Core-shell Weight Ratio Research Articles

Controllable Synthesis of Submicrometer Core–Shell Modifier and Its Effect on Toughening Polypheylene Ether/Polystyrene Blends

AbstractCore–shell polybutadiene‐graft‐polystyrene (PB‐g‐PS) graft copolymers with different ratios of PB to PS are synthesized by emulsion polymerization. Further, the PB‐g‐PS copolymers are blended with polypheylene ether (PPE) and PS to prepare PPE/PS/PB‐g‐PS blends. The effects of PB‐g‐PS copolymer structure and matrix composition on the morphological, mechanical properties, and deformation mechanism of the blends are studied. The results show that the synthesized submicrometer‐sized PB‐g‐PS copolymer has an excellent toughening efficiency, both the copolymer and PS are introduced into PPE resin to produce a ternary blend which is combined with high toughness and processing properties. The optimum toughening effect on PPE/PS matrix is observed at the core–shell weight ratio of 70/30 in PB‐g‐PS copolymer, and the impact strength of the blends increased from 101 to 550 J m−1. In addition, the dispersion pattern of rubber particles in the matrix gradually changes from uniform dispersion to aggregation as the core–shell ratio of PB‐g‐PS copolymers increases. On the other hand, with the increase of PPE content, the dispersion of rubber particles in PPE/PS matrix is improved, and the deformation mechanism is changed from cracking to a combination of crazing and shear yielding, which can lead to absorb more energy to achieve better toughness.

Nanoscale integration of oxides and metals in bulk 3D composites: leveraging SrFe12O19/Co interfaces for magnetic exchange coupling

The integration of different material classes (e.g, oxides and metals) with nanoscale dimensions in large 3D materials remains a fundamental challenge in nanocomposite fabrication. The incentive is that some of the most interesting properties occur at nanoscale interfaces, while the challenge arises from the difficulty in densifying the materials without deleterious reaction at the interface. Here, we introduce a method based on the synthesis of core–shell powders followed by efficient, relatively low-temperature densification with current-activated pressure-assisted densification. The composition of the bulk nanocomposites can be controlled by varying the core–shell weight ratio, leading to controllable thicknesses of the hard/soft magnetic phases. We demonstrate intimate mixtures of nanoscale strontium ferrite (hard magnetic phase) and Co–Fe (soft magnetic phase) with minimal reaction. The high volume content of high-quality oxide/metal interfaces leads to magnetic exchange coupling in the composites.

Influence of dual-component microcapsules on self-healing efficiency and performance of metal-epoxy composite-lap joints

ABSTRACTDual-component microcapsules were synthesized by solvent evaporation technique using epoxy resin and hardener as core materials and polymethyl methacrylate (PMMA) as shell wall materials. Morphology, core content, and size distribution of microcapsules were monitored by controlling the various processing parameters such as agitation speed, core–shell weight ratio, and concentration of emulsifiers. The molecular structure, morphologies, and thermal characteristics of the microcapsules were examined under Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and thermogravimetric analysis (TGA), respectively. Synthesized dual-component microcapsules were entrenched into the epoxy polymer to introduce the healing features in single lap shear epoxy adhesive joints. Healing efficiency as high as 89% was achieved when 10 wt% dual-component microcapsules were introduced in adhesives. Investigation of the fractured surfaces of the healing enabled adhesives reveals the presence of crack pinning and crack blunting sites represented by characteristic tails at the wake of microcapsules in cohesive zone. Such failure mechanisms responsibly influence the healing efficiency.

Properties of Poly(vinyl chloride)/PB-g-PMMA Composites

To improve the mechanical properties of poly(vinyl chloride) (PVC), the characters of combining PVC with elastomers were considered. Polybutadiene grafted poly(methyl methacrylate) (PB-g-PMMA, MB) core-shell particles were prepared by emulsion polymerization, and were used as an impact modifier for PVC. The impact resistance, fracture, brittle-ductile transition and the morphology of PVC/MB blends were investigated. It was found that MB particles had a high toughening efficiency for PVC resin, the impact strength was more than 1100 J·m-1 when MB was 8 phr. Two factors influence the impact strength and brittle-ductile transition, one is the modifier content, and the other is core-shell weight ratio. The impact curves are Ω-like shape, the impact strength value is the highest at the middle part and the PVC/ MB blends show ductile break behaviors. The core shell ratio of ductile areas are limited from 80/20 to 90/10 for PVC/MB=100/8, and 70/30 to 93/7 for PVC/MB=100/10.

