Effect of acrylic core–shell rubber particles on the particulate flow and toughening of PVC

Different types of acrylic core–shell rubber particles with a poly(butyl acrylate) (PBA) core and a grafted poly(methyl methacrylate) (PMMA) shell were synthesized. The average size of acrylic core–shell latex particles ranged from 100 to 170 nm in diameter, having the core gel content in the range of 35–80%. The melt blending behavior of the poly(vinyl chloride) (PVC) and the acrylic core–shell rubber materials having different average particle sizes and gel contents was investigated in a batch mixing process. Although the torque curves showed that the particulate flow of the PVC in the blends was dominant, some differences were observed when the size and gel content of the particles varied. This behavior can be attributed to differences in the plasticizing effect and dispersion state of various types of core–shell rubber particles, which can vary the gelatin process of the PVC in the mixing tool. On the other hand, the highest toughening efficiency was obtained using core–shell rubber particles with the smallest particle size (i.e., 100 nm). The results showed that increasing the gel content of the core–shell impact modifiers with the same particle size improved the particle dispersion state in the PVC matrix. The toughening efficiency decreased for the blends containing 100 and 170 nm rubber particles as the gel content increased. Nevertheless, unexpected behavior was observed for the blends containing 140 nm rubber particles. It was found that a high level of toughness could be achieved if the acrylic core–shell rubber particles as small as 100 nm had a lower gel content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rubber modification of unsaturated polyester resin with core–shell rubber particles: Effect of shell composition

Poly(butyl acrylate)/poly(vinyl acetate‐co‐methyl methacrylate) PBA/P(VAc‐co‐MMA) core–shell rubber particles with various shell compositions, i.e., VAc/MMA weight ratios, were used to toughen unsaturated polyester. The morphology and surface‐free energy of the rubber particles were determined by transmission electron microscopy (TEM) and contact angle measurements, respectively. The effect of shell structure on the dispersion state of rubber particles inside the unsaturated polyester resin was studied by scanning electron microscopy and TEM. Increasing MMA units in the shell changed the particle dispersion state from small agglomerates or globally well‐dispersed particles to large aggregates in the cured‐resin matrix. For the blends that contain 5 wt% rubber, the highest un‐notched impact toughness, stress‐intensity factor (K_IC), and fracture energy (G_IC) were observed for the blend containing PVAc shell particles. The results showed that by increasing the particle level from 5 to 10 wt%, the highest K_IC and G_IC values were obtained for the blend containing rubber particles with VAc/MMA (80/20 wt/wt) copolymer shell. The crack‐tip damage zone in the neat and rubber‐modified unsaturated polyester resins was observed by means of transmission optical microscopy. In addition, using PVAc shell particles exhibited a minimum reduction in the volume shrinkage and tensile properties of the rubber‐modified resin. POLYM. ENG. SCI., 52:1928–1937, 2012. © 2012 Society of Plastics Engineers     

Effect of peanut shell content on mechanical,thermal, and biodegradable properties of peanut shell/polylactic acid biocomposites

Peanut shell (PNS) was combined with polylactic acid (PLA) to form biocomposites. The biocomposites, with up to 40 wt% PNS, were prepared using a twin–screw extruder. The effect of PNS content on the thermal, mechanical, thermomechanical, morphological, and biodegradable properties was studied. The results showed that the addition of PNS caused a reduction of the melting temperature and the decomposition temperature. Furthermore, the crystallinity of the biocomposites slightly increased with increasing PNS up to 30 wt%. The morphological study showed poor interfacial adhesion between the PNS and PLA matrix. Nevertheless, the mechanical properties revealed that the maximum tensile strength and Young's modulus were at a 30 wt% PNS loading and decreased as more PNS was incorporated into the PLA matrix. The impact strength decreased with an increase in PNS content. The addition of PNS showed significantly improvement of the storage modulus of PLA at high temperature (>80°C). Moreover, the presence of PNS enhanced the biodegradability of the biocomposites. POLYM. COMPOS., 38:682–690, 2017. © 2015 Society of Plastics Engineers     

Chemical components and properties of core–shell acrylate latex containing fluorine in the shell and their films

