The colloidal behaviour of kraft lignin III. Swelling behaviour and mechanical properties of kraft lignin gels

Summary Kraft lignin gels have been synthesized by cross-linking kraft lignin (Indulin ATR) in water with varying amounts of epichlorohydrin under alkaline conditions. The effects of pH and salt concentration on the swelling behaviour and on the mechanical properties of these gels have been investigated.Swelling was determined gravimetrically and the mechanical properties of the gels were tested under uni-axial compressive creep in the time interval 1–900 s. The gels show a linear viscoelastic behaviour without viscous flow.The kraft lignin gels exhibit a swelling behaviour typical for polyelectrolytic networks, i. e. the degree of swelling increases with an increasing number of ionized groups and decreases with increasing salt concentration. The swelling behaviour and ion exchange capacity were found to be nonspecific towards type of alkaline solution (LiOH, NaOH, and KOH).The ability of the carboxylic groups to form intermolecular hydrogen bonds has a strong influence on the mechanical properties of the gels. Creep compliance and creep rate increase greatly when the carboxyl groups are dissociated. It is therefore concluded that the effective number of crosslinks in the networks in addition to chemical cross-linking is also dependent on the state of dissociation of the carboxylic groups.With 11 figures and 1 table     

Comparative Study on the Collapse Transition of Poly(N-isopropylacrylamide) Gels and Magnetic Nanoparticles Loaded Poly(N-isopropylacrylamide) Gels

A novel polymer gel exhibiting simultaneous temperature and magnetic field sensitivity has been prepared and studied. Poly(N-isopropylacrylamide) (PNIPA) and magnetic nanoparticles (magnetite, Fe₃O₄) loaded PNIPA gel beads with mm size and monolith gels with cm size were prepared. The dependence of swelling degree on the temperature has been studied. The effects of cross-linking density and the presence of magnetic nanoparticles on the equilibrium swelling degree as well as on the collapse transition have been investigated. Swelling kinetic measurements were also made. By comparing the equilibrium swelling properties of PNIPA and magnetite loaded PNIPA gels it was found that the built in magnetic nanoparticles do not modify the temperature sensitivity of these gels. Within the experimental accuracy the temperature of the collapse transition was not sensitive to the presence of magnetic particles. We have compared the swelling behaviour of mm size gel beads to the cm size monolith gels in order to study the influence of surface skin layer on the swelling equilibrium. It was established that the extent of surface skin formation was decreased by the presence of magnetic particles.     

pH敏感阳离子聚电解质凝胶的溶胀和释药性能

共聚物;pH敏感阳离子聚电解质凝胶的溶胀和释药性能     

Swelling kinetics of anisotropic filler loaded PDMS networks

The kinetics of swelling of spherical poly(dimethyl siloxane) (PDMS) composite networks in cyclohexane has been studied. The PDMS composite gels contain magnetite and iron particles built in the network either in randomly distributed form or in chain-like structure. The composite gel becomes anisotropic in the terms of both, mechanical and swelling properties. As a consequence the swelling kinetics can be characterized by direction dependent relaxation time. The swelling kinetics of these samples has been compared to that of pure PDMS gels. It was found that Li-Tanaka theory can be applied to describe the swelling kinetics of PDMS network.     

化学改性大豆蛋白凝胶溶胀过程规律的研究

将大豆蛋白(SPI)经预热处理、EDTAD酰化和戊二醛交联,制备出改性大豆蛋白凝胶.通过红外与化学法研究了改性大豆蛋白分子的结构变化,结果表明,经EDTAD改性,大豆蛋白分子的侧链基团和分子链构象均发生变化;侧链的游离氨基与EDTAD发生酰化反应,为蛋白质分子链引入羧基;基团分析数据显示,改性大豆蛋白分子中游离氨基数减少,羧基数增加,增加的羧基数与减少的氨基数之比约为3:1.研究了改性大豆蛋白凝胶的溶胀率变化,并对溶胀数据进行数学处理,分析了不同mEDTAD:mSPI的凝胶的溶胀过程规律,结果显示,mEDTAD:mSPI为0,0.05,0.1和0.2的改性大豆蛋白凝胶在水中的溶胀率为24.2,54.01,87.27和95.87,说明分子链引入一定量的EDTAD使凝胶溶胀率增大;其溶胀特征指数为0.5,表现为Fickian扩散.研究了改性凝胶在不同pH下的溶胀过程规律,结果显示,在pH4.30和6.08时,凝胶溶胀特征指数n范围是0.5n1,表现为non-Fickian扩散,而在碱性pH10.04,凝胶特征溶胀指数为0.5,仍表现为Fickian扩散.改性大豆蛋白凝胶溶胀率对pH变化具有敏感性,其溶胀-消溶过程曲线呈"W"形,显示凝胶具形状记忆功能.     

