Progress in recycling and valorization of waste silk

Green, Low-carbon Silk-based Materials in Water Treatment: Current State and Future Trends

The improper and inadequate treatment of industrial, agricultural, and household wastewater exerts substantial pressure on the existing ecosystem and poses a serious threat to the health of both humans and animals. To address these issues, different types of materials have been employed to eradicate detrimental pollutants from wastewater and facilitate the reuse of water resources. Nevertheless, owing to the challenges associated with the degradation of these traditional materials post-use and their incompatibility with the environment, natural biopolymers have garnered considerable interest. Silk protein, as a biomacromolecule, exhibits advantageous characteristics including environmental friendliness, low carbon emissions, biodegradability, sustainability, and biocompatibility. Considering recent research findings, this comprehensive review outlines the structure and properties of silk proteins and offers a detailed overview of the manufacturing techniques employed in the production of silk-based materials (SBMs) spanning different forms. Furthermore, it conducts an in-depth analysis of the state-of-the-art SBMs for water treatment purposes, encompassing adsorption, catalysis, water disinfection, desalination, and biosensing. The review highlights the potential of SBMs in addressing the challenges of wastewater treatment and provides valuable insights into prospective avenues for further research.

Silk-based wearable devices for health monitoring and medical treatment

Previous works have focused on enhancing the tensile properties, mechanical flexibility, biocompatibility, and biodegradability of wearable devices for real-time and continuous health management. Silk proteins, including silk fibroin (SF) and sericin, show great advantages in wearable devices due to their natural biodegradability, excellent biocompatibility, and low fabrication cost. Moreover, these silk proteins possess great potential for functionalization and are being explored as promising candidates for multifunctional wearable devices with sensory capabilities and therapeutic purposes. This review introduces current advancements in silk-based constituents used in the assembly of wearable sensors and adhesives for detecting essential physiological indicators, including metabolites in body fluids, body temperature, electrocardiogram (ECG), electromyogram (EMG), pulse, and respiration. SF and sericin play vital roles in addressing issues related to discomfort reduction, signal fidelity improvement, as well as facilitating medical treatment. These developments signify a transition from hospital-centered healthcare toward individual-centered health monitoring and on-demand therapeutic interventions.

Green, chemical-free, and high-yielding extraction of nanocellulose from waste cotton fabric enabled by electron beam irradiation

Recycling and high-value reutilization of waste cotton fabrics (WCFs) has attracted a widespread concern. One potential solution is to extract nanocellulose. Sulfuric acid hydrolysis is a conventional method for the production of nanocellulose with high negative charge from WCFs. However, the recycling and disposal of chemicals in nanocellulose production, along with low yields, remain significant challenges. Consequently, there is a pressing need for a sustainable method to produce nanocellulose at higher yield without the use of chemicals. Herein, we propose a green, sustainable and chemical-free method to extract nanocellulose from WCFs. The nanocellulose displayed a rod-like shape with a length of 50-300 nm, a large aspect ratio of 18.4 ± 2 and the highest yield of up to 89.9 %. The combined short-time and efficient two-step process, involving electron beam irradiation (EBI) and high-pressure homogenization (HPH), offers a simple and efficient alternative approach with a low environmental impact, to extract nanocellulose. EBI induced a noticeable degradation in WCFs and HPH exfoliated cellulose to nano-size with high uniformity via mechanical forces. The as-prepared nanocellulose exhibits excellent emulsifying ability as the Pickering emulsion emulsifier. This work provides a facile and efficient approach for nanocellulose fabrication as well as a sustainable way for recycle and reutilization of the waste cotton fabrics.

