Polydimethylsiloxane-modified polyurethane-poly(ɛ-caprolactone) nanofibrous membranes for waterproof, breathable applications

Progress in the Preparation and Application of Breathable Membranes

Breathable membranes with micropores enable the transfer of gas molecules while blocking liquids and solids, and have a wide range of applications in medical, industrial, environmental, and energy fields. Breathability is highly influenced by the nature of a material, pore size, and pore structure. Preparation methods and the incorporation of functional materials are responsible for the variety of physical properties and applications of breathable membranes. In this review, the preparation methods of breathable membranes, including blown film extrusion, cast film extrusion, phase separation, and electrospinning, are discussed. According to the antibacterial, hydrophobic, thermal insulation, conductive, and adsorption properties, the application of breathable membranes in the fields of electronics, medicine, textiles, packaging, energy, and the environment are summarized. Perspectives on the development trends and challenges of breathable membranes are discussed.

Fabrication of Waterborne Silicone-Modified Polyurethane Nanofibers for Nonfluorine Elastic Waterproof and Breathable Membranes

Waterproof and breathable membranes have a huge market demand in areas, such as textiles and medical protection. However, existing fluorinated nanofibrous membranes, while possessing good waterproof and breathable properties, pose health and environmental hazards. Consequently, fabricating fluorine-free, eco-friendly waterborne membranes by integrating outstanding waterproofing, breathability, and robust mechanical performance remains a significant challenge. Herein, we successfully prepared waterborne silicone-modified polyurethane nanofibrous membranes with excellent elasticity, waterproofing, and breathability properties through waterborne electrospinning, using a small quantity of poly(ethylene oxide) as a template polymer and in situ doping of the poly(carbodiimide) crosslinking agent, followed by a simple hot-pressing treatment. The silicone imparted the nanofibrous membrane with high hydrophobicity, and the crosslinking agent enabled its stable porous structure. The hot-pressing treatment (120 °C) further reduced the pore size and improved the water resistance. This environmentally friendly nanofibrous membrane showed a high elongation at break of 428%, an ultra-high elasticity of 67.5% (160 cycles under 400% tensile strain), an air transmission of 13.2 mm s-1, a water vapor transmission rate of 5476 g m-2 d-1, a hydrostatic pressure of 51.5 kPa, and a static water contact angle of 137.9°. The successful fabrication of these environmentally friendly, highly elastic membranes provides an important reference for applications in healthcare, protective textiles, and water purification.

Preparation of Waterborne Silicone-Modified Polyurethane Nanofibers and the Effect of Crosslinking Agents on Physical Properties

Silicone-modified polyurethane (PUSX) refers to the introduction of a silicone short chain into the polyurethane chain to make it have the dual properties of silicone and polyurethane (PU). It can be used in many fields, such as coatings, films, molding products, adhesives, and so on. The use of organic solvents to achieve the fiberization of silicone-modified polyurethane has been reported. However, it is challenging to achieve the fiberization of silicone-modified polyurethane based on an environmentally friendly water solvent. Herein, we report a simple and powerful strategy to fabricate environmentally friendly waterborne silicone-modified polyurethane nanofiber membranes through the addition of polyethylene glycol (PEG) with different molecular weights using electrospinning technology and in situ doping with three crosslinking agents with different functional groups (a polyoxazoline crosslinking agent, a polycarbodiimide crosslinking agent, and a polyisocyanate crosslinking agent) combined with various heating treatment conditions. The influence of PEG molecular weight on fiber formation was explored. The morphology, structure, water resistance, and mechanical properties were analyzed regarding the effect of the introduction of silicone into PU. The effects of the type and content of crosslinking agent on the morphology and physical properties of PUSX nanofiber membranes are discussed. These results show that the introduction of silicone can improve the water resistance and high temperature resistance of waterborne PU, and the addition of a crosslinking agent can further improve the water resistance of the sample, so that the sample can maintain good morphology after immersion. Crosslinking agents with different functional groups had different effects on the mechanical properties of PUSX nanofiber membranes due to different reactions. Among them, the oxazoline crosslinking agent had a significant effect on improving tensile strength, while the isocyanate crosslinking agent had a significant effect on improving the elongation at break. The PUSX nanofiber membrane prepared in this work did not use organic solvents that were harmful to humans and the environment, and it can be used in outdoor textiles, oil-water separation, medical health, and other fields.

