Waterborne Latex Research Articles

Integrating optical coherence tomography with gravimetric and video analysis (OCT-Gravimetry-Video method) for studying the drying process of polystyrene latex system

Latex, an aqueous dispersion of sub-micron polymer particles, is widely used as polymer binder in waterborne coatings and adhesives. Drying of a latex is inhomogeneous, during which the spatial distribution of particles is non-uniform and changes with time, usually resulting in a compromise of the integrity of a dried film. To study drying inhomogeneity of latex, we developed a system integrating optical coherence tomography (OCT) with gravimetric and video analysis (OCT-Gravimetry-Video method) to non-destructively monitor the drying process of non-film-forming latexes consisting of hard polystyrene spheres over time. OCT structural and speckle images of the latex’s internal structure show the packing process of particles, the detachment of latex and the formation of apparent shear bands in cross-sectional views. Video recordings show the formation of cracks and the propagation of the drying boundary in the horizontal direction. The drying curve, measured by gravimetry, shows the drying rate and the water content of the latex at each drying stage. Furthermore, we find that the particle size affects packing and cracking phenomena remarkably. The OCT-Gravimetry-Video method serves as a general and robust approach to investigate the drying process of waterborne latex system. This method can be employed for fundamental studies of colloids and for evaluations of industrial latex products.

Viscoelasticity and Dynamics of Intercalated Polymer/Bentonite Nanocomposites

AbstractThis research investigates confinement‐induced dynamics retardation behavior in intercalated acrylic/clay nanocomposites. Nanostructured waterborne latex contains up to 3 wt% nanoclay, and transmission electron microscopy shows well‐dispersed intercalated morphology. Dynamics in the melt is analyzed using the time‐temperature superposition principle. Confinement induces dynamics retardation, and the entanglement relaxation time τe increases over an order of magnitude. The cooperative motion retardation also reduces viscous dissipation, as measured by the damping tanδ. Moreover, the rubbery modulus increases >10‐fold. The increase of rubbery modulus suggests that confinement hinders chain mobility. The system is then naturally segregated, with intercalated chains having slow dynamics. Hence, thermal analysis of freshly cast films shows one broad glass transition with temperature T g,i for all the nanocomposites, and upon annealing the nanocomposites exhibits two T g's. The T g,high suggests regions of reduced chain mobility (i.e., intercalated chains); the T g,low is associated to the bulk material with regions of higher mobility. The breadth T g,high – T g,low increases with clay content indicating that the regions of fast and slow dynamics become more decoupled as confinement increases.

Biocoatings: challenges to expanding the functionality of waterborne latex coatings by incorporating concentrated living microorganisms

Biocoatings concentrate living, nongrowing microbes in nanoporous adhesive polymer films. Any microbial activity or trait of interest can be intensified and stabilized in biocoatings. These films will dramatically expand the functionality of waterborne coatings. Many microbes contain enzyme systems which are unstable when purified. Therefore, thin polymer coatings of active microbes are a revolutionary approach to stabilize living cells as industrial or environmental biocatalysts. We have demonstrated that some microbes survive polymer film formation embedded in nontoxic adhesive waterborne binders by controlling formulation and drying. Biocoatings can be a single layer of randomly oriented microbes or highly structured multilayer films combining monolayers of different types of microbes on solid, porous, or flexible substrates. They can be formed by drawdown or ink-jet deposition, convective sedimentation assembly, dielectrophoresis, or coated onto or embedded within papers. Controlled drying generates nanoporous microstructure; the pores are filled with a carbohydrate glass which stabilizes the entrapped dehydrated microbes. When the coating is rehydrated, the carbohydrates diffuse out generating nanopores. The activity of biocoatings can be 100s of g L−1 (coating volume) h−1 stabilized for 100–1000s of hours, and therefore, they represent a new approach to process intensification (PI) using thin liquid film bioreactors. A current challenge is that many microbes being engineered as environmental, solar, or carbon recycling biocatalysts do not naturally survive film formation. The mechanisms of dehydration damage that occur during biocoating formulation, ambient drying, and during dry storage have begun to be studied. Critical to preserving microbe viability are minimizing osmotic stress, toxic monomers, biocides, and utilizing polymer chemistries that generate strong wet adhesion with arrested coalescence (nanoporosity). Therefore, controlling desiccation, drying rate/uniformity, and residual moisture are important. Optimization of biocoating activity can be affected at multiple stages—cellular engineering prior to coating (preadaptation), formulation, deposition (film thickness), film formation/drying (generates microstructure), dry storage (minimize metabolic activity), and rehydration. Gene induction (activation) leading to enzyme synthesis following rehydration has been demonstrated. However, little is known about gene regulation in nongrowing microbes. Challenges to optimizing biocoating activity include generating stable film porosity, strong wet adhesion, control of residual water content/form/distribution, and nondestructive measurement of entrapped microbe viability and activity. Indirect methods to measure viability include vital staining, enzyme activity, reporter genes, response to light, confocal fluorescent microscopy, and ATP content. Microbes containing stress-inducible reporter genes can be used to monitor cell stress during formulation, film formation, and drying. Future cellular engineering to optimize biocoatings includes desiccation tolerance, light reactivity (photoefficiency), response to oxidative stress, and cell surface-to-polymer or substrate adhesion. Preservation of microbial activity in waterborne coatings could lead to high intensity biocatalysts for environmental cleaning, gaseous carbon recycling, to produce H2 or electricity from microbial fuel cells, delivery of probiotics, or for biosolar energy harvesting.

