Non-food industrial applications of poultry feathers.

Waste Management xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

Waste Management journal homepage: www.elsevier.com/locate/wasman

Review

Non-food industrial applications of poultry feathers Narendra Reddy ⇑ Center for Emerging Technologies, Jain University, Jain Global Campus, Jakkasandra Post, Ramanagara District, Bengaluru 562112, India

a r t i c l e

i n f o

Article history: Received 15 January 2015 Accepted 22 May 2015 Available online xxxx Keywords: Feathers Keratin Applications Bioproducts Value addition

a b s t r a c t Poultry feathers are one of the unique coproducts that have versatile applications ranging from composites, fibers, tissue engineering scaffolds, nano and micro particles, electronic devices and many others. Despite their low cost, abundant availability, wide applicability and unique properties, non-food industrial applications of feather keratin are very limited. Poor-thermoplasticity, difficulty in dissolving keratin and limited knowledge on the processability and properties of products developed are some of the limitations for the large scale use of feather/keratin. Nevertheless, increasing interests in using renewable and sustainable raw materials and need to decrease dependence on non-renewable petroleum resources make feathers an attractive raw material for bioproducts. This review provides an overview of the products developed from poultry feathers and their limitations and advantages. Ó 2015 Elsevier Ltd. All rights reserved.

Contents 1. 2.

3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feathers for electrical and electronic applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Electrodes from carbonized feathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Feather composites as dielectric materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Biodegradable PCB boards from feathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feathers as biofertilizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Films from feather keratin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Absorbents from feathers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Composites from poultry feathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. Feathers as reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2. Feathers as matrix for composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flame retardants from feathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Production of keratinases using feathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Micro and nanoparticles from feather keratin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermoplastics from chicken feathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feathers as textile yarn sizing agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Regenerated protein fibers from feather keratin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

⇑ Tel.: +91 80 27577200; fax: +91 80 27577199. E-mail address: [email protected] http://dx.doi.org/10.1016/j.wasman.2015.05.023 0956-053X/Ó 2015 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Reddy, N. Non-food industrial applications of poultry feathers. Waste Management (2015), http://dx.doi.org/10.1016/ j.wasman.2015.05.023

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N. Reddy / Waste Management xxx (2015) xxx–xxx

1. Introduction There is a critical need and increasing interest across the world to decrease the consumption of petroleum based products and to develop bioproducts using renewable and sustainable sources. Many such efforts have already been made and practiced in both the developing and developed countries. For instance, biodegradable polyesters, renewable fuels for automobiles and domestic use and sustainable farming are being aggressively promoted across the globe. Such efforts are necessary to satisfy the food, clothing and other basic needs of the future generations. Since there are limited natural resources, the recent focus is to utilize the agricultural byproducts and coproducts that are inevitably generated, inexpensive and are sustainable and renewable resources to develop bioproducts. Typically, the amount of byproducts generated during agricultural production is equivalent or higher than the amount of produce harvested. For instance, the amount of wheat straw generated (weight basis) is several times higher than the grain harvested. Currently, most of these agricultural residues are either burnt or buried with limited high value applications (Reddy and Yang, 2005; Reddy et al., 2011, 2013a,b). Several research groups have attempted to utilize the agricultural byproducts and coproducts for industrial applications. For example, lignocellulosic agricultural residues such as corn stover, wheat and rice straw have been used to produce natural cellulose fibers and also as feed stock for ethanol (Reddy and Yang, 2005). Similarly, the coproducts such as oil meals obtained during production of biodiesel have been used to extract proteins and carbohydrates for various applications (Reddy et al., 2014a,b). In addition, oil meals have been chemically modified and used as biothermoplastics. Compared to other agricultural coproducts, poultry feathers are one of the most ubiquitous, unique and inexpensive byproducts available across the world. Feathers account for up to 10% of the body weight of the birds which means that about 8–9 million tons of feathers are generated in the world every year (Lasekan et al., 2013). In addition to their low cost and large availability, poultry feathers have distinct and unique properties such as low density, a hollow honey comb structure and hierarchical architecture as seen from Fig. 1. Feathers contain >90% protein in the form of keratin which is useful for various applications. At a density of 0.9 g/cm3, feathers are considerably lighter than natural fibers such as cotton and flax (1.5 g/cm3) and similar to that of synthetic polymers such as polypropylene. At a structural level, feathers consist of quill, barbs and barbules that are arranged in a hierarchical fashion that provides them unique structural properties. Feathers can also be treated as single fibers similar to wool and silk and used for various applications. It has been demonstrated that feather fibers (barbs) can be blended with cotton and made into hand spun yarns (Reddy and Yang, 2007). A typical stress–strain curve for a feather fiber is shown in Fig. 2. Strength of up to 300 MPa and

modulus of up to 6 GPa were obtained for single feathers, better than most wool fibers (Wang et al., 2013). Despite these unique features, feathers are generally considered a waste and either disposed in landfills or used as low value animal feed. For instance, it has been reported that more than 4 billion pounds of feathers generated in the United States every year do not have any industrial application and are disposed in landfills leading to environmental pollution and discarding of a valuable resource (Huda and Yang, 2008). Realizing the unique properties and low cost of feathers, several attempts have been made to understand the potential of using feathers for high value applications. Feather or keratin extracted from feathers have been made into fibers, films, hydrogels, nano

Fig. 2. Typical stress–strain curve of a single feather fiber in chicken. Reproduced from Zhan and Wool (2013) with permission from John Wiley and Sons.

Table 1 Properties of feathers for potential use as electrodes (Wang et al., 2013). BET is Brunauere Emmette Teller method of determining surface area and ESR stands for equivalent standard resistance. % Feather

BET surface area (m2/g)

Micropore surface area (m2/ g)

Total pore volume (cm3/g)

Micropore volume (cm3/g)

Average pore diameter (nm)

ESR (X)

0 1 2 3 4 5

0.568 2426 2126 1.911 1839 1398

– 2096 1838 1191 1575 1020

0.001 0.870 0.788 1.169 1.069 0.922

– 0.856 0.747 0.508 0.850 0.555

– 1.196 1.203 1.506 1.863 1.977

0.86 0.67 2.28 0.97 0.43 0.37

Fig. 1. SEM images of feather revealing the hierarchical architecture (left) and presence of hollow honey combs (right).



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Fig. 3. (a) and (c) Low and (b) and (d) high magnification high-resolution TEM images of unmodified (top) and carbonized (bottom) chicken feathers containing 4% KOH (Wang et al., 2013). Reproduced with permission from Elsevier.

2. Feathers for electrical and electronic applications 2.1. Electrodes from carbonized feathers Feathers have been carbonized and used as electrodes for supercapacitors. The presence of hollow structure and a-helix in feathers coupled with their low cost were considered to be ideal for developing uniform microporous materials with high surface area as electrode materials that are also environmentally friendly (Zhan and Wool, 2011). Feathers were carbonized by heating up to 800 °C and later activated using potassium hydroxide at various

Fig. 4. Relationship between dielectric constant and % of chicken feathers in the feather–epoxy composites (Mishra and Nayak, 2010). Reproduced with permission from Sage Publications.

and micro particles for use in the food, cosmetology, agriculture, textile, composite, medical and other industries. Although researchers have demonstrated the usefulness of feathers for various applications, currently there are no major products or large scale industrial application of feathers. Recently, attempts have been made to dissolve feather keratin and develop regenerated protein fibers and 2D and 3D scaffolds for tissue engineering (Xu et al., 2014a). In this paper, we provide a comprehensive review of the literature available on using feather or feather keratin for non-food industrial applications.

