Zhenghong Guo

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.

Effect of graphene nanosheets and layered double hydroxides on the flame retardancy and thermal degradation of epoxy resin

The effects of graphene nanosheets (GNS) and layered double hydroxides (LDH) on morphology, flame retardancy and thermal degradation of epoxy resin (ER) were investigated. LDH was exfoliated in ER/GNS/LDH nanocomposites, while GNS was partially exfoliated and partially agglomerated into small clusters. Since not all of the GNS had good dispersion, the compactness and barrier properties of residual char in ER/GNS/LDH were inferior to ER/GNS and ER/LDH. However, the simultaneous addition of GNS and LDH created an additional GNS–LDH interface, which could increase interaction in the melt and inhibit the flammable drips of ER and thus limit the flame propagation during combustion. As a result, a synergistic effect of simultaneous addition of GNS and LDH to improve the flame retardancy of ER was realized. The LOI value of ER was increased from 15.9 to 23.6 by adding 0.5 wt% of GNS and 0.5 wt% of LDH. In comparison, the LOI value was 19.5 and 21.7 when GNS or LDH was added separately, at the same level, 1 wt%. Furthermore, both GNS and LDH can increase the thermal stability of ER; there was a synergistic effect between them to decrease the THR of ER from 33.4 to 24.6.

Carbon nanotube bridged cerium phenylphosphonate hybrids, fabrication and their effects on the thermal stability and flame retardancy of the HDPE/BFR composite

Multiwalled carbon nanotube (MWNT) bridged cerium phenylphosphonate (CeHPP) hybrids (Ce-MWNTs) were facilely prepared through the in situ introduction of MWNTs into the hydrothermal reaction system of CeHPP, aiming at enhancing the flame retardancy of the polymer. Morphological observations indicated that the MWNTs acted as bridges to connect CeHPP lamellas to form a consecutive structure. Moreover, due to the good dispersion of CeHPP and the acting force between CeHPP and the MWNTs, the hybrids were dispersed uniformly resisting the strong intermolecular attractions. The hybrids led to a reduction in the peak heat release rate (PHRR) of the conventional flame retardant high-density polyethylene (HDPE) composite and improved the UL-94 grade from V-2 to V-0, indicating that they could confer a better flame retardancy on HDPE compared to the CeHPP or MWNTs alone. The results of the pyrolysis products and the morphology of the chars gave the evidence that Ce-MWNTs could enhance the physical barrier effect to retard the vaporization of flammable gases and the transfer of heat because of the mutual complementarity of the CeHPP and MWNTs.

Thermal stability and rheological behaviors of high-density polyethylene/fullerene nanocomposites

High-density polyethylene/fullerene (HDPE/C60) nanocomposites with the C60 loading that varied from 0.5 to 5.0% by weight were prepared via melt compounding. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results showed that the presence of C60 could remarkably enhance the thermal properties of HDPE. A very low C60 loading (0.5wt%) increased the onset degradation temperature from 389°C to 459°C and decreased the heat release from 3176 J/g to 1490 J/g. The larger the loading level of C60, the better the thermal stability of HDPE/C60 nanocomposites. Rheological investigation results showed that the free radical trapping effect of C60 was responsible for the improved thermal stability of HDPE.

Influence of fullerene on the kinetics of thermal and thermo-oxidative degradation of high-density polyethylene by capturing free radicals

The influence of fullerene (C60) on the thermal and thermal-oxidative degradation of high-density polyethylene (HDPE) was studied using non-isothermal thermogravimetric analysis under nitrogen (N2) and air atmosphere. Kinetic parameters of the degradation were evaluated using the Flynn–Wall–Ozawa method, which does not require the knowledge of the reaction mechanism. The results showed that the addition of C60 enhanced the thermal stability of HDPE and increased the activation energy both in N2 and air atmosphere and especially affected the initial stage of degradation. In N2, C60-trapped carbon-centered radical originated from the degradation of HDPE to improve the thermal stability and increase the activation energy. While in air, C60 trapped the alkyl radicals and alkyl peroxide radicals to inhibit the hydrogen abstraction (especially the initial stage of thermo-oxidative degradation) and form more stable species, which improved the thermal stability and increased the activation energy during the thermal degradation of HDPE. Comparing with that of pure HDPE, the changes of activation energy for HDPE/C60 nanocomposites were higher in air than in N2, especially in the initial stage.

Compatibilization of polyamide 6/poly(2,6-dimethyl-1,4-phenylene oxide) blends by poly(styrene-co-maleic anhydride)

Abstract The properties of polyamide 6 (PA6)/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) blends (60/40, wt%) compatibilized by poly(styrene-co-maleic anhydride) (SMA) were studied. The addition of SMA can form an in situ copolymer, SMA-graft-PA6. The SMA-graft-PA6 copolymer actually plays a key role as a compatibilizer to improve the interface between PA6 and PPO. It was found that the effect of compatibilization resulted in improvement of the morphology, impact strength and water absorbability of PA6/PPO blends (60/40, wt%), but with no favorable effects for thermal stability. However, at high SMA contents, the properties of PA6/PPO (60/40, wt%) blends deteriorated to some degree.

Study of a halogen-free flame-retarded Polypropylene composition with balanced strength and toughness

A nitrogen?phosphorus (N?P) Intumescent Flame Retardant (IFR) was applied for the halogen-free flame-retarded Polypropylene (PP) composition. The matrix resin, toughening materials and strengthening materials were selected for improving the tensile and impact properties of the flame-retarded PP. Orthogonal experiments were performed to produce an optimum recipe with balanced flame retardancy, impact strength and tensile strength. The Charpy impact strength and the tensile strength of PP/IFR/R1/G2/additive (62.8/28/4/5/0.2) were 28.56 MPa and 7.74 kJ/m², respectively. At the same time, this composition could reach UL V0 level in the vertical combustion test, which is satisfied for the need of usual engineering application.