Morphology Of Latex Particles Research Articles

Fabrication of core-shell polyacrylate latex pressure sensitive adhesives modified by fluorinated monomer and film properties

In this work, a series of fluorinated core-shell polyacrylate latex pressure sensitive adhesives (PSAs) were successfully synthesized through monomer-starved seeded semi-continuous emulsion polymerization. Specifically, (meth)acrylate monomers were employed as the main materials, with dodecafluoroheptyl methacrylate (DFMA) were used as modified monomer. The impact of fluorine monomer DFMA on the resulting core-shell latex and PSA properties was thoroughly examined. FTIR analysis confirmed the successful incorporation of DFMA into the latex copolymer through emulsion polymerization. TEM images illustrated that the morphology of latex particles exhibit a distinct core-shell structure. The results also showed that with the addition of DFMA, the water absorption and water whitening of the latex films decreased, while the water contact angle and thermal stability are improved. Interestingly, the latex films with DFMA added to the shell phase exhibit a larger WCA value when compared to those with DFMA in the core phase, further confirmed by XPS results. Finally, the adhesive properties of the fluorinated core-shell acrylate PSA were evaluated. The results of shear strength and gel content demonstrate that the prepared PSA exhibits excellent cohesive properties. Thus, this work could present a feasible strategy for optimizing the comprehensive properties of acrylate latex PSAs.

Facile Synthesis of Fluorinated Polyacrylate Elastomer via Emulsion Polymerization Using Adjustable Amphiphilic Star Macro‐RAFT Agent as Surfactant

AbstractNovel thermoplastic fluorinated polyacrylate films possessing excellent mechanical performance are prepared by emulsion polymerization latex using adjustable amphiphilic star macro‐reversible addition‐fragmentation chain‐transfer (macro‐RAFT) agent as surfactants in this work. First, star macro‐RAFT agent equipped with six amphiphilic arms is synthesized via two‐step RAFT polymerization of acrylic acid (AA) and 2,2,2‐trifluoroethyl acrylate (TFEA) in the presence of hexa‐functional RAFT agents. The surface activities of the as‐synthesized amphiphilic star macro‐RAFT agents in aqueous solutions are studied. Subsequently, various fluorinated polyacrylate latexes are obtained by conducting emulsion polymerization of 2,2,3,4,4,4‐hexafluorobutyl acrylate (HFBA) and butyl acrylate (BA) using the amphiphilic star macro‐RAFT agents as both RAFT agents and surfactants. The latex particle morphologies are studied by transmission electron microscope (TEM) and particle size is measured by dynamic light scattering (DLS). The effects of PAA segment length, HFBA/BA mole ratio, and TFEA segment length on the surface morphologies of the fluorinated polyacrylate films are illustrated by investigating the surface properties using water contact angle test and atomic force microscopy (AFM). Finally, the elastomeric films obtained by directly casting the prepared fluorinated polyacrylate latexes show excellent comprehensive properties such as tensile strength over 4 MPa, elongation at break ≈700%, permanent deformation below 25%. Water absorption test is also provided as a reference.

On-line control of particle morphology of waterborne dispersed polymers using master trajectories

On-line control of the morphology of waterborne composite latex particles is an unsolved issue because of the lack of techniques for on-line monitoring of particle structure. As an alternative to online monitoring, soft sensors based on detailed mathematical models for the development of particle morphology can be used but they require knowledge of a large number of system-specific parameters and, therefore, they are not suitable for a market characterized by large portfolios of products. This work presents a new method to achieve control over final particle morphology by using master trajectories obtained from a given reference process as set points. The master trajectories are derived from the understanding of the fundamental phase separation and phase migration processes occurring during the development of the particle morphology, and can be estimated during the process from available on-line measurements (overall and instantaneous monomer conversion, and reactor temperature). The approach opens the way to on-line control of the particle morphology and can also be used for process optimization.

Waterborne Cross-Linkable Polyacrylate Latex Coatings with Good Water Resistance and Strength Stabilized by Modified Hectorite.

