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1.
    
Five ethylene‐propylene random copolymers were nucleated with two soluble nucleating agents. Ethylene content changed between 1.7 and 5.3 wt %, while nucleating agent content was adjusted according to the solubility of the additive. It changed from 0 to 5000 ppm for the sorbitol (1,2,3‐tridesoxy‐4,6:5,7‐bis‐O‐[(4‐propylphenyl) methylene]‐nonitol) and from 0 to 500 ppm for the trisamide compound (1,3,5‐benzene‐trisamide) used. Crystalline structure was analyzed in detail by various methods (DSC, XRD, and SEM). Mechanical properties were characterized by tensile and instrumented impact measurements. The results showed that most properties changed moderately upon nucleation, but impact resistance increased considerably. Spherulitic structure was not detected, but instead in the presence of the soluble nucleating agents used a microcrystalline structure formed. The large increase of impact resistance could not be related directly to changes in crystalline morphology. On the other hand, local rearrangement of morphology was detected by XRD and SEM analysis including an increase of lamella thickness, crystal orientation, and the formation of shish‐kebab structures in the core of the injection molded specimens. A small increase in the γ‐phase content of PP was also observed. These changes increased crack propagation energy considerably leading to the large improvement observed in impact resistance. Although the phenomenon could be related to ethylene content, differences in molecular weight also helped to explain the changes observed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43823.  相似文献   

2.
    
Poly(L ‐lactide‐co‐ε‐caprolactone) [P(LLA‐CL)], which is used in biodegradable biomedical materials such as drug‐delivery systems, surgical sutures, orthopedics, and scaffolds for tissue engineering, has been reported to crystallize upon storage in a dry state even at room temperature; this results in rapid changes in the mechanical properties. In biomedical applications, P(LLA‐CL) is used in the presence of water. This study investigated the effects of water on the crystallization of P(LLA‐CL) at 37°C in phosphate buffered solution, which was anticipated to alter its mechanical properties and hydrolytic degradation behavior. Surprisingly, the crystallinity of P(LLA‐CL) in the presence of water rapidly increased in 6–12 h and then slowly increased up to 120 h. The period of time for the initial rapid crystallization increase in the presence of water was much shorter than that in the absence of water. The obtained information would be useful for the selection, preparation, and use of P(LLA‐CL) in various biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

3.
    
Organo‐modified montmorillonites and poly(p‐dioxanone) (PPDO) diol prepolymers were used to prepare Poly(p‐dioxanone)‐PU/organic montmorillonite (PPDO‐PU/OMMT) nanocomposites by chain‐extending reaction. The crystallization behavior and spherulitic morphology of PPDO‐PU/OMMT nanocomposites were investigated by WXRD, differential scanning calorimetry, and polarized optical microscopy. The results show that the regularity of the chain structure plays a dominant role during the crystallization process rather than that of OMMT content and its dispersion status in PPDO matrix. With similar molecular weight and same OMMT content, PPDO‐PU/OMMT nanocomposite, which derived from lower molecular weight PPDO prepolymer, exhibits lower crystallization rate, melting point, and crystallinity. The influence of the clay content on the crystallization behavior highly depends on its dispersing state. The nucleating effect of OMMT can be only observed at high loading percentage. For the nanocomposites with low clay loading percentage, the retarding effect of exfoliated platelets on the chain‐ordering into crystal lamellae became the key factor. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

4.
DSC and time‐resolved WAXS and SAXS are used to study the structure development during isothermal crystallization of poly(glycolic acid) (PGA) in the temperature range 180–195°C. It is shown that the crystallization rate increases with degree of supercooling in the temperature range of consideration. WAXS and DSC crystallinity measurements agree well and a final crystallinity of 50% is found independently of the crystallization temperature. In‐situ SAXS measurements indicate that for PGA the final crystal thickness approaches a limiting value of 70 Å independent of the crystallization temperature in the range 195–180°C. The material develops a well‐defined lamellar structure during crystallization at the highest crystallization temperature under study (195°C). We show that by increasing the degree of supercooling it is possible to hinder the formation of the lamellar structure and crystals, resulting in a less ordered structure. We report that PGA fibers with elastic modulus in the range 20–25 GPa can be prepared by adequate control of the structure before solid‐state plastic deformation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

5.
    