PREPARATION AND PROPERTIES OF CLAY/POLY(N-ISOPROPYLACRYLAMIDE-co-ACRYL AMIDE)NANOCOMPOSITE HYDROGELS

Polymer hydrogels as a kind of soft materials have attracted increasing scientific and technological interest in past several decades. These materials have been applied widely in many fields [1], such as molecular filter [2,3], superabsorbent [4], and contact lenses [5] etc. However, synthetic polymeric hydrogels are seldom used as mechanical devices due to the lack of mechanical strength. Therefore, it is very imperative to improve their mechanical properties for wider use of polymeric hydrog…     

PREPARATION AND PROPERTIES OF CLAY/POLY（N-ISOPROPYLACRYLAMIDE-co-A CRYL AMIDE） NANOCOMPOSITE HYDROGELS

A series of clay/poly(N-isopropylacrylamide-co-acrylamide) nanocomposite hydrogels (S-N-M gels) have been successfully prepared by in situ polymerization. The mechanical properties,swelling behavior of S-N-M gels and the transparency changes during polymerization of S-N-M gels have been systematically investigated. Compared to traditional hydrogeb, S-N-M gels show excellent tensile properties and their swelling ratio increases with increasing acrylamide (AAm) content. The results of stress relaxation indicate that the stress loss decreases with increasing AAm content. It was surprisingly found that the transparency during all S-N-M gel synthesis changes abruptly, and the changes become more abrupt with increasing N-isopropylacrylamide content. It was concluded that the fact may be related to the hydrophilicity of copolymers. The weaker the hydrophilicity of copolymer, the more apparent the transparency change during S-N-M gels polymerization. We believe the relationship between hydrophilicity of copolymer and transparency changes will help to design novel nanocomposite hydrogels.     

Swelling equilibria and volume phase transition of polyelectrolyte gel with strongly dissociated groups

The peculiarities of the swelling equilibrium and volume phase transition of polyelectrolyte copolymer gels consisting of acrylamide and 2-acrylamido-2-methyl-1-propane sulphonic acid (AAm/AMPS) have been studied as a function of copolymer composition and gel structure. Equilibrium swelling for AAm/AMPS gels in buffer solutions, pure water and aqueous salt (NaCl) solutions were investigated. The swelling curves were calculated using the Hasa–Ilavský–Dušek theory and obtained experimentally. The agreement is reasonably good, and the HID theory can be used to estimate the swelling and structural parameter of AAm/AMPS gels. The volume phase transition has been generated by changing the solvent composition by progressive substitution of water by acetone. The critical interaction parameter corresponding to collapse depends strongly on the composition of the gel, since the extent of collapse is determined by composition and cross-link density of the gel.     

Swelling-contraction of sodium polyacrylate hydrogels in media with various pH values

The swelling kinetics of sodium polyacrylate gels has been studied in media with different pH values. The pH dependence of the degree of equilibrium swelling shows a maximum at pH 6. The degree of swelling decreases with an increase in the crosslink density, and this dependence follows an S-shaped pattern for all examined gels. When a gel swollen in media with pH 3–13 is dried in air, its contraction is reversible, while in the case of the gel swollen in acidic media at pH < 3, the process is irreversible owing to the replacement of sodium ions with protons.     

Swelling of hydrophobically modified poly(acrylamide) and poly(acrylamide)-co-(acrylic acid) gels in surfactant solutions

A series of hydrophobically modified polyacrylamide and polyacrylamide-co-poly(acrylic acid) gels with systematically varying hydrophobicity were prepared by free-radical polymerization of acrylamide, n-alkylacrylamides (n = 10, 12, and 14), and acrylic acid. The swelling of these gels was examined in water and in both anionic and cationic surfactant solutions. It was found that the gels which incorporated acrylic acid showed extremely high swelling in water. Maximum swelling was observed in gels which incorporated 10 mol% acrylic acid. The swelling of these gels was much less in solutions of both anionic and cationic surfactants than in water. The gels which did not incorporate acrylic acid demonstrated little swelling in water, but showed increased swelling in both anionic and cationic surfactant solutions with increased hydrophobicity of the gel. Received: 1 February 1999 Accepted in revised form: 5 March 1999     

