Authored by Jennifer Harmon*
Abstract
As consumers continue to shift towards being more environmentally conscious, new materials are emerging on the industry landscape. Bacterial cellulose applications are of particular interest. This unique material has the potential to yield more sustainably produced cellulose than traditional products. To this point, investigation into common, essential properties for apparel applications has been limited. This project compared 3 main types of media, 2 variations of these media types, 2 drying methods and 1 treatment application to ascertain the most economical and beneficial methods of cultivation for this material. The resulting material was measured for cellulose yield, strength, and elongation and abrasion resistance. Overall, it was discovered that material grown in the molasses mannitol media produced the most cellulose. The strongest cellulose was also molasses mannitol and the most resistant to abrasion. Cellulose from the treatment conditions tended to have the greatest length for elongation at the breaking point. Overcoming some of this material’s deficits will be necessary in order for it to become a more widely used source of cellulose in apparel.
Keywords: Bacterial cellulose; Yield, uniformity; Strength; Abrasion resistance; Absorbency
Abbreviations: BC- Bacterial Cellulose; HS- Hestrin Schramm; HSM- Hestrin Schramm Mannitol; MS- Molasses; MSM- Molasses Mannitol; HFCSHigh Fructose Corn Syrup; HFCSM- High Fructose Corn Syrup Mannitol
Introduction
Disposable clothing, the mode of apparel production and consumption in recent decades has increasingly emphasized “fast fashion.” Contributing to this fast fashion orientation is globalization, which has drastically lowered the cost of clothing production, resulting in prices so low that consumers may now consider clothes disposable [1]. Additionally, consumers’ now desire new clothing more often, leading to so called “season less” seasons [2]. The fast fashion process leaves an environmental impact through waste at nearly every stage of the product use cycle.
One consequence of the fast fashion system is increasing amounts of textile waste. According to the Environmental Protection Agency, the main source of textiles in municipal waste is discarded clothing [3]. Further, since 1960, acceleration in textile waste generation can be observed through the over 8 times increase in the amount of tons discarded [3]. Additional textile waste is produced during manufacturing, particularly in the cutting stage. Textile waste from this stage in apparel production can exceed 16% [4]. An additional 6 plus percent of waste products from textiles and sewing threads can be observed in the sewing process [4].
Cellulose derived waste tends to decompose more quickly than its synthetic counterparts. Cellulose is the most freely available and inexpensive carbohydrate polymer in the world [5]. It is typically derived from plants and plant wastes for fibres like cotton, linen, rayon, and more [5]. Cotton, the most popular cellulosic fibre, is one of the most commonly used raw fibre materials [6]. In fact, 17 million bales of cotton were produced in the U.S. in 2012 [7]. Cotton has numerous positive attributes which make it ideal for apparel, including the potential for flexibility and softness, moisture absorption, breathability, and moderate strength [8].
Nonetheless, cotton fibre manufacturing requires large amounts of land, water, and pesticide resources each year, making cotton less than ideal from a sustainability perspective. Cotton is a water intensive crop, requiring at least 20 inches of rainfall each year for optimal growth [9]. In countries with low annual rainfall, irrigation is necessary to cultivate this crop. Excessive irrigation often leads to land degradation. Although cotton has a small share of overall agricultural land at 2.4%, cotton cultivation accounts for 24% of insecticide and 11% of pesticides sales annually [10]. Cotton, a seed fibre, while a highly pure form of cellulose, still has impurities such as pectin and plant particulate which must be removed with additional water and chemicals. Other stem based cellulosic fibres, like flax and hemp; have to undergo further processing to remove impurities such as lignin and hemicellulose.
In addition to being more resource-intensive to cultivate, cotton garments contribute to significant waste in modern landfills. In 2014, landfills received 10.4 million tons of textile waste, roughly the total weight of two dozen modern skyscrapers [11]. The main source of this textile municipal solid waste is discarded clothing [11]. One positive aspect of cotton textile waste, and indeed all cellulosic textile waste, is that cellulose is biodegradable. Certain fabric treatments can accelerate or reduce cotton’s ability to degrade but cotton will still degrade more completely than other commonly used synthetic fibres, such as polyester [12].
Interest in reducing the environmental impacts of the textile and apparel industry is growing. Recently, textile research investigated methods aimed at replacing cotton as the primary source of cellulose in textile products [13]. One avenue being increasingly explored to reduce the environmental impact of the industry is the use of biotechnology in producing cellulose [14]. In addition to the wood pulp based fibres, bacterial cellulose (BC) has been investigated as a potential source of cellulose. In addition to traditional plant sources, cellulose is also produced by several strains of bacteria [15,16]. Bacterial Cellulose (BC), is a material produced without the impurities present in plant derived cellulosic products, such as lignin and hemi-cellulose [17]. Lacking hemicellulose and lignin, the cellulose micro fibrils interact extensively with one another via hydrogen bonds. Indeed, these interactions make for a highly crystalline, absorbent, and strong fibre-web [18].