Silk-Fabric Reinforced Silk for Artificial Bones

Bone implants for different body parts require varying mechanical properties, dimensions, and biodegradability rates. Currently, it is still challenging to produce artificial bones with perfect compatibility with human bones. In this study, a silk-fabric reinforced silk material (SFS) composed of pure silk with exceptional biocompatibility, osteogenesis, and biodegradability is reported, and demonstrates its outstanding performance as a bone implant material. The SFS is fabricated using a simple hot-pressing technique, with degummed silk fabric as the reinforcement and silk fibroin as the matrix. The SFS as a self-reinforced composite, has exceptional mechanical properties due to the almost perfect interface between the matrix and reinforcement. More importantly, its mechanical properties, biodegradability rates, and density can be tailored by adjusting the reinforcement structure and the ratio of the reinforcement to the matrix to align with the requirements for bone implantation in different parts of the human body. Besides, the SFS can improve osteoblastic proliferation and increase osteogenic activity, which is not the case with clinically used titanium alloy artificial bone. Therefore, the SFS holds significant potential to replace conventional metal or ceramic implants in the field of medical fracture repair.

Mobilisation of textile waste to recover high added value products and energy for the transition to circular economy

The textile industry is a major contributor to global waste, with millions of tons of textiles being discarded annually. Material and energy recovery within circular economy offer sustainable solutions to this problem by extending the life cycle of textiles through repurposing, recycling, and upcycling. These initiatives not only reduce waste but also contribute to the reduction of the demand for virgin materials (i.e. cotton, wool), ultimately benefiting the environment and society. The circular economy approach, which aims to recreate environmental, economic, and societal value, is based on three key principles: waste reduction, material circulation, and ecological restoration. Given these difficulties, circularity incorporates the material recovery approach, which is focused on the conversion of waste into secondary raw resources. The goal of this notion is to extract more value from resources by prolonging final disposal as long as feasible. When a textile has outlived its functional life, material recovery is critical for returning the included materials or energy into the manufacturing cycle. The aim of this paper is to examine the material and energy recovery options of main raw materials used in the fashion industry while highlighting the need of close observation of the relation between circularity and material recovery, including the investigation of barriers to the transition towards a truly circular fashion industry. The final results refer to the main barriers of circular economy transition within the industry and a framework is proposed. These insights are useful for academia, engineers, policy makers and other key stakeholders for the clear understanding of the industry from within and highlight beyond circular economy targets, SDGs interactions with energy and material recovery of textile waste (SDG 7, SDG 11, SDG 12 etc.).

Silk wastes and autoclaved degumming as an alternative for a sustainable silk process

Silk degumming is considered the first point in the preparation of silk-based materials since this process could modify the silk fiber and the properties of its related products. This study evaluated the differences in morphology, secondary structure, amino acid content, thermal stability, and mechanical properties of two types of raw materials, defective cocoons (DC) and silk fibrous waste (SW), degummed by chemical (C) and autoclaving (A) methods. Subsequently, silk fibroin films were prepared by dissolving each type of degummed fibers, and thermal and structural films properties were determined. The findings demonstrated that autoclaving is an efficient alternative to remove silk sericin, as the resulting fibers presented improved structural, thermal, and mechanical properties compared to those obtained by the chemical method. For films preparation, autoclave resulted in a good option, but dissolution parameters need to be adjusted for defective cocoons. Furthermore, similarities between the physicochemical properties of fibers and films from both fibrous wastes suggest that SW is a promising raw material for producing fibrous resources and regenerated silk fibroin materials. Overall, these findings suggest new recycling methods for fibrous waste and by-products generated in the silk textile production process.

Silk Sericin Protein: Turning Discarded Biopolymer into Ecofriendly and Valuable Reducing, Capping, and Stabilizing Agent for Nanoparticles Synthesis Using Sonication

