Toughening and reinforcing polypropylene with core–shell structured fillers

An elastomer/rigid particle filler with core–shell structure was prepared by twin‐screw extruder according to an encapulation model. It was used to toughen and reinforce polypropylene (PP). An original idea of a one‐step processing method was adopted in creating PP/polyoctene–ethylene/talc ternary composites. The rheological behavior of PP was changed and the mechanical properties were improved. SEM observation showed that the core–shell structured filler dispersed better in copolypropylene than in homopolypropylene. Two reasons were proposed and proved by the rheology test and SEM observation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2397–2403, 1999     

A continuous tubular reactor for core–shell latex particles

High solids content poly(butyl acrylate)/poly(methyl methacrylate) core–shell latex particles were produced using miniemulsion polymerisation in a continuous linear tubular reactor. The resulting products were and shown to be comparable to a batch process. Final solids contents of 41 and 48 wt.% were shown to be possible in a simple tubular reactor. Differential scanning calorimeter analysis indicated that core–shell particles were formed under these conditions. © 2011 Canadian Society for Chemical Engineering     

Toughening of unsaturated polyester resins with core–shell rubbers

The effects of core–shell rubbers (CSRs) as tougheners on the fracture properties of unsaturated polyester (UP) resins during curing at 110°C are investigated. CSRs were synthesized by two‐stage soapless emulsion polymerizations; the soft core was made from rubbery poly(n‐butyl acrylate), whereas the hard shell was made from methyl methacrylate, ethylene glycol dimethacrylate, and various concentrations of glycidyl methacrylate. Depending on the content of glycidyl methacrylate in the CSR shell and the amount of CSR added to the UP, the fracture properties of the CSR‐toughened UP resins varied. The experimental results are explained by an integrated approach of measurements of the static phase characteristics of a styrene/UP/CSR system, the reaction kinetics, the cured sample morphology, the glass‐transition temperatures, and the fracture toughness with differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, and dynamic mechanical analysis. Finally, the toughening mechanism for the CSR‐toughened UP resins is also explored. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Toughening of PA6 nanocomposites by reactive acrylonitrile–butadiene–styrene core–shell rubber particles

The effect of addition of organoclay and the reactive ABS‐g‐MA core‐shell particles on the mechanical properties and morphology of blends of polyamide (PA6) were reported. The reactive rubber particles with core‐shell structure were selected as modifier instead of conventional reactive bulk rubber. The microstructure of the ternary nanocomposites was characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Impact strength and stress–strain behavior of blends were measured as a function of organoclay content and core/shell ratio of ABS‐g‐MA. The organoclay plates affected the interfacial adhesion between polyamide and the core‐shell particles because of a shielding effect of organclay on the interacting of amine end groups of PA6 with the MA groups of ABS‐g‐MA. The poor dispersion behavior of ternary nanocomposites was observed when the core/shell ratio is 80/20, and with an increase of organoclay content, the core/shell dispersed phase size increased. Blends based on the maleated elastomer with the core/shell ratio 60/40 gave a more beneficial balance of toughness versus stiffness. POLYM. COMPOS., 35:864–871, 2014. © 2013 Society of Plastics Engineers     

Investigation of fluorinated polyacrylate latex with core–shell structure

Fluorinated polyacrylate latices with core–shell structure were prepared by semi‐continuous emulsion polymerization, using a mixed emulsifier system composed of a reactive emulsifier and a small amount of anionic emulsifier. The conversion and chemical components of the final latices were studied by gravimetric methods and Fourier‐transform infrared (FTIR) spectrometry, respectively. The structure of the latex particles was determined by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and particle size analysis. The latex films exhibited a low surface energy and high water‐contact angles. The surface analysis from X‐ray photoelectron spectroscopy (XPS) revealed that the fluorinated components preferentially self‐organized at the film–air interface. From XPS depth profiling of the film, it was found that a gradient concentration of fluorine existed in the structure of the latex film from the film–air interface to the film–glass interface. Compared with the core–shell structure with a fluorinated core, the core–shell structure with a fluorinated shell was more effective for modifying the properties of the latex films. Copyright © 2005 Society of Chemical Industry     

