Latex Formulation Research Articles

Release of dithiocarbamates into artificial sweat from latex vulcanizates: Effects of the accelerator type and storage time

AbstractThe release of commonly used dithiocarbamate accelerators, namely, zinc diethyldithiocarbamate (ZDEC), zinc dibutyldithiocarbamate (ZDBC), zinc dibenzyldithiocarbamate, zinc isobutyldithiocarbamate, and zinc diisononyldithiocarbamate, into artificial sweat from natural rubber latex vulcanizates was studied. The extent of release of ZDEC was much higher than that of ZDBC or other higher homologues, as indicated by high‐performance liquid chromatography analysis. The effect of the storage time on the extent of release of ZDEC into artificial sweat from vulcanizates prepared with various amounts of ZDEC was studied. The result showed that ZDEC migrated significantly to the surface of the vulcanizates upon storage, and the amount that migrated increased with an increase in the shelf time. Moreover, the amount of ZDEC that migrated increased with an increase in the amount of ZDEC added to the latex formulations. The rate of migration, as determined from the slopes of the migration curves, was dependent on the residual ZDEC content, which in turn depended on the initial level of ZDEC incorporated during latex compounding. The analysis of the migration data showed that the migration followed a Fickian behavior, and the diffusion coefficient of ZDEC was slightly dependent on the concentration. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2055–2061, 2006

Latex produced with carboxylic acid comonomer for waterborne coatings: Particle morphology variations with changing pH

Carboxylic acid comonomers are often added to latex formulations to improve colloidal stability and to help control the physical structure of composite (core-shell type) particles. We have performed a systematic study of the incorporation of methacrylic acid (MAA) within styrene/butyl acrylate copolymer seed latices, and determined the eventual effect on the morphology of the composite particles when using a second-stage monomer that is either polar (MMA) or nonpolar (BMA). These latices have been produced in batch and semibatch reactions in the pH range of 3–7. At low pH, the MAA groups are not ionized, but at the higher pH they may be nearly completely ionized. Here, we report that for batch reactions carried out within the above pH range, the latex particle morphologies of the PMMA second-stage systems change dramatically with increasing pH, while those for the PBMA system do not change at all. These results show that one cannot easily generalize the effect of acid comonomers on the morphology of composite latex particles, as this depends upon the choice of the copolymers in the latex and the process characteristics of the polymerization reaction.

Artificial Neural Networks Associated to Calorimetric Measurements Used as a Method to Predict Polymer Composition of High Solid Content Emulsion Copolymerizations

Inspired by biological systems, artificial neural networks (ANN) have demonstrated to be powerful tools to model non-linear systems, such as high solid content latexes produced by emulsion polymerization which have a great importance in the polymeric industry, essentially for environmental reasons, since they usually have water as a continuous phase. The quality of the produced polymer is closely related to the structure of the polymeric chain. In order to propose technical and economically feasible alternatives to control a polymeric structure, this work is aimed to develop a new methodology based on ANN associated with calorimetry to predict the polymeric structure. The designed ANN presented excellent results when tested with process condition variations (such as temperature and reaction time) as well as when they were submitted to test concerning the variation on the proportion of monomers in the latex formulation. Hence, it was possible to conclude that ANN, associated to calorimetry, lead to an efficient method to predict the polymer composition in emulsion copolymerizations.

Use of latex systems for controlling the properties of urea-formaldehyde resins

The influence of latex formulations and a filler, Vulkasil, on the processing and physicochemical properties of urea-formaldehyde resins was studied.

Cycloaliphatic epoxide crosslinkable core-shell latexes: A new strategy for waterborne epoxide coatings

New core-shell acrylic latexes designed for crosslinking with cycloaliphatic diepoxides were prepared. The core consisted of methyl methacrylate (MMA), butyl acrylate (BA), 2-hydroxyethyl met hacrylate (HEMA), and the shell MMA, BA, and methacrylic acid (MAA). A strong acid acrylate was incorporated into the shell to catalyze the crosslinking reactions. The diepoxide crosslinker was introduced into the latex formulation via three methods: (1) added with the monomers during the polymerization of the latex, (2) added after the preparation of the latex in an organic solvent, and (3) added as a separate emulsion. The stability of epoxide was shown to be dependent on latex morphology, initiator system, and reaction conditions.