Evolving empirical rheological limits to predict flow-levelling and sag resistance of waterborne architectural paints

Good flow-levelling and sag resistance are the two key properties that are expected soon after applying a waterborne latex paint. It is well established in literature that both these properties are predominantly governed by rheology. Numerous papers have been published to evolve fundamental understanding of rheology of waterborne latex paints and their use in predicting flow-levelling and sag resistance properties but most of them deal with the problem in relative scale. The current study focusses on developing an empirical rheology limit to predict the flow-levelling and sag resistance of waterborne paints. Thirteen commercially available waterborne latex paints were taken up for the study that ranged from primer-to-top coat and interior-to-exterior. Rheology studies of these products were investigated in detail at different dilutions (by volume) using hysteresis test and three interval thixotropy test. Rheology flow profiles of latex paints based on cellulosic thickener were distinctly different than that of the paint based on modified urethane thickener; therefore, rheology data of paints based on these two class of thickeners were treated separately. The viscosity after 100 s of recovery and the difference in viscosity after 100 and 10 s of recovery in a three interval thixotropy test were used to derive the rheology limits. Leneta flow-levelling and sag resistance chart tests were carried out on all the paints at different dilutions to define the criteria for acceptable flow-levelling and sag resistance. Viscosity ranges were then defined for cellulosic and modified urethane thickener based latex paints to predict the flow-levelling and sag resistance on non-absorptive surfaces. A good empirical correlation exists between rheological parameters and practical flow-levelling and sag resistance.

Highly Hydrophobic Coatings from Waterborne Latexes.

This work reports on the formation of highly hydrophobic coatings from waterborne latexes able to form films at ambient temperature. The contact angle of film forming copolymers of 2-ethylhexyl acrylate and perfluorodecyl acrylate (PFDA) was limited to 114° because flat surfaces were obtained. Attempts to increase the roughness of the film using blends of film-forming latexes with the latex of PFDA homopolymer (which is not film forming) were not successful under regular casting conditions because the PFDA particles accumulated at the film-substrate interface. Film formation engineering allowed modifying the morphology of the film obtaining a contact angle of 137°.

Performance of latexes containing nano-sized crystalline domains formed by comb-like polymers

The effect of incorporating nano-sized crystalline domains formed by comb-like polymers in waterborne latexes on the mechanical and barrier properties as well as on the water sensitivity of the films cast from these latexes was investigated. Crystalline domains were formed by homopolymerization of stearyl acrylate, which also led to the formation of a very soft amorphous phase. (Co)polymerization of short chain (meth)acrylates formed the main film-forming phase. It was found that the application properties improved with respect to regular latexes devoid of crystalline domains. In addition, the properties of poly (stearyl acrylate) containing latexes were affected by the interplay between its very soft and crystalline domains. The behavior of this system is further complicated by the fact that the Tg of short chain (meth)acrylates that depended on the polymerization strategy, strongly affected the film properties.