Fig. 5. Dielectric constant of the feather–epoxy composites at various frequencies and amounts of feathers in the composite (Mishra and Nayak, 2010). Reproduced with permission from Sage Publications.


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Table 2 Electrical properties of the maleic anhydride modified (MACFF) and unmodified feather-epoxy composites (CFF). Reproduced from Kiew et al. (2013). Composite

Fiber (%)

Dielectric constant Frequency (kHz)

Dissipation factor, tan D Frequency (kHz)

1

10

100

1000

1

10

100

1000

CFF

0 10 20 30 40

1.823 1.894 1.962 2.055 2.126

1.799 1.844 1.88 1.918 1.969

1.754 1.812 1.835 1.872 1.887

1.712 1.753 1.774 1.798 1.809

0.0112 0.0495 0.0639 0.0693 0.0736

0.0114 0.0277 0.0318 0.0352 0.0393

0.0137 0.0229 0.0252 0.0292 0.03

0.0175 0.0203 0.0234 0.0271 0.03030

MACFF

0 10 20 30 40

1.854 2.048 2.286 3.518 9.654

1.821 1.916 2.14 2.548 5.189

1.786 1.819 1.962 2.207 3.621

1.737 1.732 1.842 2.003 2.838

0.0147 0.0808 0.133 0.27 0.511

0.0148 0.047 0.0752 0.137 0.3556

0.015 0.0344 0.0502 0.086 0.225

0.0187 0.0315 0.0404 0.0617 0.14

ratios. Further, the carbonized feathers were added into acetylene black and polyvinylidene fluoride (PVDF) that was dissolved in N-methyl pyrrolidinone solution and pressed into steel mesh of 1 square centimeter and thickness of 0.2 mm. Pore size of the electrode varied from 1.2 to 3.75 nm and specific surface area was about 1454–2385 M2/g depending on the level of etching with potassium hydroxide (KOH). Table 1 provides some of the properties of the feather based electrode developed and transmission electron microscopy (TEM) image (Fig. 3) depicts the porous morphology of the electrode. A highest specific capacitance of 302 F/g at 1 A/g was obtained but the capacitance stabilized at 253 F/g after 5000 cycles. Similarly, the highest energy density achieved was 7.98 W h/kg, higher than current electrodes used in supercapacitors. The excellent performance of the feather based supercapacitor was attributed to the presence of hollow pores that could act as reservoirs for electrolytes and facilitate ion transport during high speed charge/discharge.

2.2. Feather composites as dielectric materials

Fig. 6. Changes in the dielectric constant and loss tangent of the biodegradable PCBs at various frequencies (Zhan and Wool, 2013). Reproduced with permission from Elsevier.

Dielectric materials are used in various applications including insulation, encapsulation, printed circuit boards, capacitors and other devices. Air is considered to be an ideal dielectric material with a minimum dielectric constant of 1 since it offers no resistance. However, there are very few dielectric materials in current use that have a dielectric constant close to 1. Since feathers contain hollow structures, it was supposed that composites fabricated from feathers could be useful as dielectric materials. Feathers in various ratios were mixed with epoxy and the mechanical and dielectric properties of the composites were measured (Mishra and Nayak, 2010). Increasing the amount of feathers in the composite from 5% to 30% increased flexural strength but decreased hardness. The dielectric constant of the feathers was also found to depend on the amount of feathers as seen from Figs. 4 and 5. A dielectric constant between 4.5 and 1.7 was obtained depending on the amount of the feathers in the composites. Dielectric constant decreased with increasing feather content due to higher moisture levels and hollow structures in the composites. Temperature of the composite was also found to significantly influence the dielectric constants. Dielectric constants of the feather based composites were lower than that of conventional semiconductor insulators such as silicon dioxide, epoxies and polyimides. In addition to the low dielectric constant, feather composites were light weight and rigid and therefore highly suited for electrical applications (Mishra and Nayak, 2010). In another study, feathers were combined with glass fibers and epoxy to develop composites for electrical applications. Similar to the results from the work of Mishra and Nayak, increasing concentration of fibers and frequency decreased fiber content. Hybrid composites had a dielectric

constant of 4.1 and a loss factor of 0.027 lower than that of commercially available EPON/7628 material but much higher than the ideal dielectric constant of 1.0 (Zhan and Wool, 2013). Instead of using epoxy matrix, unsaturated polyesters with and without modification with maleic anhydride were used as matrix (Table 2) and chicken feathers (up to 40%) were reinforcement to prepare composites for electrical applications. As with the epoxy composites, resistivity of the polyester–feather composites decreased with increasing ratios of feathers due to the increase in polar groups in the feathers (Kiew et al., 2013). Table 2 provides the dielectric constant and dissipation factor of the modified and unmodified polyester composites. Contrary to the data reported by other researchers, the dielectric constant was found to increase with increasing feather content. It was suggested that better transportation of charges between the polyester matrix and increase in void content were responsible for the increase in dielectric constant. Morphological studies using scanning electron microscopes showed good interfacial bonding between maleic anhydride and the feathers and the bonding was further increased after chemical modification. Composites containing 10% feathers had permittivity of 1.753 and dissipation factor (tan delta) of 0.0203 at 1000 kHz, similar to that of commercial insulation material (Kiew et al., 2013). In another study by the same authors, the dielectric properties of composites made from unsaturated polyesters and reinforced with feather fibers and kenaf fibers were investigated. As observed in previous studies, the amount of feathers and frequency of measurement influenced the dielectric constant and dissipation factor of the composites (Kiew et al., 2013). Generally, increasing



Fig. 7. Amino acid content of the feather hydrolysate obtained using mixed cultures (Gousterova et al., 2012). Concentration of the microbial population in the mixed culture varied from 7 to 33 106 cfu per gram of soil. Reproduced with permission from University of Tehran.

either feather or kenaf fiber content increased the dielectric constant, loss factor and dissipation factor of the composites. A dielectric constant of 2.02 and loss tangent of 0.0252 were obtained at frequency of 1 MHz under the optimized conditions. However, the dielectric constant (2.02) obtained in this research was considerably higher than the ideal dielectric constant of 1.0. 2.3. Biodegradable PCB boards from feathers Printed circuit boards (PCBs) are one of the most common components of electronic waste. PCBs currently used are typically

Fig. 8. Seed germination (%) (top) and grass height (bottom) of rye grass seeds before and after treating the soil with the feather hydrolysate as fertilizer (Gousterova et al., 2012). Two types of soil (park soil (V) and anthropogenic soil (B) were used at different levels (0 indicates no hydrolysate, and 1, 2 and 3 represent 0.06 ml, 0.09 ml and 0.12 ml) of hydrolysate per gram of soil, respectively). Reproduced with permission from University of Tehran.

