Polyethylene films were stressed in uniaxial tension at room temperature while the infrared (FTIR) or Raman spectra were simultaneously measured. The purpose of these experiments was to gain an understanding of the molecular origins of the stress‐induced vibrational frequency shifts Δν and determine the mechanisms of molecular deformation and fracture of PE molecules with stress σ. The PE samples consisted of ultradrawn, high‐density, ultrahigh‐molecular‐weight, solid‐state‐extruded films and the stress was applied parallel to the nearly perfectly oriented orthorhombic crystal c‐axis direction. The experimental frequency shifting coefficients α = (∂ν/∂σ)σ→0 were compared with calculated α values determined from a vibrational analysis of an isolated PE chain using conformational energy minimization methods in which both harmonic and anharmonic (Morse) potential energy functions were used for the CC stretching modes in the valence force field. The following α values were obtained and are compared with theory (anharmonic case in parentheses, in cm−1/GPa): CC symmetric stretch, α(1127) = −5.9 (−5.3); CC asymmetric stretch, α(1059) = −11.2 to −5.7 (−5.8); CH2 rock, α(730/720) = −2.0 to −3.0 (−2.2); CH2 scissors, α(1472/1462) = −1.0 to −1.2 (−1.1); CH2 twist, α(1295) ≃ 0(0.8); CH2 wag, α(1370) undetermined owing to weak bands (−4.6); CH2 stretch α(3000) ≈ 0. The largest negative frequency shifts were observed for the CC stretching modes, in agreement with the calculations using the Morse potential. The harmonic potential for CC stretching resulted in small positive α values for both the CC stretching and CH2 wagging modes, while the other modes were unaffected by this choice of potential. The relative contribution of CC bond stretching and CĈC valence angle bending to the c‐axis strain was about 1:1, in agreement with experiment. The Young's tensile modulus of a PE chain was calculated as Ec = 267 GPa.

The effect of stress and temperature on infrared frequency shifting and band asymmetry in polymers is investigated. Valence coordinate deformation of individual polypropylene chains accounts for the observed frequency shifting in samples of oriented isotactic polypropylene. Each chain may be modeled as a one-dimensional enharmonic system, whose wave functions and energies are obtained in the quasi-harmonic approximation. The theoretical stress-induced frequency shifting coefficient is related to the Gmneisen parameter and is expressed by ac = -a0 -CTosc, where a0 and C are positive constants and Toer is the temperature of the oscillators in equilibrium with the radiation field. Two mechanisms of band broadening are considered: The first is due to the presence of an average interchain perturbing force. The second is due to the existence of anisotropic crystal field forces. Each description predicts symmetric broadening. Therefore, the development of an observable asymmetry in a stressed infrared band may be associated with a nonuniform molecular stress distribution. Only the crystal field broadening mechanism, however, is consistent with the assumptions required for calculation of the linear ac(T) relation, which agrees well with experiments on oriented polypropylene. The anisotropic broadening mechanism is also investigated for oriented polyethylene.

Chronic progressive nephropathy (CPN) is a spontaneous renal disease of rats which can be a serious confounder in toxicology studies. It is a progressive disease with known physiological factors that modify disease progression, such as high dietary protein. The weight of evidence supports an absence of a renal counterpart in humans. There is extensive evidence that advanced CPN, particularly end-stage kidney, is a risk factor for development of a background incidence of atypical tubule hyperplasia and renal tubule tumors (RTT). The likely cause underlying this association with tubule neoplasia is the long-term increased tubule cell proliferation that occurs throughout CPN progression. As a variety of chemicals are able to exacerbate CPN, there is a potential for those exacerbating the severity up to and including end-stage kidney to cause a marginal increase in RTT and their precursor lesions. Extensive statistical analysis of National Toxicology Program studies shows a strong correlation between high-grade CPN, especially end-stage CPN, and renal tumor development. CPN as a mode of action (MOA) for rat RTT has received attention from regulatory authorities only recently. In the absence of toxic effects elsewhere, this does not constitute a carcinogenic effect of the chemical but can be addressed through a proposed MOA approach for regulatory purposes to reach a decision that RTT, developing as a result of CPN exacerbation in rats, have no relevance for human risk assessment. Guidelines are proposed for evaluation of exacerbation of CPN and RTT as a valid MOA for a given chemical.

