Interaction forces between particles stabilized by a hydrophobically modified inulin surfactant.

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Influence of hydrophobically modified inulin (INUTEC NRA) on the stability of vulcanized natural rubber latex

This paper is dedicated to the memory of our beloved colleague Dr. Núria Azemar Sazatornil, who passed away on 23th March 2014.The effect of a graft copolymer of inulin (linear polyfructose with degree of polymerization greater than 23) on which several C12 alkyl chains are grafted (INUTEC NRA surfactant) on the stability of vulcanized natural rubber was investigated. This surfactant showed a high adsorption affinity to latex surface, and the adsorption isotherms could be fitted to Langmuir equation. The plateau adsorption is approximately 3.4molm-2, corresponding to an area per INUTEC molecule of 4.9nm2. The polymeric surfactant adsorbed layer thickness was determined using zeta potential and dynamic light scattering (PCS techniques). This gave an electrokinetic layer thickness at the plateau adsorption of 3.5nm and a hydrodynamic thickness of 3.1nm. These values indicate that the surfactant can increase the colloidal stability of rubber latex particles, by steric repulsion. The stability of the rubber particles with the surfactant was determined by measuring the critical coagulation concentration (CCC) of calcium nitrate. The adsorption of the surfactant causes a large increase in particle stability; and it was found that the CCC of rubber particles containing the copolymer surfactant increased with the increase in surfactant concentration. Three stability regions were distinguished, namely the coagulation region, the weak flocculation region and the stable dispersion region. The weakly flocculated region may allow the formation of a more uniform layer of latex, which is a very important objective in the industry of glove manufacturing. Thin films of latex have been prepared by a dipping method, and the results clearly demonstrate that smoother films are obtained as a result of a weak flocculation behaviour induced by the presence of surfactant. The results described in this paper may allow the formation of more homogeneous thin films of latex.The authors also acknowledge the Spanish Ministry of Economy and Competitiveness for CTQ2008-06892-C03-01 and CTQ2011-23842 projects, and Generalitat de Catalunya for the 2009SGR961 grant.Peer reviewe

Stabilization of vulcanized natural rubber latex by a hydrophobically modified inulin

Trabajo presentado en la 6th International Rubber Glove Conference and Exhibition (IRGCE), celebrada en Kuala Lumpur (Malasia) entre el 3 y el 6 de septiembre de 2012.The effect of an inulin copolymer in which several alkyl chains are grafted (INUTEC NRA surfactant) on the stability of vulcanized natural rubber was investigated. The concentration of the surfactant adsorbed and the corresponding area was accessed using adsorption isotherms whereas the information on the thickness of the adsorbed layer was obtained using zeta potential measurements and Dynamic Light Scattering (DLS). The stability of the latex was accessed by measuring the critical coagulation concentration (CCC) by calcium nitrate. The results showed that in MilliQ water, INUTEC NRA adsorbed strongly onto the rubber particles, giving an adsorption amount of 1.69 mg m-2 corresponding to an area of 4.9 nm2 per INUTEC molecule. In 0.5 M Ca(NO3)2, the surfactant adsorption was higher at 2.13 mg m-2 corresponding to an area of 3.9 nm2 per surfactant molecule. The hydrodynamic and electrokinetic thickness, at pH 8, both showed values of ~ 3.1 ± 0.35 nm and 3.4 ± 0.5 nm, respectively. In increasing the INUTEC NRA concentration, the stability of the rubber particles by calcium nitrate showed three stability regions, namely the irreversible flocculation region, the reversible flocculation region and the no flocculation region.The authors would like to thank the Malaysian Rubber Board for providing the financial support in carrying out this work

Effect of calcium nitrate and a hydrophobically modified polymeric surfactant on the stability of natural rubber latex