This current study is designed to incorporate sericin protein as a reducing, capping, and stabilizing agent to synthesize sonication‐mediated silver nanoparticles. Fabrication of sericin‐reduced silver nanoparticles (Sr‐AgNPs) is confirmed using UV–visible spectrophotometry, zeta sizer, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X‐Ray diffraction (XRD), and thermogravimetric analysis (TGA). UV–Vis spectral peak of Sr‐AgNPs is observed at 420–440nm while the average size is found between 3 to 30 nm. SEM also confirms the reduction of large‐sized (1–40 µm) sericin macromolecules into nanometric hexagonal and triangular silver nanoparticles with a normal distribution (polydispersity index > 0.5). FTIR peaks from 500 to 4000cm−1 are analyzed for sericin while Sr‐AgNPs peaks with minor shifts (700–1000 cm−1 (COOCO stretching) in Sr‐AgNPs) are also observed. XRD peaks of 2θ at 27° with multiple low peaks at 38.2°, 47°, 49°, and 63.8° authenticate the amorphous nature of sericin and sharp peaks at 36°, 48°, 54.3°, and 61.9° with miller indices (hkl) of 98, 111, 200, and 211, assess the crystalline structure of Sr‐AgNPs. TGA reveals that sericin enhances the stability of silver NPs at high temperature (200–600 °C) by lowering the percentage weight loss from 70–80% to 60–65%.

A Three-Dimensional Fiber-Network-Reinforced Composite Solid-State Electrolyte from Waste Acrylic Fibers for Flexible All-Solid-State Lithium Metal Batteries

The large amount of waste chemical fiber textiles that exists has posed pressure on the sustainable development of the natural environment and of society. Therefore, it is of great importance to increase the added value of waste chemical fiber textiles and expand their applications in other fields. Herein, acrylic yarn from waste clothing is used as the raw material to construct a three-dimensional (3D) acrylic-based ceramic composite nanofiber solid electrolyte. The electrochemical properties of batteries based on this solid electrolyte are also investigated. We found that the fabricated composite electrolyte has good performance in lithium ion conduction and electrochemical stability because of its 3D acrylic-based ceramic composite fiber framework. The introduction of this composite electrolyte to a lithium symmetric battery enabled the battery to circulate stably for 2350 h at 50 °C without short-circuiting. In addition, all-solid-state batteries using a LiFePO4 cathode exhibited high reversible capacity. Lastly, a flexible lithium metal pouch battery was able to operate safely and stably under extreme conditions. This work demonstrates a strategy for upcycling waste textiles into ion-conducting polymers for energy storage applications.

Fully bio-based fire-safety composite from cotton/viscose wastes and alginate fiber as furniture materials

The increasing demand of textiles and apparel as global economy booms deepens environmental crisis associated with excessive textile waste disposed by landfill or incineration. This work implemented an eco-friendly and sustainable strategy to recycle up to 50 wt% textile waste with marine bio-based calcium alginate fiber into fire-proof fully bio-based composite textile by carding process. Incorporation of intrinsic nonflammable calcium alginate fibers endowed these needle-punching bio-composite felt with excellent inherent flame retardancy and improved safety. Horizontal burning test showed that by mixing with alginate fiber in proper ratio and pattern, extremely flammable cotton fiber and viscose fiber became totally inflammable. Analysis revealed that the generation of CaCO3 char residue and gaseous volatile of H2O inhibited the diffusion of O2 and heat, contributing to the outstanding fire proof performance of produced composite felt. The improved safety was affirmed by cone calorimetry test. It demonstrated limited heat, smoke and toxic volatile compound in the burning, as well as production of CO and CO2. All results showed that a straightforward yet economical method could recycle textile waste fibers into fully bio-based, fireproof and greener products, a potential candidate as fireproof structural filling and insulation materials for household textile or construction material.

Sustainable Antibacterial Surgical Suture Based on Recycled Silk Resource by an Internal Combination of Inorganic Nanomaterials

The current antibacterial treatment methods of silk sutures can only be finished by surface modification, leading to problems of short antibacterial effects, easy slow-release consumption, prominent toxicity, and susceptibility to drug resistance. Speculatively, surgical sutures combining antibacterial material internally will possess a more promising efficacy. Hence, we extracted recycled regenerated silk fibroin (RRSF) from waste silk resources to make RRSF solutions. Internally combining with inorganic titanium dioxide (TiO₂) nanoparticles, we fabricated antibacterial RRSF-based surgical sutures. The morphologies, mechanical and antibacterial properties, biocompatibility tests, and in vivo experiments were carried out. The results showed that the surgical sutures with 1.25 wt % TiO₂ acquired 2.40 N knot strength (143 μm diameter) and achieved a sustainable antibacterial effect of 93.58%. Surprisingly, the sutures significantly reduced inflammatory reactions and promoted wound healing. Surgical sutures in this paper realize high-value recovery of waste silk fibers and provide a novel approach to preparing multifunctional sutures.