The cleaning of polymer colloids

The current state of knowledge of the cleaning of polymer colloids is reviewed with regard to a wide range of cleaning and characterisation techniques. The type, level and quantity of impurities involved with different polymer latex formulations varies widely. Even for similar formulations, differences in the nature and number of functional groups reported are often a consequence of sometimes subtle differences in the cleaning procedures employed. Not only may surface functionality be affected but also monomer and oligomer extraction procedures may lead to morphological changes in the particles. No single technique alone is likely to be able to remove all impurities. Care is needed to avoid the introduction of new impurities from the equipment, materials and water used as well as possible contamination from atmospheric carbon dioxide, bacteria and fungi. These factors also need to be considered in the storage of latex particle standards.

Flexural behaviour of reinforced concrete beams repaired with styrene—butadiene rubber latex, silica fume and methylcellulose repair formulations

The use of plain cement mortar in repair works is limited to unimportant works because of its poor adhesive bond to the substrate and its performance from the point of view of durability. Polymer-modified cement mortar has replaced plain mortar for these reasons. Also, the incorporation of silica fume and methylcellulose in repair systems has been found to provide a better durability and overall performance. This paper presents the results of an experimental investigation of the flexural behaviour of six reinforced concrete beams. Five beams were repaired using five different repair systems, namely plain cement mortar and mortars modified with latex (L), latex and silica fume (L—S), latex silica fume and methylcellulose (L—S—M), and silica fume and methylcellulose (S—M). The sixth beam was an unrepaired control beam. The repair procedure was carried out while loading the beams, to match the on-site practice. The size of the beams was 100 X 150 X 1200 mm and they were reinforced with two 10 mm diameter steel rods with a yield strength of 551 MPa. The test results showed that beams repaired with L, L—S and L—S—M mortars successfully restored the structural capacity of the unrepaired beam, besides improving the durability, crack pattern and toughness characteristics of these beams. The use of plain or S—M mortars showed a poor structural performance since they exhibited early separation along the contact interface with the substrate, as well as reduced ductility and toughness.

Development of and results from a chromatographic technique for the analysis of competitive adsorption on stabilized TiO 2 surfaces

A unique size exclusion chromatography (SEC) technique is described and used to evaluate the competitive adsorptions of a nonionic formulation surfactant and nonionic Hydrophobe-modified Ethoxylated URethane (HEUR) thickeners on pretreated rutile titanium dioxide (TiO 2). The pigment is surface treated with Al 2O 3 and with SiO 2 before it is dispersed by grinding in the preparation of latex coating formulations. Before the latex and thickener are added to this grind, an organic oligomeric acid and a nonionic surfactant are added to the pigment slurry. The organic oligomeric acids used in this study contain maleic acid and one of three alpha-olefins, 1-hexene (C 6H 12), l-decene (C 10H 20−) or l-tetradecene (C 14H 28−). This grind is then let down into the latex formulation containing hydroxyethyl cellulose or HEUR thickener and other components. Without organic dispersant, the nonionic surfactant adsorbs on the silica treated pigment in alkaline media. Adsorptions of the oligomeric polyacid dispersant and nonionic surfactant were higher on TiO 2 containing high SiO 2 surface concentrations than those containing high Al 2O 3 surface concentrations. Nonionic HEUR polymers and nonionic surfactants do not adsorb significantly on Al 2O 3 treated TiO 2 unless the pigment is also pretreated with an organic dispersant possessing pendant hydrophobic groups. In competitive adsorption studies the HEUR polymers were not displaced from the organic dispersant stabilized TiO 2 surface by the nonionic formulation surfactant. This adsorption behavior contrasts with competitive adsorption studies on acrylic latices when the HEUR polymers have small or intermediate size terminal hydrophobes. The permanence of HEUR adsorption on inorganic and organic dispersant-treated titanium dioxide is consistent with the higher gloss noted in corresponding latex coating systems.

Shellac Coatings for Grapefruits that Favor Biological Control ofPenicillium digitatumbyCandida oleophila

Abstract Shellac coatings that support significantly high populations of the yeastCandida oleophilafor biocontrol ofPenicillium digitatumwere formulated for postharvest application to grapefruits. An aqueous shellac latex was not toxic to the yeast and was suitable for testing constituents of commercial shellac coatings. Alteration of this product to contain 2% ethanol was nontoxic, but 4, 6, 8, and 10% ethanol killed 90% of the yeast cells within 24, 4, 2, and 0.5 h, respectively. Above a pH of 8.25, cell death was rapid when amine bases were incorporated. This level of toxicity resulted from addition to the shellac latex of more than 1.5% morpholine or 0.3% ammonia; a similar death rate developed nearer to pH 9.0 with incorporation of approximately 1.5% KOH. Although higher concentrations of base were required for the preparation of experimental formulations derived from bleached shellac, shellac ester, and wood resin ester, the relationship between the pH of the liquid coating and yeast survival persisted. Particularly with wood resin ester, KOH solutions maintained higher populations of yeast. When applied to grapefruits postharvest, a shellac latex formulation and a dissolved shellac/shellac ester formulation supported surface populations of yeasts between 104and 105CFU/cm2throughout 4 months of storage at 13°C. These preparations significantly improved shelf-life when compared to fruits coated with a commercial shellac formulation.