The control of the colloidal stability of latex particles is essential to obtain homogenous films. The manufacture of latex gloves is required to control the flocculation of latex particles, induced by the addition of calcium salts. This flocculation can, however, be retarded by the addition of very small amounts of surfactants. The present publication describes the effect of Ca(NO3)2 on the stability and rheological properties of natural rubber latex in the presence of small concentrations of a hydrophobically modified polyfructose (Inutec NRA). This surfactant strongly adsorbs on the surface of the latex particles, forming a repulsion layer. However, addition of Ca(NO3)2 causes a shrinkage of this layer. The colloidal stability, as a function of surfactant and Ca(NO3)2 concentrations was studied by determining surfactant adsorption, zeta potential and rheological properties. The addition of Ca(NO3)2 increased surfactant adsorption, due to the poorer solvency of the medium for the polyfructose chains, which became less hydrated in the presence of Ca2+. The addition of calcium also reduced the absolute value of zeta potential, due to compression of the repulsion layer. However, as the surfactant was adsorbed onto the surface of the particles, the latex particles remained stable even after charge reversal at high Ca2+ concentration, due to the higher steric stabilisation conferred by the surfactant. Flow behaviour studies showed a reduction in the maximum packing fraction (ϕmax ) of latex with surfactant concentration, due to formation of the repulsion layer that increased the distance between particles. However, the presence of Ca(NO3)2 increased ϕmax , indicating a reduction in the interparticle distance caused by compression of the repulsion layer between particles. Moreover, the addition of Ca(NO3)2 also decreased the cohesive energy density of the latex, resulting in a more viscous behaviour. These results demonstrate the ability of calcium ions to dehydrate surfactant molecules, which is crucial for explaining the macroscopic properties of latex suspensions.The authors would like to thank the Director General of the Malaysian Rubber Board for the permission to publish this work. Support from the Malaysian Rubber Board, Beneo (Belgium) and CreaChem (Belgium) for this collaborative project is highly appreciated. The authors also greatly acknowledge financial support from the Malaysian Rubber Board for funding the PhD studies of Dr Manroshan Singh, as well as the Spanish Ministry of Science and Innovation (CTQ2014-52687-C3-1-P and CTQ2017-84998-P grants). Support from Generalitat de Catalunya (2014SGR1655 and 2017SGR1778 grants) is recognised. The Grupo de Nanotecnología Farmacéutica, of the University of Barcelona (UB), which forms an Associated Unit to CSIC, is also commended. Authors are equally grateful to the European Regional Development Fund (Fondo Europeo de Desarrollo Regional, FEDER), and AEI (Agencia Estatal de Investigación).Peer reviewe

Emulsion polymerization of styrene and methyl methacrylate using a hydrophobically modified inulin and comparison with other surfactants

5 pages, 6 figures, 3 tables.-- PMID: 15896021 [PubMed].-- Printed version published May 24, 2005.The use of a new class of graft polymer surfactants, based on inulin, in emulsion polymerization of poly(methyl methacrylate) (PMMA) and polystyrene (PS) particles is described. PS and PMMA were synthesized by emulsion polymerization, and stable particles with a high monomer content (50 wt %) were obtained with a very small amount of polymeric surfactant ([surfactant]/[monomer] = 0.0033). The latex dispersions were characterized by dynamic light scattering and by transmission electron microscopy to obtain the average particle size and the polydispersity index, and the stability was determined by turbidimetry measurements and expressed in terms of critical coagulation concentration. The last section gives a comparison of PMMA particles prepared by emulsion polymerization using classical surfactants from different types as emulsifiers with that obtained using the copolymer surfactant. It shows the superiority of INUTEC SP1 as it is the only one that allows stable particles at 20 wt % monomer content, with a smaller ratio [surfactant]/[monomer] = 0.002.The authors gratefully acknowledge financial support from ORAFTI Bio Based Chemicals and from the Spanish Ministry of Science and Education (PPQ2002-04514-C03-03 grant).Peer reviewe

Emulsion polymerization of styrene using mixtures of hydrophobically modified inulin (polyfructose) polymeric surfactant and nonionic surfactants

Polystyrene latex dispersions were prepared by emulsion polymerization, using a mixture of hydrophobically modified Inulin (INUTEC® SP1) and various nonionic surfactants (cosurfactants). Two series of nonionic surfactants were used, namely Synperonic A (C13-15 alkyl chain with 7, 11, and 20 moles of ethylene oxide, EO) and Synperonic NP (nonylphenol with 10 and 15 moles of EO). For 5 wt % latex, the INUTEC SP1 concentration was kept constant at 0.0165 wt % and the initiator concentration was also kept constant at 0.0125 wt %, whereas the cosurfactant concentration was varied between 0.1 and 0.5 wt %. With the exception of Synperonic A20, all other cosurfactants showed an initial increase in particle diameter followed by a decreased reaching a value comparable with that obtained using INUTEC SP1 alone. However, A20 produced a continuous reduction in particle diameter with increase of surfactant concentration, reaching a value of 100 nm at 0.5 wt % which is lower than the value obtained using INUTEC SP1 alone (188 nm). In all cases, addition of a cosurfactant enhanced the stability of latexes by coadsorption at the solid-liquid interface. The enhanced stability produced by the addition of cosurfactants to INUTEC SP1 could be illustrated by using the mixture of INUTEC SP1 and Synperonic A7 at 40 wt % of styrene latex concentration. In this case, the mixture produced lower particle size, much lower polydispersity index and much higher stability. These results are of significant value for industrial applications.Peer reviewe

Simple Method for Rheological Determination of Surfactant Layer Thickness, Adsorbed on Soft Rubber Particles