高机械性能的聚(丙烯酸-co-甲基丙烯酸十八酯)疏水缔合凝胶的溶胀行为研究

以丙烯酸(AA)、甲基丙烯酸十八酯(OMA)、十二烷基硫酸钠(SDS)为原料,采用胶束共聚的方法合成了疏水缔合(HA)凝胶.在HA凝胶内部,表面活性剂SDS与疏水单体OMA组成的增溶胶束起到物理交联作用,将亲水的聚合物链交联起来.通过单向拉伸试验证实了该凝胶具有较高的机械性能.此外,也测试了HA凝胶在不同pH值溶液中的溶胀行为.结果显示,HA凝胶具有特殊的溶胀行为,其溶胀过程可以分为凝胶溶蚀、溶胀平衡和凝胶瓦解3个阶段.在强酸性条件下,凝胶的溶胀被抑制,没有出现凝胶瓦解阶段.在强碱性条件下,凝胶的溶胀被促进,溶胀平衡阶段被越过.盐的存在也会抑制HA凝胶的溶胀,但在SDS溶液中,溶液中的SDS会促使凝胶中的疏水改性聚合物溶解到溶液中去,组成新的缔合结构,而使溶液增稠。     

Effects of counter ions of clay platelets on the swelling behavior of nanocomposite gels

The effects of replacing the native Na(+) counter ions associated with the clay platelets by various other cations on the swelling behavior of nanocomposite (NC) gels consisting of an organic (polymer)/inorganic (clay) network were investigated. The negative surface charge of the clay platelet conferred an ionic nature on the NC gels making them a type of polyelectrolyte gel; consequently, the swelling behavior of the NC gels was strongly influenced by the valence of the co-existing counter ions. NC gels containing monovalent cations such as Na(+), K(+) and Li(+) exhibited large swellings and subsequent deswelling in water after attaining maximum degrees of swelling. In contrast, introduction of multivalent cations such as Ca(2+), Mg(2+), and Al(3+) into NC gels depressed markedly both the swelling and subsequent deswelling. The decreased swelling and suppressed deswelling with multivalent ions were strongly influenced by the initial gel state and result from the formation of additional cross-links through ionic interactions between the clay platelets and the multivalent cations. Also, the similar swelling behaviors were observed for all NC gels with different clay concentration. Further, reversible absorption/desorption and selective absorption of multivalent cations were observed for the NC gels examined.     

The preparation and characterisation of novel polyether gels

Poly(ethylene oxide)s end-capped with n-alkane chains (C₁₆-C₂₁) have been found to form stable gels in aqueous media. The crosslinks are believed to occur through association of the n-alkane chains. The dependence of the degree of swelling of the gels on the lengths of the alkane and poly(ethylene oxide)(M_n= 10000, 20000 and 30000) chains were studied. Degrees of swelling have been compared with results predicted by simple network theory.     

聚丙烯酸凝胶溶胀行为的研究

本文合成了一系列不同交联度的聚丙烯酸凝胶,测定了这些凝胶在不同ｐＨ值及温度下的综合溶胀行为,包括用经典的间断称重方法测定溶胀动力学曲线,用溶胀性能自动测定仪测定溶胀应力变化的动力学曲线及平衡溶胀度等。这这类环境敏感材料的应用提供了科学数据。     

Polyampholyte gels: swelling,collapse and interaction with ionic surfactants

Two series of polyampholyte gels formed from sodium methacrylate and diallyldimethylammonium chloride with variable composition were synthesized in water and in aqueous salt solution. It is shown that the swelling properties of polyampholyte gels are directly related to their chemical structure, which is defined by the process of gel synthesis. The swelling ratio of the polyampholyte gels prepared in salt solution is large compared with the gels prepared in pure water i.e. the polyampholyte gels with balanced stoichiometry show minimal swelling.The interaction of the polyampholyte gels with ionic surfactants (cationic, cetylpyridinium chloride and anionic, sodium dodecylbenzenesulphonate) was studied. It was shown that for polyampholyte gels with an excess of the charges of one sign the addition of oppositely charged surfactant leads to the collapse of the gel. It was found that the efficiency of surfactants absorption is determined by the ratio of positive and negative charges in the chains of polyampholyte gels.     

