Degree Of Saponification Research Articles

Solvent Extraction of Zinc from a Bioleaching Solution by Modification of D2EHPA: Optimization and Thermodynamic Studies

In this work, zinc extraction from an industrial leach solution was investigated by saponified di(2-ethylhexyl)phosphoric acid (D2EHPA). The solution obtained was from a bioleaching process of a low-grade lead-zinc sulfide ore that contained 50 g/L of zinc and 6.3 g/L of iron. The selective and high Zn(II) extraction yield were obtained by modification of D2EHPA in a proposed two-step process. Firstly, a significant amount of iron (87%) was removed as sodium-jarosite via precipitation from the pregnant leaching solution (PLS) prior to zinc extraction, and secondly, the effective parameters involved in zinc extraction including the contact time, saponification degree, type of saponifier, stirring speed, pH, temperature, D2EHPA concentration, and phase ratio (A:O) were investigated. The results obtained showed that 98.4% of zinc could be extracted under the optimum conditions, i.e. 20% D2EHPA, 15% saponification degree, 650 rpm, pH 2, and an A:O ratio of 1:1 at the ambient temperature (25 ± 2 °C) during 90 s; it was 25% higher than using non-saponified D2EHPA under the same conditions. Moreover, while one theoretical step was required for the complete extraction of zinc by saponified D2EHPA, the required number of steps using D2EHPA was about three. Therefore, the advantages of the process would be two-fold: reducing the number of extraction stages and no need for neutralizing the raffinate in every extraction stage.

Instability behavior of bubble supported organic liquid membrane in extraction of low-concentration rare earths from in-situ leaching solutions of ion-adsorption ores

Gas bubble supported organic extractant liquid membrane exhibits a promising potential in enhanced extraction and separation of low-concentration rare earths from the in-situ leaching solutions of ion-adsorption ores. However, instability of organic liquid membrane on the surface of gas bubbles might result in dissolution loss of organic extractant in the flowing-out aqueous raffinates and bring serious organic pollution if the raffinates are recycled for re-leaching of rare-earth ores. The present work focuses on the mechanism of the instability of organic extractant P507 liquid membrane on the surface of bubbles during rare-earth extraction. Various effects, including volume flow rate of aqueous feed solution, initial aqueous pHs and concentrations of co-existing impurity ions, saponification degree of P507 and pre-loaded concentration of rare earths in organic phase, on the stability of organic liquid membrane are discussed. Experimental results reveal that the stability of organic liquid membrane depends on three kinds of forces exerting on the surface of bubbles, i.e., the shear force Fs, the interface tension Ft and the dispersion force Fd. The occurrence of Ft and Fd are benefit for the stability, but Fs is not. The competition of the two component forces of Fs respectively with Ft and Fd will result in instability of organic liquid membrane and an increase in the concentration of total organic phosphorus in the flowing-out raffinates. The present work provides a theoretical basis about how to control the stability of organic extractant liquid membrane on the surface of gas bubble. Based on the suggested new technique by bubble supported organic liquid membrane extraction, a green and environmentally friendly strategy is suggested for replacing the traditional ammonium bicarbonate precipitation to extract low-concentration rare earths from in-situ leaching solutions of ion-adsorption ores.

Adhesive properties of water-soluble and biodegradable hot-melt adhesive based on partially saponified poly(vinyl acetate)

Partially saponified low molecular weight (LMW) PVAc was synthesized and blended with a tackifier for use as hot-melt adhesive with water-solubility and biodegradibility. The water-solubility of the partially saponified LMW PVAc was determined as a function of the degree of saponification. PVAc prepared in this study had good water-solubility because its molecular weight was very small and it had lots of hydroxy groups in the polymer chain. As the degree of saponification increased, the solubility of PVAc in water increased. The glass transition temperature and viscoelastic properties of partially saponified PVAc were measured and analyzed by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). As the temperature increased and the degree of saponification decreased, melt viscosity decreased. The single lap-shear strength and biodegradability of the hot-melt adhesive on based PVAc were systematically evaluated. As the degree of saponification of the polymer increased, the single lap-shear strength of the hot-melt adhesive and the tendency for cohesive failure to occur decreased. The higher the degree of saponification, the faster the rate of biodegradation of the adhesive in natural water.

