Biopolymers in Textile Processing Industry

Dr. Asim Kumar Roy Choudhury,
Director Academic, KPS Institute of Polytechnic, Belmuri, Hooghly (W.B.), India
Ex-professor and Ex-HOD (Textile)
Govt. College of engineering and Textile Technology, Serampore (W.B.), India
Email: [email protected]

Abstract
The basic raw material for textile manufacturing, textile fibers, are not inherently green. They are biodegradable, but more-biodegradable polymers can be made by biological means. Biopolymers often have a well-defined structure. In contrast, most synthetic polymers possesses much simpler and more random (or stochastic) structure.

Biodegradable polymers have become of great interest in recent years mainly for biomedical applications. Biodegradable polymers break down in physiological environments by macromolecular chain scission into smaller fragments, and ultimately into simple stable end products. The use of biopolymers, i.e. fibers and plastics made from corn, sugar, starch and other renewable raw materials, has expanded in recent years.

Keywords: Textile fiber, Biopolymer, Bacterial polyester, Polylactic acid (PLA), Chitin and chitosan

1. Introduction
With advances in chemistry, technological progress and the growth of material science, a new class of synthetised or manmade materials, called polymers or plastics, has been introduced. Due to their remarkable performances, polymers or plastics are everywhere in our world and used in everyday life in a wide range of applications such as textile, food packaging, automobiles, electronics, building materials and furniture. In terms of properties, polymers are generally lighter than glass, metals or ceramics, can be rigid or flexible and, opaque or fully transparent. Most of the plastics used worldwide are still made from petroleum; a non-renewable resource. These petroleum-based polymers are extremely resistant to natural decomposition. Consequently and after using they accumulate and damage the environment and the ecosystem. The lack of biodegradability, environmental concern and the depletion of the oil have promoted worldwide research to develop biopolymers, bio-based and biodegradable polymers, as an alternative to petroleum-based plastics.

The biopolymers have been considered in the 1940s and Henry Ford used soya plastic to construct various car parts in an effort to demonstrate his belief that ‘farms are the factories of the future’. Biopolymers are produced by biological systems (i.e. microorganisms, plants and animals), or chemically synthesized from biological starting materials (e.g. sugars, starch, natural fats or oils, etc.).They are more biodegradable than vegetable or animal derived natural fibers. Biopolymers will account for just over 1% of polymers by 2015 (Doug, 2010). However, the expected growth is 3-4 times in the coming 7-8 years.

The term “biopolymers” is loosely defined as polymeric materials consisting for, at least a significant part, out of biological components. Where “biological” means (recently) produced by living organisms, i.e. not produced from petroleum. Biopolymers can be thermoplastic or thermoset, they can be composites or homogeneous and they can be biodegradable or not.

A definition for biopolymers sometimes found in patent literature is based on the amount of “modern carbon” that needs to be present in a biopolymer. “Modern carbon” is defined in the ASTM D6866 standard and is about carbon that contains a specific minimum amount of the C14 isotope. In this way it can be proven that the carbon in the material is not from fossil origin (Bleys, 2015).

Biopolymers have been known since the dawn of civilization: leather, cotton, wool, natural rubber and cork are all biopolymers. While these materials are still popular for specific applications, most polymeric materials in use today are synthetic and based on petroleum-derived resources.

In recent years the research and development of biopolymers has been gaining significant momentum, driven by “green chemistry” and sustainability principles which are increasingly adapted in the industry. The increased research and development of renewable energy sources, specifically of bio-fuels like bio-ethanol which is produced from grains or biomass and biodiesel which is produced from plant oils, also drives the development of biopolymers. Biodiesel, for example, is produced by reacting plant oils with methanol, resulting in fatty acid methylesters, which is the actual biodiesel, and large amounts of glycerol as a by-product. The glycerol can be converted to di-functional compounds, which in turn can be used as monomers in biopolymer production.

While some biopolymers like polylactic acid (PLA) are already becoming commonplace as ‘green’ and biodegradable packaging materials, others biopolymers are more esoteric. An example is BioSteel™ which are protein fibers produced from milk from goats that had been genetically modified with spider silk genes. The polymers are reportedly up to 10 times stronger than steel for the same weight (Bleys, 2015).

2. Merits and Demerits
Biopolymers slowly entering various polymer markets namely textile, plastic etc. Their advantages are sometimes shadowed by their disadvantages, at least, at the present state of development.  Before selection of a biopolymer for a particular end use, both merits and demerits are to be carefully considered.