STUDY ON ACRYLAMIDE-SODIUM ACRYLATE COPOLYMER GELS

Acrylamide-sodium acrylate copolymer hydrogels have been obtained by radiation techniques. Two different methods have been used to introduce—COONa groups into polymer chains of the gels: (1) by partial hydrolysis of acrylamide homopolymer gel; (2) by direct copolymerization and crosslinking of acrylamide and sodium acrylate in aqueous solutions. It was found that the gels obtained in different ways had different properties, the swelling character of the gels obtained by partial hydrolysis were more sensitive to pH of swelling aqueous media, in order to explain these differences, ~(13)C-NMR techniques were used to investigate the sequence distribution of monomer units of both gels.     

离子键交联的聚两性电解质凝胶在不同pH和不同电解质溶液中溶胀行为研究

以丙烯酸(AA)和甲基丙烯酸二乙氨基乙酯(DEAM)形成的离子复合物与丙烯酰胺(AAm)共聚,合成了一种新型的离子键交联的聚两性电解质凝胶(PADA).由于分子之间的氢键作用,PADA凝胶并不是在A/C(负正离子单体摩尔比)为1,而是在A/C为1.55处有最大消溶胀.与共价键交联的聚两性电解质凝胶相比,PADA凝胶的溶胀行为具有更强的pH敏感性.PADA凝胶在不同pH缓冲溶液中的溶胀行为表明,在pH 3~4之间消溶胀程度最大.在偏离该pH区域时凝胶均发生溶胀.但凝胶的溶胀程度在pH<3的酸性溶液中随A/C的增加而降低;而在pH>4的偏碱性溶液中随其增加而增加.在不同价数的离子溶液中,离子浓度对于PADA凝胶的平衡溶胀有着不同的影响.对于一价的NaCl溶液,PADA凝胶有典型的反聚电解质效应.但对于高价的CaCl2和柠檬酸三钠溶液,只在较低的浓度下,才表现出反聚电解质效应.而在较高盐浓度时,随盐浓度的增加其溶胀比反而降低.这可能与高价离子形成的离子键交联有关.与pH对PADA凝胶溶胀程度的影响相似,在CaCl2溶液中,PADA凝胶的溶胀程度随A/C的增加而降低;而在柠檬酸三钠溶液中则刚好相反.这种独特的溶胀行为似乎与高价离子电荷的正负性有关.     

Dynamic swelling performance of hydrophobic hydrogels

Conventional gels manifest monotonous swelling or shrinking performance upon immersing in solvents until reaching an equilibrium state. Recently, we discovered that the “hydrophobic hydrogels” prepared from hydrophobic polymer networks demonstrated dynamic swelling performance without equilibrium states. Upon water immersion, the gels expanded tremendously at the first stage until reaching a swelling peak; subsequently, the gels shrunk at an extremely slow rate. While this phenomenon endows the ...     

Swelling kinetics of cross-linked polymer gels based on polystyrene and poly(vinyl alcohol) in aqueous solutions of electrolytes and sucrose

The swelling kinetics of polymer gels has been studied in water and aqueous solutions by optical micrometry. Cross-linked hydrophilic polymers based on polystyrene and poly(vinyl alcohol) have been used as gel-forming materials. The effects of the natures of the matrices and polar groups of the polymers and their cross-linking densities and granule sizes, as well as the properties of external phase, on the swelling kinetics of the polymer gels have been investigated. The experimental results have been processed in terms of a heterophase kinetic model. The applicability of the model to describing the behavior of all studied systems has been shown.     

温度敏感聚(N-异丙基丙烯酰胺-co-甲基丙烯酰氧乙基二甲基辛基溴化铵)水凝胶的溶胀性能研究

由于改变亲水／疏水单体比值、与离子单体共聚心、改变凝胶内部结构等均可不同程度地调整温敏水凝胶的溶胀性能,本研究选择一种既含疏水烷基又含季铵盐正离子型亲水基团的两亲性单体——甲基丙烯酰氧乙基二甲基辛基溴化铵（ADMOAB）,结构如示意图1所示．与N-异丙基丙烯酰胺（NIPAM）聚合,制备了P（NIPAM-co-ADMOAB）共聚水凝胶,以便在引入离子型结构单元的同时,改变凝胶体系中亲水／疏水单体比值,避免单纯增加疏水单体引起的水凝胶溶胀性降低问题,并考察了ADMOAB对水凝胶溶胀性能的影响,对该类水凝胶迄今鲜见相关文献报道．该研究对进一步了解水凝胶的构效关系、探索有效控制溶胀性能的途径具有积极意义．