Polyacrylate emulsions were prepared by Pickering emulsion polymerization with multi-modified hectorite as a modifier. The proper wettability of modified hectorite and the stability of O/W emulsions prove that modified hectorite has good emulsification properties. The stability of polyacrylate latexes and the morphology of polymer latex particles were then investigated to explain the role of multi-modified hectorite in stabilizing polyacrylate latex. In addition, the improved mechanical properties and water resistance of the latex make it a potentially excellent coating. Multi-modified hectorite as an alternative modifier to conventional surfactants offers a potential application of nanosolid particles that meet the partial wetting conditions for water and oil as stabilizers for the production of latexes for coatings.

On-line control of the particle morphology of composite polymer-polymer waterborne dispersions

Particle morphology of composite polymer latexes evolves continuously throughout the polymerization process and plays an important role in the practical application of emulsion polymers. Therefore, developing on-line control strategies to control particle morphology is a long-term goal in industry that can guarantee the consistent production of latexes with the desired properties for their final application. In this article, the development of an on-line control strategy for particle morphology of polymer-polymer composite latex particles was investigated. The control strategy was based on the idea that the evolution of the morphology depends on the viscosity of the particles (that in turn depends on the monomer concentration in the particles) and the time available for cluster migration (that depends on the polymerization rate). The monomer conversion and the polymerization rate were monitored by reaction calorimetry. The robustness of the developed control strategy in the presence of disturbances during the process is assessed and the limits of the attainable particle morphology were explored.

Study on the Preparation and Anti-CO2 Corrosion Performance of Soap-Free Latex for Oil Well Cement.

To improve the resistance to CO2 corrosion of oil well cement, soap-free emulsion polymerization was used to prepare a soap-free latex (PSAC) with sodium styrene sulfonate (SSS) and nano-SiO2 (SSS/SiO2) as the ionic copolymer emulsifier. The effects of SSS/SiO2 on the performance, thermal stability, and latex particle morphology of the PSAC were investigated through zeta potential, TGA, and TEM measurements, respectively. The carbonation resistance properties of cement with PSAC were evaluated, and the anticorrosion mechanism of the PSAC cement was determined by SEM, EDS, XRD, and 29Si NMR analyses. The results showed that the PSAC particle size was uniform, the particles were monodispersed, and they had a typical core–shell structure and good heat resistance. The carbonation resistance test results showed that after 60 days of corrosion, the corrosion depth of the cement with 12.0% PSAC content was only 2.16 mm, the permeability was 0.0018 mD, and the decrease in the compressive strength was 6.65%. The porosity in the cement was reduced significantly, and the pore volume (>50 nm) of the cement was reduced by 0.24 times. The PSAC film formation decreased the contact between hydration products and CO2. In addition, the nano-SiO2 in the PSAC reacted with Ca(OH)2 to reduce the free Ca(OH)2 content in the cement and generate C–S–H gel with a low Ca/Si ratio and high polymerization, which did not react as readily with CO2.

Fabrication of fluorescent polymer latexes based on rhodamine B derivatives and their reusable films for Fe3+ detection

The stimulus-responsive P(MMA-co-BA-co-RhBUEA) latexes were prepared by miniemulsion polymerization of butyl acrylate (BA), methyl methacrylate (MMA), and a rhodamine-based probe RhBUEA. Their chemical composition and structures were characterized by FTIR and UV–Vis spectral analysis. Meanwhile, the effects of AIBN, SDS, and RhBUEA content on the miniemulsion polymerization and the morphology of latex particles were investigated. Based on the recipe of 30 mM SDS to the volume of water, 2 wt% AIBN and 5 wt% RhBUEA to the total monomers, the sensing properties of the resultant latex and its film were studied. Both the latex and the latex film displayed the noticeable color change, high sensitivity, superior selectivity, and anti-interference properties towards Fe3+ over other metal ions in aqueous solution. The detection limits of the latex and the latex film were 0.122 and 0.208 μM, respectively. Furthermore, the film sensor exhibited good recyclability thanks to the off-on switch, possessing the potential as a portable and reversible chemosensor for the naked-eye detection of Fe3+.