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made from glass fiber reinforced plastics and are therefore non-biodegradable. In an effort to develop biodegradable PCBs, various concentrations of feathers were mixed with soybean oil based resins and the composites obtained were studied as potential printed circuit boards (Zhan and Wool, 2013). Soybean oil was phthalated and then mixed with styrenebutadine to form a resin. To develop the boards, the modified soy resin was mixed with e-glass fibers and feathers (30%) and the mixture was compression molded into composites with a layer of copper sheet on one side and an antiflamming agent on the other. Printed circuit boards were made from the composites by etching the copper and removing unpolymerized portions with sodium hydroxide. The dielectric properties and loss tangent of the printed circuit boards is shown in Fig. 6. Volume and surface resistivity was in the order of 1015 considered to be good for PCBs (Zhan and Wool, 2013).

3. Feathers as biofertilizers The inexpensiveness and presence of high amounts of nitrogen in feathers is considered to be ideal for use as fertilizer. However, feathers are highly crosslinked with cysteine linkages and difficult to degrade. Therefore, the availability of nitrogen from the feathers as fertilizer is considerably low (Gurav and Jadhav, 2013; Hadas and Kautsky, 1994). To improve the release of nitrogen, feathers were degraded using Chryseobacterium sp. Degraded feathers were used as a fertilizer for banana plants and applied as 20% root dose and 5% shoot dose every 15 days. Inclusion of hydrolyzed feather as fertilizer increased chlorophyll content to 1.43 mg/g compared to 0.89 mg/g for the control plants which did not use feather as fertilizer. Similarly, the protein content in the banana fruits increased to 16 mg/g compared to 15.1 mg/g for the control and amino acids increased to 2.96 mg/g compared to 2.0 mg/g. Similar improvements were also observed in the vegetative tissue. It was concluded that hydrolyzed feather could be an inexpensive and efficient fertilizer for banana plants (Gurav and Jadhav, 2013). Feather waste was treated with thermophilic actinomycete strains and used to restore contaminated soil and also as a fertilizer for rye grass cultivation (Gousterova et al., 2012). Amino acid content of the feather hydrolysate is shown in Fig. 7. Seed germination and dynamics of growth were found to be higher in plants where the feather hydrolysate was used as fertilizer as seen from Fig. 8a and b even at a low concentration (0.06 ml/g of soil) of hydrolysate. It was suggested that feather hydrolysate could be used a biocontrol agent and also as a fertilizer.

Fig. 9. Effect of sodium sulfide (Na2S) concentration and solubilization time on the % yield of keratin when the extraction was done at 30 °C (Poole et al., 2011). Reproduced with permission from Springer.


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Table 3 Tensile properties of keratin films obtained after various extraction conditions using sodium dodecyl sulfate (SDS) and mercaptoethanol (ME) (Poole et al., 2011; Schrooyen et al., 2001; Moore et al., 2006; Taylor et al., 2004; Acar and Harper, 2000; http://www.ecfibreglasssupplies.co.uk/t-GlassReinforcedPlastics. aspx; http:// www.aoc-resins.com/images/uploads/lit_ecoteck_greenresins.pdf). Sample

Films 0.5 h Films 1.0 h Films 6 h Films 24 h Films 1 h + SDS Raw feather Films-2 ME Films- 2 ME + SDS Polyester resin

Modulus (MPa)

Strength (MPa)

Elongation (%)

Dry

Wet

Dry

Wet

Dry

Wet

1241 1568 990 – 1225 2580 1344 10 4000

121 95 23 17 73 1470 – – –

46 61 37 – 48 130 30 17 45

8 6 3 2 5 106 – – –

7 7 5 – 5 10.4 3 2 2

8 10 17 15 15 16.3 – – –

4. Films from feather keratin One of the major limitations in using feathers for industrial applications is the difficulty in dissolving feather or feather keratin and developing products. Films have been widely used in food, biotechnology, thermoplastic, packaging and other applications. Conventionally, feathers have been hydrolyzed using alkali and used to develop films and other products. However, hydrolyzing feathers decreases the molecular weight considerably resulting in products with poor mechanical properties and stability in aqueous conditions (Xu et al., 2014a). In a novel approach to prevent hydrolysis and preserve the properties of keratin, feather keratin was extracted using a three-step process that involved deoxidation with 2-mercaptoethanol as the first step (Yin et al., 2013a). Later, the extracted keratin was modified with chloroacetic acid that made the keratin dispersible in aqueous solutions. Films were cast from the keratin dispersion after adding glycerol as the plasticizer (Yin et al., 2013a). Tensile strength of the films varied from 4.5 to 7.5 MPa and modulus from 11 to 28 MPa depending on the amount of glycerol (Yin et al., 2013a). In another study, a simple and inexpensive method of dissolving keratin and producing films was developed by Poole et al. (2011) that could overcome the limitation of using mercaptoethanol or ionic liquids. In this approach, sodium sulfide was used to dissolve feathers and develop regenerated protein films. Feathers were ground to 3.2 mm diameter and were later incubated with sodium sulfide at 30 °C for up to 24 h and the extent of digestion and properties of proteins obtained were studied. Fig. 9 shows the yield of feathers after various digestion times (solubilization) using different concentrations of sodium sulfide. Properties of the keratin films obtained using various dissolution conditions are listed in Table 3. Films obtained after 1 h of digestion had the highest tensile properties and were

reported to be similar to that of films made from industrial polyester resin but considerably lower than that of native feathers. As with most biopolymeric films, the wet strength of the feather films decreased considerably and was only about 10% of the dry strength. Keratin extracted from feather was ground into particles with size between 30–80 lm and used as an additive for polyhydroxybutyrate (PHBV, a synthetic biopolymer that is biodegradable and used in medical, packaging and other applications) films containing 12% of valerate and 10% citric ester to improve performance properties. Inclusion of the additive decreased the transparency of the films but increased water permeability and limonene permeability considerably but oxygen permeability to a limited extent (Table 4). As expected, elastic modulus increased but elongation decreased when the reinforcement was included in the films. Ability to increase the water, limonene, oxygen permeability and elastic modulus even with the addition of low levels of keratin was considered to be ideally suited for food packaging applications (Pardo-Ibanez et al., 2014). Films for controlled drug release applications were developed from keratin extracted from chicken feathers (90% yield) that had a molecular weight of 20 kDa (Yin et al., 2013a,b). Extracted keratin was dispersed in water, glycerol was added as plasticizer and films were obtained by casting. Amino acid composition of the extracted keratin is shown in Table 5. Alanine and cysteine form the major constituents which mean that the films can be expected to have good mechanical properties due to the large amounts of cysteine linkages. Highest strength of the films was 7.6 MPa and modulus was 27.6 MPa but elongation was high at 111% due to the addition of glycerol. Rhodamine B loaded as a model drug showed an initial burst release followed by a sustained slow release (Fig. 10). Release of the drug was considerably quicker at pH 7.5 with 94% of the drug being released within 12 h. Keratin films were considered to be biocompatible and suitable for various medical applications (Yin et al., 2013a,b). Biocompatibility and use of feather based films for tissue engineering has been proven by many researchers. Feathers grafted with acrylates were compression molded to form films and the grafted films were shown to have excellent biocompatibility and ability to support the attachment and proliferation of fibroblasts (Reddy et al., 2013). Attachment and proliferation of NIH3T3 cells was found to be considerably higher on the grafted feather films compared to films made from the biodegradable synthetic polymer poly(lactic acid) as depicted in Fig. 11. Better cell attachment and proliferation was suggested to be due to the hydrophilic nature of the films, lower modulus and presence of specific cell adhesion sequences in keratin (Reddy et al., 2013). 5. Absorbents from feathers Keratin was extracted from pigeon feathers and made into porous sponges (Fig. 12) for absorption of oil. To prepare the

