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151.
The low‐temperature physical aging of amorphous poly(L ‐lactide) (PLLA) at 25–50°C below glass transition temperature (Tg) was carried out for 90 days. The physical aging significantly increased the Tg and glass transition enthalpy, but did not cause crystallization, regardless of aging temperature. The nonisothermal crystallization of PLLA during heating was accelerated only by physical aging at 50°C. These results indicate that the structure formed by physical aging only at 50°C induced the accelerated crystallization of PLLA during heating, whereas the structure formed by physical aging at 25 and 37°C had a negligible effect on the crystallization of PLLA during heating, except when the physical aging at 37°C was continued for the period as long as 90 days. The mechanism for the accelerated crystallization of PLLA by physical aging is discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
152.
The effects of crystallinity, water absorption, hydrolytic degradation, and tacticity on the solid structure and chain mobility of poly(lactide)s were investigated by solid-state 13C NMR spectroscopy. The following results were obtained from the line shapes of the carbonyl and methine carbons in 13C NMR spectra and their spin-lattice relaxation behavior. The crystallized poly(l-lactide) (PLLA) specimens in the dried, hydrated, and hydrolyzed states had two components, rigid and mobile components which can be, respectively, assigned to the crystalline and non-crystalline components. Upon water absorption, the chain mobility in the non-crystalline component of PLLA-C remained unvaried, reflecting a very small effect of the incorporated water molecules at room temperature. In contrast, the elevated chain mobility in the crystalline component and unclear splitting of carbonyl carbon strongly suggest that the water molecules are incorporated in the crystalline lattice. Upon removal of the non-crystalline components by hydrolytic degradation of crystallized PLLA, the chain mobility was slightly elevated in both crystalline and non-crystalline components by the lowered crystalline thickness and shortened non-crystalline chains. The non-crystalline specimens, PLLA (PLLA-Q) and poly(dl-lactide) (PDLLA), could be analyzed to contain two components, rigid and soft components, with the similar conformation but different restricted states of chains which cause high and low chain mobility. The insignificant difference in the spectral shapes and T1C values between PLLA-Q and PDLLA strongly suggests that the effects of difference in the chain regularity and interaction on the spectral shapes and T1C values are very low. 相似文献
153.
Summary: The effects of various additives: poly(D ‐lactic acid) (PDLA), talc, fullerene C60, montmorillonite, and various polysaccharides, on the non‐isothermal crystallization behavior of poly(L ‐lactic acid) (PLLA), during both the heating of melt‐quenched films from room temperature, and the cooling of as‐cast films from the melt, was investigated. When the melt‐quenched PLLA films were heated from room temperature, the overall PLLA crystallization was accelerated upon addition of PDLA or the stereocomplex crystallites formed between PDLA and PLLA, the mixtures containing PDLA, and the mixture of talc and montmorillonite. No significant effects on the overall PLLA crystallization were observed for talc, C60, montmorillonite, and the mixtures containing C60. Such rapid completion of the overall PLLA crystallization upon addition of the aforementioned additives can be ascribed to the increased density (number per unit volume or area) of PLLA spherulites. When the as‐cast PLLA films were cooled from the melt, the overall PLLA crystallization completed rapidly, upon addition of PDLA, talc, C60, montmorillonite, and their mixtures. Such rapid overall PLLA crystallization is attributable to the increased density of the PLLA spherulites and the higher nucleation temperature for PLLA crystallization. In contrast, the addition of various polysaccharides has no significant effect, or only a very small effect, on the overall PLLA crystallization during heating from room temperature or during cooling from the melt. This finding means that the polysaccharides can be utilized as low‐cost fillers for PLLA‐based materials, without disturbing the crystallization of the PLLA. The effect of additives in accelerating the overall PLLA crystallization during cooling from the melt, decreased in the following order: PDLA > talc > C60 > montmorillonite > polysaccharides.
154.
Koichiro Fukuda Ken-ichi Matsunaga Takahiro Bessho Hideto Yoshida 《Journal of the American Ceramic Society》2005,88(4):954-962
The phase stability in part of the P2 O5 -bearing pseudoquaternary system CaO–SiO2 –Al2 O3 –Fe2 O3 has been studied by electron probe microanalysis, optical microscopy, and powder X-ray diffractometry. At 1973–1653 K, the α-Ca2 SiO4 solid solution [α-C2 S(ss)] and melt coexisted in equilibrium, both chemical variations of which were determined as a function of temperature. The three phases of melt, calcium aluminoferrite solid solution (ferrite), and C2 S(ss) coexisted at 1673–1598 K. On the basis of the chemical compositions of these phases, a melt-differentiation mechanism has been, for the first time, suggested to account for the crystallization behavior of Ca3 Al2 O6 solid solution [C3 A(ss)]. When the α-C2 S(ss) and melt were cooled from high temperatures, the melt would be induced to differentiate by the crystallization of ferrite. Because the local equilibrium would be continually attained between the rims of the precipitating ferrite and coexisting melt during further cooling, the melt would progressively become enriched in Al2 O3 with respect to Fe2 O3 . The resulting ferrite crystals would show the zonal structure, with the Al/(Al+Fe) value steadily increasing up to 0.7 from the cores toward the rims. The C3 A(ss) would eventually crystallize out of the differentiated melt between the zoned ferrite crystals in contact with their rims. 相似文献
155.