Electrospun Nanofibrous Membranes: A Versatile Medium for Waterproof and Breathable Application

Waterproof and breathable membranes that prevent liquid water penetration, while allowing air and moisture transmission, have attracted significant attention for various applications. Electrospun nanofiber materials with adjustable pore structures, easily tunable wettability, and good pore connectivity, have shown significant potential for constructing waterproof and breathable membranes. Herein, a systematic overview of the recent progress in the design, fabrication, and application of waterproof and breathable nanofibrous membranes is provided. The various strategies for fabricating the membranes mainly including one-step electrospinning and post-treatment of nanofibers are given as a starting point for the discussion. The different design concepts and structural characteristics of each type of waterproof and breathable membrane are comprehensively analyzed. Then, some representative applications of the membranes are highlighted, involving personal protection, desalination, medical dressing, and electronics. Finally, the challenges and future perspectives associated with waterproof and breathable nanofibrous membranes are presented.

Recent Progress in Protective Membranes Fabricated via Electrospinning: Advanced Materials, Biomimetic Structures, and Functional Applications

Electrospinning is a significant micro/nanofiber processing technology and has been rapidly developing in the past 2 decades. It has several applications, including advanced sensing, intelligent manufacturing, and high-efficiency catalysis. Here, multifunctional protective membranes fabricated via electrospinning in terms of novel material design, construction of novel structures, and various protection requirements in different environments are reviewed. To achieve excellent comprehensive properties, such as, high water vapor transmission, high hydrostatic pressure, optimal mechanical property, and air permeability, combinations of novel materials containing nondegradable/degradable materials and functional structures inspired by nature have been investigated for decades. Currently, research is mainly focused on conventional protective membranes with multifunctional properties, such as, anti-UV, antibacterial, and electromagnetic-shielding functions. However, important aspects, such as, the properties of electrospun monofilaments, development of "green electrospinning solutions" with high solid content, and approaches for enhancing adhesion between hydrophilic and hydrophobic layers are not considered. Based on this systematic review, the development of electrospinning for protective membranes is discussed, the existing gaps in research are discussed, and solutions for the development of technology are proposed. This review will assist in promoting the diversified development of protective membranes and is of great significance for fabricating advanced materials for intelligent protection.

Environmentally Friendly, Durably Waterproof, and Highly Breathable Fibrous Fabrics Prepared by One-Step Fluorine-Free Waterborne Coating

Waterproof and breathable membranes (WBMs) have drawn broad attention due to their widespread applications in various scientific and industry fields. However, creating WBMs with environment-friendliness and high performance is still a critical and challenging task. Herein, an environmentally friendly fluorine-free WBM with high performance was prepared through electrospinning and one-step dip-coating technology. The fluorine-free waterborne hydroxyl acrylic resin (HAR) emulsion containing long hydrocarbon chains endowed the electrospun polyacrylonitrile/blocked isocyanate prepolymer (PAN/BIP) fibrous membranes with superior hydrophobicity; meanwhile, crosslinking agent BIP ensured strong chemical binding between hydrocarbon segments and fiber substrate. The as-prepared PAN/BIP@HAR fibrous membranes achieve ideal properties with waterproofness of 112.5 kPa and moisture permeability of 12.7 kg m^-2 d^-1, which are comparable to the existing high-performance fluorinated WBMs. Besides, the PAN/BIP@HAR membranes also display impressive tensile strength and durability. Significantly, the proposed technology was also applicable to other hydrophilic fiber substrates, such as cellulose acetate and polyamide 6. The successful synthesis of environmentally friendly, durably waterproof, and highly breathable PAN/BIP@HAR membranes not only opens a new avenue to materials design, but also provides promising candidates with tremendous potential in various areas.