Preparation of core–shell structured alumina–polyaniline particles and their application for corrosion protection

Polyaniline (PANI) was synthesized by chemical oxidative polymerization of aniline (ANI) in the presence of alumina (Al₂O₃) particles. The polymerization of ANI occurred preferentially on the surfaces of the particles, resulting core–shell structured alumina–polyaniline (Al₂O₃‐PANI) particles. Morphology examination showed that with decreasing of the weight ratio of Al₂O₃/ANI in the reactants, the thickness of the PANI layer increased and changed from an even surface morphology to a particulate morphology. UV–vis and Fourier transformed infrared (FTIR) spectra indicated that there is no chemical interaction between the PANI layer and the Al₂O₃ surfaces. The PANI layer adhered well to the particles and can be used as anticorrosive fillers for polymer coatings. Enhanced corrosion protection performance was achieved for the emeraldine base (EB) form of PANI deposited Al₂O₃ particles (Al₂O₃‐EB) filled epoxy coating on carbon steel in 3.0 wt % aqueous NaCl solution. The particles demonstrate both excellent corrosion protection performance and lower cost, which will be of great importance in practical applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4372–4377, 2006     

One-stage method of preparing core–shell particles

A one-stage method of preparing code–shell particles was developed for the system containing silicone oils and glycidle methacrylate (GMA). Although the formation of core–shell particles for the systems containing silicone oils and methyl methacrylate (MMA) or styrene (ST) is possible in view of thermodynamics, the core–shell particles were not obtained. Factors such as better compatibility of silicone oils with vinyl monomers, higher swelling degree of silicone rubber in the vinyl monomers, and larger addition rate of thevinyl monomers with Si—H during the crosslinking of silicone oil containing vinyl group and Si—H (SVB and SHB) do not favor the formation of core–shell particles. X-ray photoelectron spectrometer (ESCA) was used in determining the formation of core–shell particles. The mechanism of the formation of core–shell particles is discussed. © 1995 John Wiley & Sons, Inc.     

Core-shell structured latex particles. III. Structure–properties relationship in toughening of polycarbonate with poly(n-butyl acrylate)/poly(benzyl methacrylate–styrene) structured latex particles

The performance of the designed structured core-shell latex particles in toughening polycarbonate (PC) matrix was examined. Izod impact testing of the PC-core-shell latex blends were used to evaluate the influence of parameters related to the core-shell latex particles on toughening polycarbonate. Among these parameters are the particle size and levels of crosslinking of the core rubber particles, composition and molecular weight of the shell polymer, and weight ratio of shell to core polymers as well as the particle morphology. In this work, core-shell structured latex particles with thinner shells of higher molecular weight polymers were found to improve the impact resistance of polycarbonate. The role of chain entanglements in increased adhesion between the discrete rubbery phase and the continuous glassy matrix and the importance of surface-to-surface interparticle distance for toughening at various temperatures are discussed. © 1995 John Wiley & Sons, Inc.     

Preparation and characterization of core–shell polystyrene and polymethylsilsesquioxane structure latex particles by seeded polymerization

Composite polystyrene and polymethylsilsesquioxane (PS‐PMSSQ) latices were prepared by hydrolysis and polycondensation of triethoxylmethylsilane (TEOMS) in the presence of PS seed latices, obtained by gamma ray induced polymerization. Morphology of the composite latex particles was observed by transmission electronic microscopy and their size distribution was measured by dynamic laser light scattering. It was found that if 1 wt% silicon‐containing surfactant (SCS) and 0.4 wt% dodecylbenzene sulphonic acid (DBSA) were both used, core–shell/PS‐PMSSQ latex particles could be prepared at 30 °C. The core–shell structure was further characterized by X‐ray photoelectron spectrometry. With 0.5 wt% SCS or 0.2 wt% DBSA, the capsulation was incomplete. At 0 and 90 °C, the PMSSQ phase penetrated into the seed particles. No core–shell structure was observed when DBSA was replaced by hydrochloric acid or SCS was replaced by poly(ethylene glycol) monooctylphenyl ether. Copyright © 2006 Society of Chemical Industry     