Lithium recovery from effluent of spent lithium battery recycling process using solvent extraction

A novel process of lithium recovery from effluent of spent lithium batteries recycling by solvent extraction was proposed. The β-diketone extraction system used in the experiment was composed of benzoyltrifluoroacetone (HBTA), trioctylphosphine oxide (TOPO) and kerosene. The effective parameters such as solution pH value, saponification degree, initial lithium concentration and phase ratio were evaluated by experiments. More than 90% of lithium could be extracted by saponified organic phase through three-stage countercurrent extraction. The loaded organic phase was first eluted by dilute HCl solution to remove nontarget sodium, and then stripped by 6 mol/L HCl at a large phase ratio to obtain lithium-rich solution with 4.322 mol/L lithium. The lithium-rich solution from the process could be used to prepare lithium carbonate or lithium chloride. The stripped organic phase can be recycled and no crud or emulsification was observed during the process. The extraction mechanism of HBTA-TOPO was investigated via FT-IR spectroscopy, and the results indicated the two extractants showed strong synergistic effect. The thermodynamic study revealed lithium extraction is an exothermic process, which meant lower temperature promotes extraction of lithium.This work provided a novel approach to recover lithium from effluent of spent lithium battery recycling.

Detailed Structural Study on the Poly(vinyl alcohol) Adsorption Layers on a Si Substrate with Solvent Vapor-Induced Swelling.

We investigated in detail the structures in the poly(vinyl alcohol) (PVA) adsorption layers on a Si substrate, which remained on the substrate after immersing the relatively thick 30-50 nm films in hot water, by neutron reflectometry under humid conditions. For the PVA with a degree of saponification exceeding 98 mol %, the adsorption layer exhibits a three-layered structure in the thickness direction. The bottom layer is considered to be the so-called inner adsorption layer that is not fully swollen with water vapor. This may be because the polymer chains in the inner adsorption layer are strongly constrained onto the substrate, which inhibits water vapor penetration. The polymer chains in this layer have many contact points to the substrate via the hydrogen bonding between the hydroxyl groups in the polymer chain and the silanol groups on the surface of the Si substrate and consequently exhibit extremely slow dynamics. Therefore, it is inferred that the bottom layer is fully amorphous. Furthermore, we consider the middle layer to be somewhat amorphous because parts of the molecular chains are pinned below the interface between the middle and bottom layers. The molecular chains in the top layer become more mobile and ordered, owing to the large distance from the strongly constrained bottom layer; therefore, they exhibit a much lower degree of swelling compared to the middle amorphous layer. Meanwhile, for the PVA with a much lower degree of saponification, the adsorption layer structure consists of the two-layers. The bottom layer forms the inner adsorption layer that moderately swells with water vapor because the polymer chains have few contact points to the substrate. The molecular chains in the middle layer, therefore, are somewhat crystallizable because of this weak constraint.

Separation of gadolinium and europium from chloride media by the solvent extraction technique

Abstract Obtaining rare earth elements (REE) is a complicated task, due mainly to the difficulty of separating and purifying them. Solvent extraction is the most widely used technique for separating REE, and the most common extractants used are organophosphorus acids. The low selectivity of this technique leads to the need for a high number of extraction cells. To increase the selectivity and separation and avoid the practice of saponification of the extractant, the use of complexing agents has been studied, such as low-molecular-weight and biodegradable weak organic acids. The objective of this research was to study the separation of the rare earth elements Gd and Eu by the solvent extraction technique using the organophosphonic extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507). Assays were performed using non-saponified and saponified P507 extractant and adding lactic acid to the aqueous phase prior to extraction. Experimental factorial planning was used to study the effect on the extraction and separation of the Eu and Gd of the variables extractant concentration, initial feed pH, saponification degree, and lactic acid concentration. The greatest Gd extractions were obtained when lactic acid was added to the feed solution. Also, saponification of the extractant and lactic acid addition improved the Gd/Eu separation. The number of stages required to extract Gd using McCabe-Thiele diagrams was estimated, whether or not the solution was conditioned with lactic acid. The largest extraction percentage was obtained by adding lactic acid in a continuous counter-current extraction assay, achieving 94% Gd extraction.

