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In this paper, series of polyimide films with different aggregation structures were prepared through a partially pre-imidization process, and the properties were investigated in detail. The pre-imidization degree (pre-ID) was succ...
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In this paper, series of polyimide films with different aggregation structures were prepared through a partially pre-imidization process, and the properties were investigated in detail. The pre-imidization degree (pre-ID) was successfully controlled by adjusting the amount of dehydrating reagents, which was confirmed by FT-IR spectra measurement. PI films exhibited a quite different degree of crystallinity, which increased with pre-ID increasing. DSC curves showed obvious melt endothermic peaks at about 450 °C. The tensile strength, tensile moduli and elongation at break of the PI films increased obviously with pre-ID increasing. The corresponding values of PI-100 increased by 37.9%, 11.7% and 336%, respectively, compared with those of PI-0. TMA measurement showed that the coefficient of thermal expansion of PI films decreased with pre-ID increasing, indicating that the PI molecular chains were restricted by the crystalline structure. Meanwhile, those PI films obtained by the pre-imidization process still possess excellent thermal stability. The present work provided the theoretic indicators for controllable preparing of high-performance polyimide films.
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Highly ordered arrays of polyamide 6 (PA6) nanotubes were successfully prepared using photolithography via polymer solution wetting the anodic aluminum oxide (AAO) templates. The samples were examined by scanning electron microsco...
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Highly ordered arrays of polyamide 6 (PA6) nanotubes were successfully prepared using photolithography via polymer solution wetting the anodic aluminum oxide (AAO) templates. The samples were examined by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD). The crystal structure and the crystallinity of the samples were influenced by the presence of nanopores in the AAO template. Nanopore-induced crystal transformation from the α-form to the γ-form of PA6 was confirmed by XRD, and the formation of γ-form crystal was enhanced by the presence of nanopores in the AAO template. The formation of γ-form crystal was also discussed. These results indicated that nanopores provided favorable conditions for the crystallization of γ phase.
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Electrospinnability as well as dissolvability of the celluloses derived from different biomass resources are systematically studied in this work. By analyzing the essentially physical and molecular structure of cellulose in detail...
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Electrospinnability as well as dissolvability of the celluloses derived from different biomass resources are systematically studied in this work. By analyzing the essentially physical and molecular structure of cellulose in detail, dissolving efficiency and molecular chain entanglement in solution of cellulose are carefully realized. Accordingly, the original factors on electrospinnability of cellulose is revealed. Crystallinity mainly affects the dissolution of cellulose, which is the foundation to achieve electrospinning. Degree of polymerization is the decisive index of cellulose to form molecular entanglement in solution or not. Proper molecular entanglement of cellulose, just as corn cellulose II, could initiate the formation of ultrafine fiber with good morphology in electrospinning. Our research is no doubt helpful to establish a solid scientific and technical foundation for selection of cellulose to achieve high efficiency fabrication of ultrafine fiber in electrospinning.
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摘要 :AbstractIn a foregoing article, a new method based on dynamic mechanical thermal analysis(DMTA)for determining the degrees of crystallinity of the natural rubber (NR) and the eucommia ulmoides (EU) gum, with different crosslink de...