Koichiro Fukuda Ayari Takeda Akira Yamaguchi Shinobu Hashimoto Hideto Yoshida 《Journal of the American Ceramic Society》2001,84(5):1155-1160
We examined the chemistry and structure of the liquid that was exsolved by the remelting reaction of belite. Electron probe microanalysis revealed that the liquid concentrated the impurity components (e.g., Na2 O, K2 O, Al2 O3 , and Fe2 O3 ) of the parent belite. Micro-Raman spectroscopy showed the similarity of the spectra of the exsolved liquid and amorphous calcium aluminoferrite solid solution. The transition from the crystalline to the amorphous state of the solid solution was induced by increasing the excitation laser power. Accordingly, the liquid at ambient temperature was most likely in a glassy state. The chemical composition of the liquid, deduced from the above experiments, was ∼81 mass% Ca2 AlFeO5 and ∼19 mass% Ca2 SiO4 . The alkalies, which have never been detectable in crystalline calcium aluminoferrite, were probably necessary for the vitrification of the liquid. 相似文献
156.
Hideto Nakajima Takafumi Hosokawa Yoshimitu Doi Toshiyuki Ikemoto Shimon Ishida Fumiharu Kimura Toshiaki Hanafusa 《International journal of molecular sciences》2012,13(10):12213-12223
A Japanese randomized controlled study showed that Interferon â (IFN-â1b) therapy is clinically effective in decreasing the frequency of attacks in multiple sclerosis (MS), even in optico-spinal MS (OSMS). However, recent studies have shown that IFN-â (IFN-â1a/IFN-â1b) treatment was not effective in neuromyelitis optica (NMO) patients and that the diminished benefit of IFN-â treatment in NMO may be due to different immune responses to IFN-â. We determined longitudinally the expression of CCR5, CXCR3 and CCR4 on CD4+ T and CD8+ T cells in the blood from patients with NMO and MS treated with IFN-â1b. During a 12-month period of IFN-â1b therapy, the annualized relapse rate decreased in MS patients but not in NMO patients. There was no significant difference in the expression of the chemokine receptors between NMO and MS at baseline. The percentages of CD4+CCR5+ and CD4+CXCR3+ T cells, representative of the Th1 response, were decreased in both NMO and MS after treatment. The percentage of CD4+CCR4+ T cells, representative of the Th2 response, was decreased in MS, but those for NMO was significantly increased compared with the pretreatment levels. Our results indicate that IFN-â1b-induced up-modulation of the Th2 response in NMO patients may be the source of differences in the therapeutic response to IFN-â1b therapy. In the present study, Th2 predominance is involved in the pathogenesis of NMO. 相似文献
157.
The spherulite growth behavior and mechanism of l-lactide copolymers, poly(l-lactide-co-d-lactide) [P(LLA-DLA)], poly(l-lactide-co-glycolide) [P(LLA-GA)], and poly(l-lactide-co-ε-caprolactone) [P(LLA-CL)] have been studied using polarization optical microscopy in comparison with poly(l-lactide) (PLLA) having different molecular weights to elucidate the effects of incorporated comonomer units. The incorporation of comonomer units reduced the radius growth rate of spherulites (G) and increased the induction period of spherulite formation (ti), irrespective of the kind of comonomer unit. Such effects became remarkable with the content of comonomers. At a crystallization temperature (Tc) of 130 °C, the disturbance effects of comonomers on the spherulite growth decreased in the following order: d-lactide>glycolide>ε-caprolactone, when compared at the same comonomer unit or reciprocal of averaged l-lactyl unit sequence length (ll). The ti estimation indicated that the glycolide units have the lowest disturbance effects on the formation of spherulite (crystallite) nuclei. The PLLA having the number-average molecular weight (Mn) exceeding 3.1×104 g mol−1 showed the transition from regime II to regime III at Tc=120 °C, whereas PLLA with the lowest Mn of 9.2×103 g mol−1 crystallized solely in regime III kinetics and the copolymers excluding P(LLA-DLA) with 3% of d-lactide units crystallized solely according to regime II kinetics. The nucleation and front constant for regime II and III [Kg(II), Kg(III), G0(II), and G0(III), respectively] estimated with each (not with a fixed for high-molecular-weight PLLA) decreased with increasing the amount of defects per unit mass of the polymer for crystallization, i.e. with increasing the comonomer content and the density of terminal group through decreasing the molecular weight. 相似文献
158.
