共查询到20条相似文献,搜索用时 0 毫秒
1.
Present now the application of microcellular polymeric materials in biomedical field is growing rapidly, as that of guided tissue regeneration and cell transplantation. As far as guided tissue regeneration is concerned, porous implants are used as size selective membrane to promote the growth of a special tissue in a healing site. Ideally, the implant should be inherently biocompatible,have well-defined cell size and be resorbable with appropriate biodegradation rates.Poly(a-caprolactone) (PCL) is a kind of materials suit for the demands above. PCL is biocompatible and biodegradable aliphatic polyester which is nontoxic for living organisms and bioresorbable after a period of implantation. Because of its unique combination of biocompatibility, permeability and biodegradability, PCL and some of its copolymer with lactides and glycolide have been widely applied in medicine as artificial skin, artificial bone and containers for sustained drug release.Goel and Beckman have reported a new method to generate microcellular poly(methy l methacrylate) foams in which the samples are saturated with CO2 under a series of supercritical (SC)conditions, and then the system is rapidly depressurized to atmospheric pressure at constant temperature. Unlike traditional methods, it reduces glass-transition temperature (Tg) of the mixture to below the experimental temperature rather than directly heat the system above Tg. In this process of nucleation, no phase separation occurs as well as no phase boundary meets, so the cellular structure of the foam can be retained better.In this work, we have generated PCL foams by using supercritical CO2. Because of the low glass transition temperature (Tg = -60 ℃) of PCL far below the ice point, the experimental temperature in our study is much higher than Tg, which is different from the studies by others before. A series of variable factors on the foam structure as saturation temperature, saturation pressure, saturation time and depressurization time were studied. The experimental results indicate higher saturation temperature produce reduced bulk densities while holding other variable experimental conditions,and different saturation pressure produce different nucleation process. In addition, saturation time has profound effect on the structure of the product. XRD result shows that the foamed PCL is more inclined to degrade than the original PCL for the reason of its lower crystallinity. 相似文献
2.
应用超临界CO2制备微孔聚丙烯的微孔形貌 总被引:1,自引:0,他引:1
研究了应用超临界CO2技术制备微孔聚丙烯时发泡条件和聚丙烯(PP)的熔体强度对微孔形貌的影响。结果表明:在一定的饱和压力下,随着温度的升高,PP的变形能力改善,有利于泡孔的长大。随着饱和压力的增加,PP的熔点降低,升高压力和升高温度具有一定的等同作用。由于CO2在PP内分散的不同,高压低温时得到的泡孔比高温低压时得到的泡孔要规整。降压速率对泡孔形貌的影响因饱和压力的大小而异,饱和压力较高时随着降压速率的提高,孔密度增加,泡孔形貌经历了一个从球体到多面体转变的过程。由于PP熔体强度较低,在发泡温度和PP熔点之间非常接近时,CO2气体容易冲破孔壁而使泡孔呈开孔结构。 相似文献
3.
4.
5.
6.
在超临界二氧化碳中, 利用马来酸锌催化二氧化碳与环氧化物反应合成环状碳酸酯. 单独使用马来酸锌作为催化剂时, 对二氧化碳与环氧丙烷反应的催化活性较低, 而在DBU、DMAP、三乙胺、吡啶、咪唑或4-氨基吡啶等有机碱的存在下, 反应活性较高, 产物的收率得到明显提高. 有机碱作用的强弱顺序为DBU>Et3N>咪唑>4-氨基吡啶>DMAP>吡啶. 在压力为8 MPa, 温度110 ℃, 反应时间48 h条件下, 马来酸锌与DBU组成的二元催化系统可以催化二氧化碳与环氧丙烷反应, 得到83.4%产率的碳酸丙烯酯. 该二元系统也能催化其它环氧化物高产率地转化为相应的环状碳酸酯. 相似文献
7.
本文主要介绍了超临界近5年来超临界二氧化碳中的有机反应研究的最新进展,包括加氢反应、氧化反应、羰基化反应、碳碳键形成反应、酯化反应和酶催化反应的研究现状;同时,还介绍了超临界二氧化碳作为反应底物用于合成碳酸酯和氨基甲酸酯的研究进展;并对未来的发展进行了展望。 相似文献
8.