Core–shell acrylate latices containing fluorine in the shell were prepared by semicontinuous emulsion polymerization. The chemical components of the latices were determined by Fourier transform infrared, ion‐selective electrode analysis, and differential scanning calorimetry. The average size and morphology of the latex particles were characterized by photocorrelation spectroscopy and transmission electron microscopy, respectively. The latex particles were mainly composed of a non‐fluorine core and a fluorinated shell. The dynamic water contact angles of the latex films from the Wilhelmy method indicated that the latex films containing fluorine in the shell could be wetted by water only with difficulty. The amount of the fluoromonomer played an important role in the modification on the water contact angles, water absorption, and thermal stability of the latex films. In comparison with a random structure, the core–shell structure was more effective for improving the thermal properties of the latex films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 107–114, 2006     

Effect of glycidyl methacrylate-grafted natural rubber on physical properties of polylactic acid and natural rubber blends

Natural rubber (NR) was melt blended with polylactic acid (PLA) at various ratios using an internal mixer. The impact strength and elongation at break of PLA/NR blend dramatically increased with increasing NR content up to 10% (w/w). Glycidyl methacrylate-grafted natural rubber (NR-g-GMA) was used as a compatibilizer for PLA/NR blend. The effects of content and %grafting of NR-g-GMA on mechanical properties of PLA/NR blend were studied. The experimental result showed that the addition of NR-g-GMA in PLA/NR blend significantly improved impact strength and elongation at break of PLA/NR blend when compared with that of neat PLA and PLA/NR blend without NR-g-GMA. The impact strength and elongation at break of PLA/NR blend increased with increasing NR-g-GMA content up to 1% (w/w). Moreover, with increasing % grafting of NR-g-GMA in PLA/NR blend up to 4.35, the impact strength and elongation at break of the blend increased. Morphological and thermal property of PLA, PLA/NR, and PLA/NR/NR-g-GMA were elucidated as well. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Preparation of toughened PMMA through PEG-modified urethane acrylate/PMMA core–shell composite particles

Poly(urethane acrylate) (PUA)/poly(methylmethacrylate) (PMMA) core–shell composite particles were prepared by two-stage emulsion polymerization. The sizes of composite particles could be varied from 25 to 210 nm by introducing polyoxyethylene (POE) groups to the urethane acrylate molecular backbone. Core–shell morphology was identified by investigating the polarity of the surface of the core and shell polymer particles and by measuring the contact angle of the composite particles. A composite particle prepared with relatively small particles (about 20 nm) did not show the core/shell morphology, because the high polar surface of the core polymer particle and the low-stage ratio of the core to the shell cause the formation of a core/shell two-stage latex to be more thermodynamically unstable. The fracture toughness of rubber-toughened PMMA containing PUA/PMMA composite particles increased as the particle sizes decreased and the shell thickness of the composite particles increased. In particular, when the average size of the composite particle was about 43 nm and the stage ratio was 50/50, the fracture toughness of the rubber-toughened PMMA increased more than three times compared with that of pure PMMA. Furthermore, the transparency of toughened PMMA could be maintained up to 91% in the visible spectra range. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2291–2302, 1998     

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.     

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     

Formation mechanism of silicone rubber particles with core–shell structure by seeded emulsion polymerization

Silicone rubber particles with core–shell structure were prepared by polymerization of vinyl monomers in the presence of crosslinked and linear poly(dimethyl siloxane-methyl vinyl siloxane) latex. The monomers were added with either continuous or swelled-continuous addition mode. The core–shell morphology of silicone rubber/polystyrene [PST] and silicone rubber/poly(methyl methacrylate-divinyl benzene) [P(MMA-DVB)] composite particles were obtained. The effects of monomer addition mode, the compatibilities of the monomers or their homopolymer with silicone rubber, and the reactivity of polysiloxane with vinyl monomers on the formation of the core–shell structure were discussed. © 1996 John Wiley & Sons, Inc.     