Influences and Properties of Mortar Modified by Waterborne Polyurethane Latexes

Two waterborne polyurethane latexes with different tensile strength were employed to modify mortar and the properties of mortar including air entrainment, setting behavior, compressive and flexural strength were investigated. The results show that curing methods, polymer-cement ratio and water-cement ratio have a significant impact on the compressive and flexural strength. The strength of mortar increased under dry curing condition in the range of the polymer-cement ratio from 0.005 to 0.05 (by weight) at water-cement ratio of 0.5. The hydration of the cement containing waterborne polyurethane latexes was not affected and no visible film was found in SEM images.

Comparison of nanocrystalline cellulose and fumed silica in latex coatings

Exploratory work has been undertaken to compare the performance of nanocrystalline cellulose (NCC) with fumed silica in styrene/acrylic latex coatings. NCC has emerged as a promising candidate for the reinforcement of polymeric materials because of its impressive mechanical properties and renewable nature. However, a better understanding of NCC in nanocomposites, compared to more conventional fumed silica-filled systems, is critical to identify feasible commercial applications for NCC. While the dispersion of nanomaterials in polymer matrices is often a challenge, by working with hydrophilic nanoparticles in a waterborne latex, the authors demonstrate that both NCC and fumed silica were dispersed in the latex coatings (up to 9 wt% loadings). The hardness, elastic modulus, resistance to plastic deformation and impact strength were similar for coatings with both types of nanomaterials at loadings below the percolation threshold of NCC (~3 wt%); however, the mechanical performance of NCC-filled coatings was significantly better at higher loadings. In abrasion and corrosion resistance tests, NCC-filled coatings underperformed relative to unfilled and fumed silica-filled coatings. This is the first report that directly compares NCC-filled polymeric coatings with silica-filled coatings including evaluation using industry standards like nanoindentation and corrosion resistance testing. This article contains supporting information that will be made available online once the issue is published.

Incorporation of an acrylic fatty acid derivative as comonomer for oxidative cure in acrylic latex

An acrylic fatty acid derivative (AcFAD) was evaluated as comonomer for promotion of oxidative cure in waterborne latexes. AcFAD was polymerized by solvent homopolymerization and copolymerization and by emulsion copolymerization, and the final products characterized. In the two polymerization processes, NMR analyses confirmed that the reaction occurred involving both the terminal acrylic double bond and the conjugated double bonds of the aliphatic chain. Compared with a reference acrylic latex, the results obtained after AcFAD incorporation showed a time-dependent increase in gel content and in solvent resistance of dry films. These were ascribed to oxidative cure and consequent self-crosslinking of the acrylic polymer, involving the conjugated double bonds in AcFAD side chains. Oxidative cure was also confirmed by FTIR analyses. In addition, reduction in minimum film-forming temperature evidenced that AcFAD has an internal plasticization effect during film formation. Incorporation of this comonomer in acrylic paint binder formulations constitutes a promising alternative to the use of volatile coalescing agents.

Double-Layer Coating Films Prepared from Water-Borne Latexes of Acrylate–Vinylidene Chloride Copolymers: Investigating Their Heavy-Duty Anticorrosive Properties

Aqueous latexes of copolymers of vinylidene chloride (VDC) with an acrylate, namely, methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), or 2-ethylhexyl acrylate (EHA), were employed to form a double-layer coating film for the heavy-duty anticorrosion of metal. Measurements of the water-vapor transmission rate and oxygen-gas transmission rate and electrochemical impedance spectroscopy (EIS) demonstrated that the barrier properties of MA–VDC and EA–VDC films were better than those of BA–VDC and EHA–VDC films. Among the MA–VDC and EA–VDC coatings, EA–VDC85 showed better comprehensive properties and, thus, was selected as the top layer of the designed double-layer coating film. Adhesion tests demonstrated that the BA–VDC and EA–VDC coatings had better adhesion to tinplates than the MA–VDC and EA–VDC coatings and, thus, were suitable for use as the bottom layer of the designed double-layer coating film. The characterizations of the double-layer coating films by adhesion tests and EIS showed that BA–VDC75 was the optimal bottom layer. Under harsh salt-spray corrosion conditions, the optimal double-layer coating film (ca. 50-μm thickness) with EA–VDC85 as the top layer and BA–VDC75 as the bottom layer could protect tinplate well for at least 800 h, and the adhesion of the coating film to the tinplate was still excellent even after 1000 h of corrosion. Scanning electron microscopy, differential scanning calorimetry, and Fourier-transform infrared spectroscopy were used to evaluate the corroded double-layer coating films.