Modification of Natural Rubber Latex by Graft Copolymerization of 2-Ethylhexyl Acrylate and Methacrylic Acid

Natural rubber (NR) grafted with 2-ethylhexyl acrylate (2-EHA) and methacrylic acid (MAA, collectively NR-g-PEHA/MAA) was synthesized by emulsion polymerization. Tetraethylenepentamine and cumene hydroperoxide were used as redox initiators. The successful grafting of 2-EHA and MAA onto NR was confirmed by Fourier transform infrared spectroscopy. The morphology of the NR latex particles was observed by transmission electron microscopy. The effects of reaction temperature, initiator dosage, feeding mode, and hard monomer content on the mechanical properties of the modified NR film were investigated. Grafted polymer chains were unevenly wrapped on the outside of NR particles, and smaller particles were more easily grafted. Crosslinking was characterized using a toluene swelling method. Thermal stability and glass transition temperature were examined by differential scanning calorimetry and thermogravimetric analysis. The results showed that the thermal stability of NR-g-PEHA/MAA had been improved, and the glass transition temperature (Tg) was unchanged.

Design and fabrication of PVAc-based inverted core/shell (ICS) structured adhesives for improved water-resistant wood bonding performance: II. Influence of copolymerizing-grafting sequential reaction

PVAc-based inverted core/shell (ICS) structured latex adhesive with improved water- and heat-resistance was prepared by a copolymerizing-grafting sequential reaction approach. The sequential reaction process combines the function of a copolymer layer and an active grafting site to controllably achieve the thermodynamic non-equilibrium ICS morphology with hydrophilic poly(vinyl acetate) (PVAc) cores and hydrophobic polystyrene (PS) shells. The difference between the sequential reaction approach and the chemical grafting method was explored. Structured latex particle morphology, transferring from strawberry-like particles, over particles with large and irregular PS protuberances, to nearly spherical particles with a smooth surface, was microscopically visualized by changing the amount of butyl acrylate (BA) in the PVAc copolymer cores. The heat- and water-resistant bonding of PVAc-based adhesives on wood blocks were evaluated by shear strength at both dry and wet conditions, as well as the boiling water failure time. The results showed that a significant improvement of water- and heat-resistance, especially for boiling water resistance, was successfully obtained. This novel approach paves a way for controlled design and manufacture of high-performance emulsion adhesives through tailoring particle morphology.

Preparation, crystallization and properties of Bi2WO6 nanoparticles

Bismuth tungstate (Bi2WO6)-sodium polyacrylate (PAANa) latex particles were prepared by inverse miniemulsion and hydrothermal treatment. The effects of Bi(NO3)3/Na2WO4 dosage ratio and different hydrothermal treatment conditions on the particle size and morphology of Bi2WO6-PAANa latex particles were studied. The results show that the stability of the inverse microemulsion droplets was effectively improved with the increase of the soluble salt in the inverse microemulsion system, and the effect of different hydrothermal treatment on the particle size of the colloidal particles was not significant. During the formation of Bi2WO6 nanoparticles, PAANa latex particles could become a reaction site for forming Bi2WO6 nanoparticles, and Bi2WO6 nanoparticles were dispersed in the polymer. The effects of different hydrothermal treatment conditions on the size, crystal form and light absorption properties of Bi2WO6 nanocrystals were studied. The results show that Bi2WO6 nanoparticles with orthorhombic tungsten-rhenium ore structure could be prepared under different hydrothermal treatment conditions; moreover, the temperature at which the hydrothermal treatment forms the lowest Bi2WO6 nanocrystals was 130 °C. But at pH 9, the product was no longer pure phase. The prepared nanocrystals simultaneously exhibited strong ultraviolet-visible absorption characteristics and luminescence intensity. Finally, the Bi2WO6 nanoparticles with photoluminescence properties could be successfully prepared by the inverse miniemulsion method.

