Engineering Sulfur-Containing Polymeric Fire-Retardant Coatings for Fire-Safe Rigid Polyurethane Foam.

With the advantages of lightweight and low thermal conductivity properties, polymeric foams are widely employed as thermal insulation materials for energy-saving buildings but suffer from inherent flammability. Flame-retardant coatings hold great promise for improving the fire safety of these foams without deteriorating the mechanical-physical properties of the foam. In this work, four kinds of sulfur-based flame-retardant copolymers are synthesized via a facile radical copolymerization. The sulfur-containing monomers serve as flame-retardant agents including vinyl sulfonic acid sodium (SPS), ethylene sulfonic acid sodium (VS), and sodium p-styrene sulfonate (VSS). Additionally, 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate are employed to enable a strong interface adhesion with polymeric foams through interfacial H-bonding. By using as-synthesized waterborne flame-retardant polymeric coating with a thickness of 600 µm, the coated polyurethane foam (PUF) can achieve a desired V-0 rating during the vertical burning test with a high limiting oxygen index (LOI) of >31.5 vol%. By comparing these sulfur-containing polymeric fire-retardant coatings, poly(VS-co-HEA) coated PUF demonstrates the best interface adhesion capability and flame-retardant performance, with the lowest peak heat release rate of 166 kW m-2 and the highest LOI of 36.4 vol%. This work provides new avenues for the design and performance optimization of advanced fire-retardant polymeric coatings.

Molecularly Engineered Lignin-Derived Additives Enable Fire-Retardant, UV-Shielding, and Mechanically Strong Polylactide Biocomposites.

From a perspective of sustainable development and practical applications, there has been a great need for the design of advanced polylactide (PLA) biocomposites that are flame-retardant, ultraviolet (UV)-resistant, and mechanically strong by using biomass-derived additives. Unfortunately, the achievement of a desirable performance portfolio remains unsatisfactory because of improper design strategies. Herein, we report the design of lignin-derived multifunctional bioadditives (TP-g-lignin) with tunable chemical compositions through graft polymerization of a phosphorus-/nitrogen-containing vinyl monomer (TP). Our results show that the incorporation of 5.0 wt % of TP-g-lignin (at a lignin-to-TP ratio of 1:4 by mass) enables PLA to achieve a desirable flame retardancy rating meeting the UL-94 V-0 industrial standard requirements. Meanwhile, the final PLA composite exhibits an exceptional UV-shielding capability. Moreover, with 5.0 wt % of the bio-derived additive, the elastic modulus of PLA is increased by ∼26%, while mechanical strength is fully retained due to engineered favorable interfaces. This work offers an innovative and sustainable strategy for creating bio-based multifunctional additives by using industrial lignin waste and further the application of PLA in the areas of packaging, fabrics, electronics, automobiles, etc.

Largely enhanced thermal and mechanical properties of polymer nanocomposites via incorporating C60@graphene nanocarbon hybrid.

Although considerable progress has been achieved to create advanced polymer nanocomposites using nanocarbons including fullerene (C60) and graphene, it remains a major challenge to effectively disperse them in a polymer matrix and to fully exert their extraordinary properties. Here we report a novel approach to fabricate the C60@graphene nanocarbon hybrid (C60: ~47.9 wt%, graphene: ~35.1%) via three-step reactions. The presence of C60 on a graphene sheet surface can effectively prevent the aggregation of the latter which in turn helps the dispersion of the former in a polymer matrix during melt-processing. C60@graphene is found to be uniformly dispersed in a polypropylene (PP) matrix. Compared with pristine C60 or graphene, C60@graphene further improves the thermal stability and mechanical properties of PP. The incorporation of 2.0 wt% C60@graphene (relative to PP) can remarkably increase the initial degradation temperature by around 59 ° C and simultaneously enhance the tensile strength and Young's modulus by 67% and 76%, respectively, all of which are higher than those of corresponding PP/C60 (graphene) nanocomposites. These significant performance improvements are mainly due to the free-radical-trapping effect of C60, and the thermal barrier and reinforcing effects of graphene nanosheets as well as the effective stress load transfer. This work provides a new methodology to design multifunctional nanohybrids for creating advanced materials.

Striking multiple synergies created by combining reduced graphene oxides and carbon nanotubes for polymer nanocomposites.

The extraordinary properties of carbon nanotubes (CNTs) and graphene stimulate the development of advanced composites. Recently, several studies have reported significant synergies in the mechanical, electrical and thermal conductivity properties of polymer nanocomposites by incorporating their nanohybrids. In this work, we created polypropylene nanocomposites with homogeneous dispersion of CNTs and reduced graphene oxides via a facile polymer-latex-coating plus melt-mixing strategy, and investigated their synergistic effects in their viscoelastic, gas barrier, and flammability properties. Interestingly, the results show remarkable synergies, enhancing their melt modulus and viscosity, O2 barrier, and flame retardancy properties and respectively exhibiting a synergy percentage of 15.9%, 45.3%, and 20.3%. As previously reported, we also observed remarkable synergistic effects in their tensile strength (14.3%) and Young's modulus (27.1%), electrical conductivity (32.3%) and thermal conductivity (34.6%). These impressive results clearly point towards a new strategy to create advanced materials by adding binary combinations of different types of nanofillers.