2.1 Advantages of Biopolymers:

• They are fully bio-based.
• Much lower “oil (petroleum)” is needed for production
• Lower amount of green house gases emits during their production. Ingeo® (Polylactic acid or PLA from Natureworks) requires 60% less greenhouse gases and 50% less non-renewable energy than other polymers (Ditty, 2013).

2.2 Disadvantages of Biopolymers:

• The competition for biological sources for use as food and fuel
• Additional sorting during recycling to avoid contamination.
• Performance still inferior to oil based polymers – poorer heat and moisture resistance.

3. Application of Biopolymers
An increasing trend for biopolymer production and application is being seen due to environmental awareness in the past years and eco-friendliness of biopolymers. In the textile industry biopolymers occupy a relatively low market share due to their insufficient mechanical properties compared to conventional polymers, challenges during polymer processing and their higher price. The production of biopolymers (commonly known as bioplastics) is continuously increasing and recorded as 1.5 million tons in 2012, which is expected to reach to 6.7 million metric tons in 2018 (Endres, 2009).

The use of bio-based products has grown at a steady pace in the last decade. In 2005, they accounted for 7% of global sales and around US$77 billion (£49 billion) in value within the chemicals sector. One estimate is that by 2020 the global market for bio-based products will grow to US$250 billion (£158 billion) and that by 2030, one-third of chemicals and materials will be produced from biological sources, including bio-polymers and bio-plastics.

Various factors influence the production, growth of market and utilization of biopolymers worldwide, such as the convenience of their production and processing methods, properties, cost, biocompatibility and their dependence from foodstuff-based raw materials. These factors affect the interest and acceptance of customers for biopolymer products and with that the decision of polymer producers to actively introduce biopolymers in the market. Figures 1 and 2 represent the worldwide %consumption of various biopolymers in 2013 and consumption (in 1000 tons) of biopolymers in various applications in 2011, respectively (Anonymous, 2015).

Biopolymers have versatile applications. A few are mentioned below:

1. Drug delivery systems (medical field),
2. Wound closure and healing products (medical field),
3. Surgical implant devices (medical field).
4. Bio-resorbable scaffolds for tissue engineering.
5. Food containers, soil retention sheeting, agriculture film, waste bags and packaging material in general.
6. Non-woven biopolymers can also be used in agriculture, filtration, hygiene and protective clothing.

The following biopolymers have high potential for various applications:     

• Starch based polymers (packaging)
• Poly Lactide – PLA
• Polyhydroxyalkanoates (PHA)/ Polyhydroxybutyrate (PHB)
• (co)PA – (castor oil based – PA11)
• Polybutylene succinate (PBS) and biopolyester based copolymers
• Polyethylene Furanoate (PEF) – alternative for PET, made from two building blocks, Furandicarboxylic acid (FDCA) and Mono Ethylene Glycol (MEG).

Biomaterials made from proteins, polysaccharides, and synthetic biopolymers are preferred but lack the mechanical properties and stability in aqueous environments necessary for medical applications. Cross-linking improves the properties of the biomaterials, but most cross-linkers either cause undesirable changes to the functionality of the biopolymers or result in cytotoxicity. Glutaraldehyde, the most widely used cross-linking agent, is difficult to handle and contradictory views have been presented on the cytotoxicity of glutaraldehyde cross-linked materials. Recently, poly(carboxylic acids) that can cross-link in both dry and wet conditions have been shown to provide the desired improvements in tensile properties, increase in stability under aqueous conditions, and also promote cell attachment and proliferation. Green chemicals and newer cross-linking approaches are necessary to obtain biopolymeric materials with properties desired for medical applications (Reddy et al., 2015).

A special type of ‘application’ is the bio-composites. These are mostly fiber-reinforced composites. Obviously the well-known and popular ‘composite wood products’ like oriented strand board (OSB) or medium density fiberboard (MDF) are bio-composites. In many cases research into these products is focused on improving the environmental properties of the binder, especially on reducing formaldehyde emissions. For the production of fiber reinforced bio-composites all kinds of natural fibers can be used, like flax, bamboo, natural wool and many others that can be bonded together to form useful composites.