In this work, the synergistic effects of β‐modification and impact polypropylene copolymer (IPC) on brittle–ductile (B–D) transition behavior of polypropylene random copolymer (PPR) have been investigated. It is interesting to find that adding both IPC and β‐nucleating agent into PPR has three effects: (i) leading to a significant enhancement in β‐crystallization capability of PPR, (ii) contributing to the shift of B–D transition to lower temperatures, (iii) increasing the B–D transition rate. The reason for these changes can be interpreted from the following two aspects. On one hand, the transition of crystalline structure from α‐form to β‐form reduces the plastic resistance of PPR matrix, thus causing the initiation of matrix shear yielding much easier during the impact process. On the other hand, the well dispersed rubbery phase in IPC with high molecular mobility at relatively low temperatures is beneficial to the shear yielding of PPR matrix and, subsequently, the great improvement in impact toughness of the ternary blends. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

6.
    
In this study, an increase in the cooling rate of high‐density polyethylene parts was carried out via a change in the fluid flow pattern to introduce gas cooling under a gas‐assisted injection‐molding process; this was conducive to the retention of orientation chains shaped during the injection stage and further developed into much more oriented crystals. Morphological observation showed that the parts without gas cooling (WOGC) were composed of oriented crystals except the gas channel zone, whereas the parts with gas cooling (WGC) were full of oriented crystals, especially much more interlocking shish‐kebab structures in the subskin zone. The WGC parts had a higher degree of orientation than the corresponding zone of the WOGC parts. Although the lower crystallinity, the wider orientation regions, and much more interlocking shish‐kebab structures led to considerable increases from 32 and 990 MPa in the WOGC parts to 36 and 1150 MPa in the WGC parts for the yield strength and elastic modulus, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40349.  相似文献   

7.
    
Crystallization, in‐plane orientation, and hydrogen bonding interactions are three vital factors for enhancing mechanical properties of polyimide (PI) films. However, which is the dominant factor? In this study, three PI films containing heterocyclic moiety, poly(benzoxazole‐imide), poly(benzimidazole‐imide), and poly(pyrimidine‐imide) were chosen to comparative study. The crystallinity of poly(benzoxazole‐imide), poly(benzimidazole‐imide), and poly(pyrimidine‐imide) PI films are 36, 24, and 15%, respectively. The results of small angle X‐ray scattering indicate poly(benzoxazole‐imide) and poly(benzimidazole‐imide) films show periodical lamellar structures, while poly(pyrimidine‐imide) shows no long period due to low crystallinity. In‐plane orientation (P200) is calculated from polarized attenuated total reflection (ATR)‐Fourier transform infrared and refractive indices. The order of in‐plane orientation is poly(benzimidazole‐imide) < poly(benzoxazole‐imide) < poly(pyrimidine‐imide). Hydrogen bonding interactions, which restrict chain motion and hinder spontaneous in‐plane orientation, are only formed in poly(benzimidazole‐imide). The relationship between mechanical properties and three influence factors are discussed, and the order of influence extent for mechanical properties of PI films is hydrogen bonding interactions < degree of crystallization < in‐plane orientation. Two structure models for PI films are proposed in order to further confirm the dominant effect of in‐plane orientation on the mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44000.  相似文献   

8.
    
