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1.
对高分子量(Mν=2.8×105)的聚对二氧环己酮条状样品在37℃磷酸缓冲溶液(PBS)中的降解行为进行了研究,通过定期观察其吸水率与质量损失,pH,特性黏数,降解过程中样品形态与晶体结构,热力学性能与机械性能的改化,发现此高分子量的聚对二氧环己酮在体外降解过程中质量损失与吸水率变化不大,但分子量下降明显,同时样品表面缺陷逐渐增加;结晶度与玻璃化温度随之改变,但其晶体结构基本保持不变;到第6周时,其力学强度基本消失.证明高分子量PPDO具有较慢的降解速度,显示出很好的稳定性. 相似文献
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The effects of temperature and relative humidity on the hydrolytic degradation of poly(p-dioxanone)(PPDO) were investigated. The hydrolytic degradation behaviors were monitored by tracing the changes of water absorption, mechanical and crystalline properties, molecular weight and its distribution, surface morphologies, as well as infrared absorption peaks and hydrogen chemical shifts during the degradation. It is found that the water absorption increases whilst the intrinsic viscosity, tensile strength and elongation at break decrease as the temperature or relative humidity increases. With degradation time growing, the molecular weight drops and its distribution broadens. The crystallinity of PPDO has a tendency to increase at first and then to decrease, while the crystalline structure is not significantly changed. At the same time, some cracks are observed on the surface and keep growing and deepening. All results show that temperature plays more significant roles than relative humidity during the degradation. The analyses of Fourier transform infrared spectroscopy and hydrogen nuclear magnetic resonance spectroscopy reveal that the degradation of PPDO is a predominant hydrolysis of ester linkages. 相似文献
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Effect of constrained annealing on the mechanical properties of electrospun poly(ethylene oxide) webs containing multiwalled carbon nanotubes 下载免费PDF全文
Jiaxing Bao Laura I. Clarke Russell E. Gorga 《Journal of Polymer Science.Polymer Physics》2016,54(8):787-796
In this work, flexible nanofibrous membranes (mats) of poly(ethylene oxide) (PEO) with and without multiwall carbon nanotubes (MWNTs) were fabricated by electrospinning. The effects of annealing and MWNT concentration on mat morphology, MWNT dispersion within the nanofibers, and the mechanical properties of electrospun mats were studied. Annealing temperatures ranged from 60 °C to 64 °C [near the melting temperature (64 °C via differential scanning calorimetry)] for 4 minutes. Samples were annealed with and without applied tension (constrained and unconstrained annealing). Annealing at the highest temperature (64 °C), before the loss of fibrous morphology, significantly improved fiber–fiber bonding and therefore the tensile strength of the mats. Compared with unconstrained annealing, constrained annealing introduced fiber alignment (and therefore molecular orientation) along the tensile axis (direction of constraint) during annealing and resulted in a significant increase in modulus for all samples (with and without MWNTs). The use of constrained annealing may be a facile approach to enhance modulus in nanofibrous mats while maintaining high porosity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 787–796 相似文献
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Dar‐Jong Lin Hsu‐Hsien Chang Konstantinos Beltsios Trong‐Ming Don Yi‐Su Jeng Liao‐Ping Cheng 《Journal of Polymer Science.Polymer Physics》2009,47(19):1880-1893
Microporous PVDF membranes were prepared by immersion‐precipitation in 1‐octanol of casting dopes dissolved at different temperatures, with dissolution temperature affecting strongly the membrane microstructure. The effect of postcoagulation thermal annealing, which is an additional thermal parameter, on membrane microstructure and properties is probed herein. Membranes obtained were annealed at temperatures up to 160 °C, which is close to the melting point of PVDF polymer. Annealing leads to a substantial modification of the nano‐scale fine structure of the membranes, while the overall‐microporous structure is preserved. At elevated annealing temperatures, nano‐grains, fibrils, and stick‐like crystalline entities gradually eclipse, while globules develop more robust connections based on wide bands of crystal elements. Probing by X‐ray diffraction and dynamic scanning calorimetry shows that crystallinity increases when annealing temperature and time are increased. As regards mechanical properties, the tensile strength of the membranes can be enhanced substantially, up to about 10 times, upon appropriate high temperature prolonged annealing. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1880–1893, 2009 相似文献