A review of environmental friendly green composites: production methods, current progresses, and challenges

The growing concern about environmental damage and the inability to meet the demand for more versatile, environmentally friendly materials has sparked increasing interest in polymer composites derived from renewable and biodegradable plant-based materials, mainly from forests. These composites are mostly referred to as "green" and they can be widely employed in many industrial applications. Green composites are less harmful to the environment and could be potential substitutes for petroleum-based polymeric materials. It is helpful to limit usage of fossil oil assets by developing biopolymer matrices such as cellulose-reinforced biocomposites using renewable assets such as plant oils, carbohydrates, and proteins. This paper focuses on green composites processing utilizing a variety of naturally available resources, sustainable materials which are not detrimental to the environment, new scientific signs of progress in achieving green sustainable development, as well as nanotechnology and its environmental consequences. Additionally, the environmental impacts of different composite materials are examined in this paper, along with their production from eco-friendly materials. Moreover, the manufacturing aspects of green composites and some concerns related to their production are also discussed. The merits of green composite materials and valid reasons why they are a valuable substitute for the traditionally used composite materials are also covered.

Current recycling strategies and high-value utilization of waste cotton

The rapid development of the textile industry and improvement of people's living standards have led to the production of cotton textile and simultaneously increased the production of textile wastes. Cotton is one of the most common textile materials, and the waste cotton accounts for 24% of the total textile waste. To effectively manage the waste, recycling and reusing waste cotton are common practices to reduce global waste production. This paper summarizes the characteristics of waste cotton and high-value products derived from waste cotton (e.g., yarns, composite reinforcements, regenerated cellulose fibers, cellulose nanocrystals, adsorptive materials, flexible electronic devices, and biofuels) via mechanical, chemical, and biological recycling methods. The advantages and disadvantages of making high-value products from waste cotton are summarized and discussed. New technologies and products for recycling waste cotton are proposed, providing a guideline and direction for merchants and researchers. This review paper can shed light on converting textile wastes other than cotton (e.g., bast, silk, wool, and synthetic fibers) into value-added products.

Enhanced nitrate and cadmium removal performance at low carbon to nitrogen ratio through immobilized redox mediator granules and functional strains in a bioreactor

The coexistence of multiple pollutants and lack of carbon sources are challenges for the biological treatment of wastewater. To achieve simultaneous removal of nitrate (NO₃^--N) and cadmium (Cd²⁺) at low carbon to nitrogen (C/N) ratios, 2-hydroxy-1,4-naphthoquinone (HNQ) was selected from three redox mediators as an accelerator for denitrification of heterotrophic strain Pseudomonas stutzeri sp. GF2 and autotrophic strain Zoogloea sp. FY6. Then, halloysite nanotubes immobilized with 2-hydroxy-1,4-naphthoquinone (HNTs-HNQ) were prepared and a bioreactor was constructed with immobilized redox mediator granules (IRMG) as the carrier, which was immobilized with HNTs-HNQ and inoculated with the two strains. The immobilized HNQ and the inoculated strains jointly improved the removal ability of NO₃^--N and Cd²⁺ and the removal efficiency of NO₃^--N (25.0 mg L^-1) and Cd²⁺ (5.0 mg L^-1) were 92.81% and 93.94% at C/N = 1.5 and hydraulic retention time (HRT) = 4 h. The Cd²⁺ was removed by adsorption of iron oxides (FeO(OH) and Fe₃O₄) and IRMG. The electron transport system activity (ETSA) of bacteria was improved and the composition of dissolved organic matter in the effluent was not affected by HNQ. The HNQ promoted the production of FeO(OH) and up-regulated the proportion of Zoogloea (54.75% in the microbial community), indicating that Zoogloea sp. FY6 was dominant in the microbial community. In addition, HNQ influenced the metabolic pathways and improved the relative abundance of some genes involved in nitrogen metabolism and the iron redox cycle.