Dans le cas de bandes intenses des artefacts dus au processus d'apodisation peuvent apparaître dans les spectres infrarouges obtenus par transformée de Fourier. Ces effets ont déjà été étudiés sur des spectres obtenus par différence pour des fonctions d'apodisation de type boxcar ou triangulaire. Ce travail présente des simulations numériques réalisées avec une fonction d'apodisation de type Happ-Genzel couramment employée dans les instruments modernes. Pour comparer les performances des fonctions d'appareil de type boxcar, triangulaire, ou Happ-Genzel nous avons calculé (i) les artefacts apparaissant dans les spectres obtenus par différence ; (ii) la variation de l'absorbance apparente au sommet d'un pic d'absorption en fonction de l'absorbance vraie ; (iii) une mesure intégrée de l'erreur due à ces artefacts pour une bande d'absorption à profil lorentzien. L'étude est faite pour des valeurs de p (rapport de la largeur totale du pic à mi-hauteur à la résolution) qu'on rencontre couramment en spectroscopie de transmission d'échantillons solides ou translucides.Abstract. -Artifacts may occur in Fourier transform infrared (FTIR) spectra due to the apodization of the interferograms of intense bands. Selected examples of boxcar and triangular apodization effects on difference spectra have been previously reported. This paper reports the first such calculation performed for the Happ-Genzel apodization function, which is often used on modern spectrometers. In order to compare boxcar, triangular, and Happ-Genzel apodization functions we calculate (i) difference-spectrum artifacts, (ii) apparent versus true peak absorbances, and (iii) a measure of integrated artifact area for several true peak intensities of Lorentzian-band shapes. Values of p (ratio of full bandwidth at half height to nominal resolution) are emphasized which commonly occur in the transmission-mode spectroscopy of transparent or translucent solid samples.

The effect of temperature on vibrational frequency shifts in mechanically stressed polymer chains is analyzed. A single chain is modeled as a weakly coupled, one-dimensional series of anharmonic diatomic oscillators. The anharmonic potential is described as a perturbation of the harmonic potential with cubic and quartic terms. Expressions are derived for the dominant, quasiharmonic contribution to the temperature-dependent frequency shifting coefficient a c , and distinctions are drawn between the vibrational mode "mixing contribution" and the "anharmonic contribution." a c is derived in terms of the Gruneisen parameter; and the resulting expression is -a c = a o + PoT, where a o is the extrapolated T = 0 oK value of the frequency shifting coefficient, and Po is constant. The predicted linear dependence of a c on temperature was found to be in excellent qualitative agreement with experimental studies on stress-induced infrared frequency shifts versus T in polypropylene.

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Quantitative Fourier‐transform infrared (FTIR) measurements of frequency shifts Δν and absorbance profile asymmetry are reported for various polypropylene samples as a function of uniaxial stress σ. Generally, it was found that the frequency shift coefficient αχ, defined by Δν = αχσ, depended on stress rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, draw ratio, λ, molecular orientation f, tensile modulus E, and annealing conditions. With annealing, αχ decreased with increasing shrinkage in the case of highly oriented isotactic PP. The αχ values for the “helix bands” were less affected than those for the “liquid bands.” With increasing \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, generally αχ increased to an apparent asymptotic limit. With increasing λ, f, or E, αχ also increased from αχ ≃ 0 for λ = 1 (spherulitic) to maximum values for highly oriented isotactic PP. The observed variations in αχ can be interpreted in terms of the changes in the peak position and shape of the nonuniform molecular stress distribution. Analogous behavior with x‐ray diffraction peaks obtained for polymers under stress is discussed.

The paper applies classical statistical principles to yield new tools for risk assessment and makes new use of epidemiological data for human risk assessment. An extensive clinical and epidemiological study of workers engaged in the manufacturing and formulation of aldrin and dieldrin provides occupational hygiene and biological monitoring data on individual exposures over the years of employment and provides unusually accurate measures of individual lifetime average daily doses. In the cancer dose-response modeling, each worker is treated as a separate experimental unit with his own unique dose. Maximum likelihood estimates of added cancer risk are calculated for multistage, multistage-Weibull, and proportional hazards models. Distributional characterizations of added cancer risk are based on bootstrap and relative likelihood techniques. The cancer mortality data on these male workers suggest that low-dose exposures to aldrin and dieldrin do not significantly increase human cancer risk and may even decrease the human hazard rate for all types of cancer combined at low doses (e.g., 1 microgram/kg/day). The apparent hormetic effect in the best fitting dose-response models for this data set is statistically significant. The decrease in cancer risk at low doses of aldrin and dieldrin is in sharp contrast to the U.S. Environmental Protection Agency's upper bound on cancer potency based on mouse liver tumors. The EPA's upper bound implies that lifetime average daily doses of 0.0000625 and 0.00625 microgram/kg body weight/day would correspond to increased cancer risks of 0.000001 and 0.0001, respectively. However, the best estimate from the Pernis epidemiological data is that there is no increase in cancer risk in these workers at these doses or even at doses as large as 2 micrograms/kg/day.