Natural rubber latex is a colloidal suspension of particles, which is very important for many industrial applications. These latex particles are not only polydispersed but also very soft and deformable, which makes the prediction of rheological properties much difficult. Herein, the rheology of natural rubber latex has been studied at high particle concentrations, analyzing the effects of surfactant addition on colloidal stability. A hydrophobically modified inulin surfactant (INUTEC NRA) was selected for this study, since previous works had shown that this inulin surfactant imparts good colloidal stability to polystyrene latex particles. The most important objective was studying the influence of the surfactant on the particle adsorbed layer and determining the thickness of the adsorbed surfactant layer. The results showed that relative viscosity increased as a function of latex volume fraction and this increase became extremely sharp as the volume fraction approached the maximum packing volume fraction, as expected. This variation in viscosity with volume fraction has a complex behavior, which could not be analysed using conventional models based on hard-rigid spheres, such as Krieger-Dougherty (K-D) or Maron-Pierce (M-P). Herein, we describe a simple semiempirical method to determine the surfactant adsorbed layer thickness, based on the linear dependence of intrinsic viscosity with 1/(max-2, where is the volume fraction of rubber particles and max is the maximum volume fraction at which viscosity tends to infinity. The difference in maximum packing fraction, with and without surfactant, allows the calculation of the adsorbed layer thickness, ≈2.8 nm, which is a good estimate for the thickness of surfactant molecules adsorbed on latex particles. This surfactant thickness has been confirmed by direct measurements using Dynamic Light Scattering (DLS), which gave a value of 3.1 nm. Viscoelastic oscillatory measurements have also been performed, showing that natural rubber particle suspensions are predominantly elastic above =0.63 latex volume fractions. The elastic modulus has been analyzed as a function of surfactant concentration, confirming that stability of latex particles is mainly controlled by surfactant concentration.First, the authors greatly thank the Malaysian Rubber Board, Beneo (Belgium) and CreaChem (Belgium) for providing the financial support required in this joint research project. The authors also acknowledge the financial support from the Spanish Ministry of Science, Innovation and Universities (CTQ2014-52687-C3-1-P and CTQ2017-84998-P projects). Support from Generalitat de Catalunya (2014SGR1655 and 2017SGR1778 consolidated group awards; and TECCIT15-1-0009 and TECCIT16-1-0049 TECNIO awards) is also acknowledged. Characterization of latexes and rheological determinations was performed at the Nanostructured Liquid Characterization Unit, located at the Institute of Advanced Chemistry of Catalonia (IQAC) of the Spanish National Research Council (CSIC). This characterization unit is affiliated to the NANBIOSIS ICTS, ascribed to Centro de Investigación Biomédica en Red de Bioingeniería, Biomateriales y Nanomedicina, CIBER-BBN, which is financed by Instituto de Salud Carlos III. The authors also acknowledge the Grupo de Nanotecnología Farmacéutica, of the University of Barcelona (UB), in the Faculty of Pharmacy, which forms an Associated Unit to CSIC. Authors are also very grateful to the European Regional Development Fund (Fondo Europeo de Desarrollo Regional, FEDER), which provides financial support to government programs.Peer reviewe

Stabilization of latex dispersions using a graft copolymer of inulin based surfactants

Polystyrene (PS) latex dispersions were prepared by surfactant-free emulsion polymerization. Poly(methyl methacrylate) (PMMA) latex dispersions were prepared using the same procedure except by adding INUTEC SP1 as emulsifier. The two latex dispersions were characterized by photon correlation spectroscopy (PCS) to obtain the average particle size and the polydispersity index. The stability of these latex dispersions was measured by determination of the critical coagulation concentration (CCC) of three electrolytes, namely, NaCl, CaCl2, and Al2(SO4)3. The CCC was 0.375 mol·dm-3 for NaCl, 0.007 mol·dm-3 for CaCl2, and 0.0004 mol·dm-3 for Al2(SO4)3. A polymeric surfactant, namely, a graft copolymer of polyfructose on which alkyl groups were grafted to the backbone, were added to latex dispersions and their stability was investigated. On addition of this polymeric surfactant, the stability of the latex dispersions was significantly increased and the CCC became very high above a critical polymer concentration. For the PS latex, the CCC of CaCl2 was higher than 4.3 mol·dm-3 when the polymeric surfactant concentration was 0.25 wt%. The results could be rationalized in terms of the enhanced steric repulsion resulting from the adsorption of the graft copolymer. It was assumed that the molecule produces large "loops" of polyfructose between the adsorbed alkyl groups, forming a hydrated layer thickness of approximately 4 nm. In addition, these polyfructose chains were still hydrated even in the presence of high electrolyte concentrations.The authors gratefully acknowledge financial support from ORAFTI Non-Food and Generalitat de Catalunya DURSI (grant 2001 SGR-00357).Peer reviewe