The preparation of RVNRL using Malaysian - produced latices

The research project is carried out using the latices supplied by three of the suppliers in Malaysia. From the results of the studies carried out in search for the best sensitiser for RVNRL preparation, the use of n-butyl acrylate ( n-BA ) as a sensitiser seemed to give the most promising results. However, its use as a sensitiser is not universal to all latices available in the country. The problem was overcome by the use of different formulations for different latices. For the latex supplied by Golden Hope ( Hytex ), a combination of sensitisers i.e. n-BA plus 2-ethyl hexyl acrylate ( 2-EHA ) with a 10 % potassium hydroxide solution as the stabiliser, was the requirement. Latex supplied by MARDEC ( Matex ), seemed to need only n-BA as the sensitiser. Nevertheless, a stabiliser was still required and the use of a 10 % KOH solution was found to be suitable. A large range of stabilisers and sensitisers were applicable to Guthrie latex. The use of n-BA as the sensitiser and potassium laurylic acid as the stabiliser seemed the most favourable formulation. All the results are discussed in the form of correlation between dose and the tensile properties of RVNRL vulcanizates, equilibrium swelling ratio and standing time of the latex formulation.

Formulation and optimization of a modified microporous cellulose acetate latex coating for osmotic pumps.

A cellulose acetate (CA) latex was modified for use as a microporous coating for osmotic devices. Potassium chloride core tablets were coated with a CA latex formulation containing a plasticizer (triacetin) and a pore-forming agent (urea). To promote the coalescence of the cellulose acetate latex beads into a film on the surface of the tablet, it was necessary to cure the coated tablets, hereafter referred to as devices, at elevated temperatures. The objectives were to determine the effect of four formulation variables (plasticizer level, pore former level, cure time, and cure temperature) on the in vitro KCl release rate and coat burst strength using a full 2(4) factorial experimental design. Burst strength was measured as the number of grams force a depleted device could support before bursting. The results indicated that urea content was the most important variable, followed by triacetin content and cure time. Cure temperature did not influence the results. Response surfaces generated with the experimental values were used to predict a formulation which would have both a high release rate and a high burst strength. This formulation was prepared and tested both in vitro and in vivo in dogs. The in vitro release rate and burst strength results agreed with those predicted by the model. The in vitro and in vivo release rates were not statistically significantly different as determined by ALQ analysis.

Ocular therapy with nanoparticulate systems for controlled drug delivery

In recent years, several colloidal preparations for ophthalmic use have been investigated, based on nanoparticles or liposomes. However, no evidence could be found in most cases of any considerable advantage over conventional formulations. In contrast, the introduction in the early eighties of the concept of in situ gel formation by means of highly concentrated latex systems demonstrated that a considerable prolongation in duration of action could be obtained. This had previously been achieved only with inserts. In the past 15 years, the coating technology developed in the paint industry has been the driving force for the very rapid evolution in the field of aqueous dispersions. Polymers with solubility properties depending on the pH, such as cellulose derivatives, cannot be prepared by emulsion polymerization techniques. An alternative method for the preparation of polymeric dispersions in the nanometer size range is the emulsification of the polymers, their solutions or melts into water, using conventional emulsifiers, stabilizer and emulsification techniques. Different approaches for the preparation of these so-called “latex formulation” are possible, e.g., solution emulsification, phase inversion, self-emulsification, etc. Recent advances in our knowledge of in situ gel forming systems used via the ocular route by drug-carrying nanoparticles will be discussed. These systems are based on the mechanism of drug adsorption onto the surface of colloidal particles (0.3 μm average particle size) which show a good biocompatibility. These colloidal or near colloidal dosage forms have low viscosity and can accommodate solid content up to 40% w/w. The features are that these systems provide a prolonged therapeutic effect, that they can be applied as easily as existing eye drops and that they show a good tolerance, which should result in improved patient compliance.

Effect of a Single Application of Napthaleneacetic Acid on Yield and Shoot Growth of Young Lemon Trees1

Abstract Application of 1% ethyl ester of napthaleneacetic acid (NAA) in an aqueous or latex formulation to trunk and scaffold branches of pruned lemon trees [C. limon (L.) Burm.] did not affect yield during the season of application or during the year following application. Regrowth of trunk and limb sprouts was controlled for approximately 1 year.