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- ItemPolypropylene/Layered Double Hydroxide Nanocomposites: Influence of LDH Intralayer Metal Constituents on the Properties of Polypropylene(Washington, DC : ACS Publications, 2017) Nagendra, Baku; Rosely, C. V. Sijla; Leuteritz, Andreas; Reuter, Uta; Gowd, E. BhojeSonication-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.
- ItemDifferent transition metal combinations of LDH systems and their organic modifications as UV protecting materials for polypropylene (PP)(London : RSC Publishing, 2018) Naseem, Sajid; Lonkar, Sunil P.; Leuteritz, Andreas; Labuschagné, Frederick J. W. J.In this research, the use of layered double hydroxides (LDHs) as ultraviolet (UV) light-protecting additives for PP is explored. Different LDHs, such as ZnTi, ZnSn, ZnGa, ZnCr and CdCr LDHs, were prepared and their UV absorptions were characterized. The ZnTi LDHs showed higher UV absorption than the other four metallic combinations and were further organically modified with dodecylbenzene sodium sulfonate (SDBS) and lauric acid (LA). Nanocomposites of polypropylene (PP) with four different types of LDHs, ZnTi, ZnSn, ZnTi-SDBS and ZnTi-LA, were prepared at concentrations of 5%. The crystallinities and layered structures of all the metallic combinations of LDHs were characterized by wide angle X-ray spectroscopy (WAXS) and ultraviolet visible (UV-vis) absorption spectroscopy, and their crystal morphologies were studied by scanning electron microscopy (SEM). The decomposition and thermal properties of the nanocomposites and pure PP were analyzed by thermogravimetric analysis (TGA) and transmission electron microscopy (TEM) and by their photo-oxidation behavior. The addition of these organically modified and unmodified LDHs showed significant changes in the thermal decomposition of PP. The thermal stability of PP was increased to around 70 °C by the addition of SDBS-modified ZnTi LDHs (5% by weight), and an increase in induction time of about 300% was determined.
- ItemComparison of nano-structured transition metal modified tri-metal MgMAl–LDHs (M = Fe, Zn, Cu, Ni, Co) prepared using co-precipitation(Cambridge : RSC, 2019) Gevers, Bianca R.; Naseem, Sajid; Leuteritz, Andreas; Labuschagné, Frederick J. W. J.Comparison of layered double hydroxides (LDHs) synthesised using different methods, conditions and post-treatment is difficult to achieve because these greatly modify their material properties. This paper aims to provide a comparison of material properties for modified quintinite, where all LDHs were synthesised at the same conditions-thus allowing for direct comparison of the material properties obtained. Nano-structured materials were formed in all cases. The nano-structured transition metal (TM) MgMAl-LDHs were synthesised using constant pH co-precipitation. Five TMs (M = Fe, Co, Ni, Cu, Zn) were included in the LDH layers with molar substitutions of 0.5%, 1%, 5%, 10%, and 25% based on Mg-replacement for divalent TM cations and Al-replacement for trivalent TM cations. The materials were characterised using powder X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared analysis (ATR-FTIR), thermogravimetric analysis (TGA) and particle size analysis (PSA). The modified LDHs were synthesised free of major by-products and with similar morphologies. It could be shown that the crystallite dimensions varied between the different TM substitutions, that morphological changes were visible for some of the TMs used, that the processability depended on the TMs substituted, and that the substitution of TMs influenced the thermal stability of the LDHs. This journal is © 2019 The Royal Society of Chemistry.