Preparation and characterization of macrocapsules containing microencapsulated PCMs (phase change materials) for thermal energy storage

This paper was aimed to prepare, characterize and determine the comprehensive evaluation of promising composite macrocapsules containing microencapsulated PCMs (phase change materials) with calcium alginate gels as the matrix material. Macrocapsules containing microcapsules were fabricated by piercing-solidifying incuber method. Two kinds of microcapsules with n-tetradecane as core material, UF (urea-formaldehyde) and PMMA (poly(methyl methacrylate)) respectively as shell materials were prepared initially. For application concerns, thermal durability and mechanical property of macrocapsules were investigated by TGA (thermal gravimetric analysis) and Texture Analyser for the first time, respectively. The results showed excellent thermal stability and the compressive resistance of macrocapsules was sufficient for common application. The morphology and chemical structure of the prepared microcapsules and macrocapsules were characterized by SEM (scanning electron microscopy) and FT-IR (fourier transform infrared) spectroscopy method. Phase change behaviors and thermal durability of microcapsules and macrocapsules were investigated by DSC (differential scanning calorimetry). In order to improve latent heat of composite microcapsules, the core-shell weight ratio of tetradecane/UF shell microcapsules was chosen as 5.5:1 which obtained the phase change enthalpy of 194.1 J g−1 determined by DSC. In conclusion, these properties make it a feasible composite in applications of textile, building and cold-chain transportation.

Super-tough poly(butylene terephthalate) based blends by modification with core-shell structured polyacrylic nanoparticles

Abstract Core-shell structured polyacrylic nanoparticles (named CSPN) impact modifiers consisting of a rubbery poly(n-butyl acrylate) core and a rigid poly(methyl methacrylate) shell with a size of about 352 nm were synthesized by seed emulsion polymerization. The CSPN modifier with core-shell weight ratio 80/20 was used to toughen poly(butylene terephthalate) (PBT) by melt blending. With an increase in CSPN content, the impact strength and the elongation at break of PBT/CSPN blends increased significantly compared with those of PBT; however, the tensile strength decreased. It was found that the polymerization had a very high instantaneous conversion (> 93%) and overall conversion (99%). The core-shell structure of CSPN was examined by means of transmission electron microscope. Scanning electron microscope was used to observe the morphology of CSPN particle and fractured surfaces of the blends. The dynamic mechanical analyses of PBT/CSPN blends showed two merged transition peaks of PBT matrix, with the presence of CSPN modifier, which was responsible for the improvement of PBT toughness. The results indicated that the notched impact strength of PBT/CSPN blend with a weight ratio of 80/20 was 8.61 times greater than that of pure PBT where the brittle-ductile transition point appeared.

Super-tough Poly(butylene terephthalate) Materials: Blending with CSSP Nanoparticles

Core-shell structured polyacrylic (CSSP) impact modifiers, consisting of a rubbery poly(n-butyl acrylate) core and a rigid poly(methyl methacrylate) shell, were synthesized by seed emulsion polymerization. The CSSP modifier with core-shell weight ratio 75/25 was used to modify the toughness of poly(butylene terephthalate) (PBT) by melt blending. The CSSP morphology was confirmed by TEM and SEM. Dynamic mechanical analyses of PBT/CSSP blends showed two merged transition peaks of PBT matrix. Increasing CSSP content increased elongation at break and impact strength, but decreased tensile strength. The notch impact strength of PBT/CSSP blends with weight ratio 85/15 was eight times greater than pure PBT.

