BNC textile: bacterial nanocellulose as a new and sustainable material for textile yarn

Ana Catarina Barbosa Felgueiras BNC Textile: bacterial nanocellulose as a new and sustainable material for textile yarn Tese de Mestrado Mestrado Integrado em Engenharia Biológica Trabalho efetuado sob a orientação do(s) Professor Doutor Francisco Miguel Portela da Gama Professor Doutor Fernando Octávio de Queirós Dourado janeiro de 2021 iii DIREITOS DE AUTOR E CONDIÇÕES DE UTILIZAÇÃO DO TRABALHO POR TERCEIROS Este é um trabalho académico que pode ser utilizado por terceiros desde que respeitadas as regras e boas práticas internacionalmente aceites, no que concerne aos direitos de autor e direitos conexos. Assim, o presente trabalho pode ser utilizado nos termos previstos na licença abaixo indicada. Caso o utilizador necessite de permissão para poder fazer um uso do trabalho em condições não previstas no licenciamento indicado, deverá contactar o autor, através do RepositóriUM da Universidade do Minho. Licença concedida aos utilizadores deste trabalho Atribuição-NãoComercial-SemDerivações CC BY-NC-ND https://creativecommons.org/licenses/by-nc-nd/4.0/ iv AGRADECIMENTOS Gostaria de expressar a minha gratidão a todas as pessoas e instituições que de alguma forma contribuíram para a realização desta Tese de Mestrado. Ao Professor Miguel, pela oportunidade que me deu em realizar este projeto e principalmente por me ter ouvido quando, em 2018, fui ao seu gabinete e falamos sobre a possibilidade de desenvolvermos um produto para a indústria têxtil utilizando nanocelulose bacteriana. A sustentabilidade e a procura de alternativas sustentáveis para esta indústria sempre foi algo que me interessou bastante e saber que o nosso trabalho poderá trazer mudanças positivas para o planeta é de facto algo muito gratificante. Agradeço ainda pela sua disponibilidade, pelo seu investimento e dedicação a este projeto e pelos seus conselhos. Ao Professor Fernando, pelo acompanhamento e pelas conversas sobre a nanocelulose bacteriana que me ajudaram imenso a perceber um pouco mais sobre as bactérias que produzem este material, assim como qual poderá ser o seu futuro. Agradeço-lhe também por toda a disponibilidade e dedicação neste projeto. Ao Francisco, por tudo que me ensinou e pela ajuda indispensável durante todo o meu trabalho no LTEB. Foi de facto uma pessoa fundamental neste meu percurso, a quem estou muito grata. A todos os membros grupo LTEB, agradeço também os conselhos, a ajuda e a motivação. São um grupo fantástico onde é incrível trabalhar. Às minhas amigas Adriana e Catarina não só por todo o incentivo durante estes últimos meses mas também por toda a alegria que trouxeram à minha vida desde que começamos o nosso percurso académico. Às minhas amigas de infância, Joana, Ana, Andreia, Margarida, Carolina e Daniela por sempre acreditarem em mim e estarem sempre do meu lado. E por último, mas não menos importante, à minha família que sempre me apoiou e fizeram de tudo para que eu pudesse alcançar os meus objetivos. O meu maior obrigada é para vocês, pai, mãe, Ricardo e Fábio. Que eu tenha a sorte de vos ter sempre por perto. v STATEMENT OF INTEGRITY I hereby declare having conducted this academic work with integrity. I confirm that I have not used plagiarism or any form of undue use of information or falsification of results along the process leading to its elaboration. I further declare that I have fully acknowledged the Code of Ethical Conduct of the University of Minho. vi RESUMO Neste trabalho, são discutidas tecnologias de produção de fios para aplicações têxteis tendo a celulose como base. São referidas tendências recentes que visam poupar o ambiente de exploração massiva, como o uso de nanocelulose bacteriana, procurando também responder às necessidades crescentes por fibras alternativas obtidas por processos sustentáveis. A avaliação do ciclo de vida de vários métodos de produção de fibras de celulose foi também abordada. O objetivo deste trabalho foi a produção de fios a partir de fibras alternativas às existentes no mercado utilizando a nanocelulose bacteriana como matéria-prima. A nanocelulose bacteriana possui características como elevada resistência mecânica, capacidade de retenção de água, estabilidade dimensional, cristalinidade, biocompatibilidade e biodegradabilidade, o que permite explorar a sua utilização em várias áreas como biomédica, cosmética, alimentar, têxtil e papel. Além disso, a sua produção tem um impacte ambiental menor onde não ocorre a destruição de florestas e a sua produção é feita em apenas algumas semanas, um tempo bastante inferior comparativamente ao análogo vegetal que demora meses ou anos. Foram produzidos filamentos utilizando diferentes concentrações de nanocelulose bacteriana e dois sistemas de dissolução diferentes: o método de dissolução em fase sólida e o método tradicional de produção de Liocel. Pelo primeiro método foi possível obter filamentos com módulo de Young de 20,8 ± 5,4 GPa, resistência à tração de 1201,9 ± 149,2 MPa e alongamento de 11,5 ± 0,1 %. Pelo segundo, foi obtido um módulo de Young de 35,0 ± 17,2 GPa, resistência à tração de 1100,0 ± 480,0 MPa e alongamento de 6,8 ± 4,0 %. De forma a respeitar os critérios de produção de filamentos pelo processo Liocel, foi realizado, posteriormente, um estudo de despolimerização da nanocelulose bacteriana. O grau de polimerização da nanocelulose bacteriana foi reduzido do seu valor original (cerca de 2000) para 602-531, que normalmente é considerado adequado para o processo de Liocel. Métodos alternativos de produção de filamentos sem a dissolução da nanocelulose bacteriana foram também testados – dry-spinning e wet-drawing, obtendo-se resultados semelhantes em ambos os métodos, com um módulo de Young de 5,4 ± 2,2 GPa e 7,9 ± 3,4 GPa, resistência à tração de 194,6 ± 53,2 MPa e 220,2 ± 98,4 MPa , e alongamento de 9,1 ± 6,3 % e 14,3 ± 1,8 %, respetivamente. São necessários mais estudos de forma a perceber se a despolimerização da nanocelulose bacteriana é realmente necessária para o processo de Liocel. A produção de fibras sem solventes também requer um estudo mais aprofundado, sendo estas as formas mais sustentáveis de produção de fibras têxteis. vii PALAVRAS-CHAVE Nanocelulose bacteriana, fibra, têxtil, sustentabilidade, celulose, despolimerização, Liocel, fibras sem solvente viii ABSTRACT In this work, the technologies for the production of cellulose-based textiles, their surface modification and the recent trends aiming at sparing the forest from massive exploitation are discussed. The life cycle assessment of several cellulose fibre production methods is also addressed. The objective of this work was the production of cellulose filaments using an alternative source of cellulose – bacterial nanocellulose – as raw material. Bacterial nanocellulose has impressive characteristics such as high mechanical strength, water-holding capacity, dimensional stability, crystallinity, biocompatibility and biodegradability, allowing to explore its use in several areas, namely in the biomedical, cosmetic, food, textile and paper areas. Besides that, its production has less impact on the environment as no forests are destroyed and its production is faster. Filaments were produced using different BNC concentrations and two different dissolving systems: the solid-phase dissolution method and the traditional Lyocell production method. From the first method it was possible to obtain filaments with Young’s modulus of 20,8 ± 5,4 GPa, tensile strength of 1201,9 ± 149,2 MPa and elongation of 11,5 ± 0,1 %. Through the second was obtained Youngs’ modulus of 35,0 ± 17,2 GPa, tensile strength of 1100,0 ± 480,0 MPa and elongation of 6,8 ± 4,0 %. In order to meet Lyocell's production criteria, the degree of polymerization of bacterial nanocellulose was lowered from its original value (around 2000) to 602-531, which is normally considered suitable for the Lyocell process. Although it has been possible to achieve the depolymerization of BNC in a simple way using a chemical treatment, it would be preferable to process the original cellulose, without depolymerization. Alternative methods of filament production without dissolution were also tested – dry spinning and wet-drawing. Similar results were obtained for both methods with a Young’s modulus of 5,4 ± 2,2 GPa and 7,9 ± 3,4 GPa, tensile strength of 194,6 ± 53,2 MPa and 220,2 ± 98,4 MPa, and elongation of 9,1 ± 6,3 % and 14,3 ± 1,8 %, respectively. Further study on this subject is needed to understand if BNC depolymerization is really needed on a pilot or commercial scale for the Lyocell process. Fibres without solvents also need to be further studied as they are the more sustainable ways of fibre production and there is a growing need for these types of fibres on market. ix KEYWORDS Bacterial nanocellulose, fibre, textile, sustainability, cellulose, depolymerization, lyocell, fibres without solvents x CONTENTS Agradecimentos ........................................................................................................................ iv Resumo ..................................................................................................................................... vi Abstract ................................................................................................................................... viii List of figures ........................................................................................................................... xii List of tables ............................................................................................................................ xiv List of abbreviations ................................................................................................................ xv 1. Introduction ........................................................................................................................ 