As part of continuous efforts to understand the surprising synergetic effect between β‐nucleating agent and pre‐ordered structures of isotactic polypropylene (iPP) in significant enhancement of β‐crystallization (Ordered Structure Effect, OSE), two β‐nucleated iPP with different uniformities of stereo‐defect distribution (WPP‐A and WPP‐B) were prepared, their crystallization behaviors with variation of melt structures were studied in detail. The results revealed that β‐phase can hardly form in WPP‐A (whose stereo‐defect distribution is less uniform) because of its strong tendency of α‐nucleation caused by its less uniform stereo‐defect distribution, while WPP‐B is more favorable for β‐crystallization; As fusion temperature decreases, similar variation trends of crystallization temperature and β‐phase proportion can be observed from WPP‐A and WPP‐B, indicating the occurrence of OSE behavior, which provides unsurpassed β‐nucleation efficiency and induces β‐crystallization even in WPP‐A which is less favorable for β‐crystallization; moreover, the upper and lower limiting temperatures of Region II of WPP‐A and WPP‐B are identical, suggesting the uniformity of stereo‐defect distribution has little influence on temperature window for OSE (denoted as Region II). To explore the physical nature of Region II, self‐nucleation behavior and equilibrium melting temperature of PP‐A and PP‐B were studied. The lower limiting temperatures of exclusive self‐nucleation domain of both PP‐A and PP‐B are identical with the lower limiting temperatures of Region II in OSE (168°C); moreover, the Tm0 of both PP‐A and PP‐B are close to their upper limiting temperatures of Region II in OSE behavior (189°C). The possible explanation was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42632.  相似文献   

9.
    
A series of uniaxial tensile loading–unloading tests is performed on isotactic polypropylene at room temperature. Prior to mechanical testing, injection‐molded specimens are annealed for 24 h at temperatures T = 145, 150, 155, 158, 160, 163, and 165°C, which cover the entire region of high‐temperature annealing temperatures. A constitutive model is developed for the elastoplastic behavior of a semicrystalline polymer at small strains. The stress–strain relations are determined by six adjustable parameters that are found by matching observations in cyclic tests. Fair agreement is demonstrated between the experimental data and the results of numerical simulation. It is shown that all material constants are affected by the annealing temperature, which is explained by changes in the crystalline morphology driven by thermal treatment. Some of the adjustable parameters experience finite jumps in the vicinity of the critical temperature Tc = 159°C. These jumps are attributed to the α2 → α2′ phase transformation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 186–196, 2003  相似文献   

10.
    
Amorphous preforms of poly(ethylene 2,6‐naphthalate) (PEN) were biaxially drawn into bottles up to the desired volume under industrial conditions. These bottles were used to characterize the shrinkage behavior of the drawn bottles with or without heat treatment and to study structural variations during heat setting. During drawing, a rigid phase structure was induced, and the amount of the induced rigid phase structure was linearly related to the square root of the extra first strain invariant under equilibrium conditions. During the production of these bottles, this equilibrium was not attained because of high stretching conditions and rapid cooling after stretching. The structure after orientation contained a rigid amorphous phase and an oriented amorphous phase. The shrinkage behavior was a function of the temperature and time of heat setting. Long heat‐setting times, around 30 min, were used to characterize the possible structural variations of the oriented PEN after heat setting at equilibrium. Under the equilibrium conditions of heat setting, the start temperature of the shrinkage was directly related to the heat‐setting temperature and moved from 60°C without heat treatment up to a temperature of 255°C by a heat‐setting temperature of 255°C; this contrasted with poly(ethylene terephthalate) (PET), for which the start temperature of shrinkage was always around 80°C. For heat‐setting temperatures higher than 220°C, the structural variations changed rapidly as a function of the heat‐setting time, and the corresponding shrinkage of the heat‐set samples sank below 1% in a timescale of 30–60 s for a film thickness of 500 μm. The heat treatment of the oriented films taken out of the bottle walls with fixed ends stabilized the induced structures, and the shrinkage of these heat‐set films was zero for temperatures up to the heat‐setting temperature, between 220 and 265°C, if the heat‐setting time was sufficient. According to the results obtained, a heat‐setting time of 30 s, for a film thickness of 500 μm, was sufficient at a heat‐setting temperature of 255°C to stabilize the produced biaxially oriented PEN bottles and to take them out the mold without further shrinkage. During the drawing of PEN, two different types of rigid amorphous phases seemed to be induced, one with a mean shrinkage temperature of 151°C and another rigid amorphous phase, more temperature‐stable than the first one, that shrank in the temperature range of 200–310°C. During heat setting at high temperatures, a continuous transformation of the less stable phase into the very stable phase took place. The heat‐set method after blow molding is industrially possible with PEN, without the complicated process of subsequent cooling before the molds are opened, in contrast to PET. This constitutes a big advantage for the blow molding of PEN bottles and the production of oriented PEN films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1462–1473, 2003  相似文献   

