Pingan Song

Flame-retardant-wrapped carbon nanotubes for simultaneously improving the flame retardancy and mechanical properties of polypropylene

Covalently functionalized carbon nanotubes (CNTs) wrapped in intumescent flame retardant were successfully fabricated and characterized. By adjusting the ratio of CNTs and flame retardant, the diameter of the functionalized CNTs was effectively controlled to 20–90 nm. Compared with pristine CNTs, the functionalized CNTs are better dispersed in polypropylene (PP) due to the in situ compatibilization reaction between the active groups of the intumescent flame retardant on the CNT surface and the maleic anhydride groups in the compatibilizer, maleic anhydride-grafted polypropylene (PPMA). Incorporating the functionalized CNTs could confer outstanding flame retardancy on PP/PPMA, and considerably enhance the mechanical properties of the polymeric materials due to the improved interfacial adhesion and stress transfer. Therefore, use of intumescent flame-retardant-wrapped carbon nanotubes and in situ compatibilization are promising strategies for simultaneously improving the flame retardancy and mechanical properties of polymeric materials.

Fabrication of dendrimer-like fullerene (C60)-decorated oligomeric intumescent flame retardant for reducing the thermal oxidation and flammability of polypropylene nanocomposites

A novel oligomeric phosphorous–nitrogen-containing intumescent flame retardant poly (4,4-diaminodiphenylmethane-O-bicyclicpentaerythritol phosphate-phosphate) (PDBPP) is synthesized, and subsequently fullerene (C60)-decorated oligomeric intumescent flame retardant, C60-d-PDBPP, is fabricated via chemical grafting reaction and characterized. The grafting degree of C60 is as high as 70 wt%, and C60-d-PDBPP nanoparticles can homogeneously disperse in polypropylene matrix since the grafting process may prevent the aggregation of C60 particles. Upon incorporating C60-d-PDBPP, thermal oxidation degradation of polypropylene is considerably delayed. When the concentration of C60-d-PDBPP reached 2 wt%, the initial degradation temperature (T5: the temperature where 5wt% mass loss occurred) and maximum weight loss rate temperature (Tmax) display an increase of about 72 °C and 80 °C, respectively. Moreover, C60-d-PDBPP can remarkably reduce the peak heat release rate (PHRR) values of polypropylene, and consequently slow down the combustion process of nanocomposites. Additionally, to some extent it prolongs the time to ignition (tign) and time to peak heat release rate (tPHRR), all of which are very important parameters for evaluating the fire retardancy of a polymeric material.

Effects of Reactive Compatibilization on the Morphological, Thermal, Mechanical, and Rheological Properties of Intumescent Flame-Retardant Polypropylene

Flame-retardant polypropylene (PP) samples were in situ compatibilized with maleic anhydride grafted PP. Compatibilization reaction was verified by an IR spectrum and gel content measurements. Electron microscopy images showed that compatibilization could considerably reduce the size of the flame-retardant domains, control the phase morphology, and improve the interfacial adhesion between PP and intumescent flame retardant (IFR) with different IFR loading levels. The limiting oxygen index (LOI) of flame-retardant PP increased to different extents after compatibilization, indicating an improvement in the flame retardancy. Compatibilization enhanced the thermal stability to some extent and remarkably delayed thermal oxidative degradation of flame-retardant PP. For PP containing 20 wt % flame retardant, the temperature at which the maximum weight loss rate occurred was enhanced by about 99 degrees C after compatibilization. The storage modulus and glass transition temperatures were elevated to different extents. Tensile strengths of samples reduced in the presence of flame retardant alone but in the additional presence of compatibilizer were restored to levels similar to those of pure PP. Elongation-at-break values, however, showed IFR concentration-dependent reductions that were less for compatibilized samples. Furthermore, the complex viscosity of a compatibilized PP melt turned slightly smaller, which is favorable to melt processing.

Polypropylene nanocomposites based on C60-decorated carbon nanotubes: thermal properties, flammability, and mechanical properties

In the present study, the effects of covalently functionalized carbon nanotubes (CNTs) decorated with C60 (abbr. C60-d-CNT) on thermal, flame retardancy and mechanical properties of polypropylene (PP) are investigated. Compared with pristine CNTs, the C60-d-CNT is more easily dispersed in the PP matrix through reactive compatibilization. With the incorporation of C60-d-CNT, thermal oxidation degradation of PP is considerably delayed. Compared to PP, at 1.0 wt% loading of C60-d-CNT, the initial degradation temperature (T5) and maximum weight loss temperature (Tmax) in air are enhanced by 68 °C and 87 °C, respectively. Furthermore, incorporating 1.0 wt% C60-d-CNT can remarkably reduce the peak heat release rate (PHRR) by 71% relative to that of PP, and slow down the combustion process to some extent. The free-radical trapping effect of C60 and the CNTs network are responsible for the improved thermal and flame retardancy properties. Meanwhile, addition of C60-d-CNT also causes enhanced mechanical properties of PP nanocomposites to a certain degree.

Effect of Lignin Incorporation and Reactive Compatibilization on the Morphological, Rheological, and Mechanical Properties of ABS Resin

In order to develop the potential application of industrial alkali lignin, its acrylonitrile-butadiene-styrene (ABS) composites were fabricated via melt blending in the absence/presence of a compatibilizer. The lignin can uniformly disperse in the ABS matrix with number-average dispersed-phase domains of sub-micron scale, ranging from 150–250 nm, as observed by scanning electron microscopy. Infrared spectroscopy reveals that strong intermolecular interactions, mainly hydrogen bonding, were responsible for their good interfacial compatibility. Rheological behaviors show that the presence of lignin restricts to some extent the relaxation of polymer chains without affecting the processing properties of ABS resin. The presence of lignin increases storage modulus and glass transition temperature (T g) of ABS. Incorporating small amounts of lignin, e.g. 5 wt%, can produce ABS composites with enhanced tensile strength and modulus, while higher loading of lignin will reduce mechanical properties. The latter, however, can be improved by reactive compatibilization.

Nonisothermal crystallization behavior of polypropylene-C60 nanocomposites

The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C60) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (Tc), half-time for the crystallization (t1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C60 accelerates the crystallization of PP, implying a nucleating role of C60. Furthermore, due to the reduced viscosity of PP by adding 5% C60, the parameters of crystallization kinetics for the PP-5%C60 nanocomposites changed remarkably relative to that of neat PP and when lower contents of C60 were added to PP.