- ItemSynthesis and characterization of MgAl-DBS LDH/PLA composite by sonication-assisted masterbatch (SAM) melt mixing method(Cambridge : RSC, 2019) Quispe-Dominguez, Roger; Naseem, Sajid; Leuteritz, Andreas; Kuehnert, InesThis research work is based on the comparison of the mixing phenomena of magnesium-aluminum (MgAl) layered double hydroxides (LDHs) intercalated by dodecylbenzene sulfonate (MgAl-DBS) in poly(lactic acid) (PLA). Two mixing techniques were used to compare the dispersion of LDHs in PLA such as sonication-assisted masterbatch (SAM) melt mixing and direct melting (DM) methods. MgAl LDHs synthesized by the urea hydrolysis method and intercalated with DBS anions using anion exchange reaction and were used in different ratios in PLA (1.25, 2.5, and 5 wt%). MgAl LDHs and their anion intercalation were studied by the X-ray diffraction analysis (XRD) method. Different properties of LDH/PLA composites were compared to analyze the effect of these mixing techniques. Dispersion and exfoliation of LDHs in PLA were investigated by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). Influences on the rheological properties were evaluated by analyzing the complex viscosities (η*), storage modulus (G′) and loss modulus (G′′) by using a rheometer. The thermal properties, thermal stability and effect on crystallinity of composites made with the two mixing techniques were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) respectively. The mixing mechanism and amount of MgAl-DBS LDHs have a notable effect on the properties of PLA composites with sonication-assisted masterbatch melt mixing techniques giving better dispersion of LDHs in PLA composites as compared to direct melt mixing. © The Royal Society of Chemistry.
- ItemComparison of transition metal (Fe, Co, Ni, Cu, and Zn) containing tri-metal layered double hydroxides (LDHs) prepared by urea hydrolysis(Cambridge : RSC, 2019) Naseem, Sajid; Gevers, Bianca; Boldt, Regine; Labuschagné, Frederick J. W. J.; Leuteritz, AndreasThis paper details a successful synthesis and comparison of a range of tri-metal hydrotalcite-like layered double hydroxides (LDHs) using urea hydrolysis. Transition-metal-substituted MgMAl-LDHs were synthesized with M = Fe, Co, Ni, Cu or Zn. 5 mol% and 10 mol% substitutions were performed, where Mg was substituted with Co, Ni, Cu and Zn, and Al with Fe. The successful synthesis of crystalline MgMAl-LDHs was confirmed using X-ray powder diffraction (XRD) analysis. Energy-dispersive X-ray (EDX) spectroscopy was used to identify substituted metals and determine changes in composition. Changes in morphology were studied using scanning electron microscopy (SEM). Thermogravimetric analysis was used to determine the effect of Fe-, Co-, Ni-, Cu- or Zn-substitution on the thermal degradation of the MgMAl-LDH phase. The structure, morphology and thermal behavior of the LDHs were shown to be influenced by the substituted transition metals. The observed thermal stability took the order MgNiAl- > MgFeAl- = MgAl- ≥ MgCoAl- > MgCuAl- > MgZnAl-LDH. The urea hydrolysis method was shown to be a simple preparation method for well-defined crystallite structures with large hexagonal platelets and good distribution of transition metal atoms in the substituted LDHs. © 2019 The Royal Society of Chemistry.
- ItemRenewable vanillin based flame retardant for poly(lactic acid): A way to enhance flame retardancy and toughness simultaneously(London : RSC Publishing, 2018) Zhao, Pengcheng; Liu, Zhiqi; Wang, Xueyi; Pan, Ye-Tang; Kuehnert, Ines; Gehde, Michael; Wang, De-Yi; Leuteritz, AndreasIn this study, a novel bio-based flame retardant material consisting of modified vanillin and poly(lactic acid) (PLA) was developed by incorporation of newly discovered additive, bis(5-formyl-2-methoxyphenyl) phenylphosphonate (VP), into the PLA matrix. The chemical structure of VP was confirmed by 1 H-, 13 C- and 31 P NMR and FTIR. The flame retardancy, thermal behavior as well as the mechanical properties of PLA/VP composites were evaluated. With 5 wt% of VP, the LOI of PLA increased from 21.4 to 25.8 and passed the UL-94 V-0 classification. Additionally, the elongation at break was improved from 3% to 11% without sacrificing tensile strength. In an effort to understand the mechanisms, TGA-FTIR, TGA and SEM were performed. This paper suggests a new possibility to prepare polymeric composites with enhanced flame retardancy from sustainable resources.