Andreas Leuteritz

Synthesis of Organo Cobalt−Aluminum Layered Double Hydroxide via a Novel Single-Step Self-Assembling Method and Its Use as Flame Retardant Nanofiller in PP

Synthesis of polypropylene/organo-layered double hydroxide (PP/OLDH) has been carried out based on self-assembled organocobalt-aluminum LDH (O-CoAl-LDH). The novel method of synthesizing self-assembled CoAl-LDH and its characterization have also been reported in details. This method is proven to be very efficient way of producing OLDH in a single step with homogeneous composition and structure. As flame-retardant nanofiller, O-CoAl-LDH shows significant decrease in heat release rate (HRR), the total heat release (THR) and the heat release capacity (HRC) of the PP composites, though the thermal stability of the compounds decreases slightly compared to the base polymer. Morphological analyses show that the LDH particles are dispersed in PP matrix in a partially exfoliated form. The activation energy calculation based on the Kissinger method reveals that O-CoAl-LDH has a positive effect on the activation energy of thermal decomposition of PP. However, in the presence of this filler, decomposition of the composites starts at an earlier stage than that of pure PP.

Structural characteristics and flammability of fire retarding EPDM/layered double hydroxide (LDH) nanocomposites

A high performance elastomeric flame retardant nanocomposite was prepared which was based on maleic anhydride grafted ethylene-propylene-diene terpolymer (mEPDM), a one-step synthesised organo-layered double hydroxide (LDH), and an intumescent flame retardant (FR) comprised of pentaerythritol (PER), ammonium polyphosphate (APP) and methyl cyanoacetate (MCA). The morphology, fire behavior and mechanical properties of the flame-retarded mEPDM/LDH nanocomposite have been studied in detail. Wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS) and TEM observation confirmed an exfoliated structure of LDH in a particular composite containing 2 phr (parts per hundred) LDH and 38 phr FR. As an effective flame retardant synergistic agent, MgAl–LDH shows a significant decrease in the heat release rate (HRR), low mass loss (ML) and low fire growth rate (FIGRA) of the nanocomposite. The flame retardant mechanism has been proposed, which is mainly due to the condensed phase flame retardant mechanism to form reinforced char layers during combustion, leading to the low volatiles produced. Moreover, as far as the mechanical properties of the vulcanizates are concerned, in all cases of flame retardant mEPDM and flame retarded mEPDM/LDH nanocomposites, they exhibit superior values compared to the gum compound.

A new approach to reducing the flammability of layered double hydroxide (LDH)-based polymer composites: preparation and characterization of dye structure-intercalated LDH and its effect on the flammability of polypropylene-grafted maleic anhydride/d-LDH composites

Dye structure-intercalated layered double hydroxide (d-LDH) was synthesized using a one-step method, and its intercalated behaviors have been characterized by Fourier transform infrared spectroscopy (FTIR), wide angle X-ray scattering (WAXS), scanning electron microscopy, thermogravimetric analysis (TGA), etc. As a novel functional potential fire-retarding nanofiller, it was used to prepare a polypropylene-grafted maleic anhydride (PP-g-MA)/d-LDH composite by refluxing the mixture of d-LDH and PP-g-MA in xylene, aiming to investigate its effect on the flammability of the PP-g-MA composite. The morphological properties, thermal stability, and flame retardant properties of the PP-g-MA/d-LDH composite were determined by FTIR, WAXS, transmission electron microscopy, TGA, and microscale combustion calorimetry. Compared with NO3-LDH (unmodified LDH) and LDH intercalated by sodium dodecylbenzenesulfonate (conventional organo-modified LDH), d-LDH can significantly decrease the heat release rate and the total heat release of the PP-g-MA composite, offering a new approach to imparting low flammability to LDH-based polymer composites.

Preparation of zinc oxide free, transparent rubber nanocomposites using a layered double hydroxide filler

A layered double hydroxide (LDH) mineral filler particle has been designed and employed in rubber vulcanization to prepare a more environmentally friendly rubber composite. The LDH delivers zinc ions in the vulcanization process as accelerators, stearate anions as activators and simultaneously the mineral sheets act as a nanofiller to reinforce the rubber matrix whilst totally replacing the separate zinc oxide (ZnO) and stearic acid conventionally used in the formulation of rubber. This method leads to a significant reduction (nearly 10 times) of the zinc level and yields excellent transparent properties in the final rubber product. The morphological characterization, rheometric curing behaviour, mechanical properties and uniaxial multi-hysteresis behaviours of the resultant rubber/LDH nanocomposite are studied in this paper.