Polylactide,nanoclay, and core–shell rubber composites

Three types of composites, namely, polylactide (PLA)/nanoclay, PLA/core–shell rubber, and PLA/nanoclay/core–shell rubber, were melt compounded via a corotating twin‐screw extruder. The effects of two types of organically modified montmorillonite nanoclays (i.e., Cloisite®30B and 20A), two types of core (polybutylacrylate)–shell (polymethylmethacrylate) rubbers (i.e., Paraloid EXL2330 and EXL2314), and the combination of nanoclay and rubber on the mechanical and thermal properties of the composites were investigated. According to X‐ray diffraction and transmission electron microscopy analyses, both types of PLA/5 wt% nanoclay composites had an intercalated morphology. In comparison with pure PLA, both types of PLA/5 wt% nanoclay composites had an increased modulus, similar impact strength, slightly reduced tensile strength, and significantly reduced strain at break. On the other hand, PLA/EXL2330 composites with a rubber loading level of 10 wt% or higher had a much higher impact strength and strain at break, but a lower modulus and strength when compared with pure PLA. The simultaneous addition of 5 wt% nanoclay (Cloisite®30B) and 20 wt% EXL2330 resulted in a PLA composite with a 134% increase in impact strength, a 6% increase in strain at break, a similar modulus, and a 28% reduction in tensile strength in comparison with pure PLA. POLYM. ENG. SCI. 46:1419–1427, 2006. © 2006 Society of Plastics Engineers     

Effects of core‐shell acrylate particles on impact properties of chlorinated polyethylene/polyvinyl chloride blends

The impact properties of core‐shell acrylate (CS‐ACR)/chlorinated polyethylene (CPE)/poly(vinyl chloride) (PVC) blends under different temperatures were investigated. The fracture surface morphologies of the blends were observed by scanning electron microscopy (SEM). The results show that there exists significant synergistic effect between CS‐ACR particles and CPE in toughening PVC, and the impact properties of the blends generally correlate well with SEM morphologies. Besides, with increasing CS‐ACR content, ductile–brittle transition point of the ternary blends remarkably shifts to a lower temperature. Dynamic mechanical analysis exhibited that intensity and area of low‐temperature tan δ peaks of the CPE/PVC blends increase obviously after the addition of CS‐ACR particles, which to some extent are just in line with the changes in impact strength and ductile–brittle transition point of the blends. POLYM. ENG. SCI., 2009. © 2009 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     

Surface modification effects of core–shell rubber particles on the toughening of poly(butylene terephthalate)

We toughened poly(butylene terephthalate) (PBT) by loading core–shell rubber (CSR) type impact modifiers, consisting of a rubbery poly(n‐butyl acrylate) core and a rigid poly(methyl methacrylate) shell. To optimize the dispersion of CSR particles into the PBT matrix during melt compounding, the shell surface was modified with different grafting ratios of glycidyl methacrylate (GMA) reactive with PBT chain ends. In PBT blends with a 20 wt % CSR loading, the dispersed rubbery phases showed discernible shapes depending on the grafted GMA content, from predetermined spheres with 0.25 ± 0.05 μm diameters to their aggregates in the 2–3 μm diameter range. As a result, the interparticle spacing (τ) could be controlled from 0.25 to 4.0 μm in the PBT blends containing the fixed rubber loading. The Izod impact strengths of these samples increased significantly below τ = 0.4 μm. Additional thermal and morphological analyses strongly supported the hypothesis that the marked increase in toughness of the blends was related to less ordered lamellar formation of the PBT matrix under the confined geometry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study of the preparation of silicone rubber particles with core–shell structure by seeded emulsion polymerization

Silicone rubber particles with core–shell structure were prepared by polymerization of vinyl monomers in the presence of linear or cross-linked poly(dimethyl siloxane–methyl vinyl siloxane) latexes. The monomers were added in either continuous or swelled-continuous modes. Core–shell particles with poly(butyl methacrylate), or poly(methyl methacrylate), as the shell were obtained by using either addition mode. The core–shell structure was not observed for polysiloxane–polystyrene particles. The influence of monomer addition mode, the compatibilities of the monomers and their homopolymers with silicone rubber, and the reactivity ratios of the vinyl monomers with the vinyl group of linear polysiloxane particles, on the formation of the core-shell structure is discussed.     