In order for this material to be used in apparel, the potential cellulose yield, as well as basic textile properties, needs to be better established. This study investigated the use of low cost nutrient sources for the cellulose producing bacteria such as high fructose corn syrup and molasses. Additionally, the impact of air and freeze drying methods on BC’s textile properties was tested. Finally, the use of a plasticizing glycerol soak was examined for its impact on the material’s properties. Impact was assessed in terms of grams per litre of cellulose produced in each media, strength testing, and elongation and abrasion resistance [19].
Literature Review
As the textile industry engages in increasingly unstable practices to meet rising demand, consumer textile waste and pollution rest among the top concerns in the industry. The year 2017 signified a tipping point for this industry when the EPA reported that textile waste accounted for 8% of all municipal solid waste [20]. In the wake of this report, the textile industry and its consumers are attempting to identify alternative, eco-friendly textile solutions. One such textile alternative is bacterial cellulose, a material produced by widely present microscopic organisms, which holds promise due to its relative inertness, and sustainable production. Particularly exciting about this material is that bacterial cellulose requires little arable land, no pesticides, and far less water during the course of production due to the static fermentation setup typically employed. A high degree of polymerization and crystallinity, high purity, extremely high absorption and excellent biodegradability that is not restricted by extensive processing common for other cellulose materials further give this material broad potential appeal [21,22].
Bacterial cellulose, while still a cellulosic material, is easily dichotomized from traditional cellulosic textile materials by means of its macromolecular structure, nonwoven nature, and production methods. During the course of fermentation, Acetobacter sps. Produce and extrude pure microcrystalline cellulose fibrils via their trans membrane cellulose synthase enzyme that aggregate into a nonwoven cellulose network supported through both hydrogen bonds between the 3’ and 5’ hydroxyl groups of the glucose subunits and Van Der Waals interactions [23,24]. This nonwoven cellulose network, Bacterial Cellulose (BC), is ultimately comprised of highly crystalline regions interspersed with amorphous segments [23,24].
Since the discovery of bacterial cellulose, a number of cellulose-extruding microorganisms, namely gram-negative rods of the acetic acid family, have been identified. While many bacteria extrude cellulosic fibres in their formation of biofilms, research tends to focus on Acetobacter xylinum, a bacterium isolated from fruit, first shown to produce cellulose in 1886 and formerly named Gluconacetobacter xylinus [25,26]. The focus on Acetobacter xylinum is due, primarily, to the bacterium’s high yield of cellulose relative to other cellulose secreting microorganism at a total of 1%-4% W/V of fermentation media [27,28]. This cellulose production efficiency ultimately became of great importance in commercial fermentation operations such as in the production of the Filipino dessert “Nata de Coco.” [29].
With organism-specific production capacity understood, inquiries into nutritional requirements as well as the influence of the cellulose production as a function of the growth medium became commonplace; these assessments and new synthetic media often expanded on the work of Hestrin & Schramm, who typified what is now considered the standard synthetic medium for culturing Acetobacter xylinum [30]. Building on this, it was quickly discovered that the carbon source utilized for the growth of Acetobacter sps. Profoundly impacted the degree of crystallinity of the resultant bacterial cellulose [31]. This offered the potential for bacterial cellulose sheets specialized for their end use in industry because the degree of crystallinity is a critical fibre property that further determines other properties such as tensile strength and, elongation, etc. [32]. Nonetheless, the traditional synthetic media for producing bacterial cellulose requires several expensive components such as pure glucose sugars and peptone [33]. In order to achieve a cost-effective material, low-cost media for bacterial cellulose are being explored. Previous research has successfully investigated the use of molasses to replace more expensive carbon sources [34].
Irrespective of the medium used, bacterial cellulose can be produced in a variety of fermentation environments including static, agitated, and stirred cultures [5]. When comparing the fermentation methods, it was noted that agitation increases cellulose yields significantly and decreases production time by up to 90%. At the same time, agitation was discovered to result in irregularly formed cellulose with reduced strength compared to static-fermented cellulose [5]. Furthermore, agitated cultures are known to result in an increased frequency of cellulose negative mutants, which gives rise to the possibility of reduced yields by a culture over time. The uniformity of the BC pellicle is important for appropriateness of the BC in its end use. For this reason, biomedical and cosmeceutical end uses typically employ static cultivation.
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