Method for Simultaneously Improving the Thermal Stability and Mechanical Properties of Poly(lactic acid): Effect of High-Energy Electrons on the Morphological, Mechanical, and Thermal Properties of PLA/MMT Nanocomposites

Nanocomposites derived from poly(lactic acid) (PLA) and organically modified montmorillonite (oMMT) have been cross-linked by high-energy electrons in the presence of triallyl cyanurate (TAC). The morphology of untreated and cross-linked PLA/MMT nanocomposites was characterized by wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). This treatment can improve both the thermal stability and the glass-transition temperatures of the PLA nanocomposites (e.g., PLA-MMT-TAC 30kGy, 50kGy, and 70kGy) because of the formation of cross-linking structures in the nanocomposites that will considerably reduce the mobility of polymers. Interestingly, at relatively low irradiation doses (e.g., 30 and 50 kGy) a good balance between tensile strength and elongation at break for the PLA nanocomposites could be achieved. These mechanical properties are superior to those of pure PLA. Therefore, combining nanotechnology and electron beam cross-linking is a promising new method of simultaneously improving the mechanical properties (toughness and tensile strength) and thermal stability of PLA.

Self photostabilizing UV-durable MWCNT/polymer nanocomposites

A potentially active hindered amine light stabilizer (HALS) was successfully anchored onto multiwalled carbon nanotubes (MWCNTs) and used as a light-stabilizing yet reinforcing multifunctional nanofiller to obtain UV-durable polymer nanocomposites. The influence of such light stabilizing MWCNTs on the photo-oxidation behaviour and structure-properties of polypropylene (PP) was studied. The composites were prepared by solution mixing of MWCNTs followed by melt compounding with polypropylene (PP). The resulting composite exhibits excellent UV-durability showing an almost 20 fold increase in the induction period of photo-oxidation. Moreover, the hydrophobic HALS was found to be compatibilizing enough to achieve homogeneous dispersion of exfoliated nanotubes into a polymer matrix. The rheological characterizations predict the formation of a percolated network structure. The obtained nanocomposites present markedly improved mechanical properties which underline the reinforcing ability of functionalized MWCNTs. Overall combination of HALS and MWCNTs offers an attractive route to combine multifunctionality into new hybrid UV-durable polymer nanocomposites. Such materials may possess great potential for outdoors high performance applications.

Antioxidant intercalated layered double hydroxides: a new multifunctional nanofiller for polymers

An antioxidant intercalated layered double hydroxide (A.O-LDH) nanohybrid system constructed using host–guest chemistry and employed as multifunctional nanofiller to fabricate highly durable polymer composites, namely polypropylene (PP) nanocomposites. The intercalated antioxidants efficiently prolonged the degradation in PP, their high hydrophobic nature facilitated the filler dispersion and simultaneously the mineral nano sheets observed to be reinforcing the polymer matrix. The A.O-LDH/PP nanocomposites were prepared using melt intercalation technique. Both X-ray diffraction and transmission electron microscopy measurements revealed a fine dispersion of A.O-LDH nanolayers into the polymer matrices. The rheological and dynamic mechanical analysis reveals the superior toughness for such hybrid materials. Moreover, the resulting composites exhibit enhanced thermal stability and photo-oxidative durability. The crystallization behavior in PP is also found to be positively altered by the presence of A.O-LDH.

Comparative study of the synergistic effect of binary and ternary LDH with intumescent flame retardant on the properties of polypropylene composites

Organo-modified binary (MgAl-) and ternary (MgZnAl-) layered double hydroxides (LDHs) were synthesized via a co-precipitation method, and subsequently dispersed into polypropylene (PP) in combination with an intumescent flame retardant (IFR) by a melt blending process. A comparative study on the effect of binary and ternary LDHs on the mechanical, thermal properties and flammability of flame retardant PP composites was undertaken. The incorporation of either binary or ternary LDH resulted in a slightly decreased tensile strength compared to neat PP matrix; however, the Youngs modulus of PP/IFR/LDH composites was improved. The synergism between either binary or ternary LDH and IFR occurred during the combustion, but the ternary LDH showed superior char-formation ability and smoke suppression over the binary one due to the presence of the element zinc. In contrast to the binary LDH, the ternary LDH produced better quality char that effectively suppressed the spread of the flame and finally extinguished the fire.

A Novel Thermotropic Elastomer based on Highly-filled LDH-SSB Composites

Elastomeric composites are prepared based on solution styrene butadiene elastomer and zinc-aluminium layered double hydroxides (LDH), using a conventional sulphur cure system. Up to 100 parts per hundred rubber of LDH are incorporated into the elastomer matrix. The composites exhibit an interesting phenomenon of thermoreversible transparency, i.e. the transparent sample becomes opaque at warm condition and restores the transparency at room temperature. The transparency is found to be increased as the amount of LDH was increased. The addition of LDH gradually improved the mechanical, dynamic mechanical performance and thermal stability of the base elastomer. These developped elastomers could be utilised as smart materials in different applications.

Layered Double Hydroxides (LDH): A Multifunctional Versatile System for Nanocomposites

Layered Double Hydroxides gained tremendous research efforts in the last years as a filler for polymer nanocomposites similar to montmorillonite in order to increase barrier properties, improve mechanical properties and reduce flammability. Due to its broad variety in composition and possibility to organically modify the layers LDH might be used in very different applications. This summary intends to show possibilities of integration of additional functionalities apart from the benefits of LDH as platelet decomposing like the classical flame retardant magnesium hydroxide, by selecting a specific metal combination, by fine tuning structural features and by selecting an organic modification with a functionality thus providing a true added value to filler for nanocomposite applications.