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Small-angle X-ray scattering, wide-angle X-ray diffraction and differential scanning calorimetry analysis were carried out to evaluate the evolution of the supermolecular structure of poly(ethylene terephthalate) (PET) during isothermal crystallization and annealing process. PET was crystallized from the melt by isothermal treatments at 226 °C. Partially crystallized samples were prepared interrupting the crystallization by quenching, while prolonged treatments were performed to prepare annealed samples. The adopted crystallization procedures allowed to form crystals which developed during primary and secondary crystallization, and the annealing process. On the basis of X-ray data, the lamellar and amorphous phases were unambiguously attributed. The lamellar thickness and the crystallinity progressively enhance with increasing the time of thermal treatment; on the contrary, the long period decreases and this effect is mainly due to the contraction of the amorphous phase. The melting behaviour of the annealed samples indicates that the heating-induced crystal reorganization phenomena are inconsistent. The interdependency between the melting temperature and the crystal thickness allowed to extrapolate the equilibrium melting temperature. 相似文献
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Thermal decomposition of poly(1,4-dioxan-2-one) 总被引:2,自引:0,他引:2
Haruo Nishida Mitsuhiro Yamashita Norikazu Hattori Takeshi Endo Yutaka Tokiwa 《Polymer Degradation and Stability》2000,70(3):485-496
To evaluate the feasibility of poly(1,4-dioxan-2-one) (PPDO) as a feed stock recycling material, the pyrolysis kinetics of PPDO were investigated. The pyrolysis of PPDO exclusively resulted in the distillation of 1,4-dioxan-2-one (PDO). From thermogravimetric measurements conducted at different heating rates, the kinetic parameters of the pyrolysis: activation energy, Ea=127 kJ mol−1; order of reaction, n=0; and pre-exponential factor, A=2.3×109 s−1, were estimated by plural analytical methods. The estimates show that the decomposition of PPDO proceeds by unzipping depolymerization as main reaction and random degradation process with lower Ea and A values. Equivalent isothermal degradation curves calculated from the thermogravimetric curves were supported by experimental isothermal degradation data. The calculation that PPDO is converted smoothly into PDO at 270°C agrees with the reported ceiling temperature of PPDO. 相似文献
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对回收聚对苯二甲酸乙二酯(R-PET)/LLDPE-g-MA马来酸酐改性的线性低密度聚乙烯共混物进行不同条件的热处理, 采用差示扫描量热仪(DSC)研究共混物基体PET的玻璃化转变行为. 结果表明, 当热处理温度低于PET的玻璃化转变温度(Tg)时, PET的玻璃化转变区域出现热焓松弛现象. 随着热处理温度的增加, PET的Tg逐渐升高; 在50~70 ℃下热处理48 h后, PET的Tg逐渐稳定. 当热处理温度高于PET的Tg而低于100 ℃时, PET的玻璃化转变区域出现2个热流转变, FTIR分析表明, PET分子构象开始发生变化. 当热处理温度为100 ℃时, DSC曲线上PET的玻璃化转变消失, PET的结晶度明显增加, 说明PET开始冷结晶的温度在90~100 ℃之间. 相似文献
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To increase the molecular weights of the synthesized liquid crystalline aromatic/aliphatic copolyesters and to avoid crosslinking, a solution polymerization of the prepolymer and chain extender hexamethylene diisocyanate was adopted. The effects of chain extension on polyester molecular weights, thermal and mechanical properties, and biodegradable behaviors were investigated respectively. The catalysis mechanism and the copolyesters morphological textures were also investigated. The synthesized copolyesters were characterized by means of Fourier transform infrared spectra (FTIR), gel permeation chromatography (GPC), viscosity measurements, differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarizing light microscopy (PLM), scanning electron microscopy (SEM) and mechanical property measurements. It was found that inherent viscosities and the molecular weights of the copolyesters were remarkably increased under the action of catalyst, leading to a increase in the tensile strength. The degree of relative crystallinity, the melting temperature, and the rate of degradation decreased after chain extension. 相似文献
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Feng Xia Y. K. Wang Hengfeng Li Cheng Huang Y. Ma Q. M. Zhang Z.‐Y. Cheng Fred B. Bateman 《Journal of Polymer Science.Polymer Physics》2003,41(8):797-806
In this study, we investigated the influence of annealing conditions before irradiation on the ferroelectric and electromechanical properties of uniaxially stretched high‐energy‐electron‐irradiated poly(vinylidene fluoride trifluoroethylene) (HEEIP) copolymer (68/32 mol %) films. For films annealed at one fixed temperature before the irradiation (one‐step annealing), the highest crystallinity, which was highly desirable for enhancing the electromechanical response, was obtained only for films annealed between 132 and 136 °C. In addition, annealing over 10 h in this temperature window resulted in a large increase in the crystal lamellar thickness, which was required for reducing the polarization hysteresis to a minimum in the HEEIP samples. For improvements in the mechanical qualities of the uniaxially stretched films, a two‐step annealing procedure was investigated; that is, before the irradiation, the films were first annealed at a lower temperature to release the mechanical stress in the films due to the stretching and then were annealed in the high‐temperature window to raise the crystallinity and crystalline size. The experimental results indicated that this approach could produce uniaxially stretched HEEIP films with much improved mechanical qualities. Furthermore, the uniaxially stretched HEEIP films with this two‐step annealing exhibited the same electromechanical response as or an even higher one than that from the one‐step‐annealed HEEIP films. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 797–806, 2003 相似文献