1 1.1 Textile fibres .................................................................................................................... 2 1.1.1 Overview ................................................................................................................ 2 1.1.2 Novel sources of cellulose and nanocelluloses ...................................................... 4 1.1.2.1 Bacterial nanocellulose ...................................................................................... 4 1.1.2.2 Plant Nanocellulose ........................................................................................... 6 1.2.1 Regenerated cellulosic fibres ................................................................................. 8 1.2.1.1 Viscose Rayon ................................................................................................... 9 1.2.1.2 Lyocell Ryon .................................................................................................... 11 1.2.1.2.1 History of Lyocell ..................................................................................... 11 1.2.1.2.2 The solvent and the phase diagram ........................................................... 12 1.2.1.2.3 Dissolution process ................................................................................... 14 1.2.1.3 Cellulose Acetate ............................................................................................. 18 1.2.1.4 Ionic Liquids .................................................................................................... 18 1.2.2 Filaments without solvents .................................................................................. 20 1.3 Sustainability and Life Cycle Assessment ..................................................................... 24 2. Specific goals .................................................................................................................... 28 3. Materials and Methods ..................................................................................................... 29 3.1 Materials .................................................................................................................. 29 3.2 Methods .................................................................................................................... 29 3.2.1 Production and characterization of the BNC dope .............................................. 29 3.2.1.1 BNC dissolution ............................................................................................... 29 3.2.1.2 Dope viscosity – rotational rheometer ............................................................. 30 2 1.1 Textile fibres 1.1.1 Overview Fibres are the starting point for all textile products that serve the everyday needs of society. Fibres of short length, called staple fibres, as is the case of most natural fibres, range between 3 and 20 cm in length. A filament is a fibre of indefinite length, being silk the only naturally produced. Most regenerated and synthetic fibres are produced as filaments. Different methods of drawing, spinning and twisting, depending on the fibre type, are used to form a continuous strand of yarn (Sinclair, 2015). The textile is then produced. Conventional textiles are designed, developed, or used for the common decorative, or aesthetic applications. Technical textile products can be grouped into various categories, depending on their application, such as industrial, medical, packaging, sports, automotive, construction, aerospatial, geo-textiles, agro-textiles, protective clothing. Each segment has a large variety of products made from diversified fibres/raw materials using divergent manufacturing techniques and equipment (Keller & Giddings, 2020; Rasheed, 2020). Textiles were produced domestically until the XVII century, mostly from vegetable sources using cotton, hemp and flax but also from animal sources as wool and silk. Then, during the industrial revolution, the production process was mechanized, allowing totally new and faster methods of manufacturing (Texcoms, 2019). The fibres produced until the end of the XIX century were all natural (figure 1). During the 1900s, the production of man-made fibres begun, more specifically regenerated cellulose fibres by the Viscose method. The synthetic fibres appeared in the textile market only by late 1930s, made from chemically synthesized polymers (Murthy, 2016; Sinclair, 2015). Natural fibres, including animal (protein) and vegetable ones, make up almost 40 % of the textile fibres produced annually in the world. Vegetable fibre (cellulose) is extracted from plants (Yu, 2014). The most abundant natural polymer on earth is cellulose, representing about 30-40 % of all terrestrial biomass, with a biosynthesis of 1011 tons annually (Akhlaghi et al., 2020; Kafy et al., 2017; Levi et al., 2016). Being biodegradable, renewable, biocompatible and affordable polymer, cellulose has several other uses such as in paper, food additive, excipient, coatings, diapers, textiles and composites (Kim et al., 2019). While generally synthesized by plants, it is also produced by some bacteria, fungi and algae. In plants, cellulose is the main structural component of the primary cell wall (Brigham, 2018). 3 Figure 1. Classification of main natural and man-made fibres (adapted from (Murthy, 2016; Sinclair, 2015)). Cotton is the most popular natural fibre, accounting for around 90 % of all natural fibres. Cotton is one of the most important natural textile fibre crop, both from the agricultural and manufacturing sectors’ perspective. It is the biggest source of clothing as well as being used to produce apparel, home furnishings, and industrial products (Yu, 2014). The use of cellulosic fibres is expected to grow from the current level of 3.7 kg per capita to 5.4 kg by 2030 (Haemmerle, 2011). Cotton fibre contains approximately 90 % of cellulose, dried hemp has 4050 % and wood 40-55 %, commonly found combined with other substances as lignin and hemicelluloses (Ansell & Mwaikambo, 2009; Wang et al., 2019). In addition to cotton, the most commonly used natural vegetable fibres include flax, ramie, jute, kenaf, and sisal. Cultivation with cotton hybrids will expand and so, the harvest yield from 800 (2010) to 925 kg/ha (2030) will increase its production capacity. However, it will not compensate for the disappearance of arable land and growing demand. It is estimated that only 3.1 kg of cotton per capita will be available in 2030 (Haemmerle, 2011). This so-called cellulose gap offers new opportunities for man-made cellulosic fibres. The gradual replacement of cotton by pulp-based fibres is also necessary from an ecological perspective. Nowadays, new natural fibres, especially vegetable fibre sources, are being exploited, for example, kapok, pineapple, and apocynum (Yu, 2014). Synthetic fibres have dominated the market since mid 1990s, overtaking cotton. These are made from organic synthetic high-molecular mass compounds and are produced Fibres Natural Fibres Animal Silk Wool Etc. Vegetable Seed Cotton Kapok Etc. Bast Flax Hemp Jute Kenaf Ramie Etc. Leaf Abaca or manila Henequen Phormium Tenax Sisal Etc. Microbial Man-made Fibres Regenerated Viscose Acetate Cupramonium Lyocell Etc. Synthetic Polyester Nylon Acrylic Polypropylene Etc. Mineral Glass Gold Silver Etc. 4 synthetically from petroleum-based raw materials. They represented up to 63 % of the global fibre production in 2019. The most used synthetic fibre was polyester, with a market share of around 52 % of total global fibre production. Cotton was second, with 23 % (Textile Exchanges, 2020). Currently, fibres have a cost of 1,17 €/kg for cotton, 1,31 €/kg for Viscose and 0,86 €/kg for polyester (Emerging Textiles, 2020). 1.1.2 Novel sources of cellulose and nanocelluloses In recent years, several nanocelluloses (NC), from microbial and plant sources, have been texted as a source of textile fibres. The interest in NCs is essentially focused on taking advantage of their higher crystallinity, since they promote great mechanical resistance (Nunes, 2014). NC is not a single material type but rather a family of materials with very different features, mostly due to different sources and preparation methods (Clemons, 2016). 