Silk Sericin: A Promising Sustainable Biomaterial for Biomedical and Pharmaceutical Applications

Silk is a natural composite fiber composed mainly of hydrophobic fibroin and hydrophilic sericin, produced by the silkworm Bombyx mori. In the textile industry, the cocoons of B. mori are processed into silk fabric, where the sericin is substantially removed and usually discarded in wastewater. This wastewater pollutes the environment and water sources. However, sericin has been recognized as a potential biomaterial due to its biocompatibility, immunocompatibility, biodegradability, anti-inflammatory, antibacterial, antioxidant and photoprotective properties. Moreover, sericin can produce hydrogels, films, sponges, foams, dressings, particles, fibers, etc., for various biomedical and pharmaceutical applications (e.g., tissue engineering, wound healing, drug delivery, cosmetics). Given the severe environmental pollution caused by the disposal of sericin and its beneficial properties, there has been growing interest in upcycling this biomaterial, which could have a strong and positive economic, social and environmental impact.

Sustainable conversion of textile industry cotton waste into P-dopped biochar for removal of dyes from textile effluent and valorisation of spent biochar into soil conditioner towards circular economy

Effective immobilization of industrial waste into biochar development could be one of the most promising technologies for solid waste management to achieve circular economy. In this study, post-industrial cotton textile waste (PICTW), a cellulose rich industrial waste, was subjected to slow pyrolysis to develop a surface engineered biochar through phosphoric acid impregnation. Biochar produced at 500 °C designated as PICTWB500 showed a maximum methylene blue number (240 mg g^-1) with remarkable specific surface area of 1498 m² g^-1. FESEM, FTIR, XRD and Raman spectra analysis were performed to investigate the surface texture and functionalities developed in the biochar. Adsorption efficiency of the biochar was assessed using drimarene red, blue, violet, and black dyes as model dye pollutants in batch mode at different biochar dose, pH and contact time. The maximum monolayer adsorption capacity was obtained in the range 285-325 mg g^-1 for different dyes, determined from Langmuir adsorption model. The kinetic behaviour was more favourable with the pseudo second-order model. The recycling ability of PICTWB500 was proven to be effective up to 6th cycle without compromising its adsorption efficiency significantly. This study demonstrated an excellent adsorption capability of the biochar in dye laden real textile effluent and recycling of spent biochar as a precursor of bio compost. Hence, this study established a dual win strategy for waste utilization in textile industry using a closed loop approach with substantial techno-economic feasibility that may have potential applications.

Innovative Conversion of Pretreated Buxus sinica into High-Performance Biocomposites for Potential Use as Furniture Material

Traditional wood-based panels are usually made from large-diameter trees and rely on adhesives for compactness, which negatively impacts the environment and human health. However, the widely distributed small-diameter shrubs are good raw materials for wood-based panels with abundant fibers, but are often under-exploited. This research reports the preparation of self-bonding biocomposites from Buxus sinica by an innovative combined approach of extraction, alkali treatment, and hot molding. The resulted biocomposites show better mechanical properties in which the flexural modulus (7.79 GPa) and the tensile modulus (4.33 GPa) were 5 times and 1.7 times higher than the conventional fiberboard, respectively, and also demonstrated better hydrophobicity than fiberboard, which could be due to the layer of lignin that formed on its surface preventing the infiltration of water. To sum up, the biocomposites prepared from small-diameter shrubs meet the requirement of the furniture and architectural decoration materials, suggesting that the proposed approach can be used to produce high-performance biocomposites.