Influence of main ingredients on properties of latex and latex film in polysiloxane modification of styrene-butyl acrylate copolymers

Water borne latexes of styrene (St) and butyl acrylate (BA) copolymer, modified with octamethylcyclotetrasiloxane (D4) were prepared through a semi-continuous emulsion polymerization with dodecylbenzene sulfonic acid (DBSA) as the catalyst for D4 ring-opening and ammonium persulfate (APS) as the initiator for St-BA polymerization. To enhance the compatibility of the silicone with St-BA copolymer by establishing chemical bonds between the two components, 3-(methacryloxy) propyl trimethoxysilane (MPTS) or hydroxyethyl acrylate (HEA) was employed as the coupling agents. The effect of DBSA location at start of emulsion polymerization was studied. It was found that more stable latex was obtained when DBSA was initially added in the reactor in comparison with its addition to the preemulsion followed by slow feeding to the reactor. HEA was also an effective coupling agent to improve the properties of the latex and the latex film. In addition, the influences of the amounts of APS, the catalyst DBSA, and D4 on the latex properties were studied. The process was optimized with regard to the ingredients used in the polymerization. To achieve stable latex with good latex film properties, APS amount should be kept between 0.18 and 0.28 wt.%, D4 monomer no more than 8 wt.% relative to the mass of all vinyl monomers, and the molar ratio of MPTS/D4 is recommended to be 1/4. With HEA as the coupling agent, its amount should be 6.6 wt.% relative to the mass of D4. The mechanical property of the latex film and its water absorption were also characterized.

Reinforcing potential of nanofibrillated cellulose from nonwoody plants

In the present work the reinforcing potential of nanofibrillated cellulose (NFC) from five different non-woody plants, namely; abaca, sisal, hemp, jute and flax was investigated. Nanocomposite materials were prepared by casting a mixture of NFC suspension and a polymer waterborne latex dispersion, and their mechanical properties in both linear and nonlinear ranges as well as the optical properties of the ensuing films were analyzed. Irrespective of their origin, the incorporation of the NFC within the polymer matrix brings about a huge reinforcing effect above the glass transition. The percolation approach has been shown to give a reasonably accurate prediction of the stiffness over the whole range of volume fraction investigated. The evolution of the magnitude of tan δ vs. the NFC content was also analyzed and discussed in term of the effective interfacial thickness. The optical transparency of the nanocomposite film at different NFC content was also studied and compared according to the NFC origin. POLYM. COMPOS., 34:1999–2007, 2013. © 2013 Society of Plastics Engineers

The impact of coating hardness on the anti-barnacle efficacy of an embedded antifouling biocide

The efficacy of antifouling coatings designed to minimise the release of biocide, either by embedded (non-covalent) or tethered (covalently bonded) biocides, relies on sufficient bioavailability of the active compound upon contact between the organism and the coating. This investigation is focused on whether coating hardness affects the efficacy of embedded coating systems. Two experimental, non-eroding and waterborne latex paint formulations composed mainly of polystyrene (PS) or polyvinyl versatate (PV) were chosen for their difference in mechanical properties measured in terms of Buchholz indentation resistance. Ivermectin was added to both formulations to a final concentration of 0.1% (w/v) and the steady state release rate was measured according to ISO 15181 at between 34 and 70 ng cm−2 day−1 for both formulations. Field trials conducted over 3 months showed significant differences in anti-barnacle efficacy between the formulations despite their similar release profiles. The softer PV coating showed complete anti-barnacle efficacy, ie no barnacles were detected, while the harder PS coating showed no efficacy against barnacle colonisation during the same time period. The results indicate a new antifouling strategy whereby a route of intoxication is triggered by the organism itself upon interaction with the coating and its embedded biocide. This finding opens new possibilities in controlling macrofouling by low emission antifouling coatings.