Table 4 Permeability of the PHBV films containing various levels of keratin to water, limonene and oxygen (Pardo-Ibanez et al., 2014). Sample

Water permeability (1015) (kg m/s m3 Pa)

Limonene permeability (1015) (kg m/s m3 Pa)

80% RH oxygen permeability (m3 m/(m2 s Pa)

0% keratin 0.5% keratin 1% keratin 3% keratin 5% keratin 10% keratin 25% keratin 50% keratin PHBV12 casting

7.4 ± 0.6 7.8 ± 0.3 3.1 ± 0.0 7.9 ± 0.4 7.4 ± 0.6 9.0 ± 2.0 20.0 ± 2.0 62.0 ± 16.0 13.0 ± 0.1

8.3 ± 1.1 9.0 ± 2.6 3.7 ± 0.3 8.3 ± 0.5 8.4 ± 0.6 9.5 ± 5.3 8.0 ± 1.1 22.7 ± 2.3 1.3 ± 0.1

3.0 ± 0.1 3.1 ± 0.4 1.0 ± 0.2 2.6 ± 0.1 3.2 ± 0.5 – – – 1.4 ± 0.0


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N. Reddy / Waste Management xxx (2015) xxx–xxx Table 5 Amino acid composition of the keratin extracted from feathers (Yin et al., 2013a,b). Amino acid

% (mol)

Alanine Cysteine Proline Serine Glutamine Leucine Glycine Valine Aspragine Arginine Threonine Isoleucine Phenyalanine Tyrosine Lysine Histadine Methonine

29.54 14.42 10.12 6.98 5.58 5.07 4.75 4.26 3.97 3.7 3.62 3.29 2.55 1.16 0.66 0.19 0.13

sponges, feathers were dissolved using sodium metabisulfite, surfactant and urea (Zhou et al., 2014). The feather solution was heated from 30 to 100 °C for up to 45 min to obtain the reduced keratin. Extracted keratin was diluted and lyophilized to obtain the sponges. Regenerated keratin yields were between 74% and 77%. Surface analysis of the sponge revealed that the surface area was 114 m2/g and pore volume was 1.01 cm3/g. An adsorption capacity of up to 39% and holding capacity of 79% were obtained and it was suggested that the sponges could be useful to clean up oil spills (Table 6) (Zhou et al., 2014). In a similar approach, feather keratin was used as bioabsorbent to remove arsenic. Feathers were ground into fine powder and later treated with three different chemicals (aqueous alkali, sodium sulfite and methyl alcohol) to modify the carboxyl, sulfydryl and amino groups, respectively (Khosa et al., 2013). Prepared bioabsorbent (1 g) was added into known concentration of arsenic solution and the absorption capacity and thermodynamics and kinetics of absorption were studied. Fig. 13 shows the absorption of arsenic by the unmodified and modified feather keratin at various pHs. Feathers modified with methyl alcohol showed substantially higher arsenic up take and the absorption was higher at pH 4 compared to pH 7 or 14 for the modified and unmodified feathers. SEM images showed destruction of the native structure and formation of a smooth surface after treating with methyl alcohol. The smooth surface and heterogenous microstructure developed after treatment was considered to be responsible for the higher arsenic sorption (Khosa et al., 2013). SEM images in Fig. 14 show the deposition of arsenic on the feather fibers.

a

Fig. 11. Optical densities demonstrating the attachment (4 h) and proliferation (4 days) of cells on the feather scaffolds compared to PLA. Lower section (c and d) shows the corresponding confocal images of the attachment and proliferation (Reddy et al., 2013). Reproduced with permission from Elsevier.

Keratin was extracted from chicken feathers by treating with alkali and dialyzing the reduced proteins. Proteins were mixed with gelatin in various ratios and with sorbitol and cinnamaldehyde as the crosslinking agent before forming into films (Song et al., 2014). Tensile properties, water stability and antioxidant and lipid oxidation properties were investigated to evaluate the potential of using the films for salmon packaging. Table 7 provides some of the properties of the films developed. Films with strength

b

Fig. 10. Release of Rhodamine B from the keratin films (Yin et al., 2013a,b) at different time intervals (a) and pHs (b). Reproduced with permission from Royal Society of Chemistry.


8


Table 6 Capacity of regenerated keratin sponge to absorb and hold oil (Zhou et al., 2014). Test oil sample

Wo (g)

Ws (g)

Wf (g)

Adsorption capacity (g/g)

Oil holding capacity (%)

Liquid paraffin

0.04 0.06 0.03 0.07

1.33 2.38 1.09 2.36

1.05 1.88 0.86 1.86

32.25 38.66 35.33 32.70

78.95 78.99 78.89 78.81

Soybean oil

Fig. 12. Digital image of a keratin sponge (Zhou et al., 2014). Reproduced with permission from Springer. Fig. 14. SEM image of the feather fibers shows the deposition of arsenic on their surface (Zhou et al., 2014). Reproduced with permission from Royal Society of Chemistry.

6. Composites from poultry feathers 6.1. Feathers as reinforcement

Fig. 13. Absorption of arsenic by the modified and unmodified feather keratin at different pH values and 20 °C (Khosa et al., 2013). Reproduced with permission from Royal Society of Chemistry.

as high as 15 MPa and excellent elongation of 98% were obtained. More importantly, the films were stable and only had a weight loss of about 29% after immersing in 25 °C water for 24 h due to effective crosslinking by cinnamaldehyde (Song et al., 2014). Similarly, incorporating clove oil as plasticizer in the films decreased strength but increased elongation and resistance to water (Table 8). However, presence of clove oil was found to increase the antimicrobial activity for Escherichia coli and Listeria monocytogenes. Since the films developed had good antimicrobial activity, the potential of using the films for packaging salmon was studied. As seen from Table 9, adding clove oil inhibited the proliferation of both the microorganisms on the salmon.

