Optical studies of the stress‐induced crystallization of polymers

Abstract

Stress-induced crystallization may be studied by the birefringence technique and by low-angle light scattering. From measurements ofthe change in birefringence and stress during the crystallization of a polymer above its T , and from a calculation of the intrinsic birefringence of a polymer crystal, the change in volume fraction crystallinity may be calculated. The technique is illustrated for several polymers and found to give values in reasonable agreement with other methods for the study of crystallinity. Crystallization is also accompanied by the development of a low-angle light scattering pattern, the size and shape of' which i.; indicative of the amount, size and morphology of the crystalline superstructure.

Drawing and extrusion of semi-crystalline polymers

“…The same mechanism has to be active in the case of permanently by chemical crosslinks or temporarily by entanglements formed network [251] in natural [252] or polychloroprene [253] rubber that crystallizes upon stretching. Such crystallization may be followed by EM [253], X-ray scattering [254], birefringence [255], decrease of retractive force [256], or calorimetry [257]. According to Schultz [258] the crystallization of such amorphous microfibrillar structures may be explained by spinodal decomposition [104,105] of an amorphous and crystalline component with c~ = 0.5.…”

The effect of simple shear flow on the helix-coil transition of poly-L-lysine

“…These data can be quantified in terms of relative amounts of the two conformational states following the approach used to convert birefringence to volume fraction crystallinity in semicrystalline systems. 13 In this case, we assume that, in the absence of form effects, the birefringence of a PLL solution at a given shear rate and solvent ratio can be written as a linear superposition of the birefringence of the two conformational states (i.e., pure helix and pure coil), weighted by their volume fraction. Since absolute values of the amounts of the two species present are not known, we use the 95 and 0% MeOH solutions as reference states.…”

Online monitoring of birefringence development in heat‐setting polymer films with a fast dual‐wavelength optical technique. I. Uniaxially oriented poly(ethylene naphthalate)

“…The progression of crystallization was found to accompany changes in birefringence and density, whereas increasing sample elongation corresponded to higher crystallization rates. He determined that density was directly proportional to birefringence for extensions above 100%, but deviations from this proportionality were observed below 100%: Stress‐induced crystallization was studied by Stein33 on a number of polymers with birefringence measurements and small‐angle light scattering (SALS). His technique for measuring birefringence was similar to Treolar's 32.…”