Despite the great potential in fabrication of biodegradable and eco-friendly air filters by electrospinning poly­(lactic acid) (PLA) membranes, the filtering performance is frequently dwarfed by inadequate physical sieving or electrostatic adsorption mechanisms to capture airborne particulate matters (PMs). Here, using the parallel spinning approach, the unique micro/nanoscale architecture was established by conjugation of neighboring PLA nanofibers, creating bimodal fibers in electrospun PLA membranes for the enhanced slip effect to significantly reduce the air resistance. Moreover, the bone-like nanocrystalline hydroxyapatite bioelectret (HABE) was exploited to enhance the dielectric and polarization properties of electrospun PLA, accompanied by the controlled generation of junctions induced by the microaggregation of HABE (10–30 wt %). The incorporated HABE was supposed to orderly align in the applied E-field and largely promote the charging capability and surface potential, gradually increasing to 7.2 kV from the lowest level of 2.5 kV for pure PLA. This was mainly attributed to HABE-induced orientation of PLA backbone chains and CO dipoles, as well as the interfacial charges trapped at the interphases of HABE–PLA and crystalline region–amorphous PLA. Given the multiple capturing mechanisms, the micro/nanostructured PLA/HABE membranes were characterized by excellent and sustainable filtering performance, e.g., the filtration efficiency of PM0.3 was promoted from 59.38% for pure PLA to 94.38% after addition of 30 wt % HABE at a moderate airflow capacity of 32 L/min and from 30.78 to 83.75% at the highest level of 85 L/min. It is of interest that the pressure drop was significantly decreased, mainly arising from the slip effect between the ultrafine nanofibers and conjugated microfibers. The proposed combination of the nanostructured electret and the multistructuring strategy offers the function integration of efficient filtration and low resistance that are highly useful to pursue fully biodegradable filters.

No abstract

Vulcanized, foamed latex rubber features high density of intercommunicated cells and controlled elastomeric properties, rendering wide applications from elastic sponges to rubbery coatings. This provides an emergent incentive for properly recycling, devulcanizing and reusing the waste latex rubber (WLR). Here, a microwave-assisted devulcanization (MAD) approach was disclosed to cleave the cross-links without severe rupture of backbone rubber chains, strategically involving the use of a microwave-assisted hydrothermal reaction at 180 °C for several minutes and incorporation of graphene nanosheets serving as the nanoabsorbers of microwave irradiation. The MAD processing duration was examined to be a vital parameter controlling the macromolecular characteristics: a high devulcanization degree of 83.6% was obtained with 8 min MAD, whereas the soluble content was undesirably increased to 76.2% after 16 min. The devulcanization efficacy was examined by melt compounding with poly(lactic acid) (PLA), displaying extensive interfacial interactions and thereby, creating strong and resilient interfacial adhesion within the PLA composites. With the addition of 10 wt % devulcanized WLR by 8 min MAD, the tensile strength and elongation at break of PLA composites were largely promoted to 58.2 MPa and 16.6%, increasing nearly 62% and 240% compared to those of pure PLA, respectively. The proposed MAD approach may open an environment-respecting and reliable pathway to sustainable recycling of waste rubber, yielding useful components to toughen PLA without sacrificing the strength.