Materials Science and Engineering C 31 (2011) 1706–1710
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Materials Science and Engineering C
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Thermoplastic films from cyanoethylated chicken feathers
Narendra Reddy a, Chunyan Hu a,b, Kelu Yan b, Yiqi Yang a,b,c,d,⁎a Department of Textiles, Clothing & Design, 234 HECO Building, University of Nebraska-Lincoln, NE 68583-0802, USAb College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, 201620, Chinac Department of Biological Systems Engineering, 234 HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, USAd Nebraska Center for Materials and Nanoscience, 234 HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, USA
⁎ Corresponding author at: Department of Biological SBuilding, University of Nebraska-Lincoln, Lincoln, NE 6472 5197; fax: +1 402 472 0640.
This paper demonstrates that etherification can be used to develop thermoplastic films from chicken feathers.Feathers are inexpensive, abundantly available and renewable resources but have limited applications mainlydue to their non-thermoplasticity. However, it has been shown that chemical modifications such as graftingcan make feathers thermoplastic. Etherification provides better thermoplasticity to biopolymers compared tochemical modifications such as acetylation. In this research, chicken feathers were etherified usingacrylonitrile and various concentrations of catalyst. Even at low weight gain (3.6%), cyanoethylated featherswere thermoplastic and showed amelting peak at 167 °C. Films compressionmolded from the cyanoethylatedfeathers had strength ranging from 1.6 to 4.2 MPa and elongation ranging from 5.8 to 14% depending on theextent of cyanoethylation. Feathers modified by cyanoethylation had good thermoplasticity and could beuseful to develop various thermoplastics.
ystems Engineering, 234 HECO8583-0802, USA. Tel.: +1 402
Considerable efforts are being made to utilize biopolymers todevelop consumer products, especially disposable thermoplastics andpackaging materials [1]. Poultry feathers are inexpensive andabundant resources but do not have anymajor industrial applications.Most of the feathers generated are disposed in landfills leading toenvironmental concerns and discarding of a potentially valuablematerial. Feathers contain more than 90% protein in the form ofkeratin and are probably the lowest cost proteins available. Feathershave low density (0.9 g/cm3) and a unique hierarchical structureconsisting of the main rachis or quill to which are attached the barbscommonly referred to as “feather fibers” and the tiny barbules that arein-turn attached to the barbs [2]. This hierarchical structure providesthe resistance to wind and protection from the environment. Inaddition, feathers have honey comb shaped hollow centers that makefeathers lighter and provide insulation to heat and sound [3,4]. Due tothese unique features, attempts have been made to study thepotential of using feathers for various applications.
Most of the attempts on using feathers for industrial applicationshave focused on using feathers in their native form, especially asreinforcement for composites. Whole feathers, feather fibers andfeather quills were separately used as reinforcement for light-weight
automotive polypropylene composites [3–5]. It was found thatfeathers provided good sound absorption due to the presence ofhollow structures. Whole feathers provided better flexural and tensileproperties than feather fibers or feather quill reinforced composites[5]. Feathers were mixed with soybean oil to develop completelybiodegradable composites [6]. Similar to using feathers for compos-ites, feather fibers were mixed with low density polyethylene andextruded to form pellets [7,8].
Due to the non-thermoplastic nature of feathers, efforts have beenmade to use chemical modifications andmake feathers thermoplastic.Feathers were grafted with methyl methacrylate and the graftingconditions were optimized [9]. However, the melting behavior or thepotential of using the grafted feathers for thermoplastic applicationswas not studied. We have recently shown that feathers grafted withmethyl acrylates can be compression molded into thermoplastic films[10]. Methyl methacrylate grafted feathers had tensile strengthranging from 55 to 206 MPa and breaking elongations ranging from1.1 to 14% depending on the amount of glycerol used (0 to 30%). Thethermoplastic films obtained from methyl methacrylate graftedfeathers had better dry and wet tensile properties than films madefrom feather keratin and also compared to films made from starchacetate and soy proteins [10].
In addition to grafting, esterification (acetylation) and etherifica-tion (cyanoethylation) are some of the common approaches used tomake biopolymers thermoplastic. Acetylation has been used tomodify biopolymers such as cellulose, starch and also proteins forfibers, films and other thermoplastics [11,12]. Recently, we havedemonstrated that the carbohydrates and proteins in distillers driedgrains (DDG) can be simultaneously acetylated and made into
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thermoplastics [13,14]. Etherification has several advantages overacetylation. Etherification uses relatively milder conditions (lowtemperatures and pH) than acetylation and therefore will causelesser damage to polymers, especially proteins that are easilyhydrolyzed under high temperatures and strong alkaline or strongacidic conditions. In addition, ethers are more flexible than esters andtherefore ethers could provide thermoplastics with better elongationthan esters.
