Adhesiveness of polyethylene mixtures

The effect of additions to polyethylene wax on the breaking stress f of butt joints between two steel cylinders depended on the nature of the addition. Oleic acid lowered f in concentrations as small as 0.2%, and in presence of 1% oleic acid f was immeasurably small. Ethyl palmitate slightly diminished f (to about 1/5th of the initial value when the amounts of polyethylene and palmitate were equal), but this decrease was wholly due to the weakening of the polymer itself, and the ratio of f to the tensile strength of polyethylene‐palmitate mixtures was >1 at all compositions. Thus, with oleic acid above 0.2% improper, and with ethyl palmitate at all percentages, proper adhints were obtained. Stearone apparently formed a weak boundary layer and 4‐methyl‐2,6‐di‐tert‐butylphenol gave erratic results as it decomposed on heating and apparently reacted with steel. Addition of ethyl palmitate to polyethylene contaminated with oleic acid made the mixture adhesionable. The solubility of the contaminant in solid polyethylene was more important than polarity. The relation between the composition of an adhesive and the breaking stress of its adhints can be understood if the distinction between proper and improper joints is kept in mind.