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1.
On the plastic deformation of bulk syndiotactic polypropylene 总被引:1,自引:0,他引:1
The plastic deformation of syndiotactic polypropylene (sPP) bulk samples has been investigated. A structural comparison of
the initial states before and after plastic deformation by necking is carried out by X-ray diffraction observations. Independent
of the initial states (amorphous, semi-crystalline with different crystal phases), only the planar all-trans crystal form of sPP is present in the deformed samples after necking. Form these results, molecular mechanisms of the plastic
deformation in the neck zone of semi-crystalline polymers will be discussed.
Received: 11 February 1997 Accepted: 15 August 1997 相似文献
2.
Hong Zheng Wei Yu Hon-bin Zhang Chi-xing Zhou 《高分子科学》2006,(1):1-11
Finite element method is used to simulate the high-speed melt spinning process,based on the equation system proposed by Doufas et al.Calculation predicts a neck-like deformation,as well as the related profiles of velocity,diameter, temperature,chain orientation,and crystallinity in the fiber spinning process.Considering combined effects on the process such as flow-induced crystallization,viscoelasticity,filament cooling,air drag,inertia,surface tension and gravity,the simulated material flow behaviors are consistent with those observed for semi-crystalline polymers under various spinning conditions.The structure change of polymer coils in the necking region described by the evolution of conformation tensor is also investigated.Based on the relaxation mechanism of macromolecules in flow field different types of morphology change of polymer chains before and in the neck are proposed,giving a complete prospect of structure evolution and crystallization of semi-crystalline polymer in the high speed fiber spinning process. 相似文献
3.
The aim of this study was to find a satisfactory method to characterize the fatigue crack growth behavior of non-reinforced, semi-crystalline thermoplastic polymers using linear elastic fracture mechanics (LEFM). For this, crack growth curves (crack length versus cycle number) as well as crack growth kinetics curves (crack growth rate da/dN versus amplitude stress intensity factor ΔK) had to be generated. As methods suggested by ISO 15850 and ASTM E 647-11 failed to provide satisfactory results for the crack growth curves, a more advanced method was searched for and finally found in the literature. Regarding the crack growth kinetics curve, the idea of the calculation was based on methods recommended in ISO 15850 and ASTM E 647-11. However, these methods had to be considerably modified and improved in order to get accurate results with little scatter. The whole methodology was developed and verified with fatigue crack growth tests on two semi-crystalline thermoplastics (polyoxymethylene POM and polyetheretherketone PEEK). 相似文献
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5.
Behaviour of a semi-crystalline polymer, polyamide 6, described by loading curves, as well as necking and whitening phenomena, is related to its micro-structural evolution in terms of void morphology and distribution during both tensile and creep tests. Notched bars have been subjected to creep tests interrupted at the onset of the tertiary creep stage and at the onset of final rupture. Inspections of these specimens using Synchrotron Radiation Tomography have been coupled with statistical image analysis treatment to obtain spatial distributions of void length and void volume fraction. Cavitation mechanisms observed and quantified during creep and tensile tests were similar: from penny shaped voids (diameter larger than height) perpendicular to the drawing direction to cylindrical voids (diameter equal to the height) arranged in columns during the neck extension. The void volume fraction distributions along radial and axial directions presented an inverted parabolic profile with a maximum located at the centre of the sample. 相似文献
6.
Ricardo Picciochi Yaming Wang Natália M. Alves João F. Mano 《Colloid and polymer science》2007,285(5):575-580
Poly(l-lactic acid) was crystallized from the glassy state at different temperatures to produce fully transformed semi-crystalline
specimens exhibiting different lamellar morphologies. The materials were tested by dynamic mechanical analysis, where a T
g decrease was found with an increasing crystallization temperature. Considering a three-phase model, this tendency was related
to the corresponding increase in the thickness of the rigid amorphous phase. It is suggested that this phase could, in some
extent, accommodate through local translational/rotational motions the cooperative motions taking place within the mobile
amorphous phase. This could be due to the non-compact structure of the cooperatively rearranging regions, which can present
a string-like or fractal structure in their edges. The width of the loss factor peak associated to the glass transition increases
with increasing crystallization temperature, suggesting an increase in the broadness of the distribution of relaxation times.
The drop in the storage modulus across T
g varies systematically with the crystallization temperature in the different materials and could be correlated with the crystalline
content. Above T
g, the loss factor exhibits a plateau-like behaviour at significantly high values, which seems to be a rather general behaviour
in semi-crystalline systems that could be related to the contribution of pure irreversible flow in the overall viscoelastic
behaviour. 相似文献
7.
Musa Kamaci 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):805-819
In this paper, three new low band gap Schiff bases were prepared by using 3-etoxy-4-hydroxybenzaldehyde and different o-phylene diamines. Then, these Schiff bases were converted to low band gap polyurethane derivatives, and their photophysical, electrochemical, thermal, mechanical and morphological properties were investigated. Photophysical properties of the compounds were investigated by using UV-Vis and photoluminescence (PL) spectroscopy. Electrochemical properties of Schiff bases and polyurethanes containing azomethine were investigated by using cyclic voltammetry (CV). Thermal decomposition and transitions were determined by using TG-DTA, DMA and DSC techniques, respectively. Morphological properties of the compounds were also determined by using scanning electron microscopy (SEM). SEM images showed that polyurethanes containing azomethine consist of semi-crystalline particles. 相似文献
8.
Fabien Dutertre Pierre-Yves Pennarun Olivier Colombani Erwan Nicol 《European Polymer Journal》2011,(3):343-351
Lauryl (LA) and stearyl (SA) acrylates were successfully polymerized by atom transfer radical polymerization (ATRP), leading to well defined homopolymers and diblock copolymers (PDI < 1.2). Interestingly, the polymerization was very well controlled using N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), a ligand which had initially been reported to be unadvisable for the polymerization of such monomers. Both kinetic studies and chain extension reactions supported our conclusions. A PLA65-b-PSA47 diblock copolymer was characterized by differential scanning calorimetry and dynamic thermo-mechanical analysis, revealing that both blocks exhibit side-chain crystallinity and phase segregate in the crystalline state. The diblock behaves as a brittle rigid polymer when both blocks are crystalline, as a ductile material after the melting of the PLA phase and becomes a viscous liquid when both blocks are molten. This work could be extended to the preparation of PSA-b-PLA-b-PSA bio-issued thermoplastic elastomers. 相似文献
9.
Y. Men G. Strobl Fakultaet fuer Physik Albert-Ludwigs-Universitaet Freiburg Germany 《高分子科学》2002,(2):161-170
The mechanism of tensile deformation in semi-crystalline polymers was studied based on true stress-strain curvesobtained with the aid of a video-controlled tensile set-up. The deformation is affected by both the crystalline and theamorphous phases. However, the relative weights of the two portions change with the deformation stage. At lowdeformations the coupling and coarse slips of the crystalline blocks dominate the mechanical properties, which allows thesystem to maintain a homogeneous strain distribution in the sample. As the stretching increases, at a critical strain the forcegenerated from entangled fluid portions reaches a critical value to destroy the crystallites. The dominant deformationmechanism then changes into a disaggregation - recrystallization process. 相似文献
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