We have recently reported that cyanoethylated distillers driedgrains with solubles (DDGS) which is a mixture of proteins andcarbohydrates can bemade into high flexible thermoplastic films [15].Cyanoethylated DDGS could be compression molded into filmswithout the need for plasticizers. The properties of the films couldbe controlled by varying the extent of cyanoethylation or compressionmolding conditions. Films with strength as high as 651 MPa but lowelongation or films with high elongation (38%) but with lowerstrength (14 MPa) were obtained. Cyanoethylated DDGS showedgood potential to be useful for thermoplastic applications.
In this research, chicken feathers were cyanoethylated and thecyanoethylation conditions were optimized. Cyanoethylated featherswere characterized for the changes in structure and to confirmcyanoethylation and the potential of converting the cyanoethylatedfeathers into thermoplastics was evaluated.
2. Experimental section
2.1. Materials
Chicken feathers consisting of quills and barbs were supplied byFeather Fiber Corporation (Nixa, MO). Acrylonitrile required forcyanoethylation and sodium carbonate used as catalyst were reagentgrade chemicals purchased from VWR International (Bristol, CT).
2.2. Methods
2.2.1. Cyanoethylation of chicken featherCyanoethylation of the chicken feathers was carried out using
acrylonitrile and sodium carbonate as both the swelling agent andcatalyst. The reaction between the hydroxyl groups in the proteins inchicken feather and acrylonitrile in the presence of sodium carbonateis believed to be a typical nucleophilic addition reaction. The possiblemechanism of the reactions between acrylonitrile and the hydroxylgroups in the feathers is given in Scheme 1. The reaction between theacrylonitrile and the hydroxyl groups in chicken feather results in theformation of the cyanoethylated chicken feather.
To perform the cyanoethylation, chicken feather was mixed withequal amounts of various concentrations 5, 10, 15, and 20% (w/w) ofaqueous sodium carbonate for 15 min at room temperature. Later,acrylonitrile was added into the feathers at an acrylonitrile to featherweight ratio of 8:1 under constant mixing until the temperaturereached 40 °C. The cyanoethylation was completed by heating themixture containing chicken feather, acrylonitrile and sodium carbon-ate for 2 h at 40 °C. At the end of the reaction, the products formedwere added into 50% ethanol to ensure complete removal of
Scheme 1. Possible reaction between acrylonitrile and the hydroxyl groups in chickenfeather under alkaline conditions. Feather-OH represents the hydroxyl groups in theproteins in chicken feather.
acrylonitrile and the products obtained were later neutralized withacetic acid (20% w/w). The precipitate obtained was first washed withethanol, then thoroughly with distilled water at 50 °C for 30 min andrepeated five times, followed by absolute ethanol and finally dried inan oven at 50 °C for 12 h. To exclude the effect of alkali on thethermoplasticity of the feathers, the reaction was performed underthe same conditions (40 °C, 2 h) using 20% sodium carbonate butwithout acrylonitrile.
The amount of acrylonitrile consumed by the feathers wasdetermined by titrating the double bonds in acrylonitrile usingpotassium bromate. Based on the differences in the double bonds inacrylonitrile before and after the reaction, it was found that less than2% of the acrylonitrile was consumed and the remaining acrylonitrilecould be reused for etherification. Therefore, the cost of etherificationwill be low even though relatively high ratio of acrylonitrile tofeathers was used for the reaction.
2.2.2. Percent weight gainIn order to quantitatively determine the efficiency of cyanoethyla-
tion of chicken feathers, percent weight gain values which describethe percent increase in the weight of cyanoethylated chicken feathercompared to the weight of unmodified chicken feather used for thereaction were determined. Before determining the % weight gain, thecyanoethylated feather was thoroughly washed in 50 °C water for30 min under constant stirring 5 times to ensure complete removal ofunreacted chemicals and soluble impurities. The feathers were laterdried in an oven at 50 °C until constant weight was obtained. Thepercent weight gain values were calculated according to the formula
Percent Weight Gain = Wmod−Wunmodð Þ=Wunmodð Þ × 100
Where Wunmod was the initial oven-dried weight of the chickenfeather before chemical modification and Wmod was the oven-driedweight of the cyanoethylated chicken feathers.
