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应力场下聚丙烯熔体的结晶与硬弹性的形成 总被引:8,自引:0,他引:8
应力场下聚丙烯熔体的结晶与硬弹性的形成胡继文*孙友德许耀光岑美柱(中国科学院广州化学研究所广州510650)关键词聚丙烯,硬弹性,应力导致结晶1996-12-20收稿,1997-05-20修回研究表明,具有硬弹性的聚合物形态的获得最关键的因素是熔纺时... 相似文献
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本文综述了关于拉伸结晶聚合物形变机理的研究工作,重点介绍了拉伸聚合物在形成细颈过程中,从原来的球晶(或堆积片晶)结构向纤维结构的转化过程,以及有关这一形变过程。目前存在的不同观点及各方面的实验证据。指出拉伸结晶聚合物的形变机理可能依赖于拉伸条件。 相似文献
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硬弹性聚丙烯晶相和非晶相分子链取向的研究 总被引:2,自引:0,他引:2
本文用力学-振动光谱研究了硬弹性聚丙烯(HEPP)晶区和非晶区分子链在拉伸时取向的变化.我们发现在红外光谱中,1130—1190cm~(-1)波数范围内存在着三个峰,其中1167cm~(-1)处的峰是与结晶相长螺旋分子链相关的构象谱带,其谱带的强弱变化是与998cm~(-1)结晶谱带在拉伸时的变化趋势一致的.1159cm~(-1)谱带能够被归属于无定形谱带.而1152cm~(-1)处的峰也许是与短螺旋分子链构象谱带相关的.我们用计算机的二次微分、解卷积以及分峰程序测定了拉伸时HEPP晶区和非晶区分子链的取向函数,结果发现HEPP无定形分子链取向随拉伸比增加而增加,而晶区分子链的取向随拉伸比的增加先下降,直至拉伸比为1.5(第二次屈服点)后才逐渐增加. 相似文献
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随着纳米材料研究的迅速发展,聚合物由于其分子固有的纳米尺度结构,无论作为纳米器件或在模板应用方面都受到广泛瞩目.在微纳领域的应用中,特定受限环境下,结晶聚合物的结晶行为也因此受到广泛关注.本文从均聚物(及无规共聚物)和半晶型嵌段聚合物两方面总结了近年来聚合物受限结晶领域的研究进展.对于均聚物和无规共聚物,人们主要关注其在薄膜、超薄膜条件下的受限结晶性能,关注点为随着膜厚减小而引入的空间效应和界面效应对聚合物结晶性能的影响.而对于半晶型嵌段共聚物受限结晶的研究则多从本体出发,来研究纳米相分离与结晶的竞争过程、纳米相分离区域对于可结晶嵌段结晶生长的几何限制(空间效应)以及嵌段连接点(结晶嵌段的末端)对于结晶嵌段结晶行为的影响. 相似文献
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Crystal Adaptronics: Mechanically Reconfigurable Elastic and Superelastic Molecular Crystals
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Dr. Ejaz Ahmed Dr. Durga Prasad Karothu Prof. Dr. Panče Naumov 《Angewandte Chemie (International ed. in English)》2018,57(29):8837-8846
Mechanically reconfigurable molecular crystals—ordered materials that can adapt to variable operating and environmental conditions by deformation, whereby they attain motility or perform work—are quickly shaping a new research direction in materials science, crystal adaptronics. Properties such as elasticity, superelasticity, and ferroelasticity, which are normally related to inorganic materials, and phenomena such as shape‐memory and self‐healing effects, which are well‐established for soft materials, are increasingly being reported for molecular crystals, yet their mechanism, quantification, and relation to the crystal structure of organic crystals are not immediately apparent. This Minireview provides a condensed topical overview of elastic, superelastic, and ferroelastic molecular crystals, new classes of materials that bridge the gap between soft matter and inorganic materials. The occurrence and detection of these unconventional properties, and the underlying structural features of the related molecular materials are discussed and highlighted with selected prominent recent examples. 相似文献
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Dr. Soumyajit Ghosh Manish Kumar Mishra Sourabh B. Kadambi Prof. Upadrasta Ramamurty Prof. Gautam R. Desiraju 《Angewandte Chemie (International ed. in English)》2015,54(9):2674-2678
The intermolecular interactions and structural features in crystals of seven halogenated N‐benzylideneanilines (Schiff bases), all of which exhibit remarkable flexibility, were examined to identify the common packing features that are the raison d’être for the observed elasticity. The following two features, in part related, were identified as essential to obtain elastic organic crystals: 1) A multitude of weak and dispersive interactions, including halogen bonds, which may act as structural buffers for deformation through easy rupture and reformation during bending; and 2) corrugated packing patterns that would get interlocked and, in the process, prevent long‐range sliding of molecular planes. 相似文献
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The growing interest in the natural zeolite is based on some specific peculiarities of its structure, which after dehydration enables adsorption processes of some polymer molecules and/or segments to take place on the zeolite surface. The main goal of the study is to investigate the effect of dehydrated zeolite on the flow behavior, mechanical properties and morphology of immiscible blends from unsorted polymer wastes. A tetra-component blend consisting of 40 wt.% polypropylene (PP), 40 wt.% high-density polyethylene (HDPE), 15 wt.% low-density polyethylene (LDPE) and 5 wt.% polystyrene (PS), was studied as a model system of commingled plastic wastes. Compositions from recycled blend and dehydrated zeolite in a wide concentration range (from 0 to 20 wt.%) were prepared using a twin-screw extruder Brabender DSE 35/17D in the temperature range from 140 to 190 °C. The compositions were characterized by capillary rheometry, differential scanning calorimetry (DSC), site-resolved wide-angle X-ray scattering (WAXS) and mechanical tests. The results show a compatibilizing effect of dehydrated zeolite at low concentration levels (1-2 wt.%) and open wide possibilities for utilization of dehydrated zeolite in the recycling of unsorted polymer wastes. 相似文献
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M. M. Abolhasani A. Arefazar M. Mozdianfard 《Journal of Polymer Science.Polymer Physics》2010,48(3):251-259