1.1.2.1 Bacterial nanocellulose An alternative to wood/plant cellulose is bacterial nanocellulose (BNC) (Figure 2), a homopolysaccharide extruded by Gram-negative species of the genera Komagataeibacter, Acetobacter, Rhizobium, Agrobacterium, Pseudomonas, Salmonella, Alcaligenes and Sarcina, the only Gram-positive bacterial genus (Jonas & Farah, 1998; F. Dourado et al., 2016). Different bacteria produce cellulose with distinct morphology, structure, properties and yields (Wang et al., 2019). To obtain high yields of BNC, it is necessary to use the highest cellulose producer species, such as Komagataebacter xylinus (Dourado et al., 2016). Figure 2. BNC membrane before (A) and after (B) purification. The BNC biosynthesis was first observed in kombucha, a fermented beverage produced by a symbiotic colony of bacteria and yeast, where a cellulose film is formed on the culture media-air interface. It was first reported in 1886 by A. J. Brown, who identified a film with a structure chemically equivalent to that of plant cellulose (Brown, 1886). BNC consists of < 100 (A) (B) 5 nm ribbon-shaped fibrils, composed of 7-8 nm wide elementary nanofibrils aggregated randomly into bundles, without lignin or hemicellulose (Gorgieva & Trček, 2019). BNC has the same chemical structure as that of plant cellulose. Linear homopolymer of glucose monomers are linked by β-(1→4) glycosidic linkage with the chemical formula (C6H10O5)n. Nevertheless, it has different macromolecular structure and properties (Ullah et al., 2019). The polymerization degrees are within 2000 to 6000 for BNC and 13 000 to 14 000 for plant cellulose, decreasing during pulping and purification. The unbranched chains of cellulose are held together through strong intraand intermolecular hydrogen bonds to form the elementary fibres and the supramolecular structure (Choi & Shin, 2020; Fang et al., 2020). This structure possesses exclusive properties such as high mechanical strength, water-holding capacity, dimensional stability, crystallinity, biocompatibility and biodegradability (Picheth et al., 2017). Given these features, numerous applications of BNC have been studied: in the biomedical field as a wound dressing, for tissue regeneration/substitution and drug delivery systems; in the textile and paper industries for fibre composites and coatings; in the food and cosmetic industries as an emulsifier and viscosifier (Anton-Sales et al., 2020; Amorim et al., 2020; Klemm et al., 2005; Chawla et al., 2009; Müller et al., 2013; Nimeskern et al., 2013; Lee et al., 2014; Shi et al., 2014; Rajwade et al., 2015). The main application is still as a food product known as nata de coco, mostly produced and consumed in Asian countries (Dourado et al., 2016). BNC can be produced through static or agitated cultures (Wang et al., 2019), most studies being carried out using the former (Zywicka et al., 2015). In this method, BNC is produced in containers filled with nutrients and incubated for defined periods, at around 30 ºC and pH of 5.0. The efficiency of BNC production in stationary cultures is strongly connected with the air-liquid surface area (given that Komagataebacter strains are mandatory aerobes), where it is produced as a hydrogel sheet containing around 99 % of water (Wang et al., 2019). To achieve industrial scale production, major exploited alternative fermentation technologies, using specific fermentation media and overproducing mutant strains include agitated and air-lift bioreactors, membrane reactors and horizontal bioreactors. The idea behind is that the agitated/shaking culture facilitates the oxygen delivery to bacteria during cultivation (Wang et al., 2019). Under agitation and aeration conditions, fibrous suspension, or pellets can be obtained. This, however, limits BNC applications, allows cellulose-negative mutants to dominate the population of growing cells (which in turn limits the cellulose yield) and requires 6 high agitation power (due to the viscous character of the suspensions) (Czaja et al., 2004; Huang et al., 2014; Wang et al., 2019; Rodrigues et al., 2019). The textile fibres production amounts to 105,6 million tons per year, worldwide (Garside, 2019). The current BNC global production is far below this magnitude and confined to small scale production units (Phisalaphong et al., 2016; Dourado et al., 2016; Piadozo, 2016). Its potential as a sustainable alternative for the textile industry has never been assessed (Choi & Shin, 2020). 1.1.2.2 Plant Nanocellulose Cellulose is a hydrogen bond cross-linked biopolymer. The hydroxyl groups on one cellulose chain bond with the other to develop rigid and stable molecules, giving the plant stiffness and strength. The hydrogen bonding between cellulose chains makes it insoluble in common organic solvents and water (Thomas et al., 2020). Fibrils are formed by joining cellulose molecules together. These fibrils agglomerate into bundles, which the plant uses to construct its cell wall combined with hemicelluloses and lignin (figure 3) (Lundahl, 2018). The morphology of the cellulose fibrils morphology demonstrates a mesh-like structure (Thomas et al., 2020). Figure 3. (A) Hierarchical structure of wood fibres: Reprinted (adapted) with permission from (Zhu et al., 2013). Copyright (2013) American Chemical Society. Comparison microscopic image of; (B) bacterial nanocellulose (Li et al., 2017): Published by The Royal (B) (C) (D) (A) 7 Society of Chemistry, (C) nanofibrillated cellulose: Reprinted (adapted) with permission from (Saito et al., 2007). Copyright (2007) American Chemical Societyand, (D) nanocrystalline cellulose (Anžlovar et al., 2018). NC can be produced by top-down approaches, i.e. the deconstruction of fibres by chemical, enzymatic or mechanical methods in case of plant NC, or by botton-up routes for BNC (Charreau et al., 2020). Plant NC is typically divided into two main categories: cellulose nanofibres (CNFs) and cellulose nanocrystals (CNCs) (Amorim et al., 2020). The final chemical and physical properties of NC depend directly on the source and preparation conditions of the cellulose (Kargarzadeh et al., 2017). NCs have properties such as high strength and stiffness, low density, biodegradability, high surface area, and low thermal expansion, which led to much research and innovation during the last two decades. Both CNC and CNF have applications as composite materials, paper and board industry, adsorbent products, food and beverages, paints and coatings, adhesives, packaging, oil and gas, electronics, and medical, pharmaceutical and cosmetic product (Charreau et al., 2020). Different raw materials can be used to obtain NCs such as coconut husk fibre, mengkuang leaves (Pandanus tectorius), cotton, Agave tequilana, barley wastes, tomato peels, garlic straw residues, forest residues, corncob residue, Gigantochloa scortechinni bamboo culms, industrial waste cotton, cassava root bagasse and peelings, sugar palm fibres (Arenga pinnata), corn straw and sago seed shells (Ventura-Cruz & Tecante, 2019). The raw material must be pre-treated to remove lignin and hemicellulose by milling, pulping and bleaching. CNCs, also called cellulose whiskers, nanowhiskers, or nanorods, are produced by transverse cleavage of cellulose by acid hydrolysis, using strong acids such as sulfuric and hydrochloric acids (Clemons, 2016), where, under controlled conditions of temperature, agitation and time, amorphous cellulose microfibrils are preferentially cleaved, whereas crystalline regions, which have a higher resistance to acids, are maintained (Charreau et al., 2020). CNC have a nanosized distribution: a diameter of 4-55 nm and 90-400 nm in length (Zinge & Kandasubramanian, 2020). After acid hydrolysis, CNC recovery operations include washing, filtration/centrifugation and dialysis, to remove the remaining acid (Charreau et al., 2020). Due to CNC higher crystalline structure, it has less flexibility than CNF (Zinge & Kandasubramanian, 2020). Recently, CNC have been used as reinforcing components of polymeric matrices, and in the synthesis of polymers with liquid crystalline behaviour for 8 electronic applications. Currently, CNC is produced in commercial quantities of 2-260 ton/year (Charreau et al., 2020). CNFs, also called cellulose nanofibrils or nanofibrillated cellulose, are obtained by mechanical disintegration (Amorim et al., 2020). CNF are cellulose structures of high aspect ratio containing crystalline and amorphous regions which form entangled networks. Although CNF isolation is associated with mechanical destructuring methods (pressure, cavitation, shear and impact forces), the high energy consumption needed has led to the integration of pretreatments to facilitate further fibrillation (Charreau et al., 2020). A common pre-treatment uses a 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) catalyst to mediate the oxidation of native celluloses, that reduces the energy required to fibrillate (Clemons, 2016). The product obtained is a translucent firm gel. CNF can be applied in absorbent products, reinforcement of composite materials, rheology modifying agents and, especially, papermaking products such as paperboard, tissue-making, deodorant sheets and other cosmetics sheets. CNF is produced in commercial quantities of 24−560 ton/year (Charreau et al., 2020). 