Studies of polyethylene shish‐kebab structures

Abstract

An experimental method initiated by Williamson and Busse has been extended to produce veil‐free shish kebab structures in linear polyethylene without need for severe recovery treatments. The technique involves the dilution of polymer in a concentrated solution of low molecular weight paraffin followed by a simple isothermal shear. The resulting shish kebab structures are isolated from the wax matrix and subjected to electron microscopical and electron diffraction study. From the diffraction patterns, it is shown that the shish‐rich ordered structure is similar to the orthorhombic structure of crystalline linear polyethylene, but with certain significant deviations. The resolvable morphology of the shish appears to be characterized by a length‐to‐diameter ratio which is consistent with a prediction based upon Wulff's theorem utilizing certain relevant surface energy values which have been obtained by others for polymeric crystals.

Theory of flow-induced fibril formation in polymer solutions

“…George and Tuc ker [12] hav e measured th e mean diam eter a s of the fibrils that we re produced by mild s hear o[ a 3 1 /2 percent solution of polyeth ylene in n-octadecane at 84 O( and 101°C. They also measured th e mean di stance be twee n th e lamellar platelets at th ese two temperatures, whi ch we take to approximate th e characte ri stic length L s (table 1).…”

“…An investigation of eq (1) where we may defin e a reduced free energy of formation function as (12) By simply taking dy / dn = 0 , it is found that n * = 2/3, corresponding to /lcf>* = 32a-2 a-el(/lJ)2, and it is seen by inspection of eq (11) that /lcf> = 0 when n = 1, giving a A crossover on the n coordinate at n c = 1 (see fig. 2B).…”

“…The question then arises as to what connection th ere is if any between the mean interplatelet distance, and the mean length of the crystallite comprising the core fibril, i. e., the characteristic length as previously defined. In our analysis of the data given by George and Tucker [12] on specially prepared specimens where excessive additional overgrowths were minimized by appropriate techniques, we shall tentatively assume that these two quantities are approximately the same. George and Tucker assumed that the lamellar overgrowths actually occurred at the crystallite ends.…”

The morphology of fibrous polymeric crystals formed isothermally in stationary shear fields

“…The affinity for the reaction between M and X provides a multiplying effect upon the entropy production associated with the overall formation of product B from reactant molecule A. The authors have noted previously (7) that the diluent in the systems which they have used and described in this paper for producing fibrous crystals in certain cases does seem to have an influence upon the morphology of the transformed product. Similar observation has been recorded for systems of the type studied by Pennings and Keller previously referred to.…”

“…It is our purpose to discuss certain fibrous crystallizations which we have recently reported (7) produced in a flow similar to that of Pennings wherein the deformation initially is a simple shear. In contrast to the work cited above as well as more recent work of McHugh and Schultz (8), we are concerned with a solvent fluid of moderately high viscosity, namely, the viscosity of a melt of a normal p a r f i n in the region of 100°C.…”