11.
    
The structure and properties of binary blends composed of poly(lactic acid) (PLA) and fibrous poly(butylene succinate) (PBS), which were prepared by an uniaxial stretching operation in the molten state, were studied and compared with those of blends having spherical particles of PBS in a continuous PLA phase. We found from electron microscope observation that PBS nanofibers with a large aspect ratio were generated in the stretched samples. Enlargement of the surface area of the PBS particles, which showed nucleating ability for PLA, led to a high degree of crystallization and enhanced the cold crystallization in the heating process. Moreover, the PBS fibers in the stretched samples had a dominant effect on the mechanical properties in the point range between the glass‐transition temperature of PLA and the melting temperature of PBS. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

12.
    
Polymer processing methods generally play a crucial role in determining the development of microstructure in the fabricated product. In this study, isotactic polypropylene (iPP) melt containing 0.05 wt % β‐nucleating agent (β‐NA) was extruded via a melt flow rate indicator. The molten extrudate was stretched into a fiber upon various take‐up velocities (TVs). The microstructures of the fiber were investigated by differential scanning calorimeter, two‐dimensional wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering. Also, its tensile properties (including tensile strength, modulus, elongation at break, and toughness) were measured by tensile test. Interestingly, the tensile strength (135.0 MPa) of a melt‐spun β‐nucleated iPP fiber fabricated at 400 cm/min was enhanced by 115.2%, compared with that (62.7 MPa) prepared at 100 cm/min, with a considerable increment in toughness (from 661 to 853 MJ/m3). The enhancement mechanism for tensile properties was discussed based on the microstructures. This work offers a simple approach to prepare β‐nucleated iPP fibers with excellent strength and toughness. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43454.  相似文献   

13.
    
Ultra high molecular weight polyethylene/alumina (UPE/Al2O3) microcomposites with high loading micro alumina (Al2O3, 20 to 100 phr) were prepared by casting method. The composites were thermal treated (cooled slowly) and then the thermal properties were studied at temperatures from 25 to 125°C. Thermogravimetric analysis (TGA) and scanning electron microscopic (SEM) proves the homodispersion of Al2O3 microparticles in UPE. TGA indicates that the temperature of 5% weight loss of UPE/Al2O3 (100 phr) composite is 467.0°C, 10.5°C higher than that of pure UPE. Differential scanning calorimetry (DSC) shows that the melting point and the real degree of crystal (Xrc) of treated UPE/Al2O3 composite (100 phr) are 141.4°C and 65.7%, respectively, all higher than that of untreated composite, which can be described by crystal bridge mechanism. The density of the composite is also be enhanced because of crystal volume shrinkage induced by thermal treatment. The thermal conductivity of the treated UPE/Al2O3 composite (100 phr) is 1.920 W (m K)?1 at 25°C, 23.6% higher than that of the untreated composite. Crystal bridge thermal conduction mechanism is proposed. The thermal conductivity of UPE/Al2O3 composite has some dependency on the increasing Al2O3 content and also thermal treatment. These results can give some advice to design formulations for practical applications in pipe area and other wear area. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40528.  相似文献   

14.
    