Design and fabrication of PVAc-based inverted core/shell (ICS) structured adhesives for improved water-resistant wood bonding performance: I. Influence of chemical grafting

Strategy for fabricating inverted core/shell (ICS) structured latex particles to improve the water- and heat-resistance of PVAc-based adhesives was investigated. A grafting layer was fabricated with acrylonitrile (AN) to achieve a thermodynamic non-equilibrium ICS morphology with a hydrophilic poly(vinyl acetate) (PVAc) core and a hydrophobic polystyrene (PS) shell. The function of the grafting layer was explored by tuning the AN loading levels and core-to-shell ratios. Special latex particle morphologies, transferring from strawberry-like with secondary PS particles, over neat strawberry-like, to final ball-like morphology, were observed and verified by electron microcopies. The wood adhesive performance of PVAc-based latex adhesives, particularly for heat- and water-resistant bonding, were evaluated by shear strength at both dry and wet conditions, as well as the boiling water failure time, showing a significant enhancement of boiling water resistance. This general approach opens an avenue for controlled design and manufacture of high-performance emulsion-based adhesives containing structured particles.

The influence of particle morphology on the structure and mechanical properties of films cast from hybrid latexes

Two phase latex particles offer a potential route to obtain homogeneous, transparent and mechanically strong films with low minimum film formation temperature (MFFT) without the addition of any kind of volatile organic compound (VOC). In this work, we have studied how the morphology of hybrid latex particles influences the morphology and the mechanical strength of polymer films cast from latex dispersions. Hybrid particles containing a hard, high Tg seed (Styrene(S)/Acrylamide(AM), Tg = 101 °C) and a low Tg (Methyl Methacrylate(MMA)/Butyl Acrylate(BA)/Styrene(S), Tg = 13 °C) second phase polymer were synthesized. Different particle morphologies were obtained by slight variation of the amount of AM in the seed and S in the second-stage polymer. Film morphologies and properties for films cast at 60 °C were compared in order to find a link between particle morphology and film properties. Moreover, the effect of annealing temperature on film morphology was investigated. Through careful control of particle microstructure during the latex synthesis it is shown that good control over the final properties of the polymer film can be obtained, even for nominally similar polymer mixtures.

Effect of Shell Growth on the Morphology of Polyvinyl Acetate/Polystyrene Inverted Core-Shell Latex Fabricated by Acrylonitrile Grafting.

A novel strategy for fabricating inverted core-shell structured latex particles was implemented to investigate the morphology and properties of polyvinyl acetate (PVAc)-based latex. In this study, active grafting points were synthesized onto the surface of PVAc latex cores via grafting acrylonitrile (AN) to obtain a controllable coating growth of the shell monomer, styrene (St). The effect of shell growth on the morphological evolvement was explored by tuning the time of shell monomer polymerization. Unique particle morphologies, transferring from “hawthorn” type, over “peeled pomegranate” type, to final “strawberry-like” type, were observed and verified by electron microscopy. The morphological structure of latex particles exerted a significant effect on the particle size, phase structure, and mechanical properties of the obtained emulsions. The water-resistance of PVAc-based latex was also evaluated by the water absorption of latex films. More importantly, the experimental results provided a reasonable support for the controlled growth of St monomer, that is, the self-nucleation of dispersive St monomer can be transformed to in-situ coating growth on the PVAc core surface depending on the AN-active grafting points. This fabricating approach provides a reference for dynamical design and control of the latex particle morphology.