1.2 Technologies for the production of Cellulose Textile Fibres 1.2.1 Regenerated cellulosic fibres Regenerated cellulosic fibres (RCF) are obtained by derivatizing or dissolving cellulose from wood pulp or plant fibres. As the length of wood pulp fibres is too short for textile use, they have to be processed by means of a continuous spinning associated with a regenerating technology (Navard, 2013). In these processes, the structure of the starting cellulose is modified by adding a solvent, which forms an intermediate compound such as sodium or acetate derivatives. Then these intermediate compounds are processed and dissolved, followed by the regeneration of the cellulose fibre (Woodings, 2001). The improvement of cellulose dissolution is a prevailing goal. Cellulose structures undergo several transformations depending on the kind of solvent and treatment conditions. Presently, the most used industrial methods for dissolving cellulose pulp are the Viscose, Cuprammonium, Acetate and Lyocell methods. Cellulose solvents can be divided into two groups: non-derivatizing – comprises systems that dissolve the polymer by intermolecular interactions; derivatizing – relates to all the solvents where the dissolution process is combined with the formation of unstable ether, ester or acetal derivatives. Both groups include aqueous and non-aqueous solvents (Heinze & Koschella, 2005). Regenerated cellulose was the first man-made fibre applied in the textile and apparel industry, in the early days of its development, during the 1850s. These fibres have a smooth 9 and lustrous appearance much like silk (although chemically different), and the outstanding water absorption ability of cotton. In 1924 the generic name Rayon was adopted by the U.S. Department of Commerce and various industrial associations to label RCF that include Viscose, Acetate, Lyocell, Modal and Cupro (Chen, 2015; Textile Exchanges, 2020). With an annual production volume of around 7.1 million tons in 2019, the global production volume of RCF has more than double since 1990. RCF have a market share of about 6.4 % of the total fibre production volume and is expected to increase in the coming years. Viscose is the most important RCF with a market share of around 79 % of all RCF and a production volume of around 5.63 million tons in 2019. Acetate has a market share of around 13 % of all RCF with a production of approximately 0.95 million tons in 2019 but it is mainly used for non-textile applications. Lyocell was the third most used RCF after Viscose and Acetate in 2019. It had a market share of around 4.3 % and a production volume of 0.3 million tons, being this fibre expected to grow faster than the others RCF. Using a production process quite similar to that of Viscose, Modal fibres had a market share of around 2.8 % of the total RCF market in 2019 with a production of around 0.2 million tons. Cupro has a market share of less than 1 % of the total RCF market. There is only one supplier of Cupro, producing around 17,000 tons in 2019 (Textile Exchanges, 2020). RCF are being used in the most diverse materials, from sportswear to health care textiles, alone or combined with other natural or synthetic fibres, due to their characteristic properties such as tensile strength and smoothness (Karthik & Rathinamoorthy, 2017). 1.2.1.1 Viscose Rayon The Viscose process is the world's most widely used method for producing RCF. The first patent on the Viscose process was granted to Cross and Bevan in 1893. Over the past 100 years, this process underwent many alterations, although the basic chemistry is still the same, which allowed Viscose to become one of the most widely used regenerated fibres (Wilkes, 2001; Thakur et al., 2017). The process, shown in figures 4 and 5, consists in dissolving the pulp in NaOH and, after steeping for a specified period of time, shredding and ageing. The viscosity of the pulp depends on the ageing time. The aged pulp is then treated with carbon disulphide (CS2) to form the orange-colored cellulose xanthate. Lastly, this derivative is dissolved in NaOH with a lower concentration, the starting stage of Viscose formation (Shaikh et al., 2012). The polymer is finally precipitated in acid, for simultaneous neutralization and regeneration of the cellulose in a wet-spinning step. Then, several steps of washing and drawing yield a regenerated fibre of 10 pure cellulose (Olsson & Westman, 2013; Chen, 2015). Currently, carbon disulphide can be reused up to 70 %, and the remaining 30 % is converted into sulfuric acid (H2SO4), which is also recycled (Rana et al., 2014). Despite being made from wood, the fibre production by Viscose process is known to cause significant environmental problems due to the high usage of chemicals, such as sodium hydroxide, producing sodium sulphate as a by-product. The life cycle of the Viscose process encompasses other impacts, associated to how reagents are produced and recycled, as well as the consumption of energy, the use of fossil fuel and deforestation (Shen et al., 2010). Recently, the company Nanollose announced the development of a Viscose making process using BNC. This method transforms BNC into NullarborTM Tree-Free Viscose fibres using technology which is compatible with existing industry processing and manufacturing equipment (Nanollose, 2020; Jinzarli et al., 2019). Figure 4. Mechanism of Viscose fibre production (addapted from (McKeen, 2017; Rodgers & Waddell, 2013)). 11 Figure 5. Schematics of Viscose fibre production (addapted from (Alagirusamy & Das, 2015; Sayyed et al., 2019)). 1.2.1.2 Lyocell Rayon The direct dissolution of cellulose (without derivatization) has been the object of research for many years. This process may also simplify the production of regenerated cellulose by omitting several steps (Olsson & Westman, 2013; Perepelkin, 2007). The technology of direct dissolution of cellulose is a simpler process, reducing the use of chemicals by ten times in comparison to the Viscose process. Also, a direct solvent is easier to recycle, since no byproducts are formed, resulting in a more environmentally friendly process (Olsson & Westman, 2013). However, the Lyocell production costs are higher than the Viscose, due to the high cost of solvent and the use of high temperatures for cellulose dissolution (Alam & Christopher, 2017). 1.2.1.2.1 History of Lyocell Lyocell is the first successful technology of generation of cellulosic fibres by direct dissolution, resulting in fibres with exceptional properties, making it a serious competitor to the Viscose process, since it is more environmentally friendly (White, 2001; Peng et al., 2017). Lyocell fibre has higher tenacity (especially wet tenacity), higher modulus, lower shrinkage, better thermal stability, higher crystallinity, and greater degree of orientation, than Viscose (Edgar & Zhang, 2020). The Lyocell fibre market is set to grow from 760 million € in 2016 to over 1.35 billion € by 2024 (Pulidindi & Chakraborty, 2016). 18 1.2.1.3 Cellulose Acetate Although not so widely used, another method of producing fibres is available whereby cellulose acetate is obtained. Cellulose acetate is the acetate ester of cellulose. It was produced first at commercial scale by Celanese in 1923 (Sayyed et al., 2019) by reacting a cellulose pulp with acetic anhydride, to form acetate flakes (figure 9). Then, these flakes are dissolved in a solvent and filtered to obtain the spinning cellulose dope solution (Ertas & Uyar, 2017). The cellulose dissolution with acetic acid and acetic anhydride is done with sulfuric acid, in a controlled manner to remove the sulfate and a sufficient number of acetate groups, to yield a product with desired properties. The cellulose dope solution is then extruded through a spinneret and the yarns are produced by solvent evaporation. This process for producing acetate fibre is known as the dry-spinning method (Sayyed et al., 2019), and is mainly used to produce cigarette filters but also for drug delivery and nanofibres. These cellulose acetate fibres have limited use in the textile industry due to their poor strength, poor abrasion resistance and poor thermal retention (Watabe et al., 2018). Figure 9. Mechanism of the cellulose acetate preparation (adapted from (Sayyed et al., 2019; Silva et al., 2017)). 