In the present work, the fracture behavior of transcrystallization (TC) of poly(l ‐lactic acid) (PLLA) in thin film and the dependence of mechanical properties on the morphology of TC have been studied. The nucleation density of TC was merely determined by the annealing temperatures of the fibers which used for inducing nucleation, and the crystallization temperature and time of the samples were completely identical. By using in situ polarized optical microscopy, the fracture process of TCs was characterized. For the TC with high nucleating density (TC‐H), lots of cracks were generated from the TC bulk during fracture. But only few cracks were observed on the TC with low nucleation density (TC‐L), and the final fracture of TC‐L always occurred in the junctions of crystal segments. Compared to the samples which do not contain TC, the fracture strength was enhanced by 8.1% because of the presence of TC‐H. On the contrary, the presence of TC‐L can reduce the fracture strength of the samples. The fracture surfaces of TC were characterized by scanning electron microscope. It was observed that the fracture surface of TC‐H exhibited obvious fibrillation and cavitation, but the fracture surface of TC‐L was smooth and featureless. The possible fracture mechanism for two TCs was discussed in view of their intrinsic crystal organizations. © 2014 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41273.  相似文献   

15.
    
The effect of SCORIM was investigated on three grades of polybutene‐1 and one grade of ethylene–butene‐1 copolymer. The methods and processing conditions used for injection molding and the properties of the moldings are reported. Phase transformations and their relationship with mechanical properties are discussed in detail. Both, conventional and shear‐controlled orientation injection molding (SCORIM) were employed to produce moldings. SCORIM is based on the application of specific macroscopic shears to a solidifying melt. The multiple shear action enhances molecular alignment. The moldings were investigated by performing mechanical tests, fractographic analysis, differential scanning calorimetry studies, wide‐angle X‐ray diffraction, polarized light microscopy, and atomic force microscopy. The application of SCORIM improves the mechanical performance. Molecular orientation results in the formation of shish‐kebab morphology. One grade of polybutene‐1 exhibited a greater than fivefold increase in Young's modulus. The application of high cavity pressures favored the formation of the stable Form I' in polybutene‐1. The formation of Form I' led to a decrease in crystallinity and mechanical properties. However, this loss was by far smaller than the gain obtained via the formation of shish‐kebab morphology. The relationship between mechanical properties and micromorphologies of the investigated materials is explained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 814–824, 2003  相似文献   

16.
    
The influence of temperature during reactive extrusion of poly(L ‐lactide) (PLLA) on the molecular architecture and crystallization behavior was investigated for OO‐(t‐butyl) O‐(2‐ethylhexyl) peroxycarbonate‐modified polymer. The long chain–branched PLLA (LCB‐PLLA) content and its structure in the resulting slightly crosslinked PLLA (χ‐PLLA) containing linear and LCB‐PLLA were characterized by both analyses, size exclusion chromatography equipped with multiangle laser light scattering and rheological measurements. A reduction of LCB‐PLLA content in χ‐PLLA and an increase of number of branches in LCB‐PLLA were found with increasing the extrusion temperature. An increase of extrusion temperature induces different process in the polymer: decrease of the lifetime of peroxide, increase of the radical concentration due to rapid peroxide decomposition rate, and increase of the chain diffusion to the amorphous phase. Among these indices, the lifetime of peroxide is a good index for crosslinking behavior of PLLA during extrusion. As for the isothermal crystallization behavior from the melt, the Avrami crystallization rate constant of χ‐PLLA increases as an increase of LCB‐PLLA content in χ‐PLLA. This implies that LCB‐PLLA acts as a nucleating agent for PLLA. Furthermore, regime analysis and the free energy of nucleus of χ‐PLLA were investigated using Hoffman–Lauritzen theory. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

17.
    
