Polypropylene/Layered Double Hydroxide Nanocomposites: Influence of LDH Intralayer Metal Constituents on the Properties of Polypropylene

Sonication-assisted delamination of layered double hydroxides (LDHs) resulted in smaller-sized LDH nanoparticles (∼50-200 nm). Such delaminated Co-Al LDH, Zn-Al LDH, and Co-Zn-Al LDH solutions were used for the preparation of highly dispersed isotactic polypropylene (iPP) nanocomposites. Transmission electron microscopy and wide-angle X-ray diffraction results revealed that the LDH nanoparticles were well dispersed within the iPP matrix. The intention of this study is to understand the influence of the intralayer metal composition of LDH on the various properties of iPP/LDH nanocomposites. The sonicated LDH nanoparticles showed a significant increase in the crystallization rate of iPP; however, not much difference in the crystallization rate of iPP was observed in the presence of different types of LDH. The dynamic mechanical analysis results indicated that the storage modulus of iPP was increased significantly with the addition of LDH. The incorporation of different types of LDH showed no influence on the storage modulus of iPP. But considerable differences were observed in the flame retardancy and thermal stability of iPP with the type of LDH used for the preparation of nanocomposites. The thermal stability (50% weight loss temperature (T0.5)) of the iPP nanocomposite containing three-metal LDH (Co-Zn-Al LDH) is superior to that of the nanocomposites made of two-metal LDH (Co-Al LDH and Zn-Al LDH). Preliminary studies on the flame-retardant properties of iPP/LDH nanocomposites using microscale combustion calorimetry showed that the peak heat release rate was reduced by 39% in the iPP/Co-Zn-Al LDH nanocomposite containing 6 wt % LDH, which is higher than that of the two-metal LDH containing nanocomposites, iPP/Co-Al LDH (24%) and iPP/Zn-Al LDH (31%). These results demonstrated that the nanocomposites prepared using three-metal LDH showed better thermal and flame-retardant properties compared to the nanocomposites prepared using two-metal LDH. This difference might be due to the better char formation capability of three-metal LDH compared to that of two-metal LDH

Polypropylene/Layered Double Hydroxide (LDH) Nanocomposites: Influence of LDH Particle Size on the Crystallization Behavior of Polypropylene

Highly dispersed isotactic polypropylene (iPP) nanocomposites were prepared by incorporating two different sized Mg–Al LDH nanoparticles with different loadings from 1 to 10 wt % using a modified solvent mixing method. Larger sized LDH nanoparticles (∼3–4 μm) were prepared from the gel form of Mg–Al LDH, and the smaller sized nanoparticles (∼50–200 nm) were prepared by sonication of as-synthesized LDH particles. Such obtained LDH nanoparticles were carefully characterized using wide-angle X-ray diffraction (WAXD), transmission electron microscopy, and scanning electron microscopy. WAXD and atomic force microscopy results indicate that the LDH nanoparticles were highly dispersed in the iPP matrix. The influence of LDH nanoparticles size and concentration on the thermal stability, spherulitic morphology, melting behavior, isothermal crystallization kinetics, and lamellar structure of iPP were investigated. Incorporation of low loadings of sonicated LDH particles (e.g., 1–2.5 wt %) show substantial effect on thermal stability, spherulite size, crystallinity, and crystallization half-time and lamellar morphology of iPP compared to the pure iPP and that of nanocomposites with larger LDH particles with same loadings. The better nucleation ability of iPP in the presence of sonicated LDH can be attributed to the high surface area of LDH nanoparticles along with its better dispersibility within the polymer matrix. The incorporation of LDH nanoparticles does not change the crystallization growth mechanism and crystal structure of iPP

Screen-Printable Electronic Ink of Ultrathin Boron Nitride Nanosheets

Two-dimensional materials play a vital role in the current electronic industry in the fabrication of devices. In the present work, we have exfoliated and stabilized the insulating hexagonal boron nitride (hBN) by means of a polymer-assisted liquid-phase technique. Further, the highly viscous ink of hBN was prepared, and its printability on various commercially available substrates was studied. The morphology of the printed patterns reveals the layered arrangement of hBN. The various electrical and dielectric characterizations, carried out on a metal–insulator–metal capacitor, testified its potential applications in various fields of printed electronics

Syndiotactic Polystyrene/Hybrid Silica Spheres of POSS Siloxane Composites Exhibiting Ultralow Dielectric Constant

Homogeneously dispersed hybrid silica/syndiotactic polystyrene composites were investigated for low-κ dielectric applications. The composites were prepared by a solution blending method, and their microstructures were analyzed by SEM, TEM, and AFM. Crystallization and phase transformation behavior of sPS were investigated using differential scanning calorimetry and wide-angle X-ray diffraction. These composites exhibited improved thermal stability and reduced thermal expansion coefficients. Promising dielectric properties were observed for the composites in the microwave frequency region with a dielectric constant (κ = 1.95) and loss (tan δ = 10^–4) at 5 GHz