Preparation of epoxy-acrylate copolymer/nano-silica via Pickering emulsion polymerization and its application as printing binder

This paper presents a facile and efficient synthesis method to fabricate epoxy-acrylate copolymer/nano-silica latex via Pickering emulsion polymerization stabilized by silica sol. The effects of solid contents, silica concentration and polymerization time on emulsion polymerization were studied. The core-shell epoxy-acrylate copolymer/nano-silica was obtained with average diameter 690 nm, was observed by Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS). The formation mechanism of epoxy-acrylate copolymer/nano-silica emulsion polymerization was proposed through observing the morphology of latex particles at different polymerization time. Fourier Transformation Infrared (FT-IR) and Thermogravimetric Analysis (TGA) were used to study structure and thermostability of the composites. Morphology of the latex film was characterized by Scanning Electron Microscope (SEM). The results indicated that nano-silica particles existed in the composite emulsion and could improve the thermal stability of the film. The epoxy-acrylate copolymer/nano-silica latex was used as binder applied to cotton fabric for pigment printing. The application results demonstrated that Pickering emulsion stabilized by silica sol has good effects in the pigment printing binder without surfactant. Compared with commodity binder, the resistance to wet rubbing fastness and soaping fastness were improved half grade.

Novel Synthesis Method and Characterization of Poly(vinyl acetate‐butyl acrylate) Latex Particles: Effect of Silanol‐Terminated Poly(dimethylsiloxane) Surfactant on the Seeded Emulsion Copolymerization

AbstractIn a conventional semi‐batch seeded emulsion copolymerization of vinyl acetate/butyl acrylate (VA/BA) using hybrid surfactants namely, dioctyl sulfosuccinate (DOSS) as an anionic surfactant, nonylphenol ethoxylate (KENON 30) as a non‐ionic type, and polydimethylsiloxane surfactant (having hydrophilic silanol‐terminated, called PDMS). The effect of PDMS on the properties of the latex synthesized was investigated by measuring solid content, viscosity, colloidal stability, particle size distributions of the base latex, viscosity average molecular weight () of the copolymer, latex particle morphology, glass transition temperature (Tg) of a copolymer and thermal gravimetric analysis (TGA). Particle size of the base latex decreases (Z‐average from 246.48 to 143.69 nm) upon increasing the amount of PDMS surfactant in the recipe (up to 6 wt%). The presence of PDMS surfactant in the hybrid surfactants led to a significant increase in the solid content (from 48.71 to 51.31 wt%), viscosity (from 334 to 806 centipoise, cp) and (from 1.91 × 105 to 2.34 × 105 g mol−1). Thermal stability and Tg of the copolymer were increased with addition of PDMS surfactant (thermal stability from 344.77 to 389.81 °C and Tg from −20.7 to 21.7 °C). The colloidal stability evaluated using the electrolyte addition method was improved with addition of PDMS surfactant. The uniform morphological structure of the final particle is the main effect of using PDMS in the hybrid surfactants.

Control over ABA-type triblock copolymer latex morphology in RAFT miniemulsion polymerization and mechanical properties of the latex films

Thermoplastic elastomers (TPEs) are of growing commercial importance in the worldwide non-tire rubber market. It is because of their unique thermomechanical properties that associate with the phase morphologies. Controlled/living radical (mini)emulsion polymerization holds good promise for synthesis of ABA-type triblock copolymer TPEs. Both the mechanical and morphological investigations have been conducted on the solvent films of this copolymer latex. However, neither the copolymer latex particle nor the latex film has been investigated in terms of morphologies or mechanical properties. This work reports the development of triblock copolymer latex particle morphologies through reversible addition-fragmentation chain transfer (RAFT)-mediated miniemulsion polymerization. ABA-type triblock copolymers consisting of outer polystyrene blocks and inner polyacrylate blocks are synthesized in two steps through chain extension from symmetric RAFT agents. A variety of novel particle microstructures are realized by regulating either block ratios or particle surface attraction for each blocks. The nanostructured latex are also used for casting latex films. It is observed that the film morphologies do not attain thermodynamic equilibrium even after thermal annealing. In comparison to the solvent films with similar hard block contents, the latex films have higher elastic modulus, but exhibit inferior mechanical responses in terms of elongation at break and ultimate strength. The possible reason is attributed to the suppressed interparticle self-assembly of copolymers during latex film formation and scarce of bridging configuration of central block connecting different glassy domains within the final films.