Study of the separation of didymium from lanthanum using liquid-liquid extraction: Comparison between saponification of the extractant and use of lactic acid

The liquid-liquid extraction (LLE) technique is widely used for industrial-scale separation of rare-earth elements (REEs). However, the low selectivity of LLE in separating REEs, mainly adjacent elements, has prompted the investigation of modifications of this technique to find new routes that are more efficient. The selectivity of REEs separation increases when saponified extractants are used. However, saponification generates effluents containing sodium or ammonium ions that need to be removed before discharge into water bodies or be reused. As an alternative to saponification, the conditioning of the feed liquor with complexing agents has been proposed. This study compares the efficiency of didymium (Pr + Nd) and lanthanum separation with saponified and non-saponified organophosphorus extractants and with addition of lactic acid to the feed liquor. The extractants investigated were D2EHPA, P507 and Cyanex 272. The effect on the didymium/lanthanum separation of initial pH, saponification degree and lactic acid concentration and extractant were evaluated. The La and didymium separation were better when the feed solution was conditioned with lactic acid than when the extractants D2EHPA and P507 were saponified. Conversely, La and didymium separation was better when Cyanex 272 was saponified than when the feed liquor was conditioned with lactic acid. These results indicate that conditioning the feed liquor with lactic acid has the potential to replace the practice of saponification of the extractants D2EHPA and P507.

Removal of calcium and magnesium from lithium concentrated solution by solvent extraction method using D2EHPA

In this work, a solvent extraction process for Ca2+ and Mg2+ removal from Li+ concentrated solution consisted of 30 g/L Li+, 1.5 g/L Ca2+ and 1.5 g/L Mg2+ was proposed, using di-(2-ethylhexyl) phosphoric acid (D2EHPA) as extractant. The extraction process was a cation exchange mechanism, and the extraction sequence was Ca2+ > Mg2+ > Li+ > Na+. Under the optimum condition of 66% saponification degree, 3/2 phase ratio and three-stage extraction, the extraction efficiency of Ca2+, Mg2+ and Li+ reached 99.00%, 98.57% and 15.28%, respectively. The extracted cations could be completely stripped by HCl solution, and the co-extracted Li+ could be selectively stripped and separated from Ca2+ and Mg2+ using higher concentration HCl solution at higher phase ratio. A whole removal process for Ca2+ and Mg2+ involving extraction, scrubbing, stripping and saponification sections was put forward, and the process stability was continuously tested on centrifugal extractors. Removal efficiency of Ca2+ and Mg2+ reached 99.05% and 98.48% respectively. Meanwhile, the loss ratio of Li+ was as low as 5.22%.

Self‐expandable hydrogel biliary stent design utilizing the swelling property of poly(vinyl alcohol) hydrogel

ABSTRACTWe have developed a novel self‐expandable biliary stent comprising poly(vinyl alcohol) (PVA). The swelling ratio of the dried PVA hydrogels decreased from 6.7 to 2.6 as the saponification degree increased from 95 to 99.9, whereas the storage modulus and tear strength increased from 17 to 400 kPa and from 0.5 to 10 N mm−1, respectively. The dimensional ratios of the inner‐ and outer‐diameter and the length of the dried tube‐shaped hydrogels (saponification degree of 98.5) prepared by simple air drying isotropically increased 1.4–1.5 times in physiological saline. Meanwhile, the dimensional ratios of the dried hydrogels prepared by drying under extension increased by twice, whereas the length decreased slightly, indicating anisotropic swelling. The radial force of the reswollen tube‐shaped hydrogels (6.6 ± 0.6 mN mm−2) was significantly higher than that of a conventional metallic stent (4.4 ± 0.3 mN mm−2), suggesting that PVA hydrogels were applicable as self‐expandable stents. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48851.