Preparation of core-shell structured polyacrylic modifiers and effects of the core-shell weight ratio on toughening of poly(butylene terephthalate)

Core-shell structured polyacrylic (named CSSP) impact modifiers consisting of a rubbery poly(n-butyl acrylate) core and a rigid poly(methyl methacrylate) shell with a size of about 353 nm were prepared by seed emulsion polymerization. The CSSP modifiers with different core-shell weight ratios (90/10, 85/15, 80/20, 75/25, 70/30, 65/35 and 60/40) were used to modify the toughness of poly(butylene terephthalate) (PBT) by melt blending. It was found that the polymerization had a very high instantaneous conversion (> 95.7%) and overall conversion (99.7%). The morphology of the core-shell structure was confirmed by means of transmission electron microscopy. Scanning electron microscopy was used to observe the morphology of the fractured surfaces. Differential scanning calorimeter was used to study the crystallization behaviors of PBT/CSSP blends. The dynamic mechanical analyses of PBT/CSSP blends showed two merged transition peaks of PBT matrix, with the presence of CSSP core-shell structured modifier, that were responsible for the improvement of PBT toughness. The results indicated that the notch impact strength of PBT/CSSP blends with a core-shell weight ratio of 75/25 was almost 8.64 times greater than that of pure PBT, and the mechanical properties agreed well with the SEM observation.

Toughening of poly(butylene terephthalate) by polyacrylic impact modifier

Core–shell structured polyacrylic (named ACR) impact modifiers consisting of a rubbery poly(n-butyl acrylate) (BA) core and a rigid poly(methyl methacrylate) shell with a size of about 310 nm were prepared by seed emulsion polymerization. The ACR modifiers with different core–shell weight ratios (85:15; 80:20; 75:25; 70:30) were used to modify the toughness of poly(butylene terephthalate) (PBT) by melt blending. It was found that the polymerization had a very high instantaneous conversion (>90 %) and overall conversion (98 %). The ACR latexes had an obvious core–shell structure confirmed by transmission electron microscope. The mechanical properties of the PBT/ACR blends were evaluated, and scanning electron microscope (SEM) was used to observe the fractured morphology. Dynamic mechanical analysis and differential scanning calorimeter were used to study the molecular movement and crystallization behaviors of PBT/ACR blends. The results indicated that with an appropriate value of the core–shell weight ratio, poly(BA) could disperse well in the matrix and the brittle–ductile transition point could emerge. As a result, the notch impact strength of PBT/ACR blends with a core–shell weight ratio of 80:20 was 6.7 times greater than that of pure PBT, and the mechanical properties agreed well with the SEM observation.

Effects of processing conditions of poly(methylmethacrylate) encapsulated liquid curing agent on the properties of self-healing composites

A series of microcapsules were prepared by solvent evaporation technique using liquid curing agent, polyetheramine as the core material and poly(methylmethacrylate) as the shell material. The desired morphology, shell wall thickness, curing agent content, and size distribution of microcapsules have been obtained by fine tuning the processing conditions such as reaction temperature, core–shell weight ratio, agitation speed, and emulsifier concentration in the medium. The resulting microcapsules exhibit excellent thermal and curing agent storage stability. Maximum healing efficiency of 93.50% has been obtained with 15wt.% epoxy containing microcapsules. The microcapsules containing liquid curing agent can efficiently be utilized for the fabrication of epoxy-based self-healing composites.

The influence of core–shell structured modifiers on the toughness of poly (vinyl chloride)

The core–shell structured grafted copolymer particles of polybutadiene grafted polymethyl methacrylate (PB-g-PMMA, MB) were prepared by emulsion polymerization. The MB particles were used to modify poly (vinyl chloride) (PVC) by melt blending. The mechanical properties of the PVC blends were investigated. The micro-morphology of the PVC blends was observed by scanning electron microscopy (SEM). The results indicated that the samples with the best impact strength could be obtained when the core–shell weight ratio of PB to PMMA is lower than 93:7, the mechanical properties correlated well with SEM morphologies, the addition of modifier with the ratio core to shell of 93:7 could reduce the domain size of the dispersed phase. Furthermore, the compatibility and properties of the blends were greatly enhanced and improved. The modifier particles could be well dispersed in the PVC matrix.