Microstructure evolution of poly[tetrafluoroethylene-co-(perfluoropropylvinylether)] films under uniaxial deformation

Abstract

This paper presents an investigation of semi-crystalline poly[tetrafluoroethylene-co-(perfluoropropylvinylether)] (PFA) films uniaxially drawn at two temperatures. The extent of crystal unit cell orientation increased significantly with drawing at both draw temperatures as expected, but crystallinity was found to increase with draw ratio only at the lower draw temperature, remaining unchanged at the higher temperature. Considering the evolution of small-angle X-ray scattering patterns as a function of deformation, a model for the changes in PFA lamellar microstructure on drawing was developed. The observed mechanical α and γ relaxations of PFA were assigned to relaxation of rigid and mobile amorphous segments, respectively. Drawing at 200 °C to a draw ratio of 7 leads to a ~40 °C increase in the α transition temperature compared to the unoriented film, and the findings support the key role of molecular orientation in suppressing the cooperative motions of non-crystalline segments in drawn polymers.

Crystalline microstructure and dielectric properties of oriented poly(ethylene-co-tetrafluoroethylene)

“…Although their dielectric constants are in the same range as BOPP, they can be melt extruded into thin films, have high dielectric stability at elevated temperatures, and exhibit very low dielectric loss. 10 Building on our previous work, 11,12 we focus in this paper on the role of uniaxial orientation and subsequent thermal annealing on the semi-crystalline microstructure and low electric field dynamics of ETFE, as well as high field dielectric breakdown measurements on selected drawn and annealed ETFE films. Experimental Weibull dielectric breakdown strengths are found to increase with uniaxial orientation (draw ratio = 3) to values as high as 870 MV/cm, over 10% larger than commercial BOPP films measured under similar conditions.…”

Wear-Induced Microstructural and Chemical Changes in Poly[tetrafluoroethylene-co-(perfluoroalkyl vinyl ether)] (PFA)

“…and Yin et al, respectively). In these works, both authors drew films of PFA (PEVE comonomer for Fujimori et al, PPVE comonomer for Yin et al) up to 9 times their original length at elevated temperatures (200 °C, Fujimori et al tested at 280 °C, Yin et al tested at 140 °C). , Yin et al noticed that increased crystallinity began at applied stresses near 6.5 MPa, which is near the nominal contact stress (6.25 MPa) used for this study. In our wear experiments, the local stress at the PFA interface is significantly larger than the apparent contact pressure due to roughness of the steel counterface.…”

“…Fujimori et al and Yin et al both observed strain-induced crystallinity of PFA films after uniaxial tensile stress experiments (35% and 10% increase in crystallinity for Fujimori et al . and Yin et al, respectively). In these works, both authors drew films of PFA (PEVE comonomer for Fujimori et al, PPVE comonomer for Yin et al) up to 9 times their original length at elevated temperatures (200 °C, Fujimori et al tested at 280 °C, Yin et al tested at 140 °C). , Yin et al noticed that increased crystallinity began at applied stresses near 6.5 MPa, which is near the nominal contact stress (6.25 MPa) used for this study.…”

“…Specimens were then heated again to 350 °C at a rate of 10 °C/min. Percent crystallinity of the polymer was determined (eq ) by integrating the high-temperature melting peak and dividing by 82 J/g, the heat of fusion for perfectly crystalline PTFE. , …”

“…Similar reduction of this subambient transition was observed in fluorinated ethylene propylene (FEP) polymers with higher concentrations of hexafluoropropylene comonomer . Additional studies have noted similar primary melting curves for PFA, ,,− but very few authors comment on the existence and significance of the subambient transition in PFA.…”