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A new type poly(ether–ester) based on poly(trimethylene terephthalate) as rigid segments and poly(ethylene oxide terephthalate) as soft segments was synthesized and its aging behavior were investigated. Different from other polymer, the segmented block copolymers exhibited a unique aging mechanism. That is, the degradation of mechanical property within short term annealing was due to the overgrown crystals and dramatically increased crystallinity, which was proved by field emission scanning electron microscope (FE‐SEM) and differential scanning calorimetry (DSC), respectively. The deterioration in mechanical property after long term annealing was the results of both the increase in crystallinity and the decrease in molecular weight. Moreover, FE‐SEM showed many interesting flower‐like crystals presented on the surface of annealed sample. The flower‐like crystals consist of several radialized petal‐like arms and a more densely packed center, which has been seldom found in polymer bulk. Wide‐angle x‐ray diffraction results showed that the copolymer has the same crystal structure as PTT. Such poly(ether–ester) or its blends with other polymer could be suitable for rapid degradable products, such as package and vessel. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 411–416, 2010 相似文献
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Jong-Seok Park Hyun-A Kim Jong-Bae Choi Hui-Jeong Gwon Young-Min Shin Youn-Mook Lim Myung Seob Khil Young-Chang Nho 《Radiation Physics and Chemistry》2012,81(7):857-860
Poly(vinyl alcohol) (PVA) is an interesting material with good biocompatibility, high elasticity and hydrophilic characteristics. PVA hydrogels have been formed through chemical crosslinking with aldehyde, photopolymerization and physical crosslinking with freeze-thawing. In this study, crosslinked hydrogels based on PVA, and poly(ethylene glycol) (PEG) were prepared by gamma-ray irradiation, and then annealed at 120 °C. The properties of a hydrogel such as gel fraction, swelling behavior, gel strength as a function of PEG content and annealing time were investigated. Also, the thermal behaviors were examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The gel fraction decreases with an increase in PEG content and decrease in annealing time. The tensile strength increases with an increase in annealing time. The thermal behaviors have shown different patterns according to the annealing time. The improved properties suggest that PVA/PEG blend hydrogel can be a good candidate for applications in the articular cartilage. 相似文献
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Extraordinary transport behavior of gases in isothermally annealed poly(4‐methyl‐1‐pentene) membranes 下载免费PDF全文
Ywu‐Jang Fu Cheng‐Lee Lai Chien‐Chieh Hu Yi‐Ming Sun Shuan‐Ying Wu Jung‐Tsai Chen Shu‐Hsien Huang Wei‐Song Hung Kueir‐Rarn Lee 《Journal of Polymer Science.Polymer Physics》2016,54(22):2368-2376
Poly(4‐methyl‐1‐pentene) (PMP) membranes were modified through isothermal annealing to investigate the change of their crystalline structure and rigid and mobile amorphous fractions (RAF and MAF), assuming a three‐phase model, affected the gas transport behavior. The crystalline structure was characterized by wide‐angle X‐ray diffraction (WAXD) and small‐angle X‐ray scattering (SAXS) techniques, and the free volume properties were analyzed by positron annihilation lifetime spectroscopy. Compared with the pristine membrane, the annealed membranes show higher crystallinity; the crystals undergo partial structural change from form III to form I. The lamellar crystal thickness, rigid amorphous fraction thickness, and long period in the lamellar stacks increase with crystallinity. The annealed PMP membranes exhibit higher permeability due to the increase in larger size free volumes in MAF and higher selectivity due to the increase in smaller size free volumes in RAF, respectively. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2368–2376 相似文献
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Influence of multiple processing on selected properties of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) 下载免费PDF全文
Krzysztof Moraczewski 《先进技术聚合物》2016,27(6):733-739