Engineering Cellular Photocomposite Materials Using Convective Assembly.

Fabricating industrial-scale photoreactive composite materials containing living cells, requires a deposition strategy that unifies colloid science and cell biology. Convective assembly can rapidly deposit suspended particles, including whole cells and waterborne latex polymer particles into thin (<10 µm thick), organized films with engineered adhesion, composition, thickness, and particle packing. These highly ordered composites can stabilize the diverse functions of photosynthetic cells for use as biophotoabsorbers, as artificial leaves for hydrogen or oxygen evolution, carbon dioxide assimilation, and add self-cleaning capabilities for releasing or digesting surface contaminants. This paper reviews the non-biological convective assembly literature, with an emphasis on how the method can be modified to deposit living cells starting from a batch process to its current state as a continuous process capable of fabricating larger multi-layer biocomposite coatings from diverse particle suspensions. Further development of this method will help solve the challenges of engineering multi-layered cellular photocomposite materials with high reactivity, stability, and robustness by clarifying how process, substrate, and particle parameters affect coating microstructure. We also describe how these methods can be used to selectively immobilize photosynthetic cells to create biomimetic leaves and compare these biocomposite coatings to other cellular encapsulation systems.

Synthesis and Characterization of Allyl Fatty Acid Derivatives as Reactive Coalescing Agents for Latexes

AbstractThis work evaluated the use of allyl fatty acid esters derived from vegetable oil (palmitic acid, soybean and sunflower oils) as reactive coalescing agents in a waterborne latex system. Allyl fatty acid derivatives (AFAD) from vegetable oils were synthesized by two different processes. The synthesis was monitored by IR‐spectroscopy and the final product characterized by FT‐IR, GC–MS, 1H and 13C NMR. The presence of conjugated double bonds in the aliphatic chain was confirmed, which is a determinant for the proposed autoxidative latexes drying mechanism. Each of the AFAD were subsequently added to a standard acrylic emulsion, in order to study its potential as reactive coalescing agent. The minimum film‐forming temperature (MFT), glass transition temperature (Tg), drying time and rubbing resistance to solvents were evaluated. The results showed that, when added to water‐borne acrylic resins, an AFAD acts as a non‐volatile plasticizer capable of autoxidative crosslinking with itself.

Characterizing and improving performance properties of thin solid films produced by weatherable water-borne colloidal suspensions on bronze substrates

While the development and application for transparent protective coatings for metals continues and broadens, the use of these coatings on high-value outdoor bronze objects, such as statues and architectural elements, requires extensive testing before use. Recent efforts in coatings technology have produced high-performance water-borne latex dispersions containing polyacrylics and poly(vinylidene fluoride) (PVDF) targeting extended coating lifetimes and improved UV resistance. Our studies show that a two-layer polymer film with a solvent based primer (Paraloid™ B-44) and a high performance water-borne topcoat (Kynar Aquatec™ RC-10206) exhibits high impedance as measured by electrochemical impedance spectroscopy. Upon annealing, those films further increased in impedance, suggesting improved corrosion protection compared to unannealed films. When soaking in water, films that contained high loading levels of coalescing agent (Dipropylene glycol monomethyl ether, DPM) in the topcoat formulation resulted in a visible whitening of the basecoat and a decrease in coating resistance. Characterization of the whitened layer by FT-IR indicated the presence of coalescent in the basecoat, suggesting that coalescent migrated from the topcoat into the primer basecoat. Annealing studies were performed to reduce uptake and reverse or inhibit water whitening.

Miniemulsification by catastrophic phase inversion

We present an alternative method for the preparation of high solids content, water-borne latex products from a combination of catastrophic phase inversion (CPI) and miniemulsification. Miniemulsions are commonly prepared by the direct emulsification of a monomer in water and subsequent miniemulsification using a high-shear technique. Herein high solid content dispersions of up to 80w/w% solids content monomer-in-water emulsions are prepared by catastrophic phase inversion followed by miniemulsification with a rotor-stator mixer. The subsequent miniemulsification of these monomer-in-water emulsions proves to be almost four times more energy efficient than is possible with direct miniemulsification using the same mixers and recipes. The highly concentrated miniemulsions thus obtained can be successfully diluted to different solid contents for polymerisation, without compromising the droplet size distribution, and used to produce colloidally stable latexes.

