Mechanical properties and dynamic mechanical relaxations of ethylene/alpha‐olefin copolymers (original) (raw)
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Journal of Materials Science, 1990
The tensile drawing behaviour and the dynamic mechanical properties of four ethylene-1butene copolymers, with nearly the same comonomer content but obtained with slightly different catalyst systems, have been analysed. It was found that the large strain mechanical properties and the strain-hardening behaviour seem to be affected by the degree of homogeneity in the distribution of comonomer along the different chains, reflecting the differences in the catalyst systems used. However, a parallel trend was not so clear for the small-strain dynamic mechanical properties for a particular thermal history, although the dependence of the relaxations on the crystallization conditions is evident.
Journal of Applied Polymer Science, 1999
The influences of the type and concentration of ␣-olefin (1-hexene, 1-octene, 1-decene, 1-octadecene, 4-methyl-1-pentene) on the mechanical behavior and crystallinity degree of some ethylene/␣-olefin copolymers obtained by metallocene catalysts were studied by means of stress/strain experiments. The crystallinity degree of these copolymers has been determined by X-ray measurements. It has been observed that the copolymers show less resistance to strain as the comonomer content increases and the crystallinity decreases. Most of the studied copolymers exhibit a significant increase in the crystallinity level after the stress/strain experiments.
Dynamic mechanical properties of homogeneous copolymers of ethylene and 1-alkenes
Journal of Polymer Science Part B: Polymer Physics, 1987
The dynamic mechanical properties of homogeneous copolymers of ethylene with 1-butene, 1-odene, and 1-octadecene prepared by means of a vanadium-based catalyst system have been dete&ed. The 1-butene copolymers show a ' and a transitions in the 20-60OC temperature range, whereas the 1-odene and 1-octadecene copolymers show single a transitions. The intensity of the B transition increases with comonomer content in 1-butene and 1-octene copolymers and also with the amount of interfacial material present. In ethylene-1-octadecene copolymers, this intensity is comparatively low, even though there is about 20% interfacial material present. The implications of these results with regard to the nature of interfacial material are discussed.
Polymer, 2000
Viscoelastic relaxations of three samples of vinyl alcohol-ethylene copolymers, richer in the former comonomer, were studied in a wide range of temperature. The temperature location, intensity and apparent activation energy of the distinct relaxations found are discussed and compared with those of the homopolymers, poly(vinyl alcohol) and polyethylene. Differential scanning calorimetry and X-ray diffraction results of the specimens are also discussed in the frame of the dynamic mechanical analysis, showing that the polymorphism exhibited in some copolymers is a result of the thermal treatment. ᭧
Polymer, 2001
The in¯uence of the tensile drawing on the structure and dynamic mechanical relaxations of vinyl alcohol±ethylene (VAE) copolymers with higher content in the former counit is studied. The structure of VAE copolymers is considerably modi®ed by drawing, which produces a disordered crystalline form, as revealed by WAXD and DSC measurements. The structural changes have signi®cant effects on the viscoelastic relaxations of the stretched samples. A remarkable increase in the storage modulus is observed in the direction parallel to the draw direction in detriment to those found in specimens cut transverse and diagonally to the draw direction. The drawn copolymers show an additional a H relaxation, attributed to motions within the crystalline regions, taking place at temperatures higher than that of the a relaxation (glass transition). A clear anisotropy tan d 45 . tan d 0 < tan d 90 is exhibited in this a H relaxation similar to that observed in oriented LDPE where the chain axes are aligned in the draw direction while the lamellae are inclined at 458 to the draw direction, and the pattern of anisotropy thus suggests chain shear as a mechanism for the loss process. The a H process in the VAE copolymers is thus assigned to chain shear while the a and b processes are assigned to interlamellar shear. q
Tensile Properties of Crystalline Polymers: Random Copolymers of Ethylene
Macromolecules, 1995
Force-elongation curves of a set of random ethylene-l-alkene copolymers have been studied. The comonomers included l-butene, l-hexene, l-octene, and 4-methyl-l-pentene. The copolymers all had the most probable molecular weight and narrow composition distributions. A set of hydrogenated polfibutadienes), random ethyl-branched copolymers, that have very narrow molecular weight and composition distributions were also studied as reference. Only ductile type deformations were studied.
Mechanical Properties and Elastic Behavior of Syndiotactic Propene− Butene Copolymers
2009
The mechanical properties of copolymers of syndiotactic polypropylene (sPP) with 1-hexene and 1-octene have been studied and correlated with the structural transformations occurring during stretching and relaxation. These copolymers crystallize in disordered modifications of form I of sPP, with crystallinity, melting, and glass-transition temperatures that decrease with increasing comonomer content. All copolymers show remarkable mechanical properties and elastic behavior, with great improvement of flexibility and ductility with respect to the sPP homopolymer already at small comonomer concentrations. For low comonomer content up to 4−5 mol %, the elastic recovery is associated to a reversible conformational phase transition between the trans-planar form III or the trans-planar mesophase and the helical form II, which gives an enthalpic contribution to the elasticity. As the comonomer content increases, the trans-planar conformation is progressively destabilized and the observed elastic properties are not associated with any conformational transformation during stretching and relaxation. In these cases, copolymers behave as conventional thermoplastic elastomers where elasticity is purely entropic and crystals only act as topological constraints of the elastomeric network. These copolymers represent an exemplary case of the possibility to combine in the same materials desired and apparently incompatible physical properties of elasticity, crystallinity, and strength by controlling the crystallization behavior, achieved by tailoring the chemical structure in the synthetic process.
Polymer, 2004
Some structural details and the viscoelastic and mechanical response of blends of a vinyl alcohol-ethylene (VAE), and a metallocenic ethylene-1-octene copolymer (CEO), have been analyzed. Both copolymers exhibit crystalline lattices whose diffraction peaks and long spacings appear at very similar spacing intervals. More information about the crystalline region is obtained from differential scanning calorimetry (DSC) measurements due to the difference in melting temperatures found for each of them. In addition, DSC results point out an inhibition of the VAE crystallization with CEO presence that is cooling-rate dependent. A decrease of rigidity and yield stress is observed as CEO content increases in the blends. However, the changes found in the mechanical parameters are not as significant as the variation in oxygen permeability. This feature seems to be due to the disruption of intra and intermolecular hydrogen interactions. q
Dynamic mechanical study of molecular dynamics in ethylene–norbornene copolymers
Polymer, 2010
Dynamic mechanical studies of molecular dynamics have been performed for two ethylene-norbornene copolymers. The analysis of data indicates the existence of three relaxation processes: a primary (a) and two secondary (b and g) ones. It was found that the secondary processes b and g are connected with the local motions of ethylene and norbornene groups, respectively and that their rates follow the Arrhenius relation. Moreover, the b process was recognized as the Johari-Goldstein process acting as the precursor of the cooperative structural a-relaxation. Contrary to g and b processes, the motional rate of a-one follows the Vogel-Fulcher-Tammann equation indicating the cooperative nature of motions involved in this process. An increase in norbornene content in copolymer slows down the molecular dynamics of both norbornene fragments and whole chains, and in consequence shifts these relaxation processes into higher temperatures. Using the Havriliak-Negami formalism the motional parameters for the processes mentioned above were estimated.