Interrelation between long‐term viscoelasticity and viscoplastic responses of semicrystalline polymers

Abstract

Two types of linear low-density polyethylenes, prepared by metallocene catalysts were studied experimentally in terms of differential scanning calorimetry, dynamic mechanical analysis (DMA), and tensile testing. The different comonomer content and the small amounts of long branching in one of the materials studied strongly affect the crystalline distribution and morphology and, consequently, the DMA and tensile experimental data. From the experimental DMA data, the function of relaxation modulus, treated as a material property, is used to describe the corresponding tensile experimental results. A constitutive analysis that considers the viscoelastic path at small strains and the viscoplastic one at high strains proved to be capable of describing the tensile behavior of the materials.

Role of Increased Crystallinity in Deformation-Induced Structure of Segmented Thermoplastic Polyurethane Elastomers with PEO and PEO−PPO−PEO Soft Segments and HDI Hard Segments

“…The broad tan delta transition seen in PU-2-33 results from a retardation of molecular mobility by hard domains and soft segment crystallites. Its thermomechanical behavior is similar to that seen for other semicrystalline polymers . PU-3-33 possesses a small glass transition due to its highly crystalline soft domain character.…”

“…Its thermomechanical behavior is similar to that seen for other semicrystalline polymers. 27 PU-3-33 possesses a small glass transition due to its highly crystalline soft domain character. Both PEO homopolymercontaining polyurethanes display broadened tan delta transitions that point toward a retarded molecular mobility that results from interacting crystallites present within both the hard and soft domains.…”

Principles of the Morphogenesis of Polyolefin Particles

“…A number of DMA studies of polyethylene samples provide data about the dependence of viscoelastic behavior on the content of comonomer and lamellar thickness ,,− and on the thermal history of samples. , Typical relaxation times reported for the forcing frequency f = 1 Hz are between 0.3 and 1.2 s at 50 °C, cf. Table .…”

“…Copolymers and copolymer melts prepared with metallocene catalysts exhibit faster relaxation rates than those prepared by conventional Ziegler-Natta catalysts having a comparable density, average molecular weight, and branch content. 36,34 The faster relaxation of metallocene-born ethylene-butene copolymers may result from the absence of high molecular weight tails in these types of copolymers. 36 Measurements of DMA characteristics of polypropylene samples reveal similar trends as those obtained for polyethylene.…”

“…Polymer products made on two different catalysts could have almost the same density and crystallinity, but other properties could be different (e.g., the distribution of branching, the presence of the high molecular weight tail in the molecular weight distribution, the distribution of crystalline domains in the semicrystalline polymer). Different viscoelastic properties of polymers produced by the Ziegler-Natta and the metallocene catalysts 36,34 could then also explain the observed reduction of particle porosity in the case of metallocenes, cf. Figure 15.…”