One of the most common applications of feathers is to develop biocomposites using feathers in various forms as reinforcement and also as matrix. In one such approach, feathers were separated into long fibers, short fibers and powdered quill. Completely degradable biocomposites were prepared using chitosan–starch as matrix and feather components as reinforcement. Chitosan and starch were separately dissolved and feather components were added in 5–20% (w/w). The mixture was poured into glass plates and the solvents evaporated to obtain films (Flores-Hernandez et al., 2014). Figs. 15–17 show digital and corresponding SEM images of the films obtained using various forms of feathers as reinforcement in 5% (a), 10% (b), 15% (c) and 20% (d) weight ratios. SEM images revealed some interaction between the matrix and reinforcement which was also confirmed by FTIR studies (Flores-Hernandez et al., 2014). Storage modulus (295–1142 MPa) of the composites increased considerably with the addition of the feathers with short fibers providing the highest modulus 1142 MPa followed by the particles and the long fibers (527 MPa). Although films with some interaction between matrix and reinforcement and good modulus were obtained, the stability of the films at high humidity or in aqueous conditions were not studied. Since biopolymers were used as both matrix and reinforcement and no crosslinking was done, it is highly unlikely that the films would have good stability under aqueous conditions or at high humidities. Studies on developing composites using feathers have mostly been restricted to studying the mechanical and thermal behavior


9

N. Reddy / Waste Management xxx (2015) xxx–xxx Table 7 Properties of the films containing various amounts of feathers and gelatin (Song et al., 2014). Feather (g)

Gelatin (g)

Strength (MPa)

Elongation (%)

Water vapor permeability (109 g m/m2 s Pa)

Moisture content (%)

Water solubility (%)

5 4.5 4.0 3.5 3.0

0.0 0.5 1.0 1.5 2.0

1.35 ± 0.07 2.40 ± 0.13 5.20 ± 0.99 7.63 ± 0.20 15.3 ± 0.75

22.1 ± 1.06 158 ± 23 121 ± 17 100 ± 32 99 ± 16

2.67 ± 0.02 2.58 ± 0.01 2.55 ± 0.07 2.36 ± 0.04 2.13 ± 0.17

10.8 ± 0.4 10.1 ± 0.1 10.2 ± 0.6 9.5 ± 1.1 9.0 ± 1.4

100 ± 0.0 100 ± 0.0 83.5 ± 1.6 77.1 ± 2.3 71.7 ± 1.5

Table 8 Influence of clove oil on the tensile properties and permeability of the feather films (Song et al., 2014). Clove oil (g)

Strength (MPa)

Elongation (%)

Water vapor permeability (109 g m/ m2 s Pa)

Moisture content (%)

Water solubility (%)

0.0 0.5 1.0 1.5

29.4 ± 0.2 15.9 ± 0.2 15.3 ± 1.9 15.6 ± 0.8

44.1 ± 5.2 46.3 ± 8.0 46.3 ± 1.5 53.6 ± 5.5

2.3 ± 0.1 2.3 ± 0.1 2.5 ± 0.1 2.5 ± 0.3

10.2 ± 0.4 10.2 ± 1.1 10.3 ± 0.2 10.4 ± 0.7

61.0 ± 0.1 72.4 ± 0.3 73.9 ± 1.6 74.1 ± 0.9

Table 9 Antimicrobial activity of keratin films containing clove oil (Song et al., 2014). Zone of inhibition Clove oil (g)

E. coli o157:H7

L. monocytogenes

0 0.5 1.0 1.5

13.5 ± 0.3 13.6 ± 0.1 20.0 ± 0.1 22.2 ± 0.3

12.6 ± 0.7 16.5 ± 0.1 22.0 ± 0.3 26.7 ± 0.6

of the composites under standard atmospheric conditions. However, understanding the performance of the feather based composites in outdoor environments should be done to determine suitable applications. In one such attempt, feather fibers were mixed with low density polyethylene (LDPE) in 5 and 10 wt% in an extruder and later compression molded to form thin composite sheets (Spiridon et al., 2012). To evaluate the aging behavior of the composites, the composites were exposed to artificial light from a mercury lamp (200–700 nm wave length) and incident light intensity of 39 mW/cm2 at a temperature of 40 °C and humidity of 60% for up to 100 h. Fig. 18 shows the changes in the impact strength and Young’s modulus of the composites after various levels of exposure. As seen from the figure, the feather reinforced

composites generally have lower impact strength but higher modulus after various exposure times. Increasing the concentration of the feathers did not show any major change in the impact strength but the modulus increased substantially compared to pure LDPE. Oxygen barrier properties of the films also increased with the addition of feathers (Table 10). Interestingly, the oxygen barrier properties increased only after exposure to weathering for 500 h due to the higher mobility of the polymer chains after exposure (Spiridon et al., 2012). Since feathers are inherently hydrophilic, they have poor compatibility between the common hydrophobic synthetic matrix materials used. Different types of chemical modifications and addition of compatibilizers are done to improve the adhesion and enhance the properties of feather reinforced composites. Feathers were initially treated with sodium hydroxide and later with 3-aminopropyltriethoxysilane (APS) as the coupling agent. APS was reported to form hydrogen bonds with COO sites and improve adhesion with poly(lactic acid) used as the matrix. Similarly, feathers were also treated with maleinized polybutadiene rubber as an impact modifier. Treated and untreated feathers were mixed with PLA and converted into pellets using a twin screw extruder. Pellets were later compression molded to form the composites (Huda et al., 2012). Fig. 19 shows the flexural properties of the composites. It can be observed that the modifications done significantly improved the flexural strength and modulus (Huda et al., 2012). Similar results were also obtained for tensile strength and modulus (Fig. 20). SEM images clearly showed increased interfacial shear strength and good interfacial adhesion between fibers and matrix (Huda et al., 2012). Although the surface modifications improved tensile and flexural properties, the ability of the composites to withstand high humidities or aqueous conditions were not reported. Epoxidised soybean oil was reinforced with pyrolyzed chicken feather fibers and methacrylated lauric acid (MLAU) as a diluent and the effect of pyrolysis and amount of feather fibers on the

Fig. 15. Digital and SEM images of chitosan-starch films reinforced with various levels (5% – A), 10% – B, 15% – C and 20% – D of short keratin biofibers (Flores-Hernandez et al., 2014). Reproduced with permission from Multidisciplinary Digital Publishing Institute.


10


Fig. 16. Digital and SEM images of chitosan-starch films reinforced with various levels (5% – A), 10% – B, 15% – C and 20% – D of ground quill (Flores-Hernandez et al., 2014). Reproduced with permission from Multidisciplinary Digital Publishing Institute.

Fig. 17. Digital and SEM images of chitosan-starch films reinforced with various levels (5% – A), 10% – B, 15% – C and 20% – D of long feather fibers (Flores-Hernandez et al., 2014). Reproduced with permission from Multidisciplinary Digital Publishing Institute.

