Preparation of composites of laponite with alginate and alginic acid polysaccharides

Polymer/clay composites have several uses in fields such as engineering, agriculture, ceramics, surface coatings, absorbent materials, pharmaceuticals or catalysis. Polysaccharides, such as alginate and its acid derivatives, are biocompatible and biodegradable polymers, effective in the production of adsorbent systems, for encapsulation and controlled release of active ingredients such as drugs and fertilizers. In this work, alginate polysaccharide and alginic acid were used to form composites with laponite, both with the original clay or with clay previously functionalized with 3‐aminopropyltriethoxysilane. The properties of the composites prepared from laponite or functionalized laponite and alginic acid or alginate were compared. The interaction of laponite with alginic acid leads to composites with strong disorder in the clay structure. In all cases, composites with high contents of polysaccharides, with good thermal and mechanical properties, are obtained. Laponite‐derived composites showed high adsorption capability for Cr(III) and methylene blue from aqueous medium. Copyright © 2012 Society of Chemical Industry     

Polymer/Clay Nanocomposites: Influence of Ionic Strength on the Structure and Adhesion Characteristics in Multilayered Films

The aim of the present contribution is to understand how ionic strength, brought by the addition of salt to laponite/PEO nanocomposite dispersions, influences the texture and adhesion characteristics at nano‐ and microscales in multilayered nanocomposite films prepared from such dispersions. At the nano‐scale, SAXS and XRD measurements indicated that the clay platelets orient parallel to the film plane and that the polymer chains intercalate the clay platelets regardless of salt addition. A gradual transition from an agglomerated structure, containing polymer‐rich and clay‐rich domains, to a fine‐balanced structure with smaller distinct details without excess PEO was observed, via AFM, on the exposed edges of cryo‐microtomed films with increasing ionic strength.

     

聚乙烯吡咯烷酮及锂藻土对纤维素纳米结构纸的影响

在纤维素纳米结构纸（CNP）制备过程中,用聚乙烯吡咯烷酮（PVP）和锂藻土（Laponite）作为分散剂,以降低纤维素纳米纤维（CNF）分散体的黏度,提高其脱水速度,避免CNF的絮聚。结果表明,相比未添加PVP和锂藻土的CNP,添加0.4％（相对于CNF绝干质量,下同）PVP和0.3％锂藻土的CNP的脱水时间从135 min减少到48 min,透明度从82.0％提高到90.3％,同时密度降低了63.6%,平均粗糙度（Ra）和均方根粗糙度（Rq）分别降低了69.7%和69.1%。     

The meaning of surface area and porosity measurements of clays and pillared clays

Pillared clays (PC) generally present textural complexity, geometrical constraints and possible chemical heterogeneity by pillaring. As far as surface area and porosity measurements by physical adsorption of nitrogen are concerned, this overall complexity introduces interpretation difficulties. We consider two aspects of this problem in pillared clays.The textural complexity stems from the distribution of charge density, from the deformation of the host layers and from their entanglement. The microtexture is controlled by the wet preparation chemistry, to a large extent by the drying method as examplified by the titanium pillared montmorillonites.The geometrical constraints arise from the fact that the interlamellar space of the PC is (so far) microporous or just mesoporous. The small distance between the layers, of the order of one or a few molecular diameters, is therefore expected to perturb the arrangement of the pore filling molecules. The molecular confinement is a major source of underestimation of the total pore volume in the interlamellar space. It makes the surface area determination difficult and of little physical significance. Probably microporosity values are more valuable criterion of pillaring as shown in the titanium pillared samples.In addition to these two aspects, one has also to consider a possible chemical heterogeneity arising from the simultaneous presence of pillars, exchangeable ions and precipitated species. This can lead to a complex behaviour of surface area and microporosity as examplified by the mixed aluminium-iron pillared laponites.     

明胶/锂藻土纳米复合材料的制备与性能研究

通过溶液共混和溶剂蒸发的方法制备了明胶/锂藻土纳米复合材料,利用衰减全反射傅立叶红外光谱(ATR-FTIR)、广角X射线衍射(WAXD)、紫外-可见光谱(UV-Vis)、差示量热扫描(DSC)和热重分析(TGA)等仪器方法对材料的结构与性质进行了研究。结果表明:ATR-FTIR曲线中,除Si-O键外,各基团特征峰强度都随锂藻土含量增加而降低。WAXD谱图中未发现锂藻土的层状衍射峰,说明锂藻土完全剥离。锂藻土还对明胶的结晶性和结晶结构产生影响,在2θ=27.1°发现了新的衍射峰,并随着锂藻土含量增加峰强度变强。明胶/锂藻土纳米复合膜表现出良好的透明性,锂藻土含量对材料透明度影响不大。随着锂藻土含量的增加,明胶的熔点(Tm)先增加后降低,含5%锂藻土的纳米复合膜有最高的熔点。纳米复合膜的热稳定性明显好于纯明胶膜,并且随着锂藻土含量的增多,材料的热稳定性也提高,少量锂藻土即可大幅改善明胶的热稳定性。     

Development of polyampholyte hydrogels based on laponite for electrically stimulated drug release

