Zhengping Fang

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 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.

Superior flame retardancy of epoxy resin by the combined addition of graphene nanosheets and DOPO

In this paper, the thermal stability and fire retardant behavior of epoxy resin (ER) composites filled with graphene nanosheets (GNS) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were investigated. Addition of GNS and DOPO changed the decomposition pathway of ER. During combustion, DOPO played a key flame retardancy role in the gas phase and the char enhancement in the condensed phase, while GNS played an effect in the condensed phase. Addition of 5 wt% GNS and DOPO separated, the peak heat release rate (PHRR) of ER was reduced from 1194 kW m−2 to 513.9 kW m−2 and 937.1 kW m−2, respectively. With the combined addition of GNS and DOPO, the flame retardancy of ER composites was significantly improved. The PHRR was reduced to 396 kW m−2 at the addition of 2.5% GNS and 2.5% DOPO. The same tendency was obtained for the total heat release (THR), showing a synergistic effect between GNS and DOPO in improving the flame retardancy of ER composites. The combined addition of GNS and DOPO extended the diffusion path for heat and combustible gas while DOPO captured the free radicals which further retarded ER degradation.

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.

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.

Flame-retardant Coating by Alternate Assembly of Poly(vinylphosphonic acid) and Polyethylenimine for Ramie Fabrics

A novel intumescent flame retardant coating, consisting of poly(vinylphosphonic acid) (PVPA) as the acid source and branched polyethylenimine (BPEI) as the blowing agent, was constructed on the surface of ramie fabrics by alternate assembly to remarkably improve the flame retardancy of ramie. The PVPA/BPEI coating on the surface of individual fibers of ramie fabric pyrolyzes to form protective char layer upon heating/burning and improves the flame retardancy of ramie. Thermogravimetric analysis reveals that the PVPA/BPEI-coated ramie fabrics left as much as 25.8 wt% residue at 600 °C, while the control (uncoated) fabric left less than 1.4 wt% residue. Vertical flame test shows that all PVPA/BPEI-coated fabrics have shorter after-flame time, and the residues well preserved the original weave structure and fiber morphology, whereas, the uncoated fabric left only ashes. Microscale combustion calorimetry shows that the PVPA/BPEI coatings greatly reduce the total heat release by as much as 66% and the heat release capacity by 76%, relative to those of the uncoated fabric.

Effect of iron acetylacetonate on the crosslink structure, thermal and flammability properties of novel aromatic diamine-based benzoxazines containing cyano group

Iron acetylacetonate (Fe(AcAc)3) was chosen as the catalyst for a novel aromatic diamine-based benzoxazine, containing cyano group (BAPBACP). Its effect on the curing process, thermal and flammability properties of BAPBACP were investigated. The results indicated that without Fe(AcAc)3, the ring-opening polymerization of the BAPBACP monomer occurred and an arylamine Mannich bridge structure was formed at the low curing temperature stage; and then the cyclotrimerization of the cyano group followed at the high curing temperature stage, but the cyano group was not fully cyclotrimerized even after curing at 350 °C for 0.5 h. The addition of 3.5% Fe(AcAc)3 speeded up the curing reaction and the cyano group was fully cyclotrimerized at 350 °C. Thermogravimetric analysis and microscale combustion calorimetry results showed that the poly(BAPBACP) resins possess excellent thermal and flammability properties due to the existence of the arylamine Mannich bridge structure and triazine ring in their crosslinked structure.

Bioinspired Design of Strong, Tough, and Thermally Stable Polymeric Materials via Nanoconfinement

The combination of high strength, great toughness, and high heat resistance for polymeric materials is a vital factor for their practical applications. Unfortunately, until now it has remained a major challenge to achieve this performance portfolio because the mechanisms of strength and toughness are mutually exclusive. In the natural world, spider silk features the combination of high strength, great toughness, and excellent thermal stability, which are governed by the nanoconfinement of hydrogen-bonded β-sheets. Here, we report a facile bioinspired methodology for fabricating advanced polymer composite films with a high tensile strength of 152.8 MPa, a high stiffness of 4.35 GPa, and a tensile toughness of 30.3 MJ/m3 in addition to high thermal stability (69 °C higher than that of the polymer matrix) only by adding 2.0 wt % of artificial β-sheets. The mechanical and thermostable performance portfolio is superior to that of its counterparts developed to date because of the nanoconfinement and hydrogen-bond cross-linking effects of artificial β-sheets. Our study offers a facile biomimetic strategy for the design of integrated mechanically robust and thermostable polymer materials, which hold promise for many applications in electrical devices and tissue engineering fields.

Confinement of C60 nanoparticles on the dynamics of polystyrene studied by anelastic spectroscopy and rheometrics

Anelastic spectroscopy and rheometrics were used to study the viscoelastic properties of polystyrene/C60 nanocomposites. 0.1 wt%, 0.5 wt%, 1 wt% and 2 wt% C60 were added to pure polystyrene via melt compounding. Both storage modulus and viscosity decreased obviously when 0.1 wt% C60 was added and it was ascribed to the increase of free volume around C60 nanoparticles. Both glass transition and liquid-liquid transition moved to high temperature, which was associated with the confinement effect of the nanoparticles. The addition of C60 influenced chain packing of polymer melts. The increase of free volume loosened the interaction between chain segments and nanoparticles on small size scale. So, the change of segment dynamics was not very obvious. On the contrary, the change of whole chain dynamics was very obvious. This can be explained by the fact that the influence coming from the increase of free volume was neglectable and the filler confinement of nanoparticles played an important role. The C60 nanoparticles were looked as attractors of the polymer chains, which divided the long chains into several segments leading to decrease the fragility of the nanocomposites.