4. Methods of Biopolymers Manufacture
In general there are three ways to produce biopolymers, which are reflected in the patent literature:

1. Polymers directly extracted or removed from biomass such as some polysaccharides and proteins. There may be partial modification of natural bio-based polymers (e.g., starch)
2. Polymers produced by microorganisms (fermentation) or genetically modified bacteria such as followed by polymerization or direct bacterial fermentation processes (e.g., polyhydroxyalkanoates).
3. Polymers produced by classical chemical synthesis starting from renewable bio-based monomers such as polylactic acid (PLA).

The field of application for a polymer and its performance in technical textiles are depending on its mechanical properties. Thus another important factor, which affects its market value, is tensile strength. Polyethylene furanoate (PEF) is found to have better mechanical properties among the biopolymers. Polylactic acid is seen on second position in terms of tensile strength. PEF is currently used for production of bottles and the further applications are restricted due to limited production of PEF. The PLA production has already reached industrial scale and shows enormous potential in many fields of application. The melt spinning of PLA was performed at Extrusion temperature: 230 °C followed by Quench by air: 0.55 m/s, 18 °C at drawing ratio of 1.95 and Speed of 2,500 m/min, to obtain “POY” yarn 165 dtex. The yarn was textured (false-twist) at 205 °C before the manufacturing of a PLA T-shirt. The filament extrusion was performed successfully, whereas winding appeared to be challenging. The mechanical properties of the spun PLA yarn were compared with reference polyester yarn. The tenacity of PLA yarn is much lower than PET yarn while elongation is seen in same range (Anonymous, 2015).

5. Classification of Biopolymers
Biopolymers can be broadly classified into three groups namely:

• Polynucleotides (RNA and DNA), which are long polymers composed of 13 or more nucleotide monomers;
• Polypeptides, which are short polymers of amino acids; and
• Polysaccharides, which are often linear, bonded polymeric carbohydrate. This group includes alginates, microbial cellulose (MC), Chitin and Chitosan,

6. Important Biopolymers
A large number of biopolymers are available naturally or manufactured. However, only a few of them have been used commercially. A few important biopolymers are discussed here.

6.1 Soybean Fiber
Soybean fiber is a man-made regenerated protein fiber from soybean protein blended with PVA. It is biodegradable, non-allergic, and micro-biocidal. The clothing made from the soy fiber is less durable but has a soft, elastic handle. Soybean protein is a globular protein and it has to undergo denaturation by alkali/heat/enzyme and degradation in order to convert the protein solution into a spinnable dope.

6.2 Poly (Alkylenedicarboxylate) Polyesters (APDS)
Monomers for aliphatic APDs can be petroleum derived (i.e. not renewable) or biomass derived (i.e. renewable), the former being the major route. Both can be prepared to the same degree of purity, but the later is still costlier.

Common dicarboxylic and diol monomers found in APDs are shown in Figure 3. They include succinic acid (SA), adipic acid (AA), ethylene glycol (EG) and 1,4 butanediol (1,4BD). Polybutylene succinate (PBS) is aliphatic polyester with similar properties to those of PET. PBS is produced by condensation of succinic acid and 1,4-butanediol.

PBS is a semicrystalline polyester with a melting point higher than that of PLA. Its mechanical and thermal properties depend on the crystal structure and the degree of crystallinity. The Tg is approximately −32°C, and the melting temperature is approximately 115°C. In comparison with PLA, PBS is tougher in nature but with a lower rigidity and Young’s modulus (Babu et al., 2013)

Biosuccinic acid (SA) is produced directly by fermentation of bioengineered yeast and E. coli. Catalytic hydrogenation of biosuccinic acid produces 1,4 butanediol, which can also be produced by fermentation. Bioethylene glycol is produced from bioethylene, a product of catalytic dehydration of fermentation derived ethanol. Bioadipic acid can be produced by a number of fermentation based processes.

Application: Aliphatic poly(alkylenedicarboxylates) are used in polyurethanes for coatings, adhesives and foams; Flexible packaging; Agricultural films; compostable bags; and in blends and composites with other biobased polymers to enhance properties (Gotro, 2013).

6.3 Bio-Polyamide (Nylon)
Castor oil has been a non-food crop source of biopolymers. Polyamide 11 from castor oil was patented in 1944 by French scientists and from 2004 it is marketed by Arkema as Rilsan for sportwear. Toray and Radici are now marketing another castor oil-derived polyamide, PA 6-10. Sofia launched a hybrid polyamide fiber, Greenfil by texturising 70% synthetic PA 6 and 30% biosourced PA 10. A greenfil sock is 5-10 times stronger, but 2-3 times costlier too (Sofia, 2012).