Synthesis of (meth)acrylate water-borne latexes using amino-acid based surfactants: effect of surfactant on film properties

The rapidly increasing concern over environmental changes necessitates the employment of ecologically friendly surfactants for use in emulsion polymerisation without, however, compromising the latex stability or the properties of the cast films. To this end, three series of water-borne, lightly cross-linked latexes based on methyl methacrylate and butyl acrylate were prepared by free radical emulsion polymerisation. 1,4-Butanediol diacrylate served as the cross-linker. Each of the latex series was stabilised by one anionic, amino-acid based surfactant, namely: sodium lauroyl sarcosinate (SLSar), sodium myristoyl sarcosinate (SMSar) and sodium lauroyl glutamate (SLGlu). For comparison purposes, latexes stabilised by sodium dodecyl sulfate (SDS) were also prepared. Within each family, the monomer-to-surfactant molar ratio was varied systematically, whereas the monomer and initiator contents were kept constant in all cases. The hydrodynamic radii (Rh) and the radii of gyration (Rg) of the particles were found to systematically increase with increasing monomer-to-surfactant molar ratio. Films prepared from the SLSar and SDS stabilized latexes were investigated in terms of their optical and thermomechanical properties using transmittance experiments, differential scanning calorimetry, tensile strength and creep experiments. Optimal thermomechanical properties were observed for a particular monomer-to-surfactant molar ratio. Moreover, for the same monomer-to-surfactant molar ratio, the SLSar-based films exhibit remarkable resistance to breaking compared to their SDS counterparts that are relatively fragile.

Understanding the differences in film formation mechanisms of two comparable solvent based and water-borne coatings on bronze substrates by electrochemical impedance spectroscopy

Corrosion protection of bronze, a metal alloy which is commonly used in decorative architectural elements and for statuary, is a challenge particularly as new and previously untested water-borne coatings are supplanting traditionally used solvent based polymers as protective coatings. Studying film formation of coatings to better prevent corrosion of culturally significant works is an important problem in the field of conservation science. This work aims to further understanding of differences between films formed from water-borne lattices versus solvent based polymeric coatings on bronze substrates using electrochemical impedance spectroscopy and gravimetric analysis to investigate the changes of coatings as they formed solid films. Using equivalent electric circuit models, electrochemical snapshots of the developing films were produced. Those models established time points for the transitions between theoretical stages of the nascent films and allowed for a comparison between two major classes of coating types (using the water-borne Rhoplex™ WL-81 and the solvent based Paraloid™ B-44). Electrochemical analysis showed that diffusion occurs during early stages of film formation of both coating types. The prolonged coalescence of coatings produced from the water-borne latex was found to leave those films susceptible to water sorption. Annealing films as a means to drive out remaining hydrophilic additives and to facilitate film formation was investigated.

Self-aligned Graphene Sheets-Polyurethane Nanocomposites

ABSTRACTProcessing graphene and graphene polymer nanocomposites in an aqueous medium has always been a big challenge due to the hydrophobic nature of graphene (or reduced graphene oxide) nanosheets. In this work, a waterborne latex of polyurethane has been used both as the matrix material for embedding the graphene nanosheets and as a unique stabilizer to help produce an up to 5 wt% graphene/PU nanocomposites. The graphene oxide/polyurethane latex aqueous suspension is reduced in-situ using hydrazine, without any trace of aggregation/agglomeration upon completion of the reduction process, which would otherwise have occurred severely were PU not present. A highly aligned nanostructure is produced when graphene content is increased beyond 2 wt%, resulting in a remarkable improvement in electrical and mechanical properties of the nanocomposite. The exceptionally low electrical percolation threshold of 0.078%, as well as 21-fold and 14 fold increases in tensile modulus and strength, respectively, have been attained thanks to the alignment of graphene nanosheets in the polymeric matrix.