2.2.3. Fourier transform infrared (FTIR) spectrum analysisSamples for FTIR spectroscopy of unmodified and cyanoethylated
chicken feather were thoroughly washed in distilled water to removeany chemicals prior to mixing with KBr. Samples in the form of thinfilms were placed in the FTIR-cell at room temperature. FTIR spectrawere recorded on a Nicolet NEXUS 670 (Thermo-Nicolet, Waltham,MA) FTIR spectrometer. Each sample was measured from 400 to4000 cm−1 with a resolution of 4 cm−1 and 32 scans were collected.The FTIR spectrums obtained were analyzed using OMNIC software(Thermo Electron Corp).
2.2.4. Nuclear magnetic resonance studies1H NMR spectroscopy studies were conducted to understand the
changes in the modified chicken feather. The unmodified andcyanoethylated feather samples were dissolved in DMSO-d6 and theconcentration of product was adjusted to 20–30 mg/mL for the 1HNMR measurements. 1H NMR spectra were recorded at 295 K using aBruker Advance DRX-400 (Bruker, Billerica, MA) spectrometeroperating at a proton frequency of 400.13 MHz. Typically, 64 scanswere collected into 64 K data points over a spectra width of 11990 Hzwith a relaxation delay of 6 s, an acquisition time of 2.7 s, and 90° flipangle. All free induction decays (FID) were multiplied by anexponential function with a 1 Hz line broadening factor prior toFourier transformation (FT). The spectra were phase correctedinteractively using TOPSPIN. Baseline correction was carried outmanually each time using the appropriate factors. Chemical shiftswere reported using DMSO-d6 (δH 2.50) as an internal reference.
2.2.5. Pyrolysis–gas chromatography–mass spectrometry studiesMass spectrometer was also used to confirm the cyanoethylation
of feathers using a Chemical Data Systems Pyroprobe 120 pyrolyzer
Fig. 1. Effect of catalyst concentration on percent weight gain of cyanoethylated chickenfeathers. The cyanoethylation was carried out at 40 °C for 120 min with acrylonitrile tochicken feather ratio of 8:1. Data points with the same alphabets indicate that theywere not significantly different from each other.
Fig. 2. Infrared spectrums of unmodified and cyanoethylated chicken feathers.
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equipped with a platinum coil and quartz sample tube interfaced to aShimadzu QP 2010 (Japan) GC–MS device. Samples weighing 10–15 mg were pyrolyzed at 200–300 °C for 10 s. Helium carrier gas at48.2 mL/min flow rate was used to purge the pyrolysis chamber into afused silica capillary gas chromatographic column (25 m by 0.2 mm)coated with a bonded methyl silicone phase (0.33 μm). Thetemperature was 40 °C for 3 min. The injector and mass spectrometerinterface temperatures were 280 and 300 °C, respectively. The massspectrometer was operated in electron impact (EI) mode at 70 eV andsamples were scanned in the mass range from 33 to 400 atomic massunit (amu). The acceleration voltage was turned on after a solventdelay of 80 s. The detector voltage was 1100 V. Mass Spectralsimilarity searches were performed using the NIST MS Search 2.0(NIST/EPA/NIH Mass Spectral Library).
2.2.6. Thermal analysisThermogravimetric analysis (TGA) was performed on the unmo-
dified and cyanoethylated chicken feather with an instrument(Netzsch 209 F1, Germany) calibrated with nickel. Unmodified andcyanoethylated samples (10–15 mg) were placed under nitrogenatmosphere and heated from 50 to 550 °C at a heating rate of10 °C min−1. Differential scanning calorimetry (DSC) was also used tostudy the thermal behavior of the unmodified and cyanoethylatedchicken feathers using a Netzsch instrument (204 F1, Germany).Samples oven dried at 105 °C (5–10 mg) were placed in the DSC andheated at a rate of 20 °C min−1 after holding at 50 °C for 10 min toensure complete removal of moisture in the samples. The sampleswere then heated up to 200 °C at a rate of 20 °C min−1.
2.2.7. Developing thermoplasticsThe unmodified and cyanoethylated chicken feathers were
compression molded in a Carver (Carver, Wabash, IN) press toevaluate their thermoplasticity and potential for various thermoplas-tic applications. Glycerol (20%, w/w) on weight of feathers was usedas a plasticizer to improve the thermoplasticity of the feathers.Samples of about 10 g were compressed at 180 °C for 2 min. Aftercompression, the press was cooled down by running cold water andthe films formed were collected for tensile testing.