1.2.1.4 Ionic Liquids Research on the use of Ionic Liquids (ILs) for the direct dissolution of cellulose, first used in 2002, has shown promising results. Although this technology is not yet ready for industrial production, the use of ILs is expected to succeed in the future (Isik et al., 2014; J. 19 Zhang et al., 2017; Hummel et al., 2015; Swatloski et al., 2002). The IL process comes under the Lyocell technology since the cellulose solution is spun according to the NMMO-based Lyocell method, in a dry-jet wet-spinning process where the liquid filament first passes through an air gap and coagulate in a bath where the regenerated cellulosic fibres are formed (Sayyed et al., 2019). ILs are liquids made-up of cations and anions, thus they can be designated as salts in the liquid state (Singh & Savoy, 2020). Overall, the dissolution process of cellulose in ILs is still not fully clarified (Hermanutz et al., 2019). The ILs ability to dissolve cellulose is due to small hydrogen bond accepting anions that can compete with the hydrogen bonding between the cellulose chains and cations that help increase the solubility (Andersson, 2018). ILs dissolves cellulose with no prior derivatization in concentrations of up to 300 g/L and offer a potentially more environmentally friendly alternative to traditional processes. (Hina et al., 2015; Wanasekara et al., 2016). These solvents are thermostable up to 300 °C with a melting point up to 100 °C. ILs practically do not have vapor pressure, and therefore do not pollute the atmosphere (Sashina, 2019). Due to their wide range of properties, they have been increasingly used in various fields of study such as biochemistry, engineering, physics, etc. as a green solvent. The properties of ILs can be modified depending on their application by altering the combination of cations and anions (Singh & Savoy, 2020). ILs are usually composed of imidazolium, pyridinium, or organic ammonium cations and anions such as chloride, bromide, or more complex structures such as hexafluorophosphate, trifluoromethyl sulfonate, bis(trifluoro-methylsulfonyl)imide and methylimidazolium chloride ([Amim]Cl) (Sayyed et al., 2019). ILs have been investigated either to dissolve or to create appropriate media for the functionalization of cellulose. For cellulose solubility, the counter anions with halide, such as the imidazolium type, have the best performance. One disadvantage with ILs with halide anions is their relatively high viscosities, which brings processing difficulties during dissolution (Isik et al., 2014). These ILs demonstrate good dissolution characteristics, and it is possible to prepare cellulose dopes in concentration ranges that exhibit good spinnability (Sayyed et al., 2019). For industrial use, any IL selected for cellulose dissolution and processing has to match specific criteria for an economic process development: the IL should be easy to produce, recyclable in high amount (> 99.5 %), possess the lowest possible toxicity, should have literally no vapor pressure, a low melting point, a low propensity to side reactions and degeneration, have high dissolution capability for different pulp sources (Hermanutz et al., 2019; Andersson, 2018). To obtain concentrated cellulose solutions suitable 20 for spinning, the researchers have tried to use ILs based on imidazolium, pyridinium and ammonium cations (Sashina, 2019). Currently, nearly thousand ionic liquids are described in the literature (Meksi & Moussa, 2017; Wang et al., 2019; Yang et al., 2020; Zhang et al., 2019). A new class of next-generation of regenerated cellulose fibres named Ioncell have recently been developed utilizing a novel IL solvent 1,5 - diazabicyclo [4.3.0]non-5-enium acetate ([DBNH] [OAc]) (Michud et al., 2016). Ioncell fibres have been shown to exhibit better mechanical properties than all previously known ones, namely, their tensile strength reaches 0,7-0,8 GPa and elastic modulus of 30 GPa (Sashina, 2019; Wanasekara et al., 2016). Several garments have been produced and commercial production is expected by 2025 (Ioncell, 2020). 1.2.2 Filaments without solvents RCF have beneficial characteristics from both synthetic and natural fibres: they have uniform morphological, mechanical, and physical properties, as synthetic fibres. On the other hand, they bear biodegradability, CO2 neutrality, and low density of natural fibres. However, their mechanical properties are lower than those of CNF (Hooshmand et al., 2015). To preserve the characteristics of CNF, several studies have been made to elaborate a system of filament production without solvents. Spinning CNF requires lower energy use and no harmful chemicals are used (Lundahl et al., 2017). Instead of dissolution, CNF are dispersed in water and spun into air or recyclable organic solvents. This method was first reported in 2011 and has since then been developed towards increased scalability and improvement of the fibres’ mechanical properties (Iwamoto et al., 2011; Lundahl, 2018). A single cellulose crystallite has a Young’s modulus of up to 160 GPa and tensile strength of 6-7 GPa, exceeding those of carbon and Kevlar fibre, in its longitudinal direction, but only 8-57 GPa in its transverse direction (Wang et al., 2017). So the mechanical performance of cellulose can be maximized in structures where the crystallites are well oriented. This can be achieved by spinning, which involve both orientation of the structural units and their entanglement into a filament (Lundahl, 2018). Wet and dry-spinning have so far been applied on CNF at laboratory scale, using a syringe pump, extruder, capillary rheometer or 3D printer (Lundahl, 2018). In the production of filaments, 2,2,6,6-tetra-methylpiperidinyl-1-oxyl (TEMPO) oxidized CNF is used (Iwamoto et al., 2011) and extruded through a spinneret in a wet or dryspinning process (figure 10). In wet-spinning, a coagulation bath with acetone, water, ethanol or CaCl2 solution is used. The characteristics for the coagulants are miscibility with water, 21 moderate polarity and hydrogen bonding ability (Iwamoto et al., 2011; Walther et al., 2011; Kim et al., 2019). The coagulant bath rapidly induces the formation of “a skin” on the surface of the CNF extrudate, stabilizing it against interfibre aggregation, to allow the formation of distinct macrofibres (Walther et al., 2011). In dry-spinning, the dope is forced through the spinneret and the solvent removed by evaporation (Clemons, 2016). Regardless of the spinning method, a high molecular alignment is induced by drawing the fibre immediately after the spinneret. This high induced molecular alignment is key to the high stiffness and strength of the fibres (Clemons, 2016). Figure 10. Schematic illustrations of simplified systems for (A) wet-spinning and (B) dry-spinning. Reprinted (adapted) with permission from (Lundahl, 2018). Copyright (2018) American Chemical Society. Several parameters such as spinning speed, inner diameter and length of needle and drying temperature, influence the alignment of CNF and hydrogen bond formation between CFNs (Kim et al., 2019) In the first report of CNF filament production through a wet-spinning process, the influence of spinning rates (from 0,1 to 100 m/min) were studied. The highest speed rate resulted in filaments with better mechanical properties (Iwamoto et al., 2011). By using post drawing, more efficient alignment of the nanofibrils is achieved resulting in further improvement of the mechanical properties of the fibres (Walther et al., 2011). A controlled wetstretching procedure is used to induce high fibres orientation, improving their Young’s Modulus from 8,2 to 33,7 GPa (Torres-Rendon et al., 2014). Various concentrations of CNF were tested, from 1 % to 12 %, being the higher ones processed through dry-spinning and the lowers by wet-spinning (Hooshmand et al., 2015; Iwamoto et al., 2011; Kim et al., 2019). In a study using a wet-spinning system 2 % (m/m) CNF was considered the ideal solids content for (A) (B) 22 attaining a high CNF alignment and filament strength, specifically, a Young Modulus of 37,5 GPa and Tensile Strength of 543,1 MPa (Kim et al., 2019). The mechanical properties of CNF filaments produced through the various processes are summarized in table 2. Table 2. Mechanical properties of different cellulose nanofibre filaments Spinning Young’s Modulus (GPa) Tensile Strength (MPa) Elongation (%) Reference Wet-spinning 23,6 321 2,2 (Iwamoto et al., 2011) 22,5 275 - (Walther et al., 2011) 33,7 289 1,6 (Torres-Rendon et al., 2014) 28,9 369,6 - (Geng et al., 2017) 23,9 383,3 6,6 (Kafy et al., 2017) 37,5 543,1 3,7 (Kim et al., 2019) Dry-spinning 12,6 222 3,6 (Hooshmand et al., 2015) 6,5 100 - (Ghasemi et al., 2017) Flow focusing 86 1570 - (Mittal et al., 2018) BNC wetspinning 16,4 248,6 3,8 (Yao et al., 2017) BNC stretching 65,7 826 2,5 (S. Wang et al., 2017) Flow focusing is another method for CNF filaments production, resulting in fibres with the strongest tensile performance, as compared to other methods (table 2). The fibres are obtained by aligning a CNF suspension in a double flow focusing channel involving coagulation with acid, as shown in figure 11 (Mittal et al., 2018). The obtained filament has a Young’s modulus of 86 GPa and tensile strength of 1570 MPa, exceeding the mechanical properties of 23 known natural or synthetic fibres (Mittal et al., 2018). The specific strength of this CNF fibres also exceeds that of metals, alloys, and glass fibres. Figure 11. Schematic of double flow-focusing channel used for CNF assembly (Mittal et al., 2018). To our knowledge, the first and only company, to produce fibres without solvents, cellulose dissolution or any other harmful and complex chemical processes, is Spinnova Ltd (Finland). The raw material is pulp from FSC certified wood. After mechanical pulping, the finely ground pulp mass flows through a unique nozzle, where the fibres and fibrils rotate and align with the flow, creating a strong, elastic fibre network. The fibre is then spun and dried, suitable for spinning into yarn and then knitting or weaving into fabric (Salmela et al., 2016) The future goal is the recycling of the fibres for several times, minimizing the use of virgin materials. Spinnova fibre is now (2020) close to commercialization. The technology has been scaled up from a small pilot scale to an industrial pilot scale (Spinnova, 2020). Filaments based on aligned BNC nanofibres were prepared by wet-spinning and drawing procedures (Yao et al., 2017). The obtained macrofibres exhibited Young’s modulus of 16,4 GPa and tensile strength of 248,6 MPa under optimum process conditions (BNC 5.4 wt %; spinning rate 18,9 m/min), in which nanofibres displayed a high degree of alignment. The nanofibre suspension was prepared by TEMPO oxidation and then spun into an acetone coagulation bath (Yao et al., 2017). BNC Filaments without TEMPO oxidation were also 24 produced. A super-strong and super-stiff cellulose macrofibres was obtained from aligned ultralong BNC nanofibres via a facile and scalable wet-drawing and wet-twisting method (Wang et al., 2017). The macrofibres showed perfect integrity and well aligned structure, with a tensile strength of 826 MPa and Young’s modulus of 65,7 GPa. BNC membranes were cut with a width of 7 mm and were wet-draw, becoming longer and thinner. From these, BNC macrofibres with diameters of around 300 μm were fabricated by wet-twisting and subsequently drying at 90 °C for 12 h (Wang et al., 2017). 