The effect of multiple (up to 10 times) injection molding of processed poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P(3,4HB)) on its phase transition temperatures, degree of crystallinity, degradation temperature, mass flow rate, mechanical properties, dynamic mechanical properties, and Charpy's impact strength is presented. The studies have shown that the multiple injection lowers the degree of crystallinity and the thermal stability of P(3,4HB). The mass flow rate values increased with increasing the injection number. It was found that the multiple injections had no substantial effect on the tensile strength up to 10 injection cycles and the tensile strength at break, tensile strain at tensile strength, and tensile strain at break up to 6 injection cycles. The maximum value of storage modulus at 30 °C and impact strength were recorded for sample after 4 cycles of injection, while the values of storage modulus at 120 °C increased with increase of the injection cycles. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Peter P. Chu Jieh‐Ming Huang Hew‐Der Wu Chih‐Rong Chiang Feng‐Chih Chang 《Journal of Polymer Science.Polymer Physics》1999,37(11):1155-1163
The effects of the compatibilizer, styrene maleic anhydride (SMA‐8% MA) upon the change of morphology and molecular dynamics of polyamide‐6 (PA6) and poly (2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) blends were investigated by means of solid‐state NMR techniques. With increasing amounts of SMA, the domains correspond to PA6 and PPO are reduced and the polymer segmental mobility increased. The correlation between NMR relaxation time, T, and the bulk mechanical properties provide a molecular level understanding of the modification of molecular dynamics by the compatibilizer (SMA). The correlation shows that the tensile strength is governed mainly by the morphology, but modulated by the PA6 crystallinity, while the tensile elongation and impact strength are closely affected by both the molecular mobility and morphology. The annealing process improved only the tensile strength, but deteriorated tensile elongation and impact strength due to the increase of PA6 crystallinity, which induced phase separation after annealing. This study raised an important point that the polymer mechanical properties are most sensitive to the molecular structure and dynamics take place within the range of 20 Å to few hundred Å. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1155–1163, 1999 相似文献
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Poly[(R)-3-hydroxybutyrate] (P(3HB)) fibers with high tensile strength were prepared by stretching the fibers after isothermal crystallization near the glass transition temperature. Two samples with different molecular weights (Mw = 0.7 × 106 and 4.3 × 106) were used to investigate the effect on tensile strength. Increasing the time for isothermal crystallization of P(3HB) fibers resulted in a decrease in the maximum draw ratio. But, the tensile strength of P(3HB) fibers increased remarkably when the isothermal crystallization time was prolonged to more than 24 h. The tensile strength of low-molecular-weight drawn fibers was higher than that of high-molecular-weight fibers. Therefore, it can be concluded that this procedure does not increase the tensile strength of the high-molecular-weight drawn fibers. This is because, in this drawing method, small crystal nuclei grow initially during the isothermal crystallization process. Then, the molecular chains between the small crystal nuclei that acted as the entanglement points are oriented by stretching. In the case of the high-molecular-weight fibers, because the molecular length between the entanglement points of the small crystal nuclei is too long, the molecular chains are not sufficiently oriented by the stretching process. However, in the case of the low-molecular-weight fibers, the molecular length is suitable for generating the extended chains. Based on the result of X-ray analysis of P(3HB) fibers stretched after isothermal crystallization, fibers have the oriented α-form crystal with 21 helix conformation and β-form with planar zigzag conformation. The enzymatic degradation of the stretched P(3HB) fibers was performed by using an extracellular PHB depolymerase purified from Ralstonia pickettii T1. The enzymatic erosion rate of β-form was faster than that of α-form in the P(3HB) fibers stretched after isothermal crystallization. 相似文献
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C. Vanderdonckt M. Krumova F. J. Baltá Calleja H. G. Zachmann S. Fakirov 《Colloid and polymer science》1998,276(2):138-143
Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190–260 °C) for different times (10 min–24 h)
in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10 000–120 000).
Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times
give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, H
PET
c=405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30 000. It is shown that
the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase
of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity,
crystal thickness) which is formed at given heat treatment conditions.
Received: 29 April 1997 Accepted: 23 September 1997 相似文献