Wettability and spreading behavior of organic extractant and its effect on formation of gas bubble supported organic liquid membrane for large-phase-ratio extraction

Our previous works suggested a novel method by spreading and covering a layer of organic extractant on the surface of gas bubbles to perform gas bubble-supported organic liquid membrane extraction at large aqueous-to-organic phase ratios. However, details about wettability and spreading kinetic behavior of organic extractant within the annular gaps between the internal gas and the external oil needles in the injector was not clear, and so did its effect on formation of gas bubble-supported organic liquid membrane. In present work, spreading of P507 organic extractant on surface of two kinds of typical solid substrates, glass and PVC, with different hydrophilic-hydrophobicity is investigated. It is found that the spreading empirical coefficient k is a simple mathematical function of three crucial operation parameters in the process of gas bubble-supported organic membrane extraction: P507 concentration, saponification degree of P507, and pre-loading amount of rare earths in the organic phase. A feasible mathematical model is suggested for theoretical prediction of the spreading rate. Calculation based on the new model is more convenient than de Gennes’s model. The present work provides a scientific foundation for the design of hydrophilic-hydrophobicity of the materials for making the internal gas and the external oil needles in the injector.

Influence of the components of a radiochromic PVA – Iodide gel dosimeter on the optical dose response

A novel radiochromic gel dosimeter based on a poly(vinyl alcohol)-iodide complex (PVA-I) has been developed with the aim of using it in optical computed tomography (CT). The PVA-I gel dosimeter exhibits excellent characteristics such as high sensitivity, dose rate independence, a wide dose range, and especially reusability. The standard PVA-I gel dosimeter is composed of poly(vinyl alcohol) (average degree of polymerization 1000 and degree of saponification 88 mol%), iodide (potassium iodide), reducing sugar (fructose), gelling agent (gellan gum), and water. In this study, the influence on dose response is investigated upon substitution of the components by PVAs with different degrees of polymerization (500, 1500, 3500) and saponification (80 mol%, 98 mol%), different iodide salts (LiI, NaI, NH4I), and different reducing sugars (glucose, maltose, lactose). The results show that these substitutions have little effect on the dose rate dependence, while the iodide salt affects the sensitivity.

Elucidation of a Heterogeneous Layered Structure in the Thickness Direction of Poly(vinyl alcohol) Films with Solvent Vapor-Induced Swelling.

We investigated the swelling behaviors of poly(vinyl alcohol) (PVA) films deposited on Si wafers with water vapor, which is a good solvent for PVA for elucidating structural and dynamical heterogeneities in the film thickness direction. Using deuterated water vapor, structural and dynamical differences in the thickness direction can be detected easily as different degrees of swelling in the thickness direction by neutron reflectivity. Consequently, the PVA film with a degree of saponification exceeding 98 mol % exhibits a three-layered structure in the thickness direction. It is considered that an adsorption layer consisting of molecular chains that are strongly adsorbed onto the solid substrate is formed at the interface with the substrate, which is not swollen with water vapor compared with the bulk-like layer above it. The adsorption layer is considered to exhibit significantly slower dynamics than the bulk. Furthermore, a surface layer that swells excessively compared with the underneath bulk-like layer is found. This excess swelling of the surface layer may be related to a higher mobility of the molecular chains or lower crystallinity at the surface region compared to the underneath bulk-like layer. Meanwhile, for the PVA film with a much lower degree of saponification, a thin layer with a slightly lower degree of swelling than the bulk-like layer above it can be detected at the interface between the film and substrate only under a high humidity condition. This layer is considered to be the adsorption layer composed of molecular chains loosely adsorbed onto the Si substrate.