Masaaki Teramoto Nobuaki Ohnishi Nao Takeuchi Satoru Kitada Hideto Matsuyama Norifumi Matsumiya Hiroshi Mano 《Separation and Purification Technology》2003,30(3):215-227
A novel facilitated transport membrane for gas separation using a capillary membrane module is proposed in which a carrier solution is forced to permeate the membrane. Both a feed gas and a carrier solution are supplied to the lumen side (high pressure side, feed side) of the capillary ultrafiltration membrane and flow upward. Most of the carrier solution which contains dissolved solute gas, CO2 in the present case, permeates the membrane to the permeate side (low pressure side, shell side), where the solution liberates dissolved gas to form a lean solution. The lean solution is circulated to the lumen side. This type of capillary membrane module was applied to the separation of CO2 from model flue gases consisting of CO2 and N2. Monoethanolamine (MEA), diethanolamine (DEA) and 2-amino-2-methyl-1-propanol (AMP) were used as carriers or absorbents of CO2. The feed side pressure was atmospheric and the permeate side was evacuated at about 10 kPa. CO2 in the feed gas was successfully concentrated from 5–15% to more than 98%. The CO2 permeance was as high as 2.7×10−4 mol m−2 s−1 kPa−1 (8.0×10−4 cm3 cm−2 s−1 cmHg−1) when the CO2 mole fraction in the feed was 0.1 and temperature was 333 K. The selectivity of CO2 over N2 was in the range from 430 to 1790. The membrane was very stable over a discontinuous one-month testing period. 相似文献
159.
Stereocomplex crystallization between PLLA and PDLA is known to be disturbed when their molecular weights increase to >105 g · mol?1. Here, solution casting of PLLA and PDLA with different solvents was performed repeatedly to increase the time for the PLLA/PDLA solution in the concentration range in which only stereocomplex crystallites are formed and thus to elevate the stereocomplex crystallinity in the materials. The results of WAXS and DSC show that for all solvents examined the crystallinities of stereocomplex crystallites and homocrystallites increased and decreased, respectively, with increasing number of castings, indicating that repeated casting is a promising method to enhance stereocomplex crystallization.
160.
Norihisa Nishimura Kosuke Kaji Koh Kitagawa Yasuhiko Sawada Masanori Furukawa Takahiro Ozutsumi Yukihisa Fujinaga Yuki Tsuji Hiroaki Takaya Hideto Kawaratani Kei Moriya Tadashi Namisaki Takemi Akahane Hiroshi Fukui Hitoshi Yoshiji 《International journal of molecular sciences》2021,22(13)
Recent studies have suggested that an alteration in the gut microbiota and their products, particularly endotoxins derived from Gram-negative bacteria, may play a major role in the pathogenesis of liver diseases. Gut dysbiosis caused by a high-fat diet and alcohol consumption induces increased intestinal permeability, which means higher translocation of bacteria and their products and components, including endotoxins, the so-called “leaky gut”. Clinical studies have found that plasma endotoxin levels are elevated in patients with chronic liver diseases, including alcoholic liver disease and nonalcoholic liver disease. A decrease in commensal nonpathogenic bacteria including Ruminococaceae and Lactobacillus and an overgrowth of pathogenic bacteria such as Bacteroidaceae and Enterobacteriaceae are observed in cirrhotic patients. The decreased diversity of the gut microbiota in cirrhotic patients before liver transplantation is also related to a higher incidence of post-transplant infections and cognitive impairment. The exposure to endotoxins activates macrophages via Toll-like receptor 4 (TLR4), leading to a greater production of proinflammatory cytokines and chemokines including tumor necrosis factor-alpha, interleukin (IL)-6, and IL-8, which play key roles in the progression of liver diseases. TLR4 is a major receptor activated by the binding of endotoxins in macrophages, and its downstream signal induces proinflammatory cytokines. The expression of TLR4 is also observed in nonimmune cells in the liver, such as hepatic stellate cells, which play a crucial role in the progression of liver fibrosis that develops into hepatocarcinogenesis, suggesting the importance of the interaction between endotoxemia and TLR4 signaling as a target for preventing liver disease progression. In this review, we summarize the findings for the role of gut-derived endotoxemia underlying the progression of liver pathogenesis. 相似文献