Form-stable phase change films composed of a polydopamine-polyurethane polymer matrix with photothermal conversion properties and polyethylene glycol (PEG) are presented. Surfaces of environmentally friendly waterborne polyurethane (WPU) particles in aqueous dispersions were coated with polydopamine to create a stable waterborne dispersion of a polydopamine-polyurethane (PDA-WPU) matrix, which intrinsically presents significant photothermal conversion properties, and PEG was directly integrated into the PDA-WPU matrix by simple mixing in the dispersion form. Successful film formation was achieved at PDA-WPU to PEG ratios of 1:1 and higher by weight, resulting in form-stable, homogeneous PDA-WPU/PEG phase change films. Incorporation of PEG into the amorphous PDA-WPU matrix was demonstrated to impart a semicrystalline character to PDA-WPU films, which also increased their thermal stability and thermal conductivity. Young's modulus of PDA-WPU/PEG films increased while the tensile strength and elongation at break values decreased as a function of PEG content, yet all films showed a flexible behavior. For the films prepared with the highest amount of PEG (PDA-WPU:PEG 1:1), the melting and solidifying enthalpies were calculated to be 81.1 and 77.9 J/g, respectively, and enthalpies remained the same over 60 consecutive heating−cooling cycles. The temperature of the PDA-WPU:PEG 1:1 film reached 74.8 °C under 20 min of solar irradiation at 150 mW/cm 2 with a solar-to-thermal energy conversion efficiency of 72.9%. In a cold environment, PDA-WPU/PEG films and their surroundings were shown to heat up more than controls under solar light and stay warmer after the solar irradiation was stopped. The temperature of the environment surrounded with the PDA-WPU/PEG film increased 10 °C more than the temperature of the control environment under 30 min of sunlight irradiation. Upon switching the sunlight irradiation off, the PDA-WPU/PEG environment cooled down to ambient temperature 10 min later than the control environment, demonstrating that these form-stable, flexible, and durable films can efficiently harvest and store sunlight and have strong potential as solar-driven thermoregulating materials.

Ethylene, the ripening hormone produced by climacteric plants, is an important parameter that determines the shelf life of fresh fruits. Cinnamaldehyde (CA) encapsulated in halloysite nanotube (HNT) nanocarriers was studied as an ethylene production inhibition agent. The slow release of CA from HNT-CA nanohybrids was demonstrated to last for over 180 d and cause inhibition of ethylene production in bananas. The HNT-CA nanohybrids were incorporated into polypropylene (PP) via melt extrusion, resulting in PP/HNT-CA nanocomposite films with suitable mechanical properties for use as flexible packaging. Bananas stored in PP/HNT-CA nanocomposite film bags for 7 d presented significantly lower weight loss, higher firmness, and higher color scores, indicating freshness, than bananas stored in neat PP film bags. The nanocomposite films presented in this study were shown to slow down the ripening by inhibiting ethylene production, and they have strong potential as active food packaging materials that can prevent spoilage of ethylene-sensitive fresh fruits.

Antibacterial air filter media offer an important solution to indoor air pollution from bioaerosols, which pose a serious threat to global public health. In this study, we introduced an antibacterial air filter based on nanofibers functionalized with a photothermal agent, which deactivates bacteria upon near-infrared (NIR) irradiation. Halloysite nanotube (HNT) clay nanoparticles coated with polydopamine (PDA), which heat up when exposed to NIR light, were utilized as photothermal agents to be incorporated into polyacrylonitrile (PAN) nanofibers. The resulting PAN/HNT-PDA nanofibers reached 102 °C after 2 min of NIR irradiation and physically destroyed Staphylococcus aureus (S. aureus) cells that were in contact with the nanofibers. In a simulated air filtration test system, photothermal nanofibers demonstrated a bioaerosol filtration efficiency of 99.97% and a quality factor of 0.14 Pa −1 . 10 7 S. aureus cells captured on the nanofibers were killed via a 10 min NIR-light irradiation, whereas the light-activated antibacterial properties of the nanofibers were maintained over 5 bioaerosol flow/NIR-treatment cycles. The photothermal agent-containing electrospun nanofibers presented here have a strong potential for aerosol removal as light-activated antibacterial air filters.