1.3 Sustainability and Life Cycle Assessment The rapid population growth and careless consumption of natural resources are causing serious global problems, such as air and water pollution and global warming. Fossil fuels exceeds 50 % of the word’s total energy sources and based on present water consumption, water resources are likely to decrease by 30 % in 2050 (Kazan et al., 2020). In the last few decades, the environmental problems caused by humankind are reaching dangerous levels, being the search and adoption of more environmentally sustainable processes a mandatory paradigm change. In this regard, environmental impact assessment gains a significant importance to evaluate the environmental effects of industrial activities. Life cycle assessment (LCA) can be used to analyse a product, process or activity repercussions on the environment (Van Der Velden et al., 2014). “Cradle to gate” LCA studies take in account the raw materials and fuels used, as well all the processes involved until the product is delivered at the factory gate for further processing; “cradle to grave” involves, in addition to the later, post-manufacturing processes until the product (garment) end of life (Dibdiakova & Timmermann, 2014). The global textile supply chain is complex, involving many different stages (figure 12). It is widely recognized that the textile industry is a major contributor to the environmental pollution and resource consumption. Among all, this industry is placed at fifth place in terms of the release of chemical oxygen demand (COD), implying high amounts of wastewater production and chemical consumption (Zhang et al., 2018; Roos et al., 2018). Along COD, textile wastewaters may include materials with a high biological oxygen demand (BOD), total suspended solids, oil and grease, sulfides, sulfates, phosphates, chromium, copper, and/or the salts of other heavy metals. The majority of the chemical used in textile production occurs during wet processing (dyeing, washing, printing, and fabric finishing). Textile dyeing and finishing mills use as much as 200 tons of water for every metric ton of textiles produced. The 25 textile industry is a major energy-consuming industry with low efficiency in energy utilization. A large quantity of non-renewable energy sources is consumed in the form of electricity, not so much in the process of textile production (15-20 %) but mostly in subsequent laundering processes during consumer use (75-80 %) (Choudhury, 2014). Figure 12. The business involved in the textile and clothing supply chain (adapted from (Choudhury, 2014)). Although the entire process of textile production generates hazardous wastes, in this review we focus only on raw materials and fibres production. A cradle-to-gate life cycle assessment study, shown in table 3, makes possible to evaluate the environmental impact of different fibre production processes (Dibdiakova & Timmermann, 2014). It is important to mention that, for a true comparative LCA, the same framework must be used for all stages of the life-cycle of a commercial product, process, or service (this means using the same criteria for a life cycle inventory of the required resources (energy and materials) across the value chain and determining the corresponding emissions to the environment). Data here collected was obtained from different sources and therefore a direct comparison of the impact categories is not straightforward. 26 Table 3. LCA cradle-to-gate of different impact categories per 1000 kg of fibre (functional unit) produced under different methods Impact Category Cotton Fibre Tencel (lyocell) Viscose Austria Viscose Asia Polyester Water Use (m3) 5730 1 263 2 445 2 319 3 125 3 Energy Demand (GJ) 55 1 65 3 70 3 106 3 96 3 Global Warming (kg CO2 -Equiv.) 2000 1 50 3 -250 3 3800 3 4100 3 Acidification (kg SO2-Equiv.) 41 1 13 3 14 3 45 3 21 3 Eutrophication (kg phosphateEquiv.) 22 1 1,9 3 1,2 3 2,3 3 1,2 3 Ozone Depletion (x10-3 kg CFC11 Equiv.) 0,2 1 0,07 3 0,03 3 0,28 3 0,07 3 Land Use (ha/year) 1,07 1 0,22 3 0,69 2 0,35 3 0 4 1(Cotton Incorporated, 2012) 2(Taylor, 2010) 3(Shen & Patel, 2010) 4(Dibdiakova & Timmermann, 2014) Polyester, the most widely used synthetic fibre, has a lower water consumption than the other cellulose fibres, but has the highest impact on global warming from CO2 emissions and also a high demand on energy (Zambrano et al., 2019). Cotton is the most used natural raw material in textile industry (Kazan et al., 2020). Nutrients and pesticides are used in raw material production to increase quantity and product quality and so, they pollute the groundwater and surface water. Up to 25 % of global pesticide usage in agriculture corresponds to cotton production (Kazan et al., 2020). Although cotton has the advantage of being biodegradable, it has a significant water consumption, with an average global water footprint of 5730 m3/ton in crops production and required water for processing (Cotton Incorporated, 2012). Some of the negative aspects of cotton production can be overcome by growing organic crops but it still has many negative environmental aspects compared to other fibres (Textile Exchanges, 2014; La Rosa & Grammatikos, 2019). 27 Regarding the processing stage, the Viscose process has different environmental impacts depending on where it is produced (Shen et al., 2010). The problems with these fibres are the chemicals used in the regeneration process and the need for large plantation areas for wood production. Currently, the most environmentally friendly fibres on the market are produced by the Lyocell process (Shen et al., 2010). The solvent used is non-toxic and recyclable being the main challenge the sustainable sourcing of cellulose. Tencel, made of cellulose from eucalyptus, which grows quickly and requires no irrigation or pesticides, is the best option on the market regarding its environmental impact. BNC may be the solution to Lyocell flaws as it can be produced anywhere without forest destruction. An attributional LCA was applied to a projected production of BNC, by static culture, following a cradle-to-gate approach which includes the extraction of natural resources and their transformation, the production of BNC, the utilities, the energy and equipment used, as well as the treatment and disposal of the waste produced by the BNC process chain. The results showed that water was the main resource used, most of which being returned back to fresh water after treatment. The BNC manufacture facility itself contributed little extent to the consumption of resources and environmental impact of the global life cycle. The materials production (Background System) were responsible for most of natural resources used (water), and the emissions released to the environment, in this case emitted to fresh water (Forte et al., 2019). 34 tests using 3 % BNC + 1 % glycerol and 3 % BNC + 1 % CMC were performed, being the glycerol and the CMC joined in the blender during the 30 min disintegration. 3.2.5 Wet-drawing The production of BNC filaments using a BNC membrane, without disintegration, was attempted. A BNC membrane was cut into a rectangular shape of size 7 mm × 70 mm then twisted and wet-drawn using a TA.HD plus Texture Analyser machine at a crosshead speed of 1 mm/min until the strain of the sample reached 10 %, 20 %, and 30 %, respectively, shown in figure 32 in annexes. The wet-drawn samples were twisted even more immediately after drawing to reduce water evaporation and then dried at 90 °C for 24 h under tension. BNC macrofibres without wet-drawing (0 %) were prepared using the same method. Samples with glycerol and CMC were also produced by immersing the BNC membranes for 24 h, before wetdrawing process. 3.2.6 Mechanical properties of the BNC filaments The mechanical properties of the produced filaments were evaluated using the TA.HD plus Texture Analyser machine with a load range of 5 kg. The fibre diameter was measured and the values were used for the calculation of the mechanical properties. 3.2.7 Scanning electron microscope The powdered BNC and the filament samples were characterized using a desktop scanning electron microscope (SEM) (Phenom-World BV, Netherlands)). All results were acquired using the ProSuite software. The samples were added to aluminium pin stubs with electrically conductive carbon adhesive tape (PELCO Tabs™). Samples were coated with 2 nm of Au (20 Angstrom) for improved conductivity. The aluminum pin stub was then placed inside a Phenom Standard Sample Holder (SH). The analysis was conducted at 5 kV with intensity image. 