Wang Liao

Nonflammable Alginate Nanocomposite Aerogels Prepared by a Simple Freeze-Drying and Post-Cross-Linking Method

Nonflammable materials based on renewable ammonium alginate and nano fillers (nanoscale magnesium hydroxide, nanoscale aluminum hydroxide, layered double hydroxide, sodium montmorillonite, and Kaolin) were fabricated through a simple, environmentally friendly freeze-drying process, in which water was used as a solvent. A simple and economic post-cross-linking method was used to obtain homogeneous samples. The microstructure of the cross-linked alginate aerogels show three-dimensional networks. These materials exhibit low densities (0.064-0.116 g cm(-3)), low thermal conductivities (0.024-0.046 W/m K), and useful mechanical strengths (0.7-3.5 MPa). The aerogels also exhibit high thermal stabilities and achieve inherent nonflammability with limiting oxygen indexes (LOI) higher than 60. Related properties were conducted and analyzed by cone calorimeter (CC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). These results combine to suggest promising prospects for use of these aerogel nanocomposites in a range of applications.

Improvement of the flame retardancy of wood-fibre/polypropylene composites with ideal mechanical properties by a novel intumescent flame retardant system

To improve the flame retardancy and maintain the ideal mechanical properties of the widely used wood fibre (WF) reinforced polypropylene (PP) composite (WPC), a novel intumescent flame retardant (IFR) system consisting of poly[N4-bis(ethylenediamino)-phenyl phosphonic-N2,N6-bis(ethylenediamino)-1,3,5-triazine-N-phenyl phosphonate] (PTPA) and ammonium polyphosphate (APP) was developed. Addition of APP, a high performance flame retardant, improves flame retardancy but has a negative effect on flexural properties and the Notched Izod impact strength. Combining self-designed PTPA with WPC has a positive effect on the mechanical properties whereas it just slightly increases the flame retardancy. The flame retarded WPC system with both PTPA and APP, i.e. WPC/PTPA/APP, combines bilateral advantages. The selected formula has a flexural modulus of 4.4 GPa, flexural strength of 37.2 MPa and impact strength of 1.8 kJ m−2, only the flexural strength is slightly lower than that of neat WPC. And the formula has a high limiting oxygen index (LOI) of 31.5%, which passes the UL-94 V-0 rating for a vertical burning test. The results of cone calorimetry show that the heat release rate (HRR) of the WPC/PTPA/APP system is significantly reduced compared to the neat WPC. The pyrolysis and char residue of the WPC/PTPA/APP system were investigated by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). These results reveal the flame-retardant mechanism that PTPA/APP can synergistically catalyze the etherification, dehydration and char formation of WPC.

Ultrasoft gelatin aerogels for oil contaminant removal

We demonstrated the preparation of a novel aerogel simply by cross-linking a gelatin physical gel with formaldehyde (cGel) and using a subsequent freeze-drying procedure. A hydrophobic absorbent material (MTCS-cGel aerogel) was further obtained by thermal chemical vapor deposition (CVD) of methyltrichlorosilane (MTCS). Rheological tests were carried out to investigate the cross-linking between gelatin and formaldehyde. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and wettability of oil and water results proved that successful silanization occurred on/in the aerogels. These results also indicated that the MTCS-cGels had low densities (5–8 kg m−3), high porosities (>95%) with uniform pore sizes, and unique laminar/fibrous 3D networks. The oleophilic aerogels possessed high oil absorption capacities of 70–123 times that of their dry weights. Furthermore, the absorbents exhibited excellent elasticity and ultrasoftness with a stress of only 2.0 kPa at 60% strain. This property endowed the aerogels with super-recyclability where 83–85% of their full absorption capacity was maintained after 5000 times of compression. The high oil absorption performance, super-recyclability, sustainability, biodegradability and cost-efficiency make this novel absorbent a promising candidate for large-scale oceanic oil contaminant removal.

Novel Polymer Aerogel toward High Dimensional Stability, Mechanical Property, and Fire Safety

Inorganc silica-based aerogels, the earliest and widely used aerogels, have poorer mechanical properties than their organic substitutes, which are flammable. In this study, a novel polymeric aerogel with high strength, inherent flame retardancy, and cost-effectiveness, which is based on poly(vinyl alcohol) (PVA) cross-linked with melamine-formaldehyde (MF), was prepared under aqueous condition with an ecofriendly freeze-drying and postcuring process. Combined with the additional rigid MF network and benifited from the resulting unique infrastructure of inter-cross-linked flexible PVA segments and rigid MF segments, PVA-based aerogels exibited a significantly decreased degradation rate and sharply decreased peak heat release rate (PHRR) in cone calorimeter tests (by as much as 83%) compared with neat PVA. The polymer aerogels have a limiting oxygen index (LOI) as high as 36.5% and V-0 rating in UL-94 test. Furthermore, the aerogel samples exposured to harsh temperatures maintain their dimensions (<10% change), original mechanical strength and fire safety. Therefore, this work provides a novel stragegy for preparing pure organic polymeric aerogel materials with high mechanical strength, dimensional stability, and fire safety.

Photothermal Nanocomposite Hydrogel Actuator with Electric-Field-Induced Gradient and Oriented Structure

Recent research of hydrogel actuators is still not sophisticated enough to meet the requirement of fast, reversible, complex, and robust reconfiguration. Here, we present a new kind of poly( N-isopropylacrylamide)/graphene oxide gradient hydrogel by utilizing direct current electric field to induce gradient and oriented distribution of graphene oxide into poly( N-isopropylacrylamide) hydrogel. Upon near-infrared light irradiation, the hydrogel exhibited excellent comprehensive actuation performance as a result of directional bending deformation, promising great potential in the application of soft actuators and optomechanical system.

Flame-retardant and smoke-suppressant flexible polyurethane foams based on reactive phosphorus-containing polyol and expandable graphite

In this manuscript, flame-retardant and smoke-suppressant flexible polyurethane foams (FPUFs) were designed and synthesized based on novel liquid phosphorus-containing polyol named as PDEO and expandable graphite (EG). The reactive PDEO can be chemically added into the chain of FPUF, while expandable graphite was blended into the matrix of foam through foaming process. Benefitting from the incorporation of reactive PDEO with a long chain, the resultant FPUF containing EG exhibited considerable mechanical properties. More importantly, the synergistic effect of PDEO and EG can endow FPUF with great flame retardancy, anti-driping performances. Furthermore, the resultant FPUF/EG/PDEO foams exhibit considerable smoke suppression performances. The vertical burning test revealed that the FPUF containing 5 php PDEO and 10 php EG extinguished quickly without dripping and kept the original shape after removing the igniter. The cone calorimeter results demonstrated that the synergistic effect of PDEO and EG can effectively reduce the heat release rate (HRR) and total release rate (THR) of the composite foam. Remarkably, the smoke production release (SPR), total smoke production (TSP), light transmission and specific optical density results indicated significantly smoke-suppressant properties of the composite foam. The mechanism analysis confirmed that the synergistic effect of gas-condensed bi-phase action from PDEO and EG contributed the great flame retardation of the composite foam. This novel FPUF provides a promising strategy for producing the polymer foam with flame retardation, smoke suppression and anti-dripping performances.