Evaluating the comprehensive influences of heat treatment and polydimethylsiloxane on integrated performance of bamboo timber.

The main objective of this work is to analyse the influence of heat treatment with polydimethylsiloxane on integrated performance of bamboo timber. Bamboo timber was heat treated using polydimethylsiloxane as a medium at 120, 150, 180 and 210 °C for 3 h in this study. Results revealed that the equilibrium moisture content (EMC) and linear swelling ratio of heat-treated bamboo specimens was remarkable decreased with increasing heat treatment temperature. The surface contact angle of water on the bamboo specimens was observed to increase with the increasing heat treatment temperature, indicating the reduction of wettability with water. Additionally, the modulus of rupture (MOR) and modulus of elasticity (MOE) was decreased with the increasing heat treatment temperature and lower than that of untreated specimens. Cellulose crystallinity of bamboo specimens was slightly decreased with the increase of heat treatment temperature. TG-DTG results illustrated a reduction in relative content of hemicellulose, and increase in relative content of lignin and cellulose of bamboo specimens with the increase of heat treatment temperature. Presence of the stretching vibration Si-C in Si-CH3 indicated the bonding of siloxane to bamboo timber by forming covalent bonds. The colour of the heat-treated bamboo timber was even deepened after heat treatment, endowing the bamboo timber with better surface decoration performance.

Probing Chemical Changes in Holocellulose and Lignin of Timbers in Ancient Buildings.

Wooden structures in China's ancient buildings hold highly historical and cultural values. There is an urgent need to repair and replace the damaged wooden structures after hundreds and thousands of years of exposure to weather. Unfortunately, to date there is still a lack of insightful understanding on how the chemical structure, composition, and micro-morphology evolve over the long-term natural aging before artificial ancient timbers can be developed. This work aims to systematically examine the outer surface, middle layer, and inner surface of the same piece of Chinese fir (Cunninghamia lanceolate) collected from an ancient Chinese building. Based on qualitative and quantitative analysis, both cellulose and hemicellulose in aged woods are found to experience significant degrees of degradation. The crystalline regions of cellulose are also determined to undergo moderate degradation as compared to the control fresh wood. In comparison, the lignin basically remains unchanged and its content in the inner layer slightly increases, as evidenced by more free phenol groups determined. Relative to the outer and inner layer, the middle layer of the ancient wood shows the lowest degree of degradation close to that of the fresh wood. This work offers guidelines for fabricating artificial ancient woods to repair the destroyed ones in China's ancient architectures.

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 ß-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 ß-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 ß-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.

Improve Performance of Soy Flour-Based Adhesive with a Lignin-Based Resin.

A lignin-based resin (LB) was used to improve the performance of soy flour-based adhesives. Soy flour (SF), polyamidoamine-epichlorohydrin (PAE), and LB were used to develop a plywood adhesive. The solid content and viscosity of the adhesive, the functional groups, the thermo-stability, and the crystallinity of the cured adhesives were characterized, and the performance of the resultant adhesive was evaluated by fabricating three-ply plywood. Results showed that the LB and PAE mixture used to modify the SF adhesive improved both dry and wet bond strength by 66.3% and 184.2%, respectively. Therefore, the PAE improved the wet bond strength, and the LB improved the dry bond strength. The improvement was attributed to: (1) the reaction of LB/PAE with the functions of the soy protein to form a cross-linking network; (2) a polycondensation reaction between the LB molecules improved the crosslinking density of the adhesive to form an interpenetration structure with cross-linked proteins; and (3) the easy penetration of the LB into the wood surface that enhanced interlocking between the wood and adhesive. Furthermore, the denser structure created by the LB and the PAE mixture improved thermal stability and decreased the crystallinity of the cured adhesive. The use of the LB and the PAE mixture increased the solid content by 35.5%, while still making its viscosity acceptable for industrial applications.

Facile fabrication of HDPE-g-MA/nanodiamond nanocomposites via one-step reactive blending.

In this letter, nanocomposites based on maleic anhydride grafted high density polyethylene (HDPE-g-MA) and amine-functionalized nanodiamond (ND) were fabricated via one-step reactive melt-blending, generating a homogeneous dispersion of ND, as evidenced by transmission electron microscope observations. Thermal analysis results suggest that addition of ND does not affect significantly thermal stability of polymer matrix in nitrogen. However, it was interestingly found that incorporating pure ND decreases the thermal oxidation degradation stability temperature, but blending amino-functionalized ND via reactive processing significantly enhances it of HDPE in air condition. Most importantly, cone tests revealed that both ND additives and reactive blending greatly reduce the heat release rate of HDPE. The results suggest that ND has a potential application as flame retardant alternative for polymers. Tensile results show that adding ND considerably enhances Young's modulus, and reactive blending leads to further improvement in Young's modulus while hardly reducing the elongation at break of HDPE.