展开AbstractIn a foregoing article, a new method based on dynamic mechanical thermal analysis(DMTA)for determining the degrees of crystallinity of the natural rubber (NR) and the eucommia ulmoides (EU) gum, with different crosslink densities, has been established. In order to verify the effectiveness of this method, in the present paper, the degrees of crystallinity of NR andEUgum with different crosslink densities will be determined by differential scanning calorimetry (DSC). The results indicate that the degrees of crystallinity determined by DMTA are much higher than those of DSC. This is because the degree of crystallinity determined by DMTA involves not only the ratio of the crystalline zone, but also the ratio of the mesomorphic zone, while the degree of crystallinity tested by DSC includes only the ratio of the crystalline zone. So, the degree of crystallinity, the degree of mesomorphic zone and the degree of amorphous zone of NR andEUgums with different crosslink densities can be quantitatively determined by the combination of DMTA and DSC. The results show that the degree of crystallinity, the degree of mesomorphic zone and the degree of amorphous zone of NR (crystallized at??25?°C for 12?h) andEUgum are 33%, 53%, 14% and 34%, 54%, 13%, respectively. For NR, increasing the crosslink density or decreasing the induced time will decrease the degree of crystallinity and the degree of mesomorphic zone simultaneously, but will increase the degree of amorphous zones. ForEUgum, increasing the crosslink density will decrease the degree of crystallinity and increase the degree of amorphous zone, but keep the degree of mesomorphic zone invariably consistent within the critical crystallization point, which is approximately 55%. At the end of the paper, the impact of crystallization on the mechanical properties ofEUgum and NR is discussed as well.Graphical abstractThe number of free chain segments of the amorphous zone in NR andEUgum, tested through DMTA, can be used to calculate their degree of crystallinity, which involves not only the ratio of the crystalline zone, but also the ratio of the mesomorphic zone. So, the degree of crystallinity determined by DMTA is much larger than that of DSC. As a result, the degree of crystallinity, the degree of mesomorphic zone and the degree of amorphous zone of NR and EU gums can be quantitatively determined by DMTA and DSC, which are 33%, 53%, 14% and 34%, 54%, 13%, respectively.Display Omitted]]>
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摘要 :AbstractThe structural properties of extruded cast films of poly-3-hydroxybutyrate (P3HB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (P3HB-co-3HV) were analysed by Raman spectroscopy. A sensitive band for the side chain of th...
展开AbstractThe structural properties of extruded cast films of poly-3-hydroxybutyrate (P3HB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (P3HB-co-3HV) were analysed by Raman spectroscopy. A sensitive band for the side chain of the 3HV was found at 844?cm?1(νCC, νC-COO). Using an internal standard at 1101?cm?1(νsC-O-C, ρCH3), a model for calculation of the 3HV content was developed. This was based on analysis of samples with a 3HV content of 0–12?mol%. Additionally, P3HB-co-3HV samples were tempered in order to create different degrees of crystallinity. The induced changes in the Raman spectra were analysed. The Raman model to determine the degree of crystallinity considers the sensitive band at 2999?cm?1(νasCH2) and the internal standard at 1059?cm?1(νC-O, νC-CH3, ρCH2). The investigated crystallinity was in a range of 0.69–0.86.Graphical abstractDegree of crystallinity χ as a function of the 3HV content.Display Omitted收起
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The influence of ionizing radiation on ultra high molecular weight polyethylene (UHMWPE) was studied using EPR spectroscopy and GC. Two samples of various degree of crystallinity, 85% and 53%, were investigated upon exposure to el...
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The influence of ionizing radiation on ultra high molecular weight polyethylene (UHMWPE) was studied using EPR spectroscopy and GC. Two samples of various degree of crystallinity, 85% and 53%, were investigated upon exposure to electron beam. In this study it was found that radicals generated following irradiation decay much faster in amorphous than in crystalline phase. The primary product generated in both phases is second ordered alkyl radical. EPR spectra detected for the sample containing 85% crystalline regions revealed a quintet of hyperfine splitting about 2.28 mT and the signal was tentatively assigned to the product of P-fragmentation. The radiation yield of hydrogen for two studied samples of various crystallinity was similar.
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The influence of texturing parameters, such as draw ratio and heater temperature, on characteristics and dyeing behaviour of polyamide 66 yarn has been studied. It is observed that the draw ratio and heater temperature have neglig...
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The influence of texturing parameters, such as draw ratio and heater temperature, on characteristics and dyeing behaviour of polyamide 66 yarn has been studied. It is observed that the draw ratio and heater temperature have negligible influence on dye exhaustion, but they both markedly influence the dyeing kinetics. This has been measured by apparent diffusion coefficients and discussed on the basis of crystallinity and degree of orientation data.
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Background: Acid hydrolysis is a common process used for the production of microcrystalline and nanocrystalline cellulose. When the starting cellulose feedstock is treated with dilute mineral acid (2-3 M), a sharp decrease in degr...