Defibrenation and time course fermentation impact on the cyanide content of industrially and locally processed Gari food in Cross River State of Nigeria

No Abstract.GJPAS Vol. 13 (4) 2007: pp. 527-53

Influence of Boron Nitride Nanosheets on the Crystallization and Polymorphism of Poly(l‑lactide)

This work reports on the impact of delaminated boron nitride nanosheets (BNNSs) on the crystallization behavior and crystalline structure of melt-crystallized poly-L-lactic acid (PLLA). Wide-angle X-ray diffraction and scanning electron microscopy data revealed that the addition of lower loadings of BNNSs (∼0.5 wt %) resulted in the highly dispersed PLLA nanocomposites, whereas the higher loading of BNNSs (≥1 wt %) leads to the agglomerated nanocomposites. It is shown that the presence of lower loadings of the BNNSs (∼0.5 wt %) induces the formation of ordered α form when crystallizing from the melt at a cooling rate of 10 °C/min, but the mixture of α′ and α forms is formed in the presence of higher loading of BNNSs (≥1 wt %). Polarized optical microscopy images revealed that the crystallization rate of PLLA was significantly enhanced in the presence of lower loading of BNNSs (∼0.5 wt %) as corroborated by the increasing number of tiny spherulites. The strong interaction between the highly dispersed BNNSs and PLLA chains induces the conformationally ordered α form, and the various experimental techniques revealed that crystallization of PLLA occurred rapidly with the narrow distribution of crystal size and degree of crystal perfection in highly dispersed nanocomposites. Furthermore, the thermal conductivity of PLLA/BNNSs nanocomposites was found to increase significantly with BNNSs loading

Polypropylene/Layered Double Hydroxide Nanocomposites: Influence of LDH Intralayer Metal Constituents on the Properties of Polypropylene

Sonication-assisted delamination of layered double hydroxides (LDHs) resulted in smaller-sized LDH nanoparticles (∼50–200 nm). Such delaminated Co–Al LDH, Zn–Al LDH, and Co–Zn–Al LDH solutions were used for the preparation of highly dispersed isotactic polypropylene (iPP) nanocomposites. Transmission electron microscopy and wide-angle X-ray diffraction results revealed that the LDH nanoparticles were well dispersed within the iPP matrix. The intention of this study is to understand the influence of the intralayer metal composition of LDH on the various properties of iPP/LDH nanocomposites. The sonicated LDH nanoparticles showed a significant increase in the crystallization rate of iPP; however, not much difference in the crystallization rate of iPP was observed in the presence of different types of LDH. The dynamic mechanical analysis results indicated that the storage modulus of iPP was increased significantly with the addition of LDH. The incorporation of different types of LDH showed no influence on the storage modulus of iPP. But considerable differences were observed in the flame retardancy and thermal stability of iPP with the type of LDH used for the preparation of nanocomposites. The thermal stability (50% weight loss temperature (<i>T</i>_0.5)) of the iPP nanocomposite containing three-metal LDH (Co–Zn–Al LDH) is superior to that of the nanocomposites made of two-metal LDH (Co–Al LDH and Zn–Al LDH). Preliminary studies on the flame-retardant properties of iPP/LDH nanocomposites using microscale combustion calorimetry showed that the peak heat release rate was reduced by 39% in the iPP/Co–Zn–Al LDH nanocomposite containing 6 wt % LDH, which is higher than that of the two-metal LDH containing nanocomposites, iPP/Co–Al LDH (24%) and iPP/Zn–Al LDH (31%). These results demonstrated that the nanocomposites prepared using three-metal LDH showed better thermal and flame-retardant properties compared to the nanocomposites prepared using two-metal LDH. This difference might be due to the better char formation capability of three-metal LDH compared to that of two-metal LDH

Layered Double Hydroxide Nanoplatelets with Ultrahigh Specific Surface Area for Significantly Enhanced Crystallization Rate and Thermal Stability of Polypropylene

A facile method for the simultaneous delamination and the lateral size reduction of layered double hydroxides (LDH) is reported. This method directly resulted in the delaminated mesoporous LDH nanoplatelets (nanodot LDH) with the high specific surface area (lateral dimensions as low as 10–30 nm and featured a thickness of ∼1 nm). Such prepared LDH was used as fillers for isotactic polypropylene (iPP). For the purpose of comparison, LDH having different surface areas were also used as fillers for iPP. The incorporation of nanodot LDH showed a remarkable improvement in the polymer properties with only 1 wt % loading. The uniformly dispersed LDH particles have a significant effect on the nucleation ability, thermal stability, and mechanical properties of iPP. The nucleation ability of iPP in the presence of nanodot LDH is the best compared to other iPP nanocomposites reported using LDH as fillers in the literature. Furthermore, the microstructure of the iPP nanocomposites was systematically investigated at multiple length scales in the presence of different-sized LDH, which is a key to understand the polymer properties