Thermal stability, polymer hydroxides

J. Liu, G. M. Chen, and J. P. Yang, Preparation and characterization of poly(vinyl chloride)/layered double hydroxide nanocomposites with enhanced thermal stability. Polymer, 49 (2008), 3923-7. 

The first polymer prepared was from the ammonium salt of the maleamic acid 106. Acid 106 was reacted with ammonium hydroxide to form the water soluble ammonium maleamate salt which was in turn cast as a film upon glass [6]. Evaporation of the water followed by thermal curing of the salt at 175 °C provided a pale yellow coating which adhered quite well to the glass and was not affected by a variety of organic solvents. It also showed thermal stability up to... 

By reacting aluminum hydroxide with oxalic acid, basic aluminum oxalate can be produced, which is thermally stable to 330°C, losing 51% of its mass on decomposition at temperatures above 450°C. It is reported to have a flame-retarding and smoke-suppressing action similar to ATH, but because of its increased thermal stability, it can be used in polyamides and thermoplastic polyesters. However, unlike magnesium hydroxide, in these polymers it does not cause hydrolytic degradation.2... 

L. Haurie, A.I. Fernandez, J.I. Velasco, J.M. Chimenos, J.M. Lopez-Cuesta, and F. Espiell, Thermal stability and flame retardancy of LDPE/EVA blends filled with synthetic hydromagnesite/aluminium hydroxide/aluminium hydroxide/ montmorillonite mixtures, Polym. Degrad. Stabil., 2007, 92 1082-1087. 

Effects of Hydroxy Double Salts and Related Nanodimensional-Layered Metal Hydroxides on Polymer Thermal Stability... 

In order to become a viable alternative, MIP-based assays need to offer an added value to the conventional antibody-based immunoassays. Some characteristics of the MIP-based assays are summarised in Table 14.1. Superior characteristics of MIPS in comparison to antibodies are observed with respect to chemical, mechanical and thermal stability. The MIPs are compatible with autoclave conditions (120°C, 20 min) and are unaffected by acid and base treatment [7]. In fact, to achieve as complete removal of imprint molecules as possible, in the author s laboratory it is routine to include a wash step with 5 M sodium hydroxide in the MIP synthesis work-up protocol. The possibility of using a wider range of assay solvents, namely both aqueous and organic solvents, enables the solubility of the analyte to be assured and problems with non-specific adsorption minimised. Furthermore, high polymer stability leads to improved shelf life, where the MIP can be stored for several years in the dry state at ambient temperatures. 

Thermal Stabilization of Polyformals. Polyformals, built up in solution, were neutralized with a little ammonium hydroxide when they were to be isolated by concentration under reduced pressure on the steam bath. This prevented breakdown of the polymer because of the acidic catalyst. The degradation was particularly bad with polyformals obtained from primary diols (cyclohexanedimeth-anol and decanediol). In one experiment, the polyformal of decanediol was obtained with an inherent viscosity of 0.9 when the catalyst had been neutralized and 0.3 when it had not been neutralized. Breakdown under these conditions was not observed with the prepolymer of tetramethylcyclobutanediol. 

It has been observed from the above discussion that mechanical, physico-chemical and fire retardancy properties of UPE matrix increases considerably on reinforcement with surface-modified natural cellulosic fibers. The benzoylated fibers-reinforced composite materials have been found to have the best mechanical and physico-chemical properties, followed by mercerized and raw Grewia optiva fibers-reinforced composites. From the above data it is also clear that polymer composites reinforced with 30% fibers loading showed the best mechanical properties. Further, benzoylated fibers-reinforced composites were also found to have better fire retardancy properties than mercerized and raw fibers-reinforced polymer composites. Fire retardancy behavior of raw and surface-modified Grewia optiva/GPE composites have been found to increase when fire retardants were used in combination with fibers. This increase in fire retardancy behavior of resulted composites was attributed to the higher thermal stability of magnesium hydroxide/zinc borate. 

A few studies considered the effect of pH on the viscosity of xanthan solutions. Jeanes et al. observed a rapid increase in the viscosity of xanthan solution at pH 9-11 [28]. Whitcomb and Macosko [29] and Philips et al. [30] found the viscosity of xanthan to be independent of pH. Szabo examined the stability of various EOR polymers in caustic solutions at room temperature, including Kelzan MF (a biopolymer) [6]. He found a fast initial drop in the viscosity of a xanthan solution containing 2 wt% sodium chloride and 5 wt% sodium hydroxide, at 12.5 s", which virtually stopped after 10 days. Krumrine and Falcone found that the effect of alkali (sodium silicates) on the viscosity of xanthan solution depended on the concentration of sodium and calcium ions present [31]. Ryles examined the thermal stability of bio-polymers in alkaline conditions [16]. He found that xanthan was totally degraded (in anaerobic conditions) upon the addition of 0.8 wt% sodium hydroxide at temperatures from 50 to 90°C (in a 1 wt% sodium chloride brine). Seright and Henrici observed total biopolymer degradation at pH > 8 and a temperature of 120°C [26]. 

Porous carbons (e.g., activated carbons) are an important family of porous solids that have a wide spectrum of applications becanse of their remarkable properties, such as high specific surface area, chemical inertness, abundant repertory of surface functional groups, good thermal stability, and low cost of manufacture. Their chemistry and physics have been reviewed [22-25]. The most common way to produce activated carbons is to carbonize a carbon-containing precursor, followed by activation or posttreatment [26]. Becanse of practical requirements of various applications, techniques for control over the pore size of activated carbons have been the subject of research for several decades [18] for example, high burn-off activation, catalyst-assisted activation, and carbonization of polymer blends with thermally unstable components. For recent progress in the use of hydroxide activation, see Chapter 1 by Linares-Solano and coworkers in this volume [27]. However, none of these synthesis approaches is suitable for very precise control over pore structure, particle size, and morphology [19]. 

In recent years, many anionic polymers have been interleaved into LDH to form a new class of LDH-polymer nanohybrids, in which the LDH hydroxide layer and polymer anion layer alternate this topic has been reviewed by Leroux and Besse (14). LDH compounds have been added to neutral polymer as additives or fillers to improve the properties of polymeric materials, such as thermal stability, flammability, mechanical strength, and hardness. The delamination of LDH into single hydroxide layers offers a route to a new kind of polymer-LDH nanocomposite, analogous to the polymer-aluminosilicate nanocomposites extensively studied since the mid 1990s. We review these three classes next. 

Thermal stability of polymer/layered double hydroxide nanocomposites... 

C. Nyambo, E. Kandare, and C. A. Wilkie, Thermal stability and flammability characteristics of ethylene vinyl acetate (EVA) composites blended with a phenyl phosphonate-intercalated layered double hydroxide (LDH), melamine polyphosphate and/or boric acid. Polymer Degradation and Stability, 94 (2009), 513-20. 

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