2.2.8. Tensile testingThe thermoplastic feather films were tested for the tensile
strength, % breaking elongation and Young's modulus according toASTM standard D882. Samples were conditioned at 21 °C and 65%relative humidity for at least 24 h before testing. About 8 samplesfrom two different films were tested for each condition and theaverage and ± one standard deviations are reported.
2.3. Statistics
All the experiments were repeated three times unless specified.The data reported are mean±one standard deviation. Fisher's LeastSignificant Difference (LSD) was used to test the effect of variousconditions on the properties of products using SAS (SAS Institute Inc.,Cary, NC). Statistical significance was considered at pb0.05.
3. Results and discussion
3.1. Effects of catalyst concentration on percent weight gain ofcyanoethylated chicken feathers
Fig. 1 shows the effect of increasing the catalyst (sodiumcarbonate) concentration on the percent weight gain of cyanoethy-lated chicken feathers. As seen from the figure, increasing the catalystconcentration from 5 to 10% significantly increased the weight gain.The weight gain obtained at a catalyst concentration of 10% was 2.2%and at ratio of 15% catalyst, the % weight gain was slightly higher at
2.5% but the weight gain at 15% catalyst concentration was notsignificant compared to the weight gain at 10%. However, the p valuefor the weight gains between 10 and 15% was 0.0698 indicating thatthe weight gains were close to being significant. The highest % weightgain obtained was 3.6% at a catalyst concentration of 20% and whenthe pH was 11.6. Solubility of sodium carbonate reached saturation(21.7%) at 20 °C and we therefore did not use catalyst concentrationshigher than 20% [16]. Increasing weight gain with increasing catalystconcentration indicates better reaction between the acrylonitrile andfeathers. The alkali used as catalyst could hydrolyze the feathers andalso affect the thermoplasticity of the feathers. However, theweight ofthe feathers treated with 20% sodium carbonate but withoutacrylonitrile did not show any change in weight after treatmentindicating that the feathers were not damaged (hydrolyzed) duringthe treatment.
3.2. FTIR measurements
Fig. 2 shows the FTIR spectra of the unmodified and cyanoethy-lated chicken feathers.
The absorption peak attributed to the stretching of nitrile groups inacrylonitrile was seen at 2260 cm−1 for the modified feather but wasnot seen in the unmodified feather thereby confirmingcyanoethylation.
3.3. 1H NMR spectra of unmodified and cyanoethylated chicken feathers
The 1H NMR spectrums of the unmodified and cyanoethylatedchicken feather are shown in Fig. 3. In 1H NMR spectra, the signals dueto cyanoethylated methylene protons (−CH2CH2CN) δ 2.6–2.8 ppmare present (inset figure) in the modified chicken feather but are notseen in the unmodified chicken feather [17,18]. The appearance of the
Fig. 3. The 1H NMR spectrum of the unmodified and cyanoethylated chicken feather.
Fig. 5. Comparison of the thermogravimetric curves for unmodified and cyanoethylatedchicken feather.
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peak due to the methylene protons in the 1H NMR spectrum indicatedcyanoethylation.
3.4. P–GC–MS spectra of unmodified and cyanoethylated chickenfeathers
The P–GC–MS spectrums of the unmodified and cyanoethylatedchicken feather are shown in Fig. 4. The P–GC–MS peaks wereassigned with the help of a library spectrum. In P–GC–MS spectra, thesignals due to pyrolysis of cyano group (−CH2CH2CN) at 1.965 mincan be seen in the modified chicken feather but are not seen in theunmodified chicken feather. The appearance of the peak due to thecyano group in the P–GC–MS spectrum confirms the cyanoethylationof chicken feather [19].
3.5. Thermal analysis
The thermal behavior of the cyanoethylated chicken feather wascompared to the unmodified chicken feather in Figs. 5 and 6. Fig. 5shows that the cyanoethylated chicken feather had similar thermalstability compared to the unmodified chicken feather. Both thesamples show a starting degradation temperature of 240 °C andsimilar weight loss of about 77% after heating to 550 °C.