Bio-polyamides are also a subject of industrial research, e.g. by DuPont with co-polyamides prepared from plant oils, Invista with polyamide terpolymer and Rhodia.

6.4 Bio-polyethylene
Polyethylene (PE) is an important engineering polymer traditionally produced from fossil resources. Bio-based polyethylene has exactly the same chemical, physical, and mechanical properties as petrochemical polyethylene. The sequence for biological method is as follows:

Fermentation of sugarcane/sugar beet/starch crop → bioethanol → distilled at high temperature over a solid catalyst → ethylene → microbial PE or green PE

Bio-polypropylene is at least partially- made from renewable resources using methanol and metathesis chemistry (Bleys, 2015).

6.5 Biodegradable Polyurethanes (PURs)
PURs are known for toughness, durability, biocompatibility, and biostability. Unlike polyester derivatives, polyether-based PURs are quite resistant to degradation by microorganisms. Biodegradable PURs employed as thermoplastics are basically synthesized using a diisocyanate, a diol, and a chain-extension agent. The first representative example avoiding diisocyanate is the reaction between a cyclic carbonate and an amine rendering the urethane bond. In particular, the polyaddition reaction between L-lysine and a bi-functional five-member cyclic carbonate in the presence of a strong base. Some have reported the enzymatic synthesis of PERs by enzymatic polyesterification (Lendlein and Sisson, 2011).

6.6 Polylactic acid (PLA)
PLA is known since 1845 but not commercialized until early 1990. It is the only melt-processable fiber from annually renewable natural resources such as corn starch (in the United States), tapioca products (roots, chips or starch mostly in Asia) or sugar cane (in the rest of world). It is thermoplastic, aliphatic polyester similar to synthetic polyethylene terephthalate (PET). The sequence of manufacture steps is as follows:

Corn → starch → unrefined dextrose → fermentation → D- and L-lactic acid → monomer production → D-, L- and meso-lactides → polymer (PLA) production → polymer modification → fiber, film, plastic, bottle manufacture.

The polymerization reaction is shown in Equation 1.

PLA has high strength, good drape, wrinkle- and UV light- resistance properties. Its melting point is ±170 °C and density is 1.25 g/cm³. The limiting oxygen index is 25 higher than PET and much higher PP. PLA, therefore, possess reduced flammability, less flame retardants. Water uptake is low (0.4 -0.6%) higher than PET and PP. It possesses good durability under a range of conditions.

Not surprisingly a lot of research is still done on the most common biopolymer i.e. polylactic acid (PLA). The research is often focused on improving polymer properties like increasing toughness, crystallinity, impact modification etc. Companies like Metabolix, PURAC, Arkema, Biovation and others are active in this field (Bleys, 2015).

PLA is regarded as the most promising bioplastic. As a result, it has raised particular attention as a potential replacement for petroleum based polymers in many areas such as textiles, bottles, thermoformed containers, paper and cardboard coating. PLA has a low heat resistance unless it can be fully crystallised. However, PLA suffers from low crystallisation kinetics unless it is subjected to high orientations. Hence, increasing the crystallisation rate in processing techniques, such as injection moulding, where orientation levels are relatively low, is required to improve its thermal resistance. One way to improve the crystallisation kinetic is to found out a suitable bioadditives. However, understanding of nucleation and crystallisation mechanisms is required to optimise the crystallisation kinetics and subsequently to identify or develop the best bio-based additives.

Application: woven shirts (ironability), microwavable trays, hot-fill applications and even engineering plastics. Biomedical applications include as sutures, stents, dialysis media and drug delivery devices. PLA can be used for rigid thermoforms, films, labels, and bottles, but not for hot-fill containers or gaseous drinks such as beer or sodas.

6.7 Bacterial Polyesters
One of the most important fields of research are the polyhydroxyalkanoates (PHA) which are biopolymers produced biochemically by genetically modified microorganisms or modified plants. The resulting polymers are often copolymers from 3- and 4- hydroxybutyric acid and/or hydroxyvaleric acid. Companies like Metabolix, and Novomer filed patents on this topic. Using the correct bacteria PHAs can be produced from wastewater as shown in a number of patent applications or from waste fish- or palm oil or from biogas (e.g. from a landfill digesters). PHA can also be produced from glycerol, algae or even aromatic sources. Poly(3-hydroxybutyrate) or PHB can also be produced from transgenic plants. Examples of a plant that can be genetically engineered to produce PHB are grasses like switch grass. These grasses are also studied for the bioethanol production in the US.