Toughening of polyvinylchloride by methyl methacrylate–butadiene–styrene core–shell rubber particles: Influence of rubber particle size

An analysis was made on the effects of rubber particle size on the mechanical properties and deformation mechanisms of transparent polyvinyl chloride (PVC) blends containing core–shell methyl methacrylate–butadiene–styrene (MBS) impact modifiers. The critical interparticle distance was found not to be the criterion for the brittle‐ductile transition in the blends. In tensile tests, the blends with larger (100–280 nm) rubber particles exhibited intense stress‐whitening, while one blend with small (83 nm) rubber particles showed only slight stress‐whitening. These differences were due to an increase in resistance to cavitation with decreasing rubber particle size. Transmission electron microscopy studies on blends with a bimodal distribution of particle sizes showed that in the whitened zone of Izod specimens the larger rubber particles cavitated and expanded on yielding, while the smaller particles remained intact. However, Izod test results showed that small MBS rubber particles can toughen the PVC matrix very effectively, especially at low temperatures and at low rubber concentrations. The deformation mechanisms responsible for these effects were discussed. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Expansion of core–shell PS/PMMA particles

Structured micrometric polystyrene/poly(methyl methacrylate) particles were obtained by suspension polymerization and their expansion behavior was investigated using n‐pentane as blowing agent. The expanded particles presented two distinct microstructures with an outer region (PMMA‐rich shell) composed by cells of about 10 µm while the center of the particle (PS‐rich core) had much larger cells (50–100 μm). The core–shell particles did not expand at 100°C meaning that the PMMA shell hindered the expansion of the particles. Maximum expansion was dependent on the PMMA concentration and also on the heating temperature and the increase in the PMMA molar mass led to a delay in the onset of the process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4521–4527, 2013     

Core–shell particles to toughen epoxy resins. I. Preparation and characterization of core–shell particles

A two-stage, multistep soapless emulsion polymerization was employed to prepare various sizes of reactive core–shell particles (CSPs) with butyl acrylate (BA) as the core and methyl methacrylate (MMA) copolymerizing with various concentrations of glycidyl methacrylate (GMA) as the shell. Ethylene glycol dimethacrylate (EGDMA) was used to crosslink either the core or shell. The number of epoxy groups in a particle of the prepared CSP measured by chemical titration was close to the calculated value based on the assumption that the added GMA participated in the entire polymerization unless it was higher than 29 mol %. Similar results were also found for their solid-state ^13C-NMR spectroscopy. The MMA/GMA copolymerized and EGDMA-crosslinked shell of the CSP had a maximum glass transition temperature (T_g) of 140°C, which was decreased with the content of GMA at a rate of −1°C/mol %. However, the shell without crosslinking had a maximum T_g of 127°C, which decreased at a rate of −0.83°C/mol %. The T_g of the interphasial region between the core and shell was 65°C, which was invariant with the design variables. The T_g of the BA core was −43°C, but it could be increased to −35°C by crosslinking with EGDMA. The T_g values of the core and shell were also invariant with the size of the CSP. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2069–2078, 1998     

Toughening modification of PS with n‐BA/MMA/styrene core–shell structured copolymer from emulsifier‐free emulsion polymerization

