C. Graillat

Processing and characterization of new thermoset nanocomposites based on cellulose whiskers

In the present study, the processing and the mechanical properties of new thermoset nanocomposites prepared from aqueous suspensions of microcrystalline cellulose fillers and epoxy are described. The nature of cellulose fibers, which display a large aspect ratio and the ability to associate by means of H-bonds implies that the processing method chosen in this study avoids the problem of a high level of viscosity of the epoxy reactive system-whiskers mixture. The reinforcing effect of this type of natural fiber in an epoxy matrix is mainly shown from the dynamic mechanical properties in the rubbery state. This unusual reinforcement is due to (i) the strong interactions existing between the cellulose whiskers and the epoxy network and, (ii) the creation of a percolating network linked by H-bonds between cellulose fibers. The existence of such a percolation effect is evidenced from the analysis of the rubbery shear modulus of nanocomposites based on various volume fractions of whiskers with mechanical modeling such as Halpin-Kardos and percolation approaches.

New waterborne epoxy coatings based on cellulose nanofillers

New nanocomposites based on a waterborne epoxy emulsion and a suspension of cellulose crystallites were prepared by film casting in order to obtain coatings displaying both flexibility and stiffness. Tunicin cellulose whiskers are attractive reinforcing fillers due to their high aspect ratio, large interface area, and, significant mechanical properties). Typical processing problems for this type of composite are related to high viscosity values of filled polymers in the in the molten state, the incompatibility between hydrophobic matrices and hydrophilic cellulose and the formation of hydrogen bonds between cellulose of this type of natural fibres in an epoxy matrix. The aim of this work is to solve some of the problems above mentioned by selecting the nature of the components used for coating synthesis film processing. The dynamic mechanical properties display an important improvement of the composite modulus in the rubbery state of the matrix at low concentrations of fillers, which can not be expected other cellulose based fibers.

Films from styrene–butyl acrylate lattices using maleic or succinic surfactants: mechanical properties, water rebound and grafting of the surfactants

Abstract A series of anionic and zwitterionic maleic surfactants have been synthesized and engaged in styrene–butyl acrylate emulsion polymerization. Some non-reactive succinic analogs have been synthesized in order to perform their comparison with the maleic surfactants in polymerization experiments. Films from the obtained lattices were cast, and their mechanical properties and the water rebound were tested. The results of water rebound demonstrate significant difference between the films prepared with maleic or succinic surfactants. Water rebound of the films after 34 days in the case of succinic surfactants was found to be between 51 and 95%, while for maleic surfactants it is only 25–40% of the initial weight of samples, which is a significant improvement. Mechanical properties do not present essential difference, but a clear tendency has been observed in the three cases investigated—the films prepared using maleic surfactants are less resistant to the deformation and they are more extended at the rupture of the samples. Both series of results could be explained assuming heterogeneous inclusions of non-reactive surfactant (succinic derivatives) having an ionomer character. Both the results of water rebound and mechanical properties can be considered as an indirect proof of grafting of maleic surfactant on the polymer.

High solid content multisized emulsion copolymerization of styrene, butyl acrylate, and methacrylic acid

Polymer lattices with a multimodal particle size distribution (PSD) polymer latex were prepared by introducing additional surfactants during the semicontinuous emulsion polymerization of styrene, butyl acrylate, and methacrylic acid. The polymerization was investigated by following the variation of the particle size, the size distribution, the number of particles, the Tg of the different particle sizes, and the total conversion at different steps of the polymerization process. The results show that bimodal and trimodal PSD polymer lattices can be obtained by this method and that the secondary generation of particles is greatly influenced by the nature and the amount of additional surfactants, as well as the moment when they are introduced. When the amount of additional surfactants is increased, the diameters of both the small and large particles decrease and the number of particles in each of the populations increases. Earlier introduction of these surfactants favors the generation and the growth of the small particles and thereby leads to a reduction of the relative fraction of large particles in the final latex. On introduction of 7 wt % of additional surfactants, based on the total monomers, 100% of the monomers of the second-stage polymerization were consumed to form the small particles. This fraction decreases with a decreasing amount of the additional surfactants. These results were further demonstrated by measuring the Tgs of both the large and the small particles of two lattices, in which the Tgs of the copolymers produced in each of the stages were different. High solid content (>65%), low viscosity, and coagulum-free lattices have been obtained through secondary nucleation, and a minimum in viscosity was found when the weight fraction of the large particles was around 80%.

