Bioinspired Structures Made of Silicone Nanofilaments for Upcycling Waste Masks to Reusable N95 Respirators.

The increasing demand for personal protective equipment such as single-use masks has led to large amounts of nondegradable plastic waste, aggravating economic and environmental burdens. This study reports a simple and scalable approach for upcycling waste masks via a chemical vapor deposition technique, realizing a trichome-like biomimetic (TLB) N95 respirator with superhydrophobicity (water contact angle ≥150°), N95-level protection, and reusability. The TLB N95 respirator comprising templated silicone nanofilaments with an average diameter of ∼150 nm offers N95-level protection and breathability comparable to those of commercial N95 respirators. The TLB N95 respirator can still maintain its N95-level protection against particulate matter and viruses after 10 disinfection treatment cycles (i.e., ultraviolet irradiation, microwave irradiation, dry heating, and autoclaving), demonstrating durable reusability. The proposed strategy provides new insight into upcycle waste masks, breaking the existing design and preparation concept of reusable masks.

Trichome-Like Biomimetic Air Filters via Templated Silicone Nanofilaments.

Air pollution threats to human health have increased awareness of the role of filter units in air cleaning applications. As an ideal energy-saving strategy for air filters, the slip effect on nanofiber surfaces can potentially overcome the trade-off between filtration efficiency and pressure drop. However, the potential of the slip effect in nanofibrous structures is significantly limited by the tight nanofiber stacks. In this study, trichome-like biomimetic (TLB) air filters with 3D-templated silicone nanofilaments (average diameter: ≈74 nm) are prepared based on an in situ chemical vapor deposition (CVD) method inspired by plant purification. Theoretical modeling and experimental results indicate that TLB air filters make significant use of the slip effect to overcome the efficiency-resistance tradeoff. The selectable filter class (up to U15, ≈99.9995%) allows TLB air filters to meet various requirements, and their integral filtration performance surpasses that of most commodity air filters, including melt-blown cloth, ePTFE membranes, electrospun mats, and glass fiber paper. The proposed strategy directly transforms commercial filter media and filters into TLB air filters using a bottom-up, one-step approach. As a proof-of-concept, reusable N95 respirators and air purifiers equipped with TLB air filters are fabricated, overcoming the limitations of existing filter designs and fabrication methods.

Hierarchical Mg/Al hydrotalcite oxide hollow microspheres with excellent adsorption capability towards Congo red.

A novel citrate anion-intercalated Mg/Al layered double hydroxide (CA-LDH) is synthesized via a one-step hydrothermal process. The synthesized CA-LDH is a hollow flower-like microsphere composed of thin nanoflakes (10 nm in thickness). After calcination, the formed Mg/Al layered double oxide (CA-LDO) hollow microspheres possess a high specific surface area of 247.8 m2 g-1 and a high pore volume of 0.97 cm3 g-1, which endow them with excellent adsorption ability towards Congo red (CR). The maximum adsorption capacity of CR onto CA-LDO can reach up to 1883 mg g-1. The significantly improved adsorption capacity of CA-LDO can be attributed to its unique structures of hierarchical hollow microspheres, in which the hierarchical porous shell layer provides enough adsorption sites to anchor the dye molecules, and the hollow core can preserve the absorbed dye. This study provides a promising novel adsorbent which can be used for efficient water remediation.

The influence of the pavement friction coefficient evolution caused by traffic flow on the risk of motorway horizontal curves.

The friction coefficient between the tire and the road is one of the key parameters affecting road traffic safety. The purpose of this paper is to quantify the risk of skidding for the vehicles due to the friction evolution caused by the traffic polishing in the horizontal curve. Based on the reliability theory, an innovative dynamic risk assessment model is developed in the present study for passenger cars and trucks. The influence of two traffic characteristics for pavement friction is quantified: cumulative traffic volume (CTV) and annual average daily traffic of trucks (AADTT). The speed distribution on the horizontal curve of the motorway is obtained through field experiments as the basic parameter of the model. The Hasofer-Lind Method is adopted to solve the reliability and the risk probability of vehicle skidding. The results show that in the traffic characteristics, the AADTT has a significant impact on the pavement friction; When the AADTT on the road exceeds 2000 veh/d, the increasing CTV leads to friction decrease rapidly and therefore has a significant impact on the risk of horizontal curve. Especially for roads with more than 50 million vehicles of the CTV, the risk of the horizontal curve shows a sharp increase with CTV rising. The research results can provide reference for the road maintenance department to determine the timing of road maintenance.

