Transparent and super-gas-barrier PET film with surface coated by a polyelectrolyte and Borax

Thermoplastic Polyurethane Derived from CO2 for the Cathode Binder in Li-CO2 Battery

High-energy-density Li-CO2 batteries are promising candidates for large-capacity energy storage systems. However, the development of Li-CO2 batteries has been hindered by low cycle life and high overpotential. In this study, we propose a CO2-based thermoplastic polyurethane (CO2-based TPU) with CO2 adsorption properties and excellent self-healing performance to replace traditional polyvinylidene fluoride (PVDF) as the cathode binder. The CO2-based TPU enhances the interfacial concentration of CO2 at the cathode/electrolyte interfaces, effectively increasing the discharge voltage and lowering the charge voltage of Li-CO2 batteries. Moreover, the CO2 fixed by urethane groups (-NH-COO-) in the CO2-based TPU are difficult to shuttle to and corrode the Li anode, minimizing CO2 side reactions with lithium metal and improving the cycling performance of Li-CO2 batteries. In this work, Li-CO2 batteries with CO2-based TPU as the multifunctional binders exhibit stable cycling performance for 52 cycles at a current density of 0.2 A g-1, with a distinctly lower polarization voltage than PVDF bound Li-CO2 batteries.

Recent Progress of Biodegradable Polymer Package Materials: Nanotechnology Improving Both Oxygen and Water Vapor Barrier Performance

Biodegradable polymers have become a topic of great scientific and industrial interest due to their environmentally friendly nature. For the benefit of the market economy and environment, biodegradable materials should play a more critical role in packaging materials, which currently account for more than 50% of plastic products. However, various challenges remain for biodegradable polymers for practical packaging applications. Particularly pertaining to the poor oxygen/moisture barrier issues, which greatly limit the application of current biodegradable polymers in food packaging. In this review, various strategies for barrier property improvement are summarized, such as chain architecture and crystallinity tailoring, melt blending, multi-layer co-extrusion, surface coating, and nanotechnology. These strategies have also been considered effective ways for overcoming the poor oxygen or water vapor barrier properties of representative biodegradable polymers in mainstream research.

A Hydrotalcite-Based PET Composites with Enhanced Properties for Liquid Milk Packaging Applications

In the present work, the two-phase mixture (HTLc) of hydrotalcite and its oxide were used to improve the barrier properties, UV resistance and antimicrobial activity of Poly(ethylene terephthalate) (PET) for their application in liquid milk packaging. Firstly, CaZnAl-CO₃-LDHs with a two-dimensional layered structure were synthesized by hydrothermal method. CaZnAl-CO₃-LDHs precursors were characterized by XRD, TEM, ICP and dynamic light scattering. A series of PET/HTLc composite films were then prepared, characterized by XRD, FTIR and SEM, and a possible mechanism of the composite films with hydrotalcite was proposed. Barrier properties to water vapor and oxygen have been studied in PET nanocomposites, as well as their antibacterial efficacy by the colony technique and their mechanical properties after exposure to UV irradiation for 24 h. By the presence of 1.5 wt% HTLc in the PET composite film, the oxygen transmission rate (OTR) was reduced by 95.27%, the water vapor transmission rate was reduced by 72.58% and the inhibition against Staphylococcus aureus and Escherichia coli was 83.19% and 52.75%. Moreover, a simulation of the migration process in dairy products was used to prove the relative safety. This research first proposes a safe technique for fabricating hydrotalcite-based polymer composites with a high gas barrier, UV resistance and effective antibacterial activity.

Electrically programmable adhesive hydrogels for climbing robots

Although there have been notable advances in adhesive materials, the ability to program attaching and detaching behavior in these materials remains a challenge. Here, we report a borate ester polymer hydrogel that can rapidly switch between adhesive and nonadhesive states in response to a mild electrical stimulus (voltages between 3.0 and 4.5 V). This behavior is achieved by controlling the exposure and shielding of the catechol group through water electrolysis-induced reversible cleavage and reformation of the borate ester moiety. By switching the electric field direction, the hydrogel can repeatedly attach to and detach from various surfaces with a response time as low as 1 s. This programmable attaching/detaching strategy provides an alternative approach for robot climbing. The hydrogel is simply pasted onto the moving parts of climbing robots without complicated engineering and morphological designs. Using our hydrogel as feet and wheels, the tethered walking robots and wheeled robots can climb on both vertical and inverted conductive substrates (i.e., moving upside down) such as stainless steel and copper. Our study establishes an effective route for the design of smart polymer adhesives that are applicable in intelligent devices and an electrochemical strategy to regulate the adhesion.

Mica-Based Multilayer Nanocoating as a Highly Effective Flame Retardant and Smoke Suppressant

Highly flammable polyurethane foam (PUF) remains a key risk factor associated with bedding and upholstered furniture, contributing to the yearly destruction of property and loss of lives. In an attempt to tackle this issue and develop a more benign flame retardant for PUF, a mica-based nanocomposite was deposited using layer-by-layer assembly. Chitosan (CH) and poly(acrylic acid) (PAA) were used to stabilize high-aspect-ratio mica. Foam treated with eight bilayers of CH- and PAA-stabilized mica preserves the porous foam structure, prevents melt dripping, and self-extinguishes during a 10 s torch test, while uncoated foam is completely consumed. When exposed to 35 kW/m² heat flux during cone calorimetry, the peak heat release rate is reduced by 54% and less-volatile molecules are released during combustion, resulting in a 76% reduction in the total smoke release. This multilayer coating serves as an environmentally benign template for flame-retarding PUF and various other three-dimensional substrates.

Nano-Brick Wall Architectures Account for Super Oxygen Barrier PET Film by Quadlayer Assembly of Polyelectrolytes and α-ZrP Nanoplatelets

Nanobrick wall hybrid coating with super oxygen barrier properties were fabricated on polyethylene terephthalate (PET) film using a quadlayer (QL) assembly of polyelectrolytes and nanoplateles. A quadlayer assembly consists of three repeat units of polyacrylic acid (PAA), poly (dimethyl diallyl ammonium chloride) (PDDA) and layered α-zirconium phosphate (α-ZrP). PDDA with positive charges can assemble alternatively with both α-ZrP and PAA with negative charges to form nanobrick wall architectures on the surface of PET film via the electrostatic interaction. The lamellar structure of α-ZrP platelets and the dense QL assembly coating can greatly reduce the oxygen transmission rate (OTR) of PET film. Compared to pristine PET film, the OTR of PET (QL)19 is reduced from 57 to 0.87 cc/m²/day. Moreover, even with 19 QLs coating, PET (QL)19 composite film is still with an optical transparency higher than 90% and a haze lower than 10%. Therefore, the transparent PET (QL)n composite films with super oxygen barrier properties show great potential application in food packaging and flexible electronic packaging.