Polylactic acid based Janus membranes with asymmetric wettability for directional moisture transport with enhanced UV protective capabilities

Efficient directional moisture transport can remove excess sweat away from the human body and keep the body dry; fully utilizing this functionality to improve the wearing experience is urgently needed in the area of functional textiles. Herein, a facile strategy is used to design an eco-friendly and biodegradable PLA membrane with enhanced directional moisture transport and UV protection abilities. The PLA-based Janus membrane with asymmetric wettability is fabricated via sol-gel and electrospinning methods. Titanium dioxide nanoparticles (TiO2) were anchored onto the surface of the PLA fabric during the TiO2 sol-gel fabrication process using polydopamine, forming superhydrophilic TiO2@PDA-PLA. Then a thin PLA fibrous membrane layer showing hydrophobicity was electrospun onto this (PLA-E). The Janus PLA-E/TiO2@PDA-PLA membrane was successfully fabricated. Due to the asymmetric wettability and anchored TiO2, the PLA-E/TiO2@PDA-PLA Janus membrane exhibits efficient directional moisture transport and excellent UV protection abilities, and this work may provide a new pathway for fabricating multifunctional personal protective materials and have attractive potential applications in the future.

Hot-melt Adhesive Bonding of Polyurethane/Fluorinated Polyurethane/Alkylsilane-Functionalized Graphene Nanofibrous Fabrics with Enhanced Waterproofness, Breathability, and Mechanical Properties

Waterproof-breathable (WB) materials with outstanding waterproofness, breathability, and mechanical performance are critical in diverse consumer applications. Electrospun nanofibrous membranes with thin fiber diameters, small pore sizes, and high porosity have attracted significant attention in the WB fabric field. Hot-press treatment technology can induce the formation of inter-fiber fusion structures and hence improve the waterproofness and mechanical performance. By combining electrospinning and hot-press treatment technology, polyurethane/fluorinated polyurethane/thermoplastic polyurethane/alkylsilane-functionalized graphene (PU/FPU/TPU/FG) nanofiber WB fabric was fabricated. Subsequently, the morphologies, porous structure, hydrostatic pressure, water vapor transmission rate (WVTR), and stress–strain behavior of the nanofiber WB fabric were systematically investigated. The introduction of the hydrophobic FG sheet structure and the formation of the inter-fiber fusion structure greatly improved not only the waterproofness but also the mechanical performance of the nanofiber WB fabric. The optimized PU/FPU/TPU-50/FG-1.5 WB fabric exhibited an excellent comprehensive performance: a high hydrostatic pressure of 80.4 kPa, a modest WVTR of 7.6 kg m⁻² d⁻¹, and a robust tensile stress of 127.59 MPa, which could be used to achieve various applications. This work not only highlights the preparation of materials, but also provides a high-performance nanofiber WB fabric with huge potential application prospects in various fields.

Multifunctional, Waterproof, and Breathable Nanofibrous Textiles Based on Fluorine-Free, All-Water-Based Coatings

Developing environmentally benign, multifunctional waterproof and breathable membranes (WBMs) is of great importance but still faces enormous challenges. Here, an environmentally benign fluorine-free, ultraviolet (UV) blocking, and antibacterial WBM with a high level of waterproofness and breathability is developed on a large scale by combining electrospinning and step-by-step surface coating technology. Fluorine-free water-based alkylacrylates with long hydrocarbon chains were coated onto polyamide 6 fibrous membranes to construct robust hydrophobic surfaces. The subsequent titanium dioxide nanoparticle emulsion coating prominently decreased the maximum pore size, leading to higher water resistance, endowing the membranes with efficient UV-resistant and antibacterial properties. The resulting fibrous membranes possessed excellent waterproofness of 106.2 kPa, exceptional breathability of 10.3 kg m^-2 d^-1, a significant UV protection factor of 430.5, together with a definite bactericidal efficiency of 99.9%. We expect that this methodology for construction of environmentally benign and multifunctional WBMs will shed light on the material design, and the prepared membranes could implement their promising applications in covering materials, outdoor equipment, protective clothing, and high-altitude garments.