Effect of thermal annealing on the mechanical and thermal properties of polylactic acid–cellulosic fiber biocomposites

Polylactic acid (PLA) biocomposites were produced by a combination of extrusion and injection molding with three cellulosic reinforcements (agave, coir, and pine) and contents (10, 20, and 30%). In particular, some samples were subjected to thermal annealing (105 °C for 1 h) to modify the crystallinity of the materials. In all cases, morphological (scanning electron microscopy) and thermal (differential scanning calorimetry, dynamical mechanical thermal analysis) characterizations were related to the mechanical properties (Charpy impact, tensile and flexural tests). The results showed that annealing increased the crystallinity for all the materials produced, but different mechanical behaviors were observed depending on fiber type and content. For example, annealing increased the impact strength and flexural modulus of PLA and PLA biocomposites (agave, coir, and pine), while decreasing their flexural strength. But the main conclusion is that fiber addition combined with thermal annealing can substantially increase the thermal stability of the studied materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43750.     

Synthesis and characterization of fluorine‐containing polyurethane–acrylate core–shell emulsion

Fluorinated polyurethane–acrylate (FPUA) hybrid emulsion was prepared by copolymerization of polyurethane, methyl methacrylate, and 1H,1H,2H,2H‐heptadecafluorooctyl acrylate (FA) via emulsion polymerization in the presence of a perfluoronated reactive surfactant. The polyurethane was synthesized from isophorone diisocyanate, poly(propylene glycol)‐1000, dimethylolpropionic acid, 1,4‐butanediol, and 2‐hydroxyethyl methylacrylate. The influence of the monomer on the surface properties, wetting behaviors, particle size, and viscosity of the emulsion was investigated. The mechanical properties of FPUA latex films were improved, and water absorption and contact angle were improved with the addition of methyl methacrylate and FA. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43357.     

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     

Preparation and properties of core–shell alginate–carboxymethylchitosan hydrogels

BACKGROUND: Hydrogels of alginate (ALG) with partially carboxymethylated chitosan (CMCHI) have been produced for drug delivery, based on the interactions between the negative groups and an ionic crosslinker. In the present work, CMCHI was used to evaluate the influence of amino groups that are positively charged at pH = 4 and 6 on the ALG–CMCHI core–shell hydrogel preparation. An ANOVA statistics tool was used to evaluate the effect of composition, pH and chitosan chemical nature on the morphology and swelling properties of the hydrogels in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). RESULTS: The ALG–CMCHI core–shell hydrogels presented smaller (ca 2.3 µm) and more homogeneous microparticles than those with unmodified chitosan (ca 5.5 µm). The ALG–CMCHI hydrogels showed higher thermal stability and lower degree of swelling in SGF (314%) compared to those with chitosan (708%), since in the former hydrogels the protective layers that surround the particles are negatively charged. CONCLUSION: CMCHI can replace chitosan in the production of core–shell hydrogels with improved properties since the negative charge surrounding the ALG–CMCHI particles favours a lower degree of swelling. The results point out a possible prevention of burst release in SGF, sustaining the swelling ability of the ALG–CMCHI core–shell hydrogels in SIF, promising appropriate drug release. Copyright © 2009 Society of Chemical Industry     

Influence of core–shell rubber particles synthesized with different initiation systems on the impact toughness of modified polystyrene

Core–shell poly(butadiene‐graft‐styrene) (PB‐g‐PS) rubber particles were synthesized with different initiation systems by emulsion grafting polymerization. These initiation systems included the redox initiators and an oil‐soluble initiator, 1,2‐azobisisobutyronitrile (AIBN). Then the PB‐g‐PS impact modifiers were blended with polystyrene (PS) to prepare the PS/PB‐g‐PS blends. In the condition of the same tensile yield strength on both samples, the Izod test showed that the notched impact strength of PS/PB‐g‐PS(AIBN) was 237.8 J/m, almost 7 times than that of the PS/PB‐g‐PS(redox) blend, 37.2 J/m. From transmission electron microscope (TEM) photographs, using the redox initiators, some microphase PS zones existed in the core of PB rubber particles, which is called “internal‐grafting.” This grafting way was inefficient on toughening. However, using AIBN as initiator, a great scale of PS subinclusion was seen within the PB particle core, and this microstructure increased the effective volume fraction of the rubber phase with a result of improving the toughness of modified polystyrene. The dynamic mechanical analysis (DMA) on both samples showed that the glass transition temperature (T_g) of rubber phase of PS/PB‐g‐PS(AIBN) was lower than that of PS/PB‐g‐PS(redox). As a result, the PB‐g‐PS(AIBN) had better toughening efficiency on modified polystyrene than the PB‐g‐PS(redox), which accorded with the Kerner approximate equation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 738–744, 2007