Immiscible ternary blends of PET/EVA/PP (PET as the matrix and (PP/EVA) composition ratio = 1/1) were prepared by melt mixing. Scanning electron microscope results showed core‐shell type morphology for this ternary blend. Binary blends of PET/PP and PET/EVA were also prepared as control samples. Two grades of EVA with various viscosities, one higher and the other one lower than that of PP, were used to investigate the effect of components' viscosity on the droplet size of disperse phase. The effect of interfacial tension, elasticity, and viscosity on the disperse phase size of both binary and ternary blends was investigated. Variation of tensile modulus of both binary and ternary blends with dispersed phase content was also studied. Experimental results obtained for modulus of PET/EVA binary blends, showed no significant deviations from Takayanagi model, where considerable deviations were observed for PET/PP binary blends. Here, this model that has been originally proposed for binary blends was improved to become applicable for the prediction of the tensile modulus of ternary blends. The new modified model showed good agreement with the experimental data obtained in this study. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 251–259, 2010 相似文献
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Piotr Dacko Marek Kowalczuk Henryk Janeczek Michal Sobota 《Macromolecular Symposia》2006,239(1):209-216
The thermal, mechanical and thermo-mechanical properties of polymer compositions, containing synthetic biodegradable polymers i.e. polylacide (PLA) and aliphatic-aromatic copolyester (BTA), natural biopolyester n-PHB and its synthetic atactic analog (a-PHB) were investigated. Thermal properties of the polymer compositions were studied by means of DSC . The compositions of various polymer weight ratio were tested. Compositions containing BTA and n-PHB create polyphase systems, what was confirmed by DSC. In this case the two Tg and two Tm values were observed. Polymer compositions containing PLA and BTA showed different behaviours. At the BTA content up to 30 weight % only one Tg and one Tm were indicated. At the increase of the BTA content to 50% weight and above, the two Tg, and two Tm were observed. Mixtures of BTA with n-PHB, PLA and with a-PHB show considerably greater values of the strain (ε) in comparison with initial polymers (n-PHB, PLA). It was found that in contrary to mixtures containing PLA, at the BTA content in the mixture with n-PHB above 50% of weights increases not only the strain, but also the stress at break (σ). Strong increase of the ε value in PLA/a-PHB mixtures with the content of a-PHB above 30% of weights were observed. 相似文献
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We have used self-consistent field theory to calculate the tensile moduli of triblock copolymers in lamellar microstructures prepared from linear and star architectures. The extensional moduli K(33) are the main contributors to the tensile moduli, and the contribution of K(U)33 (the internal energy contribution to K(33)) is the main component of the value of K(33). We find that the tensile moduli of ABC three-miktoarm star terpolymers are smaller than those of ABC linear triblock copolymers having identical components, presumably for two main reasons. First, for the ABC three-miktoarm star terpolymers, the contributions of K(U)33 are larger than those of the linear triblock copolymers; we attribute this phenomenon to the star terpolymers having smaller lamellar domain sizes at equilibrium relative to those of the linear triblock copolymers. Second, conformational entropies play an important role in affecting the tensile moduli, mainly because of the different degrees of freedom of the various chains. In contrast, the shear moduli contribute negligibly to the tensile moduli. 相似文献
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The crystallization, special interaction, rheological behavior, and mechanical properties of PVC/ferrocene blends were studied through WAXD, FTIR, XPS, capillary rheometry, and mechanical property tests. The experimental results showed that the tensile strength of PVC/ferrocene (100/10) amounts to 82 MPa, 1.3 times as high as that of PVC. In the presence of a small amount of ferrocene, the processability of PVC is also improved. Crystallization of ferrocene in the blend is inhibited. The FTIR characteristic peaks of ferrocene shift or disappear. A new peak appears in the C1s XPS spectra and the Cl (2p) XPS spectra of PVC/ferrocene blends, and most of the ferrocene in the blends cannot be extracted by solvent alcohol, indicating the existence of some intermolecular interactions between PVC and ferrocene which cause the mechanical strength of the blends to increase. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2828–2834, 1999 相似文献
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An adaptation of the fracture toughness test method, the J-integral technique, is described within the general framework of polymer fracture behavior. It is shown that there is a strong interaction between different morphological parameters in the way they affect the fracture behavior of isotactic polypropylene (iPP). The fracture toughness decreases with increasing crystallinity at a fixed spherulite size. The fracture toughness also decreases slightly with increasing spherulite size at a constant crystallinity, but this may not be a pure spherulite size effect. The use of a nucleating agent results in a very fine spherulitic structure but facilitates crack growth and reduces the material toughness beyond the crack initiation stage. This suggests that the material behavior is dictated by the increase in crystallization temperature caused by the presence of the nucleating agent and not by the change in spherulite size. © 1995 John Wiley & Sons, Inc. 相似文献