DSC thermograms in Fig. 6 showed that the cyanoethylatedchicken feathers had different thermal behavior than the unmodifiedchicken feathers. The DSC curve for the cyanoethylated chickenfeathers had an endothermic melting peak at around 167 °C thatshould be due to the introduction of cyano group onto chicken
Fig. 4. Pyrolysis GC–MS spectra shows the signal due to the pyrolysis of the cyano groupon the modified feathers confirming cyanoethylation of the feathers.
feathers [20]. The unmodified chicken feathers did not show anymelting peak. The melting temperature obtained from DSC wascorroborated by the melting of the feathers at 180 °C duringcompression molding. However, 20% glycerol and high pressurewere necessary to obtain films from cyanoethylated feathers. Inaddition, it should also be noted that the melting temperature of thecyanoethylated chicken feathers at about 167 °C is much lower thanthose of starch acetates (270–315 °C) and cellulose acetates (230–300 °C) [21,22]. The lower melting temperature of cyanoethylatedchicken feather is beneficial because high compression temperatureswould damage the proteins and result in thermoplastic products withpoor properties.
3.6. Biothermoplastics from cyanoethylated chicken feather
The unmodified and cyanoethylated feathers were compressionmolded to verify the possibility of developing thermoplastics from themodified chicken feathers. Fig. 7 shows the digital image of themodified and unmodified feathers after compressionmolding. As seenfrom the figure, the unmodified chicken feathers (Fig. 7A) did notmeltunder the compression conditions (20% glycerol, 2 min at 180 °C)used. Similarly, films treated with 20% sodium carbonate but withoutacrylonitrile were also non-thermoplastic and could not be compres-sionmolded into films. However, the modified chicken feather meltedand formed a transparent film indicating that the cyanoethylatedchicken feathers had good thermoplasticity and could be converted tovarious thermoplastic products (Fig. 7B).
The tensile properties of the films developed from featherscyanoethylated to 1.8, 2.2, 2.5 and 3.6% weight gains using catalystconcentrations of 5, 10, 15 and 20%, respectively are shown in Table 1.As seen from the table, increasing % weight gain decreased the
Fig. 6. DSC curves of unmodified and cyanoethylated chicken feather.
Fig. 7. The unmodified chicken feather (A) is not affected by the thermal treatment andtransparent thermoplastics developed from cyanoethylated chicken feather (B) aftercompression molding at 170 °C for 15 min.
Table 1Properties of thermoplastic filmsmade from cyanoethylated chicken feathers at variousextent of etherification. The etherification was performed at 40 °C for 120 min withacrylonitrile to chicken feather ratio of 8:1 and catalyst concentrations ranging from 5to 20%. The films were compression molded at 180 °C for 2 min after mixing with 20%(w/w) glycerol.
% Weight gain Tensile strength, MPa Elongation, % Modulus, MPa
For each tensile property, data points having superscripts with the same alphabetsindicate that the data was not significantly different from each other.
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strength and modulus but increased the elongation of the featherfilms. However, there was no significant difference in strength forfilmswith 2.2 and 2.5% and 2.5 and 3.6%weight gain. Elongation of thefilmswas similar when the %weight gainwas 1.8 and 2.2% and 2.5 and3.6%. Modulus of the films showed decreasing trend except for filmsmade from 2.5 and 3.6% weight gain, 15 and 20% catalyst, respectively.The change in the properties of the feather films due to increasingweight gain should mainly be due to the better thermoplasticity. Asseen from Fig. 1, increasing catalyst concentration increased the %weight gain and therefore the amount of acrylonitrile on the feathersincreased. At low concentrations of acrylonitrile the %weight gainwaslow, the feathers partly melt and the unmelted feathers acted asreinforcement and increased the strength and modulus but decreasedthe elongation. At high weight gains, the feathers had goodthermoplasticity, could melt better and therefore the elongationincreased. Based on the data in Table 1, a catalyst concentration of 15%produced films with the best strength, elongation and modulus.
4. Conclusions
This research showed that etherification using acrylonitrile(cyanoethylation) was a viable approach to develop thermoplasticfilms from feathers. The % weight gain after cyanoethylation increasedup to 3.6% with increasing ratio of catalyst to feather from 5 to 20%.Presence of a new absorption peak belonging to the nitrile groups inthe FTIR spectrum confirmed cyanoethylation. Cyanoethylatedfeathers showed a melting peak at 167 °C and the modified featherscould be compression molded into thermoplastic films. Properties ofthe feather films could be varied by changing the cyanoethylationconditions, especially catalyst concentration. The ability of formthermoplastic films even at low levels of cyanoethylation (low %weight gain) indicated that the feather thermoplastics would be
biodegradable. Cyanoethylated feathers have good thermoplasticityand showed potential to be made into films, extrudates and otherthermoplastic products.
Acknowledgments
We thank the Agricultural Research Division at the University ofNebraska-Lincoln, China Scholarship Council, USDA Hatch Act andMulti State Project S-1026 for the financial support to complete thiswork.
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