3.2.8 Statistical Analysis Statistical analysis were supported with Prism version 8.4.3 (GraphPad Software, La Jolla California USA). Using one-way ANOVA and Turkey’s post-hoc analisys for pairwise comparison of more than two different means. Two-tailed unpaired Student’s t-test was used for comparison of the means between the two samples. Mean differences were considered statistically non-significant (ns) when p value was above 0.05. 35 4. RESULTS AND DISCUSSION The Lyocell process has been studied for many years and several parameters used in its production are widely accepted (Regau & Vocklabruck, 2013). One of the main parameters for Lyocell is the cellulose pulp DP that should be adjusted to level of 550 to 650 (Kosan et al., 2020). BNC has a much higher DP, around 2259 (table 7), hence its depolymerisation may be necessary. Thus in this work the conditions required for the depolymerisation of BNC were investigated. On the other hand, it has been hypothesised that the native BNC may be suitable for the Lyocell process. Thus, several operational conditions were tested aiming at verifying this possibility and whether it may allow the production of filaments with good properties for textile applications. 4.1 BNC solid-phase dissolution and syringe spinning BNC Lyocell fibres have already been produced through the solid-phase dissolution process (Makarov et al., 2019). A replication of this process was attempted through a simple and manual process, using a syringe device. In this method there is no water evaporation; the NMMO, water and BNC amounts stay constant throughout the process. BNC-NMMO solutions with BNC 1-2.5 % were successfully dissolved; however, for higher BNC concentrations (3-4 %), lumps were visible in the dope, an indicator of undissolved particles. This problem could be overcome with longer dissolution times. However, this may also lead to higher NMMO degradation, even using the antioxidant propyl gallate. Even without complete dissolution it was possible to form filaments using a syringe. Filaments formed from BNC at 1, 2 and 2.5 % BNC were observed by SEM (figure 14). BNC 1 % A B 36 Figure 14. BNC filaments observed by scanning electron microscope (SEM) – scale is 50 µm for A, 20 µm for B and E, and 10 µm for C, D and F. Due to their lower viscosities, the dopes with BNC concentrations of 1 and 2 %, could be spun with the 600 and the 800 µm needles. The 900 µm needle was used for all (1, 2, 2.5, 3, 3.5 and 4 % BNC) samples. For 1 % BNC, SEM images show some irregularities (lumps) on the surface of the filament, possibly due to remnants of NMMO that were not removed during washing, even after intensive washing. This concentration is too low for this syringe spinning process, thus these filaments weren’t analysed further. For the highest BNC concentrations (2 and 2.5 %), this was not observed, as the washing steep was more efficient. In all samples, especially at 2.5 % BNC, the surface showed some roughness, possibly due to some BNC that was not well dissolved, as previously discussed. Except for 1 % BNC, the obtained filaments were characterized for their mechanical properties (figure 15 and table 9 in the annexes). All filaments obtained with a needle of 900 µm yielded higher Young’s modulus and tensile strength properties for lower BNC concentrations, as shown in figure 15. The elongation was higher for BNC 3 %. It should be BNC 2 % BNC 2.5 % C D E F 37 noted that the properties of filaments produced with the syringe can vary widely, due to the variable applied speed of (manual) extrusion and drying. Figure 15. Mechanical properties of BNC with a 900 µm syringe. Filaments obtained with 2 % BNC using the 800 and 600 µm needles were also analysed and the results are presented in figure 16 and 17 respectively as in the table 10 and 11 in the annexes. As the needle diameter was smaller, filaments with lower diameter (10 µm) were produced, improving the mechanical properties. Comparing the outcome of the different needles, the filaments obtained with the 600 µm needle had the highest tensile strength 1201,9 ± 149,2 MPa (for filaments of 10 µm obtained using a 2 % BNC solution). On the other hand, Young’s modulus was not improved by lowering the needle diameter. The highest value obtained was 24,3 ± 0,7 GPa (for filaments of 20 µm obtained using a 2 % BNC solution). ** the differences are significant (P < 0.05) Figure 16. Mechanical properties of BNC (2 %) with a 800 µm syringe. Figure 17. Mechanical properties of BNC (2 %) with a 600 µm syringe. 38 Comparing the results obtained with those by Makarov et al., (Young’s Modulus of 20,2 GPa, tensile strength of 420-495 MPa and elongation of 5.5-6.5 % (table 1)), in this work superior mechanical properties were obtained (Young's modulus, tensile strength and elongation) (figures 15-17). BNC concentrations tested (2-4 %) were lower than those used by Makarov (6 %). When comparing filaments with the same diameter, the difference in mechanical properties are even higher, being the ones obtained in this work quite superior (table 1 and figure 17). Fibres with 2 % BNC concentration and smaller needle diameter (600 µm) yielded better mechanical properties (Young’s Modulus of 20,8 ± 5,4 GPa and tensile strength of 1201,9 ± 149,2 MPa). The mechanical properties obtained in this work are also superior to those of commercially available products (table 1). However, additional results under more controlled conditions, yielding more consistent results, are necessary in order to make definitive conclusions. The 2 % dope is less viscous comparative to higher BNC concentrations, which means is easier to extrude manually using a syringe than higher concentrations, while facilitating fibre alignment inside the needle. Another important aspect is the length of the needle, which is considerably longer than those used in commercial extruders, increasing the BNC fibres alignment. This aspect is measured through the L/D of the spinneret, in this work was ~50 and in commercial extruder is between 2 and 10 (Hudson & Cuculo, 2005). BNC filaments with higher BNC concentrations (> 4 %) could not be tested, due to the poor mixture between NMMO, BNC and water. One way to overcome this issue would be to use a LIST Kneader Reactor that, having high pressure capacity and high torque, could possibly allow a homogeneous mixture (LIST, 2020). Although being produced in a not very controlled way (syringe), the properties of these filaments were better than traditional Lyocell fibres (table 1), suggesting that optimization may lead to promising results regarding the possibility of using these filaments for textile applications. 4.2 BNC dissolution and dry-jet wet-spinning In this work, a dry-jet wet-spinning equipment was also tested. In order, to overcome the limitations in BNC dissolution, found using the solid-phase method, Lyocell process (excess of water and swelling in the dissolution stage) was carried out at CeNTI facilities. The excess water allowed a better mixture of the components and no lumps were visible by the end of the process, which suggests full BNC dissolution. BNC solutions with concentration of 3 , 4 , 5 and 6 % were successfully prepared within a few hours (~ 5 h); expectably, the higher the BNC 39 concentration, the longer the dissolution time. All samples were analysed in a rotational rheometer. The viscosity profiles of the dopes were measured at 80 °C, using a cone and plate geometry and the results are shown in figure 18. The viscosity remained constant up to a shear rate of 0,1 s-1 in all samples. At low shear rates it is possible to estimate the zero shear viscosity of the different samples prepared: ~70, ~280, ~1000 and ~1700 Pa.s, respectively for BNC at 3, 4, 5 and 6 %. Then, at shear rates higher than 0.1 s-1, the viscosity decreased, characteristic of a shear thinning fluid. The increase in viscosity is lower in the 6 % BNC sample, this may be due to higher entanglement of molecular chains (Z. Jiang et al., 2019). The viscosity obtained for BNC 6 % was very different from that obtained by Makarov (10000 Pa.s), although the DP of the used BNC does not differ much (DP 2000) (Makarov et al., 2020). Figure 18. Dope viscosity in a rotational rheometer at 80 ºC. Dopes comprising 3 and 5 % BNC were prepared (500 mL) and extruded in the dry-jet wet-spinning equipment. Filaments with several meters long were formed. Although the equipment allows washing and drying steps, the former wasn’t long enough to provide proper removal of the NMMO residues. Therefore, the filaments were further washed with distilled water until they became transparent and observed by SEM (figure 19). 