Fig. 18. Impact strength and Young’s modulus of LDPE composites reinforced with feather fibers and compression molded into sheets. Reproduced from (Spiridon et al., 2012) with permission from American Chemical Society.

tensile and flexural properties of the composites was investigated by Senoz et al. (2013). Table 11 shows the tensile properties of the composites containing various levels of feather fibers. Addition of the pyrolyzed feathers significantly increased the tensile properties and facilitated using liquid molding techniques to

be employed for composite fabrication without causing any degradation of the feathers (Senoz et al., 2013). In a simple approach, feathers ground to 0.1–0.0053 cm were mixed (20%) with polyethylene (HDPE) in a twin screw extruder and then compression molded to form composites. Fig. 21 shows


11

N. Reddy / Waste Management xxx (2015) xxx–xxx Table 10 Comparison of the permeability of the HDPE samples with feather samples. Sample

LDPE F1 F2

Oxygen permeability (cm3 mm/m2 (24 h) bar)

Oxygen transfer rate (cm3 mm/m2 (24 h) bar)

Normal

500 h

Normal

500 h

210 220 234

256 274 305

742 749 799

795 814 1114

Table 11 Influence of fiber content and type on the energy absorption and stress and strain of soybean oil feather composites (Senoz et al., 2013). Fiber type

Fiber content (%)

Energy absorption (kJ m2)

Stress (MPa)

Strain

Pure matrix Untreated Untreated PCFF-1 PCFF-1 PCFF-1 PCFF-1 PCFF-3

0 5 32 5 8 19 32 5

0.600 2.202 6.966 1.377 2.733 4.260 7.566 1.243

0.5 1.86 5.30 1.27 2.18 3.73 6.22 1.46

0.051 0.055 0.048 0.049 0.057 0.053 0.052 0.036

Fig. 21. Digital images of pure HDPE and HDPE reinforced with 20% of 0.1 cm long feathers (Barone et al., 2005). Reproduced with permission from Elsevier.

Fig. 19. Flexural properties of PLA matrix reinforced with unmodified and feathers modified using various chemical treatments (Huda et al., 2012). FPF is untreated poultry feather, FPFNA is alkali treated FPF, FPFSIL is silane treated FPF and FPFR is maleinized polybutadiene rubber treated FPF. Reproduced with permission from John Wiley and Sons.

Fig. 20. Tensile properties of PLA matrix reinforced with unmodified and feathers modified using various chemical treatments (Huda et al., 2012). FPF is untreated poultry feather, FPFNA is alkali treated FPF, FPFSIL is silane treated FPF and FPFR is maleinized polybutadiene rubber treated FPF Reproduced with permission from John Wiley and Sons.

digital images of the pure polyethylene and feather fiber reinforced composites. Modulus and peak stress were influenced by the compounding temperature and conditions used for composite fabrication (Barone et al., 2005). Feather fibers were also used to reinforce polymethylmethacrylate (PMMA) through bulk polymerization and the tensile and flexural properties were investigated (Martínez-Hernández et al., 2007). Fig. 22 shows an optical image of the composite developed revealing the presence of intact feather fibers. Feathers in the composites could increase the modulus but decreased the flexibility of

the composites. Obtaining uniform distribution of the feathers during bulk polymerization may also be difficult and hence properties of the composites may be inferior compared to composites containing uniformly distributed fibers (Martínez-Hernández et al., 2007). Table 12 shows the properties of the feather reinforced (1–5 wt%) PMMA composite. Addition of low levels (1–2%) of feathers increases the tensile properties as seen from the table. Additional properties such as flexural and tensile properties and the stability of the composites at various atmospheric conditions should be known to identify suitable applications for the composites. Most of the studies on developing composites from feathers have used traditional synthetic polymers such as polyethylene or polypropylene as matrix which makes the composites partially degradable. Using biodegradable synthetic polymers such as poly(lactic acid) as matrix will provide completely degradable composites. Several researchers have used this approach to develop biocomposites. In one such attempt, various ratios of feather fibers and poly(lactic acid) were mixed and extruded in a twin screw extruder in the form of dumbbell shaped specimens suitable for testing (Cheng et al., 2009). Tensile properties of the composites containing various levels of feathers (Fig. 23) Show that increasing feather content decreased the tensile strength but modulus slightly increased. Elongation of the composites increased substantially when the feather content was 2% or 4% but decreased at higher levels of feathers in the composites. Thermal behavior of

Table 12 Storage (E0 ) and loss modulus (E00 ) of the PMMA-feather composites at various conditions (Martínez-Hernández et al., 2007). Composite

E0 at 35 °C (MPa)

E0 at 80 °C (MPa)

E00 at 35 °C (MPa)

E00 Max (MPa)

0 1 2 3 4 5

1926 2076 2029 1860 1755 1725

258 931 620 633 988 757

137 159 149 140 134 127

259 274 288 270 218 219


12


Fig. 22. Optical image of feather and PMMA composite reveals the presence of long lengths of fibers (Martínez-Hernández et al., 2007). Reproduced with permission from Elsevier.

the composites was found to increase with the addition of feathers. Composites containing 5% feathers had fracture surfaces that revealed broken fibers instead of pull-out suggesting that the matrix and reinforcement had good compatibility (Cheng et al., 2009). Conventional approach of fabricating composites using compression or injection molding results in consolidated composites that have high density. In such composites, feather will also be compressed and the inherent properties of the feathers such as hollow structures related to high sound absorption cannot be realized. To obtain light-weight composites with good sound absorption properties, a new technique of composite fabrication was developed by Huda and Yang (2008,2009). In their approach, feather fibers were placed between non-woven mats made of high-density polyethylene/polypropylene sheath/core fibers. Similarly, quill portion of the feathers was powdered and mixed with the HDPE/PP fibers. The matrix and reinforcing fibers were

thoroughly mixed and compressed to form the composites. Spacers were used between the platens of the composite press to control the thickness and density of the composites. Use of spacers avoids consolidation of the matrix and reinforcement and results in light-weight low density composites. A comparison of the composites obtained using feather fibers and quill in comparison to jute fibers is shown in Table 13. It should be noted that the density of the composites due to the presence of hollow honey comb structure was considerably low compared to the consolidated composites manufactured by other researchers. The noise reduction co-efficients for the feather reinforced composites was considerably higher than the jute composites. Such light-weight composites with good tensile properties and high sound absorption properties would be ideal for automotive applications. Properties of the composites were dependent on the void content that was related to the thickness, density and amount of feathers in the composites. However, the stability of the composites and tensile and flexural properties at high humidities or in aqueous conditions were not reported (Huda and Yang, 2008, 2009).

6.2. Feathers as matrix for composites Above discussions on developing composites using feathers have concentrated on using feathers as reinforcement. Since feathers contain >90% proteins, it should be possible to melt and use feathers as matrix. However, the high level of crosslinking in feathers and the resulting poor thermoplasticity makes it difficult to melt and process feathers to develop products. One approach of using feathers as matrix is to chemically modify the feathers and make them thermoplastic. For instance, feathers grafted with acrylic monomers are thermoplastic and could be used as matrix. However, grafting or other modifications would add to the cost and also decrease the biodegradability of the feathers. In a simple approach, it has been demonstrated that feathers could be used as matrix for composites after adding 5% of glycerol into powdered feather and compression molding between 205 and 215 °C

Fig. 23. Tensile properties of feather fiber-PLA composites containing various amounts of feathers (Cheng et al., 2009). Reproduced with permission from Elsevier.