9.
近年来,超临界二氧化碳(sc-CO2)在聚合反应中的应用受到了越来越多的关注。本文主要综述了以sc-CO2为反应介质的自由基聚合、阳离子聚合、过渡金属催化聚合、热致开环聚合、溶胶-凝胶聚合以及氧化耦合聚合的研究概况。一系列研究结果表明sc-CO2是非常有前途的反应溶剂,在高分子合成领域将会有更加广阔的应用前景。 相似文献
10.
11.
12.
本文介绍了绿色化学发展方向之一 ,绿色溶剂的选择、使用 ,并重点介绍超临界二氧化碳的发现、发展、机理和应用。 相似文献
13.
本文介绍了绿色化学发展方向之一,绿色溶剂的选择、使用,并重点介绍超临界二氧化碳的发现、发展、机理和应用。 相似文献
14.
Inga A. Ronova Lev N. Nikitin Ekaterina A. Sokolova Irina Bacosca Ion Sava Maria Bruma 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):929-936
Two series of polyheteroarylenes have been investigated with regard to their physical properties before and after swelling with supercritical carbon dioxide. The study of the dependence of glass transition temperature and free volume of polymers on their conformational rigidity showed that the process of swelling in supercritical carbon dioxide is influenced by the voluminous side groups and by the high boiling solvent N-methylpyrolidinone used for the preparation of the polymers which facilitates the formation of crosslinks or complexes with the macromolecular chains. 相似文献
15.
A general,green and efficient method for the synthesis of transdiiodoalkenes in CO2(sc) has been developed.Trans-diiodoalkenes were obtained stereospecifically in quantitative yields via diiodination of both electron-rich and electron-deficient alkynes in the presence of KI,Ce(SO4)2 and water in supercritical carbon dioxide [CO2(sc)]at 40℃. 相似文献
16.
17.
Jun LIU Hong Ping LI Zhi Min LIU Bu Xing HAN* Hai Ke YAN Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2001,(5)
Over the past decade there has been a growing interest in using supercritical fluids (SCFs) to promote reactions and to replace hazardous solvents with environmentally benign solvents, such as supercritical CO2 and H2O. Many reactions in SCFs have been studied1, including polymerization in scCO22. It is known that a small change in the pressure near critical point of a fluid causes a significant change in density-dependent properties such as the solubility parameter, viscosity, and dielect… 相似文献
18.
19.
Organic reactions in supercritical carbon dioxide (scCO2) have facilitated great progress in recent years . ScCO2, as an environmentally friendly reaction medium, may be a substitute for 1 volatile and toxic organic solvents and show some special advantages. Firstly, CO2 is inexpensive, nonflammable, nontoxic and chemical inert under many conditions. Secondly, scCO2 possesses hybrid properties of both liquid and gas, to the advantage of some reactions involving gaseous reagents. Control o… 相似文献
20.
The effect of chain length on the enzymatic hydrolysis of various p-nitrophenyl esters was investigated. Specifically, the hydrolysis of various esters p-nitrophenyl butyrate (PNPB), p-nitrophenyl caprylate (PNPC), p-nitrophenyl laurate (PNPL), p-nitrophenyl myristate (PNPM) and p-nitrophenyl palmitate (PNPP) was studied in supercritical carbon dioxide (ScCO2) with lipase (Novozym 435). This indicates that the conversion of nitrophenyl esters decreases with increasing chain length.
The effect of various parameters such as amount of water added, temperature, and enzyme loading was studied. The optimum temperature
for the hydrolysis of PNPB and PNPC was 50°C but was 55°C for PNPL, PNPM, and PNPP in ScCO2. The reactions were also conducted in acetonitrile as the solvent, and it was found that the reactions reach equilibrium
much faster in ScCO2 than in acetonitrile. The kinetics of the hydrolysis reactions were modeled using a Ping Pong Bi Bi model. 相似文献