Core–shell structured particles, which comprise the rubbery core and glassy layers, were prepared by emulsifier‐free emulsion polymerization of poly(n‐butyl acrylate/methyl methacrylate)/polystyrene [P(n‐BA/MMA)/PS]. The particle diameter was about 0.22 μm, and the rubbery core was uncrosslinked and lightly crosslinked, respectively. The smaller core–shell structured particle–toughened PS blends were investigated in detail. The dynamic mechanical behavior and observation by scanning electron microscopy of the modified blend system with core–shell structured particles indicated good compatibility between PS and the particles, which is the necessary qualification for an effective toughening modifier. Notched‐impact strength and related mechanical properties were measured for further evaluation of the toughening efficiency. The notched‐impact strength of the toughened PS blends with uncrosslinked particles reached almost sixfold higher than that of the untoughened PS when 15 phr of the core–shell structured particles was added. For the crosslinked particles the toughening effect for PS was not obvious. The toughening mechanism for these smaller particles also is discussed in this article. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1290–1297, 2003     

Rheological behavior and microstructure of aqueous suspension of carboxylated core‐shell structured latex particle

Core‐shell type carboxylated particles form a flocculated structure in aqueous suspension with neutralization of carboxyl groups. Rheological behaviors of the suspension have been studied at various temperatures, and microstructures of the suspension have been discussed from the rheological behaviors and SAXS measurements. At 25°C, G′ is larger than G″ in all ω regions, and G′ is almost independent of ω, and the diffraction peak is detected by SAXS. These results mean that a three‐dimensional network of interconnected lattice‐like flocculated structure is formed. With increasing temperature, ω dependency of G′ becomes stronger and distance of the particles of the structure does not changed. These mean the network linkage is disrupted partially by thermal motion, and the interconnected lattice‐like flocculated structure changes to an isolated lattice‐like one with increasing temperature. With increasing the degree of neutralization, an isolated structure changes to an interconnected three‐dimensional structure decreasing the thermal motion just like decreasing temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1627–1633, 2001     

Modification of recycled polycarbonate with core‐shell structured latexes for enhancement of impact resistance and flame retardancy

Two types of core‐shell structured latexes, poly(methyl methacrylate‐co‐butadiene‐co‐styrene) (MBS) and poly(methyl methacrylate‐co‐methylphenyl siloxane‐co‐styrene) (MSiS) were used to modify recycled polycarbonate (PC) for the enhancement of toughness and flame retardancy. The impact strength of the modified PC blends was not improved after melt‐blending recycled PC with these two kinds of latexes, probably because the latex particles were not evenly dispersed in the PC matrix because of the incompatibility between PC and PMMA shell of the latexes. Addition of a compatibilizer, e.g. diglycidyl ether of bisphenol‐A or poly(styrene‐co‐maleic anhydride), can effectively enhance the toughening effect of recycled PC with core‐shell structured modifiers. The presence of compatibilizer in the blends reduces the interfacial tension and introduces a steric hindrance to coalescence, and thus enhances the interfacial adhesion between PC domain and PMMA shell, and improves the dispersion of core‐shell structured particles in the PC matrix. The ternary blends achieve a high impact resistance by cavitation of the particles, which relieves the triaxial stress and promotes massive shear yielding of the matrix, and then enables the matrix to fracture by the plane stress ductile tearing mode. Additionally, MSiS has a silicone‐based core and can effectively retard the combustion of recycled PC. The blends containing 7 wt % MSiS and 3 wt % compatibilizer can achieve a UL94 V‐0 rating in vertical burning test. We proposed that, during combustion, a fine dispersion of MSiS particles in the PC matrix facilitates the rapid migration of MSiS and formation of a uniform and highly flame resistant char barrier on the surface of the modified PC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and properties of fluorine–silicon modified polyacrylate hybrid latex particles with core–shell structure obtained via emulsifier‐free emulsion polymerization

