Effects of initial morphology and molecular weight on the deformability of poly(ethylene terephthalate)

Abstract

Solution‐grown crystal (SGC) mats and solution‐cast (SC) films of poly(ethylene terephthalate) (PET) were drawn by solid‐state coextrusion followed by tensile drawing of the coextrudates. Drawabilities and properties of the drawn films, such as mechanical and thermal properties, were investigated as functions of molecular weight, initial morphology, and drawing conditions. The initial morphology and molecular weight have a marked effect on the drawability and tensile properties of the resultant drawn films. The attainable maximum draw ratio increases with increasing molecular weight, and the highest draw ratio of 11.5 can be achieved by two‐stage drawing of SC films prepared from pellets with an intrinsic viscosity of 1.43 dl/g. Such highly drawn films exhibit a tensile modulus of 17.5 GPa and strength at break of 400 MPa. These values are comparable to those obtained in conventional spinning of standard grade PET. At a given draw ratio, the tensile strength of the drawn films increases with increasing molecular weight, but the molecular weight dependence is not so marked in the tensile modulus as in the tensile strength. At a given molecular weight, the drawability of SGC mats is lower than that for SC films; however, the efficiency of drawing is higher for the former than for the latter. The difference may arise from the difference in crystallinity and/or crystal perfection of predrawn samples.

Diffusion versus Cocrystallization of Very Long Polymer Chains at Interfaces: Experimental Study of Sintering of UHMWPE Nascent Powder

“…It is well-known that the strain at break of cross-linked polymer networks in the rubbery state is directly connected to the entanglement density through the relation λ max ∝ N e 1/2 , where N e is the chain length between entanglements (including cross-links) given in number of random links. This was shown to fairly apply to the elongation at break of various semicrystalline polymer networks including UHMWPE. − In the present study, it is likely that for sintering at 150 °C, healing by interface re-entanglement would not be completed at 150 °C. As a consequence the crystalline network could hide any difference until fracture, but near the fracture the material is expected to be more sensitive to the possible weakness of the entanglement network.…”

Synthesis of 2,2′‐Bipyridines: Versatile Building Blocks for Sexy Architectures and Functional Nanomaterials

“… where ϕ holds for the polymer concentration in the solution prior to crystallization. Similar behavior has been reported for poly(propylene),65 poly(ethylene terephthalate),66 poly(4‐methylpent‐1‐ene),67 and nylon 6 68. On the one hand, such experiments give evidence that only the entangled network resists drawing when the molecular mobility in the crystalline phase is high enough.…”

“…Modeling of necking dynamics was attempted by the introduction of the strain‐hardening and strain‐rate dependences in the material constitutive law 58, 74. Neck profiles of HDPE and iPP were fairly well predicted by finite element calculations, including the temperature sensitivity 66, 78–81. No structural factors have yet been proposed by the authors to account for the observed effects, as well as no physical explanation for the natural draw ratio.…”

Solid‐state polymerization of melt‐spun poly(ethylene terephthalate) fibers and their tensile properties

“…We report the effects of initial morphology on the deformation behavior and the structure of the resultant drawn films. 13,14 For the drawn samples from initially amorphous state, the crystallinity increases with increasing the DR due to the strain-induced crystallization. However, the crystallinity from initially highly crystalline material decreases with DR. During the drawing, the crystals existed in the predrawn material are destroyed, and simultaneously strain-induced crystallization happens but the degree of crystallization is not high enough to reach the original crystallinity.…”