Separation of Zn(II) from Zn-Ni-Co sulphate solution by di-(2-ethylhexyl)phosphoric acid (D2EHPA) using a slug flow microreactor

Separation of Zn2+ from sulphate solution containing Ni2+ and Co2+ using di-(2-ethylhexyl)phosphoric acid (D2EHPA) has been carried out in capillary microreactors. Well-defined slug flows are formed at total flow rates of 0.1–4 mL/min, and the slugs size and specific interfacial area are determined. The effects of saponification degree of D2EHPA, extractant concentration, and residence time on extraction and separation of these three metal ions are investigated. Meanwhile, conventional batch experiments at 94 s and equilibrium experiments at 8 h are also done in parallel at different extractant concentrations. Compared with conventional batch experiments, better extraction and separation performance, e.g. 2.7–38.9 times higher of βZn/Ni and 3.9–34.9 times higher of βZn/Co, is obtained in the slug flow microreactor. In addition, the overall volumetric mass transfer coefficient kLa and overall mass transfer coefficient kL are measured. Compared with other microreactors and the batch mixer-settler, the used slug flow microreactor shows higher kLa values of Zn.

An extraction and precipitation process for the removal of Ca and Mg from ammonium sulfate rare earth wastewaters

Softening ammonia sulfate wastewater is one of the vital issues in the rare earth industry. In this article, a novel softening process using [4,4′-isopropylidenebis (phenoxyacetate)] (H2IPOAA) for Ca2+ and Mg2+ (M2+) is developed. The effect factors, i.e., equilibrium time, pH value of aqueous phase and saponification degree are investigated. The extraction mechanism is proposed to be cation exchange. With a saponification degree of 85%, H2IPOAA is successfully used for the precipitation of Ca2+ and Mg2+ from ammonia sulfate wastewater within 10 min. The process can form precipitated particles with an average size of 35 μm, which are much larger than the precipitates formed by H2C2O4, Na2C2O4 and Na2CO3. The precipitated particles can be easily separated from the raffinate. In addition, H2IPOAA is repeatedly used for five times with a little loss. To a considerable extent, the reuse of H2IPOAA contributes to lowering the cost and reducing the pollution. The concentrations of Ca2+ and Mg2+ in the raffinate extracted by H2IPOAA are up to the MVR standard for wastewater treatment. The economical and efficient softening process meets the need of green chemistry, which is expected to replace traditional industrial processes for water softening based on H2C2O4, Na2C2O4 and Na2CO3.

Intensified solvent extraction and separation of cobalt from Ni-rich leaching solution in impinging stream-rotating packed bed contactor

ABSTRACT This work describes the separation of Ni and Co from a real feed solution in chloride media with high Ni content. The extractant used was P507 (2-ethylhexyl phosphoric acid-2-ethylhexyl ester) in a laboratory scale Impinging Stream–Rotating Packed Bed (IS-RPB) contactor. Key variables including feed solution pH, extractant concentration, saponification degree, high gravity level and total volumetric flow rate of fluids amongst other variables were examined. A McCabe–Thiele diagram of the extraction stage predicted that at a total volumetric flow rate of 90 L/h, feed solution pH of 5, saponified P507 concentration of 25% and high gravity of 83, almost 99% of cobalt, would be extracted within three stages. With regard to the scrubbing results, the co-extracted nickel was scrubbed efficiently from the loaded organic solution using a mixture of 0.02 M CoCl2 and 0.5 M hydrochloric acid solution, The purified Co solution was achieved after stripping the loaded-organic phase with 1 M HCl. The maximum value of the overall volumetric mass transfer coefficient for the IS-RPB extractor was found to be 0.16 s−1 which was superior to that of conventional extractors such as mixer-settler and centrifugal extractors, providing strong confidence for its industrial application.