Polyampholyte hydrogels (PAHs) composed of laponite, polyacrylamide and poly(3‐acrylamidopropyl)trimethylammonium chloride crosslinked with ethylene glycol dimethacrylate were synthesized and characterized for their sensitivity to external conditions and their ability to control the release of the active drug agent paracetamol. Three PAHs were synthesized by taking the weight ratio of laponite to total monomer as 7, 15 and 29%. PAHs were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis and swelling measurements carried out in various media. Equilibrium and pulsatile swelling studies were performed on all hydrogels to determine to what extent the hydrogels would respond to changes in environmental pH, ionic strength and electric field, and how fast that response would be. Paracetamol was loaded into the hydrogels, and was released into buffered solutions as a function of pulsatile changes in pH and electric field. © 2014 Society of Chemical Industry     

壳聚糖/有机锂皂石纳米复合材料的制备及抗菌性能研究

采用离子交换法将季铵盐及壳聚糖插层到锂皂石层间, 制备锂皂石基二次插层复合物。所制备的两种二次插层复合物的层间距相比于纯的锂皂石分别增加了0.276 nm和0.262 nm。用大肠杆菌(E. coli)和金黄色葡萄球菌(S. cereus)为模拟体系对二次插层复合物的抗菌性进行了检验, 利用抑菌环和平板计数法测定两种二次插层复合物的抗菌能力。抗菌结果显示, 细菌与两种复合物接触24 h后, 锂皂石/十四烷基三甲基溴化铵/壳聚糖对大肠杆菌的抗菌率可达100%, 对S.cereus的抗菌率可达85%以上, 锂皂石/十六烷基三甲基溴化铵/壳聚糖对大肠杆菌和金黄色葡萄球菌的抗菌率均可达99%以上。采用扫描电镜法及β-半乳糖苷酶活性考察了两种复合物对大肠杆菌和金黄色葡萄球菌抑菌过程及机理, 结果表明: 复合物首先通过表面带的正电荷将表面带负电的细菌吸附到材料表面, 随后借助有机物阳离子的疏水作用, 穿透细菌细胞膜, 从而达到杀菌效果。     

Nanoparticle-stabilized Alkenyl Succinic Anhydride (ASA) Emulsions: A Review

Alkenyl succinic anhydride (ASA) is a popular paper-sizing agent that is generally added to papermaking systems as an aqueous emulsion. Herein, we reviewed the recent work focusing on ASA emulsions stabilized by solid particles. Solid particle-stabilized ASA emulsions generally possess high ASA content and exhibit good sizing performance. The particles that have been used to stabilize ASA emulsions typically include montmorillonite, laponite, alumina, TiO₂, Fe₃O₄, polyaluminum sulfate (PAS), and cellulose nanocrystals (CNCs). Montmorillonite is the first extensively studied particle stabilizer for ASA emulsions. Laponite is undoubtedly the most competent particle stabilizer for preparing ASA emulsions with high sizing efficiency. Montmorillonite and laponite can be used individually as stabilizers after modification or as co-stabilizers with other particles or polymers. TiO2, alumina, PAS, and CNCs are commonly used as stabilizers either individually or with other particles.     

Swelling and mechanical behavior of modified poly(vinyl alcohol)/laponite nanocomposite membranes

Nanocomposite (NC) membranes based on hydrophobically modified PVA and laponite were synthesized with varying laponite content in the feed. The incorporation of laponite in NC membranes was investigated by FTIR spectroscopy and thermogravimetric analysis. The swelling ratio of membranes was determined as a function of temperature and laponite content. Swelling studies of NC membranes exhibited the decrease in swelling with an increase in laponite content in the NC membranes. The swelling ratio of NC membrane with 20% laponite slightly increased with an increase in temperature. Dynamic mechanical analysis showed the systematic increase in storage modulus with laponite content, which indicates the enhancement of mechanical property upon laponite addition. There was also a decrease in the tan δ peak values of NC membranes with an increase in laponite content in NCs. The permeabilities through NC membranes as a function of solute size and laponite content were studied and the results showed molecular screening based on size. The permeability of solute reduced due to the presence of well‐dispersed laponite in the NC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2896–2903, 2007     

Strengthening mechanism of poly(acrylamide)/graphene oxide/laponite dual nanocomposite hydrogels

Laponite or graphene oxide (GO) is usually used as a multifunctional crosslinker or a nanofiller to improve the nanocomposite gel strength. To explore the strengthening mechanism of GO/Laponite‐based dual nanocomposite hydrogels, we synthesized a dual nanocomposite hydrogel through in situ polymerization of acrylamide (AM) in the dispersion of GO and Laponite. The interactions between GO and Laponite were confirmed by rheological test. GO and Laponite nanosheets were exfoliated well and dispersed uniformly in the hydrogels at low concentration of GO. Crosslinking network and thermal behaviors were investigated with respect to the concentration of GO and Laponite. The gel exhibited a high mechanical strength of 391 kPa with extensibility of 1420% and a high toughness of 2.58 MJ/m³, which was expected to be applied in biological engineering field. GO is not a much more effective agent than Laponite due to formation of GO aggregates in high concentration of GO. This work provides a guidance for the synthesis of tough dual nanocomposite hydrogels. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44963.