This article explores the use of two β nucleants to improve the fracture behavior of filled and unfilled homo‐polypropylene (PP). The first was based upon an organic quinacridone, whereas the second was based upon the inorganic calcium pimelate. Formulations containing various concentrations of nucleant were prepared using single screw extrusion and then characterized by X‐ray diffraction, differential scanning calorimetry (DSC), Izod impact strength, and tensile testing. The quinacridone nucleating agent produced higher levels of β crystallinity and better improvement in strain to failure, whereas the calcium pimelate imparted greater improvement in impact strength regardless of whether the PP was filled or unfilled. No direct relationship between β crystallinity and fracture properties was observed though synergistic enhancement in impact strength was evident. By varying the concentration of calcium carbonate in the calcium pimelate from 10 : 1, 5 : 1, 2 : 1, and 1 : 1 weight composition of calcium carbonate to pimelic acid, similar property enhancements were achieved regardless of composition although the 10 : 1 sample did produce superior elongation to break. The importance of cooling rate on microstructure within each sample was explored via a through the thickness study using DSC and nano‐indenting methods. Variations in the β content through the thickness were related to cooling and found to be independent of sample composition and processing. Elastic properties varied inversely with β content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

18.
    
Polyester‐based waterborne polyurethane (WPU) dispersions having poly(ethylene glycol) adipate diol, isophorone diisocyanate, and hexamethylene diisocyanate as the main raw materials were synthesized by an acetone process. In each step of the synthesis process, the intermediate products were collected, and the crystallization morphologies and relative crystallinity (X) of the soft segments (SSs) in their films were investigated by means of polarizing optical microscopy, differential scanning calorimetry, and X‐ray diffraction. The fracture surfaces and thermostability of the intermediate films were also investigated by scanning electron microscopy (SEM) and TGA, respectively. The results show that the crystalline dimensions of the SSs decreased substantially during the synthesis process of WPU. X of the SSs decreased after the prepolymerization reaction and increased after the hydrophilic chain‐extending reaction, then decreased after emulsification, and finally increased after the secondary chain‐extending reaction. Moreover, The SEM photos indicate that with decreasing crystalline dimensions, the fracture mechanisms of the intermediate films varied gradually from brittle failure to ductile fracture. The thermostability of the intermediates obtained in each step of the synthesis process was in accordance with the variation tendency of the X of the SSs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40270.  相似文献   

19.
The effect of poly (lactic acid) (PLA) on the crystalline phase transition of poly (vinylidene fluoride) (PVDF) from α‐ to β‐phase under uniaxial stretching for immiscible PVDF/ PLA blends was investigated. The typical sea‐island structure in the blends was found to facilitate the necking of PVDF and the transition from α‐ to β‐phase due to the local stress distribution during stretching. The crystalline phase transition of PVDF in the blends is temperature‐dependent and is affected by the content of PLA. The highest content of β‐phase, F(β), was achieved in the samples stretched at 60°C, while the effect of PLA content on the crystalline phase transition of PVDF is more complex. F(β) increases slightly when the sample with a PLA content no more than 15 wt % is stretched at 60, 80, and 100°C, and decreases sharply for the sample containing 20 wt % PLA; in addition, the sample containing 10 wt % PLA exhibits the highest F(β) no matter what the stretching temperature is. The mechanism of the crystalline phase transition of PVDF during the stretching is interpreted from energy barrier of the transition from α‐ to β‐phase and the morphological structures in the blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

20.
    
The performance of carbon fibers depends on the quality of the precursor and the conditions of the thermal treatment. In detail, for a PAN precursor fiber the viscosity of a spinning dope and the draw ratio during the spinning process needs to be considered. Through wet spinning, different types of PAN precursor fibers with defined spinning parameters, including solid content, solvent content in a bath, and especially draw ratio resulting in defined cross section diameters, were fabricated and analyzed with tensile tests, density investigations, SEM, TGA‐MS, FTIR, and XRD. The results show that the mechanical properties of the fibers correlate to crystallinity. The cross section diameter is strongly related to the morphology of the fibers after thermal treatment. By extending the postdrawing of PAN fibers high tenacities were obtained at the cost of the cross section shape. In addition, TGA measurements reveal trapped residues of the wet spinning process as well as show several chemical reactions takes place at the same time at different temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43698.  相似文献   

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