Efficient modification of nanosilica particles in preparation of anti-scratch transparent polyacrylic films through miniemulsion polymerization

Surface modification of silica nanoparticles was performed chemically by using glycidyl methacrylate and the conditions were optimized to reach to a reasonable efficiency. Nanocomposite particles containing the above modified nanosilica were prepared through miniemulsion polymerization in the presence of methyl methacrylate–butyl acrylate–methacrylic acid. Latex particle size and morphology were thoroughly investigated by DLS, SEM, AFM and TEM analyses. Results showed that the silica nanoparticles were well-dispersed in the polymer matrix to induce their properties remarkably. A quantitative EDX analysis was used for indirect assessment of the encapsulation efficiency and the encapsulation efficiency of silica nanoparticles was found 92 %. The obtained nanocomposite films were highly transparent according to the UV–Vis analysis and were able to transmit more than 80 % of visible light. Excellent scratch resistances of the nanocomposite films were obtained in the presence of silica nanoparticles due to the optimum dispersion and their friction coefficients were investigated.

A new approach for mathematical modeling of the dynamic development of particle morphology

A new model for the dynamic evolution of the morphology of polymer-polymer latex particles has been developed. This model overcomes the limitations of the existing methodologies that were only able to provide the morphology of a single particle, which is only a restricted view of the real system that contains a distribution of particle morphologies. Taking into account the relevant kinetic and thermodynamic effects, the new model calculates the distribution of morphologies for the whole population of polymer particles with less computational effort than that needed by the previous models to calculate the morphology of a single particle. The model was validated by fitting the evolution of particle morphology of composite particles during polymerization of methyl methacrylate on a polystyrene seed. Furthermore, the ability of the model to predict the evolution of the particle morphology for different cases was explored.

Fabrication and evaluation of one-component core/shell structured latex adhesives containing poly(styrene) cores and poly(acrylate) shells

A one-component, non-crosslinked, and ambient temperature-cured core/shell (CS) structured waterborne poly(styrene-acrylate) (PStA) latex adhesive was prepared by two-stage seeded emulsion polymerization. The first-stage polymers were non-polar styrene-based copolymers with Tgs ranging from 86°C to 41°C and the second-stage polymer was polar acrylate-based copolymer having a Tg of 8°C. The effect of latex particle morphology and film microstructure on the CS structured PStA latex adhesive was examined by evaluating film thermal properties and mechanical performance. The results have shown that incorporation of soft shell polymers into hard core polymers can improve adhesive properties without compromising film-forming ability. Wood adhesive performances of latex adhesive were measured by shear strength and boiling water resistance of glued wood blocks. The utilization performances of the one-component CS structured PStA latex adhesive were found to largely depend on CS morphological character and the interfacial compatibility between various polymeric constituents, demonstrating that fabrication of CS latex particles provides a promising approach to realize high-performance latex adhesives.

Effect of the intermediate layer–core ratio on the morphology and opacity ability of hollow latex particles

ABSTRACTIn this study, well‐monodispersed hollow latex particles were synthesized through semicontinuous seed emulsion polymerization, and the effect of the hollow latex particles' intermediate layer–core ratios on their morphology and opacity ability were studied. The results show that when the intermediate layer–core ratios increased from 6 to 10, the swelling degree of the hollow latex particles decreased, and the intensity gradually increased, but the opacity ability increased first and then decreased. When the intermediate layer–core ratio was 8, the opacity ability of the hollow latex particles was the best. When the intermediate layer–core ratios were 6 and 7, the surface of the hollow latex particles was rough, and they showed a great swelling degree, big cavity, and thin shell, and few of latex particles collapsed or ruptured. When the intermediate layer–core ratios were 9 and 10, the hollow latex particles had a smooth surface, thick shell, and small swelling degree and cavity, and roughly, there was no collapse or rupture of the hollow latex particles. When the intermediate layer–core ratio was 8, the swelling degree of the hollow latex particles was moderate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42268.