1 10 100 1000 10000 0,00001 0,0001 0,001 0,01 0,1 110 100 1000 Viscosity (Pa.s) shear rate (1/s) BNC_3% BNC_4% BNC_5% BNC_6% 40 Figure 19. Dry-jet wet-spinning BNC filaments observed by scanning electron microscope (SEM) – scale is 20 µm for A and C, and 30 µm for B and C. As in the solid-phase dissolution method (figure 14), the 3 % BNC Lyocell SEM images (figure 19), shows some bumps and the filaments are not completely cylindrical, they present some deformations. With the increase of BNC concentration, filaments have a more cylindrical form as in 5 % BNC SEM images in figure 19, that presents a smoother surface. In figure 20 various filaments, produced with 5 % BNC are shown. Their mechanical properties are shown in table 5. BNC 3 % BNC 5 % A B C D 41 Figure 20. Dry-jet wet-spinning 5 % BNC filaments – BNC Lyocell fibre. Table 5. Mechanical properties of BNC filaments (3 and 5 %) through the Lyocell method and dry-jet wet-spinning BNC % d (µm) Young's Modulus (GPa) Tensile Strength (GPa) Elongation (%) 3 10-30 22,5 ± 7,4 * 771,9 ± 266,5 5,0 ± 1,5 ** 5 20-40 35,0 ± 17,2 * 1103,0 ± 481,4 6,8 ± 4,0 ** ** the differences are significant (P < 0.05) Filaments with 5 % BNC showed better mechanical properties compared to those with 3 %. The filaments extruded (5 % BNC) were also more resistant to hand manipulation and the NMMO washing was easier. There is a significant difference between the two concentrations for the Young’s Modulus and elongation. More concentrated solutions can be used if a more advanced equipment is used, as an integrated system of dissolution and extrusion. At CeNTI, 42 the main observed experimental difficulty concerned with the impossibility of pouring the dope in the dry-jet wet-spinning at higher viscosities. Comparing the solid phase dissolution (figures 15-17) to the Lyocell method (table 5), the Young’s modulus is superior in the later, while the tensile strength of the 5 % BNC traditional Lyocell is almost as high as the one obtained with 2 % BNC using a 600 µm needle (1201,9 MPa). Both processes allowed the production of BNC fibres with better mechanical properties than those currently used in the market (table 1). 4.3 BNC depolymerization: mechanical treatment A mechanical process was tested, to lower the DP of BNC, while obviating the use of alkaline solutions, thus reducing its environmental impact. For this, two mechanical treatments were performed – wet defibrillation and dry grinding. Defibrillated samples, at different processing times (1, 5, 10 and 30 min) were observed by optical fluorescence microscopy (figures 21-24) to compare the impact of the disintegration time on the morphology and bundle size (figure 25 and table 13 in the annexes). The bundles sizes dropped from 342,8 µm to 117,9 µm, with the disintegration time, albeit the large size distribution observed. Figure 21. Fluorescence microscopy of BNC bundles with 1 min of wet defibrillation – scale is 100 µm. 43 Figure 22. Fluorescence microscopy of BNC bundles with 5 min of wet defibrillation – scale is 100 µm. Figure 23. Fluorescence microscopy of BNC bundles with 10 min of wet defibrillation – scale is 100 µm. 50 The SEM images (figure 29) are quite different from those obtained by syringe spinning and the dry-jet wet-spinning (figure 22 and 27, respectively), which are smoother since the BNC was dissolved. Also, the dry spun BNC fibres showed a good fibre alignment but presented many surface irregularities, which compromised the mechanical properties. Still, similar results were obtained to those of plant cellulose dry-spinning filaments (table 2) (Ghasemi et al., 2017; Hooshmand et al., 2015). Filaments produced through wet-spinning shows better properties (table 1) although SEM images shows less aligned BNC fibres (Kafy et al., 2017; Yao et al., 2017). Samples with CMC and glycerol lowered the fibres tensile strength being the better properties obtained using only BNC (3 %) This BNC filaments are very stiff. The addition of glycerol and CMC, prevents this aggregation of fibres; if on the one hand it can improve flexibility, on the other it could reduce the mechanical properties, as observed (Martins et al., 2020). It was not possible to form filaments using higher concentrations as the BNC could not align well in order to form a filament with some mechanical resistance. In this work was evaluated the BNC concentration on the production of filaments through dry-spinning, various other parameters also need optimization as defibrillation time, drying temperature (Ghasemi et al., 2017) and spinning rate (Hooshmand et al., 2015). The biggest disadvantage of this filaments, compared to Lyocell, is their hydrophilicity (defibrillating in the presence of water) that can be overcome with a hydrophobic coating. There is plenty of room to improve the mechanical properties obtained with the 3 % BNC sample, such as the extrusion speed and the addition of other rheological modifiers. 4.6 Wet-drawing The wet-drawing method also does not require chemicals for BNC dissolution, nor requires the defibrillation of the BNC, which means that the properties of the native BNC are fully preserved. The mechanical properties of the macrofibres obtained were analysed and the results are presented in tables 7 and 8. It is noteworthy the difference between the Young’s modulus of neat BNC and BNC – glycerol samples, being the latter the one with better properties. Regarding tensile strength and elongation, similar values were obtained. For different % of wet-drawing, it is visible the increase of the mechanical properties with the increase of % of wet-drawing for both BNC and BNC – glycerol samples. Samples of BNC – glycerol with 30 % wet-drawing had the highest Young’s modulus (7,9 ± 3,4 GPa) although an increase in tensile strength was not observed. 51 Table 7. Mechanical properties of wet-drawing BNC macrofibres BNC % Young's Modulus (GPa) Tensile Strength (MPa) Elongation (%) 0 1,1 57,2 10,0 10 1,7 82,5 13,2 20 1,0 264,3 12,5 30 3,1 247,4 8,5 Table 8. Mechanical properties of wet-drawing BNC – glycerol macrofibres BNC – glycerol % Young's Modulus (GPa) Tensile Strength (MPa) Elongation (%) 10 3,2 ± 1,8 219,3 ± 104,7 9,6 ± 0,7 20 4,2 ± 3,4 171,0 ± 59,3 12,7 ± 4,4 30 7,9 ± 3,4 220,2 ± 98,4 14,3 ± 1,8 It would be expected to have better mechanicals properties as the membrane properties are maintained but that did not occur, the maximum Young’s modulus was 7,9 ± 3,4 GPa and tensile strength of 220,2 ± 98,4 MPa for fibres with 30 % stretching and glycerol. Others had obtained superior results using this process (Young’s modulus of 65,7 GPa and tensile strength of 826 MPa (table 2)) (S. Wang et al., 2017). 52 5. CONCLUSION Several types of fibres have been produced to fulfill people’s needs and demands, polyester, cotton and Viscose being the most used. However, these fibres have environmental implications during raw material processing and transport, filament manufacture, product and byproducts disposal. Current trends include the development of filaments without solvents, the development of new solvents and new sources of fibres, which include different nanocelluloses, namely BNC. In order to minimize the use of chemicals in the filament production, BNC filaments without depolymerization were produced, using the Lyocell method, and high mechanical properties were obtained, being superior to those currently commercialized. BNC depolymerization was then studied and achieved using NaOH. Commercial Lyocell DP parameters were obtained. Filaments without BNC dissolution, that is, without the use of chemicals harmful to the environment, were also produced. The mechanical results of these filaments weren’t as good as BNC Lyocell filaments, but they can still be greatly improved. 53 REFERENCES Akhlaghi, M. A., Bagherpour, R., & Kalhori, H. (2020). Application of bacterial nanocellulose fibers as reinforcement in cement composites. 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Mechanical properties of BNC (2 %) with a 800 µm syringe d (µm) Young's Modulus (GPa) Tensile Strength (MPa) Elongation (%) 10 19,8 ± 6,4 768,2 ± 125,4 11,45± 0,2 20 24,3 ± 0,7 691,5 ± 94,7 8,9 ± 2,0 40 12,50± 3,0 411,6 ± 69,3 11,4 ± 5,5 Table 11. Mechanical properties of BNC (2 %) with a 600 µm syringe d (µm) Young's Modulus (GPa) Tensile Strength (MPa) Elongation (%) 10 20,8 ± 5,4 1201,9 ± 149,2 11,5 ± 0,1 20 17,0± 4,0 724,2 ± 141,0 13,2 ± 3,0 30 19,7 ± 5,3 662,2 ± 198,5 8,6 ± 3,7 Figure 31. BNC dry-jet wet-spinning. 70 Table 12. Values of [ƞ] × ρ corresponding to different values of the viscosity ratio ƞratio 71 Table 12. Continued. 72 Table 12. Continued. Table 13. BNC (0.5 %) bundles length with different wet defibrillation times Treatment time (min) Length (µm) 1 342,8 ± 157,65 5 297,3 ± 179,21 10 178,4 ± 77,77 30 117,9 ± 74,26 Table 14. Powder BNC viscosity and DP with different particle size BNC fraction ρ mg/mL Time (s) [ƞ] DP < 38 µ m 5 65,70 ± 0,62 613 ± 5,67 2174 ± 17 < 63 µ m 4 56,44 ± 0,83 698,63 ± 1,59 2310 ± 3 < 125 µ m 4 62,33 ± 1,57 742,63 ± 14,67 2383 ± 24 < 500 µ m 4 65,01 ± 1,17 761,50 ± 8,13 2413 ± 3 > 500 µ m 4 64,24 ± 0,47 754,88 ± 3,36 2403 ± 5 73 Table 15. BNC viscosity and DP with chemical treatment BNC sample ρ mg/mL Time (s) [ƞ] Plant cellulose (DP > 950) Plant cellulose (DP > 950) DP BNC Control 4 78,8 813 1936 2281 2259 4.5 M NaOH 120 min 5 46,6 491 1170 1176 1750 5 M NaOH 120 min 5 45,9 483 1149 1149 1734 6 M NaOH 120 min 5 50,5 515 1227 1252 1793 7 M NaOH 120 min 5 39,6 436 1038 1005 1647 5 M NaOH Aging 4 h 5 21,62 253 602 491 1249 BNC 0.5 % 5 M NaOH – Aging 8 h 5 19,5 223 531 416 1172 Figure 32. BNC wet-drawing process (a) and drying (B). A B