Fluorine-Free Waterborne Coating for Environmentally Friendly, Robustly Water-Resistant, and Highly Breathable Fibrous Textiles

Waterproof and breathable membranes (WBMs) with simultaneous environmental friendliness and high performance are highly desirable in a broad range of applications; however, creating such materials still remains a tough challenge. Herein, we present a facile and scalable strategy to fabricate fluorine-free, efficient, and biodegradable WBMs via step-by-step dip-coating and heat curing technology. The hyperbranched polymer (ECO) coating containing long hydrocarbon chains provided an electrospun cellulose acetate (CA) fibrous matrix with high hydrophobicity; meanwhile, the blocked isocyanate cross-linker (BIC) coating ensured the strong attachment of hydrocarbon segments on CA surfaces. The resulting membranes (TCA) exhibited integrated properties with waterproofness of 102.9 kPa, breathability of 12.3 kg m^-2 d^-1, and tensile strength of 16.0 MPa, which are much superior to that of previously reported fluorine-free fibrous materials. Furthermore, TCA membranes can sustain hydrophobicity after exposure to various harsh environments. More importantly, the present strategy proved to be universally applicable and effective to several other hydrophilic fibrous substrates. This work not only highlights the material design and preparation but also provides environmentally friendly and high-performance WBMs with great potential application prospects for a variety of fields.

Facile fabrication of fluorine-free breathable poly(methylhydrosiloxane)/polyurethane fibrous membranes with enhanced water-resistant capability

HYPOTHESIS

Ideal breathable and waterproof materials contain two key elements: hydrophobic matrix and small pore size. Current high-performing breathable waterproof membranes usually employ fluorinated materials to construct hydrophobic surface, which possess alarming potential environmental hazards. Fluorine-free waterproof agents through coating treatment to obtain hydrophobicity suffer from complicated fabrication process and poor durability. Hence, non-fluorinated chemicals incorporated into fibers via a facile one-step electrospinning may be an effective approach to attain durable hydrophobic membranes.

EXPERIMENTS

Poly(methylhydrosiloxane)/polyurethane (PMHS/PU) solution with various PMHS concentration was formulated and electrospun to fibrous membranes, followed by a facile thermal treatment process. A systematic study including morphologies, porous structure, and surface wettability was performed. Breathable waterproof performance and tensile strength were also investigated.

FINDINGS

Added PMHS imparted mighty hydrophobicity to the membranes with a water contact angle of 130.2°, and the subsequent heat treatment greatly improved waterproofness, meanwhile doubled the tensile strength. The resultant membranes exhibited robust hydrostatic pressure of 54.1 kPa, medium breathability of 9.5 kg m^-2 d^-1, and excellent stretching stress of 14.1 MPa, which can meet the requirements of general use. The presented strategy on membrane fabrication is feasible and scalable, which may be considered as an effective remedy for environmental protection.

High-Performance Electronic Cloth for Facilitating the Rehabilitation of Human Joints

The concern about easily characterizing the conditions of human joints to facilitate rehabilitation during recovery training has been out of sight, even though it is acknowledged that timely recovering functions of injured joints is a must. To facilitate the situation to be addressed, a stretchable, air-permeable electronic cloth (SApEC) was fabricated by electrostatic spinning and hot-pressing. The SApEC consists of conductive-elastic fabric Ag and composite nanofibrous membrane (CNFM) with components of poly(vinylidene fluoride- co-hexa-fluoropropyiene) and thermoplastic urethane. The electronic cloth not only owns chemical stability and ultralight weight, but scavenges triboelectric signals from joint movements. These characters allow the SApEC to be an easy and convenient indicator to indicate the activity of joints, when users get rehabilitation training in non-hospital places. With the assistance of several electronic components, the SApEC could control alarms, such as a warning lamp. This favorable ability allows the SApEC to make alerts, once users face any accidents again, like sudden fall or heart failure. Given the advantages mentioned above, it is reasonable to believe that the SApEC has a promising prospect in portable and wearable electronics, involving indicating rehabilitation of joints and keeping an eye on users' safety.