13

N. Reddy / Waste Management xxx (2015) xxx–xxx Table 13 Comparison of the optimized properties of the feather and quill composites with jute reinforced composites (Huda and Yang, 2008, 2009). Composite

Thickness (mm)

Density (g cm3)

Flexural strength (MPa)

Modulus of Elasticity (MPa)

Impact resistance (J m1)

Noise reduction coefficient

Feather fiber Feather fiber Quill Jute

4.2 3.2 3.2 3.2

0.36 0.47 0.47 0.47

4.2 ± 0.2 5.6 ± 0.7 9.8 ± 1.0 9.0 ± 0.8

380 ± 31 548 ± 82 805 ± 48 1315 ± 42

41 ± 7.6 30 ± 4.1 56 ± 5.0 82 ± 5.0

0.17 0.09 0.11 0.04

and was used to treat cotton fabrics and evaluate the potential of flame retardancy imparted in comparison to commercially used flame retardants. Table 14 shows the composition of the feather based flame retardant and Table 15 provides the flame retardant properties of the cotton fabrics. As seen from the tables, considerably high flame retardancy was imparted to the fabrics after treating with the feather based flame retardant (Wang et al., 2014a,b). Concentration of the flame retardant also influenced the ability to contain the flames as seen from Table 16. It was suggested that feathers combined with borax and boric acid had the properties necessary for use as flame retardants. 8. Production of keratinases using feathers

Fig. 24. Tensile (24a top) and flexural strength (24b bottom) of the feather-jute composites in comparison to PP–jute composites at standard conditions and also after conditioning for 24 and 48 h at 90% humidity (Reddy et al., 2013).

(Reddy et al., 2013). Fig. 24 shows the tensile (24a) and flexural strength (24b) of the composites developed using feathers as matrix in comparison to composites made using polypropylene as matrix. Feather–jute composites had similar tensile strength but considerably higher flexural strength than the PP–jute composites under standard atmospheric conditions. Since feathers are hydrophilic and addition of glycerol increases the hydrophilicity and the composites absorb considerable amounts of moisture, both the tensile and flexural strength of the composites show considerable decrease after conditioning at 21 °C and 90% humidity for 24 or 48 h.

Keratinases are enzymes that find application in leather industry for de-hairing, as fertilizer, feed, detergent, and other biomedical and pharmaceutical applications. Poultry feathers have been used as substrates to produce inexpensive keratinases (Balakumar et al., 2013). Keratinase was produced by treating feathers with ammonium chloride (NH4Cl), sodium chloride and potassium phosphate for 3 days and the effect of pH, temperature and carbon and nitrogen source on keratinase production was studied. Maximum keratinase activity was obtained between pH 7 and 8 and maltose and ammonium nitrate were found to be most suitable supplements for obtaining keratinase (Balakumar et al., 2013). In addition to the changes in the keratinase production, it was found that the amino acid content also varied. For instance, addition of sugars decreased amino acid production and mannitol had significantly higher production of amino acid compared to glucose (Fig. 25). A pH of 8, temperature of 35 °C and feather concentration of 2% were ideal to obtain amino acid levels at 180 lg/ml, 148 lg/ml and 194 lg/ml (Mehta et al., 2014) but considerable degradation of the surface of the feathers was observed (Fig. 26). A fungal strain Myceliophthora thermophile (GZUIFR-H49-1) was found to effectively generate keratinase with activity of up to 1800 u/l by varying the culture conditions. Similarly, marine Actinobacterium actinoalloteichus sp. MA-32 was used to generate keratinase that was used in detergent formulation (Manivasagam

Table 14 Composition of the flame retardant (Wang et al., 2014a,b). Name of agent

1

2

3

4

P–N flame retardant agent (g/L) Borax (g/L) Boric acid (g/L)

250 0 0

0 10 60

250 10 60

0 0 0

7. Flame retardants from feathers Presence of high amounts of nitrogen in feather was considered to be suitable for developing flame retardants (Wang et al., 2014a,b). Feathers were hydrolyzed using sodium hydroxide and the precipitate obtained was collected and used to prepare the P–N based flame retardant by adding melamine, sodium pyrophosphate and feather powder in 1:8:5 ratio. Glyoxal (180% on the weight of feather) was added and the mixture was heated up to 80 °C. A yellowish feather based flame retardant was obtained

Table 15 Flame retardancy of the fabrics treated with different flame retarding agents (Wang et al., 2014a,b). Sample

Weight gain rate (%)

Char length (cm)

After glow (S)

After flame (s)

LOI

1 2 3 4

5.72 2.77 8.10 0

>30 >30 4.5 >30

180 1 2 10

7 29 0 12

30.1 29.5 39.9 18.0


14


Table 16 Flame retardant properties of the cotton fabrics treated with chicken feather protein based flame retardant containing Borax and Boric acid (Wang et al., 2014a,b). Concentration of P–N flame retardant (g/L)

Weight gain rate (%)

Char length (cm)

After glow (S)

After flame (s)

0 50 100 150 200 250

2.77 4.20 5.57 6.40 7.40 8.10

>30 >30 6.0 5.0 4.5 4.5

1 9 1 1 1 2

29 16 0 0 0 0

Fig. 25. Changes in enzymes units and amino acids generated when various substrates are used (Manivasagam et al., 2014). Reproduced with permission from Innovare academic sciences private limited.

Fig. 26. SEM image shows the degradation of the surface of the feather fibers by Actinobacterium actinoalloteichus. Reproduced with permission (Manivasagam et al., 2014) from Innovare academic sciences private limited.

et al., 2014). Fig. 27 shows a digital image of the feather being completely digested by the microorganism. The production of keratinase was about 173 U ml/l when keratin was used as a substrate and the molecular weight obtained was about 66 kDa. As an additive to various detergents, the keratinase had good stability and the detergents containing the extracted keratinase showed excellent removal of blood stains from fabrics (Fig. 28). In another report, a feather degrading Bacillus subtilis strain RM-01 was used to generate keratinase from feathers (Rai et al., 2009). Similar to a earlier study, maltose and sodium nitrate were reported to be the most optimum co-carbon and co-nitrogen sources, respectively. Keratinase obtained had a molecular weight of 20.1 kDa. The enzyme had high residual activity in various detergents and was considered to be suitable as an additive for laundry detergents (Rai et al., 2009).

Fig. 27. Digital image shows the complete degradation of the feather by the enzymes (Manivasagam et al., 2014).

9. Micro and nanoparticles from feather keratin Micro and nanoparticles made from organic and inorganic materials have been used in the food, agriculture, cosmetology, medicine and other areas. Although it is difficult to dissolve and prepare particles from feathers due to the high level of crosslinking by cysteine, researchers have adopted various approaches to prepare micro and nanoparticles from feather keratin. Using ionic liquid such as 1-butyl-3-methylimidazoliumchloride ([BMIM]Cl), keratin was made into particles for potential removal of chromium Cr (VI) (Sun et al., 2009). Feathers (up to 23%) were solubilized in the ionic solution by heating to 100 °C for 48 h. Particles formed were added into chromium solution of known concentration and the absorption was studied. Fig. 29 shows the ion uptake and removal efficiency by raw feathers and the keratin obtained after treating with the ionic liquid (Sun et al., 2009). The regenerated feathers had considerably higher absorption than the raw feathers (Fig. 30). However, the specific surface area of untreated feathers (654 m2/g) was higher than that of the treated feathers (493 m2/g). The treated feathers had higher ion sorption than the untreated feathers despite having lower surface area which was understood to be due to the hydrophilicity of the feathers (Sun et al., 2009). Recently, we have reported the development of nanoparticles from feather keratin that had the biocompatibility and stability required for controlled drug release applications (Xu et al., 2014a,b). Nanoparticles with diameters ranging between 50 and 130 nm were obtained (Fig. 30) (Xu et al., 2014a,b). The particles were able to enter various organs in mice but were predominantly found in kidney, followed by liver and spleen (Fig. 31). Unlike most nanoparticles, the keratin particles were stable in water without the need for any crosslinking or other chemical modification and therefore considered to be suitable for medical applications.