Chemical Reaction-Driven Spreading of an Organic Extractant on the Gas-Water Interface: Insight into the Controllable Formation of a Gas Bubble-Supported Organic Extractant Liquid Membrane.

The extraction and recovery of low-concentration valuable metals from various complex aqueous solutions or industrial waste waters have attracted extensive interests in recent years. In our previous works, we suggested a novel technique called bubbling organic liquid membrane extraction by spreading and covering an organic extractant with extremely small volume on the surface of gas bubbles to form a layer of the gas bubble-supported organic liquid membrane for selective extraction and enrichment of low-concentration targets from dilute aqueous solutions. It was found that for successfully performing the bubbling organic liquid membrane extraction, a prerequisite is knowing how to control the formation of a stable organic liquid membrane covered on the surface of gas bubbles. However, once the organic extractant starts to spread on the surface of gas bubbles, the extraction chemical reaction at the interface between the organic extractant liquid membrane and the rare-earth aqueous solution will occur. In the present work, the spreading behavior of the organic extractant P507 on the surface of rare-earth aqueous solutions was investigated and was compared with the behaviors on the surface of deionized water. It was revealed that the spreading of the organic extractant P507 on the surface of aqueous solutions containing rare-earth ions was accelerated because of the occurrence of the chemical reactions at the gas-water interface. The difference in the spreading rate of organic extractant P507 liquid droplets on the surface of deionized water and on that of Er(III) aqueous solutions with an increase in the P507 concentration, the saponification degrees of the P507 extractant, and the preloading amount of Er(III) in the P507 extractant revealed that the chemical reaction at the interface between the spreading P507 thin liquid membrane and the Er(III) aqueous solution would result in the Marangoni convection along the interface, which is in favor of overcoming the resistance from the viscous force when the surface tension gradient replaces gravity as a dominant driving force for the spreading. The present work provides an experimental foundation toward understanding the effect of the interfacial chemical reaction on the spreading behavior of an organic oil droplet on the gas-water interface. It is beneficial for the development of our suggested new technique of bubbling organic liquid membrane extraction and to achieve a controllable generation of a stable gas bubble-supported organic liquid membrane for performing solvent extraction at large aqueous-to-oil phase ratios.

Insights into the saponification process of di(2-ethylhexyl) phosphoric acid extractant: Thermodynamics and structural aspects

The saponification process of di(2-ethylhexyl)phosphoric acid extractant (D2EHPA) was investigated by the isothermal titration calorimetry (ITC), attenuated total reflection infrared (ATR-IR), and small-angle X-ray scattering (SAXS) spectroscopies. The effects of the temperature, types of saponifier, and diluent on the saponification process of D2EHPA were disclosed by ITC method. The saponification reaction is an exothermic process, but the contribution of temperature on the maximum saponification degree of D2EHPA is slight. The theoretical maximum saponification degree of D2EHPA is about 40%. Moreover, the maximum effective saponification degree of D2EHPA is the same at the condition of different saponifiers because the two systems release the same amount of heat. The effective saponification degree of D2EHPA in octane is larger than that in toluene at the same content of saponifier. The IR spectra indicate that the structure of organic phases varies significantly with the increase of saponification degree. The most water-in-oil microemulsion in the organic phase is formed at the 40% theoretical saponification degree. The water content and SAXS data of organic phase further verify this phenomenon. Solvent extraction results show that the saponified extractant can obviously improve extraction efficiency of cobalt. These results will be helpful for optimizing the saponification process of D2EHPA during metal extraction.