A core–shell fluorine–silicon modified polyacrylate hybrid latex was successfully prepared via emulsifier‐free emulsion polymerization. The chemical composition and core–shell morphology of the resultant hybrid particles were investigated using ¹H NMR and Fourier transform infrared spectroscopies and transmission electron microscopy (TEM), respectively. TEM analysis indicated that the core–shell hybrid particles were uniform with narrow size distributions. The particle size and zeta potential decreased with an increase of alkylvinylsulfonate surfactant from 2.5 to 6.0 wt%. X‐ray photoelectron spectroscopy revealed that fluorine concentrated preferentially at the film surface during a film‐formation process. The film formed from the fluorine–silicon modified polyacrylate showed much higher thermal stability than a film formed from polyacrylate and fluorine‐modified polyacrylate. Contact angle results showed that a finished fabric had remarkable water repellency. © 2015 Society of Chemical Industry     

Understanding the mechanical and interfacial properties of core–shell structured bamboo–plastic composites

Core–shell structured bamboo–plastic composites (BPCs) were directly prepared with a single‐screw/single‐screw coextruder system. The effects of different shell layers, such as high‐density polyethylene (HDPE), bamboo pulp fiber (BPF)/HDPE, and white mud (WM)/HDPE, were studied in the context of the mechanical properties and the characteristics of the interfacial transition zone (ITZ) of BPC. The mechanical properties of the core–shell structured BPC were characterized by flexure, short‐beam shear, and impact tests. The surface morphologies of BPC were analyzed with field emission scanning electron microscopy. The ITZ properties were studied with dynamic mechanical analysis and nano‐indentation testing. The results show that the flexural properties, short‐beam strength, and impact strength decreased profoundly in the presence of BPF or WM. The dynamic mechanical analysis results suggest that the ITZ properties decreased, as indicated by the reductions in the storage modulus, loss modulus, and loss factor; the nano‐indentation results show that on the addition of BPF or WM, a gradient in the hardness and modulus of elasticity appeared across ITZ. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43053.     

Rheological behavior and microstructure of bimodal suspensions of core‐shell structured swollen particles

The rheological behavior and microstructure of bimodal suspensions of core‐shell structured swollen particles have been examined with changing volume ratio of two different sized particles. As the volume fraction of large particles increases, the viscosity, degree of shear‐thinning, and the critical shear stress σ_c decreases, while the interparticle distance ξ of the microstructure increases. The suspensions exhibit single mode rheological behavior and have a single diffraction peak in the SAXS profiles. These results suggest that the bimodal suspensions of the core‐shell structured swollen particles behave likely to unimodal suspensions of hard spheres with alloy like single mode microstructure composed of hypothetical intermediate size particle. The relationship between σ_c and ξ can be represented as σ_c = 3kT/4πξ³, which corresponds to the dynamics of the Brownian hard sphere model with ξ being the particle diameter. These findings indicate that the shear‐thinning of the suspensions can be attributed to dynamical competition between the thermal motion and the hydrodynamic motion under shear flow and that the mechanism can be applied to bimodal suspensions of the swollen particles as well as unimodal suspensions of hard spheres. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 102: 2212–2217, 2006     

Preparation and characterization of core–shell polystyrene–polydimethylsiloxane particles by seeded polymerization

Nanometer scale particles of seed latex were successfully prepared by polymerization induced by gamma rays. By modification of the coupling agent 3‐methacryloxylpropyltrimethoxylsilane (MPS) at the surface of polystyrene (PSt) particles, polydimethylsiloxane (PDMS) was introduced outside the PSt particles and composite latex particles with a core–shell (PSt–PDMS) structure were successfully prepared. Because of the chemical bond linkage between the core and the shell, such a structure is stable. Direct evidence of the core–shell structure was observed by transmission electron microscopy (TEM). In addition the chemical bond linkage was confirmed by Fourier‐transfer infrared (FT‐IR) spectroscopy. An indirect proof of the core–shell structure was given by water absorption ratio determination of the different samples. Copyright © 2004 Society of Chemical Industry