10. Thermoplastics from chicken feathers Poultry feathers have been used to develop thermoplastic films for food packaging and other applications. Since feathers are inherently non-thermoplastic and do not melt, several chemical



15

Fig. 28. Removal of stains by detergent containing the keratinase. (A) Cloth stained with blood, (B) blood stained cloth washed only the detergent and (C) cloth washed with detergent containing the enzyme. Visible difference and better removal of stains can be seen after cleaning the cloth with enzyme containing detergent (Manivasagam et al., 2014).

Fig. 29. Removal of chromium ions by the untreated and regenerated feather particles. Reproduced from (Sun et al., 2009) with permission from Elsevier.

Fig. 31. Biodistribution of keratin nanoparticles in the various organs in mice 24– 96 h after injection (Xu et al., 2014a,b). Reproduced with permission from American Chemical Society.

suitable to develop films by compression molding. Fig. 32 shows digital image of the feather film developed using hydrolyzed chicken feathers. Films obtained were crosslinked with citric acid to improve stability in aqueous conditions (Table 17). Although exposing the films to 90% humidity resulted in considerable decrease in tensile properties, the films were stable and did not disintegrate and could be useful for packaging and other applications that have limited exposure to moisture or water. Another approach of developing water stable feather films is to add synthetic monomers on to the feathers. One such effort was to graft acrylic monomers such as methyl acrylate, methyl methacrylate and butyl acrylate and study the properties of the grafted feathers (Jin et al., 2011). Grafting imparted thermoplasticity which allowed the feathers to be made into films (Fig. 32). Grafted feathers supported the attachment and proliferation of mouse fibroblast cells, better than that of films obtained from poly(lactic acid). Similar to grafting, acetylation and etherification were also found to make feathers thermoplastic and suitable to develop various products (Reddy et al., 2013a,b; Zhen et al., 2014; Hu et al., 2011). Fig. 32 shows an image of the thermoplastic feather films obtained after etherification, acetylation and grafting. Fig. 30. TEM image of keratin nanoparticles (Xu et al., 2014a,b). Reproduced with permission from American Chemical Society.

11. Feathers as textile yarn sizing agents

modifications are done to make feathers thermoplastic. However, Reddy et al. (2013a,b) have demonstrated that a simple alkaline hydrolysis of feather makes the feathers thermoplastic and

In a unique application, chicken feathers were used as a sizing agent (a protective layer added onto the surface of yarns to improve weaving performance) for textile yarns (Reddy et al.,


16


Fig. 32. Digital image of compression molded unmodified feathers and transparent film obtained from alkali treated feathers (A). Transparent and flexible thermoplastic obtained from grafted feather keratin (b) and etherified feather compression molded into films (c) (Reddy et al., 2013a,b; Zhen et al., 2014; Hu et al., 2011). Reproduced with permission from Elsevier.

Table 17 Tensile properties of thermoplastic keratin films before and after crosslinking with citric acid at two (65% and 90%) humidity (Reddy et al., 2013). Citric acid concentration (%)

Peak stress (MPa)

Breaking elongation (%)

65%

90%

65%

90%

65%

90%

0 1 2 5

5.9 ± 0.8 5.1 ± 0.7 5.2 ± 0.7 5.5 ± 0.7

0.7 ± 0.2 1.2 ± 0.3 1.8 ± 0.2 1.2 ± 0.2

31.7 ± 6.4 15.0 ± 4.6 13.5 ± 6.7 11.3 ± 6.8

26.8 ± 6.1 19.5 ± 4.3 24.6 ± 6.2 19.4 ± 3.4

136 ± 23 162 ± 21 191 ± 38 230 ± 73

3.6 ± 0.5 12.6 ± 4.2 18.1 ± 3.7 14.2 ± 3.6

Table 18 Comparison of the properties of keratin fibers with wool and other keratin based materials (Xu et al., 2014a,b). Material

Tensile strength (MPa)

Elongation (%)

Pure keratin fibers Keratin/chitosan film Crosslinked keratin film Compression molded film Keratin–silk fibroin film Keratin PVA (5:6) fiber blend Wool

101 ± 15 34 ± 10 8 ± 2; 27 ± 6 7.9 ± 2.7; 27.8 ± 2.9 17.7 ± 4.7; 27.8 ± 6.5 87.8 ± 6.8 115–180

10.9 ± 2.9 7±2 8 ± 2; 14 ± 8 1.1 ± 0.5; 4.7 ± 0.7 1.2 ± 0.4; 2.3 ± 0.6 12.6 ± 3.2 12–18

2014a,b; Yang and Reddy, 2013). Feathers were hydrolyzed using alkali and polyester/cotton, polyester and cotton yarns were immersed in the feather solution. It was found that feathers increased the tensile strength and abrasion resistance of the yarns. Feather size was degraded in activated sludge without releasing detrimental amounts of ammonia. It was suggested that feathers could replace poly(vinyl alcohol) that is commonly used for textile sizing but is expensive and also does not easily degrade in effluent treatment plants.

Young’s Modulus (MPa)

used as a source to develop a plethora of bioproducts at a laboratory level and some of the feather based products have also been used in commercial applications. However, considerable amount of research and development work is necessary to further the use of feather based bioproducts. Difficulties in processing feathers especially in dissolving, mainly due to the high level of crosslinking is the major constraint in developing feather based bioproducts. Nevertheless, newer approaches of dissolving or modifying feathers and green technologies to process feathers into various products are necessary for large-scale utilization of feathers for industrial applications. Acknowledgements Author thanks the Ministry of Science and Technology, Department of Biotechnology, Government of India for the financial support through the Ramalingaswami Re-entry Fellowship. The Center for Emerging Technologies at Jain University is also acknowledged for their support to complete this work. References

12. Regenerated protein fibers from feather keratin Protein fibers (commonly wool and silk) have unique properties are preferred over cellulose and synthetic fibers. Unfortunately, there is limited quantity of wool and silk available and the fibers are also relatively expensive. Many attempts have been made to produce artificial (regenerated) protein fibers using plant and animal proteins. Feather keratin has also been studied as potential source for regenerated fibers. Recently, Xu et al. (2014a,b) have extracted keratin from feathers using a unique approach and developed regenerated protein fibers with properties similar to that of wool. Table 18 provides a comparison of the properties of the regenerated keratin fibers with wool and other feather based materials. Feather keratin had strength similar to that of wool but lower elongation.

13. Conclusions Low cost, large availability and unique properties make feathers desirable raw material for various applications. Feathers have been

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