Grouping separation of mixed rare earths from their coexisting aqueous solutions by liquid-column elution

Abstract A new approach was proposed for grouping separation of 14 lanthanide rare-earth ions from their co-existing mixed aqueous solutions, by performing liquid-column elution using the aqueous solution containing 14 lanthanide rare-earth ions as the stationary phase and the dispersed organic oil droplets containing P507 extractant as the mobile phase. It was revealed that 14 lanthanide rare-earth ions could be separated into four groups, according to the lanthanide tetrad effect, respectively eluting out from the liquid column at different time in a certain order. Various effects including the saponification degree of P507, the concentration of P507 in organic phase, the length and inner diameter of the extraction column on the performance of grouping separation of rare-earth ions were discussed. The changes of the mass transfer coefficients were also investigated. The separation efficiency of the four groups of rare-earth elements (REEs) was evaluated based on the elution resolution, Rs, of the elution peaks of La(III), Gd(III), Ho(III) and Lu(III), the four representative elements respectively from each of the four groups of REEs. Experimental results demonstrated that the separation of REEs by liquid-column elution mainly depended on the competitive adsorption of different rare-earth groups onto the surface of ascending P507 oil droplets. The affinity of different rare-earth groups with P507 extractant and a limited adsorption capacity of P507 molecules at the surface of the oil droplets ascending in liquid column play the important role. The present work highlights a promising technique for grouping separation of multiple lanthanide elements co-existing complex systems.

Packing structures and formation of cracks in particulate films obtained by drying colloid–polymer suspensions

We investigated the effects of polymer addition on crack formation in particulate films of colloidal silica. Two types of polyvinyl alcohol (PVA) with different degrees of saponification were compared. Partially saponified PVA (PVA-1) suppressed crack formation. In contrast, weaker suppression was observed when we used fully saponified PVA (PVA-2). Centrifugation experiments of colloid–polymer suspensions revealed that PVA-1 adsorbed on particles well whereas PVA-2 was not adsorbed effectively, suggesting that the polymer–particle interactions strongly depended on the content of polymer functional groups. In addition, we observed segregation of PVA-2 between packed particles, which contributed to a sparse packing structure. We did not observe such segregation of PVA-1 and particles were packed more tightly than for PVA-2. These results clearly showed that the affinity between polymer molecules and suspended particles affected both crack formation and packing structures. We also found that adsorption of polymer molecules did not necessarily suppress crack formation. When we added polyvinyl pyrrolidone (PVP) to silica suspensions, we observed much more cracks than in the sample without polymer even though PVP molecules adsorbed on the silica particles. We conclude that adsorption of polymer molecules on suspended particles is preferable, but does not necessarily suppress crack formation. Miscibility between polymer molecules and particles would be a key issue in crack formation and packing structure of colloid-polymer films.

Scientific investigation into the water sensitivity of twentieth century oil paints

In order to develop a better understanding at the molecular level of water sensitivity in twentieth century oil paintings, water sensitive Winsor & Newton oil paint swatches and twentieth century oil paintings were characterised using gas chromatography–mass spectrometry (GC–MS) and direct injection electrospray ionisation mass spectrometry (ESI-MS), and the data were analysed using principal component analysis. Liquid chromatography coupled with tandem mass spectrometry based on quadrupole and time of flight mass detectors and electrospray interface (HPLC-ESI-Q-ToF) was also used to obtain a better insight into the molecular composition of a selection of samples. The study highlights a strong relationship between the molecular composition of the binding medium and the type of pigment present in the paint, which relates to water sensitivity. Consistently non-water sensitive lead white, titanium white, and zinc white paints [all containing zinc oxide] contained a relatively low proportion of extractable diacids, and a relatively high proportion of extractable short chain monoacids. These paints also contained a relatively low level of unsaturated and hydroxylated glycerides. Water sensitive iron oxide and ultramarine paints are associated with both a relatively high degree of oxidation and a high proportion of extractable diacids, as well as a relatively high content of unsaturated and hydroxylated glycerides. Water sensitive cadmium red, yellow and orange paints were generally not highly oxidised, but they also contained a relatively high content of unsaturated and hydroxylated glycerides. It is hypothesised that water sensitivity relates to a low degree of saponification and crosslinking and possibly, on the relative content of dicarboxylic acids.