elastic modulus and mechanical loss at audio‐frequencies have been obtained on irradiated and nonirradiated specimens of polyhexamethylene adipamide over a broad temperature range extending from 80°K to 600°K. The irradiations were carried out at the Brookhaven and Penn State Reactors. The internal friction spectrum of unirradiated nylon 6–6 contains at least four peaks corresponding to different mechanisms being invoked as the temperature is raised. With irradiation doses from 0.3×1018 nvt to 5.5×1018 nvt, significant changes in the dispersion regions occur. At temperatures above the main softening region, an increase in modulus with temperature is found. This is evidence of rubber‐like behavior and is accounted for by the introduction of cross‐links resulting from ionization and free radical formation produced by the irradiation. At high irradiation doses the percent cross‐linking appears to become independent of dose. The various effects found are discussed in terms of molecular forces ...

Dynamic mechanical studies of irradiated polyethylene

Abstract The dynamic mechanical properties of high density polyethylene irradiated in a 60 Co source at dosages of 10 8 –10 9 r.e.p. have been investigated from 80°K to 450°K at audiofrequencies using a resonance technique. With increasing radiation dose the slope of the modulus v. temperature relation above the melting temperature, 410°K, increases, indicating an increasing degree of crosslinking of the network structure. The damping peak in the 390°K region is also observed to decrease in magnitude. At gamma-ray doses of 6 × 10 8 –10 9 r.e.p. the crosslinking efficiency is found to be somewhat greater for the high density polyethylene than for a low density polyethylene irradiated at room temperature under similar conditions. The effect of a subsequent heat treating and annealing operation has been studied for both low and high density polyethylene and for both 60 Co irradiation and pile irradiation. For doses up to 10 18 n.v.t. or so, the primary effect of heat treatment on the mechanical properties of the pile-irradiated high density samples is to decrease the values of dynamic modulus and increase the values of the mechanical loss over the entire temperature range from 100 K to 400 K. This is attributed to a reduction in crystallinity and is confirmed by room temperature measurements of crystallinity and density. It is also observed that, especially after subsequent heat treatment above the original melting temperatures, samples of high density polyethylene crosslinked to a similar degree in either a 60 Co source or a nuclear reactor exhibit comparable dynamic mechanical behaviour. For samples of high density polyethylene irradiated in a pile to a dose of 1.5 × 10 18 n.v.t. the influence of oxygen on the dynamic mechanical properties of laboratory size samples has been found to be negligible.

Nuclear Magnetic Resonance and Thermal Expansion in Partially Crystalline Polypropylene, Poly(Butene‐1), and Poly(Pentene‐1)

The specific volume of partially crystalline specimens of polypropylene, poly(butene‐1), and poly(pentene‐1) from about 160°K to above the melting point has been studied. In addition, proton spin magnetic resonance of a partially crystalline poly(butene‐1) specimen has been observed over the 77°K to 320°K temperature range. Percent crystallinities as functions of temperature for polypropylene and poly(butene‐1) calculated from the specific volume data are compared. The poly(butene‐1) specimens show higher densities than the polypropylene samples at 170–180°K although the crystalliniites of the former are 25–40% lower than the latter. In addition, the temperature dependence of the specific volume from 160–280°K is greater for poly(butene‐1) than for polypropylene. Somewhat similar trends are noted in a comparison of the NMR (nuclear magnetic resonance) second moment versus temperature curves for these two materials.

Dielectric Loss in Poly‐(Hexamethylene Adipamide) and Poly‐(Hexamethylene Sebacamide) at Low Temperatures

The dielectric behavior of samples of nylon 6–6 and nylon 6–10 has been studied in the temperature region from −160° to 60°C at frequencies of 0.1 to 100 kc/sec. The effects of thermal history, electron irradiation, and post irradiation annealing on the two dielectric loss peaks found in this frequency‐temperature range have been explored. Electron irradiation of nylon 6–6 and 6–10 and thermal quenching of nylon 6–6 lowers the γ peak (−70°C at 1 kc/sec for 66 nylon) and raises the β peak (+15°C for 66 nylon at 1 kc/sec). Post irradiation annealing of nylon 6–6 or 6–10 irradiated to low doses (25 to 100 mrad) removes the effect of the irradiation on the dielectric behavior, but on irradiation to high dosages (900–1000 mrad) the dielectric loss values in the region of the β maximum at 0.1 and 1.0 kc/sec are greatly reduced. The frequency shifts of the dielectric loss maxima for all samples give activation energies in kcal/mole which fall in the 8–15 range for the β maximum and 9–19 for the γ maximum. These ...

Proton magnetic resonance of irradiated polyethylene

Abstract The proton magnetic resonance of polyethylene in the temperature range: 80–430°K has been investigated for a series of 60 Co-irradiated high density specimens, a series of pile-irradiated heat-treated high density specimens, a series of pile-irradiated heat-treated low density specimens and a 60 Co-irradiated, heat-treated low density specimen. For the high density polyethylene samples two transitions are apparent in the second moment v. temperature plots, in agreement with dynamic elastic modulus-temperature behaviour. A gamma-ray dose of 10 8 r.e.p. from a 60 Co source introduces enough crosslinks in the amorphous regions of high density polyethylene to cause a shift of the amorphous transition at low temperatures (∼200°K) to higher temperatures as seen by changes in the peak-to-peak width of the derivative n.m.r. absorption v. temperature plot. The observed changes of the second moment v. temperature plots with increasing radiation dose provide further evidence that the first effect of pile irradiation is to increase the segmental mobility in polyethylene owing to a loss of order in the crystalline regions, and that, with further irradiation, there is a decrease in molecular mobility as a consequence of the increased crosslinking density. Samples which have been crosslinked to the same degree by irradiation in either a 60 Co source or a nuclear reactor at temperatures well below the crystalline melting point and subsequently heated above the melting point are found to exhibit essentially the same temperature dependence for both the line width and the second moment.