Effects of tensile strain on the peculiarities of PEO penetration into the nanoporous structure of PET deformed via the crazing mechanism

Abstract

Solvent crazing involves the development of a highly dispersed fibrillar-porous structure with dimensions of pores and craze fibrils of about 2-20 nm, and crazing by itself can be treated as a universal method for the development of nanoscale porosity. The penetration and release of poly(ethylene oxide) macromolecules into and from the crazes during the development of the nanoporous structure of poly(ethylene terephthalate) have been studied. In particular, PET has been deformed in dilute or semidilute (unentangled as well as entangled) solutions of PEO (a Mw of 4 and 40 kDa) via the mechanism of solvent crazing. Hydrodynamic coil radii Rh, blob sizes ξ, and concentration ranges (crossover and entanglement concentrations) have been determined for the PEO solutions. The evolution of the craze structure (change in porosity W and pore diameters d) has been described as a function of the tensile strain of PET during its drawing in an adsorption-active medium and in the PEO solutions. PEO has been shown to penetrate into the nanoporous structure of the crazes under the conditions corresponding to Rh≤d and ξ < d. It has been shown that coagulation processes in the structure of crazed PET, PEO adsorption at the highly developed surface of PET, and the mechanism of PEO transport in the nanopores are equally important factors affecting the direction of the macromolecule mass transfer in the nanopores (penetration or release) and PEO content variation as a function of PET tensile strain.

Special Features of Crazing of Glassy Poly(ethylene terephthalate) in Poly(ethylene oxide) Solutions

“…The content of PEO in PET as a function of the PET deformation rate in 5.5 wt % solution of PEO4K is shown in Figure 1. As follows from the data in Table 1, the effective diameter of pores in the PET crazes (7.6−8.4 nm at 100% tensile strain) exceeded the hydrodynamic radius of PEO4K coil (1.3 nm) 16 and hence PEO4K should have freely penetrated inside the porous structure being formed. However, a sudden increase in the PEO content in the crazed PET was observed above certain tensile strain (Figure 1).…”

“…Herein we will report and discuss the effect of the deformation rate and the flow mechanism on the penetration of PEO macromolecules inside the developing structure of crazed PET as studied in the following concentration regimes (Table ; the studies of the PEO solutions have been reported by us earlier , ).…”