An anomaly in the necking behavior of polyethylene

Tensile creep measurements at constant load on nonoriented polyethylene have shown a marked transition at a certain stress level from a neck formation followed by instantaneous fracture to the formation of a neck which resists fracture for a considerable time. The transition, which shifts towards shorter time and higher nominal stress with increasing molecular weight, has been studied for 16 polyethylenes of different molecular weights, degrees of branching and crystalline structures. The marked. transition has only been observed for high density polyethylene of high molecular weight. Deformation measurements show a more distinct necking for the high density than for the medium density polyethylenes. This is consistent with current molecular deformation theories. A hypothesis for the transition is proposed based on the distinctness of the neck process in the high density polyethylene and the large difference in strength between the spherulitic structure and the fibrillar structure. The dependence of the transition on molecular weight is expected since the number of tic chains incrcrtses with increasing molecular weight.     

The production of salad oil by fractional crystallization with solvents

A fractional crystallization method for the winterization of cottonseed oil with solvents was developed in our laboratories and pilot plant. Small amounts of solvent (e.g., 10% by weight of acetone) were mixed with the oil. This mixture was rapidly chilled to 0°C. and kept at this temperature for 3–4 hrs.; the liquid portion was separated from the solids. After solvent evaporation a salad oil of good quality was obtained. The yield is equal to or better than that obtained with conventional methods. The method is suitable for a continuous operation since rapid chilling can be used, and only a short over-all time is necessary. Great advantages of the process are the use of low amounts of solvent and of a refrigeration system not requiring temperatures below 0°C.     

Characterization of Grain-Boundary Segregation in MgO

Using Auger electron spectroscopy, segregation of Ca and Si corresponding to the adsorption of a partial monolayer adjacent the boundary in polycrystalline MgO was observed. Segregation of Sc is different in nature; the distribution consists of a 3.0-nm wide region corresponding to a positive space charge layer balancing a negative boundary charge. Various segregation models are applied to the observed behavior.     

The problem of correction for ohmic potential drop in linear potential sweep experiments and the derivation of s0 values for electrode surface processes

Rate constants or exchange current densities of electrode surface processes involving adatom arrays are conveniently evaluated by determining that sweep rate, s₀ (the reversibility parameter), in a linear potential sweep (LPS) experiment, below which the process just remains kinetically reversible, ie its overpotential is sensibly zero. Transition to irreversibility is characterized by peak potentials, E_p, becoming linear in the log of the sweep rate, s, following a region of independence of s for < s₀. A suitable extrapolation procedure enables s₀ to be evaluated. However, if s₀ is large and/or the resistivity of the solution is appreciable, the IR_u drop associated with uncompensated resistance in the measurement system can be comparable with the increase of E_p with log s, when s > s₀, rendering evaluation of s₀ inaccurate. While compensation or empirical correction for this may be made, it is desirable that the nature of the IR_u effect of the LPS I vs E profiles be understood in a more fundamental way. It is the purpose of this communication to provide such a treatment of this effect through evaluation of the actual time-dependent potential that becomes applied to the electrode, and to propose criteria based on the product of s₀, R_u and the reaction pseudocapacitance, C_φ for indicating the anticipated extent of the IR_u effect in the evaluation of s₀. While the transition in the E_p vs log s plot may be due to IR_u effects as well as to kinetic irreversibility, when the former are appreciable, it is shown that the corresponding transition in the value of C_φ with increasing log s can usually allow spurious IR_u and significant irreversibility effects to be distinguished.     

Trends in industrial markets for fats and oils and derivatives

During the past decade, research by industry and government has developed numerous new chemical markets for fats and oils derivatives. Lower prices for competitive raw materials have forced some of these new products into specialty markets. Economic factors, such as the continual growth of the chemical industry, population increases, and high consumer demand, have allowed for steady growth in the fat-derivative market. New fat-type plasticizers are currently consuming about 60 million pounds of fats annually. Synthetic lubricants will probably be consuming 20 million pounds of fatty diesters annually by 1965. Animal feeds consume approximately 600 million pounds of fats and fat derivatives annually and may eventually become the leading domestic nonfood market for fats. The protective coating market as an outlet for fats continues to decline, and the continuing shift to nonfat materials and changes in pain formulas indicate that, while the demand for protective coatings may increase, the use of fats in their manufacture may not share in the increase. Nonfat chemical raw materials provide intense price competition for fatty raw materials. Fat prices are influenced by the demand for use in food, soap, paints, and possibly animal feeds rather than by the demand for use as chemical raw materials. Presented before the American Oil Chemists' Society, New York, October, 17, 1960.     

The lead dioxide electrode

The recent literature dealing with the redox mechanism of the lead-acid cell positive electrode is reviewed. The basis electrochemistry of lead dioxide in its various polymorphic modifications and states of subdivision is considered in relation to the important aspects of electrode technology of which the major industrial application of the material is the conventional lead-acid cell. The proposed mechanism of the reduction (discharge) of lead dioxide in various acidic solutions are considered in relation to the present state of electrode kinetic theory. The reverse reaction by which lead dioxide is formed and the parasitic intrusion of the self discharge are dealt with as a precursor to the total cyclic process. It is concluded that in a number of respects the mechanisms proposed do not adequately represent the totality of the experimental observations. Such shortcomings are emphasized and extensions to present research are proposed.     

Potentiostatic step experiments on pasted Pb-Sb and Pb-Sn-Ca electrodes

A range of cyclic electrochemical experiments have been carried out on electrodes of porous PbO₂ supported on a number of Pb-Sb and Pb-Sn-Ca alloys using micro-computer controlled potentiostatic stepping techniques. The results show that, in certain cases, the differences in electrochemical behaviour of the PbO₂ can be interpreted as being due to the effect of the support alloy.     

The temperature dependence of the electrochemistry of the lithium-sulphur dioxide system

Value for the activation energy, U ^act, and the entropy change, S, for the reaction 2Li + S₂O ₄ ^2– Li₂S₂O₄+2e in acetonitrile have been found to be 72 kJ mol^–11 and — 0.3 kJ mol^–1 K^–1, respectively, by a combination of impedance techniques and the use of a temperature-controlled environment on commercially manufactured cells which acted as constant volume containers.     

The reaction of activated vinyl compounds with cotton cellulose via internal catalysis

The reactions of a variety of activated vinyl compounds with cotton cellulose fabric containing quaternary ammonium hydroxide substituents were explored. Each reaction, catalyzed by the basic groups in the cellulose, was followed to or near the point of leveling off. The results are analyzed and discussed in terms of accessibility of the cellulosic compositions and in terms of the efficiency of the quaternary ammonium substituents as catalysts for the addition reactions. Estimates of relative forward rate constants (k_f) and equilibrium constants (K) for the reactions were made. The values of k_f for reactions of the vinyl compounds with the quaternary ammonium celluloses show a relative order which is similar to that for the reactions of the vinyl compounds with simple alcohols. Evidence is presented to indicate that, in some cases, the addition of vinyl compounds is accompanied by anionic-catalyzed graft polymerization.