Hemiesters and hemiamides of maleic and succinic acid: synthesis and application of surfactants in emulsion polymerization with styrene and butyl acrylate

Hemiesters and hemiamides of maleic acid with different chain lengths of the hydrophobic alkyl group (R = C8H17, C10H21, C12H25, C16H33) have been synthesized and used as surfactants in the emulsion polymerization of styrene and butyl acrylate. The same polymerization experiments were also carried out using nonreactive surfactants with an analogous succinic structure. The chemical structure of the surfactants was confirmed by 1H nuclear magnetic resonance. The melting point and critical micelle concentration of the reactive surfactants described herein were measured. All of the surfactants studied provided good stability of styrene/butyl acrylate latexes, when compared with a reference latex of a styrene/butyl acrylate copolymer prepared with a surfactant sodium dodecyl sulfate. The amount of surfactant grafted onto the particles of the final latex was estimated by conductimetric titration. Between 33 and 68% of surfactant used in emulsion polymerization was found on the surface of latex particles. Electrolyte addition at high concentration and freeze/thaw cycle cause flocculation of latexes. Copyright

Preparation and characterization of low size polystyrene latex particles with various strong acid surface charges

Abstract Small polystyrene latex particles in the size range 30–120 nm have been prepared by emulsion polymerization at 70°C in the presence of a zwitterionic surfactant N , N -dodecyldimethylammoniopropane sulfonate (NC12). The influence of various initiating systems on the particle size and distribution and on the strong acid surface charge density has been investigated. It was found that the potassium persulfate—sodium metabisulfite mixture was an efficient system, especially for producing monodisperse latexes having the same particle size but exhibiting various (sulfate + sulfonate) surface charge densities.

Influence of the texture of phosphinated polystyrene resins on the stability and catalytic activity of supported rhodium complexes

Abstract The Cramer complex, Rh2Cl2(C2H4)2, was fixed onto 3polystyrene — co divinylbenzene (DVB) resins previously chloromethylated and phosphinated. The resins differ by their DVB amount and their porosity. The intrinsic catalytic activity versus hexene hydrogenation is dependent not only on the Rh contents, but more significantly on the localization, and then on the availability of the sites, which depends on the preparation process. The changes that are observed after ageing under hydrogen are related to the formation of metallic particles active for benzene hydrogenation. This evolution of the complex strongly depends on the texture of the resin and on the temperature. A tentative explanation is given.

Contributions to defining the rate constants for the homo- and copolymerisation of butyl acrylate and vinyl acetate

SummaryFree radical homo- and copolymerisations of vinyl acetate and butyl acrylate were carried out in solution. Initial differences in data from homopolymerisation experiments lead us to investigate the influence of an eventual oxygen inhibition on the observed rate of polymerisation.A kinetic study at 70 °C was carried out both with and without a nitrogen purge. A decrease in the rate of polymerisation in the second instance was attributed to the presence of dissolved oxygen in the solution. Estimates of the apparent inhibition constant from different experiments are used to model both homopolymerisation and copolymerisation with vinyl acetate. The importance of taking this phenomenon into account during kinetic studies is demonstrated.

Stabilization optimization of aqueous monomer solutions in oil emulsions using the cohesive energy ratio concept

ABSTRACT The Beerbower-Hill approach based on the Cohesive Energy Ratio concept (CER) has been applied in order to optimize the stabilization of Acrylamide-water or Acrylic Acid (pure and 80% neutralized)- water mixtures in cyclohexane emulsions. Using surface tension measurements for the determination of the solubility parameter of the aqueous phase ( δw), it was found that the presence and amount of the water-soluble monomer could be accounted for the evaluation of the optimal HLB. Predictions were compared to experimental HLB values obtained by using various blends of a low-HLB emulsifier (a sorbitan monooleate named MONTANE 80) and high-HLB emulsifiers (either a nonylphenolpolyoxyethylene [40 EO] or a pOE [20 EO] sorbitan trioleate, MONTANOX 85).

Nonionic Maleic Surfmers

ABSTRACT A set of nonionic maleic surfactants have been prepared, all coming from the derivatization of maleic hemiesters with a long alkyl chain. They are either amidoesters or diester products. In the case of amidoesters, the acid group was first activated and then reacted with primary or secondary or tertiary ethanolamine compounds. In the case of diesters, the hemiester was reacted directly with glycidol, in acid or basic conditions. These surfactants were characterized for their structure by 1H NMR, and for their surface active properties, by surface tension measurements. They were also used in batch emulsion polymerisation of styrene, and seeded core-shell copolymerisation of a 1/1 mixture of styrene and butylacrylate in a semi-continuous process. In both cases, stable latexes with high monomer conversion, and limited amounts of floc were produced, with about the targetted particle size. It was shown that these reactive surfactants are incorporated with high yields, and they are not extracted with acetone or ethanol. However, these latexes do not display the expected steric stabilization observed with other usual nonionic surfactants.