Effects of strain rate and temperature upon tensile properties of acetal copolymers (original) (raw)
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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.
The influence of a tensile drawing on the crystalline organisation of ethylene-vinyl acetate copolymers (EVA) of different molecular weights has been investigated by differential scanning calorimetry (d.s.c.). The consequence of the crystalline organization changes on the mobility of the amorphous phase has been also investigated, through the study of the glass transition. The results show that more disorganized crystals appear after the tensile test, specially for the higher molecular weight. These more disorganized crystals constitute physical ties reducing the mobility of the amorphous chains which link them, as shown by the significant increase of the glass transition temperature of these high molecular weight EVA after tensile drawing.
Mechanical properties and dynamic mechanical relaxations of ethylene/alpha‐olefin copolymers
British Polymer Journal
The tensile drawing behaviour and the viscoelastic relaxations of three different copolymers of ethylene, containing I-butene, 1-hexene and 4-methyl-lpentene as comonomer, have been studied. The composition of the copolymers is increasingly poorer in comonomer following the above order. However, they show similar mechanical properties, both large-strain and small-strain dynamic mechanical, because the minor differences which have been found can generally be explained by the thermal and mechanical histories of the samples. Thus, it seems that the higher disrupting effect produced in the copolymer structure by the comonomers of greater size and volume is counterbalanced by the corresponding smaller concentration, and that only thermal treatment produces appreciable differences in properties.
Viscosity and creep compliance of polyoxymethylene copolymers of various average molecular weights
Polimery, 2015
The effect of average molecular weight (M w ) of polyoxymethylene (POM) on melt viscosity and solid state creep compliance were investigated. Viscosity follows the power function of M w . Creep compliance results indicate that time-temperature superposition applies to POM copolymers. Creep compliance in a short time (0.25 s) is independent of M w , but in a longer time (10 years) it follows an inverse power law relation with M w , up to a critical value of M w = 81 100, where creep compliance becomes independent of M w . At intermediate time , similar to short one, no effect on susceptibility to creep compliance was observed. It was also stated that the activation energy is independent of M w .
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.
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.
Creep rupture properties of homopolymer, copolymer, and terpolymer based on poly(oxymethylene)
Journal of Applied Polymer Science, 2010
Polyacetal copolymers were prepared by cationic ring-opening copolymerizations of 1,3,5-trioxane (TOX) with 1,3-dioxolane (DOX), and polyacetal terpolymers were prepared by terpolymerizations of TOX, DOX, and 2-ethylhexyl glycidyl ether (EHGE). Polyacetal polymers with three different structures such as polyacetal homopolymers, polyacetal copolymers, and polyacetal terpolymers were compared in the mechanical properties and the creep characteristics, and discussed from the view point of the polymer structure. The polyacetal copolymers and the polyacetal terpolymers were determined by 1 H-MNR measurement. About 80 mol % of DOX and EHGE amounts in feed were incorporated randomly into the each polymer. From the plots of the degree of crystallinity (X c) versus the tensile strength, the tensile strength and crystallintiy of the polyacetal homopoymers are higher than those of the polyacetal copolymers and the polyacetal terpolymers. However, the tensile strength does not decrease linearly with a decrease in the crystallinity among the polyacetal polymers with three different structures, the polyacetal homopolymer, the polyacetal copolymers, and the polyacetal terpolymers. Creep rupture was characterized by the activation volume, t c , value in Zhurkov's equation, which can be estimated from the slope in the plots of load versus log (rupture time) at 80 C. The polyacetal polymers with higher molecular weight have larger values of the activation volume than those with lower molecular weight. When the activation volume values are compared among the polyacetal polymers with the same molecular weights, they increase in the following order: the polyacetal homopolymers < the polyacetal copolymers < polyacetal terpolymers. V
Journal of Polymer Science Part B: Polymer Physics, 1998
The linear viscoelastic behavior of a poly(paraphenylene) with a benzoyl substituent has been examined using tensile, dynamic mechanical, and creep experiments. This amorphous polymer was shown to have a tensile modulus of 1-1.5 Msi, nearly twice that of most common engineering thermoplastics. The relaxation behavior, which is similar to that of common thermoplastics, can be described by the WLF equation. Outstanding creep resistance was observed at low temperatures, with rubbery-like behavior being exhibited as the temperature approached T g . Physical aging was shown to interact with long-term creep, rendering time-temperature superposition invalid for predicting the long-term properties. The effect of physical aging on the creep behavior was characterized by the shift rate .