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Background: Acid hydrolysis is a common process used for the production of microcrystalline and nanocrystalline cellulose. When the starting cellulose feedstock is treated with dilute mineral acid (2-3 M), a sharp decrease in degree of polymerization (DP) is observed until a minimum constant value called level-off degree of polymerization (DP_m) is achieved, which is associated with DP of elementary nanocrystallites. After such chemical treatment, despite achieving P_m, the particles of microcrystalline cellulose (MCC) are formed instead of cellulose nanocrystallites (CNCs), which require further explanation. Methods: Observation of DP, crystallinity degree, particle size and charge depending on the acid concentration and type. Results: It was found that dilute acid causes a selective degradation of non-crystalline domains (NCD), which leads to transverse splitting of relatively long fibers and obtaining of shorter low-molecular fragments of the fibers, namely micron-size particles of MCC. On the other hand, concentrated acid causes not only the degradation of NCD, but also tightly packed lateral surfaces between nanocrystallites connected via strong inter-crystalline contacts, thus facilitating the release of free CNCs.
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Thermotropic liquid-crystalline polymers (TLCPs) have aroused considerable interest due to their attractive properties as high-performance materials. Significant research attention has been devoted to investigating the relationshi...
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Thermotropic liquid-crystalline polymers (TLCPs) have aroused considerable interest due to their attractive properties as high-performance materials. Significant research attention has been devoted to investigating the relationship among monomer structures, syntheses and end-use properties of TLCPs. The study reported here concerns the preparation, characterization and melt spinning of novel copolyesters containing two different flexible units together with two different aromatic units in the polymer chains. A range of copolyesters based on p-hydroxybenzoic acid (p-HBA), m-hydroxybenzoic acid, p-hydroxyphenylacetic acid and poly(ethylene terephthalate) were synthesized. The liquid crystallinity, thermal properties and degrees of crystallinity of these copolyesters were investigated using hot-stage polarized light microscopy, differential scanning calorimetry, thermogravimetry and wide-angle X-ray diffraction. Copolyester fibres were characterized using scanning electron microscopy. The copolyesters were melt-processable, thermally stable and could be processed above their melting temperatures without degradation. The degree of crystal structure was found to depend upon the content of p-HBA. The fibres prepared showed that polymer chains had a well-developed fibrillar structure. Novel TLCPs containing flexible units in the main chain were synthesized and characterized. Copolyesters containing p-HBA units ranging from 55 to 70 mol% exhibited phase-separated liquid-crystalline morphology, appropriate melting temperatures and high thermal stability for melt processing.
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The ionoSolv pretreatment generates a cellulose pulp by extracting hemicellulose and lignin using low-cost ionic liquids. In this study, cellulose pulp was obtained from Miscanthus x giganteus using the protic ionic liquid triethy...
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The ionoSolv pretreatment generates a cellulose pulp by extracting hemicellulose and lignin using low-cost ionic liquids. In this study, cellulose pulp was obtained from Miscanthus x giganteus using the protic ionic liquid triethylammonium hydrogen sulfate [N-2220][HSO4] with 20% water as a co-solvent and characterised in detail for its material properties as a function of pretreatment severity. We measured the particle size distribution, porosity and crystallinity of the unbleached pulps and the molar weight distribution of the cellulose contained within. We report that the surface area increased and the size of the pulp particles decreased as ionoSolv processing progressed. While the native cellulose I structure was maintained, the average degree of polymerisation of the cellulose was reduced to a DPn of around 300, showing the cellulose polymers are shortened. We correlate the pulp properties with enzymatic saccharification yields, concluding that enzymatic saccharification of the cellulose after ionoSolv pretreatment is mainly enhanced by removing hemicellulose and lignin. We also observed that overtreatment deteriorated saccharification yield and that this coincides with cellulose fibrils becoming coated with pseudolignin redeposited from the ionic liquid solution, as demonstrated by FT-IR spectroscopy. Pseudolignin deposition increases the apparent lignin content, which is likely to increase chemical demand in bleaching, suggesting that both glucose release and material use benefit from a minimum lignin content. Overall, this study demonstrates that cellulose pulps isolated with ionoSolv processing are not only a promising intermediate for high-yield release of purified glucose for biorefining, but also have attractive properties for materials applications that require cellulose I fibrils. Graphic abstract
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