The bacterial polyesters, polyhydroxyalkanoates (PHAs) with poly-(R)-3-hydroxybutyrate (P3HB) as the first homologue (Figure 4), produced by microorganisms. Bacterial storage compound polyhydroxybutyrate copolymer (PHBV) named “Biopol” is developed by Zeneca Bioproducts through fermentation of PH3B followed by copolymerisation with PHV. It is high molecular weight polyester and thermoplastic (melts at 1800C) and can be melt spun into biocompatible and biodegradable fibers suitable for surgical use.

Advantages include production from fully renewable resources, fast and complete biodegradability and excellent strength and stiffness. The disadvantages are high thermal degradability, brittleness and high price (Chod´ak, 2009).

6.8 Sodium Alginate Fibre
Sodium alginate is a polymeric acid, composed of two monomer units:

(a) L-guluronic acid (G) (b) D- mannuronic acid (M) (Figure 5)

It is non toxic and non irritant. Alginate fiber generates a moist healing environment and is used for wound dressing. Calcium alginate is created by adding aqueous calcium chloride to aqueous sodium alginate.

6.9 Chitin and chitosan
Both polysaccharides may be regarded as derivatives of cellulose, where chitin bears an acetamido group and chitosan bears a amino group instead of the C-2 hydroxyl group in cellulose (Figure 6).

Chitosan is obtained by deacetylation of chitin. Chitosan is a linear polyamine having reactive amino and hydroxyl groups. It chelates many transitional metal ions. Currently, the commercial source of chitin is shrimp shells. But the polymer also occurs in the shells of crabs and lobsters.

Derivatives of chitin have been used to impart antistatic and soil release finishing to the textiles. While chitin is used in printing and finishing preparations, while chitosan is able to remove dyes from discharge water. Both have remarkable contribution to medical related textile sutures, threads and fibers.

Chitosan, a Million Dollar Natural Polymer, was discovered by Rouget in 1859, is a technologically important polysaccharide biopolymer. Chemically it is composed of glucosamine and N-acetylglucosamine units linked by 1−4 glucosidic bonds. Being nontoxic, biodegradable, biocompatible, and microbe resistant has given it huge potential in a broad range of scientific areas such as biomedical, food, agricultural, cosmetics, textiles, pharmaceutical, and other industries (Raafat et al., 2009).

For shrink resistant finishing enzyme treated woollen fabric was finished with three different finishing polymers and the performance properties of chitosan finished woollen fabric are found to be better than in other finished fabrics. Thermal properties of chitosan finished wool are similar to synthetic polymer finish. Chitosan finish resists the denaturation of wool fiber better than that of other synthetic finishes. Surface morphology of wool fiber shows that masking of cuticle scales by chitosan finish is better than that of other synthetic finishes. Cross-sectional view study infers that chitosan can also be diffused well inside the wool fiber. It is concluded that chitosan based shrink resistant finishing could be preferred over synthetic polymer finish for woollen materials (Lakshmanan et al., 2015).

Increased sustainability, environment friendliness, reduced pollution, green chemistry, renewability and intrinsic biological activity are some of the attributes which make chitosan, cyclodextrin, sericin protein, and alginate suitable alternative agents for the functional finishing of textile materials (Islam, 2013).

Recent bio-polymer related patent literature covers a lot of different types of bio-monomers which can be turned into polymers using classical chemical synthesis. For example, quite some research is be done on bio-based “polymer grade” acrylic acid and methacrylic acid (US patents, US20140206831, US20130165690) which can be produced from bio-derived glycols and polyols like glycerol and sorbitol.

7. Conclusions
Biopolymers are very important in all aspects of medicine, surgery and healthcare and extend of application on which the materials used because of the versatility of biopolymer. Oil is the fuel that drives the global economy, but oil reserves are going down. And there are major concerns about the future because of our great dependency on oil and its impact on the environment.

The global trend towards sustainability, green chemistry and renewable energy and raw materials also has a big impact on the research and development of polymers. A large number of patent applications relating to bio-polymers are being filed, covering an impressive amount of new polymers and monomers. While real-life applications appear to be limited still, this research can be the basis for a strong growth in the near future (Bleys, 2015) .

8. References:

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1. Sustainability in Textile Processing
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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