Phosphorous-Nitrogen Modification of Epoxy Grafted Poly-Acrylic Resin: Synergistic Flame Retardment Effect.

A novel high-efficient flame retardant epoxy grafted poly-acrylic resin modified by phosphorus and nitrogen was successfully synthesized by radical grafting polymerization and solution polymerization simultaneously. The flame retardancy of copolymer resin was investigated using thermogravimetric analysis (TGA), cone calorimetric test (CONE), limiting oxygen index (LOI) and so on. The micro-morphology and chemical composition of char formed after a CONE calorimetric test was analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The Kissinger method was used to evaluate the kinetics of thermal decomposition on copolymer resin. The results showed that the flame retardant property of copolymer resin increased with the increase in phosphorus content. With the increase in nitrogen content, however, the flame retardant property first increased and then decreased. The flame retardant property of the resin was the best and the limiting oxygen index could reach 34.3% when the phosphorus content and nitrogen content of the copolymer resin were 6.45 wt% and 2.33 wt%, respectively. Meanwhile, nitrogen-containing compounds will interact with phosphorus-containing compounds to form P-N intermediates during combustion, which have stronger dehydration and carbonization and could further enhance the flame retardant performance of the resin and generate phosphorus-nitrogen synergistic interactions.

Preparation of a Novel Phosphorus-Nitrogen Containing Novolac Curing Agent for Epoxy Resin and flame-retardancy of its cured epoxy resin.

In this study, DICY (dicyandiamide)-containing novolac (NN) was first prepared, and then DOPO (9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) was introduced to react with the unsaturated bonds from DICY to obtain a novel phosphorus-nitrogen-containing novolac resin (PNN), which was used as a curing agent for epoxy resins. The curing condition was confirmed by a non-isothermal curing kinetics study. The thermal stability and flame retardancy of the cured epoxy resin system were studied by thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL-94 test and cone calorimeter. The morphology of the burned chard residues was observed by Scanning electron microscopy (SEM). The results show that epoxy resin cured by the prepared PNN curing system presents excellent flame retardancy. The cured resin system, which contains only 1.31wt% phosphorus and 2.48wt% nitrogen, can achieve UL 94 V-0 rating.

Preparation, characterization and flame retardancy of phosphorus-containing poly-styrene-acrylate emulsion.

Phosphorus (P)-containing monomer (P-monomer) was firstly prepared by condensation reaction between 2-hydroxyethyl methacrylate and phosphorus pentoxide (P2O5) and then used to prepare P-containing poly-styrene-acrylate (P-PSA) emulsion by semi-continuous emulsion polymerization. The components of the prepared P-monomer were characterized by potentiometric titration method. The chemical composition of the P-PSA co-polymer was studied by Fourier-transform infrared spectra. The storage stability properties of P-PSA emulsion were tested by Ca2+, centrifugal and mechanical stability tests. The thermal stability and flame retardancy of the P-PSA co-polymer were studied by thermogravimetric analysis, limiting oxygen index and UL-94 method. The results show that stable P-PSA emulsions can be successfully prepared, and the latex particles present a spherical structure. When the P-monomer content is 30 wt%, the P-PSA co-polymer can pass the UL-94 test (V0 level) and the char yield is 54 wt% at 700°C. Scanning electron microscopy results indicate that incorporation of the P-monomer shows a condensed-phase flame-retardant effect. This study provides useful suggestions for the application of the flame-retardant P-PSA emulsion in the coating industry.