Influence of degree of grafting and grafting temperature on the permeabilities of grafted polypropylene membranes

Polypropylene dialysis membranes were prepared using cobalt-60 gamma radiation to directly graft 2-hydroxyethyl methacrylate (HEMA) onto polypropylene (PP) membranes. The surface structures of both the grafted membranes and the PP membrane were observed by using FTIR–PAS and ESCA methods. The X-ray diffraction diagrams of the PP and PP-g-HEMA membranes indicated a transformation process of the β-form toward the α-form crystallinity with increasing degree of grafting. The SEM data of the membrane grafted under a low grafting temperature showed many spheres of PHEMA embedded in the PP matrix, whose size was well distributed and increased with the degree of grafting. The influences of the degree of grafting and grafting temperature on the permeabilities of PP-g-HEMA membranes toward urea and creatinine were studied in a dialyzer. In all cases, the PP-g-HEMA membrane obtained under higher grafting temperature showed higher permeability toward those solutes. The permeation coefficients of urea and creatinine through the PP-g-HEMA membrane obtained at 59°C were about 10.4 and 28.8 times that through the PP membrane, respectively. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:83–89, 1998     

X-ray diffraction studies of some halatopolymers

The crystal structure and degree of crystallinity of a number of melt-spinnable halatopolymers has been investigated. These materials can be characterized by a well defined ‘ionic’ peak at low diffraction angle. In general they have a tetragonal unit cell, although the more perfectly crystalline materials may well belong to a triclinic crystal system. Changes in crystallinity were investigated in terms of method and conditions of preparation, and of thermal treatment. Stannous dicar?ylates had the most widely variable crystallinity.     

聚丙烯蜡接枝丙烯酰胺的合成工艺研究

用熔融接枝方法制备了聚丙烯蜡接枝聚丙烯酰胺(PPW-g-PAM),用红外光谱、化学滴定法对接枝产物进行了定性和定量的表征。讨论了单体、引发剂、反应时间对接枝率和接枝效率的影响,并利用红外光谱分析证实了PPW-g-PAM的存在。结果表明:在100～110℃下,PPW用量为50 g,AM用量为10 g,BPO用量为2．0g,反应时间为2 h时,可获得最佳的接枝率和接枝效率。     

柠檬酸钠对纳米碳酸钙结晶的影响

用石灰乳液碳酸化法制备纳米碳酸钙,在不添加任何添加剂的条件下制备出平均粒径为40 nm的立方状方解石型碳酸钙,以柠檬酸钠为添加剂,制备出最大长径比为9的链状方解石型碳酸钙。利用SEM,TEM和XRD分析手段,研究了柠檬酸钠及其加入量对碳酸钙产品颗粒形貌和结构的影响。柠檬酸钠用量为氢氧化钙质量的2%,进行碳酸化反应,在制得的长径比为9的链状碳酸钙悬浮液中,连续补加同质量分数的石灰乳,同时控制二氧化碳的通入速度,继续碳酸化,得到类似雪花状和链状两种形态同时存在的碳酸钙产品。     

预处理方式对淀粉酯化效果的影响

采用酶进行先活化再催化的双效作用,将玉米淀粉酶解预处理,然后在有机溶剂及酶催化条件下制备硬脂酸淀粉酯。用IR、DSC、SEM及X-ray衍射对硬脂酸淀粉的结构进行表征。结果表明,酶解对淀粉改性效果最明显,酶解预处理后淀粉颗粒表面粗糙,并出现微孔,其衍射峰强度较原淀粉低,但晶型未变;活化后的淀粉酯化取代度提高最显著,且酶解预处理90min的取代度,其值为0.1174,高于酶解40min的取代度,DS为0.0179。     

微晶纤维素的性质与应用

微晶纤维素是一种新兴的纤维素功能材料。微晶纤维素的独特性质使它在医药、食品、日用化学品等领域获得广泛的应用。本文从应用角度阐述了微晶纤维素的理化性质和形态结构，介绍了微晶纤维素的工业产品的主要应用途径。     

Effect of solvents on radiation‐induced grafting of styrene onto fluorinated polymer films

The effect of solvents on radiation‐induced grafting of styrene onto commercial fluorinated polymer films such as poly(tetrafluoroethylene) (PTFE), poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) and poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA) was investigated by a simultaneous irradiation technique. Three solvents, ie methanol, benzene and dichloromethane, were used to dilute styrene under various irradiation doses, dose rates and monomer concentrations. The effect of addition of mineral and organic acids on the degree of grafting in the presence of the three solvents was also studied. The degree of grafting was found to be strongly dependent upon the type of solvent and composition of the monomer/solvent mixture. Dilution of styrene with dichloromethane in various grafting conditions was found to enhance dramatically the degree of grafting compared with other solvents, and the maximum degree of grafting was achieved at a monomer/solvent mixture having a composition of 60:40 (v/v). The formation of polystyrene grafts in the three fluorinated films was verified using FTIR spectrometry. © 2001 Society of Chemical Industry     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. II. Characterization of sulfonated graft copolymer membranes

PFA‐g‐polystyrene sulfonic acid membranes were prepared by simultaneous radiation‐induced graft copolymerization of styrene onto poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA) film followed by sulfonation. The membrane physico‐chemical properties such as swelling behavior, ion exchange capacity, hydration number, and ionic conductivity were studied as a function of the degree of grafting. Thermal as well as chemical stability of the membranes was also investigated. The membrane properties were found to be mainly dependent upon the degree of grafting. The water uptake, ion exchange capacity, hydration number, and ionic conductivity of the membranes were increased, whereas the chemical stability decreased as the degree of grafting increased. The membranes showed reasonable physico‐chemical properties compared to Nafion 117 membranes. However, their chemical stability has to be further improved to make them acceptable for practical use in electrochemical applications. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1–11, 2000     

Grafting of acrylamide to nylon-6 by the electron beam preirradiation technique: 3. Degree of crystallinity at high grafting yields

X-ray diffraction measurements of nylon-6 grafted with acrylamide indicate that the crystallites of the nylon-6 are only marginally affected by very extensive radiation grafting. Considerable stresses are built up in the samples during their grafting. Fusion endotherms of the grafted samples are masked to a large extent by the stress-release exotherms. Consequently, values of ΔH_f derived from d.s.c. measurements of the unannealed samples are not reliable. Stresses built up during grafting may be at least partially released by treating them with 65% formic acid at room temperature. This annealing procedure is preferable to thermal annealing because of the decomposition of polyacrylamide at elevated temperatures. Perfection and size of the nylon-6 crystallites also increases significantly as result of such treatment.     

纤维素的酸活化

以合成醋酸丙酸纤维素中的酸活化为例对纤维素的酸活化进行了研究。发现酸活化温度和活化时间对结晶破坏影响很大,在活化温度为40～60℃、活化时间小于2 h时,结晶破坏速率较快;活化温度对纤维素平均聚合度的影响较大,当活化温度高于80℃时,纤维素降解显著;活化前期,平均聚合度下降明显;活化过程通氮可以减少纤维素的氧化和水解;红外和X-射线衍射结果表明酸活化过程中主要发生物理溶胀,除了降解,无其它化学反应发生。