Highly Sensitive, Breathable, and Flexible Pressure Sensor Based on Electrospun Membrane with Assistance of AgNW/TPU as Composite Dielectric Layer

Pressure sensors have been widely used in electronic wearable devices and medical devices to detect tiny physical movements and mechanical deformation. However, it remains a challenge to fabricate desirable, comfortable wearing, and highly sensitive as well as fast responsive sensors to capture human body physiological signs. Here, a new capacitive flexible pressure sensor that is likely to solve this problem was constructed using thermoplastic polyurethane elastomer rubber (TPU) electrospinning nanofiber membranes as a stretchable substrate with the incorporation of silver nanowires (AgNWs) to build a composite dielectric layer. In addition, carbon nanotubes (CNTs) were painted on the TPU membranes as flexible electrodes by screen printing to maintain the flexibility and breathability of the sensors. The flexible pressure sensor could detect tiny body signs; fairly small physical presses and mechanical deformation based on the variation in capacitance due to the synergistic effects of microstructure and easily altered composite permittivity of AgNW/TPU composite dielectric layers. The resultant sensors exhibited high sensitivity (7.24 kPa^-1 within the range of 9.0 × 10^-3 ~ 0.98 kPa), low detection limit (9.24 Pa), and remarkable breathability as well as fast responsiveness (<55 ms). Moreover, both continuously pressing/releasing cycle over 1000 s and bending over 1000 times did not impair the sensitivity, stability, and durability of this flexible pressure sensor. This proposed strategy combining the elastomer nanofiber membrane and AgNW dopant demonstrates a cost-effective and scalable fabrication of capacitive pressure sensors as a promising application in electronic skins and wearable devices.

Facile preparation and characterization of fibrous carbon nanomaterial from waste polyethylene terephthalate

Efficient reduction of environmental pollution caused by waste polyethylene terephthalate (PET) and production of carbon nanomaterials are desirable for nanotechnology, printable electronics, composites and environment protection. Here we report a simple top-down micro/nano-fabrication process to prepare fibrous carbon nanomaterial from waste PET bottles. This process is highly efficient, facile, and catalyst-free in preparing fibrous carbon nanomaterial with promising hydrophobic and electrical properties. The fibrous carbon nanomaterial can be used both in the form of sheet or powder, and it supplies a versatile surface for preparing novel carbon-based composites with significant optical properties and conductivity. The prepared carbon nanomaterial from waste PET has also been used in fabricating strain sensor with good durability.

Structure and thermal properties of various alcoholysis products from waste poly(ethylene terephthalate)

Waste polyethylene terephthalate (PET) has been a core member in plastic polluters due to the great amount consumption in food packaging, soft-drink bottles, fibers and films. It is essential to recycle waste PET and alcoholysis is a significant way to accomplish chemical recycling. In this work, three kinds of dihydric alcohols, including neopentyl glycol (NPG), dipropylene glycol (DPG) and poly(propylene glycol) (PPG), were employed to decompose waste PET with different temperatures, catalysts, and PET. A series of alcoholysis products with different appearance were obtained. The bulk structure and thermal properties of alcoholysis products were investigated by FTIR, ¹H NMR, MALDI-TOF, DSC and TG experiments. It is found that poly(propylene glycol) may react with waste PET to generate copolymer instead of oligomer products, dimers or trimers, etc. This product possesses excellent shelf stability and present transparent appearance, which may hold a great potential application in chemical industry. Moreover, the alcoholysis activity of DPG is the lowest comparing with NPG and EG in degradation of waste PET.

Polyurethane elastomer composites reinforced with waste natural cellulosic fibers from office paper in thermal properties

Polyurethane elastomer (PUE) composites were synthesized with a low additive content of waste natural cellulosic fibers from office paper. A new technology combining prepolymer method with physical blending and modification was adopted. The results showed that cellulosic fibers were covalently bonded to polyurethane molecular chains and served as a cross-linking agent making the degree of phase separation decrease. Even so, the lowest additive content of cellulosic fibers (1 wt%) in this work could make polyurethane still hold a certain degree of phase separation. Besides, thermal stability of polyurethane was improved from 288 to around 300 °C even at the low cellulosic fibers content. PUE with 3% cellulosic fibers had the better interfacial compatibility between cellulosic fibers and polyurethane causing the greater thermal reinforcement. PUE with 4% and 5% cellulosic fibers had the worse interfacial compatibility generating the better damping capacity indicating that cellulosic fibers could improve damping performance of polyurethane, especially polyurethane with 5 wt% fibers. It meant that cellulosic fibers had a potential application in damping materials.

Cellulose nanocrystals obtained from office waste paper and their potential application in PET packing materials

Annually a tremendous amount of office waste paper (OWP) is discarded creating environmental pollution. Therefore, how to make this paper from waste to wealth and use it in new approaches have become a meaningful and challenging work. In this work, OWP being a cellulose rich biomass was employed for the production of cellulose nanocrystals (CNCs) by acid hydrolysis with different acid concentrations but without subjecting OWP to alkali and bleaching treatments. The testing results showed that CNCs prepared using sulfuric acid concentration of 59% with respect to OWP had the highest crystallinity and this concentration was the transition concentration for the production of opaque CNCs film with convoluted nanofibers to transparent one with orientated nanofibers. Besides, CNCs prepared using acid concentration of 65% coated on PET sheet not only had a better water vapor barrier property but also was on a par with the transparency of PET, which was hopeful to be used as coating materials in packaging materials.